The characteristic in the process of sodium chloride electrolysis is the separation of the cathode products hydrogen and caustic soda from the anode product chlorine. They would otherwise form sodium hypochlorite or an explosive mixture of hydrogen and chlorine. The three processes described in this text differ in how the separation is achieved.  In the mercury cell electrolysis the cathode is a stream of mercury at the bottom of the cell. Sodium is reduced on the mercury and they immediately form an amalgam. The amalgam stream is fed into a converter where it is mixed with water to form caustic soda and hydrogen and to regenerate the mercury cathode. There are multiple anodes made of graphite where chloride ions are reformed into chlorine gas.  The diaphragm cell electrolysis uses an asbestos diaphragm on an iron grid to separate the anode and cathode reaction chambers. The sodium chloride solution is led through the anode chamber through the diaphragm into the cathode chamber. This process uses less energy than the mercury cell process but the products (caustic soda and chlorine) need extensive concentration and cleansing as they contain sodium chloride and oxygen. Thus, overall energy consumption is slightly higher than using the mercury cell process.  The third process is the membrane cell electrolysis. The membrane separating the reaction chambers consists of modified Teflon that is penetratable for sodium ions but not for water molecules. The main advantages of this process are its energy efficiency, the purity of the product caustic soda (it is virtually free of chloride) and the fact that it does not involve dangerous substances like asbestos or mercury. However, it needs relatively pure salt as input.      
The background system is addressed as follows:   
Electricity, Thermal energy: The electricity (and thermal energy as by-product) used is modelled according to the individual country-specific situation. The country-specific modelling is achieved on multiple levels. Firstly the individual power plants in service are modelled according to the current national grid. This includes net losses and imported electricity. Second, the national emission and efficiency standards of the power plants are modelled. Third, the country-specific fuel supply (share of resources used, by import and / or domestic supply) including the country-specific properties (e.g. element and energy contents) are accounted for. Fourth, the import, transport, mining and exploration processes for the energy carrier supply chain are modelled according to the specific situation of each power-producing country. The different mining and exploration techniques (emissions and efficiencies) in the different exploration countries are accounted for according to current engineering knowledge and information.    
Steam: The steam supply is modelled according to the individual country-specific situation with regard to the technology efficiencies and energy carriers used. Efficiencies range from 84% to 94% in relation to the representative energy carrier (gas, oil, coal). Coal, crude oil and natural gas used for the generation of steam are modelled according to the specific import situation (see electricity).   
Transports: All relevant and known transport processes used are included. Overseas transport including rail and truck transport to and from major ports for imported bulk resources are included. Furthermore all relevant and known pipeline and / or tanker transport of gases and oil imports are included.   
Energy carriers: Coal, crude oil, natural gas and uranium are modelled according to the specific import situation (see electricity).   
Refinery products: Diesel, gasoline, technical gases, fuel oils, basic oils and residues such as bitumen are modelled via a country-specific, refinery parameterized model. The refinery model represents the current national standard in refinery techniques (e.g. emission level, internal energy consumption,...) as well as the individual country-specific product output spectrum, which can be quite different from country to country. Hence the refinery products used show the individual country-specific use of resources. The supply of crude oil is modelled, again, according to the country-specific crude oil situation with the respective properties of the resources.