US20120123079A1 - Polyimide membranes made of polymerization solutions - Google Patents

Polyimide membranes made of polymerization solutions Download PDF

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US20120123079A1
US20120123079A1 US13/384,685 US201013384685A US2012123079A1 US 20120123079 A1 US20120123079 A1 US 20120123079A1 US 201013384685 A US201013384685 A US 201013384685A US 2012123079 A1 US2012123079 A1 US 2012123079A1
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polyimide
membrane
solution
water
hollow fiber
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Markus Ungerank
Goetz Baumgarten
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Evonik Fibres GmbH
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Evonik Fibres GmbH
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
    • B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
    • B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
    • B01D67/00091—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching by evaporation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
    • B01D67/0011—Casting solutions therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
    • B01D67/0013—Casting processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/08—Hollow fibre membranes
    • B01D69/087—Details relating to the spinning process
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1042—Copolyimides derived from at least two different tetracarboxylic compounds or two different diamino compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1067—Wholly aromatic polyimides, i.e. having both tetracarboxylic and diamino moieties aromatically bound
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L79/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen or carbon only, not provided for in groups C08L61/00 - C08L77/00
    • C08L79/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
    • C08L79/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/15—Use of additives
    • B01D2323/18—Pore-control agents or pore formers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/02—Details relating to pores or porosity of the membranes
    • B01D2325/022—Asymmetric membranes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

  • the invention concerns polyimide membranes produced directly from a polyimide polymerization solution without the polyimide having been isolated in the form of a solid material, particularly not as dried solid material and more particularly not as dried powder, and then redissolved.
  • the polyimide membranes concerning the invention can be either flat sheet membranes or hollow fiber membranes.
  • the polyimide membranes can be not only porous membranes in the form of micro-, ultra- or nanofiltration membranes but also aporous membranes for separation of gases. All the membranes are integrally asymmetrical membranes and are produced by a phase inversion process.
  • This invention has for its object to provide a production process for polyimides that does not use any substances which would be a disruptive influence in the subsequent membrane production process. It further has for its object that the process provided by the invention shall make it possible to produce membranes having sufficient mechanical properties.
  • phase inversion membranes generally requires polymers that are soluble in conventional water-miscible solvents. This process is currently being used to produce thousands of metric tons of polyether sulfone membranes.
  • Possible solvents include inter alia but not exclusively dimethylformamide (DMF), dimethylacetamide or N-methylpyrrolidone.
  • DMF dimethylformamide
  • Many additives such as cosolvents, nonsolvents, pore-formers, hydrophilicizers etc are admixed in order to influence the properties of the membranes.
  • the starting point for this is usually a pellet material, the casting solution being produced by pasting up with the solvents and the additives. Success in membrane production, as elsewhere, depends decisively on the molar mass and the distribution of the polymer used. In general, polymers with high molar masses and narrow distribution are required.
  • P84 is a polymer which is well known in the literature and is used for the production of flat sheet membranes and hollow fiber membranes (US 2006/0156920, WO 04050223, U.S. Pat. No. 7,018,445, U.S. Pat. No. 5,635,067, EP 1457253, U.S. Pat. No. 7,169,885, US 20040177753, U.S. Pat. No. 7,025,804).
  • P84 is marketed in 2 modifications (P84 type 70 and P84 HT) in powder form by HP Polymer of Lenzing in Austria. The customers then redissolve this powder in aprotic dipolar solvents and admix it with additives. Membranes can then be produced therefrom.
  • P84 is also made into a blend with other polymers (US 2006/156920), so that the membranes produced therefrom have sufficiently high stabilities.
  • the disadvantage here is that very good separation properties for gases, plasticization stabilities to CO 2 and chemical stabilities to many solvents are in part disruptively influenced, or even destroyed, by admixing other polymers.
  • the cause for the low molar mass resides in the production process of the P84 powder. It is at this stage that the polymer loses molar mass.
  • the molar masses directly after polymerization and after production of the powder are depicted in Table 1.
  • P84 powder is also used for the production of flat sheet membranes (WO 2007/125367, WO 2000/06293). There are the same problems here as in the production of hollow fiber membranes.
  • Dynamic viscosity ⁇ is ascertained by shearing the polymer solution in a cylindrical gap at a constant 25° C. once by mandating various rotation rates ⁇ (or shear gradients ⁇ ) and then by mandating various shear stresses ⁇ .
