Environmental challenges of the chlor-alkali production: Seeking answers from a life cycle approach

Abstract

Life Cycle Assessment (LCA) has been used to assess the environmental sustainability of the chlor-alkali production in Europe. The three current technologies applied nowadays are mercury, diaphragm, and membrane cell technology. Despite, having achieved higher energy efficiencies since the introduction of membrane technology, energy consumption is still one of the most important issues in this sector. An emerging technology namely oxygen-depolarised cathodes (ODC) is suggested as a promising approach for reducing the electrolysis energy demand. However, its requirement of pure oxygen and the lack of production of hydrogen, which could otherwise be valorised, are controversial features for greener chlorine production. The aim of this work is to evaluate and compare the environmental profiles of the current and emerging technologies for chlorine production and to identify the main hot spots of the process. Salt mining, brine preparation, electrolysis technology and products treatment are included inside the system boundaries. Twelve environmental impact categories grouped into natural resources usage and environmental burdens are assessed from cradle to gate and further normalised and weighted. Furthermore, hydrogen valorisation, current density and allocation procedure are subjected to sensitivity analysis. Results show that the electrolysis stage is the main contributor to the environmental impacts due to energy consumption, causing 99.5-72% of these impacts. Mercury is the less environmentally sustainable technology, closely followed by diaphragm. This difference becomes bigger after normalisation, owing to hazardous waste generated by mercury technique. Conversely, best results are obtained for ODC instead of membrane scenario, although the reduction in energy requirements is lesser than expected (7%).

Measuring the Vulnerability of an Energy Intensive Sector to the EU ETS under a Life Cycle Approach: The Case of the Chlor-Alkali Industry

“…Since in the chlor-alkali sector there is no possibility of independently control the production of the three products, all the data and equations in the study are referred to the mixed tonne, which consists of 1 tonne of chlorine, 1.1 tonnes of caustic soda (sodium hydroxide) and 0.03 tonnes of hydrogen [20]. EEESA methodology comprises the four following steps (Figure 1): definition of the goal and scope, life cycle inventory (LCI) of the main consumptions and prices, energetic, economic and environmental impact assessment (EEEIA) and interpretation.…”

“…An energetic, economic and environmental sustainability assessment will be conducted to study and compare the current available technologies to the emerging ODC technique. Several studies discussing the environmental sustainability of the chlor-alki sector were compiled in a previous work [20]. This bibliographic review of the state of the art showed the existing gap regarding the nexus energy-environment-economy of this energy demanding industry highlighting the novelty and interest of this paper.…”

“…Hence, all the data in the study refer to this mixed tonne, consisting of 1 tonne of chlorine, 1.1 tonnes of caustic soda (sodium hydroxide) and 0.03 tonnes of hydrogen. This combination, also called electrochemical unit (ECU), was selected as functional unit [20].…”

“…A more detailed description of the data sources as well as other methodological aspects can be found in a previous work [20]. The specific consumptions of the scenarios under study are displayed …”

Connecting wastes to resources for clean technologies in the chlor-alkali industry: a life cycle approach

“…Since electrolytic technologies can reduce energy consumption, the impacts of other stages, such as raw material extraction and production, become more significant (Garcia-Herrero et al, 2017). To assess the opportunities for integrating this novel technique into the chlor-alkali industry, the processing requirements of the cell itself must be considered in addition to the electricity requirements.…”