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Propylene’s Manufacturing Techniques and Multiple Applications

Propylene is a vital chemical in the field of chemical engineering as it is considered as one of the most important basic chemicals that are used for the production of a number of other compounds. From Propylene oxide to acrylonitrile, cumene and acrylic acid, the derivatives derived from Propylene are a crucial factor in the production of a diverse range of products that we use in our everyday life. These chemicals are used in the production of films, fibers, containers, packaging materials and caps and closures to demonstrate the significance and usefulness of Propylene in modern industry. Let us explore the role of Propylene in various industries and the new solutions it inspires.

Introduction

Propene, also referred to as Propylene, serves as a crucial building block akin to ethene, particularly in the production of poly(propene) or Polypropylene. Unlike ethene, propene readily participates in substitution reactions, yielding a diverse array of significant chemicals. Its primary applications include the production of Polypropylene, acrolein, acrylonitrile, cumene, Propylene oxide, and butanal. These derivatives are instrumental in the manufacturing of acrylic polymers, phenol, acetone, polyurethanes, and surface coating solvents, showcasing propene's pivotal role in various industrial processes and product formulations.

Manufacturing Process

The production of Propylene is not direct, but indirectly through various other major industrial processes. Here are the two main ways Propylene is produced:

Steam Cracking: This is one of the largest processes accountings for the bulk of Propylene in the world today. Steam cracking is a process in which heavier hydrocarbons such as naphtha or natural gas liquids are cracked in a cracking furnace at high temperatures and with the use of steam. This process produces a mixture of several hydrocarbons with different chain lengths – the main product is ethylene and Propylene as a by-product.

Fluid Catalytic Cracking (FCC): This process is carried out in FCC units in refineries. FCC is mainly used to upgrade heavier gas oil from crude oil into gasoline. This process also produces a lighter stream of byproducts consisting of Propylene and other hydrocarbons. The significance of FCC as a Propylene source is expanding because it can process different feedstocks and likely to meet the growing Propylene demand.

Steam Cracking Units

The steam cracking process plays a pivotal role in the petrochemical sector, serving as the primary method for producing light olefins like ethylene and Propylene. It involves thermal cracking, utilizing either gas or naphtha, to generate these olefins. This review focuses on the naphtha steam cracking process, which primarily involves straight run naphtha sourced from crude oil distillation units. To qualify as petrochemical naphtha, the stream typically requires a high paraffin content, exceeding 66%.

Cracking reactions take place within the furnace tubes, and a significant concern and constraint for the operational lifespan of steam cracking units is the formation of coke deposits in these tubes. These reactions occur at elevated temperatures, typically ranging from 500°C to 700°C, depending on the feedstock's properties. For heavier feeds like gas oil, lower temperatures are employed to minimize coke formation.

The steam cracking process is characterized by high temperatures and short residence times. While the primary focus of a naphtha steam cracking unit is typically ethylene production, the yield of Propylene in such units can reach up to 15%.

Fluid Catalytic Cracking (FCC)

Presently, a significant portion of the Propylene market relies on steam cracking units for supply. However, a considerable share of the global Propylene demand stems from the separation of LPG generated in Fluid Catalytic Cracking Units (FCC).

Typically, LPG generated in FCC units contains approximately 30% Propylene, and the added value of Propylene is nearly 2.5 times that of LPG. In local markets, the installation of Propylene separation units proves to be a financially rewarding investment. However, a drawback of separating Propylene from LPG is that it results in a heavier fuel, causing specification issues, particularly in colder regions. In such cases, alternatives include segregating the butanes and redirecting them to the gasoline pool, adding propane to the LPG, or supplementing LPG with natural gas. It's important to note that some of these alternatives may decrease the availability of LPG, which could pose a significant constraint based on market demand.

A challenge in Propylene production lies in the separation of propane and Propylene, a task complicated by their close relative volatility of approximately 1.1. Traditional distillation methods struggle due to this narrow gap, necessitating distillation columns with numerous equilibrium stages and high internal reflux flow rates.

