Valorization of brines in the chlor-alkaly industry using membrane technology

Abstract

In this master thesis, the reuse Seawater Reverse Osmosis (SWD-RO) brine extracted from the El Prat Desalination plant was studied and valorised, in order to assess the possible usage in the chlor-alkali industry. The brine was chemically characterized using different analytical methods adapted to the high salinities of the samples. Experiments were carried out in order to study nanofiltration for brine purification and electrodialysis for brines concentration. Moreover, as free chlorine was obtained in the ED anode chamber due to the current passing the cell, the production of hypochlorite from this stream using membrane contactors was studied in order to reuse this by-product. Electrodialysis demonstrated to be a feasible technology for SWD-RO brine concentration, as it concentrated the brine and at the same time produced some useful by-products that were further valorised. Nanofiltration efficiently removed polyvalent ions from studied brine. Nevertheless, brine compositions obtained after both treatments were not enough to meet the membrane electrolysis requirements. A secondary treatment will be required to polish the brines to reach the ppb levels required. Hypochlorite produced using a liquid-gas membrane contactor for disinfection purposes of potable water was obtained. However, some modifications should be done to the system in order to improve the overall efficiency of the process. Finally, a mathematical model to predict the concentration performance and design future experiments was developed and validated with the results obtained in the pilot plant.