Indian Patents. 279260:A POROUS ABPBI (PHOSPHORIC ACID DOPED POLY(2,5-BENZIMIDAZOLE)) MEMBRANE

Title of Invention	A POROUS ABPBI (PHOSPHORIC ACID DOPED POLY(2,5-BENZIMIDAZOLE)) MEMBRANE
Abstract	A stable porous ABPBI membrane stable to acids, bases, solvents and autoclaving is disclosed. The membrane finds use for separation of solutes in solution in acids, bases and solvents.

Full Text	Technical field of the invention: The present invention relates to the stable porous ABPBI membrane. More particularly, the present invention provides a process for the preparation of ABPBI based porous membranes. The ABPBI porous membranes have excellent stability towards strong acids, bases, common organic solvents and harsh environmental conditions. Background and prior art: Polybenzimidazole(PBI) based on diaminobenzidine (DAB) and isophthalic acid (IPA) is known as PBI-I and is soluble in polar aprotic solvents such as N,N-dimethyl acetamide [Li et al. Chem. Mater. 15 (2003) pp. 4896-4915]; while AB(polybenzimidazole) (ABPBI) is soluble only in strong acids such as sulfuric acid, formic acid, trifluoroacetic acid, phosphoric and poly(phosphoric acid) [Asensio et al. Fuel cells 5 No. 3 (2005) pp. 336-343]. Monomer cost and synthesis time for ABPBI are much lower than that for PBI- I. Chung et al. in US 4842740 disclosed a membrane prepared from the blend of polyarylates with PBI-I polymer. The addition of polyarylate to the polybenzimidazole membrane allows the composition to be more thermally processable and less susceptible to moisture. These membranes show high regeneration capacity while retaining good flux ranges. Asensio et al. in J. Electrochem. Soc. 151 (2) (2004) pp. A304-A310 prepared membrane based on poly(2,5-benzimidazole) (ABPBI) by simultaneously doping and casting from ABPBI/phosphoric acid/methane sulfonic acid solution. However, these membranes are used for polymer electrolyte membrane fuel cell (PEMFC). Wang et al. in AlChe 52 (2006) pp. 1363-1377 reported PBI based nanofiltration (NF) membranes (hollow fibers) with mean effective pore radius of 0.348 run for cephalexin separation, which was dependent on the pore size and the electrostatic interactions between solute and the membrane. Wang et al, J. Membr. Sci. 281 (2006) pp. 307-315 prepared PBI based NF membranes with molecular weight cut-off (MWCO) of 525 Da exhibited V-shaped chromate rejection curve with an increase in pH. The above prior arts show PBI based porous membranes are based on (poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole) (PBI-I) polymer. However, these PBI membranes suffer from drawbacks with respect to stability and solubility in solvents such as NaOH (2.5N) and H2SO4 (25N). Dense ABPBI membranes with good thermo chemical properties are known for PEMFC applications, but are not known for their stability towards strong acid, bases and organic solvents. Therefore there is a clear need in prior art for porous ABPBI membranes with stability to acids, bases and solvents. Further the need for porous ABPBI membranes that can withstand concentrated acid, base and organic solvents under harsh operating conditions has not been addressed by prior art documents. Objective of the present invention The main objective of the present invention is to provide stable porous ABPBI membrane that can be used for separation of solutes from solutions in acids, bases and organic solvents. Another objective of the invention is to prepare membrane by varying its membrane preparation parameters to improve membrane performance. It is also an objective of the present invention to provide a single membrane which has a potential to withstand harsher environmental conditions such as concentrated acid, base, organic solvents and autoclaving conditions without need of any treatment processes such as cross linking, annealing and such like. Summary of the invention: Accordingly, the present invention relates to stable porous ABPBI membrane. The present invention also provides a method for the preparation of porous ABPBI membrane. This porous ABPBI membrane is stable to acids, bases, solvents and autoclaving. The membrane is stable to 25 N sulfuric acid at ambient and 2.5N sodium hydroxide at 100 °C. The membrane of the present invention finds its use for separation of solutes in solution in acids, bases and solvents. In an embodiment of the present invention, wherein a porous ABPBI membrane is stable to acids, bases, organic solvents and autoclaving. In another embodiment of the present invention, wherein said membrane is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents. In another embodiment of the present invention, wherein said membrane is stable in concentrated inorganic acids. In another embodiment of the present invention, wherein said membrane is stable in concentrated base solutions. In another embodiment of the present invention, wherein the concentrated acid is 25 N sulfuric acid and the concentrated base is 2.5N sodium hydroxide. In another embodiment of the present invention, wherein the concentration of used ABPBI is up to 15%. In another embodiment of the present invention, a process for the preparation of the porous ABPBI membrane as claimed in claim 1, wherein said process comprises: a. dissolving ABPBI polymer in a solvent to form dope solution; b. casting a film of dope solution as obtained in step (a) optionally on a porous support; c. holding film as obtained in step (b) in air up to 5 minutes in ambient condition and d. coagulating film as obtained in step (c) in a non solvent bath at temperature from 0 -150 °C to obtain porous membrane. In another embodiment of the present invention, wherein solvent used in step (a) is concentrated acid, selected from the group consisting of methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof. In another embodiment