Two primary technologies employed for Propylene-propane separation are Heat-Pump and High Pressure configurations. The High Pressure approach relies on conventional separation methods, requiring sufficient pressure to condense products at ambient temperature, with a reboiler utilizing steam or another heat source. However, this method's reliance on low-pressure steam availability in refining hardware can be limiting. Alternatively, the Heat-Pump technology utilizes the heat from condensing top products in the reboiler, effectively combining the reboiler and condenser into a single unit. To address non-idealities, an auxiliary condenser with cooling water may be installed.

Implementing Heat-Pump technology enables a reduction in operating pressure from approximately 20 bar to 10 bar, thereby increasing the relative volatility of Propylene-propane and simplifying the separation process. Typically, Heat-Pump technology proves more attractive when distillation becomes challenging, particularly when relative volatilities are below 1.5.

Several variables must be considered when selecting the optimal technology for Propylene separation, including utility availability, temperature differentials in the column, and installation costs.

Propylene produced in refineries typically adheres to specific grades: Polymer grade, with a minimum purity of 99.5%, is directed towards the Polypropylene market, while Chemical grade, with purities ranging from 90 to 95%, is allocated for other applications. A comprehensive process flow diagram for a standard Propylene separation unit utilizing Heat-Pump configuration is illustrated in the following Figure.

The LPG extracted from the FCC unit undergoes a series of separation processes to isolate the light fraction, primarily comprising propane and Propylene. This fraction is then directed to a deethanizer column, while the heavier fraction, containing butanes, is either routed to the LPG or gasoline pool, depending on refinery configuration. The lighter fraction from the deethanizer column is often recycled back to the FCC unit for incorporation into the refinery fuel gas pool. Alternatively, it may be directed to petrochemical plants for the recovery of light olefins, particularly ethylene. The bottom fraction from the deethanizer column undergoes further separation in the C3 splitter column to separate propane and Propylene. Propane is recovered from the bottom of the C3 splitter and sent to the LPG pool, while Propylene is directed to the Propylene storage park. Before processing, the feed stream undergoes a caustic wash treatment to remove contaminants, such as carbonyl sulfide (COS), which can adversely affect petrochemical processes and may be produced in the FCC unit through the reaction between carbon monoxide and sulfur in the Riser.

Major Technologies Used for Producing Propylene

Process: OCT Process

Lummus Technology, one of the leading technology providers, presents two deliberate pathways to Propylene: Olefins Conversion Technology (OCT), which employs olefins metathesis, and CATOFIN propane dehydrogenation.

Traditionally, commercial on-purpose Propylene production methods have contributed to less than 5% of the global Propylene output, with the majority sourced as a by-product of steam crackers and fluid catalytic cracking (FCC) units.

Through the OCT process, low- value butylenes are subjected to reaction with ethylene to yield Propylene. The ethylene feedstock can range from diluted ethylene, typical of an FCC unit, to polymer-grade ethylene. Potential C4 feedstocks encompass mixed C4s generated in steam cracking, raffinate C4s from MTBE or butadiene extraction, and C4s produced within an FCC unit.

The ultra-high purity Propylene yielded by the OCT process surpasses polymer-grade specifications and promises potential cost savings in downstream Polypropylene facilities.

The mixture of ethylene feed and recycled ethylene is combined with the C4/C5 feed and recycled butenes/pentenes, and then heated before entering the fixed-bed metathesis reactor. Within the reactor, the catalyst facilitates the reaction of ethylene with butene-2 to produce Propylene, and the conversion of ethylene and pentenes to Propylene and butenes, while also isomerizing butene-1 to butene-2. Some coke buildup occurs on the catalyst, necessitating periodic regeneration of the beds using nitrogen-diluted air. The process is engineered for high utilization of olefins, typically ranging from 90 to 97%, with a Propylene selectivity of around 94 to 95%. After cooling and fractionation to remove ethylene for recycling, a portion of the recycle stream is purged to eliminate methane, ethane, and other light impurities. The bottoms from the ethylene column are directed to the Propylene column, where butenes/pentenes are separated for recycling to the reactor, and some are purged to eliminate unreacted butenes, isobutenes, butanes, unreacted pentenes, isopentenes, pentanes, and heavier compounds from the process. The overhead product from the Propylene column constitutes high-purity, polymer-grade Propylene.

