Research On Direct Synthesis Of Dimethyl Carbonate From Carbon Dioxide And Methanol Under Supercritical Condition

Countries are more and more attention to the environmental pollution problemsaround the world, and the environmentally friendly “green compounds” are the favor ofthe public. DMC is the fastest-growing products of green chemistry in the20th century.Especially DMC thoughed the registration of the Non Toxic Substance in Europe in1992,it has been widespread concern in recent yeas. DMC is mainly used for organic synthesisindustry as the green organic synthesis intermediate. DMC is not only a safe and greensolvent, but also a new additive to improve gasoline octane. In addition, DMC is widelyused in pesticides, pharmaceuticals, dyes, food additives, fine chemicals, surfactants andantioxidants. Several reaction routes have been reported for DMC synthesis so far. Thetwo methods for synthesis of DMC mainly are phosgene and non-phosgene. Since the20th century, there are lots of researches on the synthesis of DMC in domestic and foreign.Methods of synthesis of DMC are toward for simple、non-toxic and non-pollution. Amongthese methods, the direct synthesis of DMC from CO₂and CH3OH is the more preferredroute. The method has drow more and more attention.CO₂is an emission product from industries, and is also one of the main gases causingthe greenhouse effect. And it is a potential carbon resource. Therefore, the utilization ofCO₂has attracted extensive attention. The direct synthesis of DMC from CO₂and CH3OHhas been attempted to match the view of the so-called “Green Chemistry” and“Sustainable Society”. It is of great significance no matter form environment point of viewand energy point of view.The following researches have been carried out in four aspects and the results asfollowed:1)Selection of catalyst: According to the researches on the catalysts for synthesis ofDMC selected four catalysts which have higher catalytic efficiency. The four catalysts areMagnesium, nickel acetate, potassium carbonate and methyl iodide. Compared theircatalytic properties and prices, selected the magnesium for this experiment.2)Determine the testing conditions: The product of methanol with carbon dioxide todimethyl carbonate was analyzed by GCMS-QP2010which was made of Shimadzu inJapan. The conditions were as follows: Column:BD-5weakly polar column; InletTemperature:200℃; Column Temperature: initial temperature40℃, maintain for3minutes, then at the rate of25℃per minute up to150℃, and keep for3minutes; Detector: flame ionization detector （FID）; Detector Temperature:200℃; Split Ratio:1:100. MS Conditions: ion source temperature200℃; Connection port temperature:200℃; Solvent removal time:3minutes; Full scan:45-800m/z. The retention time ofDMC is3.43minutes.3)Determine the optimum conditions: In the paper, the direct synthesis of dimethylcarbonate by the reaction of methanol with carbon dioxide in the presence of Mg powderwas studied in the autoclave near the critical point of CO₂. When the ratio of Mg in themethanol is1:25, the efficiency of catalytic is the best. The influences of reactiontemperature, reaction stress, reaction time etc. On the production of DMC wereinvestigated by the experiment. Eventually determined the optimum technologicalconditions by the single factor and orthogonal experiment: the optimum reactiontemperature is190℃, reaction stress is7.5MPa, reaction time is7h. In the optimalconditions, the yield of dimethyl carbonate is2.55%.4)Discuss the reaction mechanism that synthesis DMC by supercritical carbondioxide: Reaction mechanism: First, the formation of methoxide magnesium compound.Second, the formation of reaction intermediate-methoxy magnesium carbonate. At last, thereaction between methoxy magnesium carbonate and methanol. The production isdimethyl carbonate, and the actual catalyst for the reaction is methoxy magnesium.