Carbon negative syngas production with controlled H2/CO ratio from fruit processing byproducts via CO2-assisted pyrolysis

초록

The global fruit processing byproducts generation reaches approximately 500 million tons annually, and their conventional disposal methods, including landfilling, incineration, and composting raise environmental concerns. Pyrolysis has emerged as a sustainable thermochemical conversion technology that transforms fruit waste into syngas, bio-crude, and biochar. Despite the potential of bio-crude to be utilized as fuel and chemical feedstock, the complex composition of bio-crude requires post-treatment processes, limiting its economic feasibility. Therefore, further cracking of bio-crude into syngas during pyrolysis could be a more practical strategy, as syngas can be directly utilized in downstream applications. In this study, CO2, acting as a mild oxidizing agent, was supplied as the pyrolysis atmosphere to promote syngas production. Pomegranate processing byproducts (PPB) were selected as a case study because it leaves about 50 wt% of byproducts. Single-stage pyrolysis of PPB under CO2 atmosphere resulted in increased CO formation above 550 °C compared with N2 atmosphere due to the homogeneous gas-phase reactions between CO2 and volatile matters. To facilitate the effect of CO2, a 5 wt% Ni/Al2O3 was employed in pyrolysis at 700 °C with catalyst-to-feedstock ratio of 1:1 (w:w). Catalytic pyrolysis under CO2 achieved a gas yield of 51.8 wt% and produced 10.5 times more CO than single-stage pyrolysis under N2. By adjusting the CO2 concentration, the H2/CO ratio for downstream syngas utilization was tunable from 0.23 to 2.03. Furthermore, the amount of CO2 consumed during CO2-assisted catalytic pyrolysis offset the CO2 emitted under N2, resulting in a net CO2 emission reduction of 689.28 mg gPPB-1.

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