  • the shear stress ⁇ is measured at a particular shear gradient.
  • Dynamic viscosity ⁇ computes from ensuing formulae and is reported at a shear gradient of 10 s ⁇ 1 in Pa ⁇ s.
  • Molar mass is determined using a gel permeation chromatography system. The system is calibrated with polystyrene standards. The molar masses reported are therefore to be understood as relative molar masses.
  • Permeabilities to gases are measured by the pressure rise method.
  • a flat sheet film between 10 and 70 ⁇ in thickness has a gas or gas mixture applied to it from one side.
  • the permeate side there is a vacuum (ca. 10 ⁇ 2 mbar) at the start of the test. Then, pressure rise on the permeate side over time is reported.
  • the polymer's permeability can be computed by the following formula:
  • the permeability of hollow fibers is measured using the same pressure rise method.
  • the selectivities of various pairs of gases are pure-gas selectivities.
  • the selectivity between two gases computes from the ratio of permeabilities:
  • Permeances of flat sheet membranes are determined using a Milipore stirred cell pressurized with 5 to 6 bar of nitrogen. What is measured is permeate flux per unit time at a defined pressure. Permeance is given by:
  • Retention R is obtained from the following formula:
  • the problem of molar mass degradation in the production of P84 powder is circumvented by the polymer after the polymerization in an aprotic dipolar solvent not being isolated in the form of a solid material, particularly not as dried solid material and more particularly not as dried powder, but instead the polymerization solution being used directly for producing the membranes.
  • the membrane production process involves the following subsidiary steps:
  • the polyimides are produced via a polycondensation of an aromatic tetracarboxylic anhydride with an aromatic diisocyanate by release of carbon dioxide.
  • Preferably used substances and combinations thereof are described hereinbelow:
  • the polymerization takes place in an aprotic dipolar solvent.
  • Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone and sulfolane are used preferably but not exclusively singly or in mixtures.
  • aromatic dianhydride or mixtures of aromatic dianhydrides being dissolved in concentrations of 10% by weight to 40% by weight, preferably between 18% by weight and 32% by weight and more preferably between 22% by weight and 28% by weight in an aprotic dipolar solvent and heated to from 50° C. to 150° C., preferably 70° C. to 120° C. and more preferably to from 80° C. to 100° C.
  • This solution is admixed with 0.01% by weight to 5% by weight, preferably 0.05% by weight to 1% by weight and more preferably 0.1% by weight to 0.3% by weight of a basic catalyst.
  • Useful catalysts include:
  • the diisocyanate is then added over a period of 1 to 25 hours, preferably 3 to 15 hours and more preferably 5 to 10 hours.
  • R is selected from the group consisting of
  • the result is a clear golden yellow to dark brown polymer solution having a viscosity between 1 and 300 Pa ⁇ s, preferably 20 to 150 Pa ⁇ s and more preferably 40 to 90 Pa ⁇ s.
  • the molar masses Mp are greater than 100 000 g ⁇ mol ⁇ 1 and therefore differ distinctly from the polyimide polymer powders, especially the P84 polymer powders.
  • the polyimide polymer of the present invention is obtained after the reaction as a solute in an aprotic dipolar solvent. There are no disruptive concomitants or by-products in the polymer solution. The viscosity is very high and suitable for production of membranes. For that reason, it is also economically advantageous for the polymer not to be precipitated and then redissolved in the same solvent. The solutions are therefore used directly—without isolating the polymer and preferably also without any other further treatment—for producing the casting solution.
  • the polymer solutions obtained from the polymer condensation have a solids content between 22% by weight and 28% by weight and can be used for producing the casting solution without further treatment.
  • the casting solution of the present invention is notable for the following properties:
  • Casting solution viscosity is ideal when it corresponds to the entanglement point in viscosity plotted as a function of solids content. This point is that point where the function of viscosity versus solids turns from linear to exponential. This point is also very highly dependent on molar mass. The higher the molar mass, the lower the solids content at which entanglement occurs.
  • the casting solutions obtainable via the process according to the present invention differ distinctly from the casting solutions of the prior art. It is only the process of the present invention that provides casting solutions combining a high viscosity with a high molar mass and a narrow molar mass distribution for the polyimide. The processes of the present invention thus make it possible to obtain membranes that have outstanding mechanical properties.
