Direct Synthesis Of Dimethyl Ether From Biomass-Derived Syngas

With the reduction of fossil fuel and the increase of CO2 in the atmosphere, the development of alternative fuels and the reduction of carbon dioxide emissions attracted global concern. Dimethyl ether as an alternative to liquefied petroleum gas and clean diesel fuel, and biomass as renewable energy can be used to transform into the carbon fuels. So synthesis of DME by biomass-derived syngas has attracted more and more academic and industrial attention.Our group has developed a novel bifunctional Cu-Mn-Zn/HZSM-5 catalyst by the mechanical mixing method from Cu, Mn, Zn and HZSM-5 zeolite for the direct synthesis of DME. We mainly study the effect of different hydrogenation components; precipitation sequence; reaction conditions; additives on the catalytic performance in direct DME synthesis from CO2. In addition, we also studied the effect of CO2 ratio on activity and selectivity of catalyst in direct DME synthesis from syngas, and the effect of different hydrogenation components on the catalytic performance in direct DME synthesis from biomass-derived syngas; comparison of carbon monoxide hydrogenation and carbon dioxide hydrogenation in DME synthesis.The specific conclusions are as follows:The CO2 conversion and DME selectivity were enhanced when Manganese or zinc added into Cu/HZSM-5 catalyst. Co-addition of manganese and zinc into Cu/HZSM-5 obtained the Cu-Zn-Mn/HZSM-5 catalyst, which showed the highest CO2 conversion and DME selectivity. Mn can improve the dispersion of the hydrogenation components in the catalysts and increase the adsorption capability of CO2; Zn can increase the reducibility of CuO and the adsorption capability of H2. Thus, the synergic effects of Zn and Mn in Cu-Zn-Mn/HZSM-5 catalyst increase the adsorption ability of H2 and CO2, made a favorable catalytic activity for the direct DME synthesis from CO2 hydrogenation.The degree and pattern of the interaction between Cu, Zn, Mn, is related to the preparation method. The catalysts were prepared by co-precipitation Cu-Zn-Mn or Zn-Mn at the same time, which showed the better catalytic performance. Highly dispersed Zn and effectively contacted with the copper species, causing a good CO2 and H2 adsorption capacity.A certain amount of Zr addition to Cu-Zn-Mn will promote the dispersion of main hydrogenation components.It was found that 5%Zr addition catalyst showed the best catalytic activity for dimethyl ether synthesis via CO2 hydrogenation.Because of thermodynamics limit, the activity of CO2 hydrogenation was significan-ly lower than CO hydrogenation on the same catalyst. Thus the hydrogenation of mixed feed gas of CO and CO2 is mainly apparent on the hydrogenation of carbon monoxide. When CO2 addition was less than 10%, the CO conversion will reduce, but the DME selectivity increased, and thus it has little effect on the whole yield of dimethyl ether. Increase the H2/(CO2+CO) ratio can improve CO conversion and the yield of dimethyl ether.The presence of too much CO2 will great reduce the conversion of CO hydrogenation.