of the present invention, wherein, the ABPBI polymer is dissolved in solvent or combination of solvents. In another embodiment of the present invention, wherein the solvent is optionally heated to dissolve the polymer. In another embodiment of the present invention, wherein the membrane is casted on support selected from the group consisting of glass, polyester, polypropylene, polyethylene, polyetheretherketone, metallic plates and ceramics. In another embodiment of the present invention, wherein, the coagulation bath comprises non solvent, alone or in combination with a solvent. In another embodiment of the present invention, wherein, the non solvent is selected from water, alcohol, and base solution, preferably inorganic base. In another embodiment of the present invention, wherein, the solvent is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof. Description of figures: Figure 1 Rejection (R) of ABPBI membranes prepared by varying polymer concentration in dope solution and nonsolvent. Figure 2 Rejection (R) of membranes prepared using different supports and 6% ABPBI in dope solution. Detailed description of the invention: In accordance with the invention, a porous ABPBI membrane is disclosed. The membrane of the invention is up to 300 u in thickness comprising up to 15% by weight of the polymer. The membrane of the invention is prepared by a process comprising: a. Dissolving ABPBI polymer in a solvent to form dope solution; b. Casting a film of dope solution optionally on a porous support; c. Coagulating the dope solution in the non solvent bath to obtain porous membrane. The solvent for dissolving the ABPBI polymer is concentrated acids selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid and poly (phosphoric acid). In one embodiment of the invention the solvent is used alone. In another embodiment of the invention, the solvents are used in combinations. The ABPBI polymer is dissolved in the solvent optionally with the aid of heat. The solution is heated to temperature up to 150 °C to dissolve the polymer in the solvent. The membranes are casted by varying gelation temperature and air dry time prior to dipping in non solvent bath. Water and 0.5N NaOH are used as a non solvent. The membrane is prepared by phase inversion. Supported membranes are prepared using appropriate porous support material selected from polyester, polypropylene, polyethylene, polyetheretherketone, glass, ceramic, metallic plates and such like. The dope solution may optionally comprise additives. For the membrane formation, the film of polymer is exposed to air for different time durations up to 5 minutes. The resulting polymer film is placed in coagulation bath. The coagulation bath comprises non solvent or combination of non solvent and solvent. The non solvent is selected from water, base solution, preferably inorganic base and alcohols. The preferred non-solvent is water. The temperature of coagulation bath is maintained in the range of 0 - 150 °C. The solvent is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly (phosphoric acid), alone or in combinations thereof. The membrane of the invention is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents. The membrane is stable in concentrated inorganic acids and concentrated base solutions. The membrane is stable in 25 N sulfuric acid and 2.5N sodium hydroxide as exemplified herein. The membrane is stable at high pressure and high temperature conditions as exemplified herein in autoclaving conditions. The effect on water flux of the membrane of the invention is studied after treatment of membrane such as acid, base, organic solvent and autoclaving and compared with the initial flux exhibited by the membrane. The membrane of the invention is found to be stable to various treatment conditions subjected to with no substantial effect on flux as exemplified herein. The membrane of the invention finds its use for separations of solute from solvents. The solutes are in solvents selected from acids, bases and organic solvents. The solvents for the solutes are used alone or in combinations of said solvents. The solutes are selected from carboxylic acids, polymers, high molecular weight dyes, auxiliary chemicals, enzymes, surfactants, oxidizing and reducing agents, crude oil, effluents from textile and dyeing industry, lignin, caustic pulp, black liquor, phospholipids, free fatty acids, waxes, coloring pigments and such like. The following examples are given as a specific illustration of the invention. However, the invention is not limited to the details of these examples. Example 1 ABPBI was synthesized by self condensation of 3,4-diaminobenzoic acid (DABA) in polyphophoric acid (PPA) as shown in Scheme 1 below. (Table Removed) 3,4-Diaminobenzoic acid Scheme 1. Synthetic route of ABPBI A three necked 1 liter round-bottom flask equipped with an overhead stirrer, N2 inlet and CaCl2 guard tube was charged with PPA ( polyphosphoric acid) (500 g) and heated at 170 °C. DABA (3, 4 diamino benzoic acid) (25 g) was added with continuous stirring and heating continued for 1 hour. The temperature was raised to 200 °C and allowed to stir for 30 minutes. Then reaction mixture was precipitated in water, the polymer thus obtained was crushed and thoroughly washed with water till neutral to pH. It was then kept in 10% NaOH solution for 16 hours, washed with water till neutral to pH, soaked in acetone for 15 hour and dried in vacuum oven at 80 °C for 24 hours. Example 2 The dope solution of ABPBI was prepared by dissolving 4 g of polymer as obtained in example 1 into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient (at 27 °C) and then degassed to remove trapped gases. This dope solution was casted on to a non-woven polypropylene fabric (FO2470) with air-dry time of 8 sec, before it entered into the gelation bath containing water as the non-solvent at 20 °C. The formed membrane was designated as M-6. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1. Example 3 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-l. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1. Example 4 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membrane was prepared on FO2470 non-woven support fabric and was designated as M-5. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was 0.5N NaOH. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1. Example 5 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 10 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-7. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 6 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 10 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-8. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 7 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 40 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-9. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 8 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 40 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The membrane was designated as M-10. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 9 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 60 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-11. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 10 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 60 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-12. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 11 The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polyester H3160, 3324 and 3265 non-woven support fabric and designated as M-2, M-3 and M-4 respectively. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was water. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 2. Example 12 The stability in different organic solvents (DMF, DMAc, IP A, hexane, chloroform, toluene and THF) and autoclaving condition (at 15 psi pressure and 121 °C for 20 min.) was analyzed by using membranes of Example 2. Solvent flux through the membrane was measured after dipping into the respective solvent for 24 hours. In case of water immiscible solvents like chloroform, toluene and hexane, membranes were dipped initially in IP A (24 hours) and then in the respective solvents (24 hours). Effect of solvent treatment on the membrane morphology was analyzed by measuring water flux after the solventtreatment and compared with initial flux. Membranes showed excellent stability in almost all solvents except hexane. The results are summarized in Table 3. Example 13 The stability in hexane was analyzed by using membranes of Example 3 and 11. Change in water flux was measured by following the procedure as given in Example 12. The results are summarized in Table 4. Example 14 The stability in 25N H2SO4 and 2.5N NaOH was analyzed by using membranes of Example 2 and 3. Change in water flux was measured by following the procedure as given in Example 12. The results are summarized in Table 5. Table 1 Water flux analysis of membranes prepared using different porous supports. a: At 1 bar pressure. Table 2 Effect of air dry time and coagulation bath temperature on membrane flux. (Table Removed) Table 4 Hexane stability of membranes prepared using different porous supports. (Table Removed) Table 5 Change in water flux after treatment of concentrated acid and base. (Table Removed) We Claim: 1. A porous ABPBI (Phosphoric Acid Doped Poly(2,5-benzimidazole)) membrane wherein the membrane is stable to acids, bases, organic solvents and autoclaving. 2. The membrane of claim 1, wherein said membrane is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents. 3. The membrane of claim 1, wherein said membrane is stable in concentrated inorganic acids. 4. The membrane of claim 1, wherein said membrane is stable in concentrated base solutions. 5. The membrane of claims 3 and 4, wherein the concentrated acid is 25 N sulfuric acid and the concentrated base is 2.5N sodium hydroxide. 6. The membrane as claimed in any of the preceding claims wherein the concentration of used ABPBI is up to 15%. 7. A process for the preparation of the porous ABPBI membrane as claimed in claim 1, wherein said process comprises: a. dissolving ABPBI polymer in a solvent to form dope solution; b. casting a film of dope solution as obtained in step (a) optionally, on a porous support; c. holding film as obtained in step (b) in air up to 5 minutes in ambient condition and d. coagulating film as obtained in step (c) in a non solvent bath at temperature from 0 -150 °C to obtain porous membrane. 8. The process of claim 7, wherein solvent used in step (a) is concentrated acid, selected from the group consisting of methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof. 9. The process of claim 7, wherein, the ABPBI polymer is dissolved in a solvent or combination of solvents. 10. The process of claim 7, wherein the solvent is optionally heated to dissolve the polymer. 11. The process of claim 7, wherein the membrane is casted on support selected from the group consisting of glass, polyester, polypropylene, polyethylene, polyetheretherketone, metallic plates and ceramics. 12. The process of claim 7, wherein, the coagulation bath comprises non solvent, alone or in combination with a solvent. 13. The process of claim 13, wherein, the non solvent used is selected from water, alcohol, and base solution, preferably inorganic base. 14. The process of claim 13, wherein, the solvent used is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof. 15. The membrane as claimed in any of the preceding claims, wherein said membrane is used for separations of solute from solvents selected from acids, bases and organic solvents, alone or in combinations thereof.

