Potential and Challenges of Life-Cycle Assessment as a Tool for Green Chemistry Mina Yekkalar1, Elham Abazarian2 1) MS.c. in Civil and Environmental Engineering, Researcher at Office of Sustainability, Amirkabir University of Technology 2) BS.c. in Chemical Engineering, Amirkabir University of Technology email@example.com Abstract “Green Chemistry” is the term that is accepted widely for explaining the tendency towards sustainability and chemical processes and products that are more environmentally friendly. LifeCycle Assessment is an important assessment tool for decision making; In particular, it can determine process stages exactly with a high environmental effect when it is applied throughout the planning phase. Therefore, it can provide guidelines regarding the optimization of applying the actual technology. Life cycle assessment has been described as a tool for comparing products and processes or different components during a life-cycle. The current study provides a profound review with respect to the principal descriptions of Green Chemistry as well as Life-Cycle Assessment (LCA) as a tool that evaluate environmentally the chemical products and processes. This paper tries to consider challenges of LCA methodologies to green chemistry as well. Keyword: Sustainability, Green Chemistry, Life-Cycle Assessment, Environmentally Friendly Chemical Processes and Products, Challenges of LCA 1. Introduction “Green Chemistry” is the term that is accepted universally to describe the tendency towards chemical processes and products that are more suitable for the environment . Various studies in the field of green chemistry often advance new products or methods as ‘green’ or ‘more environmentally friendly’ than their conventional partner, in spite of the fact that these articles usually do not evaluate the environmental performance quantitatively. Fortunately, in the last decades a variety of procedures and their ready-to-use guidance have emerged to design products and processes in an environmentally friendly manner. Life-cycle assessment (LCA) is one of the most important tools. The basis of this paper is a profound review of the definitions of Green Chemistry and investigation of the operators that are the sources of the movement towards Green and Sustainable Chemistry, and then Life-Cycle Assessment (LCA) is considered from an environmental point of view as a tool for assessing chemical products and processes. Furthermore, it is attempted to investigate the most important challenges of LCA methodologies to green chemistry. 2. Objectives for Green Chemistry Extensive information about chemicals, and categorizing a growing number of chemical substances as being “hazardous”, will be involved in health and safety, and also leads to difficulty and high cost in using those substances. It will certainly results in the restriction of waste which consists of those substances, by local authorities and governments as well as increase in the costs of disposal. Therefore, legislation will progressively compel chemical industries that are the biggest sources of hazardous substances to improve their products and processes by replacing hazardous substances with other safe substances in their processes or products and also by minimizing the amount of their waste and its hazards . As shown in Figure 1, the costs and other constraints for a chemical product are obvious all over the supply chain from the growing expenses of raw materials, due to increasing rareness of petroleum and penalties exerted by carbon taxes for using it, to an increasing knowledge concerning the risks that are often related to that chemicals among end-users, and their awareness about the necessity to separate themselves from any chemical which is recognized as being hazardous in their supply chain. Figure1. Supply chain pressure  In addition, as shown in Figure 2, in this situation Green Chemistry may be considered as a chain of reductions. These reductions result in benefits including economic, environmental, and social improvements . Waste reduction causes costs to be saved because waste disposal is increasingly becoming expensive, especially when it is hazardous. In addition, costs are saved when energy usage is lessened and also more efficient processes are made by decrease in materials consumption. Furthermore, these reductions result in environmental advantages regarding the consumption of feedstock and also end-of-life disposal. Moreover, an expanding use of renewable resources will lead to the more sustainable manufacturing industry . Figure2. Chain of reductions in green chemistry  3. Development of Life-Cycle Assessment in Green Chemistry Chemical industry is getting more informed about environmental burdens and some companies can understand that Green Chemistry may offer the business advantage and competitive benefit. In this situation, it is crucial that the benefits which are presented by Green Chemistry can be quantified. Legislation or supply chain compulsions can convince a company to use a process or substance that is environmentally benign, but how can they choose a really “greener” option? Trying to apply Green Chemistry during the life-cycle of a chemical product is specifically important . Figure 3 presents the life-cycle of a product in the area of Green Chemistry. These requirements have resulted in developing life-cycle assessment (LCA) . LCA is usually used to determine the environmental impacts of one economic activity, commonly at a particular place and one point in time . Considering all feasible environmental and socio-economic issues related to the proposed project in terms of quality and quantity, as well as giving the obtained information to decision makers is its primary purpose. Then, environmental damage from the proposed project can be reduced and any environmental benefits can be determined. Figure3. Life-cycle of a product in Green Chemistry  A large number of chemical products used conventionally today were not made for end-of-life. In addition, entire supply-chain issues including resource and energy consumption and production of waste were not necessarily regarded. The Green Chemistry method in design stage should help to promise the sustainability of novel products across their entire life-cycle and decrease the number of mistakes that we make, when it is implemented at the design section. Some of the research relating to Green Chemistry has concentrated on chemical producing processes. It can be believed here that Green Chemistry leads us towards the “ideal synthesis” . Figure 4 shows the elements of the "ideal synthesis". Figure4. "ideal synthesis" elements  Yield is the metric which is recognized widely in chemistry research for estimating the efficiency of a chemical synthesis. LCA presents a simple and comprehensible method for measuring the success of a synthetic route and comparing it to other routes. 