Pyrolysis of poplar, cellulose and lignin: Effects of acidity and alkalinity of the metal oxide catalysts

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.