US-12623925-B2 - Extractive desalination of sea water using a special class of polar organic solvents

US12623925B2US 12623925 B2US12623925 B2US 12623925B2US-12623925-B2

Abstract

A solvent extraction process for desalination of seawater. The process uses a special class of polar organic solvents to preferentially dissolve salt-free water from salty water, which exhibits a reverse solubility-temperature behavior (i.e., the solubility of water in the solvent is high at room temperature but significantly lower at higher temperatures). The desalination process includes adding these special class of solvents to sea or salty water at room temperature, separating the solvent-water phase (organic phase) from the remaining mass of salt-rich water (aqueous phase), heating the solvent-water phase to a higher temperature and recovering the relatively salt-free water that separates out. The process is simple, fast, ecologically safe and energy efficient.

Inventors

Deven Charles Chakrabarti

Assignees

Deven Charles Chakrabarti

Dates

Publication Date: 20260512
Application Date: 20220603

Claims (15)

1 . A method for extracting water from saltwater, the method comprising the steps of: (a) adding a polar organic solvent to the saltwater to form a mixture, where the polar organic solvent has the following properties: (i) dissolves water at or above 10% v/v at room temperature; (ii) has a water solubility that decreases with increasing temperature; (iii) is liquid at room temperature; (iv) has a boiling point above that of water at a standard pressure (760 mm Hg); and (v) derives its polarity from one or more groups selected from unsubstituted or substituted amide, sulfoxide, sulfone, hydroxyl, and ether groups; (b) heating the mixture to form a first organic phase and a first aqueous phase; and (c) separating the first organic phase from the mixture, wherein the organic solvent has the formula (I): where (a) R 1 is selected from acyclic or cyclic hydrocarbon having 1 to 12 carbon atoms, optionally substituted with one or more of chloro, hydroxy, methoxy, ethoxy, or —NO 2 ; and R 2 and R 3 are independently selected from hydrogen, acyclic or cyclic hydrocarbon having 1 to 12 carbon atoms, optionally substituted with one or more of chloro, hydroxy, methoxy, ethoxy, or —NO 2 ; or (b) R 1 and R 2 are joined to form a 5- or 6-member ring; and R 3 is selected from hydrogen, acyclic or cyclic hydrocarbon having 1 to 12 carbon atoms, optionally substituted with one or more of chloro, hydroxy, methoxy, ethoxy, or —NO 2 .
2 . The method of claim 1 , wherein step (a) is performed at ambient temperature.
3 . The method of claim 1 , wherein the mixture is heated in step (b) to no more than about 5° C. above a cloud point of the organic solvent as determined by mixing one part of the organic solvent in 99 parts of water.
4 . The method of claim 1 , wherein the mixture is heated in step (b) to about 3 to 5° C. above a cloud point of the organic solvent as determined by mixing one part of the organic solvent in 99 parts of water.
5 . The method of claim 1 , further comprising (d) heating the first organic phase from step (c) to form a second mixture having a second organic phase and a second aqueous phase and (e) separating the second aqueous phase from the second mixture.
6 . The method of claim 1 , wherein the saltwater is sea water.
7 . The method of claim 1 , wherein the mixture has a ratio of saltwater to organic solvent of about 1:0.01 to about 1:1.
8 . The method of claim 1 , wherein the mixture has a ratio of saltwater to solvent of about 1:0.1 to about 1:1.
9 . The method of claim 5 , further comprising the step of refining the separated second aqueous phase to remove residual organic solvent.
10 . The method of claim 9 , wherein the refining step includes one or more of (a) extracting the residual organic solvent with a hydrocarbon or (b) absorbing the residual solvent.
11 . The method of claim 1 , wherein the polar organic solvent has a boiling point above 150° C.
12 . The method of claim 1 , wherein the organic solvent includes at least one additional polar group selected from halogen, nitro, and ester.
13 . The method of claim 1 , wherein the organic solvent has the formula (I): where R 3 is independently selected from hydrogen, acyclic or cyclic hydrocarbon having 1 to 12 carbon atoms, optionally substituted with one or more of chloro, hydroxy, methoxy, ethoxy, or —NO 2 ; and R 1 and R 2 are joined to form a 5- or 6-member ring.
14 . The method of claim 1 , wherein the organic solvent is cyclohexyl pyrrolidone.
15 . The method of claim 1 , wherein the organic solvent is N-dodecyl pyrrolidone.

