BACKGROUND

[0001] This invention relates generally to water treatment. More particularly, the invention relates to methods for treating aqueous solutions.

[0002] Both unused natural water and various wastewater, such as municipal wastewater and industrial wastewater, contain suspending or dissolved impurities. Therefore, multiple water treatment technologies are developed to remove the impurities before the water is used or discharged.

[0003] For example, US patent No. 6,365,051 discloses a method of treating an aqueous stream having inorganic material dissolved therein, comprising the steps of: (a) adding organic solvent to the aqueous stream in an amount effective to form an inorganic precipitate comprising at least a portion of the inorganic material; (b) removing at least most of the organic solvent from the aqueous stream by vacuum membrane distillation; and (c) after step (b), removing at least most of the inorganic precipitate from the aqueous stream.

[0004] The method described above may somewhat be unsatisfactory since it uses vacuum membrane distillation before the removal of inorganic precipitate, and the inorganic precipitate may block the pores of the membrane or scale on the membrane. In addition, the aqueous stream may contain organic impurities, the removal of which is not mentioned in the above method.

[0005] The other existing water treatment technologies cannot meet all the current practical needs, either.

[0006] Therefore, there is a need for new or improved methods for treatment of aqueous solutions. BRIEF DESCRIPTION

[0007] A method for treating an aqueous solution is provided in accordance with one embodiment of the invention. The method comprises combining an effective amount of miscible organic solvent with the aqueous solution at a first pressure to produce solids and a first liquid phase; separating the solids from the first liquid phase; and applying a second pressure lower than the first pressure to separate the first liquid phase into a gaseous organic phase and a second liquid phase.

DETAILED DESCRIPTION OF THE INVENTION

[0008] Approximating language, as used herein throughout the specification, may be applied to modify any quantitative representation that is not to be limited to the specific quantity specified and could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.

[0009] Any numerical value ranges recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and corresponding higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, rate, time and the like is, for example, from 1 to 90, preferred from 20 to 80, more preferred from 30 to70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0010] The aqueous solution referred to herein may be unused natural water or various wastewaters, such as municipal wastewater and industrial wastewater. In some embodiments, the aqueous solution is the wastewater generated from the crude oil extraction process, such as steam assisted gravity drainage (SAGD) process. Before combining with the organic solvent, the aqueous solution may be pretreated, if needed, to, e.g., remove solid impurities suspending in the aqueous solution through filtration, precipitation, etc.

[0011] The aqueous solution may comprise inorganic salt, organic substance or any combination thereof. In some embodiments, the aqueous solution is a saline solution with total dissolved solid higher than 6% or 10%. In some embodiments, the aqueous solution comprises at least one of ammonium, metal (like sodium, calcium, magnesium, potassium) ions, acid radical ions (such as sulfate ions, chloride ions, carbonate ions, silicic acid radical ions, nitrate ions, and phosphate ions) and organic substances.

[0012] The "miscible organic solvent" as used herein refers to any organic substance that can be partially or completely miscible with water on one or multiple conditions, and can be at least partially turned into a gaseous phase through one or multiple steps to separate from water.

[0013] The miscible organic solvent may be different according to different application requirements. In some embodiments, the miscible organic solvent is gaseous at the ambient temperature (about 25 °C) and the atmospheric pressure (about 1 bar), and is liquefied when the pressure is increased appropriately (e.g., to be about 20 bar). In some embodiments, the miscible organic solvent is dimethyl ether, aether, methyl ethyl ether, methylamine, dimethylamine or any combination thereof.

[0014] The first pressure as used herein refers to the pressure that the miscible organic solvent is at least partially liquefied and at least partially miscible with water, which relates to temperature. For example, the lower the temperature is, the lower the pressure needed to completely liquefy the organic solvent is, and correspondingly, the lower the first pressure applied. In some embodiments, the first pressure is in a range of from about 1 bar to about 20 bar, and the combining of miscible organic solvent and the aqueous solution is at a temperature lower than about 80 °C. [0015] The miscible organic solvent may be combined with the aqueous solution directly in the form of liquid at the first pressure after liquefaction, or it may be introduced in the form of gas to liquefy and combine with the aqueous solution at the first pressure.

[0016] When the effective amount of miscible organic solvent is combined with the aqueous solution at the first pressure, they are at least partially miscible with each other, producing solids and a first liquid phase. The solids are precipitates or crystals of the solute in the aqueous solution, such as sodium chloride, calcium chloride, potassium chloride, calcium carbonate and etc. The first liquid phase is the mixture of water and the miscible organic solvent, and may also contain remnant of solute of the aqueous solution. The first liquid phase may be one unified liquid phase in which the miscible organic solvent is completely miscible with water, or two or more liquid phases in a layered arrangement while the miscible organic solvent is partially miscible with water.

[0017] The separation of the solids from the first liquid phase may be achieved through any facilities or methods for seperation of solids and liquids, such as hydrocyclone, centrifuge, filter pressing, filtration or any combination thereof.

[0018] The second pressure is lower than the first pressure, and may be of any pressure that is between the pressures needed for the miscible organic solvent to begin and end the gasification. The second pressure may be applied for several times, with the same or different value for each time.

