| Alkyiation of methylnaphthalene (MN) and methanol (ME) over zeolites is one of the more foreground processes to prepare 2,6-dimethylnaphthalene(2,6-DMN). The shape-selective property of zeolites can make it possible to synthesize 2,6-DMN with much higher selectivity than its thermodynamic composition, whereas the main problems in such process are low p-MN conversion, and easily deactivation of catalyst for coking on the catalyst surface.In this paper, the effect of zeolite catalysts and solvents on alkyiation of MN and ME was investigated. It was found that HZSM-5 and H(3 zeolites are suitable catalysts and 1,3,5-trimethylbenzene (TMB) is a suitable solvent. When the mixed MN (with a molar ratio of α-MN/β-MN being 1/3) is used in the place of β-MN, the cost of feedstock will drop and the activity of catalysts be improved. For HZSM-5, the effects of molar ratio of SiO2/Al2O3, reaction temperature, space velocity (WHSV) and the molar ratio of MN, ME and TMB on alkyiation reaction were studied. It was found that HZSM-5 with 38 SiO2/Al2O3 ratio is the suitable catalyst, and the suitable reaction conditions are 460℃, 0.5 h-1 of WHSV (referring to MN) and 0.6/1/3 of ME/MN/TMB. For Hβ zeolite with relative large pore size, the experiments were respectively carried out by the methods of ion exchange of Mg2+,Zn2+,Co2+,Ce3+, impregnation of H3BO3, H3PO4 and chemical liquid deposition of Si(OC2H5)4 to improve its catalytic performance in alkyiation of MN and ME. The results showed that the MN conversion has more than 60% rise over modified Hβ by Mg2+ and Zn2+ ion exchange, and selectivity of 2,6-DMN has more than 30% increase over modified Hβ by chemical liquid deposition of Si(OC2H5)4 .The weak acid site is the active site catalyzing alkyiation of MN and ME, and the strong acid site increases side reaction and accelerates deactivation of catalysts.Referring to the problem of easy deactivation of catalysts in alkylation of MN and ME over HZSM-5 zeolite, the experiment was carried out under the supercritical reaction condition to investigate the possibility to reduce the deactivation of catalysts. It was shown that under the supercritical pressure of 1,3,5-TMB, the MN conversion is about 3 to 4times higher and catalyst life extends 30 times longer than these in ambient pressure over HZSM-5. The supercritical fluid may resume the activity of catalysts if only not complete deactivation. By the GC-MS, ]HNMR analysis of reaction products and the surface area, NH3-TPD, Py-IR, XRD, IR, SEM and TG characterization of used catalysts from ambient pressure and supercritical condition, The mechanism of supercritical fluid improving the catalytic activity and catalyst life was discussed.
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