Synthesis Of 2,6-dimethylnaphthalene By Methylation Of 2-methylnaphthalene With Methanol

2,6-dimethylnaphthalene is an important precursor for synthesis of the next-generation polyester such as PEN. At present 2,6-DMN is commercially synthesized only in AMCRO from a benzene-ring compound by a mutli-step process using alkali metal as catalyst and a large quantity of solvent that put a huge burden on the environment. For this purpose, a shape-selectivity zeolite catalytic process for 2,6-DMN synthesis by methylation of 2-methylnaphthalene was employed in this paper。Catalytic performance over HY, HZSM-5, HZSM-48 and SAPO-11 were compared by ambient pressure. The results indicated that the pore structure and acid properties are the two most important factors affecting catalytic performance. The initial activity order of those zeolites is HY>SAPO-11>HZSM-5>HZSM-48, and medium pore zeolite SAPO-11 and ZSM-5 show much higher β,β'-selectivity than HY. Among the HZSM-5 with difference SiO₂/Al₂O₃ ratio and crystal size, best catalytic performance was achieved over micro-meters HZSM-5 with SiO₂/Al₂O₃=38. Also during experiment it was found that boehmite was not only as binder but also serve as a co-catalyst for it can obvious enhance product selectivity and suppress catalyst deactivation.The effect of reaction parameters such as reaction temperature, space velocity, mole ratio of 2-MN and methanol in the starting material on catalytic performance was investigated on HZSM-5 (38). The optimization conditions are as follows: temperature: 400℃, WHSV: 0.5 h^-1, N₂ flux: 10 ml/min.Appropriate modification of zeolite can decrease the isomerization reaction on its external surface, increase the. 2,6-DMN selectivity. SAPO-11 and HZSM-5 were modified by magnesium and phosphorus salts and tested in catalytic reaction. In the case of ZSM-5, such modification has no obvious effects on catalytic activity, the 2,6-/2,7-DMN sometimes even lower than parent ZSM-5. Better results were found over modified SAPO-11. Over Ni/SAPO-11, 2-MN conversion is 16% with 2,6-DMN selectivity of 45% and 2,6-/2,7-DMN ratio of 2.7.Under supercritical condition, the influence of reaction temperature and pressure was tested over ZSM-5, conversion of 2-MN is gradually increased with temperature increase while 2,6-DMN selectivity is slightly decrease; reaction pressure have no obviously effect on 2,6-DMN selectivity in the supercritical region. More interesting results were found over Mg²⁺ modified SAPO-11 under supercritical state, conversion of 2-MN and catalyst stability is obviously improved without any loss of 2,6-DMN selectivity.