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Application of Nanomaterials in Drilling and Completion Operations-Juniper Publishers

Abstract

This paper reviews the recent challenges faced in oil and gas operations specifically the drilling and completion sector. The application of nanomaterials in drilling and completion operations in mitigating these challenges were analyzed as well as the factors retarding the growth of the application of this emerging technology.

Introduction

Nanomaterials are now a growing trend in this current age of technology. Its applications have cut across different kinds of sectors of the modern age industries. According to the US Foresight Institute, Nanomaterials can be defined as a group of emerging technologies in which the structure of matter is controlled at the nano scale to produce novel materials and devices that have useful and unique properties. This also brings about the creation of new materials with enhanced properties such as mechanically, optically, magnetically and many others. The oil and gas have also capitalized on this new technology to help to improve upon the operations in oilfields.

Drilling and completion challenges are encountered in a lot of oilfields. Some of these problems are

The ineffectiveness of the conventional tools to withstand adverse environmental conditions, shale instability, fluid loss, bit balling, fines migration, exposure to harmful gases like hydrogen sulfide and many others [1]. These numerous challenges tend to place restrictions and income loss constraints on the drilling and completion operation.

Nanomaterials are basically materials which are constructed at the atomic or molecular scale with a dimension of a nanometer, and hence it can be assembled to give a preferred feature or product [2]. These materials possess some distinct structural features like large fraction grain boundaries, triple junction and high surface area per unit mass or volume. The distinctive structure features of the nanomaterials give it enhanced properties compared to their bulk materials [3,4]. The nanomaterials have emerged to be a suitable and efficient solution to major challenges faced in the drilling and completion operations due to its robust features. It has been applied in drilling and completion operation to mitigate various challenges. The areas of application for nanomaterials in drilling and completion are expressed below.

High-Performance Drilling Fluids

Shale Inhibitors

Coatings

Lubricants

Drilling Bits

Plugging Materials for Reservoir Protection

Cement

Eventhough the nanomaterials has proven to be themost efficient solution to various drilling and completion challenges, its growth seems to be retarded. This emerging material lacks enough support from the various E&P bodies due its observed cost and risk associated with the materials [5]. Also, the health, safety and environmental issues allied to the nanomaterial is still under debate and there is a little or no available technology to measure the toxicity of these materials to the environment. All the above summed up to be the various issues retarding the growth of the application of nanomaterial in the oil industry [6-8].

Conclusion

This paper summarized the various drilling and completion challenges faced in the oilfield. Also, the application of nanomaterials in solving the most of this related issue and the various factors retarding the growth of this technology was summarized. It can be concluded that the robustness of the nanomaterials give it the capacity to withstand and overcome various challenges faced during drilling and completion operation

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Optimization of Gas Lift Allocation Using Different Models-Juniper Publishers

Abstract

Gas lift for oil-gas extraction is a common practice; however, obtaining maximum productivity of a series of set is not a simple tax because high amount of gas lift makes the optimization of few wells at the same time a very hard task. Therefore, data processing approaches based on calculations and computerized modeling has been receiving attention. By modeling well, it could be possible to obtain higher production rate versus less gas consumption. The present paper is a new approach that uses neural functions and genetic algorithm and studies the different aspects of problem solving for gas allocation optimization in five wells. The results showed that artificial neural networks have very good function in modeling gas lift process and creating gas lift performance curve versus classic methods. The differences between the results obtained by artificial neural network in comparison with results that are obtained in classic methods prove this claim.

Keywords: Genetic algorithm; Artificial neural network; Gas lift; Allocation optimization

Introduction

The normal yield of an oil well does not meet the demands of oil industry due to increasing rate of collection. For that reason, using some methods for increasing collection is inevitable. Pump and gas lift is one of the artificial lift approaches; however, it could not be used in all wells with maximum power due to energy consumption problem. In another word, gas lift in a series of well by optimization of the approach is an economic-functional issue [1].

Studying gas lift is usually performed by using gas lift performance curve. For the first time, Roy & Cataporan [2] used an analytical method to create gas lift performance curve in a well. This curve is obtained by drawing the data of oil collection values vs. gas lift amount [3].

There are various methods for fitting the gas lift performance curve; including line fitting by using regression and obtaining equation coefficient. The regression method by calculating equation coefficient is a relatively simple method for modeling gas lift performance in oil wells; however, it lacks flexibility and does not pay attention to the nature of data and their logic; therefore, it is opt to be erroneous in using for different wells. In another word, the same model could not be used in all wells. Modeling based on artificial neural network is an approach that could be discussed due to considering the logic of data and withdrawal from placing the data in a cliché frame. The artificial neural network, which is mostly called as neural network in brief, is a mathematical model that acts by being inspired form human neural system [4].

A neural network consist of one or few groups of artificial connected neural cells that process data by using connective and interactive methods. In most cases, neural networks lack compatibility system; that is, changes in their structure take place in learning phase and they improve themselves for modeling. Artificial neural networks have already been used in modeling complicated relations between inputs and outputs/entry-exits and finding existing patterns in data. For gas lift optimization too, these functions have been used for lift optimization particularly when it was difficult to obtain mathematical functions [5].

The genetic algorithm (GA) is an explorative search method that copies the natural evolution process. The algorithm model relies on repetitions and using that repetition and accident in genetic algorithm to optimize production and search for maximum power. In another word, GA belongs to a larger class known as evolutionary algorithms that is a solution for optimization problems by using the evolutionary techniques such as inheritance, mutation, selection and etc. [6].

GA has application in bioinformatics, calculation disciplines, engineering, economic, mathematics, physics and other areas. There is a history of using GA in optimizing gas allocation of a single well or a series of few wells. Martinez used this algorithm for the first time for optimization of gas lift collection [7].

A combination of neural network as a model and GA as an optimizer could be used in solving optimization issues. In 1999, Stoisits et al used modeling of a series of well with neural network and optimizing it with GA. Their perspective in using this optimization system was more in the direction of operational parameters such as the pressure of well and lacked the intensive economical aspect [8]. In present paper, five neural models are linked to a GA with suitable inputs for optimizing the five wells at the same time under different operational conditions and the economy of the process has been summed up as well.

Development of Gas Lift Performance Curve by Modeling with Neural Network

Many models have been suggested for modeling the amount of oil collection against gas lift. For example, second degree model is one of those models that due to unsymmetrical form of gas lift performance curve, it does not create suitable fitting [9]. For this reason, other models have been suggested by the researchers of this field. Alarcon et al. [10] in 2002 and Khishvand [11] tried to determine a suitable model. The Alarcon’s model (equation 1) and Khishvand (equation 2) are as follows:

For modeling with the neural network, a multi-layer feedforward network with 4 hidden layers with 10 tansig neurons in each layer was used. Then, the results of fitting the two models mentioned above (equations 1 and 2) were used to compare the function of the neural network model vs. mentioned classic methods. The results are listed in (Table 1).

The results of Table 1 show that the artificial neural network, Alarcon and Khishvand model has desire fitness. In addition, as Table 1 shows, the highest correlation coefficient and lowest sum of squared errors were obtained by artificial neural networks. Khishvand’s model showed weaker results in comparison with Alarcon model on the wells subject of this paper.

It should be mentioned that the above-mentioned result were obtained by using the most usual neural networks without manipulating geometric parameters of the network. Therefore, most probably, by designing network and using more data, those results could be improved considerably. In continuation, the results of drawing gas lift performance curve by using artificial neural networks for five wells are shown (Figure 1).

In Figure 1, the marked dots show the empirical values and the corresponding line of each set of knot shows the neural network model of each well. As it is shown and could be seen in (Table 1) too, suitable agreement of the empirical values and artificial neural network could be seen. On the other hand, by using the model of each one of the wells, quantities such as minimum collection of each well, maximum collection of each well and potential for additional collection of each well could be obtained. This information was obtained for all five wells and is listed in (Table 2).

The amount of potential of increasing collection in the process of gas lift has been obtained by differentiating the maximum collection with gas lift and collection in no gas lift conditions. This parameter is independent from gain without gas lift; that is, primary conditions of wells. Due to studying optimized answers, it is interesting to calculate this parameter in order to find out how much the gas allocation between wells in an optimized state would be in relationship with the potential of the wells involved in optimization.

