Abstract
AbstractThe industrial oxidation of cyclohexane is currently performed with very low conversion level, i.e. 4-6% conversion and poor selectivity for cyclohexanone and cyclohexanol (K-A oil), i.e.70-85%, at above 150oC reaction temperature and above 10atm reaction pressure using molecular oxygen oxidant and homogeneous catalyst. Several disadvantages are, however, associated with the process, such as, complex catalyst-product separation, high power input, and low safe operation. Therefore, the oxidation of cyclohexane using heterogeneous catalyst oxygen oxidant from air at mild conditions has received particular attention. Aerobic oxidation of cyclohexane over ionic liquids modified cobalt/ZSM-5 (IL-Co/ZSM-5) in absence of solvents was developed in this article. The prepared catalysts were characterized by XRD, FT-IR, N2 adsorption-desorption, SEM, TEM and XPS analyses. The influence of reaction parameters on the oxidation of cyclohexane was researched, such as the various catalysts, reaction temperature, reaction time, and the reaction pressure, on the process. Highly selective synthesis of KA oil was performed by aerobic oxidation of cyclohexane using ionic liquids modified cobalt/ZSM-5 (IL-Co/ZSM-5) as the catalyst in absence of solvents for the first time. A selectivity of up to 93.6% of KA oil with 9.2% conversion of cyclohexane was produced at 150℃ and 1.5 MPa after 3 h, with about 0.1 mol cyclohexane, C7mimHSO4-Co/ZSM-5 catalyst equal to 6.0 wt%, respectively. The induction period of oxidation was greatly shortened when the ionic liquid was supported on ZSM-5. The catalyst was easy to centrifuge and was reused after five cycles. It was found that both the characterization and performance of the catalysts revealed that both the presence of oxygen vacancies with incorporation of Co ions into the framework of ZSM-5 and the introduction of C7mimHSO4 into the ZSM-5 leads to the both satisfactory selectivity and robust stability of the C7mimHSO4-Co/ZSM-5 heterogeneous catalyst.
Highlights
In the modern chemical industry, selective oxidation of cyclohexane is an important chemical process
The conversion of cyclohexane increased from 2.5% to 9.2% when the reaction temperature was increased from 130oC to 150oC
This can be attributed to the channel range of the ZSM-5 molecular sieve that results in a difficult loss of the C7mimHSO4 ionic liquid, and on the other hand, a micro-reactor with high concentration of C7mimHSO4 ionic liquid was constructed with the C7mimHSO4 ionic liquids were introduced into the pores of ZSM-5 molecular sieve
Summary
In the modern chemical industry, selective oxidation of cyclohexane is an important chemical process. The selectivity of KA oil is generally not high in the system of direct catalytic cyclohexane oxidation of metal/ZSM-5. The anionic or cationic groups of ionic liquids may interact with the surface of the molecular sieve, which will be favorable for improving the selectivity of products. Even though this is promising research is related to industrialization, there is little reported, especially for the aerobic oxidation of cyclohexane in absence of solvents, are relatively scanty. Ionic liquids were used to modify the metal supported on ZSM-5 to prepare one kind of stable catalyst, which was applied in the aerobic oxidation of cyclohexane under solvent-free conditions. The effects of different reaction conditions on cyclohexane oxidation were studied, such as the various catalysts, reaction temperature, reaction time, and the reaction pressure, on the process
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