Alkylation Of Biphenyl In The Fixed Bed Reactor

4,4’-Dialkylbiphenyls are important as precursors in advanced polymer materials, such as engineering plastics, liquid crystalline polymers, and polyester fibers. Among the4,4’-dialkyl substituted biphenyl (BP), the synthesis of4,4’-dimethylbiphenyl (4,4’-DMBP) has attracted attention, because its oxidation can proceed under mild conditions without carbon loss. The synthesis of4,4’-diisopropylbiphenyl (4,4’-DIPB) has also been studied extensively due to the stability of the catalyst and the shape-selective synthesis is relatively easier to control. The work in this thesis aims at improving the stability of zeolite catalysts for biphenyl methylation and at clarifying the effects of the conditions of biphenyl isopropylation in a fixed-bed reactor.In the methylation of biphenyl to4-methylbiphenyl over HZSM-5the effects of hydro thermal treatment with and without subsequent HNO3leaching, respectively and alkali treatment were studied. The results are as follows:(1) Over the monodisperse HZSM-5(80) with small amount of acid sites, BP conversion and catalyst stability were better than those of HZSM-5(26) with agglomerated crystal particle.(2) Both hydrothermal (HT550) and combined hydrothermal-HNO3(HNO3-HT550) acid treatments improved catalyst stability, with the latter exhibiting better stability. BP conversion behavior resembled a parabolic shape vs time on stream over HT550and HNO3-HT550without the addition of water. Both catalyst stability and selectivity of4-MBP were improved upon the addition of water. BP conversion after30h on stream was8.6%, and the selectivity of4-MBP was as high as-60%. Elevating the reaction temperature to500℃in the presence of water led to increased BP conversion with time on stream up to30h, and the selectivity was stable at-58%.(3) HZSM-5(80) was alkali-treated, and became a hollow structure nano-cube structure (Hol-HZ-5). BP conversion and4-MBP selectivity was higher over Hol-HZ-5than with the parent; however, Hol-HZ-5with TEOS treatment deactivated more rapidly because of no selective alkylation in the hollow.Isopropylation of biphenyl to4,4’-diisopropylbiphenyl(4,4’-DIPB) was studied over different types of zeolite catalysts. Mordenite HM was the appropriate catalyst for this reaction. Over HM, which had the least acidity among catalysts, BP conversion was similar to those with HMCM-22and HBeta, and yield of n-propylbiphenyl and other by-products was lower. For biphenyl isopropylation over HM, mesitylene and isopropylbiphenyl were examined as solvents. When mesitylene was the solvent, the conversion of biphenyl increased from-55%to65%, the selectivity of4,4’-DIPB increased from-30%to-65%at supra atmospheric pressure. The effect of reaction temperature on the products distribution was dramatic. When the temperature was decreased from220to190℃,4.4’-DIPB selectivity increased by about50percent, the maximum is80%. When isopropylbiphenyl was the solven, main reactants were BP and4-isopropylbiphenyl, catalyst stability and para selectivity were improved, BP conversion was about30%,4,41-DIPB selectivity was about65%. The temperature of220℃was the appropriate reaction temperature.