Isopropylation Of Isopropylbiphenyl In The Fixed Bed Reactor

Biphenyl derivatives especially para-alkylated substituted biphenyl is a kind of important chemical raw material. Their oxides is important for preparation of liquid crystalline polymers, engineering plastics and polyester fibers with high performance as a monomer. Because the shape-selectivity could be easily controlled, the synthesis of 4,4’-diisopropylbiphenyl (4,4’-DIPB) has been widely studied. The synthesis of 4,4’-DIPB on traditional Friedel-Crafts catalysts such as Lewis acid or silica/alumina catalyst could always produce a large number of undesired products, which made low para-selectivity. Zeolite has been used as catalysts for synthesis of 4,4’-DIPB due to its shape-selectivity, easy separation of product, regeneration ability and environment friendly.In this paper, the alkylation of isopropylbiphenyl(IPBP) with propylene(Pr) over mordenite (HM) in the fixed bed reactor has been investigated. The influences of reaction conditions and modifications are expiored. The results are followed:(1) The type of catalyst and reaction conditions both have effect on the alkylation of isopropylbiphenyl. HM is a suitble catalyst for this reaction. With the increase of pressure, the conversion of IPBP increased, while the para-selectivity decreased. It can improve the para-selectivity by increasing propylene feeding. The conversion of IPBP increased at first then decreased with the increase of temperature. From the abtained results, the optimal reaction conditions are followed:the reaction temperature is 200℃, the reaction presusure is 3.5 MPa, the molar ration of reactants is n(IPBP):n(Pr)=1:1.(2) Cerium modification can change the acidity of the catalyst, improving the reaction stability. It can improve the para-selectivity without decreasing the conversion. At a high temperature of 250℃, the para-selectivity can reach 39.8% over the mordenite with impregnation of 10% cerium which was 9 percentage higher than the unmodified zeolite.(3) NaOH solution would cause the mordenite zeolite desilication and produce mesoporous, which can improve the IPBP conversion by speeding up the diffusion rate of molecules in the catalyst pore channels. But it also decreased the para-selectivity. Adding tetrapropylammonium hydroxide(TPAOH) into NaOH solution was an effective way to improve the para-selectivity, which can protect microporous as well as produce mesporous, In addition, it could increase the content of silicon on the surface of the catalyst. Acid treatment can remove non-framework aluminum and dredge the channel. The mesoporous mordenite had a much higher catalytic activity than conventional mordenite in the alkylation of IPBP with propylene in the fixed bed reactor. In the initial reaction period, the conversion of IPBP over hierarchical mesoporous mordenite was 50%, whereas the conversion over conventional mordenite was 38%. What’s more, the reaction stability over hierarchical mesoporous was improved. The conversion of IPBP can still achieve 44% after 152 h, while it reduced 5% after 52 h on the pristine zeolite.