Niklas von der Assen

Life cycle assessment of polyols for polyurethane production using CO2 as feedstock: insights from an industrial case study

Polyethercarbonate polyols from carbon dioxide (CO2) are starting to be synthesized on industrial scale. These polyols can be further processed into polyurethanes enabling CO2 to be utilized in large amounts. Utilization of CO2 as alternative carbon feedstock for polyols is motivated from the potential to reduce greenhouse gas (GHG) emissions and fossil resource depletion. This article presents a life cycle assessment for production of CO2-based polyethercarbonate polyols in a real industrial pilot plant. The considered cradle-to-gate system boundaries include polyol production and all upstream processes such as provision of energy and feedstocks. In particular, provision of CO2 from a lignite power plant equipped with a pilot plant for CO2 capture is considered. Production of polyols with 20 wt% CO2 in the polymer chains causes GHG emissions of 2.65–2.86 kg CO2-eq kg−1 and thus, does not act as GHG sink. However, compared to production of conventional polyether polyols, production of polyols with 20 wt% CO2 allows for GHG reductions of 11–19%. Relating GHG emission reductions to the amount of CO2 incorporated, up to three kg CO2-eq emissions can be avoided per kg CO2 utilized. The use of fossil resources can be reduced by 13–16%. The impacts reductions increase with further increasing the CO2 content in the polyols. All other investigated environmental impacts such as eutrophication, ionizing radiation, ozone depletion, particulate matter formation, photochemical oxidant formation, and terrestrial acidification are also lowered. Therefore, synthesis of polyethercarbonate polyols from CO2 is clearly favorable compared to conventional polyether polyols from an environmental point of view.

Life-cycle assessment of carbon dioxide capture and utilization: avoiding the pitfalls

Carbon dioxide (CO2) capture and utilization (CCU) aims at reducing both greenhouse-gas emissions and fossil-resource depletion. Assessment of these aims requires quantitative environmental evaluation. So far, evaluation of CCU is based on ad hoc criteria such as the amount of CO2 utilized, simplified CO2 balances or CO2 storage duration. Albeit these criteria may be useful for very early stages of potential research pathways, we show that they are insufficient as basis for decisions on implementations and that they may lead to even qualitatively wrong environmental evaluation of CCU. Therefore, a holistic evaluation using life-cycle assessment (LCA) is mandatory. However, the application of LCA to CCU is subject to methodological pitfalls: (i) utilized CO2 might intuitively be considered as negative GHG emissions; (ii) since CCU usually generates products both in the capture and in the utilization process, choices exist how to allocate emissions to the individual products and (iii) CO2 storage duration is not reflected in traditional LCA. To avoid the existing pitfalls, we provide a systematic framework for LCA of CCU in which (i) the utilized CO2 is correctly considered as regular feedstock with its own production emissions; (ii) recommendations for obtaining product-specific LCA results for CCU processes are given and (iii) the CO2 storage duration is incorporated into a time-resolved global warming metric. The developed framework is illustrated by simplified LCA of CO2 capture from the atmosphere and from coal power plants, and of CO2 utilization for methanol and polymer production. Overall, the presented framework allows for the sound environmental evaluation of CCU.

Selecting CO2 Sources for CO2 Utilization by Environmental-Merit-Order Curves

Capture and utilization of CO2 as alternative carbon feedstock for fuels, chemicals, and materials aims at reducing greenhouse gas emissions and fossil resource use. For capture of CO2, a large variety of CO2 sources exists. Since they emit much more CO2 than the expected demand for CO2 utilization, the environmentally most favorable CO2 sources should be selected. For this purpose, we introduce the environmental-merit-order (EMO) curve to rank CO2 sources according to their environmental impacts over the available CO2 supply. To determine the environmental impacts of CO2 capture, compression and transport, we conducted a comprehensive literature study for the energy demands of CO2 supply, and constructed a database for CO2 sources in Europe. Mapping these CO2 sources reveals that CO2 transport distances are usually small. Thus, neglecting transport in a first step, we find that environmental impacts are minimized by capturing CO2 first from chemical plants and natural gas processing, then from paper mills, power plants, and iron and steel plants. In a second step, we computed regional EMO curves considering transport and country-specific impacts for energy supply. Building upon regional EMO curves, we identify favorable locations for CO2 utilization with lowest environmental impacts of CO2 supply, so-called CO2 oases.

