KOH-Based Modified Solvay Process for Removing Na Ions from High Salinity Reject Brine at High Temperatures

Abstract

The traditional Solvay process and other modifications that are based on different types of alkaline material and waste promise to be effective in the reduction of reject brine salinity and the capture of CO2. These processes, however, require low temperatures (10–20 °C) to increase the solubility of CO2 and enhance the precipitation of metallic salts, while reject brine is usually discharged from desalination plants at relatively high temperatures (40–55 °C). A modified Solvay process based on potassium hydroxide (KOH) has emerged as a promising technique for simultaneously capturing carbon dioxide (CO2) and reducing ions from reject brine in a combined reaction. In this study, the ability of the KOH-based Solvay process to reduce brine salinity at relatively high temperatures was investigated. The impact of different operating conditions, including pressure, KOH concentration, temperature, and CO2 gas flowrate, on CO2 uptake and ion removal was investigated and optimized. The optimization was performed using the response surface methodology based on a central composite design. A CO2 uptake of 0.50 g CO2/g KOH and maximum removal rates of sodium (Na+), chloride (Cl−), calcium (Ca2+), and magnesium (Mg2+) of 45.6%, 29.8%, 100%, and 91.2%, respectively, were obtained at a gauge pressure, gas flowrate, and KOH concentration of 2 bar, 776 mL/min, and 30 g/L, respectively, and at high temperature of 50 °C. These results confirm the effectiveness of the process in salinity reduction at a relatively high temperature that is near the actual reject brine temperature without prior cooling. The structural and chemical characteristics of the produced solids were investigated, confirming the presence of valuable products such as sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3) and potassium chloride (KCl).

Total Resource Circulation of Desalination Brine: A Review

“…The reactions of using Ca(OH) 2 , KOH, and Al(OH) 3 to conduct the Modified Solvay Process are listed in Equations () to (). [ 63–66 ] M. H. El‐Naas et al. directly added CaO to the bubble column reactor, which converts to calcium hydroxide as soon as it contacts the brine.…”

“…The solids generated in the two processes were characterized using SEM, XRD, and FTIR analysis, and they were NaHCO 3 , KHCO 3 , K 2 CO 3 , and KCl. [ 66,67 ] $$$$\begin{equation}{\mathrm{2NaCl + 2C}}{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{ + Ca}}{\left( {{\mathrm{OH}}} \right)}_{\mathrm{2}} \rightleftharpoons {\mathrm{2NaHC}}{{\mathrm{O}}}_{\mathrm{3}}{\mathrm{ + CaC}}{{\mathrm{l}}}_{\mathrm{2}}\end{equation}$$$$ $$$$\begin{equation}{\mathrm{NaCl + C}}{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{ + KOH}} \rightleftharpoons {\mathrm{NaHCO}}_{\mathrm{3}}{\mathrm{ + KCl}}\end{equation}$$$$ $$$$\begin{equation}{\mathrm{6NaCl + C}}{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{ + A}}{{\mathrm{l}}}_{\mathrm{2}}{{\mathrm{O}}}_{\mathrm{3}}{\mathrm{ + 3}}{{\mathrm{H}}}_{\mathrm{2}}{{\mathrm{O}}} \rightleftharpoons {\mathrm{6NaHC}}{{\mathrm{O}}}_{\mathrm{3}}{\mathrm{ + 2AlC}}{{\mathrm{l}}}_{\mathrm{3}}\end{equation}$$$$…”

A New Method for Capturing CO2 from Effluent Gases Using a Rice-Based Product

“…As can be seen from Figure 7, as a result of this process, gas bubbles gradually became trapped inside the rice structure. The experiment was terminated once full CO 2 loading (zero CO 2 capture) was achieved [43][44][45][46], as this was considered to signify a complete reaction. The number of moles of CO 2 absorbed and trapped by the rice cake layers was calculated according to the following equation [45,46]:…”

Reducing the Environmental Impacts of Desalination Reject Brine Using Modified Solvay Process Based on Calcium Oxide

“…A 77.1% ammonia recovery in NH 4 OH form was also accomplished. Mourad et al [19] considered a modified Solvay process based on potassium hydroxide that could simultaneously capture carbon dioxide and reduce the reject brine ions. At relatively high temperatures, the Solvay method was tested for its capacity to reduce brine salinity.…”