  • the process of the present invention also makes it possible to add additives.
  • Various amounts of additives result in different solids contents, which would then shift the entanglement point. Modulating the molar mass in the polymerization can be used to shift this entanglement point again.
  • voids which are also known as macrovoids, are responsible for lower stability of the membranes to pressure in use, and limit their usefulness for example in use in natural gas cleanup.
  • the formation of macrovoids can be prevented by addition of nonsolvents. Suitable for this are the following water-miscible solvents or mixtures thereof.
  • evaporative removal of volatile cosolvents will also lead to very thin selective layers not only in the gas separation membrane sector but also in the nano- and ultrafiltration membrane sector.
  • the degree of evaporative removal and hence the pore size is influenced by the species of volatile solvent, its concentration, the evaporation time, the casting solution temperature, the amount and temperature of ambient gas in the evaporative removal zone.
  • Useful volatile solvents include the following. They should be water miscible, for example acetone, tetrahydrofuran, methanol, ethanol, propanol, isopropanol, dioxane, diethyl ether.
  • Producing the casting solution is preferably effected by adding additives by metered addition of the mixture of additives or separately from each other in succession.
  • the additives are gradually metered into the mixture under agitation.
  • the metered addition takes between 10 min and 3 hours for preference and between 30 min and 2 hours for particular preference.
  • Adding the cosolvents causes partial precipitation of polyimide at the drop entry point. But the solids dissolve again after a few minutes without leaving a residue.
  • the clear solution is then additionally filtered through a 15 ⁇ steel mesh sieve in order to remove destructive concomitants which would lead to imperfections in the membrane surface.
  • the devolatilized, filtered and additivized polyimide polymer solution is thermostated—preferably to from 20 to 100° C. and more preferably to from 30 to 70° C.
  • the solution is gear pumped through the outer part of a two-material die.
  • the external diameter of the two-material die is 600 ⁇ m, the internal diameter is 160 ⁇ m, pump rate is between 1.3 and 13.5 ml/min.
  • a liquid mixture of water and one or more than one aprotic dipolar solvent in admixture is pumped in the inner part of the two-material die.
  • Useful solvents include inter alia but not exclusively dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone, N-ethylpyrrolidone, sulfolane or dimethyl sulfoxide.
  • the composition is between solvent and water is between 10% by weight and 95% by weight of solvent and 90% by weight and 5% by weight of water, preferably between 30% by weight and 90% by weight of solvent and 70% by weight and 10% by weight of water and more preferably between 50% by weight and 80% by weight of solvent and 50% by weight and 20% by weight of water.
  • Pump rate is between 0.2 ml/min and 10 ml/min.
  • the resulting hollow fiber then enters a tube flooded with a dry thermostated gas.
  • gases include: nitrogen, air, argon, helium, carbon dioxide, methane or other industrial inert gases.
  • Gas temperature is adjusted via a heat exchanger and is preferably between 20 and 250° C., more preferably between 30 and 150° C. and even more preferably between 40 and 120° C.
  • Gas velocity in the tube is preferably between 0.1 and 10 m/min, more preferably between 0.5 and 5 m/min and even more preferably between 1 and 3 m/min.
  • the distance and hence tube length is preferably between 5 cm and one meter and more preferably between 10 and 50 cm.
  • the thread thus conditioned then dips into a water bath to coagulate the polymer mass and thus form the membrane.
  • Water bath temperature is preferably between 1 and 60° C., more preferably between 5 and 30° C. and more preferably between 8 and 16° C.
  • concentration of aprotic dipolar and other solvents such as for example but not exclusively dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone, N-ethylpyrrolidone, sulfolane, dimethyl sulfoxide, tetrahydrofuran, dioxane, isopropanol, ethanol or glycerol in the coagulation bath is between 0.01% by weight and 20% by weight, preferably between 0.1% by weight and 10% by weight and more preferably between 0.2% by weight and 1% by weight.
  • the hollow fibers are hauled off at between 2 and 100 m/min, preferably between 10 and 50 m/min and more preferably between 20 and 40 m/min.
  • the fibers are wound up onto a bobbin and washed in water until the residual solvent content is below 1%. This is followed by treatment in ethanol and hexane.
  • the fibers are then dried—preferably between room temperature and 150° C. and more preferably between 50 and 100° C. Fibers are obtained with external diameters of 100 to 1000 ⁇ m, preferably between 200 and 700 ⁇ m and more preferably between 250 and 400 ⁇ .
