Preparation Of Catalyst With High Stability For Toluene Alkylation With Methanol Into Para-xylene

Para-xylene is an important basic organic chemical material which is used for producing terephthalic acid and dimethyl terephthalate, its demand in industry is big. The traditional way of producing para-xylene has been challenged. Starting from the non-oil route to produce para-xylene by using relative excess toluene and methanol which derived from coal chemical industry as material is a very worthful process route. The research of toluene alkylation with methanol into para-xylene grew up all over the world in1970s, most of the catalysts using for this reaction was molecular sieve. High para-selectivity catalysts were prepared by modification of pore structure and acidity of zeolite. Rich experience was accumulated by catalytic workers form exploration and practice in long time. However, the catalysts of zeolite will deposite carbon during reaction inevitably result in deactivation by coking. So far there is no effective way to inhibit the process of carbon deposition or improve the stability of catalysts. Finding effective and sample way to restrain the process of carbon deposition to improve the catalysts stability has been the important tobic of realizing the industrializing of this technology.In this article Si-P-Mg modified HZSM-5was used as parent catalyst, on the basic of analysis and summarization of the predecessors’achievement, we believe that the process of catalyst deactivation can be described as macromolecular hydrocarbon material was formed in the pore of ZSM-5from methanol while this kind of hydrocarbon material was the active center of methanol reaction, on the one hand methy was brought in successively, on the other hand low-carbon alkene was formed by dealkylation reaction constantly, these alkenes are major carbon precursors which are easy to take place polymerization or alkylation with aromatic to form polycyclic aromatic to block the pore of ZSM-5. A series of Ni modified HZSM-5catalysts were prepared using for toluene alkylation with methanol in hydrogen atmosphere, dealkylation of macromolecular hydrocarbon material was promoted by hydrogenation properties of Ni, the generation chance of methane was improved and generated low-carbon alkene was hydrogenated to reduce the proportion of low-carbon alkene. The generation of carbon precursors was inhibited while the process of carbon deposition was postponed, the stability of catalyst was improved.The influence of nickel precursors for reaction performance of catalysts was investigated, finding that the catalyst prepared with nickel nitrate as precursor had better alkylation properties and hydrogenation properties. The effect of different nickel content on stability of catalyst was analyzed, the catalyst with5%Ni was thought to had better stability. On this basic, combination of Ni and Si modified catalyst were prepared so that the higher para-selectivity and better stability was achieved. Under the condition of460℃, atmospheric pressure, WHSV of feed(toluene and methanol) was2h-1(WHSV=2h-1), the mole ratio of Hi to feed was2(nH2/n(T+M)=2), the mole ratio of H2O to feed was2(nH2O/n(T+M)=2), the mole ratio of toluene/methanol was6(nT/nM=6:1), reaction for1200h on stream, the conversion of toluene per pass (CT) was11-8%and para-selectivity (SPX) was94-97%.