Life cycle assessment of waste tire recycling: Upgraded pyrolytic products for new tire production

Abstract

Waste tire (WT) pyrolysis is an attractive option for material and energy recovery. Further upgrading of pyrolytic products demonstrates greater environmental and economic advantages than conventional pyrolysis. However, the advance in economic benefits brought by quality improvement of pyrolytic products is not significant. Therefore, this study proposed the circulation case of upgraded pyrolytic products for new tire production from WTs. This case recycles the products produced from WT pyrolysis into new tire production to establish a closed-loop between end-life and beginning-life of WTs. Three circulation cases using different modification methods of pyrolytic carbon black (CBp) were evaluated by several circular economy indicators. Results show that Case M1 (modified CBp (M-CBp) by physical modification) has the best resource-environmental performance (resource benefit to environmental cost ratio, RBECR), which is 20.35 % and 4.62 % higher than those of Cases M2 (M-CBp by nitric acid modification) and M3 (M-CBp by plasma modification), respectively. Case M3 has the best comprehensive performance (economic profit to environmental cost ratio, EPECR), which is 1.62 % and 2.82 % higher than that of Case M1 and Case M2, respectively. To acquire higher profits, the coupled-circulation case that combined M-CBp and reclaimed rubber for new tire production was further proposed, as reclaimed rubber was a major raw material for tire production with higher profitability. The proposed process recycles more materials into new tire production so that the EPECR and RBECR of coupled-circulation case increase by 55.7 % and 147.7 % as compared to the basic circulation case, respectively. Therefore, the coupled-circulation case demonstrates an efficient pathway for WT utilization. The sensitivity analyses further show that both the replacement rate of M-CBp prepared by plasma modification (M3-CBp) and price of crude oil significantly influence the resource-environmental performance, with the sensitivities reaching 101.3 % and 100 %, respectively. The replacement rate of reclaimed rubber is the most important factor for comprehensive environmental-economic performance, with the sensitivity reaching 44.1 %. Generally, coupled-circulation case can maintain good comprehensive benefits when various influencing factors change within the scope discussed in this paper.