Challenges for Model-Based Life Cycle Inventories and Impact Assessment in Early to Basic Process Design Stages
Papadokonstantakis, S., Karka, P., Kikuchi, Y., Kokossis, A.
Sustainability in the Design, Synthesis and Analysis of Chemical Engineering Processes, p.295-326, 2016
Allocation; Biorefineries; CO2 capture; LCA; Multifunctional processes; PMMA recycling; Process flowsheeting; Process scale; Short-cut models; Standardization
Sustainability assessment can be quite advantageous in the early stages of process design, where a vast number of alternatives are screened and changes are easier to implement. Among various sustainability assessment frameworks for process design, the life cycle assessment (LCA) is widely used for the environmental impact of normal process operation based on systematic procedures, well defined in ISO norms. However, LCA often requires data that are not available in conceptual-to-basic design stages or can only be estimated with great inaccuracy. In particular a detailed cradle-to-gate analysis of mass and energy flows can be a cumbersome task; typically, only a specific gate-to-gate part is detailed based on the specific interest and know-how of the process designer (e.g., a chemical production company). Thus short-cut approaches for filling life cycle-related data gaps are an interesting alternative. This chapter discusses diverse challenges for estimating life cycle inventories (LCIs), which lie in the core of any LCA study, using model-based approaches. Issues such as the availability of LCIs in existing databases and their compatibility with model-based LCI estimations, and the importance of the process scale and its impact on allocation approaches in multifunctional processes are highlighted and further demonstrated in three case studies. The first case study refers to the design of solvent-based CO2 capture in the very early stage of solvent screening. It focuses on dealing with severe data gaps for the cradle-to-gate life cycle impacts associated with the production of make-up solvent because of solvent degradation and fugitive emissions. The second case study refers to model-based assessment in upcoming processes converting biomass to fuels and chemicals in a biorefinery concept. The impact of various allocation methods is discussed and the importance of information about subdivision of the multifunctional systems into its main building blocks is emphasized. The third case study refers to the design of recycling processes for poly(methyl methacrylate) (PMMA), a multifunctional material found in many end products of everyday use. Besides using process modeling for comparing alternatives and filling in data gaps for LCA, this case study highlights the importance of specific information such as the impurities following the PMMA-containing waste material, the degree of process integration depending on the type of the purification processes, and the availability of market-related information for estimating the generated PMMA-containing waste material. Throughout this chapter the use of models for LCA lies at the center of discussion. Considering the standardized procedures of LCA, this chapter concludes with a discussion about the need for further standardizing the respective model-based approaches used for filling data gaps in the estimation of LCIs.