  • the process of the present invention thus provides hollow fiber membranes of polyimides that exhibit high separation performances for various gases.
  • An excerpt for various polymers and gases is summarized in Table 2.
  • membranes even under high CO 2 partial pressures scarcely exhibit any increase in methane permeance, retain their selectivity and therefore are scarcely plasticized. This property is necessary to process sour gases with high CO 2 contents and high pressures, as is the case for example with the workup of crude natural gas or crude biogas.
  • the hollow fiber membranes can also be crosslinked with amines.
  • the hollow fiber is crosslinked, this is done subsequent to the washing step.
  • the hollow fiber is passed through a bath containing an amine with 2 or more amino groups per molecule such as, for example, a diamine, triamine, tetraamine or a polyamine.
  • the amine may be primary or secondary or consist of mixtures of primary, secondary and tertiary amines in one molecule.
  • Useful amines include aliphatic amines, aromatic amines and mixed aliphatic-aromatic amines. Silicone-based amines are also possible.
  • aliphatic diamines include inter alia but not exclusively: diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminodecane or diamino compounds of branched or cyclic aliphatics (e.g. cis- and trans-1,4-cyclohexane) and of longer-chain compounds.
  • diaminoethane diaminopropane, diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminodecane or diamino compounds of branched or cyclic aliphatics (e.g. cis- and trans-1,4-cyclohexane) and of longer-chain compounds.
  • Useful aromatic compounds include inter alia but not exclusively: p-phenylenediamines, m-phenylenediamines, 2,4-tolylenediamines, 2,6-tolylenediamines, 4,4′-diaminodiphenyl ether.
  • mixed aliphatic-aromatic amines include inter alia but not exclusively: aminoalkyl-substituted aromatics such as, for example, p-bis(aminomethyl)-benzene.
  • Useful siliconic-based amines include inter alia but not exclusively: bis(aminoalkyl)siloxanes of differing chain length.
  • polyfunctional amines include inter alia but not exclusively the following compounds: oligo- or polyethyleneimines having various molar masses (400 to 200 000 g/mol), N,N′,N′′-trimethylbis-(hexamethylene)triamine, bis(6-aminohexyl)amine
  • Crosslinking is effected by emplacement into or continuous pulling of the entire hollow fiber through a solution of the particular diamine in water or a mixture of water and water-miscible solvents or other solvents which do not influence the membrane structure and which dissolves the particular amines.
  • Possibilities for this are for example but not exclusively:
  • the concentration of diamines is between 0.01% by weight and 10% by weight, but preferably between 0.05% by weight and 5% by weight and more preferably between 0.1% by weight and 1% by weight.
  • the crosslinking solution temperature is between 1 and 100° C., preferably between 10 and 70° C. and more preferably between 20 and 50° C.
  • Residence time is between 10 seconds and 10 hours, preferably between 1 minutes and 60 minutes and more preferably between 2 and 10 min.
  • wash bath temperature is between 10 and 90° C. and preferably between 20 and 60° C.
  • Wash bath residence time is from 1 to 200 minutes, preferably between 2 and 50 minutes and more preferably between 3 and 10 minutes.
  • Hollow fibers are obtained that are no longer soluble in traditional organic solvents such as for example but not exclusively dimethylformamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethyl-urea, dimethyl sulfoxide or sulfolane, acetone, methyl ethyl ketone, diethyl ether, tetrahydrofuran, dioxane, ethyl acetate, dichloromethane, chloroform, toluene, xylene, hexane, heptane or cyclohexane. They can therefore be used in nano-, ultra- and microfiltration in organic solvents.
  • organic solvents such as for example but not exclusively dimethylformamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, tetramethyl-urea, dimethyl sulfoxide or sulfolane,
  • Applicator width can be up to 1.2 m.
  • a calendered backing fleece of polymer fibers preferably but not exclusively in polyimide, polypropylene, polyamide, polyester or polyphenylene sulfide, passes underneath the applicator at a speed of 0.1 to 10 m/min and preferably 1 to 5 m/min.
  • Fleece thickness is between 30 and 300 ⁇ and preferably between 100 and 200 ⁇ .
  • Basis weight is between 20 and 300 g/m 2 and preferably between 50 and 150 g/m 2 .
