Ionic Liquid As An Efficient Promoting Medium For Synthesis Of Dimethyl Carbonate By Oxidative Carbonylation Of Methanol

Dimethyl carbonate (DMC) is an attractive green chemical due to itsversatile chemical reactivity, unique physical property, low toxicity and rapidbiodegradability. Much attention has been paid to the synthesis and application ofdimethyl carbonate (DMC) because of its low toxicity and versatile chemical property.Dimethyl carbonate (DMC) is an environmentally friendly chemicals. It can be used asan environment-friendly intermediate and starting material for organic synthesissubstituting the poisonous phosgene and dimethyl sulfate in carbonylation andmethylation reaction. In addition, DMC can be regarded as an option to meeting theoxygenate specifications on gasoline.Synthesis of oxygenates from carbon monoxide continues to be full of activity inboth academic and industrial fields. At present DMC is synthesized mainly via oxidativecarbonylation of methanol. Over the past decade, synthesis of dimethyl carbonatefrom carbon monoxide and methanol oxidation carbonylation in a liquid phasehas attracted much attention. Among the methods for synthesis of dimethyl carbonate,oxidation carbonylation for dimethyl carbonate synthesis in liquid phase apparently hasmany advantages such as advanced technology, low consumption of energy reasonablyand easily available raw materials, no pollution and moderate reaction conditions, etc.Room temperature ionic liquids consist of an organic cation and inorganic anion,the ions do not pack well and remain liquid at room temperature. They are low - melting(＜100℃), and the properties of ionic liqulds largely depend on the cation and anion.Ionic liquids as a new kind of green solvent, has been taken great interests by more andmore researchers. Due to their wide liquid range, nonvolatility, adjustability of chemicalphysical properties and large windows of electrochemistry, ionic liquids are becomingever-expanding applications as alternative reaction media and catalysts for organicsynthesis, solvents and extractants for separation and electrolytes for electrochemistry.In search for an environmentally benign chemistry, more and more novel ionic liquidsare widely investigated to expand the utility of ionic liquids and open up a new field ofionic liquid chemistry. The most recent publications in this area focus on the synthesisof new ionic liquids, systematic investigations of their properties and further applications. It is very important to accumulate a substantial body of scientific andtechnological data for these fascinating fluid materials as solvents and catalysts inchemical synthesis and separation processes can be realized.In order to explore ionic liquid as an efficient promoting medium for synthesis ofdimethyl carbonate by oxidative carbonylation of methanol, four parts of work havebeen done in the thesis.Part one. The catalysis of copper complexes using various ionic liquids as reactionmedia is systematically studied in the reaction of oxidative carbonylation of methanol todimethyl carbonate. The presence of ionic liquid containing Cl^-,Br^-,PF₆^- anions causedpartial deactivation of the copper catalyst. The best promoter N-butylpyridiumtetrafluoroborate, which has better performance on solubility and promoting catalysisfor oxidative carbonylation has been found.Part two. The influences of reaction temperature, reaction time, total reactionpressure, mole rate of carbon monoxide to oxygen and amount of ionic liquid mole rateof carbon monoxide to oxygen were evaluated as well. The optimum operatingconditions as follow had been obtained: reaction temperature of 120℃, reaction time of2～4h, mole rate of carbon monoxide to oxygen 2:1 and mass of ionic liquid of 2.0g.The higher reaction pressure also favors the the conversion of methanol. Experimentalresults indicated that under the selected reaction conditions (120℃, 2.4MPa,P_O2/P_CO=1:2, 0.1g-Catalyst/5mL-MeOH, 2.0g-IL, 4h), the conversion of methanol couldachieve 20% and the selectivity of DMC could exceed 97%.Part three. This catalytic system can be reusable for at least five times with slightloss of activity, while the selectivity of DMC remains almost the same. The gradualdecrease in the activities could be due to the loss of the catalyst during handling andtransferring the reaction mixture.Part four. The mechanism of oxidative carbonylation of methanol has also beendiscussed. In comparison with FT-IR spectra of pure CuCl and N-butylpyridiumtetrafluoroborate, no strong or new peaks appeared, when CuCl was added intoN-butylpyridium tetrafluoroborate. It suggested that there were no strong interactionsbetween the ionic liquid and the CuCl. The experiments show that cuprous chloridecould have better solubility in N-butylpyridium tetrafluoroborate than in methanol or inwater. It suggested that IL N-butylpyridium tetrafluoroborate dramatically enhanced thereaction possibly due to the catalysts being well dispersed in the IL-rich phase.Although the mechanism of the improvement of the CuCl catalyst with the IL needs tobe further clarified, this work presents a highly efficient methanol for improving thesynthesis of DMC under homogeneous conditions.