PERFORMANCE EVALUATION OF DIAPHRAGM ELECTROLYSIS CELL OF CONCENTRATED BRINE FOR ALKALI PRODUCTION

Abstract

Seawater desalination technology is important for solving water shortage problems. RO desalination is the most frequently used process for obtaining fresh water from salt water. RO systems driven by gas and steam turbines have a lower cost than other alternatives. However, disposal of concentrated brine currently is only achieved through discharge into oceans or use of evaporation ponds. Also, there are more two kinds of methods such as land application and deep well injection. Electrolysis is also one way of reusing the enriched brine. Alkali-activated products can be made by producing NaOH after electrolysis. There are three kinds of brine electrolysis methods including diaphragm, membrane, and mercury methods. This study was conducted using a 200 mL electrolysis diaphragm cell. Tedlar bags were used in order to gather gases such as Cl2, O2, and H2. The head was less than 8 cm when a diaphragm with a 10 μm pore size was used. The data in this study were collected to evaluate NaOH concentration, Cl– removal, and current efficiency (CE) by changing the concentrated degree and electrode material. When changing the concentrated brine to degrees of raw, triple, and quintuple, NaOH concentration was 1.6%, 2.3%, and 2.8% and Cl– removal was 75%, 39%, and 28%, respectively. These tendencies were caused by decreasing internal resistance. CE was inversely proportional to temperature, caused by ion quantity. Because iridium has a lower electrical resistivity than ruthenium, electrical resistivity has a decisive effect on electricity consumption. When highly concentrated brine was used in electrolysis, around 3% NaOH alkaline water was produced. Because of the thermal resistance of reactor in acrylic, the maximum temperature of operating reactor was until 90°C. Current density can be higher in the reactor if brine concentration is higher. The right options for catalyst material selection depend on the designated purpose of the catalyst material. To compare the performances (Cl-removal, NaOH concentration and etc.) with single reactor, two same reactors were connected with each other. The correlation coefficient for an exponential fit of the data was >0.95 at 63 and 75 mA/cm2. the CD was absolutely the main factors for producing high concentrations of NaOH. It performed a variety of experiments to analyze what relationships exist between concentration, chloride removal and CD. When the CD increased, the chloride removal rate also increased. However, the temperature of the reactor was also higher, and thus the CD increased as well. Variation of CD is therefore not a viable solution for producing high NaOH concentrations. Regulation of flow rate showed more efficient cell operation than regulation of CD.