  • Gap width between applicator and fleece is between 100 and 800 ⁇ and preferably between 200 and 400 ⁇ .
  • the coated fleece enters a channel flooded with a countercurrent stream of gas.
  • gases include inter alia but not exclusively dry air, nitrogen, argon or helium.
  • the gas flowing over the coated fleece moves at a speed in the range from 100 to 5000 m/h and preferably between 200 and 1000 m/h, gas temperatures can be between 10 and 150° C. and preferably between 15 and 90° C.
  • the coated fleece then enters a coagulation bath, the polymer coagulates and forms the desired membrane.
  • the coagulation bath consists of water or mixtures of water and one or more solvents that are miscible with water.
  • Coagulation bath temperature is between 1 and 90° C. and preferably between 10 and 50° C. Following a short residence time of 10 s to 10 min and preferably 1 to 5 min the membrane is wound up in the wet state.
  • wash bath temperature is between 10 and 90° C. and preferably between 20 and 60° C.
  • Wash bath residence time is from 1 to 200 minutes, preferably between 2 and minutes and more preferably between 3 and 10 minutes.
  • the membrane is crosslinked, this is done subsequent to the washing step.
  • the membrane is passed through a bath containing an amine with 2 or more amino groups per molecule such as, for example, a diamine, triamine, tetraamine or polyamine.
  • the amine may be primary or secondary or consist of mixtures of primary, secondary and tertiary amines in one molecule.
  • Useful amines include aliphatic amines, aromatic amines and mixed aliphatic-aromatic amines. Silicone-based amines are also possible.
  • aliphatic diamines include inter alia but not exclusively: diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminodecane or diamino compounds of branched or cyclic aliphatics (e.g. cis- and trans-1,4-cyclohexane) and of longer-chain compounds.
  • diaminoethane diaminopropane, diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminodecane or diamino compounds of branched or cyclic aliphatics (e.g. cis- and trans-1,4-cyclohexane) and of longer-chain compounds.
  • Useful aromatic compounds include inter alia but not exclusively: p-phenylenediamines, m-phenylenediamines, 2,4-tolylenediamines, 2,6-tolylenediamines, 4,4′-diaminodiphenyl ether.
  • mixed aliphatic-aromatic amines include inter alia but not exclusively: aminoalkyl-substituted aromatics such as, for example, p-bis(aminomethyl)-benzene.
  • Useful siliconic-based amines include inter alia but not exclusively: bis(aminoalkyl)siloxanes of differing chain length.
  • Useful representatives of polyfunctional amines include inter alia but not exclusively the following compounds: oligo- or polyethyleneimines having various molar masses (400 to 200 000 g/mol), N,N′,N′′-trimethylbis(hexamethylene)triamine, bis(6-aminohexyl)amine
  • Crosslinking is effected by emplacing the entire membrane into a solution of the particular diamine in water or a mixture of water and water-miscible solvents or other solvents which do not influence the membrane structure and which dissolves the particular amines.
  • the concentration of diamines, the crosslinking solution temperature, the residence time and the way the washing step is carried out correspond to the values and procedures, respectively, indicated above for crosslinking the hollow fibers.
  • the membrane is impregnated to ensure pore preservation during subsequent drying. This is done by dipping the membrane into a mixture of water and a water-miscible high boiler.
  • Possibilities for this are for example but not exclusively: glycerol, polyethylene glycols of differing chain length in admixture or singly, polyethylene glycol dialkyl ethers of different chain lengths in admixture or singly as methyl or ethyl ethers, mono- or diols having a boiling point above 200° C. such as, for example, decanol, 1,4-butanediol, 1,6-hexanediol.
  • the concentration of high boiler in water is between 5% and 95%, but preferably between 25% by weight and 75% by weight.
  • Impregnating solution temperature is between 1 and 100° C., preferably between 10 and 70° C. and more preferably between 20 and 50° C.
  • the residence time is between 10 seconds and 10 hours, preferably between 1 minutes and 60 minutes and more preferably between 2 and 10 min.
  • the membrane After impregnation, the membrane is dried. Drying can be done in the ambient air or continuously in a convective dryer. Drying temperature is in the range from 20 to 200° C. and preferably between 50 and 120° C. Drying time is between 10 seconds and 10 hours, preferably between 1 minutes and 60 minutes and more preferably between 2 and 10 min. After drying, the final membrane is wound up and can be further processed into spiral-wound elements or pocket modules.
