• Energy Research

This study investigated the conversion of furfural to 5-hydroxymethylfurfural (HMF) and further to levulinic acid/ester in dimethoxymethane under acidic conditions, with the particular focus on understanding the mechanism for polymer formation. The results showed that furfural could react with dimethoxymethane via electrophilic substitution reaction to form HMF or the ether/acetal of HMF, which were further converted to levulinic acid and methyl levulinate. The polymerization of furfural and the cross-polymerization between dimethoxymethane and the levulinic acid/ester produced were the main side reactions leading to the decreased yields of levulinic acid/ester. Comparing to the other solvent, methanol as the co-solvent helped to alleviate but not totally inhibited the occurrences of the polymerization, as the polymerization reactions via aldol condensation did not eliminate the CO functionalities. As a consequence, the polymerization reactions continued to proceed. Other co-solvent used such as guaiacol, dimethyl sulfoxide and acetone interfered with the transformation of furfural to HMF or aided the polymerization reactions. The polymer produced from the reactions between furfural and DMM was different from that produced from levulinic acid/ester. The former had a higher crystallinity, while the latter was more aliphatic. The DRIFTS and TG-MS studies showed that the polymer had the carboxylic group, methyl group and the aliphatic structure in the skeleton. The removal of these functionalities was accompanied by the aromatization of the polymer. The condensation of DMM with levulinic acid/ester was the key reason for the diminished production of levulinic acid/ester. Keywords: Furfural, Dimethoxymethane, Levulinic acid/ester, Mechanism for polymerization, Properties of the polymer

Abstract This study investigated the effects of the acidity/alkalinity of seven oxides (Al2O3, SiO2, ZnO, K2O, MgO, CaO, La2O3) on the pyrolysis of poplar, cellulose and lignin. The results showed that the basic supports such as CaO and MgO promoted the formation of gaseous products. CO, CO2, and CH4 were the main gaseous products in the pyrolysis of poplar, cellulose and lignin, and CO was formed first, followed by CO2 and CH4. Some H2 was also formed from the dehydrogenation reactions over CaO with cellulose as the feedstock. The acidic oxides promoted the tar formation, while the basic oxides suppressed tar formation. The oxides like CaO could remarkably suppress the production of phenolic compounds. The coke formation over the basic oxides were also much more significant than that over the acidic oxides, and the tar from cellulose contributed more towards coking. The heating of the coke in inert gas released CO2, CO, H2, CH4 via probably decarboxylation/decarbonylation, dehydrogenation and etc. The coke from the pyrolysis of lignin was much more stable. CaO and La2O3 reacted with the CO2 produced in pyrolysis and form the carbonates, while MgO could not. The TPO–MS characterization showed that the coke species were multiple types over CaO, and a single type over MgO. The cellulose–derivatives and the lignin–derivatives have distinct effects on the structural configuration of the coke.