Unrestricted Optimization of Gas Allocation In Wells and Its Effects on Total Collection

There are different approaches in optimization of a series of well [11]. The approaches could endure different restrictions on the optimization issue. I any way, restrictions such as the range of gas imposing to each well are necessary and inevitable while restrictions such as entry gas originates from economic necessities and studying them is a farther priority than the conditions of gas lift for each well. In this study, we used a trained neural function and linking it to genetic algorithm tool box to optimize the amount of oil production of a series of well and studying the factors. We benefitted from the method of developing the total utilization function and the target function in our issue in most simple situation was maximum total production. This target function could be solved per case without boundaries. For example, the genetic algorithm could be used to obtain maximum total production when less gas lift complex is accessible. In continuation, development and solving little suitable target function is discussed by using common concept in the literature of this discipline and some new suggestions are proposed as well.

Development of the Target Function Of Total Production without Economic Boundaries and Restriction

In this situation, optimization of the sum of wells production will be performed, conditioned by using the amount of gas lift in the scope of model information. The proposed target function and its requisite are described in equations 3 and 4.

Development of the target function of total production by economic restriction and studying the effects of economic restriction in productivity

This situation is like previous one with the difference that the sum of entering gas should be less than or equal to a constant amount. In practice, the sum of lift gas should be less than the amount of gas in access. In addition, high costs of the gas make this value to be as low as possible.

The amount of accessible gas might differ as per operational conditions and therefore, it is interesting to study the effects of gas restriction on the maximum collection conditions. To study this, GA was used. Figure 2 shows the results (55 points) of the calculations. As diagram in (Figure 2) shows, change in total production vs. restriction in total gas lift had an initially strong function and by the increase in amount of gas, the amount of changes and functionality vs. amount of lift restriction reduces accordingly.

This means that by increasing as to optimized level without restriction (last point in curve), the amount of production increase against consumed gas will be so trivial that would not have economic justification. Hatton et al; too, in studying a field with one hundred wells obtained similar results [12]. In many papers, the limit of 3 million cubic foot standard (MMscf/D) has been defined for total gas arrival in access and observing those conditions in our study could led to 27% increase in oil production. Due to the importance of using least gas and obtaining highest output, it is important to determine the suitable degree of lift restriction. In following parts, two target functions have been proposed for economic optimization and their results are compared.

Suggestion of Production Target Functions for Achieving Economic Optimizations

The amount of oil production increase per gas consumption unit could be considered as an important index in lifting operations and the largeness of number leads to economic productivity of the oil field. For this reason, this index could be considered as target function to be maximized by using genetic algorithm. For this purpose, two target functions are suggested: The function of sum of net productions of wells and the function of net production of wells and their only difference is in the method of modeling for gas lift production. The function of sum of net production of wells is defined as follows:

In addition, total net production function is standardized as follows:

Maximum functions (equations 6 and 7) are maximum collection in minimum gas lift. The reason that the denominator of both functions are plus 1 is for keeping the function continuous and preventing infinite answers. (Table 3) lists the results of optimization of those two target functions and optimization without restriction issues:

Economic- performance desirability of the conditions obtained from each target function could be defined with respect to the increase in production divided into sum of lift gas in optimized state. The scale is million cubic foot standard in one power (1/stbd/D). In this case, the boundless optimization desirability of wells will be 2.75 (percent collection improvement/ amount of lift gas), the desirability obtained from optimization function of sum of net production of wells (equation 6) is 17.15 and desirability of optimization of total net production (equation 7) will be 21.59. On the other hand, in many papers, the restricted optimization or maximum accessible gas was concerned while in our study, by including lift restriction of total 3 million cubic foot standard gas per day, the perspective will end to desirability value of 9 which is less than the desirability of suggested target functions.

Therefore, it could be claimed that it is not economical to use all the gas accessible for gas lift project and optimizing the amount of gas lift is a delicate issue; therefore, modeling with neural network and optimizing with GA could be a solution.

Another interesting point is the approach of gas allocation by genetic algorithm. The arrangement of potentials magnitude of wells subject of study is as follows: well 2, well 3, well 1, well 5 and well 4. In optimizing with target function in equations 6 and 7, as Table 3 shows, wells 4, 5 and 1 were not gas lifted and since those functions (equations 6 and 7) show the desirable economic point too, it seems that GA has withdrawn from optimizing the mentioned wells for maximizing economic profit.

It is highly interesting that the mentioned wells were among the poorest wells in the issue and potential in terms of parameter and this shows the importance of potential parameters in gas lift optimization process; because, if only highly potential wells are selected as gas under lift process, most probably, this would lead the load of optimization calculation load and increase in lift output.

Effects of the Number Of Wells Involved In Gas Allocation Optimization

Resource management in a gas lift project could be performed in various forms. The number of wells in optimization process is one of the issues that are important in this regards. As an example, in a gas lift network with five wells, the subject could be handled in one of the following approaches:

Optimization of all five wells by using restriction of sum of input gas

Optimization of a number of wells without restriction and not optimizing other wells

Optimization of a number of wells with the restriction in total entry gas and not optimizing other well

The first scenario has been receiving more anticipation; however, scenarios 2 and 3 did not seem much favorable and of course, no suitable comparative study has been performed regarding those approaches. The logic of the first scenarios is its attention to all wells proportion to their potential and economic abilities. In addition, scenario 2 and 3 are elite adoption scenarios and supporting highly potential wells in production with gas stimulation and withdrawal from spending for wells with no potentials. Each one of those scenarios could be studied with respect to the potential of production under gas lift conditions. Here, we plan to study the effect of the number of wells subject of study in an optimization issue without restriction of entry gas. For this purpose, a full fivefactorial trial design matrix was used. The optimization issues with 0 to 5 wells involved in optimization issue were solved by GA in accordance with the developed matrix. In addition the total amount of gas consumption was calculated and the results were listed in following table

The results of (Table 4) show that by increase in number of involved wells, the slope of production increase percentage curve gradually moves down. In another word, for the present five wells, it is predicted that infinite increase in the number of wells subject of optimization will not cause an increase in optimization output. In another word, in our study, increase in the output caused by optimization has a limit and after reaching that limit, the production increase percent will remain fixed. Therefore, observations and calculations made by authors emphasis that the irregular enlargement of the optimization issue of gas lift does not contain economic profit especially for the reason that the facilities and equipment of gas lift are expensive and require using personnel of the utilization party. In addition, enlarging optimization issue prolongs it and makes it difficult to solve. Results of (Table 5) could be used to draw Pareto diagram and determine the general effect of each well on total amount of collection form series of wells. (Figure 3) shows this diagram.

As it could be seen, the effects calculated for wells correspondence with their potentials and since measuring potentials of wells is easier, by considering the results of Table 4, it is suggested to take the optimization spaces as small as possible and in selecting the wells for optimization, consider the potential factor.

Conclusion

The most important results obtained in recent research are:

Acknowledgement

We take this opportunity to extend our best appreciation to South Oil fields utilization Company for providing us with the information of wells performance curves.

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Study of the Growth of Magnesium Oxide Thin Films Using X-Ray Diffraction Technique: Mini Review-Juniper Publishers

Abstract

X-ray diffraction method has been used by many researchers in order to study the structure of films. In this work, amorphous structure or polycrystalline magnesium oxide thin films could be identified using this technique. Furthermore, the grain sizes could be measured using X-ray diffraction data as well.

Keywords: Magnesium oxide, Thin films, Semiconductor, Deposition, Grain size

Introduction

Oxide materials [1-12] and metal chalcogenide thin films [13-21] are widely employed in the producing of solar cells, sensor devices, laser devices, optoelectronics devices, integrated circuits, and microelectronics. There are many groups of scientists from different countries involved to study these materials [22-29].

In this work, magnesium oxide (MgO) films were prepared using various deposition techniques. Magnesium oxide was chosen due to it has a high melting temperature, stable at atmospheric and large yield of secondary electrons during the bombardment by ions. The obtained films will be investigated using X-ray diffraction technique.

Literature Survey

X-ray diffraction (XRD) technique is mostly employed in materials sciences for the measurement of compounds. Many scientists point out some advantages of XRD such as it gives qualitative and quantitative of crystalline compounds [30-36].

Metal organic chemical vapor deposition (MOCVD) method has been used to prepare MgO films as described by Boo et al. [37]. The XRD patterns confirm that the obtained films with high crystalline and a preferred (111) plane on both Si (100) and c-plane sapphire substrates. Similar growth texture was also detected when the films were synthesized using RF ion plating method as proposed by Kenichi et al. [38]. Manin et al. [39] produced MgO films using MOCVD method. The obtained experimental results support that the oxygen low rate and temperature of the substrate were considered to be the most critical in order to determine the structure of samples. Dyachenko et al. [40] have reported that MgO films were deposited onto glass substrate using spray pyrolysis method under various substrate temperatures. The XRD data confirm that the quality of MgO film’s textures increases with increasing the substrate temperature from 370 °C to 420 °C. In other case, (200) preferential orientation was observed for the films prepared at 800 °C using sol-gel method as concluded by Ho et al. [41]. Chemical vapor deposition method was used to prepare MgO films as reported by Toshiro et al. [42]. They found that highly (100) orientation can be seen in XRD patterns for the films prepared at a reaction temperature above 450 °C.