  • the flat and hollow fiber membranes of the present invention thus comprise a polyimide having an Mp>100 000 g ⁇ mol ⁇ 1 , preferably 110 000 to 200 000 g ⁇ mol ⁇ 1 and more preferably 120 000 to 170 000 g ⁇ mol ⁇ 1 and a PDI in the range from 1.7 to 2.3 and preferably in the range from 1.8 to 2.1.
  • Mp here corresponds to the peak maximum of the molar mass distribution on calibration against polystyrene standards in 0.01 mol/l of lithium bromide in dimethylformamide.
  • the high molar mass effectuates an improvement in mechanical properties regarding membrane strength and toughness. This is more particularly required at high pressures in the applications.
  • Flat sheet membranes have to withstand at least 40 bar in operation and certain hollow fiber membranes above 100 bar in natural gas enrichment.
  • a high molar mass is also advantageous to achieve a sufficiently high viscosity even at moderate solids contents.
  • Casting solutions require a certain viscosity for stable processing into membranes and hollow fibers and in order that dense and selective layers on the surface may be produced therewith.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1622 g of anhydrous dimethylacetamide.
  • a quantity of 456.4 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 0.45 g of sodium hydroxide.
  • 266.8 g of a mixture of 64% of 2,4-tolylene diisocyanate, 16% of 2,6-tolylene diisocyanate and 20% of 4,4′-diisocyanatodiphenylmethane are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 25% and a viscosity of 49 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1622 g of anhydrous dimethylformamide.
  • a quantity of 456.4 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 0.45 g of sodium hydroxide.
  • 266.8 g of a mixture of 64% of 2,4-tolylene diisocyanate, 16% of 2,6-tolylene diisocyanate and 20% of 4,4′-diisocyanatodiphenylmethane are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 27% and a viscosity of 48 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1800 g of anhydrous N-methylpyrrolidone.
  • a quantity of 456.4 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 0.45 g of sodium hydroxide.
  • 266.8 g of a mixture of 64% of 2,4-tolylene diisocyanate, 16% of 2,6-tolylene diisocyanate and 20% of 4,4′-diisocyanatodiphenylmethane are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 25% and a viscosity of 45 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1622 g of anhydrous N-ethylpyrrolidone.
  • a quantity of 456.4 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 0.45 g of sodium hydroxide.
  • 266.8 g of a mixture of 64% of 2,4-tolylene diisocyanate, 16% of 2,6-tolylene diisocyanate and 20% of 4,4′-diisocyanatodiphenylmethane are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 27% and a viscosity of 87 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1800 g of anhydrous dimethylformamide.
  • a quantity of 473.6 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 1.8 g of diazabicyclooctane.
  • 254.4 g of a mixture of 2,4-tolylene diisocyanate are metered during several hours. In the process, CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 25% and a viscosity of 59 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1622 g of anhydrous dimethylformamide.
  • a quantity of 473.6 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 1.8 g of diazabicyclooctane.
  • 254.4 g of a mixture of 80% of 2,4-tolylene diisocyanate and 20% of 2,6-tolylene diisocyanate are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 27% and a viscosity of 108 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1800 g of anhydrous dimethylformamide.
  • a quantity of 316.4 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 142.8 g of pyromellitic dianhyhdride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 1.8 g of diazabicyclooctane.
  • 283.4 g of a mixture of 80% of 2,4-tolylene diisocyanate and 20% of 2,6-tolylene diisocyanate are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a golden color, a solids content of 27% and a viscosity of 70 Pa ⁇ s.
  • a 3 l glass reactor equipped with stirrer and reflux condenser is initially charged with 1500 g of anhydrous dimethylformamide.
  • a quantity of 369.2 g of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride are dissolved therein and the solution is heated to 90° C.
  • To this solution is added 1.5 g of diazabicyclooctane.
  • 222.3 g of 2,4,6-trimethyl-1,3-phenylene diisocyanate are metered during several hours.
  • CO2 escapes as by-product and a polyimide results directly in solution.
  • the highly viscous solution obtained has a pale yellow color, a solids content of 25% and a viscosity of 5 Pa ⁇ s.
  • the polymerization solutions are filtered neat through a 15 ⁇ metal sieve.
  • the films are produced using an instrument from Elcometer (Elcometer 4340) with an applicator. Glass plates are coated with the polymer solutions using an applicator and a gap size of 250 ⁇ .
