Production method of ethylene propylene rubber

There are three main production technologies of ethylene propylene rubber: solution polymerization, suspension polymerization and gas phase polymerization.

Solution polymerization is a homogeneous reaction in solvent, which can not only dissolve the product, but also dissolve the monomer and catalyst system. Straight-chain alkanes are usually used as solvents (such as n-hexane). At present, solution polymerization is the main production method of ethylene-propylene rubber, which is adopted by most foreign manufacturers. There are two industrialized solution polymerization technologies: low-temperature solution polymerization of Ziegler-Natta series catalysts and high-temperature solution polymerization of metallocene series catalysts. The ethylene-propylene rubber produced by vanadium-based catalyst solution method has the largest output, the most brands and strong market adaptability, and its output accounts for about 80% of the world's ethylene-propylene rubber production.

The advantages of Ziegler-Natta solution polymerization are relatively mature technology, stable operation, many product brands, uniform quality, less ash and wide application range. Disadvantages are that the mass transfer and heat transfer are limited because the polymerization reaction is carried out in the solvent, and the polymer mass concentration is generally controlled at 6% ~ 9%, and the highest is only 1 1% ~ 14%, so the polymerization efficiency is low; In addition, due to the use of solvents, it needs to be recovered and refined, and the production process is long, there are many equipments, and the construction investment and operation cost are high.

Suspension polymerization does not need additional solvent, and propylene is both a reactive monomer and a suspension medium. Because the ethylene-propylene rubber product is insoluble in propylene, it is suspended in it and becomes polymer liquid propylene slurry. The characteristics of suspension polymerization method are that the mass concentration of polymer in polymerization solution can reach 33% ~ 40%; Removing the reaction heat by evaporating the monomer; Evaporated propylene can be recycled; Polymer colloidal particles are large and need to be crushed and washed; Because there is no solvent, the process of solvent recovery and refining is omitted; Wet coagulation is adopted; The third monomer is evenly distributed in the molecular chain and has high utilization rate, which is beneficial to improve the processability of the product. At present, only Bayer Company of Germany and Enichem Company of Italy produce ethylene-propylene rubber by suspension polymerization, and the production capacity only accounts for about 1 1% of the total production capacity of ethylene-propylene rubber in the world. This method has few brands and is mainly used for polyolefin modification.

The gas phase method was successfully developed by UCC (United Carbide) Company of the United States, and the world's first production unit (9 1kt/a) was built in DuPont Dow Chemical Company of the United States in 1998, with the production capacity accounting for about 9% of the total production capacity of ethylene-propylene rubber in the world. Compared with solution polymerization and suspension polymerization, gas phase polymerization does not use solvents, and does not need solvent removal, recovery and drying. Not only is the process simple, but also the energy consumption can be greatly reduced, and there is almost no discharge of three wastes, with less investment and low cost. The disadvantage of gas phase polymerization method is that the product contains carbon black, the product is not universal, and the rubber properties are not suitable for some purposes. Therefore, it has limitations and cannot be widely promoted. In 2008, the Dow 9 1kt/a gas phase unit was shut down.