Seaweed polysaccharide based superhydrophilic foam membrane for energy-efficient oil-water separation

Abstract

The present invention relates to a superhydrophilic biodegradable cross linked foam membrane and a process for preparation of said foam membrane from a seaweed polysaccharides by blending with amino biopolymers/amino acids/proteins/amino compounds followed by crosslinking with a naturally occurring cross linker, genipin. The foam membrane can be used as a substitute for synthetic membrane for varied applications including membrane separation for oil-water emulsions, oil-water mixtures and other aqueous-organic mixtures under ambient conditions. These foam membranes can be recycled and reused more than three times without considerable decrease in flux rate and stability. The separation methodology of the mixtures using the foam membrane of the present invention is gravity-driven and therefore, simple and energy-efficient.

Claims

1. A hydrophilic biodegradable hybrid foam membrane consisting of: a seaweed derived polysaccharide in the range of 50 to 95 wt %, wherein the seaweed derived polysaccharide comprises at least one of agar, agarose, and carrageenan; an amino compound in the range of 5 to 50 wt %, wherein the amino compound comprises at least one of gelatin, chitosan, and bovine serum albumin; and a crosslinker in the range of 0.01 to 0.1 wt %, wherein the crosslinker comprises genipin; wherein the hydrophilic biodegradable hybrid foam membrane has been lyophilized to have a moisture content in the range of 5 to 15 wt %.

2. A method of separating a mixture comprising an oil-water mixture and/or emulsion under ambient conditions at a flux rate in the range of 260 to 900 L.Math.m.sup.2.Math.h.sup.1 and an oil rejection percentage in the range of 96 to 99% comprising: obtaining a hydrophilic biodegradable hybrid foam membrane of claim 1; and using the membrane to separate the mixture.

3. A process for preparing the hydrophilic biodegradable hybrid foam membrane of claim 1, comprising: dissolving 0.5 to 7 wt % of a seaweed derived polysaccharide comprising at least one of agar, agarose, and carrageenan by heating at a temperature in the range of 100 to 120 C. for a period in the range of 5 to 45 minutes to obtain a homogenous solution; adding 0.05 to 4 wt % of an amino compound comprising at least one of gelatin, chitosan, and bovine serumalbumin dissolved in water to the homogenous solution at a temperature in the range of 40 to 85 C. under constant stirring for a period in the range of 1 to 60 minutes to obtain a reaction mixture; adding 0.01 to 1.0 wt % of genipin with respect to the reaction mixture and keeping the reaction mixture at a temperature in the range of 25 to 80 C. for a period in the range of 20 min to 12 days to obtain a crosslinked hydrogel; and slicing the crosslinked hydrogel and lyophilizing it for a period in the range of 10 to 40 hours to obtain a hydrophilic biodegradable hybrid foam membrane.

4. The process of claim 3, wherein the crosslinking is done in a bulk hydrogel having a thickness in the range of 5 cm to 50 cm or in a hydrogel cast in a thin layer of thickness 0.2 cm to 2 cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A illustrates schematically representation of the process for preparation of biodegradable hybrid foam membrane.

(2) FIG. 1B illustrates the crosslinking between the agarose and gelatine by genipin before and after lyophilisation.

(3) FIG. 2 illustrates photographic images of the hybrid foam membrane, first sample from left as control, second to fourth sample as cross-linked agarose and gelatine with different blend concentrations.

(4) FIG. 3A illustrates a gravity-driven oil-water separation apparatus with 50:50 (v:v) of different oil-water mixtures.

(5) FIG. 3B shows the FTIR characterization of crude oil to evaluate separation performance of feed and permeate samples, disappearance of the characteristic peaks for CO of esters and CH stretching of oils confirms the purity of permeate.

(6) FIG. 3C shows the FTIR characterization of hexane to evaluate separation performance of feed and permeate samples, disappearance of the characteristic peaks for CO of esters and CH stretching of oils confirms the purity of permeate, FIG. 3D displays the permeate flux (L m.sup.2 h.sup.1) and % rejection of various oil-water mixtures.

(7) FIG. 4 illustrates genipin leach-out study conducted prior to testing.

(8) FIG. 5A illustrates swelling studies conducted on different foam membrane to confirm their water uptake capacities in pure water.