  • the solvent is subsequently evaporated off in a circulating air drying cabinet at 70° C. (0.5 h), 150° C. (2 h) and 250° C. (12 h).
  • the films are then virtually free of solvents (content ⁇ 0.1%) and are detached from the glass plates.
  • the films obtained have a thickness of about 30 to 40 ⁇ m. None of the films was brittle and all exhibited good mechanical properties.
  • a single gas e.g. nitrogen, oxygen, methane or carbon dioxide
  • the devolatized, filtered and additized solution of P84 type 70 in dimethylformamide from Example 10 is thermostated to 50° C. and gear pumped through a two-material die. Flux is 162 g/h. While the polymer solution is conveyed in the outer region of the two-material die, a mixture of 70% of dimethylformamide and 30% of water is conveyed in the inner region in order to produce the hole in the hollow fiber. Flux is 58 ml/h. After a distance of 40 cm, the hollow fiber enters cold water at 10° C. The hollow fiber is enveloped here with a tube. This tube is flooded with a 2 l/min stream of nitrogen, tube internal temperature being 41° C.
  • the fiber is then pulled through a water wash bath and finally wound up at a speed of 15 m/min. After extraction with water for several hours, the hollow fibers are dipped first in ethanol and then in heptane and subsequently air dried to obtain hollow fibers having an outer diameter of 412 ⁇ , a hole diameter of 250 ⁇ and a wall thickness of 81 ⁇ .
  • the devolatized, filtered and additized solution of P84 type 70 in dimethylformamide from Example 11 is thermostated to 50° C. and gear pumped through a two-material die. Flux is 162 g/h. While the polymer solution is conveyed in the outer region of the two-material die, a mixture of 70% of dimethylformamide and 30% of water is conveyed in the inner region in order to produce the hole in the hollow fiber. Flux is 58 ml/h. After a distance of 42 cm, the hollow fiber enters cold water at 10° C. The hollow fiber is enveloped here with a tube. This tube is flooded with a 2 l/min stream of nitrogen, tube internal temperature being 46° C.
  • the fiber is then pulled through a water wash bath and finally wound up at a speed of 24 m/min. After extraction with water for several hours, the hollow fibers are dipped first in ethanol and then in heptane and subsequently air dried to obtain hollow fibers having an outer diameter of 310 ⁇ , a hole diameter of 188 ⁇ and a wall thickness of 61 ⁇ .
  • the devolatized, filtered and additized solution of P84 T100 in dimethylformamide from Example 13 is thermostated to 50° C. and gear pumped through a two-material die. Flux is 162 g/h. While the polymer solution is conveyed in the outer region of the two-material die, a mixture of 70% of dimethylformamide and 30% of water is conveyed in the inner region in order to produce the hole in the hollow fiber. Flux is 58 ml/h. After a distance of 42 cm, the hollow fiber enters cold water at 10° C. The hollow fiber is enveloped here with a tube. This tube is flooded with a 2 l/min stream of nitrogen, tube internal temperature being 46° C.
  • the fiber is then pulled through a water wash bath and finally wound up at a speed of 20 m/min. After extraction with water for several hours, the hollow fibers are dipped first in ethanol and then in heptane and subsequently air dried to obtain hollow fibers having an outer diameter of 339 ⁇ , a hole diameter of 189 ⁇ and a wall thickness of 75 ⁇ .
  • the devolatized, filtered and additized solution of P84 HT in dimethylformamide from Example 12 is thermostated to 50° C. and gear pumped through a two-material die. Flux is 162 g/h. While the polymer solution is conveyed in the outer region of the two-material die, a mixture of 700 of dimethylformamide and 30% of water is conveyed in the inner region in order to produce the hole in the hollow fiber. Flux is 58 ml/h. After a distance of 15 cm, the hollow fiber enters cold water at 10° C. The hollow fiber is enveloped here with a tube. This tube is flooded with a 1 l/min stream of nitrogen, tube internal temperature being 40° C.
  • the fiber is then pulled through a water wash bath and finally wound up at a speed of 24 m/min. After extraction with water for several hours, the hollow fibers are dipped first in ethanol and then in heptane and subsequently air dried to obtain hollow fibers having an outer diameter of 306 ⁇ , a hole diameter of 180 ⁇ and a wall thickness of 63 ⁇ .
