Solid fuel production from co-hydrothermal carbonization of polyvinyl chloride and corncob: Higher dechlorination efficiency and process water recycling

• Published in: The Science of the total environment Vol. 843; p. 157082
• Main Authors: Li, Zhaoyang, Niu, Shengli, Liu, Jiangwei, Wang, Yongzheng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-10-2022
• Subjects: Biomass; Co-HTC; Hydrochar; PVC; Recirculation; Thermochemical process; Co-HTC; Thermochemical process; Hydrochar; Recirculation; Biomass; PVC
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.157082

The hydrothermal carbonization (HTC) of polyvinyl chloride (PVC) and wet herbal agricultural wastes for solid fuel production remains bleak economics and sustainability because of high chloride residual, wastewater burden and low production capacity. In this study, the HTC dechlorination was investigated using the first-order reaction kinetic analysis. We found that the co-hydrothermal carbonization (co-HTC) of PVC and the typical biomass (corncob) achieved a staggering drop of dechlorination activation energy from 189.95 kJ/mol to 110.04 kJ/mol. The co-HTC process achieved rapid dechlorination and carbonization due to synergistic effect, to suppress the chlorine content in bituminous-coal-like hydrochar less than 0.05 %. The process wastewater (process water) from co-HTC was recycled four times to evaluate the reusability and chemical evolution. The organics in co-HTC environment enhanced the carbonization which was confirmed by the improved heating value (30.06 to 32.42 MJ·kg−1), hydrochar yield (33.33 % to 36.47 %) and energy recovery efficiency (57.73 % to 68.13 %). The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) evidenced the process water recirculation maintained high chloride removal. Moreover, the possible formation pathways of two kinds of hydrochars were discussed through the chemical composition of the aqueous phase and the characteristic structures of hydrochar. The co-HTC and process water recycling strategies provide a more promising prospect to convert PVC and biomass wastes into solid fuels.
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•Co-hydrothermal dechlorination activation energy is investigated.•The synergy mechanism of PVC and corncob is revealed from the kinetic perspective.•The obtained hydrochar is chlorine free with high heating value.•The hydrochar yield and HHV step increase with successive process water recycling.•The organic matter in aqueous phase is responsible for the secondary char formation.