Preparation Of Carbon-based Solid Acid With Large Specific Surface Area For Synthesis Of Cyclohexanol

Cyclohexanol is an important chemical intermediate in the synthesis of adipic acid,caprolactam and so on. The synthesis of cyclohexanol by indirect hydration of cyclohexene consists of the esterification of cyclohexene with carboxylic acid and the following hydrolysis of cyclohexyl carboxylate to cyclohexanol. It can overcome the drawbacks existing in the process of direct hydration of cyclohexene to cyclohexanol, such as the poor miscibility of water and cyclohexene, and the subsequent low reaction rate.In the previous study, it was found that there was a serious side reaction during the hydrolysis of cyclohexyl acetate over HZSM-5 when cyclohexanol was synthesized by the indirect hydration of cyclohexene via cyclohexyl acetate. The selectivity to cyclohexanol was only 30.4% and most cyclohexyl acetate underwent pyrolysis to cyclohexene.Carbon-based solid acid was prepared by partially carbonization-sulfonation method using peanut shell as raw material. When it was used as catalyst for the hydrolysis of cyclohexyl acetate, cyclohexanol selectivity could reach up to 99.4%, but cyclohexyl acetate conversion was only 25.0%. The low activity may be assigned to the small specific surface area of the peanut shell-derived carbon-based solid acid, 10.1 m2/g. Therefore, the aim of this study is exploring a carbon-based solid acid with large specific surface area and then the catalytic evaluation for hydrolysis of cyclohexyl acetate to cyclohexanol.The carbon-based solid acid with large surface area was prepared by partially carbonization of H3PO4 pre-treated peanut shell and following sulfonation with concentrated H2SO4. The structure and acidity of the catalyst was characterized by N2adsorption-desorption, SEM, XRD, NMR, FT-IR, XPS, titration and elemental analysis.The results showed that the carbon-based solid acid had a specific surface area of 387.4m2/g and SO3 H group density of 0.46 mmol/g. It exhibited good catalytic performance for hydrolysis of cyclohexyl acetate to cyclohexanol. At the optimal reaction conditions,cyclohexyl acetate conversion was 86.6% with 97.3 selectivity to cyclohexanol. The high activity could be attributed to the high density of COOH(1.11 mmol/g) and large surface area, which can provide good access for the hydrophobic cyclohexyl acetate molecules to approach to the active acid sites.The catalytic performance of several acidic ionic liquids(ILs) was evaluated for hydrolysis of cyclohexyl acetate to cyclohexanol. Cyclohexyl acetate conversion increased with increasing acid strength of the ILs, but the five SO3H-functionalized ILs with differentacidity had similar high activity(conversion 81.3%~83.6%). And, all of the ILs exhibited high selectivity to cyclohexanol(>96%). This can be attributed to the high polarity of the ILs, which inhibits the formation of the transition state for the side reaction, pyrolysis of cyclohexyl acetate to cyclohexene, and then increases cyclohexanol selectivity.