Construction Of An Electrocatalytic Membrane Reactor And Mechanism Of Action Of Electrocatalytically Activated Sodium Persulfate Catalyzed Oxidation Of Cyclohexane

The C-H bond energy of alkane organics is relatively large,and its activation has been received wide attention in the academic research.In particular,cyclohexane（CHA）oxidation is an internationally recognized large-scale chemical process with the lowest efficiency,which severely restricts the development of nylon and other related industries.How to enhance the conversion rate of cyclohexane and the selectivity of adipic acid is a critical issue for academic and industry.The aim of this study is to fabricate nano-catalysts（r-V₂O₅ and Pt）loaded porous metal titanium membrane（r-V₂O₅/Ti and Pt/Ti）by electrochemical deposition,which is used as a cathode to construct an electrocatalytic membrane reactor（ECMR）for the electric field activated sodium persulfate（Na₂S₂O₈）to produce adipic acid from the oxidation of cyclohexane.Using vanadium（IV）sulfate oxide hydrate as the vanadium source,the r-V₂O₅NRs/Ti membrane electrode with oxygen vacancy defects was prepared by electrodeposition,high-temperature pyrolysis,and H₂ reduction.The morphology,structure and electrochemical performance of the catalyst were characterized using field emission scanning electron microscope（FESEM）,X-ray diffractometer（XRD）,X-ray photoelectron spectrometer（XPS）,and electrochemical workstation.The results show that the diameter of the prepared V₂O₅ nanorods is approciately 20-50 nm.The electrochemically active area of the membrane electrode is 145.3 cm²,showing a fairly good electrochemical activity.The r-V₂O₅ NRs/Ti membrane electrode as an anode,a stainless steel mesh as a cathode and Na₂S₂O₈ as the electrolyte and active agent were employed to constitute ECMR for the oxidation of cyclohexane.The operating parameters of ECMR were optimized by single factor experiment and response surface method.The results showed that the conversion rate of cyclohexane was 68.5%（theoretical value 72.81%）,the selectivity of adipic acid was 45.2%（theoretical value 48.70%）,in which the theoretical value was good consistent with the experimental value.It is noted that the sequence of the effect on the selectivity of adipic acid was residence time>sodium persulfate concentration>current density>reaction temperature.Besides,Pt/Ti as the membrane electrode was employed to constitute ECMR for the oxidation of cyclohexane.It was found that the conversion rate of cyclohexane was 22.5%,and the selectivity of adipic acid was 63.4%.It implied that the selectivity of adipic acid has been significantly improved.In short,the constructed ECMR can be successfully used to produce adipic acid by one-step electrocatalytic oxidation of cyclohexane.Further,The ECMR with r-V₂O₅ NRs/Ti membrane electrode as the anode was employed to explore the reaction kinetics of the oxidation of cyclohexane with Na₂S₂O₈as the electrolyte and active agent.The reaction mechanism was studied by through electron paramagnetic resonance test（ESR）.Tert-butanol and phenol were used as free radical quenchers to interpret the contribution rate of free radicals during the oxidation of cyclohexane.The activation energy of cyclohexanone,cyclohexanol,adipic acid,glutaric acid and succinic acid in the electrocatalytic oxidation of cyclohexane is 4.03KJ·mol^-1,20.15 KJ·mol^-1,22.87 KJ·mol^-1,32.22 KJ·mol^-1 and 44.42 KJ·mol^-1,respectively.The ESR test results showed that SO₄-·,and·OH are the main oxidizing active substances.The contribution rates of·OH,SO₄-·and non-radicals to the oxidation of cyclohexane were 20.2%,46.5%and 33.2%,respectively.Also,it can be seen that electron transfer existed between electron donor（cyclohexane）,electron acceptor（persulfate）and electron transfer medium（electrode）.At the same time,it was found that the intermediate products of the catalytic oxidation of cyclohexane on r-V₂O₅NRs/Ti and Pt/Ti membrane electrodes were 1,2-cyclohexanedione and?-caprolactone,respectively,showing different catalytic pathways.In short,this study provides a new idea for the one-step green preparation of adipic acid by the oxidation of cyclohexane using ECMR.