US 11,814,309 B1Granted

Multistage desalination process with carbon dioxide capture

AssigneeUnited Arab Emirates University

InventorsAmeera Mohammad, Ali H. Al-Marzouqi, Aya A. Mourad, Muftah El-Naas

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Abstract

A system and method of desalinating a brine stream are provided. The multistage desalination process with carbon dioxide capture recovers valuable products where the reject brine is passed through seven stages. In each stage, a specific metal ion is recovered. In stage 1, a ˜100% recovery of magnesium ions as magnesium hydroxide solid was obtained by chemical reaction with ammonia solution. In stage 2, Na+ reduction, as sodium bicarbonate, and CO2 uptake was achieved. In stage 3, electrocoagulation (EC) was used to recover sulfate ions as pure calcium sulfate solid and to regenerate NH3 as ammonium hydroxide. In stage 4, CaO was added to the treated brine. In stage 5, more recovery of NaHCO3 was attained by adding ammonium bicarbonate, while in stage 6, the treated brine mixture was passed through another modified Solvay process. In stage 7, EC was again used to recover CaCl2 solution and NH3 compounds.

A method of desalinating brine with carbon dioxide capture, comprising the steps of:

a. mixing a brine with an ammonia solution, whereby NH3 in the ammonia reacts with magnesium carbonate (MgCO3) in the brine to produce NH4HCO3 and magnesium hydroxide Mg(OH)2 solids, with the magnesium hydroxide solids being precipitated from the brine and recovered via filtration, resulting in a first treated brine;
b. reacting the first treated brine with a first CO2-air gas mixture to produce first sodium bicarbonate (NaHCO3) solids and ammonium chloride (NH4Cl) and capture CO2, with the first sodium bicarbonate solids being precipitated from the first treated brine and recovered via filtration, resulting in a second treated brine;
c. reacting the second treated brine with first calcium oxide (CaO) to recover sulphate content from the second treated brine in the form of gypsum (CaSO4) solids and to recover most remaining ammonia added in step a. as ammonium hydroxide, with the gypsum solids being precipitated from the second treated brine and recovered via filtration, resulting in a third treated brine;
d. reacting the third treated brine with second calcium oxide (CaO) and a second CO2-air gas mixture to produce second sodium bicarbonate (NaHCO3) solids and capture further CO2, with the second sodium bicarbonate solids being precipitated from the third treated brine and recovered via filtration, resulting in a fourth treated brine;
e. reacting the fourth treated brine with ammonium bicarbonate (NH4HCO3) solids to decrease solubility of and thereby produce third sodium bicarbonate (NaHCO3) solids, with the third sodium bicarbonate solids being precipitated from the fourth treated brine and recovered via filtration, resulting in a fifth treated brine;
f. reacting the fifth treated brine with third calcium oxide (CaO) and a third CO2-air gas mixture to produce fourth sodium bicarbonate (NaHCO3) solids and capture additional further CO2, with the fourth sodium bicarbonate solids being precipitated from the fifth treated brine and recovered via filtration, resulting in a sixth treated brine;
and
g. recovering ammonium added in step e., calcium ions added in step f., and chloride ions from the sixth treated brine, with the ammonium mostly being recovered as NH3 gas, the calcium and chloride ions being recovered as precipitated calcium hydroxide (Ca(OH)2) solids, Cl2 gas, and CaCl2 solution, resulting in a desalinated brine.

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Abstract

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