Full Text

Technical field of the invention:
The present invention relates to the stable porous ABPBI membrane. More particularly, the present invention provides a process for the preparation of ABPBI based porous membranes. The ABPBI porous membranes have excellent stability towards strong acids, bases, common organic solvents and harsh environmental conditions.
Background and prior art:
Polybenzimidazole(PBI) based on diaminobenzidine (DAB) and isophthalic acid (IPA) is
known as PBI-I and is soluble in polar aprotic solvents such as N,N-dimethyl acetamide
[Li et al. Chem. Mater. 15 (2003) pp. 4896-4915]; while AB(polybenzimidazole)
(ABPBI) is soluble only in strong acids such as sulfuric acid, formic acid, trifluoroacetic
acid, phosphoric and poly(phosphoric acid) [Asensio et al. Fuel cells 5 No. 3 (2005) pp.
336-343]. Monomer cost and synthesis time for ABPBI are much lower than that for PBI-
I.
Chung et al. in US 4842740 disclosed a membrane prepared from the blend of
polyarylates with PBI-I polymer. The addition of polyarylate to the polybenzimidazole
membrane allows the composition to be more thermally processable and less susceptible
to moisture. These membranes show high regeneration capacity while retaining good flux
ranges.
Asensio et al. in J. Electrochem. Soc. 151 (2) (2004) pp. A304-A310 prepared membrane
based on poly(2,5-benzimidazole) (ABPBI) by simultaneously doping and casting from
ABPBI/phosphoric acid/methane sulfonic acid solution. However, these membranes are
used for polymer electrolyte membrane fuel cell (PEMFC).
Wang et al. in AlChe 52 (2006) pp. 1363-1377 reported PBI based nanofiltration (NF)
membranes (hollow fibers) with mean effective pore radius of 0.348 run for cephalexin
separation, which was dependent on the pore size and the electrostatic interactions
between solute and the membrane.
Wang et al, J. Membr. Sci. 281 (2006) pp. 307-315 prepared PBI based NF membranes
with molecular weight cut-off (MWCO) of 525 Da exhibited V-shaped chromate
rejection curve with an increase in pH.
The above prior arts show PBI based porous membranes are based on (poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole) (PBI-I) polymer. However, these PBI membranes suffer from drawbacks with respect to stability and solubility in solvents such as NaOH (2.5N) and H2SO4 (25N). Dense ABPBI membranes with good thermo chemical properties are known for PEMFC applications, but are not known for their stability towards strong acid, bases and organic solvents.
Therefore there is a clear need in prior art for porous ABPBI membranes with stability to acids, bases and solvents. Further the need for porous ABPBI membranes that can withstand concentrated acid, base and organic solvents under harsh operating conditions has not been addressed by prior art documents.
Objective of the present invention
The main objective of the present invention is to provide stable porous ABPBI membrane that can be used for separation of solutes from solutions in acids, bases and organic solvents.
Another objective of the invention is to prepare membrane by varying its membrane preparation parameters to improve membrane performance.
It is also an objective of the present invention to provide a single membrane which has a potential to withstand harsher environmental conditions such as concentrated acid, base, organic solvents and autoclaving conditions without need of any treatment processes such as cross linking, annealing and such like.
Summary of the invention:
Accordingly, the present invention relates to stable porous ABPBI membrane. The present invention also provides a method for the preparation of porous ABPBI membrane. This porous ABPBI membrane is stable to acids, bases, solvents and autoclaving. The membrane is stable to 25 N sulfuric acid at ambient and 2.5N sodium hydroxide at 100 °C. The membrane of the present invention finds its use for separation of solutes in solution in acids, bases and solvents.
In an embodiment of the present invention, wherein a porous ABPBI membrane is stable to acids, bases, organic solvents and autoclaving.
In another embodiment of the present invention, wherein said membrane is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents.
In another embodiment of the present invention, wherein said membrane is stable in concentrated inorganic acids.
In another embodiment of the present invention, wherein said membrane is stable in concentrated base solutions.
In another embodiment of the present invention, wherein the concentrated acid is 25 N sulfuric acid and the concentrated base is 2.5N sodium hydroxide.
In another embodiment of the present invention, wherein the concentration of used ABPBI is up to 15%.
In another embodiment of the present invention, a process for the preparation of the porous ABPBI membrane as claimed in claim 1, wherein said process comprises:
a. dissolving ABPBI polymer in a solvent to form dope solution;
b. casting a film of dope solution as obtained in step (a) optionally on a
porous support;
c. holding film as obtained in step (b) in air up to 5 minutes in ambient
condition and
