Experimental Research On Dimethyl Ether And Ethylene Glycol Synthesis From Syngas

Biomass utilization has received greater attention all over the world, with concerns about the global climate change, fossil fuel depletion and crude oil prices rise. Dimethyl ether (DME) can be used as a clean high-efficiency compression ignition fuel with reduced NOx, SOX, and PM emissions, while ethylene glycol (EG) is a multi-purpose chemical product which is mainly used in polyester manufacture or as antifreeze. Converting biomass into DME or EG is accepted as a feasible and viable green route to obtain renewable liquid fuels and chemicals, via biomass gasification and catalytic synthesis.Firstly, thermodynamic simulation of DME synthesis from biomass-derived syngas was presented based on Aspen Plus. In the thermodynamic analysis of hydrogenation of CO and CO2, the equilibrium product compositions were investigated with different reaction parameters such as temperature (160-320℃), reactor pressure (2-8 MPa) and the H2 to (CO+CO2) mole ratio (0.5-6) and CO2 to CO mole ratio (0.2-2) in the feed gas. Meanwhile, the influences of these parameters on CO and CO2 conversion and DME yield were investigated. The results showed that lower temperature and higher pressure were beneficial to the synthesis of DME and the composition of feed gas was a key factor to the DME production. Increasing the mole ratio of H2 to (CO+CO2) or reducing the CO2 to CO mole ratio can improve the yield of DME.A new technical route of pseudo-one-step synthesis was proposed to produce DME. The reactor was operated together with a two-stage catalyst system, which was set up for methanol synthesis and methanol dehydration separately in the same fixed-bed. The influences of the operating conditions, including temperature, reactor pressure, H2 to CO mole ratio in the feed gas and space velocity, on CO conversion, selectivity of DME and DME yield were investigated. Based on the experimental results, the optimum conditions for pseudo-one-step synthesis of DME were shown as follows:top stage temperature in the range of 270～280℃; bottom stage temperature in the range of 235～245℃; the optimum ratio of H2 to CO above 2 and space velocity in the range of 1000～1300 h-1. It was also indicated that the new route of pseudo-one-step synthesis of DME can achieve higher CO conversion, higher DME selectivity and good catalyst stability. Both methanol synthesis catalyst and methanol dehydration catalyst had good stability over a 100 h period operation.The indirect synthesis of EG from biomass-derived syngas is a promising new process to sustainable production of EG. This indirect synthesis process has two steps, the CO coupling reaction to produce oxalates and then the hydrogenation of oxalates to EG The reactor system for the coupling of CO with nitrite esters to dimethyl oxalate (DMO) was established using Pd/α-Al203 based catalyst prepared by incipient wet impregnation. Under optimum reaction conditions, the conversion of CO can reach 35%, while the selectivity of DMO is 93%. The hydrogenation of DMO to EG was carried out in a continuous-flow fix-bed reactor. Cu/SiO2 catalysts were prepared by impregnation and deposition precipitation methods for the hydrogenation of DMO to EG. XRD, TEM, H2-TPR, SEM, EDS and N2 physisorption were performed to characterize the textural and structural properties of the catalysts. The results showed that Cu particles from the deposition precipitation preparation were homogeneously dispersed on the support and their sizes were found to be smaller than those from the impregnation method, and the catalyst produced by the deposition precipitation method gave higher EG yields at lower reaction temperatures and lower H2/DMO mole ratio.High active Cu/SiO2 catalyst was in situ prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in one phase solution using ethanol as co-solvent with PH value of 12-13, followed by the precipitation of copper on SiO2 by ammonia evaporation. The DMO conversion reaches 100% and the EG selectivity reaches 95% at 498 K and 2 MPa with a high liquid hourly space velocity for the DMO over the 25% Cu/SiO2 catalyst. Ethanol was the excellent co-solvent for Cu-TEOS catalyst than the other selected solvents. The effect of water/ethanol (W/E) volume ratio on the hydrogenation of DMO to EG was investigated. At 488-503 K, the catalyst prepared with water/ethanol volume ratio of 3:1 exhibited 90-95% EG selectivity. The higher catalytic activity and EG selectivity on this series of catalysts is attributed to the higher BET surface area and pore volume which facilitate the mass transport and as a result improve the catalytic performance.