Technology

Dow is using its own, proprietary Bipolar Asbestos Diaphragm cell design, which is optimized for low current densities of 0.55–0.7 kA/m² and which uses large active areas (~100 m² for a single bipolar element).

The electrolyzers are operated at ~80°C, which is lower than the more typical operating temperature of 95°C for other cell types.

Advantages of this design include simplicity, ruggedness, low electricity consumption and long lifetimes of the PMA diaphragms.

However, investment costs are high due to the low chlorine production rate per surface area.

In 2011, Dow reported that, despite a long history of research and development activities including several large production runs, no suitable alternative diaphragms had been found.

Asbestos-free diaphragms available on the market were developed for the more usual higher current densities and are, according to Dow, not suitable for their bipolar cells. One of the limiting factors is the large diaphragm area which sets tighter requirements on diaphragm homogeneity, both for a single diaphragm and within a series.

Source: Thomas Brinkmann et al., 2014: Best available techniques (BAT) reference document for the production of chlor-alkali. Industrial Emissions Directive 2010/75/EU (integrated pollution prevention and control), JRC Science and Policy Reports, European Commission.