d. coagulating film as obtained in step (c) in a non solvent bath at
temperature from 0 -150 °C to obtain porous membrane.
In another embodiment of the present invention, wherein solvent used in step (a) is concentrated acid, selected from the group consisting of methane sulfonic acid, sulfuric
acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof.
In another embodiment of the present invention, wherein, the ABPBI polymer is dissolved in solvent or combination of solvents.
In another embodiment of the present invention, wherein the solvent is optionally heated to dissolve the polymer.
In another embodiment of the present invention, wherein the membrane is casted on support selected from the group consisting of glass, polyester, polypropylene, polyethylene, polyetheretherketone, metallic plates and ceramics.
In another embodiment of the present invention, wherein, the coagulation bath comprises non solvent, alone or in combination with a solvent.
In another embodiment of the present invention, wherein, the non solvent is selected from water, alcohol, and base solution, preferably inorganic base.
In another embodiment of the present invention, wherein, the solvent is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof.
Description of figures:
Figure 1 Rejection (R) of ABPBI membranes prepared by varying polymer concentration
in dope solution and nonsolvent.
Figure 2 Rejection (R) of membranes prepared using different supports and 6% ABPBI
in dope solution.
Detailed description of the invention:
In accordance with the invention, a porous ABPBI membrane is disclosed. The membrane of the invention is up to 300 u in thickness comprising up to 15% by weight of the polymer. The membrane of the invention is prepared by a process comprising:
a. Dissolving ABPBI polymer in a solvent to form dope solution;
b. Casting a film of dope solution optionally on a porous support;
c. Coagulating the dope solution in the non solvent bath to obtain porous
membrane.
The solvent for dissolving the ABPBI polymer is concentrated acids selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid and poly (phosphoric acid). In one embodiment of the invention the solvent is used alone. In another embodiment of the invention, the solvents are used in combinations. The ABPBI polymer is dissolved in the solvent optionally with the aid of heat. The solution is heated to temperature up to 150 °C to dissolve the polymer in the solvent.
The membranes are casted by varying gelation temperature and air dry time prior to dipping in non solvent bath. Water and 0.5N NaOH are used as a non solvent.
The membrane is prepared by phase inversion. Supported membranes are prepared using appropriate porous support material selected from polyester, polypropylene, polyethylene, polyetheretherketone, glass, ceramic, metallic plates and such like. The dope solution may optionally comprise additives.
For the membrane formation, the film of polymer is exposed to air for different time durations up to 5 minutes. The resulting polymer film is placed in coagulation bath. The coagulation bath comprises non solvent or combination of non solvent and solvent. The non solvent is selected from water, base solution, preferably inorganic base and alcohols. The preferred non-solvent is water. The temperature of coagulation bath is maintained in the range of 0 - 150 °C. The solvent is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly (phosphoric acid), alone or in combinations thereof.
The membrane of the invention is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents. The membrane is stable in concentrated inorganic acids and concentrated base solutions. The membrane is stable in 25 N sulfuric acid and 2.5N sodium hydroxide as exemplified herein. The membrane is stable at high pressure and high temperature conditions as exemplified herein in autoclaving conditions. The effect on water flux of the membrane of the invention is studied after treatment of membrane such as acid, base, organic solvent and autoclaving and compared with the initial flux exhibited by the membrane. The membrane of the invention is found to be stable to various treatment conditions subjected to with no substantial effect on flux as exemplified herein.
The membrane of the invention finds its use for separations of solute from solvents. The solutes are in solvents selected from acids, bases and organic solvents. The solvents for the solutes are used alone or in combinations of said solvents. The solutes are selected from carboxylic acids, polymers, high molecular weight dyes, auxiliary chemicals, enzymes, surfactants, oxidizing and reducing agents, crude oil, effluents from textile and dyeing industry, lignin, caustic pulp, black liquor, phospholipids, free fatty acids, waxes, coloring pigments and such like.
The following examples are given as a specific illustration of the invention. However, the invention is not limited to the details of these examples. Example 1
ABPBI was synthesized by self condensation of 3,4-diaminobenzoic acid (DABA) in polyphophoric acid (PPA) as shown in Scheme 1 below.

