Citation:

Pimentel, J., G. Ruiz-Mercado, AND F. Friedler. Technoeconomic Assessment of Recycling Routes for Chemicals: A Case Study of n-Hexane. In Proceedings, The 26th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, ThessalonikiG, October 08 - 11, 2023. AIDIC, Italian Association of Chemical Engineering, Milano, Italy, 349-354, (2023). https://doi.org/10.3303/CET23103059

Impact/Purpose:

The chemical industry employs various chemical compounds as raw materials and auxiliary substances for manufacturing valuable goods. A fraction of these feedstocks is transformed into valuable products, but some quantities are lost or managed as waste in end-of-life (EoL) streams. Since various chemical compounds are classified as toxic by the US Environmental Protection Agency (EPA), disposal operations and destructive treatments are usually performed to minimize their potential release into the environment. The destructive nature of these treatments has difficulties in their recovery and recycling. Thus, ensuring the sustainable circular economy for these substances requires the correct allocation of EoL materials to treatment facilities with plausible recovery treatments, from which it is possible to transport the recovered material to the new manufacturing facilities. This work proposes a solution to a such problem by determining the most cost-effective recovery and recycling pathways for the target chemical of concern from a set of EoL materials, according to the specifications of plausible consumers. Also, this work identifies the best system constituents (i.e., treatment facilities, treatment alternatives, transport units, and consumers) and their most convenient connectivity so that the chemicals of interest return to the productive chain. A substance worthy of examination for recovery and recycling is n-hexane. N-hexane is a hydrocarbon mainly employed as a component in fuels and other petroleum products. Moreover, it is extensively utilized as a solvent for plastics and resins, in adhesive formulations, as an edible oil extractant for seed crops, and as a solvent in biodiesel production. However, despite its extended use, n-hexane has been reported to exhibit aquatic life toxicity and damage to organs and fertility functions. Therefore, this chemical is a relevant case study due to its applications and environmental and health concerns. TRI tracking information and RCRAInfo were utilized to construct the case study with realistic values related to recycling n-hexane into the productive chain. Our method finds the best solutions for which the EoL materials from all generators are allocated into treatment facilities and subsequently into suitable consumers. Distinct alternative recycling routes were generated by resorting to the formulation of a synthesis problem and its subsequent solution. The best structure and two alternatives are presented and compared in terms of cost and n-hexane recovered. This work presents the initial attempt at solving this problem, and future work can focus on addressing the high level of uncertainty in the data. The proposed method will assist internal and external stakeholders in achieving cost-effective models of circular economy and resource conservation in the chemical industry.

Description:

The circular economy has become one of the most popular topics in worldwide sustainability research. The imperious necessity of reducing resource consumption and decreasing waste generation has led to reincorporating materials at the end-of-life (EoL) stage into the productive chain. Nonetheless, the presence of hazardous substances in the EoL stage materials poses a significant challenge for the transition toward the production model. The adequate transformation of these materials into feedstocks requires their correct allocation into recovery plants and final destinations. Such an allocation can be decided by resorting to optimisation by generating the best alternative networks, from where the stakeholders may decide the most suitable recycling scheme. In this work, a graph-theoretic approach is introduced to identify the best alternatives to reincorporate industrial EoL chemicals into the productive chain. This contribution presents the initial approach to this problem, demonstrated through a case study considering the data reported on the public-access release inventory data for n-hexane. Different recycling routes are proposed for the case study by optimising the total treatment cost, and their advantages and disadvantages are discussed; moreover, their efficiency concerning the circular economy is measured by comparing the amount of recovered chemicals. By generating plausible recycling alternatives, this work contributes positively to analysing potential alternatives for circular economy and resource conservation in industry.

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