Studies Of Catalytic Oxidative Carbonylation Of Methanol To DMC By Cu/Zeolite And Modified Catalysts With Water Treatment

Dimethyl carbonate (DMC) is a nontoxic compound that has recently attracted much attention as an important green chemical. The vapor phase oxidative carbonylation of methanol has been considered as the most promising way to produce DMC for its unique advantage. Two main kinds of catalyst CuCl2/A.C and PdCl2-CuCl2/A.C used in this process deactivate quickly because of losing Cl^. Cu/zeolite catalyst prepared by solid-state ion-exchange of CuCl with H-zeolite is more stable because of no Cl" exiting. It was also reported that the formation of Cu2(OH)3Cl phase on catalysts can improve the catalytic performance.In this thesis, a serial of Cu/zeolite catalyst were prepared by solid-state ion-exchange method and Cu/zeolite-T catalysts were prepared by water treatment of Cu/zeolite catalyst. The catalytic activites of the two kinds of catalyst were evaluated in continous flow system with a fixed bed reactor at atmosphere pressure. The effects of zeolite supports, preparation temperature and reactioncondition on catalytic activity were studied and XRD, XPS, SEM and IR were used to characterize those catalysts. After comparing the results of evaluation and characterization, following conclusions were obtained:(1) The kind of zeolite support has remarkable influence on catalytic activity. Zeolites with low ratio of SiO2/Al2O3 are more benefit for the catalyst's performance. The active sequence is DASY(8.1) > DASY2.0(8.1) > Hβ(20-30) > HZSM-5(55). Generally speaking, the lower the SiO2/Al2O3 ratio is, the more exchange degree gets, and the better performance catalyst has. But the exchange degree of Hβ(20-30) is far lower than that of HZSM-5(55) which indicates that both the ratio of SiO₂/Al2O₃ and the structure of zeolite determine the activity of catalyst.(2) For Cu/DASY catalyst, the higher the preparation temperature, the better catalytic activity, but when the temperature reached 750 ℃ , catalytic activity drops remarkably because of the collapsed structure of zeolite DASY. The best preparation temperature is 650℃ and the best reaction temperature is 160℃.(3) With the increase of the concentration of CO, the STY of DMC begins to increase and then become stable, the most suitable concentration of CO is 75%(mol). The concentration of methanol has the same effect on the STY of DMC and thebest value is 35%(mol). The most suitable ratio of the feed is CO:MeOH:O2=l5:6:1 and the best space velocity is IOO8OI1"1 when the feed ratio is CO:MeOH:O2(mol)=4:5:l(4) There is an inducement period for Cu/DASY catalyst, the maximum activity is reached after 6h and then being stable for 42h.(5) The results of XRD and Element Analysis indicates that no ion-exchange happenes when heating the mixture of CuCl and H(3. The activity of CuCl/H P catalyst is related to the CuCl dispersed on the surface of catalyst.(6) XRD and IR show that the strong absorption of CO on Cu+ occurred and no new phase appeared during the reaction process. EDX and XPS indicates the Cu moved from the zeolite cage to the catalyst surface during the reaction process. XPS also indicates that Cu! and Cu "co-exists in catalyst and the deactivation of catalyst is because the ratio of Cu ! /Cu11 become higher after reaction.(7) The effect of support, preparation temperature and reaction conditions on water treated catalysts are almost the same as those on Cu/DASY catalyst. Catalyst Cu2(OH)3Cl/DASY has catalytic activity on oxidation carbonylation of methanol reaction.(8) The water treated catalyst Cu/DASY-T has better performance than Cu/DASY catalyst when the preparationtempreture is lower than 450°C. While when the tempreture is higher than 450°C,the activity of Cu/DASY-T is lower than Cu/DASY catalyst.(9) For water treated catalyst, IR shows that the hydroxyl group disappears. XRD shows that Cu2(OH)3Cl phase disappears and CuCl occurrs after lOh reaction. XPS indicates that the ratio of Cu /Cu increases after lOh reaction.