WO1997006888A1

WO1997006888A1 - A composite material

Info

Publication number: WO1997006888A1
Application number: PCT/GB1996/001979
Authority: WO
Inventors: Andrew Livingston; Peter Robert Brookes
Original assignee: Imperial College Of Science Technology And Medicine
Priority date: 1995-08-16
Filing date: 1996-08-14
Publication date: 1997-02-27
Also published as: AU6748096A; GB9516915D0

Abstract

A composite material for removing molecules from a medium is described. The composite comprises a support and an adsorbent wherein the adsorbent is dispersed within and on the support.

Description

A COMPOSITE MATERIAL

The present invention relates to a composite material, especially a composite material for removing molecules, particularly pollutant molecules, from a medium, such as a solution.

Removal of pollutant molecules has previously been carried out using adsorbents such as activated carbon. Activated carbon is considered to be a good adsorbent because it has a very high surface area and it is porous, typically having a porosity of about 200 to about 400 nr m°. The surface is activated through chemical processes so that surface groups on the carbon surface interact with specific molecules. These interactions are responsible for the binding of molecules to the carbon surface, thereby removing many molecules from solutions.

Thus, an adsorbent, such as activated carbon, can be "loaded up" with, for example, inorganic pollutants and/or organic pollutants. The adsorbent is said to be "loaded" when all the sites for adsorption are occupied. For subsequent use, the loaded adsorbent material must be then regenerated such as by a thermal process or by using steam stripping. These processes shift the equilibrium of the adsorbed molecules and cause them to leave the adsorbent phase.

Until now, when activated carbon has been used as an adsorbent it has been generally in powder or granulated form. However, despite the fact that good mass transfer is obtained using these forms of activated carbon when immersed in a liquid, as a result of their high surface area per unit volume and the short diffusion lengths required for a molecule to pass from the waste water to the adsoφtion site, they are mechanically weak and suffer from attrition.

It is also known that activated carbon may be used in the form of carbon fibres. However, even this form of activated carbon appears to suffer from the same problems as the powder or granulated forms of activated carbon when used as an adsorbent. It is therefore an object of the present invention to overcome some or all of the problems associated with the adsorbents of the prior art.

According to a first aspect of the present invention there is provided a composite material for removing molecules from a medium, the composite material comprising a support; and an adsorbent; wherein the adsorbent is dispersed within and on the support.

According to a second aspect of the present invention there is provided a plurality of composite materials according to the present invention.

According to a third aspect of the present invention there is provided the use of a composite material according to the present invention to remove pollutants from a medium.

According to a fourth aspect of the present invention there is provided a process of removing pollutants from a medium, the process comprising contacting a medium with a composite material according to the present invention.

According to a fifth aspect of the present invention there is provided a process of preparing a composite material according to the present invention, the process comprising dispersing an adsorbent within a support.

Preferably, the support is a substantially homogeneous support.

Preferably, the adsorbent is substantially homogeneously dispersed within and on the support.

Depending on the application for the composite material, preferably the adsorbent is present in an amount of up to about 80% of the total weight of the composite material. In some instances, preferably the adsorbent is present in an amount of up to about 60% of the total weight of the composite material. In other instances, preferably the adsorbent is present in an amount of up to about 50%, more preferably up to about 30%, of the total weight of the composite material.

For some applications, it is preferred that the adsorbent is capable of adsorbing just organic molecules or just inorganic molecules. However, in other applications it is preferred that the adsorbent is capable of adsorbing organic molecules and inorganic molecules.

Preferably, the support is derived from a shapeable material, for example an extrudable or a castable material. In this regard, for some applications, preferably, the composite material is in sheet form. In this instance, or in other instances, preferably the composite material is folded, bent, curved, cylindrical or coiled or in the form of a spirally wound sheet. Also in this instance, or in other instances, preferably, facing layers of the composite material are not in contact with each other.

However, for other applications, the composite material may be in the form of solid rods or in the form of lumps or rocks.

For some applications, preferably a plurality of composite materials are used. In this case, preferably at least two composite materials do not touch each other. Preferably with the plurality of composite materials, substantially all of the composite materials do not touch each other.

Preferably, the support is a polymer. The polymer may be a hydrophilic polymer and/or a hydrophobic polymer. Preferably, the support comprises a hydrophobic polymer. Preferably, the support is a hydrophobic polymer.

