NL8700758A - Semipermeable membrane with poly:phenylene:triazole gps, - used in micro-filtration, ultrafiltration, reversed osmosis, pervaporation, vapour permeation, and gas, liq. and vapour sepn. - Google Patents

Abstract

A semi-permeable membrane contains repeating units of poly(phenylene)-triazole of formula (I) where R1, R2, R3 = H, halogen, N02, amine, amide, alkyl, alkoxy, acyl, CN, 0H, C00H and/or S03H; R4, R5 = aromatic hydrocarbon gps., opt. combined with heterocyclic gps.

Description

4 NL 34070-Kp / cs

Semi-permeable membranes and method for their preparation.

Inventors: Bert Gebben in Hengelo (0)

Marcellinus Hendrikus Vincentius Mulder in Enschede Cornells Antonius Smolders in Hengelo (0)

The invention relates to semipermeable membranes, as well as to a process for their preparation.

Semi-permeable membranes are widely used for separation purposes. The membrane has the ability to transport one component faster than any other component.

The separation problem occurs with particles with dimensions from a few microns to molecules with dimensions of

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some Angstroms. Transport through the membranes takes place under the influence of a driving force which is exerted on the mixture to be separated. The driving force for the transport can be distinguished by a difference in pressure, concentration, temperature or electrical potential across the membrane. Pressure-based separation processes include micro-filtration, ultrafiltration and reverse osmosis.

Microfiltration is a membrane process, in which particles of 0.1 µm or larger are retained by the membrane, while the solvent flows freely through the membrane. The average pore diameter of the microfiltration membranes is in the range of 0.1-10 µm. Because the hydro-20 dynamic resistance of the membrane is low, low pressures are therefore exerted, from less than 1 bar to a few bars. Microfiltration can be successfully used in the case of particles, emulsions or suspensions with a diameter larger than the diameter of the pores of the membrane. Examples of application possibilities are sterile filtration, cell extraction, pre-filtration for reverse osmosis or gas separation.

Ultrafiltration is a process in which solutes with molecular dimensions larger than those of the solvent molecules are trapped through the membrane, while the solvent molecules pass through the membrane without difficulty. The range within which the macromolecular solutes can be separated is at molecular weights of 500 Daltons and above. The hydrodynamic weather

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i - 2 - Μ *> position of these membranes is greater than that of the microfiltration membranes. As a result, the applied pressure is greater and is in the range from a few bars to 10 bar. Ultrafiltration is mainly applied in the 5 food and dairy industry. Ultrafiltration can be successfully used in concentrating milk, whey, starch, proteins, etc.

Reverse osmosis is a process of separating molecules, solvent and solutes at a molecular size of the same order of magnitude. As the upper limit for the solutes, a molecular weight of 500 Daltons can be mentioned. Since the hydrodynamic resistance of the membrane is high and the osmotic pressures of the solutes can also be high, pressures of 20-100 bar are used. Reverse osmosis is mainly used for the desalination of sea water or brackish water. Furthermore, reverse osmosis is used in the food and dairy industry and is mainly used for fractionated separation of low molecular components from high molecular components.

Pervaporation is a separation process, in which a liquid mixture to be separated is brought into contact with a suitable membrane. If, on the permeate side of the membrane, the partial pressures of the components present in the liquid mixture are kept below the partial pressures of the components on the supply side, a driving force for transport of these components is obtained.

The reduction of the partial pressure on the permeate side is obtained either by applying a vacuum or by discharging the permeate using an inert carrier gas. The separation principle is based on different membrane solubilities and different diffusion rates through the membrane. These two parameters, solubility and diffusion, are a complex function of a number of different parameters, such as nature and concentration of the liquid mixture to be separated, nature and structure of the membrane, temperature of the liquid mixture to be separated and pressure on the permeate side. Pervaporation can be used to separate azeotropic and isomeric mixtures £ V (:: t 4 - 3 - *

Pervaporation can also be used for the dehydration of all types of organic solvents.

In the pervaporation process, the mixture to be separated is a liquid. When the mixture to be separated is evaporated, the process is called vapor / vapor permeation. The membranes and applications used are the same as for the pervaporation process.

Gas separation is a membrane process in which two or more gases and / or vapors are separated from each other. The difference between a vapor and a gas can be defined as follows: a vapor can be condensed at standard conditions (at 1 bar and 0 ° C) into a liquid, while gas remains gaseous under standard conditions. The driving force in gas separation is a partial pressure difference across the membrane. This can be achieved either by creating a high pressure on the supply side or by reducing the partial pressure on the permeate side by means of a vacuum pump. As with pervaporation, the separation principle is based on the different solubilities and on different diffusions of the gases and vapors to be separated. Areas of application are the recovery of hydrogen, separation of carbon dioxide / methane, separation of oxygen / nitrogen, removal of organic vapors from air.

It is noted that for each membrane process and every application, specifically tailored membranes are required. For example, a membrane developed for ultrafiltration cannot be used for hyperfiltration, while a membrane developed for hyperfiltration cannot be used for pervaporation with the same effectiveness.

Usually, membranes currently in use are prepared from polymers such as cellulose esters, polyacrylonitrile and polysulfone. However, these have the disadvantage that they are unusable above 100-150 ° C, because they decompose or soften at those high temperatures, so that they completely or partially lose their separating effect. An important drawback of such membranes is furthermore that they are soluble in a large number of solvents.

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In addition to the above membranes, three membranes are known with better chemical and thermal stability than the membranes discussed above.

The first category of these membranes includes membranes made from fluoropolymers, including Teflon (polytetrafluoroethylene). An important drawback of this polymer is that it is very poorly processable and that it is very expensive.

The second category includes membranes made from heterocyclic and aromatic polymers, of which polyimides and polybenzimidazoles are the best known. The disadvantage of such membranes is that they are soluble in a number of solvents, such as DMSO, DMAc, NMP, DMF, etc. In addition, the gas separation properties of these membranes are poor in both selectivity and permeability.

The latter category includes membranes that are thermally and chemically stable, but which are made of ceramic materials instead of polymers. Obviously, such ceramic membranes are more thermally stable than membranes made from polymers. An important drawback of such membranes is that they are very brittle. Furthermore, they cannot be processed into any desired morphology. Their gas separation properties leave much to be desired.

The present invention aims to provide semi-permeable membranes which lack the disadvantages of the above-described known semi-permeable membranes and which are suitable for use in microfiltration, ultrafiltration, reverse osmosis, pervaporation, gas separation and vapor permeation.

To this end, the invention provides semipermeable membranes, which are characterized by thermal and chemical stability and by building up repeating structural units of poly (phenylene) triazole of the formula of the formula sheet, wherein

R1, R2 and R3, whether or not the same, represent hydrogen, halogen, nitrate, amine, amide, alkyl, alkoxy, acyl, cyanide, hydroxyl, carboxyl or sulfonic acid and derivatives thereof, while & '' * '.. Γ-. . V - 5 - R4 and R5 are aromatic hydrocarbons or combinations thereof with heterocycles.

Aromatic hydrocarbons are understood to include phenyl, naphthalene, etc., while heterocyclic hydrocarbons are understood to include oxadiazole, etc.

The term "halogen" includes all halogens and can be fluorine, chlorine, bromine or iodine.

The term "alkyl" means straight or branched chain aliphatic hydrocarbon groups of 1-6 carbon atoms.

The term "alkoxy" means straight or branched chain alkoxy groups of 1-6 carbon atoms.

The semi-permeable membranes according to the invention can be used as flat membranes or tubular membranes or as hollow fibers.

The membranes can also be arranged on a porous support, in which case a so-called composite support is involved. The thickness of the separating polymer-membrane layer is 0.1-5 µm.

As a porous support, use can be made of metal, glass, a ceramic material or a plastic.

The semi-permeable membranes of the invention are resistant to temperatures up to 500 ° C and, moreover, they are resistant to all common organic solvents, except formic acid.

Surprisingly, it has been found that the semi-permeable membranes of the invention are suitable for use in gas / vapor separation, liquid / vapor separation, vapor / vapor separation, gas / gas separation, microfiltration, ultrafiltration, or reverse osmosis.

The semipermeable membranes of the invention can be either isotropic or anisotropic.

The aforementioned composite membranes are particularly suitable for gas separation, pervaporation and vapor permeation. As mentioned above, these composite membranes consist of two layers, a porous layer on which is a dense top layer of poly (phenylene) triazole. The porous second membrane layer can be a plastic, metal, ceramic material or glass. Ceramic material, glass and metal are preferred because of their thermal stability.

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Both layers are manufactured separately.

As mentioned above, poly (phenylene) triazole can be used as a membrane material at a temperature up to 500 ° C. Above 500eC, decomposition occurs. The polymer is only soluble in formic acid and is resistant to all other organic solvents.

In addition to very good chemical and thermal stability, the material has excellent inherent gas separation properties. For the separation of nitrogen and oxygen, for most polymeric materials, separation factors of 3 to 5 are found, as shown in the table. These are also the values that apply to commercially available membranes. Even lower values are found for silicone rubber (see table).

15 TABLE

Permeability constants and separation factors of a number of polymeric materials for oxygen and nitrogen

Polymer T P (Oo) * xl0 ^ P (N „) * xl0 ^ (° C) (S.l.units) (S.I.units)

Dimethyl silicone rubber 30 4500 1950 2.3

Dimethylic acid / polycarbonate 20 block copolymer 25 1200 525 2.3

Poly-4-methylpentene-1 25 203 48.8 4.15

Polybutadiene 30 143 48.8 2.9

Poly (2,6-dimethyl-1,4-phenylene oxide) 30 119 25 Ethyl cellulose 30 72.0 21.0 3.4

Polystyrene 30 48.0 16.5 2.9

Polyethylene (d = 0.914) 25 21.8 7.28 2.99

Polysulfone 35 9.00 1.53 5.88 • Cellulose acetate 30 6.00 2.10 2.86 30 Polyvinylidene chloride 30 0.0398 0.0071 5.6

Polyacrylonitrile 30 0.0023 * P is the flux in m3 / sec through a membrane surface of 1 m2 at a pressure difference of 1 pascal per meter over the membrane.

