Electrochemical Oxidation Of Methanol Into Dimethoxymethane From In Ionic Liquid

The most attractive attribute of the electrochemical synthesis of chemicals is that one can control the reaction at the electrode through controlling the potential or current. The efforts toward studies on electrooxidation of methanol have been mostly made for methanol fuel cells.Eight imidazolium ionic liquids including 1-ethyl-3-methylimidazolium tetrafluoroborate(EmimBF4), 1-ethyl-3-methylimidazolium bromide(EmimBr), 1-ethyl-3-methylimidazolium hydroxide(EmimOH), 1-butyl-3-methylimidazolium tetrafluoroborate(BmimBF4), 1-butyl-3-methylimidazolium bromide(BmimBr), 1-butyl-3-methylimidazolium chloride(BmimCl), 1-butyl-3-methylimidazolium hydroxide(BmimOH) and 1-benzyl-3-methylimidazolium chloride(BzmimCl) were synthesized in this paper, as proved by 1H NMR and FT-IR. Electrochemical oxidation of methanol on Pt electrode was tested using these ionic liquids as supporting electrolytes. Cyclic voltammetry of these ionic liquids indicated that the ox-red reaction was taken place on the electrode. Based on the above results in the ionic liquid-methanol system, electrochemical conversion of methanol into dimethoxymethane(DMM) was conducted in various ionic liquids as supporting electrolytes by Bulk Electrolysis with Coulometry and Constant-potential Electrolysis. The experimental results showed that EmimBF4 exhibited excellent characters with high conversion of methanol. The effect of cations and counter anions composed of these ionic liquids on the electrolysis and the contrast between inorganic salt NH4BF4 and the ionic liquid EmimBF4 were explored. The nature of the ionic liquid EmimBF4 acting as both electrolyte and electrocatalyst was confirmed. At the same time, the effect of the electrolysis conditions such as electrolysis votage, electrolysis temperature, reaction time and dose of ionic liquid were investigated. The optimal operating conditions were determined: work and counter electrodes Pt electrode, electrolysis voltage 3.0 V, electrolysis temperature 30℃, reaction time 24 h, amount of methanol 0.035 mol, ionic liquid 0.024 mol. Conversion of methanol 34.7%, 96.9% selectivity to DMM and 88.2% current efficiency were achieved under these optimal conditions.In addition, The reaction mechanism on electrochemical activation and conversion of methanol was proposed according to the experimental results and reported literatures.