XRD technique has been used by Kurtaran et al. [43] in order to investigate the structure of sprayed MgO films. They claim that amorphous structure and polycrystalline nature could be seen for as-deposited films and annealed samples, respectively. On the other hand, Mahadeva et al. [44] discussed the XRD patterns for the MgO films prepared under various oxygen partial pressures in the working gas. They found that the films are mostly amorphous in the as-deposited conditions. However, the MgO peaks are more significantly appear in the films deposited in oxygen partial pressure of 10 % and annealed films.

The grain size could be determined using XRD data. MgO films were prepared using spray pyrolysis at various temperatures (425-525 °C).The grain size indicates a slight increase as the temperature increased as pointed out by Faraq et al. [45]. On the other hand, MgO films were synthesized using spray pyrolysis method by Nisatharaju et al. [46]. The average grain size was calculated and was in the order of nanometer (14nm).

Conclusion

X-ray diffraction analysis was employed as the characterization tool for optimizing the magnesium oxide films growth conditions. The crystalline structure, amorphous and grain size could be determined using this tool.

Acknowledgement

INTI INTERNATIONAL UNIVERSITY is gratefully acknowledged for the financial support of this work.

Conflict of Interest

Author has declared that no competing interests exist.

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A Comparative Study of Phosphonate and Phosphorus-Free Antiscalant Efficiency by Static and Dynamic Methods. Do We Have Reliable Tools For An Adequate Reagent Selection?-Juniper PUblishers

Abstract

A relative ability of four industrial samples of phosphorus-free polymers (polyaspartate, PASP; polyepoxysuccinate, PESA; polyacrylic acid sodium salt, PAAS; copolymer of maleic and acrylic acid, MA-AA) and of two phosphonates (aminotris(methylenephosphonic acid), ATMP; 1-hydroxyethane-1,1-bis(phosphonic acid), HEDP) to inhibit calcium carbonate precipitation at a dosage 10 mg•dm-3 is tested in static experiments following the NACE Standard TM0374-2007 and in a dynamic modeоfevaporation plant for Caspian Sea water imitate. The reagent efficiency ranking following NACE Standard gives evidently a preference to phosphonates over polymers: ATMP~HEDP>PESA (400-1,500 Da) ~PASP (1,000–5,000 Da)>PAAS (3,000–5,000 Da) ~MA-AA. At the same time the kinetic tests exhibit the better efficiency of PESA and MA-AA: PESA>MA-AA>PAAS~HEDP>ATMP~PASP. Therefore, a lot of work is still needed to elaborate a system of laboratory tests for antiscalants in order to provide reliable assessment and selection on their way from laboratory to industry.

Keywords: Scale inhibition; Calcium carbonate; Polymers; Phosphonates; NACE

Introduction

Scale formation in the oil and gas industry, evaporation plants, reverse osmosis desalination processes, steam generators, boilers, cooling water towers and pipes is a serious problem, causing significant plugging of wells, pipe-lines, membranes, and increasing the production expenses [1,2]. A widely used technique for controlling scale deposition is an application of chemical inhibitors [1-4]. Commonly used commercial antiscalants are represented by organophosphonates and numerous modifications of polyacrylates (PA). Among these the organophosphonates are dominating recently at the World market [5]. At the same time phosphorus-based inhibitors are hardly biodegradable and persist for many years after their disposal, which leads to eutrofication problems. Phosphorus discharges are therefore regulated in many countries worldwide, and permissible limits are constantly decreasing.

Increasing environmental concerns and discharge limitations have forced the scale-inhibitor chemistry to move toward “green antiscalants” that are readily biodegradable and have minimal environmental impact. Intensive efforts are applied recently to develop the “green” alternatives to organophosphonates and nonbiodegradable polyacrylates [1-4]. Among these novel inhibitors, such chemicals as polymaleates (MA), polyaspartates (PASP), polyepoxysuccinates (PESA), as well as their various derivatives, including co-polymers with PA are the most promising. It is important to note, that the new antiscalants should have acceptable levels of performance at a cost-effective dose rate. This requirement raises a problem of reliable tests, which permit a correct “old red” and “novel green” inhibitors efficiency comparison [6]. Indeed, most of the data published on CaCO3 (CaSO4) deposition are studied under hardly comparable conditions, e.g., different CaCO3 supersaturationindex, brine composition, temperature, pH, measurement technique, etc. This leads to the quite opposite opinions on the relative Antiscalant’s efficacy, reported by different research groups for one and the same set of reagents proposed for one and the same scale (see [1,7,8] and references there).

Specific Technology Group (STG) 31 on Oil and Gas Production-Corrosion and Scale Inhibition has elaborated a procedure of static laboratory antiscalants screening- NACE Standard TM0374-2007 [9]. These test methods are recommended only for ranking the performance of different scale inhibitors under laboratory conditions set by these methods. They are not intended to provide actual field treating rates. Surely, the scale inhibitor concentration required for a field application is likely to be different from that determined under these laboratory conditions. However, it is assumed, that for a particular set of reagents the ranking would be the same, and an inhibitor evaluation prior to final scale inhibitor selection is valid for the field use as well. Although particularly the NACE Standard is not very common, a lot of researchers use recently very similar approaches [1,7,8].

Present paper is therefore focused on the assessment of relative antiscalants efficacy against CaCO3 scale formation predicted following NACE protocol, and their ranking found by kinetic experiments run under conditions close to those used at evaporation plants.

Materials and Methods

Polymer based industrialantiscalants, polyasparticacid sodium salt (PASP, 1000–5000 Da), copolymer of maleic and acrylic acid (MA-AA), polyepoxysuccinic acid (PESA, 400–1500 Da), and sodium salt of polyacrylic acid (PAAS, 3000–5000 Da), have been kindly supplied by Shandong Taihe Water Treatment Technologies Co., Ltd., while industrial solid posphonates aminotris (methylenephosphonic acid), ATMP and 1-hydroxyethane-1,1-bis (phosphonic acid), HEDP have been supplied by a manufacturer OAO “Khimprom,” Novocheboksarsk, Russia.

Kinetic tests have been run operating with a model evaporation plant bench-scale facility. A freshly prepared imitate of the Caspian Sea water ([Ca2+] 0.35 g•dm−3, 0.0088 mol•dm−3; [HCO3-] 0.22g•dm−3, 0.0037 mol•dm−3; NaCl 8.57 g•dm−3, 0.15 mol•dm−3; pH 8.5-9.8) was kept boiling at 85 °С under reduced pressure (59kPa) for a period of 240 minutes. A reflux condenser provided the total liquid phase volume constancy. Periodically the boiling brine was sampled and analyzed for [Ca2+] content by EDTA titration procedure. Then the induction precipitation time (τind, min) and a half deposition time (τ1/2) have been calculated. Here τ1/2 is denoted as a moment, when (С – Сf )/(С0 – С f ) = 0,5; where С- current calcium concentration; Сf – final calcium concentration found from a blank experiment, С0– initial calcium concentration. All experiments were run in duplicates. The difference between duplicate run results was less than 10%.

Following the NACE Standard TM0374-2007 [9] two synthetic brines was prepared with distilled water: calciumcontaining brine (12.15 g•dm−3 CaCl2•2H2O; 3 .68 g •dm−3 MgCl2•6H2O; 33.0 g•dm−3 NaCl) and bicarbonate-containing brine (7.36 g•dm−3 NaHCO3; 33.0 g•dm−3NaCl) saturated by CO2. Being mixed at 1:1 volume ratio, these brines give a supersaturated calcium carbonate solution: 6.07 g•dm−3(6,070 ppm) CaCl2•2H2O, 1.84 g•dm−3(1,840 ppm) MgCl2•6H2O, 3.68 g•dm−3 (3,680 ppm) NaHCO3and 33.0 g•dm−3(33,000 ppm) NaCl. The ionic strength of this solution provided mostly by NaCl by the end of the precipitation process wasaround 0.71mol•dm-3. Supersaturated solution of calcium carbonate with a calculated amount of inhibitor (10 g•dm-3) was then kept for 24 h at 71°C, cooled and analyzed for residual calcium content by EDTA titration. The pH of the solutions at 25°C was about 7. All experiments were run in duplicates. The difference between duplicate run results was less than 5%.The performance of the tested compounds as calcium carbonate antiscalants was calculated as inhibition percentage (I, %):

I,% = 100 ×([Ca]exp-[Ca]final)/([Ca]init-[Ca]final). Where: [Ca] exp: concentration of calcium in the filtrate in the presence of an inhibitor at 24 hours; [Ca]final: concentration of calcium in the filtrate in the absence of an inhibitor at 24 hours; [Ca]init : concentration of calcium at the beginning of the experiment. All experimental results are presented in a Table.

