CS276168B6 - Composite polymer membranes for gas mixture separation and method for their preparation - Google Patents

Abstract

Composite polymer membranes for separating gas mixtures, consisting of a microporous substrate based on aromatic polyimides of formula II, or polyamidoimides of formula IV, and a polymer selective layer formed by derivatives of poly-2,6-dimethyl-1,4-phenylene oxide of general formula I. The method of preparing these membranes consists in forming a thin polymer selective layer based on derivatives of poly-2,6-dimethyl-1,4-phenylene oxide of formula I on a previously prepared and dried microporous polymer substrate formed by aromatic polyimide of formula II, or polyamidoimide of formula IV. General formula II General formula IV CO-NH General formula I R. CH, '.OH.

Description

The invention relates to composite polymeric membranes, in particular for the separation of gas mixtures and to a process for their preparation.

The basic requirements for membranes used in gas separation on membranes are high permeability and selective separation (Kesting R.B. Synthetic Polymeric Membranes ”, New York, A Wiley-Interscience publication, 1985, p. 22). Specific membranes must be selected to separate the different gas vapors. To achieve high gas permeability while maintaining selectivity, the minimum thickness of the membranes must be 2 μm, but the physical and technical parameters become unsatisfactory: microcracks, pores appear, the membrane does not withstand the load.

These shortcomings are overcome by composite membranes, which are formed by a thin non-porous gas separation layer formed on a microporous polymeric substrate. The pad provides the required mechanical and utility properties and at the same time practically does not affect permeability and selectivity. Conversely, a selective separating layer can form a very thin to molecular coating.

There are various methods for preparing composite gas separation membranes, in particular a method for preparing selectively permeable membranes is known (3ap. Published application No. 58-180206, pat. Class B 01 D 53/22, published October 21, 1983), which is carried out by immersing a porous polymeric substrate with a pore diameter of 0.001 to 5 [mu] m in a bath with a precipitant which improves the pores of the substrate and forms a thin layer on the surface. A film is formed on a substrate prepared in this manner by applying a solution of the polymer in an organic solvent, and the obtained product is then dried. 3polymers, vinyl polymers and their copolymers, polycarbonates, polyesters, cellulose derivatives dissolved in organic solvents (halogenated carbohydrates, aliphatic and cyclic hydrocarbons, esters, ketones, aldehydes, amines) are used as polymers, z a formed film is used as a porous support. polypropylene, polysulfone, polyvinyl chloride, polytetrafluoroethylene, cellulose acetate. Water, alcohols, ethers or mixtures thereof are used as pore-filling coagulants. The membrane prepared in this way was evaluated on the basis of permeability of the mixture oxygen, nitrogen, selectivity coefficient <J- ° ₂ / ^N 2 ^{= 1.7} “ ² · ³ ' _s The basic disadvantage of the known method lies in the low selectivity of prepared membranes, which was determined only from distribution of the oxygen / nitrogen gas mixture.

Composite membranes of similar construction with a selective layer based on aromatic polyimides or polymers with an imide structure in the chain have increased selectivity of helium / nitrogen gas mixtures, but especially oxygen / nitrogen.

These membranes have a high selectivity for selected groups of gases. The higher structure and chemical composition do not allow to extend the selectivity of the division to other gases by chemical modification. Their use in at least partially universal modules for separation or purification of gas mixtures is also problematic.

It has now been found that an increase in versatility can be achieved with the composite membranes of the present invention.

The present invention relates to composite polymeric membranes for the separation of gas mixtures, the essence of which consists in that they consist of a microporous polymeric substrate and a thin polymeric selective layer, the microporous polymeric substrate consisting of an aromatic polyimide of general formula II

CS 276 168 86

wherein n = 150 to 240, optionally with a polyamidoimide of the general formula IV

IV where n = 140 to 220,

and the thin polymeric selective layer is formed by poly-2,6-dimethyl-1,4-phenyl oxide, or its derivatives of general formula I f-R nn _ n

where n = 500-1000, R = SO 2 Br.