[0019] When the second pressure lower than the first pressure is applied, such as the second pressure is about 80% of the first pressure, or atmosphere pressure or negative pressure, the miscible organic solvent is at least partially gasified, and the first liquid phase is separated into a gaseous organic phase and a second liquid phase. The gaseous organic phase may be released directly, be recycled to treat the aqueous solution, or be applied for other uses. The second liquid phase may contain water, residue miscible organic solvent and remnant solute. The second liquid phase is used or released directly if it meets the reqirement. Otherwise, it may be further treated using various water treatment technologies. For example, if there is miscible organic solvent completely or partially miscible with water in the second liquid phase, and the second liquid phase may be a unified liquid phase in which the miscible organic solvent is completely miscible with water, or two or more liquid phases in a layered arrangement while the miscible organic solvent is partially miscible with water. The liquid miscible organic solvent and water may be separated by any technology for liquid-liquid seperation, or by reducing the pressure through one or more steps to enhance the gasification of miscible organic solvent, until all the miscible organic solvent is gasified and separated from water. If there is a need for further treatment of the remnant solute in the second liquid phase, the method of the present invention can be applied repeatly, or other methods can be applied, such as extracting the gas dissolved in water (such as the gaseous miscible organic solvent dissolved in water) through applying negative pressure.

[0020] The separation of solids from the first liquid phase and the separation of miscible organic solvent from the first liquid phase may be carried out simultaneously, or one by one. In some embodiments, the solids are separated from the first liquid phase at the first pressure. The second pressure is then applied to at least partially gasify the miscible organic solvent and separate the first liquid phase into a gaseous organic phase and a second liquid phase. In some embodiments, the gaseous organic phase and the solids are separated at the same time at the second pressure to produce the second liquid phase. For example, when filtrating, at the atmospheric pressure and the ambient temperature, the solids produced in the process of combining dimethyl ether and the aqueous solution under the condition of the liquefaction of dimethyl ether, the dimethyl ether turns to be gaseous and solids, gaseous dimethyl ether and the second liquid phase are produced at the same time.

[0021] At the first pressure, the aqueous solution and the miscible organic solvent are at least partially miscible with each other, and the solute of the aqueous solution with low solubility in the miscible organic solvent may mostly precipitate or crystalize to be solids. When applying the second pressure lower than the first pressure, the miscible organic solvent may be at least partially gaseous to be separated from the aqueous solution. The aqueous solution and miscible organic solvent are combined and separated under different conditions, and the miscible organic solvent and the aqueous solution may be at least partially separated by liquid-gas separation. It is easy to operate with low requirement for energy. For example, the dimethyl ether is gaseous at the ambient temperature and atmospheric pressure, and is easy to be separated from water.

EXAMPLES

[0022] The following examples are included to provide additional guidance to those of ordinary skill in the art in practicing the claimed invention. These examples do not limit the invention as defined in the appended claims.

Example 1

[0023] An aqueous solution of sodium chloride (5 ml, 25 wt%) was added through one of two inlets of a capped glass bottle into the bottle.

[0024] A vessel comprising gaseous dimethyl ether of a pressure of about 4 bar was connected to the bottle through the other of the two inlets to feed the gaseous dimethyl ether into the bottle. The bottle was put into a chiller of about -20 °C for about 5 minutes.

[0025] Another capped glass bottle with 5 ml of 25 wt% sodium chloride solution therein but not fed with the gaseous dimethyl ether was also put into the chiller of about -20 °C for about 5 minutes.

[0026] Solids and a first liquid phase were observed in the bottle fed with dimethyl ether after the bottle was taken out of the chiller, indicating that sodium chloride was precipitated out. The volume of the first liquid phase was about 15 ml, greater than the aqueous solution, indicating that dimethyl ether was liquefied. As to the bottle not fed with gaseous dimethyl ether, no change was observed after being taken out of the chiller.

Example 2 [0027] An aqueous solution (5 ml, analysis data of samples thereof is shown in table 1 below) was added through one of two inlets of a capped glass bottle into the bottle.

[0028] A vessel was connected to the bottle to feed gaseous dimethyl ether of a pressure of about 4 bar through the other of the two inlets into the bottle. The bottle was put into a chiller of about -20 °C for about 5 minutes.

[0029] After the bottle was taken out of the chiller, solids and a first liquid phase were observed in the bottle. The first liquid phase of about 10 ml was greater in volume thereof than the aqueous solution. The first liquid phase and the solids were separated by filtration at atmospheric pressure and ambient temperature, during which at least a portion of dimethyl ether turned to be gaseous and were separated from the first liquid phase to yield a gaseous organic phase, a second liquid phase of 5 ml and the solids of about 0.29 g. Samples of the second liquid phase and the solids were analyzed and the results are shown in table 1 below.

Table 1

[0030] The H in table 1 was tested in a sample solution diluted in a 1 :50 ratio. It can be seen from table 1 that most analytes in the second liquid phase have concentrations lower than those in the aqueous solution. The concentration of acid insoluble matter in the second liquid phase was higher than those in the aqueous solution possibly because glass was used as reaction and storage vessels and silica in the glass dissolved by the basic solutions.

[0031] It can also be seen from table 1 that in the solids, sodium, potassium, chloride, and calcium carbonate were detected and the concentration of sodium chloride was very high. This experiment indicates that the method could be used to reduce/eliminate salts and oil from highly salty (Total Dissolved Solids) and oily (Total Organic Carbon) aqueous solutions.

[0032] While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be through the spirit and scope of the disclosure as defined by the subsequent claims.