Life Cycle Assessment model for the chlor-alkali process: A comprehensive review of resources and available technologies

Abstract

Currently, the chlor-alkali sector is shared by three main electrolysis technologies: mercury, membrane and diaphragm cell. As the energy demand of the process is one of its main drawbacks, new technological improvements are emerging such as the replacement of the standard hydrogen-evolving cathode in membrane technology by an oxygen-depolarised cathode (ODC). In this sense, the environmental impacts of novel techniques must be analysed over their entire life cycle to assess properly their integration opportunities. This work develops a life cycle assessment (LCA) model to describe the chlor-alkali European industry. The multi-functional production of chlorine, sodium hydroxide and hydrogen is studied from cradle to gate, including salt production, products treatment and waste management within the system boundaries. While the worst scenario results mercury technique, ODC technology emerges as the most environmentally sustainable process. The results suggest the importance of considering every process included, especially salt production and brine preparation, which can involve up to 20% of the total environmental impacts. In fact, taken as reference membrane scenario, results demonstrated that the environmental profile can be reduced by up to 18% when lower energy demanding processes for salt production and NaOH concentration were selected. This improvement percentage overcomes the competitive advantage shown by ODC versus membrane technology (7%). This model is a useful tool not only for the comparative assessment of the environmental sustainability of the different chlor-alkali installations, but also to guide and support the decision-making process in the introduction of emergent technologies in the sector.