A holistic approach towards incorporating and/or improving the green sustainability of chemical process plant systems

Abstract

Truly holistically green sustainability has yet to be fully realised within chemical process industries, particularly in consideration of socio-political perspectives that extend beyond operational compliance and workplace safety. The proposed project endeavoured to address this gap by incorporating/enhancing holistically green and sustainable approaches in the design and operation of chemical process plants (CPPs), using progressively more intricate multi-criteria decision-making (MCDM) frameworks. The frameworks acted as the project’s analytical backbone that aimed to balance environmental, economic, social, and technical dimensions more equitably and rigorously.
To validate the methodology frameworks, four representative small-scale, modular CPP case studies were selected. Each of the following case studies reflected diverse sustainability challenges and process configurations: (i) sustainable water desalination, with a focus on low-energy membrane and solar-assisted distillation systems; (ii) isopropanol (IPA) synthesis via isopropyl acetate hydrolysis, emphasising green reaction pathways; (iii) green ammonia production via electrochemical nitrogen fixation and renewable hydrogen; (iv) lignocellulosic bioethanol production that integrates waste biomass valorisation. Process simulation for the IPA and green ammonia cases was carried out via Aspen Plus v12, to ensure realistic thermodynamic modelling and energy integration.
The MCDM frameworks were tailored for each case, with respect to their unique sustainability(-based) criteria and sub-criteria. Fuzzy Analytical Hierarchy Process (FAHP) was employed to rank and prioritise sustainable water desalination pathways. An integrated “hybrid” FAHP-TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) framework was implemented for IPA and green ammonia. Due to its strategic importance and complexity, green ammonia was further assessed via FAHP-VIKOR with PROMETHEE-II (Preference Rank Organisation Method for Enrichment Evaluations), to provide more nuanced rankings with regard to trade-offs and stakeholder value conflicts.
As a core outcome, a final (and most optimised) methodology framework was developed that facilitated the systematic integration of process systems engineering (PSE) tools with FAHP-VIKOR & PROMETHEE-II. This integrative approach proved to be particularly valuable as a viable decision-support tool for early-stage design and policy evaluation, that balances quantitative process modelling with qualitative sustainability assessments. Comprehensive sensitivity analyses evaluated robustness of the Posteriori MCDM frameworks. The proposed MCDM frameworks exhibited overall high stability, particularly within the final and most optimised framework, which remained largely consistent under perturbations of input weights and ranking thresholds. However, certain instabilities were observed and attributable to
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uncertainties within VIKOR for specific sub-criterion, such as precise total equipment costs, which were often derived/estimated from secondary sources. Moreover, despite the methodological advancements, the frameworks retained a notable reliance on literature-derived values, especially for life cycle cost analysis (LCCA) and social-LCA (life cycle assessment). This dependency was primarily due to practical constraints, project resources, and scope limitations. These constraints highlight areas for potential enhancement.
Future research should aim towards addressing these gaps by incorporating real-time (primary) data, refining cost estimation models, and expanding the methodological framework to accommodate dynamic stakeholder input. Furthermore, a more in-depth and case-specific exploration of socio-political variables should be undertaken to elevate the framework from a primary technical tool, to a comprehensive sustainability governance platform.

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Identifiers

ORCID for Daniel Danyang Li: orcid.org/0000-0002-5664-0344

ORCID for Mohamed Hassan- Sayed: orcid.org/0000-0003-3729-4543

ORCID for Nuno Bimbo: orcid.org/0000-0001-8740-8284

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