WO2007094524A1

WO2007094524A1 - Method for purifying oil-contaminated water, organoclay used in the method, and method for preparing the organoclay

Info

Publication number: WO2007094524A1
Application number: PCT/KR2006/000532
Authority: WO
Inventors: Hyoung Soo Kim; Yoon Young Kim; Jeong Jin Kim
Original assignee: Korea Water Resources Corporation; Digital Water Co., Ltd.
Priority date: 2006-02-16
Filing date: 2006-02-16
Publication date: 2007-08-23

Abstract

Provided are a method for purifying oil-contaminated water, and an organoclay for use in the same method and preparation thereof. More specifically, the present invention relates to a technology for remediation of oil-contaminated groundwater by adsorption of organic con¬ taminants in water onto an organoclay. The present invention provides an organoclay having a surfactant adsorbed between layers of clay mineral with high swellability such that organic compounds can be effectively adsorbed and a method for preparing the same, and a technology for purification of oil-contamination using such an organoclay. The organoclay in accordance with the present invention can effectively adsorb and remove organic contaminants from oil- contamination and therefore can be usefully used for remediation of oil-contaminated groundwater.

Description

METHOD FOR PURIFYING OIL-CONTAMINATED WATER,

ORGANOCLAY USED IN THE METHOD, AND METHOD FOR

PREPARING THE ORGANOCLAY

Technical Field

[1] The present invention relates to a method for purifying oil-contaminated water, and an organoclay for use in the same method and preparation thereof. More specifically, the present invention relates to a technique for remediation of oil-contaminated groundwater by adsorption of organic contaminants in water on an organoclay.

[2]

Background Art

[3] In recent years, as oil-induced groundwater and soil pollution has raised social concern, evaluation of groundwater environment in oil-contaminated regions has become daily routine of environmental hydrogeologists or engineers. Oil- contamination usually involves leakage of gasoline, kerosene, light gas oil or the like. Groundwater and soil pollution may be broadly subdivided into two types depending upon characteristics and features thereof as follows: the first type appears as free products floating on the water surface, and the second type appears as a state in which oil is dissolved in water. Gasoline usually has high contents of BTEX (Benzene, Toluene, Ethylbenzene and Xylene) ingredients that receive a great deal of attention and have relatively high solubility in water, thereby appearing as the dissolved state,

[4] Gasoline can be relatively easily characterized by analysis of a dissolved concentration of BTEX in groundwater. Whereas, since kerosene and light gas oil contain low amounts of BTEX ingredients, it can often seem that such ingredients are not present in a high concentration of dissolved state even when significant quantities of oil in the form of free products are afloat on the groundwater or the groundwater gives off the smell of oil. Therefore, in confirmation or evaluation of soil and groundwater contamination, selection and application of inappropriate methods may often result in false results and interpretation.

[5] All scientists, who have studied a field of soil and groundwater, recognize that understanding of water flow taking into consideration a flow rate of groundwater is primarily very important. Known conventional arts directed to remediation of oil- contaminated groundwater are as follows:

[6]

[7] 1. Ozone Oxidation Process

[8] Ozone Oxidation Process is a non-drilling type of in-situ remediation technology in volving direct injection of ozone having strong oxidation power into the zone of soil which is unsaturated with contaminated groundwater, which results in fast and effective degradation of non- volatile oils and non-degradable or recalcitrant organic compounds. However, ozone is a strong oxidant having the second highest oxidation- reduction potential second only to fluorine, but exhibits low reactivity with organic compounds and sometimes no reactivity for a certain organic compound.

[9] 2. Multi-phase Extraction (MPE)

[10] Multi-phase Extraction (MPE) is a simultaneous extraction treatment technology of gas type and/or liquid type oils with groundwater by vacuuming in the soil.

[11] 3. Bioventing

[12] Bioventing is a method of degrading contaminating materials by promoting activity of indigenous microorganisms living in soil via injection of oxygen or nutrients.

[13] 4. Soil Vapor Extraction

[14] Soil Vapor Extraction is a method of removing contaminating materials by installing a tube well in soil (an unsaturated layer) and inducing vaporization of volatile and/or sub-volatile contaminants in contaminated soil via vacuum pumping.

[15]

[16] Recently, according to overseas trends, a treatment method utilizing an OH radical as an oxidant is frequently used as an advanced oxidation process (AOP). The OH radical is an oxidant having a reaction constant for the same organic compound several tens to several tens of thousands higher than ozone and therefore can rapidly react with almost all organic compounds. Although the OH radical may be formed when ozone is decomposed by hydroxide ions (OH^") in an aqueous solution having a pH value exceeding a certain limit, methods for conversion of ozone into the OH radical via addition of hydrogen peroxide (H O ) to ozone or reaction of ozone with UV are widely used in terms of generation efficiency. At this time, oxidation power of the OH radical in water is determined by organic compounds, bicarbonate ions (HCO ^"), carbonate ions (CO 3 ), H 2 O 2 , and other compounds dissolved in water.

