Hierarchical HZSM-5 were synthesised by controlled desilication in alkaline medium and characterised by field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, inductively coupled plasma–atomic emission spectrometry, N2 adsorption–desorption, and Fourier transform infrared spectroscopy. The catalytic performance of HZSM-5 towards the selective oxidation of 2,3,6-trimethylphenol by H2O2 was evaluated. Recyclability tests were also carried out. The results showed that 2,3,5-trimethyl-1,4-benzoquinone was produced in high yields (i.e. 90 %), corresponding to a 2,3,6-trimethylphenol percentage of 98 %. The N2 adsorption–desorption and XRD studies suggested that mesopores with an average size of 5 nm were produced and that the structural character of HZSM-5 was preserved after desilication. Transmission electron microscopy analysis of the spent catalyst indicated good stability of the hierarchical structure. The Fourier transform infrared spectroscopy studies revealed the development of acid sites. The combined results suggested that the nature of the solvent, intrinsic acidity, and shape selectivity of the hierarchical structure of the catalyst ensured high catalytic properties.
2.3.5-trimethyl-1.4-benzoquinone (TMQ) is an important intermediate in the synthesis of vitamin E, and the oxygen oxidation of 2.3.6-trimethylphenol (TMP) is commonly used to prepare TMQ in the industry. However, the slow mass transfer of oxygen from the gas phase to the liquid phase in the gas-liquid two-phase reaction greatly limits the oxidation reaction rate. Therefore, this study presents a mild and efficient synthesis of TMQ by catalytic oxidation of TMP using high-velocity air as an oxidant in a self-built continuous flow microreactor. The continuous flow microreactor shows excellent mass transfer performance, and high- velocity air was used to drive the feedstock liquid to do circular motion. The effects of different operating conditions and microreactor parameters on TMP conversion and TMQ yield were investigated. The results show that the TMP conversion and TMQ yield reach 100% and 89.9% under the optimal conditions of the continuous flow microreactor, respectively. Compared with the tank reactors, this continuous-flow microreactor has broad application prospects in the production of TMP catalytic oxidation. In a state of continuous high-speed circular motion, efficient mass transfer in a narrow pipe enables full contact between the liquid and gas phases. As a result, reaction time is reduced from approximately 5 hours to merely 78.5 seconds.
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