Process for the preparation of polymeric absorbents

Details Process for the preparation of polymeric absorbents Process for the preparation of polymeric absorbents

2000-03-27

2004-09-21

Zalukaeva, Tatyana (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S141000, C526S171000, C526S184000, C526S219600, C526S230000, C526S142000, C526S288000, C526S140000, C526S303100, C526S307200, C526S318300

Reexamination Certificate

active

06794467

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the preparation of polymeric absorbents useful for the gelling of organic liquids. More particularly, the present invention relates to a process for the preparation of polymeric absorbents which are cross-linked (5 to 50%) and are capable of absorbing organic liquids in the presence of a ppm level metal additive. The polymers prepared by the process of the present invention have a proper balance of hydrophilic and hydrophobic character in its chemical structure. The polymers prepared by this technique are known in the art as polymer gels or more commonly and hereinafter referred to as gels.
BACKGROUND OF THE INVENTION
Polymer gels consist of cross-linked macromolecules that form a three dimensional network in which solvent molecules are absorbed by osmotic forces. Polymer gels have an equilibrium absorption capacity, which is governed by a balance of osmotic pressure of the solvent and the elastic stress of the network. Polymer gels, which absorb water, are referred to as hydrogels. Those hydrogels, which can absorb large quantities of water, such as in excess of 100 gram of water per gram of dry gel, are called superabsorbants. Polymeric superabsorbents have been widely used in personal care products such as sanitary napkins and diapers. They have also been used in agricultural applications such as for irrigating dry and arid land. Recent developments and new applications of superabsorbents have been outlined in literature (Bucholz, F. L.,
Chemtech
, Sep. 38, (1994)). Superabsorbing gels are prepared by polymerising highly hydrophilic monomers such as acrylamide and acrylic acid along with a small quantity of multifunctional monomers and using a suitable initiator, typically a radical initiator, in water as a solvent.
Superabsorbing hydrogels do not absorb organic solvents. In fact, many of them collapse in organic solvents such as acetone and alcohol. Gels, which can absorb organic solvents, have been developed to a limited extent. Examples of such gels are chlorosulfonated polyethylene gels (Varma, A. J., Lele, A. K. and Mashelkar, R. A.,
Chem. Engg. Sci.,
50, 3835 (1995)) and polyethylene oxide gels (Graham, N. B., Nwachuku, N. E. and Walsh, D. J.,
Polymer ,
23, 1345 (1982)).
There are several advantages of absorbing organic liquids into gels. For example, the liquid can be transformed into a soft solid by entrapping into a three dimensional matrix of a gel. Soft solids have typical properties that are intermediate between solids and liquids. For example, gelled organic liquids can have a high viscosity as well as a finite modulus. In general, gelled liquids find applications in pastes, lotions, creams, shampoos, oil drilling fluids and in fuels. Gelled fuels are particularly useful for cooking and chafing dishes. They are easier and safer to transport and are more effective owing to the slower diffusive release of the fuel from the gelled matrix. Such gelled fuels typically contain an alcohol, usually methanol or ethanol as the fuel, which may be mixed with other C
1
to C
6
alcohols. It is desirable to gel the fuel in such a manner that it does not separate from the matrix on standing or on application of pressure.
Alcohol based gels have been formed by different gelling agents. U.S. Pat. No. 3,754,877 discloses the use of olefin modified hydroxyalkyl cellulose as the gelling agent. U.S. Pat. No. 4,436,525 discloses the gelling of a 3:1 mixture of methyl alcohol and isopropyl alcohol with a fatty acid soap and sodium hydroxide. U.S. Pat. No. 3,759,674 discloses the dispersions of ethylene-acrylic acid copolymers and amine emulsifiers in water, which form gels when mixed with alcohols. These gels contain about 10 to 30% by weight of solids. U.S. Pat. No. 3,148,958, U.S. Pat. No. 4,261,700 and U.S. Pat. No. 4,365,971 disclose the use of carboxy vinyl polymers such as Carbopol ethylene acrylic acid copolymer partially neutralised by weak amines as gelling agents for alcohols. U.S. Pat. No. 5,641,890 discloses the use of an amine neutralised anionic polymer such as Carbopol 676 along with an amphoteric Theological additive such as dispersed alumina for gelling alcohol. The gel so formed contains about 20 to 30% by weight of water. The gel is formed by non-covalent physical cross-links originating from interactions between the polymer and the amine. A typical gel contains about 70 weight % alcohol and about 1 weight % each of the polymer and the amine.
While the disclosures referred to above are interesting, they do not provide any teaching as to the structural features of the polymer absorbent. Also, no teaching is provided for synthesizing a solvent absorbing covalently cross-linked polymer gel. Whereas the disclosures of the above references have used a commercial polymer, in the present invention the polymer gel is prepared in situ by polymerizing selected monomers which contain a proper balance of hydrophilic and hydrophobic character in the presence or absence of a suitable transition metal compound. The proper choice of monomers containing hydrophilic and hydrophobic functional groups is particularly necessary for absorption of C
1
to C
6
alcohol and their mixtures, without the need for presence of water. Also in the prior art, the gels prepared inevitably required additional gels in order to increase the viscosity thereof.
The gel of the invention does not require any other gelling agents besides the polymer itself. The gelled fuels may or may not contain any water. Absence of water can significantly improve the burning characteristics thus giving an improved gel. Polymerisation of the monomer in the presence of a suitable transition metal compound helps in controlling the level of cross-linking reaction as well as forming structural complexes with the organic liquid. This improves the absorption capacity of the polymer for the organic liquid. The gel so prepared does not require any other gelling agent or thickening agent to increase the viscosity besides the polymer unlike the disclosures of the above references.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a polymer gel that can osmotically absorb large quantities of organic solvents to form gelled liquids.
It is another object of the invention to provide polymer gels that can be used for the formation of gelled fuels.
It is further object of the invention to provide a process for the preparation of polymer gels that can be used for preparing gelled fuels useful in cooking and heating food.
It is yet another object to provide polymer gels that do not require further gelling and/or thickening agents to increase the viscosity thereof
It is a further object to provide a process for the preparation of polymer gels that have improved absorption capacity for organic liquids, particularly organic solvents.
It is another object of the invention to provide a process for the preparation of polymer gels that absorb C
1
to C
6
alcohols or mixtures thereof without the need for the presence of water.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the preparation of polymeric absorbents useful for gelling organic liquids which comprises mixing one or more monomers with a cross-linking agent, a free radical initiator, an optional solvent, optionally in the presence of a transition metal source and subjecting the mixture so obtained to a conventional polymerisation method, removing the polymer, crushing the polymer to obtain polymer powder, washing with solvent, drying the polymer by conventional methods to remove unreacted monomers, followed by swelling in alcohols to obtain the desired product.
In one embodiment of the present invention, the process is optionally carried out in the presence of a transition metal source.
In yet another embodiment of the invention, the source of the transition metal may be metal, metal salts or metal complexes of cobalt, chromium, copper, manganese and iron.
In a further embodiment of the invention, the transition metal source is selected from chromium trioxide

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