Preparation Method Of Hydrogenated Nitrile Rubber

There are three main preparation methods of HNBR: ethylene-acrylonitrile copolymerization method, NBR solution hydrogenation method and NBR emulsion hydrogenation method.
1. Copolymerization method
Ethylene-acrylonitrile copolymerization
When preparing HNBR by acrylonitrile-ethylene copolymerization, due to the great difference in the reaction rate of each monomer in the copolymerization reaction (rAN=0.04, rE=0.8), it is difficult to control, and the performance of the polymer is not very good. It is still in the stage of small-scale research.
2. Emulsion hydrogenation
The emulsion hydrogenation method of NBR uses the thermal decomposition of p-methylsulfonyl hydrazide to produce diimide, which is an effective hydrogenation reducing agent. In 1984, WideMan first published the emulsion HNBR using diimide as a reducing agent. He found that NBR latex can directly generate HNBR under the action of hydrazine hydrate, oxygen or hydrogen peroxide and other oxidants, as well as metal ion initiators such as copper and iron. Parker of GoodYear Rubber Tire Company in the U.S. produced HNBR latex by the emulsion hydrogenation method. The formula is (parts by mass): NBR latex, 100g, CuSO4 5H2O: 0.008g, sodium lauryl sulfate: 0.15g, defoamer, Hydrazine hydrate: 15.6g, H2O2: 16.66g. Add NBR latex, CuSO4·5H2O, surfactant into the reactor, heat to 45-50°C, add hydrazine hydrate, then add H2O2 within the next 7 hours, add defoamer, stir at constant temperature for 1 hour to obtain HNBR. Because the hydrogenation precursor (p-toluenesulfonyl hydrazide) is expensive and the hydrogenation rate is slow, this method is still in the small test stage.
3. Solution hydrogenation
The solution hydrogenation method of NBR is in the NBR solution, using the noble metal palladium, calcium and rhodium as catalysts, and hydrogenation with hydrogen. The content of acrylonitrile in the NBR molecular chain determines its oil resistance. When hydrogenating NBR, only the double bond of the diene unit is selectively hydrogenated and reduced to a saturated bond, and the side chain nitrile group of the acrylonitrile unit is not hydrogenated—C≡ N. This hydrogenation method mainly uses two kinds of catalysts, namely heterogeneous carrier catalyst and homogeneous coordination catalyst. The first heterogeneous carrier catalyst that came out was a carbon-supported Pd/C catalyst. This catalyst has high selectivity and a hydrogenation rate of up to 95.6%. It is easy to be adsorbed on the surface of carbon black, and carbon black is easy to agglomerate into agglomerates when stirring, and exists in HNBR, which will have a bad influence on its vulcanization characteristics. Zeon Corporation of Japan chose SiO2 as the carrier of Pd/SiO2 catalyst, which has realized industrialization. When these two supported catalysts hydrogenate NBR, NBR catalyst residues or additives used in the polymerization reaction may adhere to the surface of the support or remain in the micropores, causing a sharp drop in catalyst activity and affecting reuse.
There are three common types of homogeneous coordination catalysts: palladium catalyst, rhodium catalyst and iridium catalyst. The palladium catalyst is stable to water and air, easy to store and transport, and can be recycled repeatedly, but its activity and selectivity are poor. The hydrogenation of NBR by the iridium catalyst has a very high The activity and selectivity of HNBR have become one of the hotspots in the development of HNBR. The rhodium type catalyst has the highest activity and selectivity. The RhH(PPh3)3 type rhodium hydride catalyst can carry out catalytic hydrogenation of NBR in solution or emulsion. The solvent used in the reaction is benzene, the temperature is 80-160°C, and the hydrogen pressure is 0.05 ～3MPa, time 2～10 hours. In order to stabilize the catalyst, PPh3 needs to be added. The dosages of catalyst and PPh3 are 0.05% to 20%, and 1% to 25% (based on NBR), respectively, and the mass ratio of the two is 0.6/1 to 20/1. The catalytic system has high activity and selectivity, and the hydrogenation rate is at least 95%. However, rhodium resources are scarce and expensive, and large-scale production should be recycled. Some people use triaminosilane to absorb 81% of the residual rhodium in HNBR.