Effect of CaO on Pyrolysis Products and Reaction Mechanisms of a Corn Stover

Abstract

To better realize how CaO promoted the pyrolysis process of a corn stover, which was important for further development of its technology, various effects of calcium oxide (CaO) on the pyrolysis of the corn stover at different temperatures were studied. The pyrolysis of the corn stover mainly occurred at 90, 291, 335, and 385 °C, which were correspondent to the pyrolysis temperatures of water, hemicellulose, cellulose, and lignin, respectively. Moreover, CaO was found to absorb some CO₂ and H₂O produced during the pyrolysis, as well as promote the occurrence of pyrolysis, and reduce the activation energy required for the reaction. According to the calculation of the activation energy, the optimal addition ratio of CaO and the corn stover should be between 1:2 and 1:1. The analysis of the release of pyrolysis gas showed that CaO had a beneficial effect on deacidification and the production of hydrocarbons and aromatic compound gas. When the addition ratio was 1:1, the release amount of the acidic substance was the lowest. When the ratio of CaO and the corn stover was 1:2, the release amount of H₂O, CO₂, and aromatic rings was at the maximum. The change of content of tri-state products generated during pyrolysis at different final temperatures was also studied by the pyrolysis experiment. The changes of functional groups in char were observed by Fourier-transform infrared spectroscopy. The results showed that with the addition of CaO, the content of H₂O in char, and the absorption of CO₂ increased, which generated alkaline substances, while reacting with acidic substances, and the thermal decomposition of acidic substances in the corn stover was promoted, which caused the pyrolysis reaction of the corn stover to occur in the positive direction. With the increase of pyrolysis temperature, phenol and carboxylic acid became thermally resolved or neutralized. When the catalyst amount or temperature was gradually increased, the aliphatic group was steadily pyrolyzed while char increasingly became aromatized. Based on the comprehensive analysis of the above experimental results, it was believed that the optimal addition ratio of CaO and the corn stover should be between 1:2 and 1:1.