ارزیابی چرخه حیات یک مبدل کاتالیستی برای ماشین های مسافربری Life cycle assessment of a catalytic converter for passenger cars

۱٫ Introduction Cars, the dominant source of road transport emissions, are one of the most important contributors to air pollution problems. To reduce the atmospheric emissions from passenger cars, the catalytic converter, an “end-of pipe” solution, was introduced and has become one of the most effective technologies. Since the introduction of cars with three-way catalytic converters, emissions of hydrocarbons, carbon monoxide, nitrogen oxides and other atmospheric pollutants from car exhausts have declined substantially. Nevertheless, it is essential not only to consider the clear benefits of a catalytic converter only at the exhaust pipe, but also to take into account the environmental impact entailed in extracting raw materials and producing a catalytic converter as part of its life cycle. From a local and global perspective, it is therefore important to investigate whether this tech- nology is reducing the environmental impact from car exhausts locally while increasing environmental burdens globally. Life cycle assessment is the approach chosen to investigate the environmental performance of a catalytic converter. The paper starts by defining the goal, scope, and assumptions of the study. In later sections, the paper discusses the comparisons of the environmental impacts and benefits of a catalytic converter. ۲٫ Method ۲٫۱٫ Goal definition The goal of this study is to assess and compare the environmental impacts occurring in the life cycle of a catalytic converter and the environmental benefits in terms of atmospheric emission reductions at the exhaust pipe. ۲٫۲٫ Functional unit The assessment and comparison of the total environmental impacts and benefits are based on the functional unit of one catalytic converter over 160,000 kilometers (km) of use. This is the guaranteed service lifetime of catalytic converters from the manufacturer [1] and is assumed to be the average service lifetime of the catalytic converter in this study. Over this service lifetime, it is assumed that the catalytic converter is not broken or malfunctions because of damage to the catalyst through accidental impacts or engine misfires. ۲٫۳٫ Studied product Of several designs and techniques for catalytic emission control for passenger cars, the ceramic monolithic three-way catalytic converter is one of the most widely used. In this study, a typical ceramic three-way catalytic converter manufactured for a Swedish passenger car is considered. It consists essentially of three parts: 1) A monolithic ceramic support that carries the catalyst, 2) A mat that surrounds the monolithic support made of ceramic material, 3) A converter housing made out of high quality, corrosion-resistant steel [2]. Table 1 shows the catalyst formulation taken from the typical values of the upper middle segment of Swedish passenger cars [3,2]. The amount of average fuel consumption of the cars is 3.4 Megajoule (MJ)/km or 0.109 litre/km [3,4]. ۲٫۴٫ System boundaries ۲٫۴٫۱٫ Geographical It is assumed that the catalytic converter is manufactured in England using Platinum Group Elements (PGEs) mined and produced from a PGE mining company in South Africa (Fig. 1). Raw materials such as ceramic monolith and wire mesh are assumed to have been produced in Germany. Steel is assumed to be produced in Wales. The catalytic converter is installed and used in Sweden. Spent catalytic converters are recycled in Sweden but PGEs are recovered and refined by the manufacturer in England. The environmental impacts are assessed in each area where the activities in the life cycle of the catalytic converter take place. ۲٫۴٫۲٫ Life cycle The production of raw materials for the catalytic converter production such as washcoat, ceramic monolith and ceramic wire mesh are included in the system boundaries but the extraction and transportation of the corresponding raw materials are excluded since data are not available and are assumed negligible. The mining and production of PGEs and the production of steel are included. Data regarding the extraction and production are also included for most energy carriers including electricity and fuels. In order for the catalytic converter to be able to effectively reduce the exhaust emissions, an oxygen sensor and electronic fuel management system is required to monitor the exhaust gas composition and to control the air to fuel ratio, respectively. This sensor consists of an electrolytic cell with “platinum” electrolytes [5]. However, the environmental impacts occurring in the life cycle of the oxygen sensor and the associated control system are not included in this study.