Liquid-Phase Catalytic Oxidative Carbonylation Of Methanol To DMC By Heteropoly Acid Assisted CuCl₂ And CuCl

Dimethyl carbonate(DMC) is an environmental-friendly green chemistry, the synthesis route of methanol oxidative carbonylation to DMC in liquid-phase is in accord with the concept of the 21th century green chemistry, at the same time, it is very advantageous in thermodynamic and mature in technic with cheap materials and attracting more and more attention all over the world. It has been proved that the industrialized CuCl catalyst possesses the defect of deactive easily, serious causticity to equipment and polluting production. Researchers are used to carring CuCl and adding promoter or auxiliary agent to solve the above problems.As an excellent catalyst with strong oxidative and acid power,three Keggin-type heteropoly acids and their copper salts were evaluated to catalyse methanol to DMC.At the same time,the aidant function of heteropoly acids to homogeneous catalyst CuCl2 and loaded catalyst CuCl was studied.These catalysts were characteristic by XRD, FTIR, H2-TPR, TG-DTA,Through experiment research and analysis, the conclusion shows as below:(1) H3PMo12O40 , H3SiW12O40, H3PW12O40 and their copper salts with Keggin-type can not catalyse methanol to DMC effectively.It shows unconspicuous activity in methanol carbonylation reaction.Heteropoly acid negative ion can not provide an elevtronic environment like Cl- for active center Cu.(2) CuCl2-H3PW12O40/Al2O3 shows preferable repeated activity in heteropoly acid modified catalysts,the Cm and Sm of DMC exceeded 4%,80% respectively.While catalysts prepared with CuSO4 and Cu(NO3)2 show no activity in reaction of methanol to DMC.It means that active component is CuCl2.(3) Keggin-type heteropoly acid possess aidant function to homogeneous catalyst CuCl2.HPA- CuCl2 keeps quite activity after several times used with no Keggin structure altered.The Cm and Sm of DMC reach 11.92% and 85.42% respectively in continuous reaction. High CO pressure can enhace Sm of DMC and the maximum is 93.66%.(4) The assisted function of heteropoly acid exist in loaded catalyst all the same.Heteropoly acid keeps Keggin structure and no reaction was found between heteropoly acid and alkalescent carrierγ-Al2O3.There is a direct connection that the more oxidation capability HPA has,the more activity catalyst shows(HPMo>HPW>HSiW).The most suitable condition for preparing catalyst of CuCl2-HPA/Al2O3 is as following: catalyst cacined at 200°C, W(CuCl2)/W(HPW)=1, V(CO):V(O2)=2:1.Under this condition,the Cm and Sm of DMC reach the maximum and are 8.31% and 88.65% repectively in interrupted reaction. (5) Keggin-type heteropoly acid modified catalyst CuCl-HPA/Al2O3 shows better activity than CuCl and simple loaded catalyst CuCl/Al2O3.Prepared and reaction condition have great effects on loaded catalyst modified by heteropoly acid.The most suitable condition for preparing catalyst and reaction is as following: calcined for 4h at 400°C, W(CuCl)/W(carrier)=1:3, Wcatalyst=3g,reacting for 2h.Under this condition, he Cm and Sm of DMC reach the maximum and are 7.98% and 98.95% ,respectively.(6) The XRD,TG-DTA character and the study on effects of calcinations temperature on catalytic activity show that,with the calcinations temperature rising,the characteristic diffraction peaks of crystalline phase of CuCl, CuCl2 and heteropoly acid become weaker and dispersed on the surface of the support by single layer.However,when the calcinations temperature is over 450°C,heat decomposition occurred on heteropoly acid and the Keggin structure broke down. Decomposed substance blocked the holes of carrier and make the activity of catalyst depressed.It shows better activity that calcined CuCl2-HPA/Al2O3 at low temperature and CuCl-HPW/Al2O3 at high remperature.