[17]

[ 18] Other technologies used in treatment of oil-contamination may include the following methods:

[19] 1. Oil/Water Separation

[20] Oil/Water Separation is a method of removing light non-aqueous phase liquids

(LNAPLs) that are lighter than water. This technique removes only LNAPLs from contaminated groundwater. Here, in order to prevent dispersion and emulsification of entrained oils, use of centrifugal water pumps that have strong shearing forces should be avoided, and in order to prevent chemical emulsification of oils, wastes containing surfactants should not be mixed with other oil-laden contamination. Oil/Water Separation is fundamentally based on gravity separation techniques. Separated oils may be subjected to air flotation, centrifugation and the like, and subsequently may be subjected to filtration, biological treatments, carbon adsorption and the like as the secondary treatment, if necessary.

[21] 2. Air Stripping

[22] A countercurrent packed column is the most common air stripping configuration applied for groundwater treatment systems. In this method, treatment is typically conducted in a manner that contaminated groundwater flows into the top of a packed column and air flows into the bottom of the column. The water and air flow counter- currently and are mixed with each other, which then results in the mass transfer of contaminants from water to air. The mass transfer process of contaminants is governed by physical/chemical properties of each contaminant, the water temperature, the air to water ratio, the height of air/water contact column, physical properties of packing media used in the column and the like. For conducting this system, there are required basic assumptions that the air stream is free of any organic materials and Henry's law is applicable.

[23] 3. Multiple Chamber Fine Bubble Aeration System

[24] This technology is a method involving injection of air bubbles wherein fine or coarse bubble diffusers are used to produce air bubbles in the water to be treated. The mass transfer process takes place at the air-water interface of each bubble. This process occurs until the bubbles either leave the water or become saturated with contaminants. Furthermore, the chambers are interconnected so as to force the flow in a sinuous route, thereby increasing the air to fluid contact time. Due to no use of any packing material to enhance the mass transfer efficiency, the air to water ratios in a diffused air stripper should be relatively higher as compared to a packed column air stripper. The advantages of this method lie in its small and economical size, and the possible removal of inorganic materials via the filtration chambers which are adjacent to downstream, thereby reducing the cost of operation and maintenance.

[25] 4. Low Profile Sieve Tray Air Stripper

[26] In this configuration, air flows upward through the tray orifices, creating a turbulent froth where the mass transfer process takes place. Therefore, the turbulence that occurs on the tray reduces the frequency of fouling of the stripper itself. Removal efficiencies can be enhanced by increasing the number of trays and the air/fluid contact time.

[27] 5. Effluent Air Treatment

[28] There are three types of technologies commonly applied for the treatment of air discharges: vapor-phase activated carbon, thermal oxidation, and biofiltration. Selection of any of the above technologies will depend on the airflow rate, the type of contaminants, and the mass loading. When the level of volatile organics being discharged from an air stripper exceeds the guidelines, it is necessary to treat the effluent air discharge.

[29] 6. Steam Stripping

[30] Steam stripping is a groundwater treatment technology via a distillation process where volatile organic materials, which were mixed with water, are light-weight products. The process of steam stripping takes place at higher temperatures compared to air stripping, usually close to the boiling point of water. This process is suitable for contaminants such as acetone, methyl ethyl ketone (MEK), methyl tertiary butyl ether (MTBE) and alcohols, which are very volatile and have a low Henry's law constant due to their high solubility. Important feature of steam stripping is in the fact that no off- gas treatment is needed and the only waste stream generated is a small amount of very concentrated organics.

[31] 7. Carbon Adsorption

[32] Activated carbon is manufactured from sources of carbonaceous material such as coal, lignite and coconut shells. Adsorption occurs when organic molecules migrate to the activated carbon surface by diffusion and are held thereon by physical and/or chemical forces. The quantity of a compound that can be adsorbed by activated carbon is determined by balance between the forces that keep the compound in solution and those that attract the compound to the carbon surface. Adsorptivity increases with lower solubility, higher molecular weight, low polarity, and low volatility. Generally, organic acids adsorb better under acidic conditions, whereas amino compounds adsorb better under alkaline conditions. Regarding the class of chemical compounds, aromatic and halogenated compounds adsorb better than aliphatic compounds. In addition, adsorption capacity decreases with increasing temperature.