  • the devolatized filtered solution of P84 HT in dimethylformamide from Example 7 is thermostated to 50° C. and gear pumped through a two-material die. Flux is 162 g/h. While the polymer solution is conveyed in the outer region of the two-material die, a mixture of 70% of dimethylformamide and 30% of water is conveyed in the inner region in order to produce the hole in the hollow fiber. Flux is 58 ml/h. After a distance of 15 cm, the hollow fiber enters cold water at 10° C. The hollow fiber is enveloped here with a tube. This tube is flooded with a 1 l/min stream of nitrogen, tube internal temperature being 70° C.
  • the fiber is then pulled through a water wash bath and finally wound up at a speed of 24 m/min. After extraction with water for several hours, the hollow fibers are dipped first in ethanol and then in heptane and subsequently air dried to obtain hollow fibers having an outer diameter of 307 ⁇ , a hole diameter of 189 ⁇ and a wall thickness of 59 ⁇ .
  • the fiber was additionally measured at higher pressures in order to measure plasticization characteristics and pressure stability.
  • a flat sheet membrane rig is used to produce 35 cm wide membranes from a casting solution described in Example 14.
  • the casting solution is coated using an application and a casting gap of 200 ⁇ onto a calendered polyester fleece having a basis weight of 100 g/m 2 and a speed of 5 m/min.
  • the coated polyester fleece is then passed through a shaft through which nitrogen is flowed. The speed of flow is 339 m/h. The residence time thus achieved is 3 s.
  • the coated fleece then dips into cold water at 10° C.
  • the crude membrane is then wound up wet.
  • the membrane is at 70° C. extracted in water and impregnated with a conditioning agent (25% of polyethylene glycol dimethyl ether (PGDME 250 from Clariant) in water). It is dried in a festoon dryer at a temperature of 60° C.
  • a conditioning agent (25% of polyethylene glycol dimethyl ether (PGDME 250 from Clariant) in water. It is dried in a festoon dryer at a temperature of 60° C.
  • the membrane is characterized in a Milipore stirred cell at a pressure of 5 bar.
  • the solvent used is heptane in which hexaphenylbenzene is dissolved in a concentration of 12 mg/l. Measurement revealed a flux of 1.7 l ⁇ m ⁇ 2 ⁇ h ⁇ 1 ⁇ bar ⁇ 1 coupled with a retention of 94%
  • the membrane is subsequently also tested at a pressure of 30 bar and 30° C. in toluene. Oligostyrenes are used as test molecules. Flux in this test with toluene was 90 l ⁇ m ⁇ 2 ⁇ h ⁇ 1 . The membrane exhibits very high retention over the entire molar mass range and has a sharp cut-off in the region between 200 and 300 daltons (see FIG. 3 ).
  • the flat sheet membrane from Example 20 was placed for 16 h into a 0.1% ethanolic solution of an oligoethyleneimine ((#468533, Aldrich, typical molecular weight 423, contains 5-20% of tetraethylene-pentamine).
  • the membrane crosslinks and exhibits no solubility in hexane, heptane, toluene, xylene, acetone, butanone, methanol, ethanol, isopropanol, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone, dimethyl sulfoxide and ethyl acetate.
  • the membrane is characterized in a Milipore stirred cell at a pressure of 5 bar.
  • the solvent used is dimethylformamide in which hexaphenylbenzene is dissolved in a concentration of 2.2 mg/l. Measurement revealed a flux of 1.3l ⁇ m ⁇ 2 ⁇ h ⁇ 1 ⁇ bar ⁇ 1 coupled with a retention of 89%.
  • the hollow fiber membrane from Example 19 was placed for 16 h into a 0.1% solution of hexamethylenediamine in ethanol.
  • the membrane crosslinks and exhibits no solubility in hexane, heptane, toluene, xylene, acetone, butanone, methanol, ethanol, isopropanol, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone, dimethyl sulfoxide and ethyl acetate.
  • FIG. 1 Influence of concentrations of P84 type 70 in DMF on viscosity of solution: comparing a P84 polymerization solution and a P84 solution prepared from a precipitated and redissolved polymer at 25° C.
  • FIG. 2 Cross sections of hollow fiber membranes with macrovoids (picture at left) and without macrovoids (picture at right)
  • FIG. 3 is a diagrammatic representation of FIG. 3 :

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