The process for the preparation of composite polymer membranes consists in forming a thin selective layer of 1 to 6% by weight of a solution of poly-2,6-dimethyl- 1,4-phenylene oxide or its derivatives of general formula I.

Composite polymeric membranes can also be prepared by forming a microporous polymeric substrate based on a polyimide of the formula II from 10 to 15% by weight of an acid solution of the formula III.

wherein n 150 to 240 in a polar solvent followed by chemical imidization and then, after removal of the solvent and drying, a selective polymer layer based on poly-2,6-dimethyl-1,4-phenylene oxide or its derivatives of general formula is formed on this support. AND.

Furthermore, composite polymeric membranes can be prepared by forming a microporous polymeric substrate from 10 to 15% by weight of a solution of polyamidoimide in a solution of a polar aprotic solvent and then, after removing the solvent and drying, forming a selective polymeric layer based on poly-2,6- dimethyl-1,4-phenylene oxide or its derivatives of general formula I.

The possibility of forming membranes for the separation of gases from polyarylene oxides of the general formula V is known from the analysis of the state of the art

CS 276 168 B6

where X, Y, are Η, CH- to CH _O , Cl, Br, F, CH - O- to CH ..- O-, n => 100-800, in the form of foils or asymmetric membranes of 0.75- thickness 25 [mu] m (U.S. Pat. No. 3,350,844). The selectivity of such membranes prepared according to the invention and their substantially greater thickness also results in less permeability. The preparation of new types of composite membranes makes it possible to achieve membranes with high permeability while achieving good mechanical properties and, thanks to the materials used, also chemical and thermal resistance. The selectivity coefficients are also higher for composite membranes than for comparable membranes from one type of polymer.

In the following, the invention is elucidated by means of exemplary embodiments, without being limited thereto

Example 1

From a 15% solution of polymeric acid type III in dimethylformamide, a layer 400 μm thick was made on a 12 x 12 cm glass plate. It was immersed in an ethanol bath for 2 hours at room temperature and then in a pyridine-acetic anhydride mixture (1: 1 by volume) for 3 hours. After this imidization treatment, the prepared membrane was washed with benzene and ethanol, dried at room temperature, and finally at less than 300 ° C for 30 minutes. The thickness of the microporous substrate is 140 μm. A 2% solution of poly-2,6-dimethyl-1,4-phenylene oxide in chloroform was poured onto this support, and after removing the excess and drying at 40 ° C under vacuum, a membrane with an active layer thickness of 0.8 μm was obtained. The membrane was characterized by permeability and selectivity values ^p He ^{= 4} . ⁹⁵ - ^{10 6cin3} / ^cm2 « ^c « ^cmH g

P _N2 = 0.061.10 ~ ⁶ cm ³ / cm ² .c.cmHg

P _Q2 = 0,31.10 ⁶ cm ³ / cm ² .c.cmHg c ^ He / N ₂ = 81, o (He / N ₂ = 16, <kO ₂ / N ₂ = 5,1

Example 2

A 12% solution of polymeric type III acid in a mixture of dimethylformamide and ethylene glycol (9: 1 by weight) was poured onto a 12 x 12 cm glass substrate 400 μm thick and immersed at room temperature in an ethanol precipitation bath for 2 hours. subsequent chemical treatment in a mixture of pyrridine + acetic anhydride (1 1 1 vol.) for 3 h. The microporous membrane was air-dried and then heated for 30 min. to 200 ° C. A 3% solution of polyphenylene oxide in chloroform was poured onto this membrane, and after removing the excess by standing in a vertical position, the membrane was dried under vacuum at 40 ° C. The membrane was characterized by permeability and selectivity coefficients. ^p He = 4.6.10 ~ ^ cm ³ /cm2.g.cmHg ^P N2 ⁼ $ cm ³ / cm ² .s.cmHg ^P C02 ⁼ $ cm ³ / cm ² .s, cmHg cLHe / N ₂ 74, eC00 ₂ / N ₂ = 26 The membrane was tested for permeability of 0 ₂ and N ₂ from the air.

