Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2001-09-21
2004-03-23
Metzmaier, Daniel S. (Department: 1712)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C516S136000, C203S010000
Reexamination Certificate
active
06709600
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the removal of organics from water, particularly to the removal of organic liquids from aqueous solutions and mixtures employing a porous material, and more particularly to the use of porous materials in a granular form and having small pores and a large specific area that is hydrophobic so that liquid water does not readily wet its surface.
A common approach to remove organics from water and water solutions is by filtration. In order to enhance the absorption capacity, highly porous materials like activated carbon granules are selected for the filter medium. Such materials have huge internal surfaces for adsorbed molecules to reside. These materials separate the organics from aqueous solutions by diffusion of the organic molecules into the pores and consequent adsorption onto the surfaces. However, since liquid water also fills the available pores and thus competes with the organics for the available surface sites, the maximum possible separations are not obtained. A preferred approach is to inhibit the liquid water from entering the pores, thereby allowing the vapors to enter the porous materials. In this case, the more volatile constituents of the solution preferentially enter the porous material and reside at most of the available adsorption sites. Hence, separations are enhanced for the organic solvents which are generally more volatile than water under normal conditions of temperature and pressure. Furthermore, organics that do not readily mix with water, and thus form separate phases in mixtures with water, generally have surface energies which are less than that of water. This property of organic liquids allows them to easily wet the surfaces of the porous material and be preferentially drawn into the pores by capillarity, leaving the water behind. Very large separation factors are possible for this case.
The key property of the porous material to inhibit wetting by liquid water is hydrophobicity. This property requires that the surface energy of the solid be greater than the surface energy of the liquid water, so that the liquid does not spread out to cover the available surface. Such a property is inherent for many polymers, the best examples of which are polythylene, and polytetrafluoroethylne (Teflon). Other materials such as carbons and inorganic oxides have low surface energies and their surfaces have to be chemically modified to raise their surface energies above that for water.
The present invention involves a method for removing organic liquids from aqueous solutions and mixtures by the use of semi-solid gel materials or aerogels. Aerogels have small pores and a large specific surface area and can be fabricated so that liquid water does not readily wet the surface, a hydrophobic aerogel. The invention has been demonstrated using silica aerogels which have either been chemically treated or produced directly to be hydrophobic. However, organic or functionalized carbon aerogels may also be used. The aerogel material may be in either granular or powdered form. Separation capacities of porous materials (hydrophobic aerogels) greatly exceed those for non-hydrophobic porous materials.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for removing organic liquids from aqueous solutions and mixtures.
It is a further object of the invention is to provide a hydrophobic aerogel.
A further object of the invention is to provide an aerogel which has been treated chemically or produced directly to be hydrophobic, whereby liquid water does not readily wet the surface of the aerogel.
Another object of the invention is to enable organics, especially organic solutions that mix with and are more volatile than water, to be separated from an aqueous solution by preferentially evaporating across the liquid/solid boundary formed on the surfaces of the hydrophobic aerogel material.
Another object of the invention is to enable separation of organic solvents that are immiscible with water and which preferentially wet the surfaces of a hydrophobic aerogel and are drawn within the aerogel by capillary action.
Another object of the invention is to significantly increase the separation capacities of hydrophobic porous materials over those for non-hydrophobic materials because the pores do not preferentially fill with water before separation can occur.
Other objects and advantages will become apparent from the following description. This invention is a method for removing organic liquids from aqueous solutions and mixtures. While the invention may employ any porous material or a semi-solid gel material, it is preferred that the material is in granular form and has small pores and a large specific surface area, that is hydrophobic so that liquid water does not readily wet its surface. The preferred material may be composed of hydrophobic inorganic or organic aerogels. The separation capacities of hydrophobic aerogels greatly exceed those for non-hydrophobic porous materials because the pores do not preferentially fill with water before separation can occur. Applications for the hydrophobic aerogel separators include water or other fluid purification, extraction of microscopic particles from body fluids, toxic waste cleanup, bandages and sterile absorbers.
DETAILED DESCRIPTION OF THE INVENTION
This invention is a method for removing organic liquids from aqueous solutions and mixtures. The invention involves a semi-solid gel material or a solid material, such as an aerogel, consisting of a solid network of connected, generally spheroidal shaped sub-micrometer sized particles, in which the interstitial spaces between the particles define continuous pores through the material. Such pores have an average size scale which is generally less than 1 micromedia and which can be changed over a selected range by proper choice of chemicals and process conditions. Solution chemistry, also known as sol-gel processing, is used to make the semi-solid or solid material using selected chemicals and process conditions. The surfaces within the material can be chemically modified, made hydrophobic, either during the solution chemical synthesis, or after the structure is formed, including also, after the gel is dried (i.e., an aerogel or xerogel), when that state is desired. The surfaces are chemically modified to provide variations in surface energies and/or particles relative to the carrier fluid.
The invention employs any porous material, preferably in granular form and having small pores and a large specific surface area, that is hydrophobic so that liquid water does not readily wet its surface. In this invention, organics, especially organic solvents that mix with and are more volatile than water, are separated from aqueous solution by preferentially evaporating across the liquid/solid boundary formed at the surfaces of the hydrophobic porous materials. Also, organic solvents that are immiscible with water, preferentially wet the surfaces of the hydrophobic material and are drawn within the porous material by capillary action. Separation capacities of porous materials for this method greatly exceed those for non-hydrophobic porous materials because the pores do not preferentially fill with water before separations can occur.
While the method of this invention may be utilized with any porous semi-solid or solid material having small pores, a large specific surface area, and which is hydrophobic so that liquid water does not readily wet its surface, the preferred porus material comprises an inorganic or organic aerogel, with the experimental data set forth below being from highly hydrophobic silica aerogels.
One embodiment of the invention is an aerogel made of silicon-dioxide (silica), with surfaces that are chemically modified to repel liquid water. This material will selectively draw (wick) fluids which are immiscible with water when it is placed in contact with such a mixture. Nanosized particles entrained by the immiscible fluid are also carried into the material and trapped therein. Almost the entire volume of
Coronado Paul R.
Dow Jerome P.
Hrubesh Lawrence W.
Lee Ann M.
Metzmaier Daniel S.
Scott Eddie E.
The Regents of the University of California
Thompson Alan H.
LandOfFree
Method for removing organic liquids from aqueous solutions... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing organic liquids from aqueous solutions..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing organic liquids from aqueous solutions... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3251325