Results and Discussion

The reagent efficiency ranking following NACE Standard gives evidently a preference to phosphonates over polymers: ATMP ~ HEDP > PESA (400-1,500 Da) ~ PASP (1,000-5,000 Da) >PAAS (3,000-5,000 Da) ~MA-AA. Thus, among the studied set of reagents ATMP and HEDP should be expected to become a matter of choice for carbonate scaling. However, an attempt to implement these reagents to evaporation plants gives a sufficiently different ranking. According to τind: PESA~MAAA> PASP>PAAS>HEDP~ATMP

The τ1/2 datareveals in turn another sequence: PESA>MAAA> PAAS~HEDP>ATMP~PASP.

In any case PESA and MA-AA look more preferable than phosphonates for evaporation plants. Actually τ1/2 seems to be a more adequate indicator than τind. The latter characterizes only the initial nucleation step, while the former is responsible for both: initial nucleation and further crystal growth kinetics. Anyhow the data given above demonstrates clearly that a lot of work is still needed to elaborate a system of laboratory tests for antiscalants in order to provide reliable assessment and selection on their way from laboratory to industry.

Conclusion

A comparison of static and dynamic laboratory testaments of scale inhibitors indicates for one and the same set of reagents rather conflicting results. Static test gives preference to the phosphonates ATMP and HEDP, while the dynamic one - to polymers PESA and MA-AA. Thus a lot of work is still needed to elaborate some conventional methods for the reliable, particular case-focused reagent efficiency prediction.

Acknowledgement

The authors would like to thank the Russian Foundation for Basic Research (Project No. 17-08-00061) and partly the Ministry of Education and Science of the Russian Federation.

Conflict of Interest

For a present study no any economic interest or any conflict of interest exists.

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Nano-Emptiness Space of Oil-Bearing Rocks-Juniper Publishers

Introduction

The electron microscopic and X-ray tomography studies of oil-bearing rocks showed a great variety and wide volume limits of an emptiness space. It includes macro- and with the corresponding micro-fragments of space closely connected each other. Micro-emptiness space predominates in volume in thin-grained terrigenous rocks, especially in argillites. But even in carbonate rocks it plays very important role as system of canals for oil migration.

Micro-emptiness space is composed by micro-cracks, micro-pores, and micro-cavities, as well as intermediate and transitional morphological types. The nature of the micro-emptiness space (structure, volume, filling in organic or mineral matter, etc.) determines many properties of reservoir rocks and their oil saturation. Its study is carried out by many methods, and it is very useful for sorting out the geophysical information used in the correlation of oil-bearing strata sections.

This short communication devoted to the problems of emptiness space study under a high-resolution scanning electron microscope. The objects of the author’s investigation were some oil deposits of the Perm Region, Russia. The methods of high-resolution electron microscopy were applied to study the nano-sized fragments of rock emptiness space. The polished sections of terrigenous and carbonate rocks were studied under JSM 7500F (Jeol) microscope with cool emission. The regime for standard scanning electron image for analysis was acceleration voltage of 15 kV, emission current of 10 μA, work distance of 8 mm.

The use of high-resolution electron microscopy methods has shown that the micro-emptiness space of reservoir rocks is practically inextricably linked with the nano-emptiness one. The main structural fragments of the nano-emptiness space are nano-cracks and nano-pores, which directly contacted with the corresponding micro-fragments. The wide spread of nano-cracks is due to the fact that virtually every micro-crack before the wedging along the strike and into the depth turns into nano-tracks, the extent of which can significantly exceed that of the mother micro-crack. Besides, many micro-cracks narrow up to nano-sized width in definite their parts (Figure 1).

Accordingly, the study of micro-pores under an electron microscope with high resolution shows that they gradually narrow to the depth, and several deeper canals of nano-scale width usually remain at the bottom (Figure 2).

Besides the common joint systems of micro- and nano-defects, there are the separate analogous nano-systems. Presumably, they fix the places of weak influences of external factors: tectonic and catagenesis processes, interstitial solution, etc.

At present, the share of the nano-emptiness space in the total volume of reservoir rock can be estimated only very approximately, and the oil industry does not particularly interest this task in connection with the impossibility of oil migration through the nano-canals. However, in some cases nano-space can play a significant role. As an example we may discuss on thin-layered argillites.

The nano-emptiness space in argillites is the important component of their structure, and its transformation may remarkably influence on oil migration. Note that a significant part of the basic mineral matter of argillites (montmorillonite, hydromica, and kaolinite) in particle size refers to the nanoscale range if we take into account the thickness of flakes. They can largely fill the nano-cracks, and gradually expand them due to the swelling of montmorillonite packets.

In some argillaceous strata the extensive systems of crossing and interlayer micro-cracks have been forming during the stage of catagenesis. It is assumed that many of them pass into nano-cracks in separate segments and when they are wedged out. This factor may be disregarded. However, the abundance of micro- and nano-cracks leads to a noticeable change in the petro-physical properties of the reservoir rocks, which must be taken into account in the correlation of the strata. In addition, such rock behaves differently under the drilling process.

The processes in the nano-emptiness space should be examined when assessing the effect of drilling fluids on oil reservoirs. In particular, the precipitation of salt nano-crystals constantly occurs from these solutions. They arbitrarily fill the micro- and especially the nano-emptiness space. In the future, salt nano-crystals begin to grow and, due to the crystallization force, they make significant changes in the structure of the reservoir rocks (such as expansion and elongation of cracks and pores). These transformations lead to the appearance of the secondary emptiness space of another nature.

The processes that take place in the reservoir are also directly related to the structure of the nano-emptiness space when solving the problems of increasing of oil recovery from thin-grained rocks. Many of them require special consideration from theoretical positions and by setting appropriate experiments.

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The Relationship between Carbonate Reservoir Unit Features and Well Test Double Logarithmic Curves-Juniper Publishers

Introduction

Naturally fractured-vuggy carbonate reservoirs have various type so f units, and making full use of the well test data to study reservoir characteristics is the quit important to enhance oil production. The classification of the reservoir units and identification methods are analyzed. Combination of the results interpreted by multiple medium model and radial composite model, the well test double logarithmic curves are divided into five types corresponding to different reservoir unit’s characteristics.

a. The oil well does not drill in any fractured-vuggy unit, but abundant fractured-vuggy units exist in the reservoir

b. The oil well drill in the fractured-vuggyunits and many fractured-vuggy units exist in the reservoir.

c. The oil well drill in multiple connected water-eroded caves.

d. Carbonate reservoirs contain primarily matric.

e. The oil well drill in some individual water-eroded caves, but the fractured-vuggy reservoir does not develop.

The measured data of 65 Wells in HalaHatang block is classified and summarized, and we find that well test curves is given priority to type I and II, accounted for 26.2% and 53.8% respectively. Two kinds of curves are different because the location relationship between the well and the fractured-vuggy units, so the large scale fractured-vuggy units and their interferences determine the flow of reservoir [1-2] (Figure 1).

Naturally fractured - vuggy carbonate reservoirs, quite developed in Tarim basin, are given priority to with caves, fracture and pore structure. One fractured vuggy unit is composed of one or more interconnected reservoir bodies, and has a uniform pressure and fluid system of reservoir. Well test is widely used to obtain reservoir parameters. Because of well test of strong, parameter interpretation must always be combined with static data, using the data of other constraints on well test interpretation. According to the study of the characteristics of block within a large number of well test curves can be divided into several different types, and then can be according to the classification results summarized well test curve and the corresponding relation of reservoir characteristics. Classification has the role of two aspects: on the one hand, can use classification to find out the laws governing the process of well test interpretation, reduce the uncertainty of well test interpretation. On the other hand, establish the well test curve corresponding relationship and reservoir geological characteristics, can be very intuitive judgment through test curve form the basic characteristics of reservoir.

