SummaryCurrent life cycle assessment (LCA) interpretation practices typically emphasize hotspot identification and improvement assessment. However, these interpretation practices fail in the context of a decision-driven comparative LCA where the goal is to select the best option from a set of dissimilar alternatives. Interpretation of comparative LCA results requires understanding of the trade-offs between alternatives-instances in which one alternative performs better or worse than another-to identify the environmental implications of a specific decision. In this case, analysis must elucidate relative trade-offs between decision alternatives, rather than absolute description of the alternatives individually. Here, typical practices fail. This article introduces a probability distribution-based approach to assess the significance of performance differences among alternatives that allows LCA practitioners to focus analyses on those aspects most influential to the decision, identify the areas that would benefit the most from data refinement given the level of uncertainty, and complement existing hotspot analyses. In a case study of a comparative LCA of five photovoltaic technologies, findings show that thin-film cadmium telluride and amorphous silicon cell panels are most likely to perform better than other alternatives. Additionally, the impact categories highlighted by the new approach are different than those highlighted by typical external normalization practices, suggesting that a decision-driven approach to interpretation would redirect environmental research efforts. Decision-Driven Comparative Life Cycle AssessmentsComparative life cycle assessments (LCAs) quantify the life cycle environmental impacts of equivalent products technologies or processes throughout all the life phases, from raw material extraction to final disposal (Prado et al. 2012). A decision-driven comparative LCA, where the goal is to identify the most environmentally viable alternative(s) among a set of options, can guide material and processing selection in industry, identify a best policy scenario to inform environmental regulations, and lead researchers toward the most promising areas for reduction of environmental impacts in technology development. However, the results are seldom conclusive, and when one alternative performs best in some aspects, it often also performs worse in others-these trade-offs among the different impact categories make it difficult to identify the most viable alternative. Because International Organization for Standardization (ISO) guidelines leave all steps after characterization as optional, the majority of comparative LCAs truncate analysis at characterization (ISO 2006). Thus, comparative LCA results
A multimodel scheduling approach is proposed for controlling strongly nonlinear processes. A global controller is built from a weighted combination of local linear controller outputs with the weights being functions of a defined closed-loop gap metric. The control algorithm is hybrid in that the global controller continuously weights the outputs of the local controllers whereas the weights are updated at constant time intervals. The proposed strategy is then implemented on two simulated processes, one of which exhibits output multiplicity and the other exhibits input multiplicity.
Alcohol ethoxylates surfactants are produced via ethoxylation of fatty alcohol (FA) with ethylene oxide. The source of FA could be either palm kernel oil (PKO) or petrochemicals. The study aimed to compare the potential environmental impacts for PKO-derived FA (PKO-FA) and petrochemicals-derived FA (petro-FA). Cradle-to-gate life cycle assessment has been performed for this purpose because it enables understanding of the impacts across the life cycle and impact categories. The results show that petro-FA has overall lower average greenhouse gas (GHG) emissions (~2.97 kg CO2e) compared to PKO-FA (~5.27 kg CO2e). (1) The practices in land use change for palm plantations, (2) end-of-life treatment for palm oil mill wastewater effluent and (3) end-of-life treatment for empty fruit bunches are the three determining factors for the environmental impacts of PKO-FA. For petro-FA, n-olefin production, ethylene production and thermal energy production are the main factors. We found the judicious decisions on land use change, effluent treatment and solid waste treatment are key to making PKO-FA environmentally sustainable. The sensitivity results show the broad distribution for PKO-FA due to varying practices in palm cultivation. PKO-FA has higher impacts on average for 12 out of 18 impact categories evaluated. For the base case, when accounted for uncertainty and sensitivity analyses results, the study finds that marine eutrophication, agricultural land occupation, natural land occupation, fossil depletion, particulate matter formation, and water depletion are affected by the sourcing decision. The sourcing of FA involves trade-offs and depends on the specific practices through the PKO life cycle from an environmental impact perspective.Electronic supplementary materialThe online version of this article (doi:10.1007/s11743-016-1867-y) contains supplementary material, which is available to authorized users.
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