Description

This application claims the priority of U.S. Patent Application No. 63/235,224, filed Aug. 20, 2021, which is hereby incorporated by reference. FIELD OF THE INVENTION The present invention relates to the desalination of saltwater (such as sea water) using a solvent based extraction process. BACKGROUND OF THE INVENTION Fresh water is a staple of life in all regions of the world. We need fresh water for drinking, household purposes, agriculture, husbandry, and industrial use. It is a key determinant of our lifestyle and economic viability of a country. This precious resource is being quickly depleted with global warming and increased extraction of ground water to meet the current demand. According to many scientific studies it is believed that by the end of this century half of the world will suffer from such water scarcity that it will push the world to a breaking point. Though the shortages will hit almost all regions, the less affluent regions will suffer the most. In view of such dire predictions, finding sustainable and inexpensive sources of fresh water has become an urgent global priority. The problem, as we all know, is not that the world does not have enough water. In fact, 71% of the earth surface is water and most of it is the salty ocean. When saltwater lakes and brackish water are added to the ocean water, about 97.2% of all water on earth is salty. Of the remaining 2.8%, that constitutes fresh water, most of it (2.14%) is locked up in polar ice caps and another 0.61% is stored underground. This leaves a tiny 0.05% to be present in accessible streams, rivers, ponds, freshwater lakes, and aquifers for human consumption. The problem of availability of fresh water is further aggravated by the fact that this tiny fraction that is fresh water is not necessarily evenly distributed among different regions of the world. Unless an affordable solution to the freshwater problem can be found, many predict that future wars will not be fought over oil but rather on water. The solution to the problem thus lies on finding affordable desalination processes to seawater to fresh water. Here we use the term seawater to represent a broad range of saline water from high salinity, like those from the ocean containing 35,000 ppm to 40,000 ppm salt, to water of medium salinity, containing 10,000 to 35,000 ppm salt like the ones found in “brackish water” from salt lakes and other inland saline sources. The problem—desalination—has thus been easy to describe but difficult to solve. Simply speaking, desalination refers to processes for removing salt from seawater resulting in fresh water for use for human consumption, agriculture, and industrial purposes. Four different technologies—distillation, reverse osmosis, electrodialysis, and freezing—are currently available for this purpose. There are a total of 12,500 desalination plants in operation on a worldwide basis, the users being mostly affluent countries. The largest users of desalination technologies in the world today are the Arab countries (over 70%)—Saudi Arabia, United Arab Emirates, and Kuwait—as well as the United States, Spain and Japan. The technology most in use is reverse osmosis. Reverse osmosis is the most extensively used. Reverse osmosis is based upon the use of semipermeable membranes which allow water but not dissolved salts to pass. Water is passed at pressures up to 1500 psi across the membrane to generate adequate flow. The energy involved in pumping the water at this pressure, as well as the high capital costs of this technology, result in a high cost solution which only affluent countries can afford. Distillation involves heating seawater to its boiling point, converting the water into water vapor, and condensing it back to liquid water. The process is very energy intensive, not necessarily because water has to be heated to its boiling point, but because of the large amount of latent heat of evaporation that has to be supplied to convert it into vapor. Improvements involve implementing multiple-effect evaporators, where the heat released during condensation is partially recovered in heating a fresh batch of seawater. Other modifications involve vacuum distillation and multistage flash distillation. In spite of these modifications, distillation remains the costliest approach to desalination. The freeze-thaw process is generally practiced in arctic regions. In this process, seawater is sprayed under freezing conditions into pads, where the water in its salt-free condition accumulates as ice. When seasons change, and the weather becomes warm, the ice melts to provide fresh water. The process necessarily has regional limitations. Electrodialysis utilizes electrical potential to remove salts through pairs of charged membranes which trapping salt in alternating channels. Electrodialysis suffers from the same deficiencies of being energy and capital intensive as reverse osmosis and can only be attractive to regions where hydroelectric power is inexpensive a