SYNTHESIS OF 1,3-CYCLOHEXADIENE THROUGH L IQUID-PHASE DEHYDRATION OF 2-CYCLOHEXEN-1-OL IN AQUEOUS-SOLUTION USING ZEOLITE CATALYST

Synthesis of 1,3-cyclohexadiene through liquid phase dehydration of 2- cyclohexen-1-ol in aqueous solution was examined using zeolite and ion -exchange resin catalysts with various reaction methods. As the result s, significant improvement has been achieved for the problem of by-pro duction of dicyclohexenyl ether and activity deterioration, which was the problem found in one-liquid phase system of 2-cyclohexen-1-ol repo rted previously. Two-liquid phase reaction system involving oil-and-wa ter two phase gave a good 1,3-cyclohexadiene yield of 50% or higher wi th H-ZSM-5 and Amberlist-15, but H-Y, H-beta, and H-mordenite gave onl y extremely low yield of the same level as obtained in one-liquid phas e system. It was suggested that hydrophobicity of highly silicious zeo lite was required for catalytic activity to appear in the aqueous reac tion system, based on the comparison with hydrophobicity determined by adsorption method of aqueous solution of l-propanol. The separation s peed of oil/water in two-liquid phase system was compared with that of cyclohexene hydration system. It was found that the separation speed of two-liquid phase system was slower by an order of magnitude than th e latter and furthermore decreased with time. The reaction system whic h uses homogeneous dilute aqueous solution of 2-cyclohexen-1-ol was th en examined. In this system, the by-production of dicyclohexenyl ether was suppressed through equilibrium,and only little amounts of its for mation was observed. Comparison in the activity between H-ZSM-5 and Am berlist-15 revealed that H-ZSM-5 exhibited higher activity than Amberl ist-15. By using a reaction system which uses the combination of homog eneous dilute aqueous solution and reactive distillation with slurry o f H-ZSMd, 1,3-cyclohexadiene was obtained at the yield of nearly 90%. No catalyst deactivation was observed for 80 h. It is considered that quick removal of formed 1,3-cyclohexadiene from the reaction system as the minimum azeotropic mixture with water results in the suppression of deterioration due to polymer formation, which should lead to the hi gh yield.