(Table Removed)
3,4-Diaminobenzoic acid
Scheme 1. Synthetic route of ABPBI
A three necked 1 liter round-bottom flask equipped with an overhead stirrer, N2 inlet and CaCl2 guard tube was charged with PPA ( polyphosphoric acid) (500 g) and heated at 170 °C. DABA (3, 4 diamino benzoic acid) (25 g) was added with continuous stirring and heating continued for 1 hour. The temperature was raised to 200 °C and allowed to stir for 30 minutes. Then reaction mixture was precipitated in water, the polymer thus obtained was crushed and thoroughly washed with water till neutral to pH. It was then kept in 10% NaOH solution for 16 hours, washed with water till neutral to pH, soaked in acetone for 15 hour and dried in vacuum oven at 80 °C for 24 hours.
Example 2
The dope solution of ABPBI was prepared by dissolving 4 g of polymer as obtained in example 1 into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient (at 27 °C) and then degassed to remove trapped gases. This dope solution was casted on to a non-woven polypropylene fabric (FO2470) with air-dry time of 8 sec, before it entered into the gelation bath containing water as the non-solvent at 20 °C. The formed membrane was designated as M-6. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1. Example 3
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-l. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1.
Example 4
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membrane was prepared on FO2470 non-woven support fabric and was designated as M-5. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was 0.5N NaOH. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 1.
Example 5
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 10 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-7. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2.
Example 6
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 10 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-8. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2.
Example 7
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 40 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-9. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2.
Example 8
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 40 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The membrane was designated as M-10. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2.
Example 9
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 60 °C gelation temperature and exposed in air for 32 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-11. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2.
Example 10
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polypropylene (FO2470) non-woven support fabric. Membranes were casted at 60 °C gelation temperature and exposed in air for 64 seconds prior to dipping in the non solvent bath. The non solvent used was water. The formed membrane was designated as M-12. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 2. Example 11
The dope solution of ABPBI was prepared by dissolving 6 g of polymer into 100 g of methane sulfonic acid (MSA) at 70 °C. The solution was stirred under dry atmosphere for 48 hours. The formed solution was cooled at ambient and then degassed to remove trapped gases. Membranes were prepared on polyester H3160, 3324 and 3265 non-woven support fabric and designated as M-2, M-3 and M-4 respectively. Membranes were casted at 20 °C gelation temperature and exposed in air for 8 seconds prior to dipping in the non solvent bath. The non solvent used was water. The thickness of the formed membrane was ~ 200 µ. Water flux of this membrane is given in Table 1 while MWCO is given in Figure 2. Example 12
The stability in different organic solvents (DMF, DMAc, IP A, hexane, chloroform, toluene and THF) and autoclaving condition (at 15 psi pressure and 121 °C for 20 min.) was analyzed by using membranes of Example 2. Solvent flux through the membrane was measured after dipping into the respective solvent for 24 hours. In case of water immiscible solvents like chloroform, toluene and hexane, membranes were dipped
initially in IP A (24 hours) and then in the respective solvents (24 hours). Effect of solvent treatment on the membrane morphology was analyzed by measuring water flux after the
solventtreatment and compared with initial flux. Membranes showed excellent stability in almost all solvents except hexane. The results are summarized in Table 3.
Example 13
The stability in hexane was analyzed by using membranes of Example 3 and 11. Change in water flux was measured by following the procedure as given in Example 12. The results are summarized in Table 4.
Example 14
The stability in 25N H2SO4 and 2.5N NaOH was analyzed by using membranes of Example 2 and 3. Change in water flux was measured by following the procedure as given in Example 12. The results are summarized in Table 5.
Table 1 Water flux analysis of membranes prepared using different porous supports.
a: At 1 bar pressure.
Table 2 Effect of air dry time and coagulation bath temperature on membrane flux.
(Table Removed)
Table 4 Hexane stability of membranes prepared using different porous supports.
(Table Removed)
Table 5 Change in water flux after treatment of concentrated acid and base.
(Table Removed)