[33]

Disclosure of Invention Technical Problem

[34] There are more than about 1600 kinds of organic compounds in nature and contaminated environments and most of them are organic compounds related to petroleum products. Such organic compounds are largely of lower specific gravity as compared to water, are partially soluble in water and are volatile. A variety of technologies as described above are applied for treatment of oil contamination, but they suffer from their own limitations and problems and still exhibit difficulty in effective removal of organic compounds which were thoroughly dispersed in groundwater. Therefore, it is an object of the present invention to provide a novel method which is capable of effectively removing various kinds of organic compounds present in the groundwater, as contaminants. Particularly, the present invention is intended to provide a technology that can effectively remove organic compounds and can remediate oil-contaminated groundwater, via combined use of an adsorption method using an organoclay in accordance with the present invention, in conjunction with a variety of conventional technologies for treatment of oil contamination, such as advanced oxidation process (AOP) and the like.

[35] Conventionally, activated carbon or surfactants have been used to adsorb and remove organic contaminants contained in the groundwater and the like, but they exhibit low adsorptivity of organic contaminants and suffer from difficulty in recovery and removal of secondary products that have adsorbed organic contaminants. In addition, use of pure clay mineral itself cannot accomplish elimination of organic contaminants. Therefore, the present invention is intended to provide an organoclay having a surfactant adsorbed between layers of clay mineral with high swellability, such that organic compounds can be effectively adsorbed. Such an organoclay leads to significantly increased adsorption capability of organic materials as compared to when the surfactant is used as it is, and the organic materials thus adsorbed can be easily recovered and removed from the groundwater by means of appropriate methods such as precipitation.

[36] It is a further object of the present invention to provide a method for preparing such an organoclay.

[37] Other objects and advantages are described hereinafter and will be fully understood with reference to the following examples.

[38]

Technical Solution

[39] In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for purifying oil-contaminated water, comprising:

[40] adsorbing a surfactant on a clay mineral to prepare an organoclay;

[41] introducing the organoclay into contaminated water to adsorb organic contaminants; and

[42] separating and removing the adsorbed mixture of the organoclay and organic contaminants from the water.

[43] The contaminated water may be particularly groundwater.

[44] Preferably, before and/or after adsorbing/removing processes, a conventional treatment technology for oil-contamination such as advanced oxidation process (AOP) may be combined to more effectively purify oil-contamination.

[45]

[46] In accordance with another aspect of the present invention, there is provided an organoclay having a surfactant adsorbed on a clay mineral such that organic compounds can be adsorbed.

[47] As the clay mineral, minerals belonging to a montmorillonite group having high swellability are particularly preferred. For example, nontronite, saponite, vermiculite and the like may be used. As the surfactant, a cationic surfactant may be preferably used. Specific examples of the cationic surfactant that can be used in the present invention include, but are not limited to, higher amine halides, quaternary ammonium salts, ester-containing quaternary ammonium salts, alkyl pyridinium salts, phosphonium salts, sulfonium salts and imidazolium salts.

[48]

[49] In accordance with a further aspect of the present invention, there is provided a method for preparing an organoclay, comprising:

[50] adding a powder of a clay mineral to a solution in which a surfactant was dissolved in water;

[51] maintaining the resulting mixture at a temperature of 30 to 90°C for 12 hours to 4 days such that the surfactant is adsorbed between layers of the clay mineral; and

[52] separating and drying the resulting product.

[53] Adsorption capability of the organoclay on organic contaminants is increased depending upon a degree of adsorption of the surfactant between layers of the clay mineral, and the degree of adsorption of the surfactant on the clay mineral is critically affected by temperature. In addition, it is also important to maintain the surfactant in the solution in a saturated state. In the above method, preferably the powder of the clay mineral is added to a saturated solution of the surfactant which is then maintained at a temperature of 60+10°C for 36 to 60 hours, thereby resulting in adsorption of the surfactant between layers of the clay mineral, and the powder of the clay mineral having less than 200 mesh in size is preferably used.

[54]

Brief Description of the Drawings

[55] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [56] Fig. 1 schematically shows swellable clay mineral;

[57] Fig. 2 schematically shows organoclay in accordance with the present invention; and [58] Fig. 3 schematically shows a process for purifying organic contaminants using organoclay. [59] Best Mode for Carrying Out the Invention

[60] Hereinafter, an organoclay in accordance with the present invention and a method for purifying oil contamination using the same will be described in more detail with reference to the accompanying drawings.

[61] Fig. 1 schematically shows a swellable clay mineral. Even when they have high cation exchange capacity (CEC), clay minerals exhibit little adsorption capability for organic materials. As shown in Fig. 1, the clay mineral has negative (-) charges on the surface thereof and between layers thereof and thereby adsorbs positively (+) charged materials. Therefore, materials that can be adsorbed on the clay mineral are mostly metal ions which are present as cations. However, organic materials are generally not present in charged state and therefore are unlikely to be adsorbed on natural clay mineral without any processing or treatment.

[62] Fig. 2 schematically shows clay mineral which was reacted with a surfactant, i.e., an organoclay. The organoclay is prepared by reacting a cationic surfactant having positive (+) charges in a solution with a clay mineral having negative (-) charges between layers thereof. As a result, positively (+) charged surfactant is adsorbed between negatively (-) charged layers of the clay, and organic contaminants are then adsorbed on the layers of surfactant. As discussed hereinbefore, activated carbon or surfactants have been also used to remove organic contaminants in the conventional arts. However, such activated carbon or surfactants have exhibited low adsorptivity of organic contaminants when they are used alone, and suffered from difficulty in recovery of secondary products that have adsorbed organic contaminants even when they adsorbed organic contaminants. Whereas, upon using the organoclay in which the surfactant was adsorbed on the clay, it could be confirmed that organic material- adsorption capability was substantially increased as compared to when the surfactant itself was used.

[63] Fig. 3 is a schematic process for purifying organic contaminants using an organoclay. It is possible to remediate oil-contaminated groundwater via adsorption of organic contaminants on the organoclay in which a surfactant was adsorbed on a clay mineral. For this purpose, the clay mineral is first reacted with a cationic surfactant such that positively (+) charged cationic surfactant is adsorbed between negatively (-) charged layers of the clay mineral, thereby preparing an organoclay. Next, the thus- prepared organoclay is added to oil-contaminated water to thereby adsorb oil contaminants on the surfactant layer of the organoclay. Then, the adsorbed materials (organoclay + organic contaminants) are precipitated, and then can be easily separated and removed.

[64] [65] EXAMPLE

[66] Now, the present invention will be described in more detail with reference to the following example. This example is provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention. Therefore, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[67]

[68] Example 1

[69] Powdered nontronite (less than 200 mesh size) was added to a saturated solution of dialkyldimethylammonium chloride (DDAC), and the resulting mixture was reacted while being maintained at a temperature of about 60°C, such that large quantities of a surfactant were adsorbed between layers of a clay mineral. After adsorption for about 48 hours, the remaining solution was removed and the clay mineral was dried to thereby prepare an organoclay.

[70]

Industrial Applicability

[71] In accordance with the present invention, an organoclay having superior adsorption capability of organic contaminants is prepared by adsorption of a surfactant on a swellable clay mineral which has high adsorption capability of inorganic materials or high cation exchange capacity (CEC) but exhibits low adsorption capability for organic materials in a solution. The organoclay in accordance with the present invention can effectively adsorb and remove organic contaminants from oil-contamination and therefore can be used particularly for remediation of oil-contaminated groundwater.

Claims

[I] A method for purifying oil-contaminated water, comprising: adsorbing a surfactant on a clay mineral to prepare an organoclay; introducing the organoclay into contaminated water to adsorb organic contaminants; and separating and removing the adsorbed mixture of the organoclay and organic contaminants from the water.

[2] The method according to claim 1, wherein the contaminated water is groundwater.

[3] The method according to claim 1 or 2, further comprising: an advanced oxidation process (AOP) before and/or after the adsorbing/ removing processes.

[4] An organoclay having a surfactant adsorbed on a clay mineral such that organic compounds can be adsorbed.

[5] The organoclay according to claim 4, wherein the clay mineral is a mineral belonging to a montmorillonite group.

[6] The organoclay according to claim 4 or 5, wherein the surfactant is a cationic surfactant.

[7] A method for preparing an organoclay, comprising: adding a powder of a clay mineral to a solution in which a surfactant was dissolved in water; maintaining the mixture at a temperature of 30 to 90? for 12 hours to 4 days such that the surfactant is adsorbed on the clay mineral; and separating and drying the resulting product.

[8] The method according to claim 7, wherein the clay mineral is a mineral belonging to a montmorillonite group.

[9] The method according to claim 7, wherein the surfactant is a cationic surfactant.

[10] The method according to any one of claims 7 to 9, wherein the powder of the clay mineral is added to a saturated solution of the surfactant and the mixture is maintained at a temperature of 60+10°C for 36 to 60 hours, thereby adsorbing the surfactant on the clay mineral.

[II] The method according to claim 10, wherein the powder of the clay mineral has less than 200 mesh in size.