CO2-assisted catalytic pyrolysis of cellulose acetate using Ni-based catalysts

Abstract

Cellulose acetate (CA) is one of widely used polymers for chemical and medical applications due to its versatile physico-chemical functionalities. Although its recycle is available after a deacetylation process, the recycle process releases a huge amount of wastewater. Thus, this study investigated a direct disposal process of CA with its valorization to syngas (H-2 and CO) through pyrolysis. To construct more environmentally benign process, CO2 was used as a co-feedstock with CA to simultaneously convert them into syngas. Pyrolysis of CA in N-2 was performed as a reference study to examine the effectiveness of CO2 on valorization of CA. Acetic acid and methyl acetate were main volatile pyrolysates (VPs) from CA pyrolysis, and the further thermal cracking of VPs resulted in syngas and CH4 formations under both N-2 and CO2 conditions. To expedite syngas formations, multi-stage pyrolysis (two-stage pyrolysis) and catalytic pyrolysis were employed. With the increased thermal energy through two-stage pyrolysis, four times more production of syngas was shown, comparing to the result of a single-stage pyrolysis. With Ni catalysts, the syngas formation was the two orders of magnitude higher than the single-stage pyrolysis, and the significant enhancement of CO formation was shown in the presence of CO2 due to combined effects of CO2 and the Ni-based catalysts. This CO enhancement resulted from catalytically expedited gas phase reactions between CO2 and VPs evolved from CA. In addition, the CO2 contributed to the suppression of coke deposition on the catalyst, thereby suggesting more technical and environmental benefits of CO2 as a reactive co-feedstock of pyrolysis in reference to N-2. Therefore, this study proved the direct and versatile technical platform to convert CA and CO2 into syngas.