We Claim:
1. A porous ABPBI (Phosphoric Acid Doped Poly(2,5-benzimidazole)) membrane wherein the membrane is stable to acids, bases, organic solvents and autoclaving.
2. The membrane of claim 1, wherein said membrane is stable to organic solvents comprising of protic and aprotic polar solvents and non polar solvents.
3. The membrane of claim 1, wherein said membrane is stable in concentrated inorganic acids.
4. The membrane of claim 1, wherein said membrane is stable in concentrated base solutions.
5. The membrane of claims 3 and 4, wherein the concentrated acid is 25 N sulfuric acid and the concentrated base is 2.5N sodium hydroxide.
6. The membrane as claimed in any of the preceding claims wherein the concentration of used ABPBI is up to 15%.
7. A process for the preparation of the porous ABPBI membrane as claimed in claim 1, wherein said process comprises:
a. dissolving ABPBI polymer in a solvent to form dope solution;
b. casting a film of dope solution as obtained in step (a) optionally, on a
porous support;
c. holding film as obtained in step (b) in air up to 5 minutes in ambient
condition and
d. coagulating film as obtained in step (c) in a non solvent bath at
temperature from 0 -150 °C to obtain porous membrane.
8. The process of claim 7, wherein solvent used in step (a) is concentrated acid, selected from the group consisting of methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof.
9. The process of claim 7, wherein, the ABPBI polymer is dissolved in a solvent or combination of solvents.
10. The process of claim 7, wherein the solvent is optionally heated to dissolve the polymer.
11. The process of claim 7, wherein the membrane is casted on support selected from the group consisting of glass, polyester, polypropylene, polyethylene, polyetheretherketone, metallic plates and ceramics.
12. The process of claim 7, wherein, the coagulation bath comprises non solvent, alone or in combination with a solvent.
13. The process of claim 13, wherein, the non solvent used is selected from water, alcohol, and base solution, preferably inorganic base.
14. The process of claim 13, wherein, the solvent used is acid selected from methane sulfonic acid, sulfuric acid, phosphoric acid, formic acid, trifluoro acetic acid, poly(phosphoric acid), alone or in combinations thereof.
15. The membrane as claimed in any of the preceding claims, wherein said membrane is used for separations of solute from solvents selected from acids, bases and organic solvents, alone or in combinations thereof.

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Patent Number

279260

Indian Patent Application Number

434/DEL/2010

PG Journal Number

03/2017

Publication Date

20-Jan-2017

Grant Date

17-Jan-2017

Date of Filing

26-Feb-2010

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001

Inventors:

#	Inventor's Name	Inventor's Address
1	ULHAS KANJAIYALAL KHARUL	NATIONAL CHEMICAL LABORATORY DR. HOMI BHABHA ROAD PUNE-411008 (MAHARASHTRA) INDIA
2	HARSHADA RAMESH LOHOKARE	NATIONAL CHEMICAL LABORATORY DR. HOMI BHABHA ROAD PUNE411008 (MAHARASHTRA) INDIA

PCT International Classification Number

B01D67/00;

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA