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Equipment and processes of oil chemical industry 09.12.2019 00:00
Oil chemical industry is closely connected to refinery industry because products of refineries are basic feed for oil chemical industry.
Oil chemical industry produces a wide range of national consumption goods as well as products for further processing and has an important role in industry system of national economy. Oil chemical industry makes it possible to process hydrocarbon feed complexly.
Main feed for oil chemical industry is ethylene. It is a product of oil feed pyrolysis. Ethylene is a simplest olefin hydrocarbon i.e. it has one carbon-carbon double bond. Ethylene can react with oxygen at special conditions and in the presence of catalyst and in this case it forms ethylene oxide. The ethylene oxide is a raw material for manufacturing of ethylene glycol that is a liquid used as antifreeze (liquid freezing at low temperature). Mixtures of ethylene glycol with water in different ratios with different freezing points are applied in industry. In Russia the mixtures have trade name “Tosol”. Furthermore, ethanol can be produced by direct hydration of ethylene in the presence of catalyst (phosphoric acid on solid support (aluminosilicate or silica gel)). Formerly ethanol was produced only by fermentation of different organic feed but now the manufacturing method is considered as commercially unreasonable for production of ethanol of technical grade. Ethyl alcohol (ethanol) is used as organic solvent and as feed for manufacturing of other products such as acetic acid, acetic anhydride, acetate fiber and cellophane. Acetic anhydride can be manufactured by direct oxidation of ethylene (Wacker process). Acetic acid is produced from acetic anhydride. Polyethylene is manufactured by direct polymerization of ethylene. Polyethylene is a polymer having very valuable properties. Polyethylene is a thermoplastic substance i.e. in case of heating it softens and therefore we can obtain required form of it, and then after cooling it hardens. It is a very valuable property as it makes it possible to produce a wide range of different products from it. Oil chemical industry manufactures two types of polyethylene: low-density polyethylene and high-density polyethylene. Low-density polyethylene is produced by radical polymerization at high temperature and high pressure. High-density polyethylene is manufactured at lower temperature and significantly lower pressure with the use of catalyst (coordinate polymerization). Low-pressure polyethylene (high-density polyethylene) is used for manufacturing of polyethylene packing film, tape, polyethylene pipes applied as non-pressurized pipelines and for laying cables in them, packages (bottles, containers, casks etc.), household goods. High-pressure polyethylene (low-density polyethylene) is applied for film manufacturing, particularly polyethylene bags for shopping and garbage, plastic packages, electric isolation products.
Another important feed for manufacturing a wide range of oil chemistry products is propylene. Propylene, or propene, is an olefin hydrocarbon including three carbon atoms. Isopropyl alcohol is produced from propylene. The isopropyl alcohol is used for manufacturing of acetone which is the most important organic solvent. Furthermore, propylene is used for production of glycerol which is polyhydric alcohol and which is widely applied in industry. In addition, in the same way as ethylene oxide is produced from ethylene, propylene oxide is produced from propylene. The propylene oxide is used for propylene glycol production. Propylene glycol is the most important feed for polyurethane manufacturing. Polyurethanes are a wide group of polymers including urethane group and having different physical and chemical properties. Polyurethanes are elastomers. They can be both plastic resins and solids depending on their internal structure. Polyurethanes are applied in industry as resin substitutes. They are used for production of soles, sport equipment, machine parts (for example, bushings). Foamed polyurethane is widely used as structural material in building.
Propylene is used for production of acrolein and the latter is applied for production of acrylic acid. Acrylic acid is used for production of paints and lacquers, for impregnation of fabrics and fibers. Significant quantities of acrylic acid are used for production of polyacrylonitrile which is a raw material for synthetic fiber manufacturing.
Next representative of olefin hydrocarbons is butylene (buten). It is applied for production of butadiene. Butadiene is a main component for synthetic rubber manufacturing. Rubber is an elastic and waterproof material, it can interact with sulphur i.e. vulcanize. During vulcanization sulphur atoms create cross-links between linear rubber chains so forming vulcanized resins and ebonites. In addition to butadiene resin that was the first synthetic resin manufactured in industry in large volumes, now oil chemical industry produces isoprene rubber (formed by isoprene polymerization), butyl rubber (isoprene-isobutylene copolymer), nitrile-butadiene rubber, chloroprene rubber, fluorine rubber, etc. in large volumes. Rubber is applied during production of automobile tires, sport goods, sealing materials used in building and equipment.
Another important product of oil chemistry is polyvinylchloride (PVC) manufactured from vinyl chloride. Vinyl chloride is produced from dichloroethane. PVC is used for production of pipes, electric isolation materials, machine parts, films, stretch ceiling films, floor cloth, clothes. The simplest aromatic hydrocarbon – benzene – is used for production of styrene. Styrene can be polymerized and therefore polystyrene is formed. Polystyrene is used for plastic manufacturing. Furthermore, benzene is applied for phenol synthesis. And phenol is used for production of phenolformaldehyde resin and plastic. In addition, benzene is applied for aniline synthesis. Aniline is used for production of dyes, vulcanization accelerators, polyurethanes and pesticides. Another aromatic hydrocarbon – toluene – is applied for production of trinitrotoluene (TNT) used for explosives manufacturing. Xylol is used for production of wide range of polymer coatings.
Equipment applied at oil chemical plants is different by type and by its structural arrangement. Firstly, at oil chemical plants different reactors are used. In the reactors chemical substances are transformed to other ones. The transformations often are performed at high temperature, therefore the reactors can be equipped with heating systems (jacket or coil). There are chemical reactions with heat release (exothermic reactions) and reactions with heat adsorption (endothermic reactions). Reactions requiring medium heating for their start but proceeding with heat release are a special challenge in oil chemistry. In this case after reaction medium heating up to temperature of chemical reaction starting, it is required to carry off heat. Such processes are performed with the use of heating / cooling agent with variable temperature. Furthermore, many chemical reactions in oil chemistry are performed with the use of catalyst. Generally it is a solid catalyst with a large area of external surface. The larger the catalyst surface area is, the more active centers it has, therefore the higher reaction velocity is. In order to increase area of contact between reaction medium and catalyst, special vessels are used, for example, vessels with fluid bed are widely applied. At such vessel catalyst is laid on special grids and reaction gas is blown from its bottom to its top with high velocity ensuring formation of catalyst fluid bed. Reaction gas velocity shall be sufficient for picking up catalyst particles from the grid but at the same time it shall be not sufficient for particle entrainment.
As many processes are performed at high pressure, compressor units are required for performing these processes. There are the following types of compressors used at oil chemical plants: piston compressors, screw compressors, spiral compressors, diaphragm compressors. Pumps are used for pumping liquid medium. For heating and cooling the following heat exchangers are applied: double pipe heat exchangers, plate heat exchangers, tube heat exchangers, etc. Fractionation processes are performed at fractionation columns. Adsorption processes are performed in adsorption columns. Absorption processes are performed at absorption columns. Vessels with mechanical agitators, cyclones for separation of solids from gas stream, filters (filter presses, vacuum filters including drum filters), separators, settling tanks, steam traps are widely applied. Gates, gate valves, valves, expansion bends, pipeline insulation components are used as pipeline elements. Cooling equipment, furnaces for product heating and burning and other similar equipment are applied. Instruments as well as automatic process control systems are used for process control.