4. life-Cycle Methodology 4.1. LCA Background The beginning of the LCA methodology may be found in the late 1960s. Concerns regarding the limitations of raw materials and energy resources stimulated interest to find ways in order to explain cumulatively the energy usage and to estimate future resource supplies and use . Early researches applied various methods without a common theoretical structure. Since 1990, efforts have been done in order to develop and standardize the LCA methodology under the coordination of the Society of Environmental Toxicology and Chemistry (SETAC). International Standardization Organization (ISO) presented an international standard for LCA which has recently been revealed and is going through assessment and revision . The methodology system for ISO is similar to that for SETAC but it has some differences for the interpretation phase. In this phase, additional analysis and sensitivity studies have been included in ISO . 4.2. Framework of LCA The LCA methodology in fact consists of a group of different methods in a common structure. The technical framework for the management of LCA and its applications under ISO 14040 are shown in Figure 5. Figure5. Technical framework of LCA and its applications Based on ISO 14040, 1997  The items determined in the goal and scope definition phase include definition of the study objective, the system boundaries that specify which unit processes must be involved inside the LCA, environmental impacts which will be reviewed for evaluation and functional unit that is a source for assuring the comparability of LCA results . Collecting data and calculation mechanisms are mainly included in the inventory analysis phase of life cycle assessment in order to quantify appropriate inputs and outputs of a product system. These inputs and outputs may involve the resources usage and discharges to water, air, and land that are related to the system. These data comprise the input to the life-cycle impact assessment too . The impact assessment phase of LCA is intended to assess the significance of potential environmental effects by using the results of the second phase, i.e. the life-cycle inventory analysis. This process generally includes the connection of inventory data with particular environmental effects and trying to comprehend them. The extent of detail, selection of impacts that are assessed and methodologies used depend on the goal and scope of the study . In the interpretation phase of LCA, results of the inventory analysis and the impact assessment are taken into account simultaneously and in the case of LCI studies, only the results from the inventory analysis are considered. This phase should describe limitations and give the decisionmakers interpretations and suggestions that are compatible with the goal and scope of the study. Life-cycle interpretation is also aimed at providing an introduction of the results of an LCA which is easily comprehensible, perfect and consistent and is in agreement with the goal and scope definition of the study . 5. Challenges of LCA LCA is the prominent tool for the evaluation of environmental impacts generated by products and processes from ‘cradle to grave’. Although it is popular and is codified by organizations such as the International Organization for Standards and the Society of Environmental Toxicology and Chemistry, LCA is a tool that requires improvement. It is usually told in the reports that LCA has not developed yet to a well-defined tool. Table 1 determines 15 most important problem areas and arranges them according to LCA phases. This section addresses main challenges which are related to Green Chemistry. Table1. LCA problems by Phase  Phase Goal and Scope Definition Life-Cycle Inventory Analysis Life-Cycle Impact Assessment Problem Functional definition Boundary selection Social and economic impacts Alternative scenario considerations Allocation Negligible Contribution (Cutoff) Criteria Local technical uniqueness Impact category and methodology selection Spatial variation Local environmental uniqueness Dynamics of the environment Time horizon Life-Cycle Interpretation Weighting and valuation Uncertainty in the decision process All Data availability and quality 5.1. System Boundaries Decisions regarding inclusion and exclusion lead to some problems during goal and scope definition, while problems in inventory analysis include flows and transformations. Fundamental decisions with respect to the borders of the study, base of comparison (functional unit) and physical relationships between processes involved determine mostly the representativeness and consequently, the value of an LCA. Therefore, problems in functional unit definition, selecting boundary, and allocation are the most important problems studied in the first part of this review . While the philosophy of LCA is to investigate the beginning of all processes and pursue them thoroughly to their ends, the analysis becomes unmanageable if boundaries are not delineated . As Hendrickson, Horvath, Joshi, and Lave (1998) discuss, defining a system boundary that does not include life-cycle stages in the evaluation, will definitely underestimate environmental impacts . However, this is a practical imperfection of the data collection process . Determining the system boundaries depends on the individual goals and scope of the study . For example, when processes are common to all options compared, they may be kept out of system boundaries. It is very important to present an exact determination of the system boundaries as part of the final results in any LCA -. 