Many scholars studied the carbonate reservoir well test models in recent years, a lot of work propose a carbonate reservoir description fractured - vuggy triple porosity model. The existing carbonate well test models are divided into double porosity model, double and triple medium permeability model, and the factors affecting the reservoir in the form of curve are analyzed. In order to solve the well test interpretation of bottom water carbonate reservoir, one [3]. Doil-water two phase numerical well test model of bottom water double pore carbonate reservoir is established. According to the actual geological data in Tahe oil field, a single-phase flow well test interpretation model of triple medium reservoir is established, and a genetic algorithm is proposed for fracturedvuggy reservoir on fitting well test interpretation methods. The comprehensive analysis of well test theory according to the fractured - vuggy carbonate research data, and the main characteristics of this reservoir well test curves are summarized. Combined with the single-well static data and production characteristics, the reservoir percolation medium types can be divided into initial matrix skeleton, constant volume cavity, and double medium and beaded reservoir.

Tarimoil field’s well test curves mainly contain type I (26.2%) and type II (53.8%), c aused t he main r eason t hat t he different two types of curve is the relationship between the well and the location of the joint body piercing. The seam of large scale body piercing determines the seepage law of reservoir. For a type I curve characteristics of the wells can be appropriately selecting fracturing, acidizing process, communication with the seam around the hole, in order to gain a higher capacity. When seam hole Wells in the unit well test curve type I and III I characteristics, should be in the later production deployment of injection wells in order to complement formation energy, make it get longer stable production period. In addition corresponding reservoir fracture development of well test curves (III, IV) proportion reaches 14% that has certain mutual interference between seam body piercing.

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What can be done to Prevent Accidental Toxic Release, Fire & Explosion in Chemical Process Industry?-Juniper Publishers

Abstract

Public perceptions are significantly affected by industrial incidents and the contribution and essential societal role of different industries are often overlooked when any catastrophic incident occurs. What can be done to prevent release of toxic chemical, fire & explosion or any other catastrophic incidents? Majority of the incidents occurred in the process industries due to lack of competence, system failure, human error and/or someone did not do what they were supposed to do. The root causes of the incidents in process industries are more or less same. The incidents can be avoided if the organization maintains a positive safety culture to improve its process safety performance and take advantage of lesson learned from the previous incidents. Everyone in any organization starting from the Chairman and Chief Executive Officer, senior executives, supervisors and operators should be accountable and responsible for their appropriate roles to ensure health and safety performance of the company.

Keywords: Bangladesh; Chemical Incidents; PSM Standard; Lesson Learned; Toxic release and Fire & Explosion

Introduction

The toxic and hazardous chemicals release, fire & explosion were pretty frequent which caused multiple fatalities, injuries, significant property and environmental damage [1-3]. The question remains that can the occurrence of these disastrous accidents be reduced in the future and their consequences minimized? An effective implementation of Process Safety Management (PSM) program in the process industries could significantly reduce the risk and avoid catastrophic fires, explosions, releases of hazardous substances and/or minimized its consequences. In United States, process industries are required to meet OSHA PSM standard. OSHA Process Safety Management (PSM) standard has fourteen majors’ interrelated elements [4]. Employee Participation, Process Safety Information, Process Hazard Analysis (PHA), Safe Operating Procedures, Training, Contractors, Pre-startup Safety Review, Mechanical Integrity, Hot Work Permit, Management of Change, Incident Investigation, Emergency Planning and Response, Compliance Audits and Trade Secrets. All of these elements are equally important. Among them, process hazard analysis (PHA) is heart of OSHA’s Process Safety Management (PSM) standard. Process hazard analysis is a thorough, orderly and systematic approach or technique to identify, assess and control the potential hazard associated in process industries. Process hazard analysis must need be conducted to identify all causes, estimate the risk and develop strategies to address the risk in chemical process industries.

Many of the developing countries (e.g. Bangladesh) do not have the process safety regulations/standards for process industries. There are significant numbers of industries in Bangladesh dealing with toxic, flammable and others hazardous chemical or materials those have potential to cause serious harm to employees, public and the environment. The number of chemical incidents is also increasing in Bangladesh these days. There were three major chemical incidents in 2016 which caused 40 fatalities, significant property and environmental damage. Quite often the accidental release of toxic chemicals, fire and explosion are narrowly defined and include only the ones that caused serious or catastrophic consequences [2].

The government or regulatory authorities should adopt the process safety management standard for process industries if they don’t have yet. An effective implementation of process safety management program in the process industries and monitoring the process safety performance are required to avoid any future catastrophe. The process industries should have a good incident investigation procedures necessary to take advantage of the lessons learned.

Major Safety Incidents

Piper Alpha, a North Sea Oil Production Platform was located approximately 120 miles Northeast of Aberdeen. On 6th July 1988, an explosion occurred on a North Sea oil production platform known as Piper Alpha which killed 167 employees. Total property damage from the explosion was estimated to be approximately $1.4 bn. A safety relief valve for a spare condensate pump was removed and temporarily sealed with a blind flange by the day shift operators. Unaware of the temporary replacement the night shift operators restarted the spare pump and gas condensate leaked from the flanges and ignited. The incident was attributed mainly to human error and an eye opener for the offshore industries regarding the safety issues. Inadequate maintenance and safety procedures, lack of communication between shift, faulty design and improper emergency response and planning led to the catastrophe [1,3]. After Piper Alpha, safety policies and regulations were developed and implemented in United Kingdom.

The incidents of Flixborough (1974), Seveso (1976) and Bhopal (1984) showed the world its catastrophic potential of process industry that can cause harm to people and environment [1]. Bhopal tragedy became the worst ever industrial accident in the history. On 3rd December 1984 40 ton of highly toxic methyl isocyanate (MIC) was released due to runway reaction in MIC storage tank. Water was accidentally entered into the MIC storage tank and reacted with MIC exothermally. This caused runway reaction and produced excessive heat inside the tank. Consequently, MIC was vaporized and released to the atmosphere. The toxic exposure immediately killed over 2000 people of Bhopal due to respiratory distress [4] and caused a significant increase of morbidity and thousands of premature deaths in the subsequent years. The fundamental causes of the incident were inadequate reactive hazard assessment, faulty instruments and ineffective release management system [5].

Process Safety Management and Legislation

Bhopal incident was the wake-up call for the Indian government. After the disaster, environmental policies and regulation enacted including the Air Act (1987), the Hazardous Waste (Management and Handling) Rules and the Environment Protection (2nd Amendment) Rules 1992. The Bhopal incident received widespread media attention and changed world view on the importance of process safety issues. U. S Unions begin to lobby for a Process Safety Standard. By investigating the underline causes of major industrial incidents, OSHA proposed a process safety management (PSM) standard for highly hazardous chemicals in 1990. After an extensive public hearing and debate, PSM standard was effective in 1992 aiming to prevent accidental release of chemicals that could pose a threat to employees or the environment. Seveso incident was main driver to develop process safety regulations for European Union. EU process safety management and legislations were introduced as Seveso I Directive (1982), Seveso II Directive (1996), later modified in 2003 and Seveso III Directive (2012).

Case Study: Effect of Deficiencies in Process Safety Management Program

Let’s look at the case of a recent incident at Williams Geismar Olifins Plant, Geismar, Louisiana. A reboiler (shell & tube heat exchanger) that supplied heat to distillation column was catastrophically ruptured on 13th June 2013, causing a boiling liquid expanding vapor explosion and fire. The incident killed two operators and injured 167 individuals [6]. What went wrong? In original design, two reboilers were continuously in operation to feed the distillation unit. However, it requires shutdown of the distillation unit for periodic maintenance and cleaning due to fouling on the tube surface of the reboiler. For reduction of process downtime, Willium decided to change the process and installed new valves and piping in 2001 so that it allows one reboiler at a time and the other can be kept standby or ready to use. These changes introduced a new process hazard as the additional valves isolated the reboiler from its relief valves that located on the top of the distillation column.

