Hydrogenolysis Of Glucose Into Low Carbon Glycols

With the increased exhaustion of the fossil resources and the urgency of environmental problems, chemical industry which is closely linked with the human beings does require accessible, economic, and renewable source of organic carbon to replace oil, to produce high value-added chemicals. Low carbon glycols, including ethylene glycol, propylene glycol and butylene glycol, are important high value-added chemicals. However, low carbon glycols, especially ethylene glycol, rely on import in the long term in China, resulting in high external dependency. Therefore, utilizing biomass instead of oil as raw material to produce low carbon glycols with high added value has very considerable energy, environmental and economic benefits. As one important route of converting cellulose into bio-based products, conversion of sugars has caught the attention of many researchers. Hydrogenolysis of sugars is the conversion of carbonhydrate to polyols by hydrogenation and chain scission under the appropriate reaction temperature and hydrogen pressure. The difficulties of this process are high temperature, high pressure and acid/alkali additives; furthermore, the selectivity of low-carbon glycols is not enough. Therefore, the aim of this study is to develop high-performance catalyst for efficient catalytic conversion of glucose to low carbon glycols under milder reaction conditions.In this study, the effects of W promoter and applied supports on Ru-based catalysts in hydrogenolysis of glucose were investigated in the fixed bed under milder reaction conditions, combining with the characterizations of NH3-TPD, H2-TPR, XRD, Raman, TEM and DRIFTS. Based on the obtained results, we got the conclusions as:1) W promoter enhanced the acidity of catalyst in terms of number strength and number, and improved the dispersion of the active component of Ru, contributing to promoting the selectivity of low carbon glycols to 87.28%; Ru induced the hydrogen spillover, enhancing the reducibility of W species; 2) W species with low valences, such as a-W and β-W, were gained after reduction using various supports, including SiO2, AC, CNFs and WO3; Among them, the catalyst using SiO2 support had the most amount of acidic sites, and achieved the highest conversion of glucose and the selectivity of low carbon glycols.In order to further improve the selectivity of low carbon glycols, the RuW/SiO2 catalysts were modified by pretreatment of SiO2 using polyethylene glycol 600 (PEG-600) and citric acid (CA). The obtained catalysts were characterized by NH3-TPD, H2-TPR, XRD, XPS, TEM and DRIFTS to gain an insight into the effects of pretreatments. According to the results, we got the following conclusions:1) the pretreatment by PEG-600 and CA improved the dispersion of supported metals, and enhanced the interaction between metal and support, but decreased reducibility of supported metal; 2) An increase of the number of acidic sites was gained by pretreating SiO2 with PEG-600, contributing to the increase of the selectivity of low carbon glycols to over 90%. However, the number of acidic sites was decreased by pretreating SiO2 with CA, resulting in the molar selectivity of low carbon glycols falling to 70.88%.In this study, the efficient catalytic conversion of glucose to low carbon glycols under milder reaction conditions was achieved, realizing the selectivity of low carbon glycols up to 91.59%. This study provided a potential route of the production of bio-based low carbon glycols.