Applications of Propylene

Polypropylene

The vast majority of Propylene, a key industrial ingredient, goes into making Polypropylene. This versatile plastic is used in everything from clothes and water bottles to patio furniture and countless other items. The most prominent among Propylene’s stars is Polypropylene (PP). This is a strong plastic that is used in packaging and is significantly lightweight. PP dominates the food container and beverage bottle market as well as the textile bag and carpet industry. It is resistant to moisture, chemicals, and heat that makes it ideal for food packaging and protecting some items when being transported. And its price makes it the first choice of the manufacturers.

Cumene

Cumene, a crucial intermediate compound, is predominantly synthesized through the Friedel-Crafts alkylation process involving Propylene and Benzene. This organic chemical holds significant value and finds widespread application in various products including plastics, pharmaceuticals, and adhesives. Moreover, cumene's exceptional solvency properties make it a preferred solvent in formulations for paints, inks, and cleaners. Its derivatives play a pivotal role in the production of polymers such as PET and polycarbonates, essential materials utilized in packaging, electronics, and construction industries. Additionally, cumene serves as an effective octane booster in gasoline, enhancing combustion efficiency and engine performance while reducing exhaust emissions.

Oxo Alcohol

Oxo alcohols form an important class of chemical intermediates that are used to produce plasticizers, coatings, and detergents. Oxo alcohols are used in a wide variety of industries from plastics and coatings to pharmaceuticals and cosmetics industries thus emphasizing their significance in various industrial processes.

Isopropanol

In the indirect-hydration method, Propylene undergoes a reaction with sulfuric acid to generate mono- and diisopropyl sulfates, which are subsequently hydrolyzed to produce isopropanol. This versatile compound is commonly diluted with water and employed as a rubbing-alcohol antiseptic, and it also serves as a key ingredient in aftershave lotions, hand lotions, and various cosmetic products. In industrial applications, isopropanol functions as a cost-effective solvent for cosmetics, medications, shellacs, and gums, in addition to its role in denaturing ethanol (ethyl alcohol).

Market Outlook

The majority of globally produced Propylene is utilized in the manufacturing of Polypropylene through polymerization. Propylene and its derivatives play crucial roles in various industries, including packaging, electronics, automotive, textiles, cosmetics, food and beverage, pharmaceuticals, construction, and others. Polypropylene stands as the predominant thermoplastic polymer, serving as a pivotal material for plastic components across a multitude of industries such as packaging, electronics, automotive, textiles, and beyond. Furthermore, various derivatives of Propylene are utilized across an array of sectors including cosmetics, personal care, food and beverage, pharmaceuticals, construction, automotive, and others, encompassing textiles, paper, pulp, electronics, consumer goods, and chemicals. As these sectors expand, the demand for Propylene is expected to increase.

Propylene Major Global Producers

Notable players in the Global Propylene market are Reliance Industries Limited, Indian Oil Corporation Limited, HPCL-Mittal Energy Limited, Haldia Petrochemicals Limited, Mangalore Refinery & Petrochemicals Ltd, Brahmaputra Cracker and Polymers Limited, Shenhua Ningxia Coal Group Corporation Limited, Bharat Petroleum Corporation Limited, Hindustan Petroleum Corporation Limited, GAIL (India) Limited, Nayara Energy Limited, Fujian Refining & Petrochemical Co Ltd, Zhong Tian He Chuang Energy, Sinopec Sabic Tianjin Petrochemical Co., Ltd., Wanhua Chemical Group Co., Ltd,  and Others.

Conclusion:

In summary, Propylene can be considered as a highly important, versatile and indispensable chemical compound that is used as an input for various industries around the globe. Its importance as a major producer of Polypropylene, an important thermoplastic material used in packaging and automobile industries, among others, attests to its significance in the economy. Furthermore, Propylene and other derivatives are used in various chemical industries such as cosmetics, pharmaceuticals, and construction industries. The anticipated growth of the Polypropylene industry is expected to significantly propel the market in the coming years. Additionally, various derivatives of Propylene, including Propylene oxide, acrylic acid, acetone, IPA, Polypropylene glycol, and cumene, find extensive applications across numerous industries, further driving demand for Propylene in the forecast period. Moreover, the rapidly expanding construction, automotive, and packaging industries present promising growth prospects in the global Propylene market.