Experimental Research On Indirect Synthesis Of Fuel Ethanol From Syngas

In recent years, with the development of social economy, fossil resource-oriented energy consumption increases rapidly, leading to serious problems of energy shortage and environmental pollution. Biomass energy is clean and renewable, and thus the development and utilization of biomass energy can effectively solve the problem of energy shortage and environmental pollution. Fuel ethanol technology is one of the most promising technologies in the field of biomass energy utilization, and by far fuel ethanol is the most realistic alternative to oil. Fuel ethanol has high oxygen content and octane number. Mixing a certain amount of fuel ethanol into gasoline as power fuel can resultfully improve combustion efficiency and antiknock performance of gasoline, and reduce the emission of pollutants.In industry, fuel ethanol is mainly produced through traditional fermentation or ethylene hydration. However, traditional fermentation is criticised for consuming a great mass of grain and increasing its price. Ethylene hydration depends on oil resource badly and has poor economical efficiency, so it has been gradually obsoleted. Therefore, it is of great practical significance to develop non-grain and non-oil route of ethanol production. Syngas can be obtained by gasification of renewable biomass resource. After being purified and adjusted, syngas can be used to synthesize fuel ethanol. Since the developed catalysts have poor catalytic activity and ethanol selectivity, direct (one-step) conversion of syngas to ethanol has not yet gained substantial progress. Indirect (multiple-step) conversion of syngas via acetyl product to ethanol is more likely to be implemented, of which the key technical problem is the development of methanol carbonylation catalyst and methyl acetate hydrogenation catalyst. Therefore, this paper carried out the experimental research on methanol carbonylation and methyl acetate hydrogenation in order to find an effective synthesis method of fuel ethanol.Liquid carbonylation of methanol based on Rh-I or Ir-I catalyst system has already realized industrialization.The catalyst system with iodide as additive, however, is expensive and has serious equipment corrosion. And the separation and refinement of product are difficult. Recently, non-rhodium and non-iodide catalytic system for vapor carbonylation of methanol has received wide attention. In this paper, a series of NiCl2-CuCl2/HMOR catalysts were prepared by impregnation method to investigate the catalytic performance for vapor carbonylation of methanol. The results showed that the loading amount of NiCl2and CuCl2had a great effect on catalytic activity. NiCl2/HMOR catalyst and CuCl2/HMOR catalyst both had high methanol conversion, and over5%NiCl2-15%CuCl2/HMOR catalyst, due to the synergistic effect of NiCl2and CuCl2, high methanol conversion as well as high selectivity to target product was obtained. Under the condition of1.5MPa and350℃, the methanol conversion could reach84.2%, selectivity to acetic acid and methyl acetate were48.4%and25.1%respectively, the total selectivity and total yield were73.5%and61.9%respectively, while the selectivity to the main by-product dimethyl ether was only13.2%.Cu-based catalysts selectively exhibit high C-O hydrogenation activity and low C-C hydrogenation activity, and SiO2has weak acidity and weak alkalinity, therefore, the Cu/SiO2catalyst shows high hydrogenation activity. In this paper, a series of Cu/SiO2catalysts were prepared by urea hydrolysis method to study influence of Cu loading and reduction temperature on catalytic activity.It was found that20%Cu/SiO2catalyst had small and uniformly-dispersed copper particles, relatively-concentrated pore diameter distribution and more active centers, and thus showed best hydrogenation performance. Cu/SiO2catalyst prepared by urea hydrolysis method had strong interaction between active component and carrier. The reduction of active component was limited. After reduced at350℃,20%Cu/SiO2catalyst had the best hydrogenation activity, which could be attributed to its highest value of Cu0/(Cu0+Cu+). Under the condition of2MPa,240℃, H2/MA=5, methyl acetate conversion and selectivity to ethanol could reach93.2%and60.9%respectively. And the catalytic activity increased with the increase of H2/MA.