For some applications, preferably the support is an elastomer, more preferably silicone rubber. For other applications, preferably the support is a rubber.

Preferably, the support may be derivatised, i.e. it may contain certain functional groups which may be the same or different.

Preferably, the composite material has been extruded or cast.

Preferably, the adsorbent is activated charcoal.

Preferably, the activated charcoal is dispersed in the form of a powder.

Key advantages of the adsorbent composite materials of the present invention are that they do not suffer from attrition and that they are mechanically strong.

In a preferred embodiment the composite is shapeable. This has the advantage that the composite can be shaped in one or more configurations that affect, for example enhance or maximise, the operational ability of the composite to remove molecules from a medium.

In addition, and in particular, the present invention overcomes the problems associated with the use of activated carbon as adsorbents by forming composite materials comprising activated carbon dispersed within and/or on the support. In this way powdered carbon can be used as a discrete phase in a homogeneous phase of the support, wherein the support provides an overall strength to the adsorbent.

The term "medium" includes gases, vapours, VOCs and solutions. For certain applications, it is highly preferred that the medium is a solution.

The term "solution" includes organic and/or inorganic solutions or liquids. The term "adsorbent" is used in its normal sense as meaning any substance upon whose surface (e.g. internal surface and/or external surface) the process of adsorption occurs.

Preferred adsorbents which may be used in the present invention are listed below:

1. Activated carbon

2. Carbon Molecular Sieve

3. Styrene based polymers (polystyrene) 4. Divinylbenzene based polymers

5. Poly (vinyl acetate)

6. Polyacrylic ester

7. Phenolic and Phenolic Amine Resins

including derivatives and combinations thereof.

The term "support" as used herein means any suitable support that can impart structural strength to the adsorbent by supporting it (e.g. holding it in a dispersed phase) and which is permeable to molecules to be removed from the medium, such as a solution. Thus, the support provides some of the structural strength of the composite material and in addition holds the absorbent as a dispersed phase. However, it is to be understood that in certain instances the overall structural strength of the composite can be attributable to both the support and the adsorbent. For example, some supports, such as polydimethylsiloxane, can be structurally weak on their own (i.e. in the absence of adsorbent) but those supports become structurally stronger when adsorbent is dispersed therein.

A typical support comprises a substantially homogeneous material which is preferably preferentially permeable to certain types of molecules, such as inorganic and/or organic pollutants, wherein the molecules permeate through the support to reach the adsorbent particles. Preferably, the support material has a greater permeability to the molecules than to water or to other polar species such as chloride ions.

The support material is preferably a polymer. The polymer is preferably prepared from polymerisable monomers.

The support may be a hydrophobic support such as silicone rubber or a hydrophilic support such as modified polydimethylsiloxane (PDMS). By using a hydrophobic support hydrophobic molecules, such as benzene or toluene, can more easily diffuse through the homogenous phase of the support to the adsorbent material. By using a hydrophilic support hydrophilic molecules, such as phenol or aniline, can more easily diffuse through the homogenous phase of the support to the adsorbent material. If the molecule which is to be extracted from the medium, such as a solution, is slightly hydrophilic then diffusion through a hydrophobic support could be rate limiting. If the molecules to be extracted are hydrophobic, then the support is preferably an elastomer such as silicone rubber.

Preferred supports which may be used in the present invention are listed below. :

1. Silicone rubber (essentially PDMS, usually mixed with 0-30% silica filler to give strength)

2. Silicone based polymers

3. Polydimethylsiloxane (PDMS)

4. Modified PDMS 5. Poly-(trimethylsilyl propyne)

6. Poly (dimethyl silmethylene)

7. Poly (cis-isoproprene)

8. Poly (butadiene-styrene)

9. Natural rubber 10. Polyetherblockamide (PEB A)

11. Polypropylene

12. Polyethylene 13. Polyvinylchloride

including derivatives and combinations thereof.

An example of modified PDMS is when some of the methyl side chains have been substituted. For example, the PDMS can be modified by the inclusion of hydrophilic side chains, such as amine groups, to improve the permeability of slightly hydrophilic pollutants, such as phenol and aniline. Alternatively, the PDMS can be modified by the inclusion of more chemically resistant side groups, such as fluorines (e.g. fluorosilicones).

