Catalytic Hydrogenation of Corn Stalk to Ethylene Glycol and 1,2-Propylene Glycol

The use of whole lignocellulosic biomass as the feedstock for cellulose conversion is of great significance for large-scale, low-cost biomass conversion to biofuel and other useful chemicals. We recently achieved the direct conversion of cellulose (pure microcrystalline cellulose) into ethylene glycol at high yields over tungsten carbide catalysts. Here, corn stalk, an agricultural residue available in large quantities, was used as a lignocellulosic feedstock for conversion over nickel-promoted tungsten carbide catalysts under hydrothermal conditions and a hydrogen atmosphere. Nine different pretreatment methods were employed to convert the raw corn stalk to cellulosic feedstock with different chemical components and structures before the catalytic reaction. We found that corn stalks pretreated with 1,4-butanediol, NaOH, H2O2, and ammonia produced much higher yields of ethylene glycol (EG) and 1,2-propylene glycol (1,2-PG) compared to raw corn stalks, whereas pretreatments with ethanol solution, hot water, hot limewater, and supercritical CO2 just slightly improved the EG and 1,2-PG yields and corn stalk conversion. The hemicellulose in the corn stalk can be effectively converted to EG and 1,2-PG without hindering the cellulose conversion. In contrast, the lignin was resistant to degradation in the reaction and also inhibited EG and 1,2-PG production. The crystallinity of cellulose did not appear to have notable influence on the EG and 1,2-PG production. In view of the environmental benignity and low cost, pretreatment with ammonia and/or diluted H2O2 solution might be a practical method for corn stalk conversion, after which the derived cellulosic feedstock is readily converted into EG and 1,2-PG at an overall yield of 48% in the reaction.