Semi-mechanistic model for predicting current efficiency in industrial membrane chlor-alkali electrolysis

Current efficiency has been recognized as a key performance indicator in membrane chlor-alkali electrolysis because it directly determines product yield at a given electrical load. This study developed a semi-mechanistic model to estimate current efficiency in industrial membrane chlor-alkali cells by integrating OH⁻ back-migration, oxygen evolution, and secondary chlorine chemistry. The framework combined literature-based electrochemical and transport relationships with selected empirical corrections derived from industrial operation. The effects of current density, anolyte pH, catholyte NaOH mass fraction, and catholyte temperature were evaluated over operating ranges representative of an industrial plant. Industrial data from 177 cells were used to parameterize selected empirical relationships and assess model consistency with aggregated plant observations. Relative differences between model predictions and industrial observations were below 1% for current efficiency, whereas larger discrepancies were observed for chlorate concentration. The results showed that anolyte pH was the most influential operating variable because of its simultaneous effect on oxygen evolution and the formation of HClO and ClO 3 − . Higher current efficiencies were favored by lower anolyte pH and catholyte NaOH concentrations near 32 wt%, while current density became more influential at higher pH and catholyte temperature had only a minor effect within the investigated range. Appropriate adjustment of the operating variables increased current efficiency by up to approximately 3% points, corresponding to about 5.5 × 10 3 t year −1 of additional chlorine production for a representative 1000-cell plant. The proposed framework provided a physically interpretable basis for identifying dominant efficiency-loss mechanisms, screening industrial operating conditions, and supporting optimization of membrane chlor-alkali electrolysis.