The support is preferably of a very tough and durable material and may be cast or extruded in a variety of shapes. In this regard, the composite material of the present invention could be used in a variety of configurations. For example, by rolling a flat sheet up into the form of a spiral with spaces between the leaves. In this case, a medium, such as a solution, can be passed through the roll. Alternatively, the composite material could be in the form of a tube. In this case, a medium, such as a solution, can be passed through the tube. The composite material may, however, be used in many other configurations.

In some cases it is possible to have up to 80% adsorbent added to the support. For example, it has been found that 30%, and even up 60%, by weight powdered activated carbon can be added to silicone rubber without any detrimental affect on the integrity of the material.

In summation, the present invention relates to a composite material for removing molecules from a medium, such as a solution, wherein the composite material comprises a support and an adsorbent, and wherein the adsorbent is dispersed within and on the support. A preferred embodiment of the present invention is a composite material for removing molecules from a medium, such as a solution, wherein the composite material comprises a support and an adsorbent; wherein the adsorbent is dispersed within and on the support; and wherein the support is a polymer.

An alternative preferred embodiment of the present invention is a composite material for removing molecules from a medium, such as a solution, wherein the composite material comprises a support and an adsorbent; wherein the adsorbent is dispersed within and on the support; and wherein the adsorbent is activated charcoal.

A further preferred embodiment of the present invention is a composite material for removing molecules from a medium, such as a solution, wherein the composite material comprises a support and an adsorbent; wherein the adsorbent is dispersed within and on the support; wherein the support is a polymer; and wherein the adsorbent is activated charcoal.

A highly preferred embodiment of the present invention is a composite material for removing molecules from a medium, such as a solution, wherein the composite material comprises a support and an adsorbent; wherein the adsorbent is dispersed within and on the support; wherein the support is a polymer; wherein the adsorbent is activated charcoal; and wherein the support is silicone rubber.

A more highly preferred embodiment of the present invention is a composite material for removing molecules from a solution, wherein the composite material comprises a support and an adsorbent; wherein the adsorbent is dispersed within and on the suppon; wherein the support is a polymer; wherein the adsorbent is activated charcoal; and wherein the support is silicone rubber.

The present invention will now be described only by way of example. Preparation of Silicone Rubber Activated Carbon Composite Material

In brief, to prepare a silicone rubber/activated carbon composite material according to the present invention, activated carbon is dispersed in a 2 pot silicone rubber elastomer.

In more detail, two pot silicone rubber elastomer RTV 615 (supplied by GE Silicones Ltd) was used to produce the high strength silicone rubber. This silicone rubber elastomer consists of ten parts (wt) of RTV615A (Base Rubber) with one part of RTV615B (Curing Agent).

The two components were thoroughly mixed and then activated carbon BL F400 Powder having a particle size < 87μm (supplied Chemviron Carbon) was added in the required proportions (5, 10,20,30% wt%).

The mixture was then thoroughly mixed and degassed in a vacuum to remove any entrapped air.

After de-aeration, the liquid mixture was poured into a Perspex casting plate and cured at 100°C for 2 hours on a hot plate press. After this period the composite material was removed from the casting plate and allowed to dry for 24 hours at 70°C.

The polydimethylsiloxane/powdered activated carbon composite materials were then analysed for their ability to remove molecules from a medium, such as a solution. In this regard, the solution from which molecules are to be extracted is preferably an aqueous solution but may be any other kind of solution. Also, the molecules to be removed are preferably organic molecules but may be any type of molecule which can be extracted by means of an adsorbent. Therefore, for the purposes of this example, an aqueous solution of aniline was used (with water phase concentrations of aniline less than 500 mg L^"1) wherein the aniline was used as the "organic pollutant" . The ability of the composite material to remove aniline molecules from the aqueous solution was expressed as the equilibrium partition coefficient K, which is defined as:

Concentration of Pollutant in Composite Adsorbent K =

Concentration of Pollutant in Water

wherein K is generally constant for pollutant concentrations in the range of less than 500 mg IΛ

Values of K for the composite materials according to the present invention and a control (i.e. when there is no activated carbon) when aniline is used as the pollutant are given below.

wt% carbon K

0 <1

5 10

10 43

20 110

30 113

The above data show that the organic loading at equilibrium of the composite adsorbent of the present invention is a strong function of the percentage by weight of activated carbon added to polydimethylsiloxane.

