The methods of NBR hydrogenation to prepare HNBR include solution hydrogenation, emulsion hydrogenation, catalytic hydrogenation of olefin complex decomposition, acrylonitrile-ethylene copolymerization hydrogenation, etc. At present, HNBR is mainly prepared by solution hydrogenation in industrial plants.
1.
Solution hydrogenation
At present, solution hydrogenation is the main process for the industrial production of HNBR. Under high temperature and pressure, NBR dissolved in chlorobenzene, xylene, acetone, ethyl acetate and other organic solvents, the double bond of butadiene unit in NBR was selectively hydrogenated to saturated bond under the action of catalyst, while the side chain cyanide group of acrylonitrile unit was retained. Commonly used catalysts are rhodium, ruthenium, palladium, iridium, osmium and other precious metal complexes, commonly used ligands are amines and metal oxides.
The solution hydrogenation method has good mass and heat transfer performance, effectively improves the hydrogenation efficiency, and shows high activity and high selectivity. According to the different solubility of catalyst, the solution hydrogenation method can be divided into homogeneous solution hydrogenation method and heterogeneous solution hydrogenation method, both of which have been applied in industry. Compared with heterogeneous catalyst, homogeneous catalyst can be uniformly dispersed in the reaction solution, so that its active component is fully in contact with the substrate, which has higher reactivity and selectivity. But the production cost of homogeneous catalyst is high.
2.
Other methods
(1) Emulsion hydrogenation method: emulsion hydrogenation method refers to the selective hydrogenation reaction of unsaturated chain segment directly in the state of NBR latex to produce HNBR latex. Compared with the solution hydrogenation process, the emulsion hydrogenation process does not require or only requires a small amount of organic solvents, and the environmental pollution is small, and the process is simple and easy to operate. But it is easy to produce gel and affect the performance of the product. At present, the process technology is still in the pilot stage and has not been industrialized.
(2) Olefin catalytic hydrogenation method: The olefin catalytic hydrogenation method is divided into two steps. First, in an inert atmosphere, NBR performs the decomposition reaction under the action of ruthenium carbene catalyst to reduce molecular weight or introduce functional groups; After the complex decomposition process to a certain extent, hydrogen was introduced into the system and hydrogenated under the catalysis of ruthenium complex to prepare HNBR. At present, the domestic Zannan technology company has preliminarily realized the industrialization process of HNBR made by this process.
(3) acrylonitrile-ethylene copolymerization hydrogenation method: Ethylene-acrylonitrile copolymerization method refers to the direct synthesis of HNBR by free radical copolymerization of ethylene monomer and methacrylonitrile monomer under high pressure. Due to the large difference in reaction rate of each monomer (Racrylonitrile =0.04, Rethylene =0.8), copolymerization reaction conditions are harsh, and side reactions such as chain rearrangement and chain transfer are prone to occur. The product molecular chain branching degree is high, the randomness is poor, the polymer properties are poor, this process is still in the stage of pilot study.
(4) Non-organic solvent hydrogenation method: At present, the industrialized HNBR production process requires the use of organic solvents, which has caused some pollution to the environment. In view of this, researchers are exploring the bulk hydrogenation method, hydrogen storage alloy hydrogenation method, supercritical carbon dioxide hydrogenation method, ionic liquid hydrogenation method, temperature controlled phase transfer hydrogenation method, biotechnology hydrogenation method and other green hydrogenation technology without organic solvents, but the relevant technologies are currently in the laboratory research stage.
At present, China's HNBR industry ushered in great development, among which, Shandong Dao has built an annual output of 3,000 tons of HNBR production line (process for homogeneous solution hydrogenation); Zhejiang Zansheng New Materials, a subsidiary of Shanghai Zannan Technology, has built an HNBR industrial production plant with an annual output of 2,000 tons (the process is homogeneous solution hydrogenation), and related products are applied in synchronous belts and seals; Sinopec Qilu Petrochemical Branch will complete the HNBR production line with an annual output of 5,000 tons by the end of 2022.