On the day of the incident, Willium operators noticed the flow rate of hot water in functioning reboiler was decreasing last couple of days. It could be because of fouling. So operators decided to switch the standby reboiler online. Unknown to the operators the reboiler shell side process valve was closed and blocked-in with partially filled liquid propane due to valve leaking or inadvertent opening of a valve. When reboiler hot water valves were opened, liquid propane inside the shell begun to heat up. Due to thermal expansion of liquid propane, a dramatic pressure rise within the shell caused boiling liquid vapor explosion and fire. Process safety management program weaknesses at Willium facility during 12 years led to the reboiler to be unprotected from overpressure. These weaknesses include deficiencies in implementing Management of Change (MOC), Pre-Startup Safety Review (PSSR) and Process Hazard Analysis (PHA). Chemical Safety Board investigated the incident and identified a number of process safety management program deficiencies that contribute to the incidents which includes

A. Willium didn’t perform adequate Management of Change,

B. Willium did perform three process hazard analysis during 2001 to 2013, but they didn’t implement the action items from PHAs or recommendation from a contracted pressure relief system engineering analysis

C. Willium didn’t assess the hazard before the start up of standby reboiler which was a crucial mistake. The incident of Willium facility could be avoided if they performed MOC appropriately, assessed the overpressure hazard and/or implemented the recommendation of PHAs. One of key lesson from the incident is that overpressure protection is essential for all pressure vessels and PHA team must need to ensure the effective overpressure protection system for all the pressure vessels in process industry.

Conclusion

Despite all the rules and regulations, chemical accidents are still happening. The analysis of the past catastrophic incident clearly indicates the lack of scientific and technical competencies as well as deficiencies in managing safety issues. Therefore, a three-way partnership is required from academia, industry and the government. Academics from the universities/ research/training institutions should recognize the importance of process safety to improve the technical competency level for both practicing engineers and new graduates. The process safety education should be integrated into the engineering curriculum. The government regulatory authority should set a minimum safety program requirements or standards for process industries. The process industries should implement various programs aiming to improve process safety management performance and develop a good safety culture.

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Oil Spill: Are We Doing Enough to Avoid It?-Juniper Publishers

Abstract

This paper reviews the recent studies on the identification and cleaning methods, as well as the consequences of oil spill. The future progression on oil spill prevention studies are also projected here.

Mini Review

Pharmaceutical excipients

Oil spill represents a devastating form of environmental disaster which causes irreversible impacts to the sea and marine creatures. The increase demand of petroleum due to the intensified growth of worldwide consumption leads to the threat of oil spill in various oceans during its shipping. Study by [1] in worldwide oil spill hotspots further identified that European Atlantic to be a key battlefield to avoid oil spill judging by its annual accommodation of crude oil shipping.

The crude oil spilled contains of high risk substances and in the form that is hard to be removed by current technology and removal methods as stated by the review in [2]. Besides, it also causes several of negative side-effects to the open seas, such as changing sea temperature, destroying natural habitats and disturbing shipping routes and activities. In the detailed study by the proposed combined hydrodynamic numerical and temperature statistical approach in [3]. The change of sea temperature is found to be related to the shrinking of coral reefs, which can further affect the marine creature habitats and natural coastal protection provided by the existence of coral reefs.

After the recent oil spill disasters, such as Hebei Spirit [4-6]. Dalian oil tank explosion [7-8] and Gulf of Mexico [9-10]. The public awareness of such issue has been re-heated. Even though, the engineering mitigation methods are of vital importance to oil spill events, the current techniques of removal are far from satisfaction. In the review of current techniques employed for oil spill removal, majority of them are either utilizing the mechanical or chemical approach. The mechanical approach uses physical measures to clean up the spills, such as by deployment of booms, skimmers or in-situ burning, and is generally dangerous to manage, slow and less efficient as its treatment is usually time- consuming. Furthermore, it is usually incapable to totally remove oil spilled before its natural hardening takes place. On the other hand, the chemical approach represents a method usually functions by speeding up the natural biodegradation of spills. It works by using dispersants to break down oil spill into droplets to make it easier to mix with water and absorb into aquatic system. This method usually associates with high environmental risk due to the chemical side-effects.

Viewing the limitation of the afore-mentioned cleaning methods, various of studies including via numerical [11] and fingerprinting approaches [5,7] have been further investigated to enhance the effectiveness to trace the sources and full impacts of oil spill and to incorporate into the use of cleaning methods. Out of these numerical and fingerprinting studies, there are several clear guidelines being established, include the importance of reaction time for cleaning and the sea environment impacts (such as sea waves and tides that increase the oil spreading). Hence further and more advance studies on numerical modelling of hydrodynamics [12] and flow turbulence [13] are crucial to understand the pattern of oil spreading to inform the cleaning process. Recent events have taught us the lesson that prevention is better than solution when considering the treat of oil spill, which have also been concluded in most of the cleaning approach studies discussed in this review paper.

Conclusion

This paper summarized the research efforts to minimize the impacts of oil spill in various major seas and oceans. From various suggested cleaning methods as well as oil spill source and impact predictions, it can be concluded that the oil spill is hard to be traced and cleaned effectively without proper guideline and technology advancement. This further suggests that precaution will be the best solution to prevent oil spill.

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An Overview of Enhanced Oil Recovery Methods in Fractured Carbonated Reservoirs-Juniper Publishers

Abstract

In some cases that the fluid (oil) enter in the bottom of the well and the fluid pressure in the bottom of the well is not capable to bring them to wellhead, other techniques such as gas lift (gas is injected from the surface into the well and this gas with well oil creates mixed miscibility that the density is less than primary oil density and can be transmitted oil to wellhead with that bottom pressure) or down-hole pumps (the oil is pumped from the bottom to wellhead by this device) is used. But, this technique is not mentioned as one of EOR methods.

Introduction

When a reservoir was being drilled, firstly it was produced by the natural mechanisms. Natural mechanisms provided the substantial energy to push the fluid mainly included oil and gas to the surface [1,2]. Oil expansion is a very important part among those mechanisms if without availability of other artificial introduced energy. The rock and fluids expand due to their individual compressibility [3,4]. Since the fluid was expanded and the matrix pore volume was imbibed by the surrounding fluid, the reservoir pressure was plunged. As a result, the crude oil and water will be forced out of the pore space to the wellbore [5,6].

Primary recovery or natural production is applied for oil extraction under natural driving mechanisms in reservoir without the use of external energy such as gas and water. As it mentioned before, a reservoir has economic production for a short period. In the natural production of reservoir, oil drift is run due to certain mechanisms; we will express them as below [7,8].

A. Rock and Fluid expansion

B. Solution Gas Drive

C. Gas Cap Drive

D. Water table Drive

E. Gravity Drive

F. Enhanced Oil Recovery

Certainly, enhanced oil recovery (EOR) methods are named as techniques that the fluid inject into the reservoir and this process energize the fluid so, the aim of these methods, is reducing amount of waste oil reservoir. These methods are divided into two categories:

A. Secondary Recovery

B. Tertiary Recovery

Conclusion

The importance of oil reservoirs injection is being classified as below:

Gas injection in oil fields is one of the top priorities of Oil Companies in context of quality target. This major is important for several reasons:

A. The necessary of hydrocarbon resources protection for posterity rights.

B. The necessary of national wealth preservation providing long-term investment in oil section and other sectors of the economy and the strength of countries economic infrastructure.

C. Dependence of countries economy on revenues from crude oil exports.

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Pseudo-Lignin Formation during Dilute acid Pretreatment for Cellulosic Ethanol-Juniper Publishers

Pseudo-Lignin Formation during Dilute acid Pretreatment for Cellulosic Ethanol-Juniper Publishers

Abstract

Dilute acid-based pretreatment represents one of the most important pretreatment technologies to reduce biomass recalcitrance and it has been successfully applied to a wide range of feedstocks. During this type of pretreatment, the relative lignin content usually increases partially due to the loss of carbohydrates. More importantly, it has been reported that the increase of lignin content after dilute acid pretreatment is mainly due to the formation of pseudo-lignin. The exact reaction mechanisms leading to the formation of pseudo-lignin is still under investigation. However, it has been proposed that rearrangement of hydroxymethylfurfural (HMF) or furfural can produce aromatic type of compounds which can further undergo polymerization reactions to from a lignin-like polyphenolic structures termed as pseudo-lignin. This mini-review mainly covers recent advances in understanding the fundamentals of pseudo-lignin formation during dilute acid pretreatment, the impact of its formation on enzymatic hydrolysis, and how to suppress its formation during dilute acid pretreatment.