Sensitivity coefficient-based uncertainty analysis for multi-functionality in LCA

PurposeIn LCA, a multi-functionality problem exists whenever the environmental impacts of a multi-functional process have to be allocated between its multiple functions. Methods for fixing this multi-functionality problem are controversially discussed because the methods include ambiguous choices. To study the influence of these choices, the ISO standard requires a sensitivity analysis. This work presents an analytical method for analyzing sensitivities and uncertainties of LCA results with respect to the choices made when a multi-functionality problem is fixed.MethodsThe existing matrix algebra for LCA is expanded by explicit equations for methods that fix multi-functionality problems: allocation and avoided burden. For allocation, choices exist between alternative allocation factors. The expanded equations allow calculating LCA results as a function of allocation factors. For avoided burden, choices exist in selecting an avoided burden process from multiple candidates. This choice is represented by so-called aggregation factors. For avoided burden, the expanded equations calculate LCA results as a function of aggregation factors. The expanded equations are used to derive sensitivity coefficients for LCA results with respect to allocation factors and aggregation factors. Based on the sensitivity coefficients, uncertainties due to fixing a multi-functionality problem by allocation or avoided burden are analytically propagated. The method is illustrated using a virtual numerical example.Results and discussionThe presented approach rigorously quantifies sensitivities of LCA results with respect to the choices made when multi-functionality problems are fixed with allocation and avoided burden. The uncertainties due to fixing multi-functionality problems are analytically propagated to uncertainties in LCA results using a first-order approximation. For uncertainties in allocation factors, the first-order approximation is exact if no loops of the allocated functional flows exist. The contribution of uncertainties due to fixing multi-functionality problems can be directly compared to the uncertainty contributions induced by uncertain process data or characterization factors. The presented method allows the computationally efficient study of uncertainties due to fixing multi-functionality problems and could be automated in software tools.ConclusionsThis work provides a systematic method for the sensitivity analysis required by the ISO standard in case choices between alternative allocation procedures exist. The resulting analytical approach includes contributions of uncertainties in process data, characterization factors, and—in extension to existing methods—uncertainties due to fixing multi-functionality problems in a unifying rigorous framework. Based on the uncertainty contributions, LCA practitioners can select fields for data refinement to decrease the overall uncertainty in LCA results.

Comparative LCA of multi-product processes with non-common products: a systematic approach applied to chlorine electrolysis technologies

PurposeMulti-product processes are one source of multi-functionality causing widely discussed methodological problems within life cycle assessment. A multi-functionality problem exists for comparative life cycle assessment (LCA) of multi-product processes with non-common products. This work develops a systematic workflow for fixing the multi-functionality problem caused by the non-common products. A novel technology for chlor-alkali electrolysis is analyzed and compared to the industrial standard technology to illustrate the approach and to benchmark the new technologys environmental impact.MethodsA matrix-based workflow for comparative LCA of multi-product systems is presented. Products are distinguished in main products and by-products based on the reason of process operation. We argue that only main products form the reference flows of the compared multi-product systems. Fixing the multi-functionality problem follows directly from the chosen reference flows. The framework suggests system expansion to fix the multi-functionality problem if non-common main products exist. Non-common by-products still cause a multi-functionality problem. These by-products are systematically identified and the multi-functionality problem is fixed with avoided burden and allocation. A case study applies the workflow for comparing environmental impacts of the standard chlorine electrolysis to a novel process using oxygen-depolarized cathodes. Three scenarios are derived and evaluated. The assessed impact categories are cumulative energy demand, global warming potential, acidification potential, photochemical ozone creation potential, eutrophication potential, and human toxicity potential.Results and discussionThe proposed workflow minimizes the methodological choices. The multi-functionality problem is systematically fixed based on the distinction between the main products and by-products. Inconsistent solutions are prevented by rigorous identification of unequal by-products within the compared systems. Selecting avoided burden processes or allocation factors is the remaining ambiguous choice common to the standard methods. The case study demonstrates the applicability of the workflow to comparative LCA of multi-product systems. The case study results show lower environmental impacts for the novel electrolysis technology in all practically relevant scenarios and impact categories.ConclusionsThe framework for comparative LCA of multi-product systems with non-common products adds systematic clarity to the general ISO standards. The approach reduces the subjective choices of LCA practitioners to the identification of reason of process operation. This reason is defined if the site-specific economic conditions are known. The matrix-based formulation allows identification of inconsistencies caused by multi-functionality. For the novel electrolysis technology, the results indicate significant potential for environmental impact reduction.

