Preparation of highly pure tetrapropyl ammonium hydroxide using continuous bipolar membrane electrodialysis

Conventional methods of tetrapropyl ammonium hydroxide (TPAOH) production via electrolysis, reaction of tetrapropyl ammonium halide with silver oxide, and ion-exchange suffer from high production costs, low quality, and environmental pollution. In this work, continuous bipolar membrane electrodialysis (BMED) is employed for the preparation of TPAOH from its halide as a sustainable alternative process. Novel ion-exchange membranes were developed for lab and pilot scale experiments, which indicate an acceptable current efficiency and energy consumption. The results indicate that a cell configuration with four compartments yielded the best results when the salt concentration was 0.3 mol L−1 and the current density was 200 A m−2. The highest conversion in electrodialysis was 91.6%, with a high purity of trace alkali metal ions and low Br− content (176 ppm) at a TPAOH concentration of 25%. The energy consumption is 1.897 kW h kg−1. Continuous pilot experiments demonstrate the feasibility of manufacturing TPAOH by direct splitting its halide for industrial application.

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► BMED in a novel configuration was adopted for TPAOH production.
► A high purity TPAOH solution of concentration 25% was obtained.
► Continuous pilot experiments demonstrate the feasibility of manufacturing TPAOH.