Abstract
A carbon solid acid with large surface area (CSALA) was prepared by partial carbonization of H3PO4 pre-treated peanut shells followed by sulfonation with concentrated H2SO4. The structure and acidity of CSALA were characterized by N2 adsorption–desorption, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), 13C cross polarization (CP)/magic angle spinning (MAS) nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), titration, and elemental analysis. The results demonstrated that the CSALA was an amorphous carbon material with a surface area of 387.4 m2/g. SO3H groups formed on the surface with a density of 0.46 mmol/g, with 1.11 mmol/g of COOH and 0.39 mmol/g of phenolic OH. Densities of the latter two groups were notably greater than those observed on a carbon solid acid (CSA) with a surface area of 10.1 m2/g. The CSALA catalyst showed better performance than the CSA for the hydrolysis of cyclohexyl acetate to cyclohexanol. Under optimal reaction conditions, cyclohexyl acetate conversion was 86.6% with 97.3% selectivity for cyclohexanol, while the results were 25.0% and 99.4%, respectively, catalyzed by CSA. The high activity of the CSALA could be attributed to its high density of COOH and large surface area. Moreover, the CSALA showed good reusability. Its catalytic activity decreased slightly during the first two cycles due to the leaching of polycyclic aromatic hydrocarbon-containing SO3H groups, and then remained constant during following uses.
Highlights
Cyclohexanol is an important intermediate in the chemical fiber industry for the production of nylon-6 and nylon-66 [1]
The same bands appear in the spectrum of carbon solid acid (CSA). This illustrates that sulfonic acid groups have been formed on the surface of the CSA and carbon solid acid with large surface area (CSALA) by the sulfonation process.2016, The band at 1702 cm−1 is attributable to the C=O stretching mode of the COOH groups
The results indicate that COOH can catalyze the hydrolysis of cyclohexyl acetate
Summary
Cyclohexanol is an important intermediate in the chemical fiber industry for the production of nylon-6 and nylon-66 [1]. In the 1990s, Asahi Chemical Industry Co. developed a process to synthesize cyclohexanol via the hydration of cyclohexene [3], which is a promising route because of very high selectivity and minimal disposal problems, owing to the use of an acidic zeolite catalyst, HZSM-5. This reaction is restricted by the poor miscibility of water and cyclohexene, and the reaction rate is very low. The synthesis of cyclohexanol from cyclohexene via cyclohexyl carboxylate—which can be referred to as an indirect hydration of cyclohexene—overcomes the above-mentioned drawbacks in the direct hydration of cyclohexene [4].
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