(9) FIG. 5B illustrates swelling studies conducted on different foam membrane to confirm their water uptake capacities in oil-water mixtures.

(10) FIG. 6 illustrates biodegradability of the hybrid foam membrane under soil conditions.

DETAILED DESCRIPTION OF THE INVENTION

(11) The seaweed derived phycocolloids used for the purposes of the present invention are selected from agar bacteriological (product code: 0140132), agarose (product code 014011) and alginate (product code: 1947295) which were commercially procured from M/s Sisco Research Laboratories (SRL) Pvt. Ltd. Mumbai400 093, Maharashtra, India, and semi refined carrageenan (product code: Aqua gel 250) which was commercially procured from M/s Aquagri Processing Pvt. Ltd., New Delhi, India.

(12) The present invention relates to biodegradable superhydrophilic foam membranes exhibiting high mechanical stability and good flexibility. The present invention also describes a simple, eco-friendly and one-step crosslinking for the preparation of said foam membrane materials from the seaweed derived polysaccharides and amino polymers/compounds blends through crosslinking reaction with naturally occurring crosslinker like genipin (FIG. 1). The process comprising: dissolving 0.5 to 7 wt % of the seaweed derived polysaccharides or combination thereof in water by heating at 100 to 120 C. for 5 to 45 minutes to obtain a homogenous solution; adding 0.05 to 4 wt % amino polymers or compounds in the homogenous solution at 40 to 85 C. under constant stirring for 1 to 60 min to obtain a reaction mixture and then followed by addition of 0.01 to 1.0 wt % (with respect to seaweed polysaccharides) of the crosslinker, genipin into the reaction mixture and keeping at room temperature (25 C.) for 20 min to 12 days to obtain the crosslinked hydrogels; slicing the crosslinked hydrogel at a temperature of 25 to 40 degree C. and lyophilizing for a period of 10 to 40 hours to yield the hydrophilic biodegradable hybrid foam membrane suitable for multifarious applications including oil-water separations under gravity driven force.

(13) The invention relates to the preparation of hydrophilic biodegradable hybrid foam membranes from natural polymers such as seaweed polysaccharides through blending with amino natural polymers or amino compounds followed by crosslinking reaction with naturally occurring crosslinker. The developed crosslinked hydrogel can be moulded in the form of foam membranes, beads etc., which can be used as a substitute for synthetic membrane separation for varied applications including oil-water mixtures and emulsions. The results of separation experiments showed that the prepared hybrid foam membranes are suitable for separation of oil-water under ambient conditions at atmospheric pressure, and yield ca. <98% purity of water. These foam membranes are very flexible and easy to handle. These foam membranes are suitable for recovery and reuse for more than six times without considerable change in the performance. In addition, foam membranes can also be used for the separation of oil-spills, crude oil-water, hexane-water, toluene-water, etc. under ambient conditions.

EXAMPLES

(14) Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1

(15) 1900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 15 min under microwave/autoclave conditions. 100 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in to agarose solution under stirring condition at 50 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes (FIG. 1). The foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Water was separate out from oil-water mixture with 300 L m.sup.2 h.sup.1 flux with 96% purity.

(16) No weight loss on washing with water and organic solvents (e.g. etanol, methasnol, ios-Propanol, acetone) is observed from the final freeze-dried product indicates that most of the reactants amount presence in the crosslinked product after completion of crosslinking reaction, and yield of the final crosslinked foam membrane matter is almost the same of the total quantities of the reactants (e.g. agarose, gelatin and crosslinker) used in the crosslinking reaction at initial stage. Hence the compositions of the products are purely based of the initial weights of the reactants used in this invention.

Example 2

(17) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room (25 C.) temperature to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was flexible, spongy and having negligible water uptake capacity. Easy to recycle and reuse through simple washing and performance was identical after five cycles. Separation performance for the various solvent systems has been given in the Table 1 (FIG. 2 and FIG. 3A-3D).

