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membranes Article A New Method Based on a Zero Gap Electrolysis Cell for Producing Bleach: Concept Validation Rihab Belhadj Ammar 1,2, Takoua Ounissi 2, Lassaad Baklouti 3 , Christian Larchet 1 , Lasâad Dammak 1,*, Arthur Mofakhami 4 and Emna Selmane Belhadj Hmida 2,5 1 2 3 4 5 * Correspondence: dammak@u-pec.fr; Tel.: +33-145-171-786 Abstract: Commercial bleach (3.6 wt% active chlorine) is prepared by diluting highly concentrated industrial solutions of sodium hypochlorite (about 13 wt% active chlorine) obtained mainly by bubbling chlorine gas into dilute caustic soda. The chlorine and soda used are often obtained by electrolyzing a sodium chloride solution in two-compartment cells (chlorine-soda processes). On a smaller scale, small units used for swimming pool water treatment, for example, allow the production of low-concentration bleach (0.3 to 1 wt% active chlorine) by use of a direct electrolysis of sodium chloride brine. The oxidation and degradation reaction of hypochlorite ion (ClO−) at the anode is the major limiting element of this two-compartment process. In this study, we have developed a new process to obtain higher levels of active chlorine up to 3.6%, or 12◦ chlorometric degree. For this purpose, we tested a device consisting of a zero-gap electrolysis cell, with three compartments separated by a pair of membranes that can be porous or ion-exchange. The idea is to generate in the anode compartment hypochlorous acid (HClO) at high levels by continuously adjusting its pH to a value between 4.5 and 5.5. In the cathodic compartment, caustic soda is obtained, while the central compartment is supplied with brine. The hypochlorous acid solution is then neutralized with a concentrated solution of NaOH to obtain bleach. In this work, we studied several membrane couples that allowed us to optimize the operating conditions and to obtain bleach with contents close to 1.8 wt% of active chlorine. The results obtained according to the properties of the membranes, their durability, and the imposed electrochemical conditions were discussed. Keywords: bleach production; composite membrane; ion-exchange membrane; membrane electrolysis; zero-gap electrolysis cell 1. Introduction Sodium chloride electrolysis is a practical means of producing hypochlorite for the purpose of sterilization or disinfection procedures. It only requires salt and energy in- put and works under particular but well-controlled safety conditions in domestic or industrial installations. This method is based on the generation of chlorine by anodic reduction of chloride. There are many variants of the process that allow very different forms and concentrations to be generated, ranging from diluted solutions that can be directly injected into drinking water or disinfection circuits to industrial-scale production of concentrated chlorine and soda. The process can work with salt solution but it can also use brackish water or even CNRS, ICMPE, Université Paris-Est Créteil, UMR 7182, 2 rue Henri Dunant, 94320 Thiais, France; belhadj.rihab25@gmail.com (R.B.A.); larchet@u-pec.fr (C.L.) Laboratoire de Chimie Analytique et D’électrochimie, Département de Chimie, Faculté des Sciences de Tunis, Campus Universitaire, Tunis 2092, Tunisia; ounissi.takoua@gmail.com (T.O.); emnaselmane@gmail.com (E.S.B.H.) Department of Chemistry, College of Sciences and Arts at Ar Rass, Qassim University, Ar Rass 51921, Saudi Arabia; blkoty@qu.edu.sa Gen-Hy, Rue de la Soie, 94310 Orly, France; amofakhami@gen-hy.com Institut Préparatoire aux Études D’ingénieurs El Manar (IPEIEM), B.P 244, Tunis 2092, Tunisia Citation: Belhadj Ammar, R.; Ounissi, T.; Baklouti, L.; Larchet, C.; Dammak, L.; Mofakhami, A.; Selmane Belhadj Hmida, E. A New Method Based on a Zero Gap Electrolysis Cell for Producing Bleach: Concept Validation. Membranes 2022, 12, 602. https://doi.org/10.3390/ membranes12060602 Academic Editor: Diogo M. F. Santos Received: 28 April 2022 Accepted: 28 May 2022 Published: 10 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Membranes 2022, 12, 602. https://doi.org/10.3390/membranes12060602 https://www.mdpi.com/journal/membranesPDF Image | Zero Gap Electrolysis Cell for Producing Bleach
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