Use of carbon dioxide for carbon-negative syngas production from the pyrolysis of cork waste

Abstract

Although pyrolysis enables comprehensive utilization of such feedstocks, the direct application of resulting biocrude in energy production is constrained by its compositional heterogeneity. In this context, the conversion of biomass into syngas (H2 and CO) presents a promising option considering its simple composition. This study investigates a strategy to enhance syngas production from the pyrolysis of cork waste (CW), with a primary focus on using carbon dioxide (CO2) as a soft oxidant. CW is primarily composed of suberin, a polyester-based biopolymer crosslinked with aliphatic and phenolic moieties. CW pyrolysis under the existence of CO2, however, produced liquid pyrolysates with a broad carbon-number distribution (C3-C30), originating from suberin decomposition, indicating limited activation of CO2 associated with gas-phase reactions with suberin-derived volatile compounds (VCs). To overcome this limitation, a nickel (Ni)-based catalytic pyrolysis was employed by controlling catalyst bed temperatures from 500 to 700 ˚C. Increase in the catalyst bed temperature led to the enhanced thermal cracking of VCs into lighter species. Under these conditions, CO2 participated in catalytic gas-phase reactions, enhancing carbon monoxide (CO) formation and thereby providing carbon-negative properties to pyrolytic products. Overall, this study demonstrates that integrating CO2 with Ni-catalyzed pyrolysis can achieve net CO2 emissions of −2.32 g CO2 g CW−1, highlighting the feasibility of this approach as a carbon-negative platform for waste valorization into syngas.