(18) TABLE-US-00001 TABLE 1 Flux rate dependency on the type of solvent mixtures. Flux rate Type of mixture (L.m.sup.2 .Math. h.sup.1) % Oil rejection Oil spill 420 99.0 Crude oil-water 510 97.5 Edible oil-water 530 98.0 Hexane-water 560 97.0 Toluene-water 500 99.0

Example 3

(19) 1700 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 300 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 60 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Water was separate out from oil-water mixture with 350 L m.sup.2 h.sup.1 flux with 94% purity. Slightly color leaching was observed (FIG. 4).

(20) Membranes were extensively characterised for their characteristic changes and crosslinking of genipin in the network. .sup.1H NMR spectrum of gelatin (Gel) exhibited characteristics peaks at 7.83 and 8.05 ppm. No peaks at 7.83 and 8.05 ppm are observed in the NMR spectrum of the crosslinked product (Agarose-Gelatin-Genipin or Agr+Gel+Gen) after crosslinking confirmed the crosslinking of genipin with gelatin.

Example 4

(21) 1500 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 35 min under microwave/autoclave conditions. 500 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 80 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Separation was not proper on this foam membrane, as leaching of gelatin was observed.

Example 5

(22) 1000 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 5 min under microwave/autoclave conditions. 1000 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 40 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper and collapsed during aqueous contact. Separation was not proper on this foam membrane, as leaching of gelatin was observed.

Example 6

(23) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 85 degree Celsius followed by the addition of 10 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 120 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity (FIG. 5), and less stabile under experimental conditions. Recycling and washing are not proper. Separation was not proper on this foam membrane, as leaching of colour was observed.

Example 7

(24) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 20 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Separation was not proper on this foam membrane, as leaching of color was observed.

Example 8

(25) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 45 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 30 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are possible but color leaching was observed.

Example 9

(26) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 60 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 7 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. The crosslinking reaction was homogeneous throughout the hydrogel mass. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was less flexible, spongy, and washable with negligible water uptake capacity. Membrane was recycled more than five times and performance was almost identical up to five cycles with 350 L m.sup.2 h.sup.1 continuous flux with 98% pure product water. Foam membranes have soil degradability under environmental conditions (FIG. 6).

Example 10

(27) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 100 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 5 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was less flexible, spongy, and washable with negligible water uptake capacity. Membrane was recycled more than five times and performance was almost identical up to five cycles with 440 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

Example 11

(28) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and unstable under experimental conditions with high water uptake capacity. Membrane was collapsed during separation experiments and color leaching was observed.

Example 12

(29) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 5 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and unstable under experimental conditions with high water uptake capacity, and color leaching was observed.

Example 13

(30) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 7 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and stable under experimental conditions with low water uptake capacity. Membrane was used for separation and flux rate was 500 L m.sup.2 h.sup.1, but recycling was proper up to two cycles.

Example 14

(31) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 200 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 7 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for complete crosslinking reaction. The crosslinking reaction was homogeneous throughout the hydrogel mass. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and washable with negligible water uptake capacity. Membrane was recycled more than five times and performance was almost identical up to five cycles with 490 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

Example 15

(32) 2700 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 300 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was considerably rigid, brittle, with high water uptake capacity. Foam membrane was not homogeneous and purity of water product was 70% along with color leaching.

Example 16

(33) 3600 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 45 min under microwave/autoclave conditions. 400 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 15 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was rigid, brittle, with high water uptake capacity. Foam membrane was not homogeneous and no separation experiments were performed. Color leaching was observed during aqueous contact.

Example 17

(34) 4500 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 500 mg gelatin was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 15 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was very rigid, brittle and with high water uptake capacity. Foam membrane was not homogeneous and no separation experiments were performed. Color leaching was observed during aqueous contact.

(35) Examples 1 to 17 thought us that best quality foam membranes were obtained with 2 wt % total polymer concentration having 0.2 wt % gelatin, 0.04 wt % crosslinker concentration and crosslinking time is 10 days under ambient conditions.

Example 18

(36) 450 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 50 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinked hydrogel was weak and slicing of gel was not suitable.

Example 19

(37) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in to agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes.

(38) Membranes were extensively characterised for their characteristic changes and crosslinking of genipin with amino groups. UV spectra of chitosan and agarose does not exhibit any absorption peaks in the UV spectra, while crosslinker genipin showed characteristic peak at 240 nm. The appearance of the new peaks at 282 nm and 600 nm confirmed the crosslinking of genipin with amino moieties of chitosan. Hereafter, UV spectrum of the crosslinked product agarose-Chitosan-Genipin (Agr+CH+Gen) confirmed use of amino groups in the crosslinking with genipin.

