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

Highlights • Less gases while more tar formed over acidic oxides than that over basic oxides. • Over CaO, the production of phenolic compounds was suppressed. • Coking was more significant over the basic oxides than that over the acidic oxides. • The tar from cellulose contributed more to coking than that from lignin. • Cellulose–derivatives and lignin–derivatives affect coke structures in varied ways. Abstract This study investigated the effects of the acidity/alkalinity of seven oxides (Al 2 O 3 , SiO 2 , ZnO, K 2 O, MgO, CaO, La 2 O 3) 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, CO 2 , and CH 4 were the main gaseous products in the pyrolysis of poplar, cellulose and lignin, and CO was formed first, followed by CO 2 and CH 4. Some H 2 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 CO 2 , CO, H 2 , CH 4 via probably decarboxylation/decarbonylation, dehydrogenation and etc. The coke from the pyrolysis of lignin was much more stable. CaO and La 2 O 3 reacted with the CO 2 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. [ABSTRACT FROM AUTHOR]