Study On The Hydrolysis Of Dimethyl Carbonate On Cu/AC Catalysts

Dimethyl carbonate(DMC)is a kind of green chemicals having a wide range of applications,and liquid-phase oxidative carbonylation of methanol is one of the most promising method for the synthesis of DMC.Our previous work used chlorine-free copper source(such as copper acetate,copper nitrate)as precursor,activated carbon as carrier,through thermal decomposition of the copper source successfully prepared chlorine-free Cu/AC catalysts which have a good catalytic activity in the liquid phase oxidative carbonylation of methanol.In the further research of chlorine-free copper-based catalyst,we found that the Cu/AC catalysts still have problem in low DMC yield and further promotion of catalytic activity of catalyst not easily.In the oxidative carbonylation of methanol synthesis DMC process,there will generate water inevitably,and many articles report byproduct water could react with DMC,then reducing the methanol conversion and DMC yield.However,the hydrolysis behavior of DMC on the chlorine-free Copper-based catalyst has not been reported,and the influence of the hydrolysis reaction is not clear.Therefore,on the basis of preliminary work,we used chlorine-free Cu/AC as catalyst,investigated the effect of DMC hydrolysis reaction on the liquid phase oxidative carbonylation of methanol reaction in the continuous slurry bed,and the hydrolysis reaction conditions of DMC were also studied.Then,Boehm titration,XPS,NH3-TPD and CO2-TPD were employed to investigate the relationship between the acid-base properties of AC or Cu/AC and hydrolysis activity of DMC,and the Cu/AC catalyst was optimized.The results are as follows:(1)DMC did not react with water in no catalyst conditions,but could react with water in the conditions of Cu/AC catalyst catalyzed.In the oxidative carbonylation reaction,the reaction time from 12 h extended to 24 hours,due to the influence of hydrolysis reaction of DMC,DMC yield in system dropped from 16.7%to 15.5%;when the water content increased from 0%to 9.1%,DMC yield dropped from 9.0%to 0.6%.Continue to increase the content of water,hydrolysis reaction will consume DMC,resulting the DMC content in the system further declined.(2)AC could catalyze the DMC hydrolysis reaction,and the DMC hydrolysis performance of AC(H350-AC)which roasted in 350? N2 atmosphere was slightly higher than the Cu/AC catalyst prepared in the same conditions.The effect of reaction conditions on the hydrolysis reaction of DMC was as follows(H350-AC as DMC hydrolysis catalyst):the increased reaction temperature accelerated the hydrolysis reaction rate,and increased water content in the system prompted hydrolysis reaction equilibrium shifted to the positive direction,these both prompted the degree of hydrolysis of DMC increased;increasing reaction pressure,methanol content or in the atmosphere of CO2,due to inhibiting the formation of CH3OH and CO2,the degree of hydrolysis of DMC decreased;CO,N2 and O2 as reaction atmosphere has little impact on DMC hydrolysis reaction.(3)AC surface acidic groups could not catalyze the hydrolysis reaction of DMC but the basic sites on AC were the main DMC hydrolysis active site.The basic group of the surface increased from 0.16 to 1.69 mmol·g-1,the hydrolysis degree of DMC increased from 2.5%to 31.7%,while surface acidic group increased from 0.33 to 1.88 mmol·g-1,the hydrolysis degree of DMC decreased from 8.0%to 2.5%.Moreover,the higher the content of basic groups of AC,the stronger alkaline of the Cu/AC catalyst prepared,and there were more DMC reacted with water.While acid treatment could effectively reduce the surface basic groups of AC,the alkaline of Cu/AC catalyst would be weakened,thereby inhibiting the DMC hydrolysis.(4)Cu/AC-10N(AC treated with 10 M HNO3)with low hydrolytic activity had higher oxidative carbonylation performance,while the Cu/AC-10M(AC treated with 10 M HNO3 then treated with sodium hydroxide)with higher hydrolytic activity had poor carbonylation activity.When the reaction temperature is 120?,their DMC yield were 14.6%and 13.4%,respectively.In particular,for the optimized Cu/AC-10N catalyst which had poor hydrolytic and high carbonylation activity,the final DMC yield in continuous oxidative carbonylation reaction increased by 10%compared to the Cu/AC(AC with no treated),reached 24.4%.