(39) The foam membrane was flexible, spongy with negligible water uptake capacity, and stabile under experimental conditions. Easy to recycle and wash. Water was separate out from oil-water mixture with 750 L m.sup.2 h.sup.1 flux with 97% purity. The performance was identical up to three cycles.

(40) TABLE-US-00002 TABLE 2 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 770 98.0 Reuse three times Crude oil-water 700 97.5 Reuse three times Edible oil-water 730 98.0 Reuse three times Hexane-water Separation was not proper Toluene-water 700 97.0 Reuse three times

Example 20

(41) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was flexible, spongy and having negligible water uptake capacity. Easy to recycle and reuse through simple washing and performance was identical up to three cycles. Water was separate out from oil-water mixture with 700 L m.sup.2 h.sup.1 flux with 98% purity.

(42) No weight loss on washing with water and organic solvents (e.g. etanol, methasnol, ios-Propanol, acetone) is observed from the final freeze-dried product indicates that most of the reactants amount presence in the crosslinked product after completion of crosslinking reaction, and yield of the final crosslinked foam membrane matter is almost the same of the total quantities of the reactants (e.g. agarose, chitosan/BSA and crosslinker) used in the crosslinking reaction at initial stage. Hence the compositions of the products are purely based of the initial weights of the reactants used in this invention.

Example 21

(43) 500 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 30 min under microwave/autoclave conditions. 500 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The foam membrane was not homogeneous, spongy with low water uptake capacity, and stabile under experimental conditions. Water was separate out from oil-water mixture with 450 L m.sup.2 h.sup.1 flux with 92% purity.

Example 22

(44) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 5 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 10 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Separation was not proper on this foam membrane.

Example 23

(45) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 15 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 20 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions. Recycling and washing are not proper. Separation was not proper on this foam membrane.

Example 24

(46) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 30 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The crosslinking was not complete and resulting foam membrane was flexible, spongy with high water uptake capacity, and less stabile under experimental conditions.

Example 25

(47) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 50 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 7 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. The crosslinking reaction was homogeneous throughout the hydrogel mass. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and washable with negligible water uptake capacity. Membrane was recycled more than three times and performance was almost identical up to three cycles with 700 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

(48) CP-MAS .sup.13C NMR (solid NMR) spectrum of agarose shows characteristics peaks: 62.66, 70.02, 76.08, 80.02, 98.43 and 102.18 ppm; and solid NMR spectrum of chitosan exhibited characteristics peaks: 23.38, 57.32, 61.0, 75.29, 82.91, 105.06 and 174.39 ppm. The solid NMR spectrum of crosslinked product Agarose-Chitosan-Genipin shows most of the characteristics peaks of agarose and chitosan in the range of 23-173.43 ppm along with the characteristics peaks of genipin at 111.88, 133.61, 152.72 and 166.20 ppm indicates crosslinking and insertion of genipin in the crosslinked product.

Example 26

(49) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 60 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 5 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was less flexible, and washable. Membrane was recycled more than five times and performance was almost identical up to three cycles with 650 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

(50) FTIR spectrum of agarose exhibited characteristics IR bands including peak at 932 cm.sup.1 (due to 3, 6-anhydrogalactose linkage). IR spectrum of chitosan also shows characteristic peaks at 3352 cm.sup.1 (OH groups), 2878 cm.sup.1 (CH.sub.3 groups), 1560 (NH group bending vibration) and 1404 cm.sup.1 typical of the vibrations of OH group of the primary alcoholic group, respectively. In addition, chitosan shows the bands at 1320 and 1077 cm.sup.1 correspond to the stretching of CON and CO groups. The appearance of the characteristics peaks of agarose (at 1162, 1076 and 932 cm.sup.1) and chitosan (at 1560, 1320, 1154, 1077 and 897 cm.sup.1) with slight broadening or shifting and/or with varied intensities in the FTIR spectrum of the crosslinked product confirms the presence of both agarose and chitosan in the crosslinked products and crosslinking. Significant decreases in absorbance were also observed for the various peaks along with a new peak appeared at about 1630 cm.sup.1 after the reaction of crosslinking also indicates crosslinking. In addition, noticeable change appeared in the shift of broader Agarose stretching peak (OH) at 3438 cm.sup.1 upon blending with chitosan (3435 cm.sup.1) to 3400 cm.sup.1, and this remained unchanged upon genipin crosslinking. Therefore, hydroxyl (OH) groups present in agarose make hydrogen bonding interaction with chitosan resulting in lamellar structures in which chitosan holding agarose either side. So, it leads to confirm that superhydrophilic agarose micro-pore is surrounded by chitosan walls used for selective separation from oil-water emulsions.

