polyisoprene

Production process
① A continuous solution polymerization process using Ziegler-Natta catalyst and hexane (or butane) as solvent. This process was first industrialized by Goodyear Tire and Rubber Company in the United States in 1963. The process includes: preparation of catalyst (titanium tetrachloride-trialkylaluminum or titanium tetrachloride-polyiminoaluminum alkane), polymerization, removal of catalyst residue, dehydration and drying, and molding and packaging. The polymerization is carried out in 3 to 6 series reactors with a single reactor volume of 40 to 50m3. The operating process parameters are: monomer concentration 12% to 25%, polymerization temperature 0 to 50°C, reaction time 3 to 5h, conversion rate can reach 80% to 90%, Mooney viscosity of the obtained raw rubber is 80 to 90, gel content <1%, and cis-1,4 content of isoprene rubber>95%.
② Intermittent solution polymerization process using lithium or alkyl lithium (RLi) as catalyst and cyclohexane (or hexane) as solvent. This process was first industrialized by Shell Company of the United States in 1962 using the patent of Goodrich Chemical Company. The cis-1,4 content of the obtained isoprene rubber is 92% to 93%. Because the amount of lithium-based catalyst is small and the conversion rate is high, the monomer recovery and catalyst residue removal processes can be omitted in the process. Compared with continuous solution polymerization, this process has high requirements for raw material purity and stricter control of polymerization conditions, and the performance of the obtained isoprene rubber is slightly worse.
In 1974, China published the experimental results of synthesizing cis-1,4-polyisoprene with cyclohexane acid rare earth-triisobutylaluminum-halide for the first time, and then carried out catalyst screening, polymer structure and performance, and intermediate test development. This rare earth catalyst can produce isoprene rubber with a cis-1,4 content of more than 94% in hydrogenated gasoline, which is a new catalyst system with industrial prospects.
Development status
The important bottleneck restricting the development of China's rubber industry is the tight supply of rubber, especially natural rubber, and the high price. Due to geographical conditions, the growth rate of natural rubber production in my country is slow. It is predicted that my country's annual output of natural rubber can increase by more than 700,000 tons at most, which is difficult to meet the needs of the rapid development of the domestic rubber industry; but the output of synthetic rubber has increased with the development of China's petrochemical industry. Among the main varieties of synthetic rubber, my country can produce styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, butyl rubber, chloroprene rubber, nitrile rubber and other rubbers, but the production of isoprene rubber is still blank; and the above synthetic rubber varieties cannot completely replace natural rubber, only isoprene rubber can replace natural rubber. How to improve the "no rice to cook" status of natural rubber, an important raw material for the rubber industry, has become a common concern in the industry. my country's annual rubber consumption exceeds 3.1 million tons, ranking first in the world. It is expected that by 2010, it will exceed 5 million tons, with an average annual growth rate of more than 5.5%; in 2015, it will exceed 6 million tons, maintaining a growth rate of 4%. In order to make up for the shortage of domestic natural rubber resources, my country has imported more than 1 million tons of natural rubber every year in the past two years. It is expected that my country's annual import of natural rubber will exceed 2 million tons in the future, accounting for more than 20% of the world's total natural rubber resources.
In addition, from the perspective of the development of my country's tire industry, the isoprene rubber required for some parts of all-steel load-bearing radial tires is imported from Russia, and the import volume has exceeded 10,000 tons, and the price is also gradually rising. When the price was lower in the early stage, bias tires also used imported isoprene rubber, and tire manufacturers achieved good benefits. If isoprene rubber replaces natural rubber at a ratio of 20%, the formulation process can be used smoothly without adjustment. Based on the tire industry's consumption of 2.5 million tons of rubber in 2010, the consumption of isoprene rubber can reach 500,000 tons, which can reduce the import of natural rubber by 500,000 tons, which is very beneficial to both the country and the people. Russia uses isoprene rubber in 50% of tire production. If this ratio is reached domestically, the demand for isoprene rubber will be even greater. Therefore, my country should encourage the domestic rubber industry to actively develop isoprene rubber and form large-scale production from a strategic perspective.