Keywords: Biomass recalcitrance; Pseudo-lignin; Dilute acid pretreatment; Enzymatic hydrolysis; Hydroxymethylfurfural; furfural

Abbreviations: MW: Molecular Weight; Mw: Weight-average molecular weight; Mn: Number-average molecular weight; BTO: 1,2,4-benzenetriol; DMSO: Dimethyl Sulfoxide; HMF: Hydroxymethylfurfural

Introduction

Pharmaceutical excipients

Increasing global energy demand and environment concerns have led to rapid development of converting renewable resources such as lignocelluloses biomass to biofuels such as cellulosic ethanol [1]. Relatively high costs associated with the bioprocess and the sub-optimal yield of ethanol production remains a great challenge due to the natural resistance of the plant cell wall to enzymatic deconstruction. As a result, a chemical or physical pretreatment is usually required prior to the enzymatic hydrolysis step to disrupt the lignin-hemicellulose matrix and increase cellulose accessibility, which subsequently increases the following hydrolysis efficiency [2].

Over the past decades, different pretreatment technologies have been developed to reduce biomass recalcitrance [3]. Among all the available pretreatment technologies up-to-date, dilute acid-based pretreatment using a variety of acids including sulfuric acid, nitric acid, or hydrochloric acid remains as one of the most important technologies for cellulosic ethanol. It is normally performed with acid concentration less than 4wt% over a wide range of temperature (120 to 210 °C) [4]. It also has been applied on a wide range of feedstock such as poplar [5], switch grass [6], wheat straw [7], rice straw [8], bagasse [9], maize stems [10], and corn stover [11]. It is well known that this acidic type of pretreatment, in the absence of an organic solvent, is less effective in terms of lignin removal, and in fact, the relative content of Klason lignin is normally found to be increased after dilute acid pretreatment. For example, Foston et al. reported that the Klason lignin content significantly increased from ~25% to ~40% after dilute acid pretreatment of Populus [6]. This is of course partially due to the loss of carbohydrates especially the hemicellulose during pretreatment. However, Sannigrahi et al. reported that the formation of pseudo-lignin by the dehydration and polymerization of carbohydrates should be responsible for this unusual increase of lignin content [12]. In addition, it was also reported by Li et al. that only ~50% of the Klason lignin extracted from a hot water pretreated aspen was actual lignin [13].

Understanding the fundamentals of pseudo-lignin chemistry is important from the bioconversion process perspective. Optimization of current pretreatment technologies is often guided b carbohydrate loss during pretreatment and lignin residue content and/or structure after pretreatment. Lignin is well known to effect enzymatic hydrolysis negatively due to its physical barrier role and its unproductively binding to enzymes [14,15]. Therefore, development of novel low pH pretreatments with diminished pseudo-lignin formation will significantly reduce the enzyme loadings required for an efficient enzymatic hydrolysis, hence improve the overall process economics. In conclusion, the formation of pseudo-lignin during any low pH pretreatment is unfavorable as it originates from carbohydrate degradation and more importantly, it may be even more detrimental to enzymatic hydrolysis compared to native lignin. This mini-review highlights recent advances in understanding the fundamentals of pseudo-lignin formation, the impact of its formation on enzymatic hydrolysis rate and yield, and how to suppress its formation during pretreatment.

Structural Characterization of Pseudo-Lignin

For characterization purposes, pseudo-lignin is normally produced and isolated from dilute acid pretreated lignin-free materials such as a-cellulose and holocellulose. Table 1 shows some typical yields of pseudo-lignin isolated from different resources under different pretreatment conditions. A variety of analytical techniques including GPC, FTIR, NMR, SEM have been utilized to characterize pseudo-lignin. Molecular weight (MW) of isolated pseudo-lignin from different resources is shown in Table 2. In general, the MW of pseudo-lignin is much lower than that of milled wood lignin. For example, the weight average MW (Mw) of milled poplar lignin and pseudo-lignin derived from dilute acid pretreated poplar holocellulose at 180 °C were found to be 10002g/mol and 5050g/mol, respectively [16,17]. Pretreatment severity was not found to be a huge impact factor on the MW of pseudo-lignin (Table 2) [18–20]. In addition, MW of pseudolignin derived from dilute acid pretreated holocellulose was found larger than that of pseudo-lignin extracted from pretreated a-cellulose (Table 2) [16]. FTIR and 13C NMR analysis were also used to provide additional information on the chemical structure of pseudo-lignin, which indicated that pseudo-lignin was mainly composed of hydroxyl, carbonyl and aromatic structures [12]. These results clearly indicated that pseudo-lignin was a polyphenolic, lignin-like material with aliphatic, aromatic, and carbonyl structures derived from cellulose/hemicellulose fragments released during acid hydrolysis reactions.

Lignin can be redistributed during dilute acid pretreatment, leading to the formation of lignin droplets of various morphologies [10,21–24]. During the dilute acid pretreatment, lignin was reported to coalesce on plant cell wall and then migrate into the bulk liquid phase in form of droplets or balls [21]. This kind of lignin aggregation normally requires the pretreatment temperature to exceed the lignin phase transition temperature. Similar to this kind of re-deposit lignin droplets, pseudo-lignin can be also exist as discrete spherical droplets on the surface of pretreated holocellulose with a range of sizes from 0.3 to 8.0mmm [12]. Figure 1 illustrates a SEM image of pseudolignin deposition on surface of poplar holocellulose during dilute acid pretreatment.

Reaction Mechanisms Leading to the Formation of Pseudo-Lignin

The exact mechanisms leading to the formation of pseudolignin are still under investigation due to the complexity of pseudo-lignin structure and the heterogeneity of reaction sources and media. However, the presence of high proportions of unsaturated carbons in pseudo-lignin structure strongly indicated that acid hydrolysis of carbohydrates polymers to their corresponding monosaccharide’s and the subsequent dehydration and fragmentation of sugars probably took place during the acid pretreatment. Hydroxymethylfurfural (HMF) and furfural can be produced from 6 and 5-carbon sugars such as glucose and xylems via acid catalyzed dehydration reactions [25,26]. HMF and furfural can be further subjected to rearrangements to produce other aromatic compounds which might be the key intermediates for pseudo-lignin formation. For example, 3,8-dihydroxyl-2-methylchromone was reported as one of the main aromatic products in the acidic degradation of xylems [27]. Similarly, hydrolytic ring-opening reaction of HMF was reported to generate 1,2,4-benzenetriol (BTO) in yields of 46% [28]. These intermediates can be then converted to pseudolignin via polymerization/polycondensation reactions. For instance, it has been reported that BTO could react with HMF or furfural to produce a three-dimensional polymer via acid catalyzed aromatic electrophonic substitution [18]. Figure 2 summarized the reaction mechanisms mentioned above, which highly suggested presence of acid and high temperatures are probably two crucial conditions for the pseudo-lignin formation. Understanding the reaction pathways leading to the formation of pseudo-lignin will provide insights into how to suppress pseudolignin generation, though much work still needed to be done.

Impact of Pseudo-Lignin on Enzymatic Hydrolysis

Li and co-workers reported that the lignin droplets deposited on the surface of plant cell wall significantly inhibited cellulose hydrolysis, mainly through surface blockage [21]. Their study indicated the nonspecific binding of lignin droplets to enzymes was not the key source of inhibition. Similar to the lignin redeposit droplets, pseudo-lignin formed during dilute acid pretreatment can also exist as discrete spherical droplets on the surface of pretreated materials, and its formation is obviously not desired due to the fact that pseudo-lignin can directly decrease cellulose accessibility by blocking the surface binding sites. On the other hand, pseudo-lignin is also known to unproductively bind to cellulase and inhibit its action [29]. Kumar et al. studied the enzymatic hydrolysis of Avicel cellulose mixed with pseudo-lignin derived from pure xylose, and it was reported that even a small amount of pseudo-lignin addition could have a noticeable negative impact on enzymatic hydrolysis yield [20]. Further protein adsorption experiments revealed that pseudo-lignin bound to enzymes unproductively. A recent study by Hu et al. further demonstrated the formation of pseudolignin needed to be avoided as they proved that pseudo-lignin is much more detrimental to enzymatic hydrolysis than regular dilute acid pretreated lignin (Figure 3)[30]. More specifically, dilute acid pretreated lignin only inhibited enzymatic hydrolysis in its initial stage and had a nearly negligible impact on the overall conversion percentage after 48 h as shown in Figure 3, whereas pseudo-lignin addition could decrease enzymatic hydrolysis yield up to 25% [30]. It is worth mentioning pseudolignin is insoluble in water, therefore the hydrophobic structural functionality of pseudo-lignin is probably responsible for its nonproductive association with enzymes.