Example 27

(51) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 3 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was less flexible, and washable. Membrane was recycled more than five times and performance was almost identical up to three cycles with 700 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

Example 28

(52) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 35 min under microwave/autoclave conditions. 100 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 5 days at room temperature (25 C.) to allow for crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was less flexible, and washable. Membrane was recycled more than five times and performance was almost identical up to three cycles with 650 L m.sup.2 h.sup.1 continuous flux with 98% pure product water.

Example 29

(53) 2700 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 300 mg chitosan was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 7 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 2 days at room temperature (25 C.) to allow for complete crosslinking reaction. The crosslinking reaction was homogeneous throughout the hydrogel mass. The crosslinked hydrogel was not homogeneous and slicing was not proper. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was also not homogeneous and was not used for separation experiments.

(54) Examples 18 to 29 thought us that best quality foam membranes were obtained with 1 wt % total polymer concentration having 0.1 wt % chitosan, 0.04 wt % crosslinker concentration and crosslinking time is 2 days under ambient conditions.

Example 30

(55) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 10 min under microwave/autoclave conditions. 200 mg Bovine Serum albumin (BSA) was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 10 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and washable. Membrane was recycled more than three times and performance was almost identical up to three cycles with 850 L m.sup.2 h.sup.1 continuous flux with 97% pure product water.

(56) TABLE-US-00003 TABLE 3 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 850 98 Reuse three times Crude oil-water 900 98 Reuse three times Edible oil-water 840 98 Reuse three times Hexane-water Separation was not proper Toluene-water 830 97 Reuse three times

Example 31

(57) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg Bovine Serum albumin (BSA) was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 85 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and suitable for separation experiments.

(58) TABLE-US-00004 TABLE 4 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 800 99 Reuse three times Crude oil-water 850 99 Reuse three times Edible oil-water 780 99 Reuse three times Hexane-water Separation was not proper Toluene-water 800 98 Reuse three times

Example 32

(59) 900 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 40 min under microwave/autoclave conditions. 100 mg Bovine Serum albumin (BSA) was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 60 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, but not suitable for separation experiments. Colour leaching was observed in aqueous solutions.

Example 33

(60) 2700 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 25 min under microwave/autoclave conditions. 300 mg Bovine Serum albumin (BSA) was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, but not suitable for separation experiments. Colour leaching was observed in aqueous solutions.

Example 34

(61) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 30 min under microwave/autoclave conditions. 200 mg phenylalanine was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin, and gradually cooled to room temperature (25 C.) to form a hydrogel. After 10 min, the colour of the whole solution started changing from a transparent solution to light blue in colour due to cross-linking, and the resultant hydrogel was left for 12 days at room temperature (25 C.) to allow for complete crosslinking reaction. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and suitable for separation experiments. Membrane was recycled more than three times and performance was almost identical up to three cycles.

(62) TABLE-US-00005 TABLE 5 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 520 98 Reuse three times Crude oil-water 500 98 Reuse three times Edible oil-water 530 98 Reuse three times Hexane-water Separation was not proper Toluene-water 450 97 Reuse three times

Example 35

(63) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 20 min under microwave/autoclave conditions. 200 mg BSA was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin. Heat at 80 degree Celsius for 20 min on hot plate then gradually cooled to room (25 C.) temperature to form a hydrogel. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and suitable for separation experiments. Membrane was recycled more than two times and performance was almost identical up to two cycles.