5.2. Inventory Analysis Difficulties Studies relating to Life-cycle that is based on the quantification of raw materials and wastes discharged to the environment have been done for over 20 years. However, the inventory analysis still needs agreement about several critical points, although it is the more factual part of LCA. In addition, inventory outcomes of studies with similar systems can still be notably different . 5.3. Allocation Rules Allocation may be defined as the relative distribution of the responsibility for resource usage, emissions and waste streams of the processes in the life-cycle . For instance, when several products under the study are able to be sold or leave the system for advantageous utilization in other systems, discount should be performed for their share of environmental burdens and thus, their share of the inventory data. This problem of co-product allotment to multiple output flows is tackled using an allocation parameter that indicates the physical behavior of the system, as pragmatically as possible . According to the report of Stromberg et al. (1997), assignment of all environmental effects to the main product would really be the simplest approach to allocation . However, this approach would not be suitable when the process being considered supports notably the overall environmental impact of the system or when a considerable amount of coproducts exist. A single solution to allocation problems appears to never be settled. As a result, it might be better to undertake the problem using sensitivity analysis for all important allocation procedures in subsequent case studies . 5.4. Impact Assessment Methods Although, the required tools for implementation of the inventory analysis are improved well, interpretation of the results leads to more problems, because transforming the inventory data into human health or ecological effects are not well comprehended yet -. Besides, the lack of a standard impact assessment methodology intensifies the problem, as different methods all have their own advantages and shortcomings. The most controversial and subjective step of life-cycle studies is to allocate relative weights to each impact group, because tradeoffs between the various environmental problems is required . Difficulties related to the normalization component of the impact assessment also exist, and there is no international agreement on how to perform this stage . The main problems are associated with the selection of reference area and finding the suitable data . 5.5. Temporal and Spatial Features Impact assessment is involved in possible impacts in the majority of life-cycle studies and it does not have a linear relation between the extent of the industrial processes and their actual impacts. Temporal and spatial features are usually disregarded, because LCA is basically an implement to preserve resource as well as prevent pollution . However, it is possible to incorporate time and space features by considering information such as the background levels of substances. It is believed that all processes in the inventory analysis take place at a reference time. Huppes (1996) claims that while LCA is not described dynamically in time, time features should be considered in the advance of present LCA methodology since they are necessary in taking into consideration, for example, the environmental impacts of heavy metals in mining wastes . However, the spatial representativeness of the system should be defined in the goal definition phase of an LCA (i.e. global, continental, regional, national or company level). When equivalency factors for some of the impact groups in LCA are used, spatial differentiation is often investigated . Differentiation is required in local problems like acidification, although this is not essential for global problems such as global warming. 5.6. Data Quality The quality of the data which is used in LCA is critical, because the accuracy of the LCA outputs is just as good as the accuracy of the input data --. However, lack of available inventory data has led to make LCA an expensive and time-consuming procedure . As Guinee et al. (1993) and Udo de Haes (1993) propose the development of databases and software by applying accepted data would support the problem solution. Furthermore, this would be especially helpful for documenting the global resource use and emissions data, which is essential for the normalization stage of the impact assessment. Lack of such data often impedes the normalization stage -. 6. Conclusion Green Chemistry arises from a number of items mentioned below as a tendency to the development of chemical processes and products that are more suitable for environment. 1) Hazardous chemicals need high costs to be disposed of. 2) Public pressure and knowledge concerning chemicals is growing, and an increasing number of chemical substances are categorized as being “hazardous” substances. Although a number of studies have been conducted in the field of Green Chemistry, they have not evaluated the environmental performance quantitatively in many cases. Studying Green Chemistry quantitatively in every part of the life-cycle of a chemical product is crucial. These requirements and reality checks have caused the life-cycle assessment (LCA) to emerge, which is usually used for the determination of the environmental impacts of a new product or process compared to traditional products or processes. Although LCA is popular and codified, it needs progress. Main reported problems of LCA related to Green Chemistry include: determining the system boundaries, problems associated with inventory analysis, allocation rules, impact assessment procedures, temporal and spatial features, data quality. Therefore, explaining clearly each stage of the selected methodology and the problems encountered should be one of the purposes of prospective LCA studies which comprise the assessment of process. 7. References  Anastas, P.T., Warner, J.C., "Green Chemistry, Theory and Practice", Oxford: Oxford University Press, 1998.  Clark, J. H., "Part 1: Green Chemistry for Sustainable Development, Green Separation Processes", WILEY-VCH Verlag GmbH & Co. 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