Three-step reactions for selective production of 2,6-rich dimethylnaphthalene from 2,7-rich dimethylnaphthalene

Selective production of 2,6-dimethylnaphthalene (2,6-DMN) from 2,7-rich DMN has been investigated, with one-step and successive three-step isomerization containing (i) hydrogenation of 2,7-rich DMN to 2,7-rich dimethyl tetralin, (ii) isomerization of 2,7-rich DMT to 2,6-rich DMT, and (iii) dehydrogenation of 2,6-rich DMT into 2,6-rich DMN, respectively. It was found that the intra-triad isomerization of DMN was possible even at 200 °C, but for the inter-triad isomerization at least 250 °C was required. If the reaction temperature is higher than 300 °C, the yield of 2,6-DMN decreases rapidly due to the side reactions such as dealkylation, cracking and transalkylation. It was also found that 2,6-DMN or 2,6-DMT selectivity were strongly dependant on the Si/Al ratio of H-BEA (or the Brönsted site) and the maximum yield of 2,6-DMN (or 2,6-DMT) was obtained at the Si/Al ratio of 12.5. In the case of DMT, inter- and intra-triads did not show difference in isomerization temperature and were possible even at 180 °C. 14.9% yield of 2,6-DMT was obtained through the three-step isomerization over H-BEA(12.5) at 200 °C, while 10% yield of 2,6-DMN was achieved by one-step isomerization over H-BEA(12.5) at 250 °C.