(64) TABLE-US-00006 TABLE 5 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 330 97 Reuse two times Crude oil-water 320 97 Reuse two times Edible oil-water 340 98 Reuse two times Toluene-water 300 97 Reuse two times

Example 36

(65) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 30 min under microwave/autoclave conditions. 200 mg BSA was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 80 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin. After that heat at 80 degree Celsius for 120 min on hot plate then gradually cooled to room (25 C.) temperature to form a hydrogel. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and suitable for separation experiments.

(66) TABLE-US-00007 TABLE 5 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Oil spill 370 97 Not reuse Crude oil-water 410 98 Not reuse Edible oil-water 380 98 Not reuse Toluene-water 340 97 Not reuse

Example 37

(67) 1800 mg agarose was dissolved in 75 ml distilled water by heating at 100 degree Celsius for 30 min under microwave/autoclave conditions. 200 mg BSA was dissolved in 25 ml distilled water under ambient conditions, and was added in agarose solution under stirring condition at 70 degree Celsius followed by the addition of 40 mg naturally occurring crosslinker genipin. After that heat at 80 degree Celsius for 300 min on hot plate then gradually cooled to room (25 C.) temperature to form a hydrogel. After that, crosslinked hydrogel was cut to 0.4 mm thick slices and lyophilized at a freeze-drying temperature of 85 C. under vacuum to obtain porous foam membranes. The resulting membrane was flexible, spongy, and suitable for separation experiments.

(68) TABLE-US-00008 TABLE 5 Flux rate dependency on the type of solvent mixtures. Flux rate % Oil Type of mixture (L.m.sup.2 .Math. h.sup.1) rejection Remarks Crude oil-water 260 98 Not reuse Edible oil-water 250 98 Not reuse
Novel Feature of the Invention Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using eco-friendly materials. Recognizing that, preparation of superhydrophilic biodegradable patible crosslinked foam membranes using natural polymers. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using seaweed derived polysaccharides. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using seaweed derived polysaccharides. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using hybrids of natural polymers. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using hybrids of seaweed polysaccharides and other biopolymers. Recognizing that, preparation of superhydrophilic biodegradable cross linked foam membranes using hybrids of seaweed polysaccharides and amino polymers. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes using hybrids of seaweed polysaccharides and amino compounds. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes having porous structure. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes with the tailored porosity. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes as a substitute of conventional membrane working under high pressure for numerous applications including the separation of oil-water emulsions. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes as a substitute of conventional membrane working under high pressure for potential applications including the separation of hexane-water mixtures. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes as a substitute of conventional membrane working under high pressure for potential applications including the separation of toluene-water mixtures. Recognizing that, preparation of superhydrophilic biodegradable crosslinked foam membranes as a substitute of conventional membrane working under high pressure for potential applications including the separation of oil spell-water mixtures. Recognizing that, the environmental pollution arises by synthetic membranes may be harmful but the superhydrophilic biodegradable crosslinked foam membranes produced with this process will be better for the eco-system. Recognizing that, sterilization of the superhydrophilic biodegradable crosslinked foam membranes up to 90 C. can be done under autoclave conditions may be useful in pharmaceutical applications with required specifications. Recognizing that, these superhydrophilic biodegradable crosslinked foam membranes can be used for making ion exchange tools/electrochemical tools/films/membranes with required specifications for the targeted applications.
Advantages of the Invention Recognizing the fact that separations of different mixtures including oil-water mixtures and emulsions inevitably requires the use of suitable membranes and that the non-biodegradability of existing membranes can pose a serious threat where separation is undertaken on very large scale, leading to massive problem of pollution with solid waste, the present invention provides a solution to the problem by providing superhydrophilic biodegradable foam membranes which can be used for energy-efficient and eco-friendly membrane separations. By blending amino compounds and amino polymers such as gelatin, chitosan, etc. onto the hydrophilic seaweed polysaccharides it is possible to impart stability to the prepared foam membranes without compromising excessively on their biodegradability, especially in soil. The prepared superhydrophilic biodegradable foam membranes exhibit high thermal stability which allows them to be sterilized at high temperature for wider applications such as in pharmaceutical applications. The prepared superhydrophilic biodegradable foam membranes exhibit stability in water up to 90 degree Celsius which may be used for wider aqueous applications such as oil-water separation.