Utilization of Desalination Brine for Sodium Hydroxide Production: Technologies, Engineering Principles, Recovery Limits, and Future Directions

Abstract

As global desalination capacity continues its rapid growth, the impetus for reducing the adverse environmental impacts of brine discharge grows concurrently. Although modern brine outfall designs have significantly limited such impacts, they are costly. Recovering valuable components and chemical derivatives from brine has potential to resolve both environmental and economic concerns. In this article, methods for producing sodium hydroxide ("caustic") from seawater reverse osmosis (SWRO) brine for internal re-use, which typically involve brine purification, brine concentration, and sodium chloride electrolysis, are reviewed. Because process energy consumption drives process cost and caustic purity determines product usability in drinking water systems, reviewed technologies are benchmarked against thermodynamic minimum energy consumption and maximum (stoichiometric) NaOH production rates. After individual reviews of brine purification, concentration, and electrolysis technologies, five existing facilities for caustic production from seawater and seawater concentrates are discussed. Bipolar membrane electrodialysis appears to have the best potential to meet the technoeconomic requirements of small-scale caustic production from SWRO brine. Finally, future research and demonstration needs, to bring the technology to commercial feasibility, are identified.

Integrated Valorization of Desalination Brine through NaOH Recovery: Opportunities and Challenges

“…Furthermore,N aOH is ac ommon ingredient in membrane cleaning solutions for foulants; [4] the organic fouling of membranes has been shown to decrease at higher pH values. [7] Ty pically,d irect current is passed through an aqueous sodium chloride (NaCl) solution, causing an electrochemical reaction that produces NaOH, hydrogen (H 2 ), and chlorine (Cl 2 ). [6] Three types of chlor-alkali processes currently exist, membrane,diaphragm, and mercury processes.…”

“…[7] In one case,alab-scale ED system was tested with SWRO brine and optimized in terms of flowrate, applied voltage,a nd operating mode;a saresult, the system [7] In one case,alab-scale ED system was tested with SWRO brine and optimized in terms of flowrate, applied voltage,a nd operating mode;a saresult, the system …”

“…[7] Furthermore,v arious chlorine-based byproducts can be used within the desalination plant. [7] Furthermore,v arious chlorine-based byproducts can be used within the desalination plant.…”

“…[69][70][71] Today,membrane desalination by renewable sources,including solar and wind power, is feasible at both small and large scale. [73] Because [7] 1.56-1.64 [7] 0.65 and 0.81 [7] 0.65 and 0.81 [7] Experimentally realized energy usage (kWh/kg NaOH) Electrical:2.10-2.15 [67,68] , Heat**: 0.038-0.047 [67,68] Electrical:1.94-2.51 [67,68] , Heat**: 0.128-0.196 [67,68] 1.8-3.6 [67] *n.a. [73] Because [7] 1.56-1.64 [7] 0.65 and 0.81 [7] 0.65 and 0.81 [7] Experimentally realized energy usage (kWh/kg NaOH) Electrical:2.10-2.15 [67,68] , Heat**: 0.038-0.047 [67,68] Electrical:1.94-2.51 [67,68] , Heat**: 0.128-0.196 [67,68] 1.8-3.6 [67] *n.a.…”

“…Recent thermodynamic limits analyses [7,9] and the above discussion focus on the energy requirements for caustic production, which are promising compared to the incumbent chlor-alkali process. Recent thermodynamic limits analyses [7,9] and the above discussion focus on the energy requirements for caustic production, which are promising compared to the incumbent chlor-alkali process.…”