^P 02 ^{a 9} »28 ^s « 10 ~ ^ ^cffl3 / ^cm2 · ⁸ » ^cm Hg ^P N2“ ⁹ «058.10“ ®cm ³ / cm ² .s.cmHg ^ ° 2 ^{/ Ν} 2 ^a 4. ⁹

CS 276 168 B6

Example 3

A 10% solution of polyamidoimide in N-methylpyrrolidone was used to prepare a microporous film. A pad for pouring a 4% solution of polyphenylene oxide in chloroform was obtained from a 350 μm thick layer by plating on a glass plate after drying at 40 ° C. After removing the excess and drying at 40 ° C, the obtained membrane was characterized by the following permeability and selectivity:

P _u „= 9.5.10 ^- ®cm ³ / cm ² .s.cmHg

-6 3 2 ^P N2 ^cm / ^cm oS ^ cmHg

P__ = 0.59.10 ~ ⁶ cm ³ / cm ² .s.cmHg

Ufc oo ^P C02 “3,31.10 cm / cm .S.cmHg ^ He / 0 ₂ = 86. ó- He / 0 ₂ a 16, Á70 ₂ / N ₂ = 5,4, ^ LC0 ₂ / N ₂ = 30

Example 4

A layer of a 5% solution of sulfonated polyphenylene oxide (S content = 7%) in methanol was poured onto a microporous support prepared according to Example 3, and a membrane with the following properties was obtained after removing the excess amount and drying:

2

P _u „= 2,4.10 cm / cm .s.cmHg“ 0 ”3 Q

P _N2 0.092.10 cm / cm .s.cmHg

P _Q2 = 0,029.10 ⁵ cm ³ / cm ² .s.cmHg $ -He / N ₂ a 26, / -0 ₂ / N ₂ = 3,15

Example 5

Following the method described in Example 1, a microporous support was prepared, poured onto a dried layer of a polyphenylene oxide bromo derivative from a 30% solution in chloroform. The properties of the membranes prepared in this way and some others are given in the table.

Claims (4)

PATENT CLAIMS 1, Composite polymeric membranes for separating a gas mixture, characterized in that they consist of a microporous polymeric substrate and a thin polymeric selective layer, the microporous polymeric substrate being formed by an aromatic polyimide of general formula II. wherein n 4 150-240, optionally with a polyamidoimide of general formula IV where n = 140-220, and the thin polymer selective layer consists of poly-2,6-dimethyl-1,4-phenyl oxide, or its derivatives of general formula I · <I>, where n = 500-1000, R = SOgH, Br. 2. A process for the preparation of composite polymer membranes according to claim 1, characterized in that a thin selective layer of 1 to 6% by weight of a poly-2 solution is formed on a dry microporous polymeric substrate consisting of an aromatic polyimide of the formula II or a polyamidoimide of the formula IV. 6-dimethyl-1,4-phenylene oxide or its derivatives of general formula I. 3. The process according to claim 2, characterized in that a microporous polymeric support based on a polyimide of the general formula II is first formed from a 10 to 15% by weight solution of an acid of the general formula III. HN-Target / X / COOH Ί OJ HO.CO 2 X / CO 'NH (ΠΙ) 7 where n 150-240 in a polar solvent followed by chemical imidization and then, after removal of the solvent and drying, a selective polymer layer based on poly-2,6-dimethyl-1,4'-phenylene oxide is formed on this support, or its derivatives of formula I. CS 276 168 B6 4. The method of claim 2, wherein first forming a microporous polymeric substrate of 10 to 15% by weight, a solution of polyamidoimide in a solution of a polar aprotic solvent, and then, after removing the solvent and drying, forming a selective polymer layer based on poly-2. , 6-dimethyl-1,4-phenylene oxide or its devuents of general formula I.