Suppression of Pseudo-Lignin Formation during Dilute Acid Pretreatment

Lignin redeposits droplets and pseudo-lignin only can be formed at elevated temperatures, therefore reducing the pretreatment severity is obviously one of the ways to reduce or avoid the formation of pseudo-lignin. However, as the pretreatment severity decreases, so do the efficient of pretreatment in terms of hemicellulose removal and cellulose accessibility increase. Compared to the typical batch pretreatment, flow through reactor system was shown to dramatically increase lignin removal as much as over 90% [31]. More importantly, its ability to constantly remove lignin into the aqueous phase effectively restricts the condensation reactions. As a result, flow through pretreatment can reduce the chances of pseudo-lignin formation [31,32].Oxidative polymerization seems to play an important role in pseudo-lignin formation based on the proposed pathway, therefore performing dilute acid pretreatment under non-oxygen environment could be another possible alternative method. It was also reported that introduction of dimethyl sulfoxide (DMSO) to the acidic medium could effectively suppress HMF productions which is one of key intermediates during the pseudo-lignin formation [33]. A recent study modified a series of dilute acid pretreatment by using N2, surfactant Tween-80, or DMSO-water mixture as the reaction medium to test these hypotheses for new methods of suppressing pseudo-lignin formation without significantly reducing the pretreatment severity [34]. As shown in Table 3, addition of N2 was not effective in terms of pseudo-lignin suppression although extra oxygen significantly facilitated pseudo-lignin formation as expected. Apparently, introduction of DMSO significantly reduced the pseudo-lignin content by ~30%. The coordination of HMF with water can be reduced in the presence of DMSO due to the stronger interaction of DMSO oxygen with water [35]. From the reaction mechanism perspective, the reduction of HMFwater coordination could protect the HMF molecule from further reactions to form pseudo-lignin [34].

Conclusion

Lignin-like materials originated from acid catalyzed dehydration of carbohydrate, termed pseudo-lignin, are responsible for the increased Klason lignin content after acidbased biomass pretreatment. Pseudo-lignin can be deposit on the surface of biomass during the dilute acid pretreatment in forms of discrete spherical droplets or balls, and it is detrimental to the subsequent enzymatic hydrolysis, even more detrimental than dilute acid pretreated lignin. Therefore, it became essential to develop techniques to effectively impeded pseudo-lignin formation. Current ongoing pseudo-lignin researches are still quite limited to carbohydrate-derived pseudo-lignins, it is quite possible that lignin would somehow react with carbohydrate degradation products vis polycondensation reactions, contributing to the yield of pseudo-lignin. The understanding of the most fundamental chemistry associated with pseudolignin formation is crucial for the future bioethanol production. Therefore, future work is much needed to fully unlock the secret of pseudo-lignin chemistry.

Acknowledgement

This manuscript has been authored by UT-Battle, LLC under contract no. DE-AC05–00OR22725 with the U.S. Department of Energy. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in according with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-accessplan). This study was supported and performed as part of the BioEnergy Science Center (BESC). The BESC is a U.S. Department of Energy BioEnergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science.

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Anionic Surfactant Adsorption: Insight for Enhanced Oil Recovery

Authored by  wan Sulaiman WR

Surfactant flooding is a known enhanced oil recovery technique used in the oil and gas industry for decades. The primary principle of surfactant flooding is to reduce interfacial tension, wettability between the oil, water and rock, a lot of attention on research has been devoted to this area of study but the problem is the economical factor due to the high rate of surfactant loss to rock formation and clay minerals, as a result of surfactant retention. This paper therefore, is to review the basic concepts of surfactant nature, mineralogy, electorlyte, temperature and pH as future guide lines in addressing the surfactant losses due to the adsorption.

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Tolerance of Plants in Response to Abiotic Stress Factors

Authored by  Rupnarayan Sett

Immobile plants can't evade abiotic stress factor, this feature enables them to develop distinctive molecular mechanisms to deal with different pressure aspects; though, variations do exist in tolerance mechanisms. In some plants, morphological modifications have made them able to avoid stress factors. The best option lies for them is to change their biochemical and physiological activities to combat the stress. Abiotic stresses are caused by water scarcity or drought, excess of salts or over-salinity, beyond-tolerance temperatures, intensity and photoperiodicity of light, nutrient-deficiency or excessiveness, prevalence of heavy-metal elements, air- or water- pollution, etc. These factors may affect the plants as individual factor or in combinations, which may change the metabolic processes affecting to less growth, development and productivity (Figure 1). In case of extreme stress, it will cause unbearable metabolic load on the cells leading to death of the plant. The plants are not totally free from stress in nature. To fight these stresses, plants develop several procedures to combat that with the generation of unique molecules and metabolic pathways for stress acceptance.

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An Overview on Development of Countermeasures for Breakwater against Earthquake and Tsunami Induced Damage

Authored by  Chaudhary B

The compound disaster triggered by earthquake and tsunami imposes devastating damage to structures and human lives living near seacoasts. In past few years, breakwaters (which are used to protect coastal areas from devastating damage of tsunamis) failed during tsunami. It led to enter the tsunami waves into the coastal areas, and created deep devastation there. It was observed that the breakwaters collapsed mainly due to failure of their foundations. Recently, some research works have been done to make breakwater resilient against tsunami induced damaged in order to protect coastal areas from devastating damage of tsunami. This paper mainly reviews some recent studies towards making the breakwater resilient against earthquake and tsunami induced damage.

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Biodiesel Production using Trans-Esterification Process and Investigation of Fuel Properties: A Review Study

Authored by  Hossein Esmaeili

Biodiesel is a renewable fuel that, due to increasing environmental pollution and global warming caused by fossil fuels, its production is increased. Nowadays, low prices renewable sources like waste edible oil which has been disposed from restaurants, is used to produce the biodiesel. One of methods for biodiesel production is trans-Esterification. In the trans-Esterification process, the reaction takes place in the presence of catalysts such as alkaline, acidic and enzymatic catalysts. Finally, properties of biodiesel such as flash point, kinematic viscosity, density, cloud point and pour point will obtain based on the international standard ASTM D6751 and the properties are compared with diesel fuel.

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Fundamental Processes of Photo induced Charge Transfer in Quantum Dot-Based PV Systems

Authored by  Isa Amos P

In a quest to explore the field of renewable energy sources, Semiconductor Quantum dots has received several nods as light harvesters, emitters and as potential markers in imaging owing to their opto-electronic properties which are size dependent. One of the fundamental but little known aspect of Quantum dots’ solar photo conversion is the dynamics of charge transfer. This paper discusses the fundamental processes of charge transfer i.e. Electron injection in Quantum dots to metal oxides composites, Charge trapping in Quantum dots, and finally, Exciton vs Energy Transfer.

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An Evaluation of the Chemical Composition and Antibacterial Activities of Mormodica balsamina Seeds Extract

Authored by  Uchegbu RI

The chemical composition of the seed extract of Mormodica balsamina and its antibacterial activity against some human pathogens were studied. The study was designed to identify the phytochemical and nutritive values of the seeds and to test the inhibitory ability of the plant extract on human pathogens. Chemical composition of Mormodica balsamina seeds was determined using standard methods. The antibacterial activity was performed by filter paper disc diffusion technique. Phytochemical studies revealed the presence of alkaloids (0.34%), flavonoids (1.08%), tannins (0.28%), phenols (0.65%) and saponins (2.20%). The mineral constituents were Ca (1.76%), Mg (1.10%), K (0.83%), Na (0.20%), P (0.34%) and N (1.40%). The plant samples were found to be rich in vitamins comprising riboflavin (0.30mg/100g), thiamin (0.09mg/100g), niacin (0.21mg/100g) and ascorbic acid (4.44mg/100). The proximate composition revealed the presence of protein (8.75%), crude fibre (1.95%), fats/oil (1.45%), ash (4.50%), carbohydrates (83.35%) and food energy (381.5g/cal). The ethanol extract inhibited all the tested organisms E.coli., K. pneumonia, S. aureus, P. mirabilis and Salmonina indicating that Mormodica balsamina seeds can serve as a potential food and antibacterial agents.

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Effective Heat Transfer Design for Solid and Cavity wall configuration

Authored by  Acakpovi A

This paper seeks to outline good practice in the design, installation and operation of building cooling systems. It encompasses the discussion on the different types of cooling systems that must be applied for particular needs. The paper also deals with the philosophy of building heat gain, the methodology in the prediction of cooling load energy and ultimately the importance of optimizing heat transfer. In the methodology section, Fourier's law was used to design the cooling systems for a solid wall and a cavity wall of same area made from material of similar heat transfer coefficient. Results showed that the cavity wall permitted less heat transfer into the confined space hence less electricity required to cool it. It is recommended therefore that, large public buildings should be designed in this manner so as to reduce the need for unnecessary electrical power to maintain them.

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