Industry-Cost-Curve Approach for Modeling the Environmental Impact of Introducing New Technologies in Life Cycle Assessment

The environmental costs and benefits of introducing a new technology depend not only on the technology itself, but also on the responses of the market where substitution or displacement of competing technologies may occur. An internationally accepted method taking both technological and market-mediated effects into account, however, is still lacking in life cycle assessment (LCA). For the introduction of a new technology, we here present a new approach for modeling the environmental impacts within the framework of LCA. Our approach is motivated by consequential life cycle assessment (CLCA) and aims to contribute to the discussion on how to operationalize consequential thinking in LCA practice. In our approach, we focus on new technologies producing homogeneous products such as chemicals or raw materials. We employ the industry cost-curve (ICC) for modeling market-mediated effects. Thereby, we can determine substitution effects at a level of granularity sufficient to distinguish between competing technologies. In our approach, a new technology alters the ICC potentially replacing the highest-cost producer(s). The technologies that remain competitive after the new technologys introduction determine the new environmental impact profile of the product. We apply our approach in a case study on a new technology for chlor-alkali electrolysis to be introduced in Germany.

Assessing the environmental potential of carbon dioxide utilization: A graphical targeting approach

Abstract Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO 2 is intrinsically difficult due to its low energetic state. Thus, a positive environmental effect of a CO 2 -consuming reaction cannot be taken for granted. In this work, we therefore present a graphical method to identify promising reaction schemes using CO 2 as a feedstock. Reactant mixtures leading to minimal life-cycle greenhouse gas (GHG) emissions are determined. The optimal reaction schemes strongly depend on the reactants global warming potential (GWP); in the case of CCU, the future GWP values of CO2 and H 2 are particularly critical and subject to major uncertainty today. The graphical method therefore provides GWP targets for CO 2 capture and H 2 production technologies. The method is demonstrated for the production of methanol. Five optimal reaction schemes are identified depending on the GWP values of CO 2 and H 2 . Thus, four threshold relations for the GWP of CO 2 and H 2 are derived showing directly under which conditions the utilization of CO 2 as a feedstock is environmentally preferential.

Environmental Assessment of CO2 Capture and Utilisation

This chapter provides an introduction to the application of life cycle assessment (LCA) for a reliable environmental assessment of CO2 capture and utilisation (CCU). Utilisation of CO2 as chemical feedstock aims at saving fossil fuels and reducing greenhouse gas emissions by providing an alternative carbon feedstock and closing the carbon cycle. However, these features do not necessarily render CO2 utilisation routes environmentally favourable since both CO2 capture and activation might require substantial amounts of energy. This chapter should enable the reader to understand the general concept of LCA and to identify the key environmental factors driving CCU.

An Uncertainty Assessment Framework for LCA-based Environmental Process Design

Abstract Environmental process design methods often incorporate life-cycle assessment (LCA) as a deterministic black-box methodology. However, LCA suffers from several sources of ambiguity and uncertainty. These limitations are particularly severe for the multi-functional processes typical for the chemical industry. This work introduces a rigorous uncertainty assessment framework. The framework quantifies data uncertainties and also uncertainties that result from fixing multi-functionality in LCA by allocation. The method is derived from a matrix-framework for LCA and applied to a comparison of alternative chlorine electrolysis technologies.

Life-Cycle Assessment Principles for the Integrated Product and Process Design of Polymers from CO2

Abstract To minimize environmental impacts, coupling integrated product and process design with life-cycle assessment (LCA) is a powerful yet challenging approach. A challenge in LCA is the proper accounting for all co-products occurring along the entire supply chain, known as allocation problem. In this paper, we provide a systematic analysis for LCA-based product and process design including alternative allocation methods. We apply the approach to polyol production from CO 2 . Here, alternative allocation methods lead to very different polyol products and processes. Finally, we derive general principles regarding co-product allocation in LCA-based product and process design.