It should be noted that the composite material according to the present invention is not limited to the use of activated carbon as the adsorbent material, though in a preferred embodiment it is so limited, as other kinds of adsorbent materials could be used in this invention. Furthermore, the support of the present invention is not limited to the use of silicone rubber, though in a preferred embodiment it is so limited, as the support may be formed of any material which is permeable to the molecules to be removed from the solution.

It should also be noted that the composite according to the present invention may be used to remove molecules from any solution and not just aqueous solutions.

Finally it should also be noted that the composite according to the present invention may be used to remove molecules from any medium, and not just solutions.

In another preferred embodiment the composite material of the present invention can be formed into a discrete body, such as a sphere or a cube. A number of discrete bodies, which may be the same or different, can then be packed (tightly or loosely) into a column, which column can have sieve-like portions as its wall. For example, substantially all of the column wall can be a sieve and a plurality of cubes of the composite material can be packed in the column.

The discrete bodies can then be used to support a biomass. This has the advantage that when a plurality of discrete bodies are present in a column the biomass supported thereon can be easily transported from one location to another.

In addition to supporting the growth of a biomass the discrete bodies also have the further advantage in that they reduce or eliminate any harmful effects brought about by transferring the biomass from one location to another, for example moving the supported biomass from one medium to another. In this regard, each of the discrete bodies can act as a capacitor - ie each is able to soak up harmful and/or excess amounts of organic materials and then release those organic materials if and when required by the biomass supported thereon. Accordingly, the present invention also relates to the use of the composite material of the present invention to support growth of biomass thereon.

Additionally, the present invention relates to the use of the composite material of the present invention to reduce or to eliminate the effect of biological and/or chemical shock of biomass supported thereon.

The present invention also relates to the use of the composite material of the present invention to at least dampen shocks in a biological system.

Other modifications of the present invention will be apparent to those skilled in the art.

Claims

1. A composite material for removing molecules from a medium, the composite material comprising

a support; and

an adsorbent;

wherein the adsorbent is dispersed within and on the support.

2. A composite material according to claim 1 wherein the support is a substantially homogeneous support.

3. A composite material according to claim 1 or claim 2 wherein the adsorbent is substantially homogeneously dispersed within and on the support.

4. A composite material according to any one of the preceding claims wherein the adsorbent is present in an amount of up to about 80% of the total weight of the composite material.

5. A composite material according any one of the preceding claims wherein the adsorbent is capable of adsorbing organic molecules.

6. A composite material according to any one of the preceding claims wherein the support is derived from a shapeable (e.g. extrudable or castable) material.

7. A composite material according to any one of claims 1 to 6, wherein the support is a polymer.

8. A composite material according to claim 7, wherein the support is a hydrophilic polymer.

9. A composite material according to claim 7, wherein the support is a hydrophobic polymer.

10. A composite material according to any one of the preceding claims wherein the support is an elastomer.

11. A composite material according to claim 10 wherein the support is silicone rubber.

12. A composite material according to any one of claims 1 to 10 wherein the support is a rubber.

13. A composite material according to any one of the preceding claims wherein the composite material is shaped.

14. A composite material according to any one of the preceding claims wherein the composite material is in sheet form.

15. A composite material according to claim 14 wherein the composite material is folded, bent, curved, cylindrical or coiled.

16. A composite material according to claim 15 wherein the composite material is in the form of a spirally wound sheet.

17. A composite material according to any one of claims 14 to 16 wherein facing layers of the composite material are not in contact with each other.

18. A composite material according to any one of the preceding claims wherein the adsorbent is activated charcoal.

19. A composite material according to claim 18 wherein the adsorbent is powdered activated charcoal.

20. A plurality of composite materials according to any one of the preceding claims.

21. A plurality of composite materials according to claim 20 wherein at least two composite materials do not touch each other.

22. A plurality of composite materials according to claim 21 wherein substantially all of the composite materials do not touch each other.

23. Use of a composite material according to any one of claims 1 to 18 or a plurality of composite materials according to any one of claims 19 to 22 to support growth of biomass thereon.

24. Use of a composite material according to any one of claims 1 to 18 or a plurality of composite materials according to any one of claims 19 to 22 to reduce or eliminate the effect of biological and/or chemical shock of biomass supported thereon.

25. Use of a composite material according to any one of claims 1 to 18 or a plurality of composite materials according to any one of claims 19 to 22 to dampen shocks in a biological system.

26. A composite material substantially as hereinbefore described.