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In the present work, membrane electrolysis of nearly saturated borax solution prepared from borax pentahydrate (Na 2 B 4 O 7 .5H 2 O) was studied. Mono layer cation-exchange membrane (Nafion 551) was used as a separator in a two-compartment electrolysis cell for the production of sodium hydroxide and boric acid. The anolyte concentration was adjusted in order to obtain a Na 2 O/B 2 O 3 mol ratio of 0.1 by dissolving boric acid and borax pentahydrate together. Experiments were performed in continuous operation mode by feeding nearly saturated borax solution. The effects of different catholyte concentrations (10, 20, and 30% NaOH) on the current efficiency and the specific energy consumption were calculated and the quality of boric acid products was determined.Membrane electrolysis is one of the processes used in the chloralkali industry. The industry is one of the largest industries producing annually more than 48 million tons of sodium hydroxide (NaOH) and more than 42 million tons of chlorine (Cl 2 ). 1 The raw material is sodium chloride (NaCl) and the reaction proceeds according to:Chlorine gas, caustic soda, and hydrogen gas are produced simultaneously in the chlor-alkali process. Approximately 0.9 tons of chlorine gas is produced together with a ton of sodium hydroxide. Generally, sodium hydroxide production cannot be increased to meet the demand, because a market cannot be found for all the chlorine gas produced. Therefore, it is thought that sodium hydroxide could be produced from other sodium salts, i.e. sodium borates. 2 On the other hand, current boric acid production processes have some disadvantages such as high consumption of sulphuric acid and accumulation of a large amount of gypsum wastes. 3 In conventional boric acid production process, colemanite mineral (Ca 2 B 6 O 11 .5H 2 O) is reacted with sulfuric acid solution at 88-92 • C (Eq. 2).[2] Precipitated gypsum is removed by filtration and boric acid is crystallized by adiabatic evaporation of the filtrate. 4 Approximately, 400.000 tons of gypsum waste (on dry basis) is generated in Turkey every year by boric acid production. 5 To overcome the environmental problems existing in the conventional production methods of boric acid and sodium hydroxide and to meet the demand of sodium hydroxide in Turkey, membrane electrolysis process was applied to sodium borate solution. In the proposed process, boric acid and oxygen are produced in the anodic compartment, sodium hydroxide and hydrogen are produced in cathodic compartment. The anode compartment provides Na + ions for the reaction and Na + ions penetrate through the membrane from the anode to the cathode compartment. The reactions are given as follows: 2,8 Dissolution and Hydrolysis:Anodic Reaction:Cathodic Reaction:] Total Reaction: Overall : Na 2 B 4 O 7 · 5H 2 O + 3H 2 O → 4H 3 BO 3 + 2NaOH + 1/2O 2(g) + H 2(g) [6] z E-mail: iffet.elbeyli@tubitak.gov.trAccording to the stoichiometry, 3.5 tons of boric acid is produced together with 1 ton of sodium hydroxide. 2 The ion exchange membrane is one of t...

BACKGROUND Boric acid (H3BO3) was electrochemically produced from borax pentahydrate (Na2B4O7.5H2O) using membrane electrolysis, and a flow diagram of the production process was developed. The effect of different catholyte concentrations (10, 20 and 30% aqueous NaOH) and current densities (1.2, 1.8 and 2.9 kA m−2) on current efficiency was studied. The electrical power consumption per ton of boric acid produced was calculated and the qualities of boric acid products were determined. RESULTS The current efficiency ranged between 94% and 74% depending on operating conditions. Optimum process conditions for electrochemical boric acid production were determined to be 1.8 kA m−2 current density and 20% aqueous NaOH catholyte concentration. In these conditions, the specific energy consumption for 1 ton of boric acid produced was calculated at 2000 kWh (i.e. specific energy consumption 2000 kWh ton−1 at 7.5 V and 1.8 kA m−2). CONCLUSIONS The production of boric acid by an electrochemical method is more attractive than the current commercial process and other production methods described in the literature. The process is environment friendly since it does not generate solid waste, and oxygen is produced instead of chlorine as in the well‐known chlor‐alkali process. © 2014 Society of Chemical Industry