At present, domestic pentane production technology mainly comes from Tianjin University and Beijing Research Institute of chemical industry. The main raw materials are light hydrocarbon in oil field, topping oil in crude oil pretreatment unit, light naphtha in hydrogenation unit, mixed hydrocarbon after reforming and hydrogenation, C5 in refinery gas separation unit and C5 fraction from cracking by-product of ethylene unit. It can also be obtained by separation and refining of mixed C5 after C5 etherification, or by hydrogenation of cyclopentadiene.
The C5 fraction obtained from straight run gasoline, natural gas condensate, hydrocracking tail oil and reforming gasoline is mainly obtained from pentane separation column and isopentane column by high-efficiency distillation. The main process flow is as follows (taking natural gas condensate as an example): it is heated to 55 ℃ in the preheater before entering the debutanizer. The operating pressure of the debutanizer is 0.34 MPa. Propane and butane fraction are taken out from the top of the tower (the top temperature is 48 ℃), part of the top condensate is used as reflux liquid, and the excess condensate is heated to 76 ℃ through the heat exchanger before entering the depropanizer. The operating pressure of depropanizer is 2 MPa. Propane is removed from the top of depropanizer (the top temperature is 50 ℃) and butane is removed from the bottom of depropanizer. The gasoline from the debutanizer kettle enters the depentanizer. The number of depentanizer plates is 30, the operating pressure is 2.2 MPa, the reflux ratio is 1.5, and the overhead fraction is condensed and then enters the isopentane separator. The number of plates of isopentane separator is 60-80, the top temperature is 58 ℃, the reflux ratio is 10.0, and the operating pressure is 0.2 MPa. The purity of the distillate from the top of the tower is 95% isopentane, and the distillate from the bottom of the tower is 90% n-pentane.
Pentane and other products can be separated from mixed C5 separated from FCC LPG and ethylene units. The main process is hydrogenation under the condition of new Ziegler type catalyst. The reaction temperature is 60-80 ℃, and the pressure is 0.8-1.0 MPa. After hydrogenation, C5 can be separated into isopentane, n-pentane and cyclopentane by distillation
Solvent carrier for linear low density polyethylene (LLDPE)
N-pentane is mainly used as carrier solvent for LLDPE. China’s LLDPE production began in the 1960s. By the end of 2000, with the rapid development of China’s light industry and plastic industry, the consumption of LLDPE has increased rapidly. Many enterprises have built more than 10 sets of large-scale and technologically advanced production units by introducing foreign technology and equipment, and the production capacity has reached 1.05 MT / A. According to the process requirements of products, the proportion of n-pentane per ton of LLDPE is generally 0.3%. Therefore, the annual consumption of n-pentane in LLDPE field is about 3 KT.
Puffing agent for cut tobacco
Isopentane was used as solvent for tobacco expansion. The main function of tobacco puffing is to reduce the consumption of tobacco leaves, reduce the tar and nicotine content of cigarettes, and improve the quality of tobacco leaves. The puffing technology can save 2.5-3.0 kg of cut tobacco per box of cigarettes (about 50 kg cut tobacco), and effectively improve the quality of cut tobacco. Imperial Tobacco has developed IMPEX tobacco expansion technology and equipment with isopentane as solvent to replace CFC (Freon) tobacco expansion system. Since 1995, IMPEX system has been used to expand cut tobacco for cigar. Compared with CO2 expansion system, this system has higher expansion rate and higher filling capacity of tobacco.
Among 179 cigarette factories in China, 57 use CFC-11 expansion process, and the consumption of CFC-11 in 1998 was 1 003 t. At present, some large-scale tobacco enterprises in China use liquid CO2 to expand instead of CFC-11. According to the substitution situation of foreign tobacco industry, isopentane as expansion agent has a certain market prospect in tobacco expansion technology.
