Preparation of furans from catalytic conversion of corn stover in H2O–THF co-solvent system – The effects of acids combined with alkali metal cations

The preparation of furans from catalytic conversion of corn stover is investigated in H2O–THF (tetrahydrofuran) co-solvent system, and the effects of Bronsted acids (H2SO4, HCl, HNO3) combined with alkali metal cations (Li+, Na+, K+) are studied systematically. It is found that the effect of individual acid in promoting the summary yield of 5-hydroxymethylfurfural (HMF) and furfural (FF) can be ordered as Cl− > SO42− > NO3−. When combined with a salt, the anion effect can be ranked in SO42− > Cl− > NO3−, both for the HMF yield and the summary yield of furans. Based on the best anion of SO42−, the impacts of the combined cations can be finely ranked as Na+ > K+ > Li+. For the system with Cl−, it ranks in K+ > Li+ > Na+ for the HMF yield or the summary yield of furans. The performance of NO3− is so poor that no liquid product can be detected when any alkali metal cations is combined with HNO3. The performance of H2SO4/Na2SO4 is the best among 9 tested combined catalysts, and the yield of HMF and FF from corn stover conversion under optimized conditions are 76% and 81% respectively.