Abstract
Bifunctional nickel tungsten carbide catalysis was used for the conversion of aqueous sugar solutions into short-chain polyols such as ethylene glycol. It is shown that very concentrated sugar solutions, viz. up to 0.2 kg L−1, can be converted without loss of ethylene glycol selectivity by gradually feeding the sugar solution. Detailed investigation of the reaction network shows that, under the applied reaction conditions, glucose is converted via a retro-aldol reaction into glycol aldehyde, which is further transformed into ethylene glycol by hydrogenation. The main byproducts are sorbitol, erythritol, glycerol and 1,2-propanediol. They are formed through a series of unwanted side reactions including hydrogenation, isomerisation, hydrogenolysis and dehydration. Hydrogenolysis of sorbitol is only a minor source of ethylene glycol. To assess the relevance of the fed-batch system in biomass conversions, both the influence of the catalyst composition and the reactor setup parameters like temperature, pressure and glucose addition rate were optimized, culminating in ethylene glycol yields up to 66% and separately, volume productivities of nearly 300 gEG L−1 h−1.
Highlights
Biomass has great potential as a substitute for fossil feedstock for the renewable production of transportation fuels and industrially important chemicals
It is estimated that more than 90% of the global annual amount of terrestrial plant biomass produced through photosynthesis – corresponding to 57 × 109 tonnes of elemental carbon – is not digestible by humans and this renewable resource may be used for fuel or chemical purposes without competition with the foodindustry.[1,2,3,4]
Ethylene glycol is a valuable product used in antifreeze liquids and as a precursor for polymers such as polyethylene terephthalate (PET)
Summary
Biomass has great potential as a substitute for fossil feedstock for the renewable production of transportation fuels and industrially important chemicals. Product distributions varied with the catalyst type, additives like CaO and reaction conditions ( pressure, substrate concentration and temperature), 1,2propanediol always appeared to be one of the most dominant products. It was only since the recent discovery by Ji et al.,[42,43] who reported the direct catalytic conversion of cellulose to ethylene glycol, that the selective formation of ethylene glycol was conceivable. Others recently reported the use of near-stoichiometric amounts of WO3 in
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