Ot = separation factor - 7 - 'a

It is noted that the poly (phenylene) triazoles according to the invention have a significantly higher separation factor for O2 / N2t, namely more than 9.

Also for the separation of carbon dioxide (OO2) and methane (CH4) very high separation factors have been found with the present membranes, much higher than for the comparable commercial membranes.

For example, for commercially available cellulose acetate gas separation membranes, separation factors of 10 to 25 are specified, while for the poly (phenylene) triazole of the invention, values of up to 60 are achieved.

The present invention further relates to a process for the preparation of the above-mentioned semi-permeable membranes, characterized in that a poly (phenylene) -15 triazole of the formula of the formula sheet, wherein Κχ, R2, R3, R4 and R5 having the above meanings, it is dissolved in a suitable solvent in an amount of 1-50% by weight, after which the resulting solution is subjected to a phase inversion technique, such as removal of the solvent by evaporation or replacement of the solvent by a non-solvent.

Formic acid is preferably used as the solvent for the poly (phenylene) triazole. Combinations of formic acid with other organic substances are also possible. However, strong inorganic acids can also be used, such as sulfuric acid, nitric acid, etc.

Usually, according to the invention, the polymer solution is applied to a suitable support, for example by spreading or immersing the support in the polymer solution, after which the membrane obtained in this way is separated or not from the support. The polymer solution can also be applied by spraying.

A porous support can be successfully used, in which case the membrane is not separated from the support.

The membrane and porous support assembly thus obtained is called composite membrane, which membrane is particularly suitable for the separation of gases, pervaporation and vapor permeation, as described previously.

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Metal, glass or a ceramic material is preferably used as a porous support because of their thermal stability. Suitable porous plastics can also be used.

A special embodiment of the present method comprises spinning the polymer solution into hollow fibers.

It is noted that the spinning of poly (phenylene) triazole fibers is described in Journal of Polymer 10 Science, Vol. 3 (1969), 3905. In addition, it is known that they can be processed into thermally stable fibers. In addition, it is known from this article that such poly (phenylen) triazoles can be used for coating stainless steel and aluminum, which coating has been found to have good adhesion.

No mention is made in this article of semipermeable membranes or a process for their preparation.

Furthermore, U.S. Pat. 3,318,728 poly (phenylene) triazole coated metal articles, such as copper, steel, aluminum and bronze.

Neither does this patent refer to semi-permeable membranes prepared from the poly (phenylene) triazole.

Finally, the Belgian patent no.

645,926 relates to a process for the preparation of poly (phenylene) triazoles and their processing into fibers, filaments and coatings.

In this document, too, no mention is made of semi-permeable membranes based on poly-30 (phenylene) triazoles.

The invention is now further elucidated by means of the following examples, to which the invention is in no way limited.

EXAMPLE I

Preparation of poly (4-phenyl) 1,2,4-triazole 488.75 g of polyphosphoric acid was slowly heated to 157 ° C. Then 122.20 g of aniline was added over 2.5 hours. Then 20 g of poly (1,3-, 1,4-phenylene) hydrazide k. "9 * - 9 - * (with an inherent viscosity 9inh = 1 * 3 dl / g, measured in a 0.5% w / w solution in dimethyl sulfoxide) was added and the temperature was raised to 170-255 ° C. After standing for 8 days, the dark solution was poured into a large volume of water to precipitate the polymer. Sodium hydroxide pills were added to the water until a pH of 7 was reached. The gray-green precipitate was filtered and then washed in 5% sodium hydroxide three times, followed by a Soxhlet extraction in methanol overnight, then dried under vacuum at 100 ° C. The remaining polymer was examined by infrared (IR), thermographic analysis (TGA) and viscometry.

The inherent viscosity, measured from 0.5 wt% solution in formic acid, was ninh = 1/4 dl / g.

EXAMPLE II

15.2 g of 1,2,4-phenyl-polytriazole, consisting of alternating meta and para-substituted phenyl rings with an inherent viscosity of 1.4 dl / g, measured in formic acid at 30 ° C, were dissolved in 85.1 ml formic acid at room temperature. The solution was then filtered through a 5 µm filter. The solution was then poured onto a glass plate using a doctor blade (also known as a "doctor knife") to form a film having a thickness of 0.15 mm. The formic acid was evaporated from the film in a nitrogen atmosphere at 80 ° C for 4 hours to form a solid transparent film which could be removed from the glass plate by immersion in water. Finally, the film was dried in an oven at 200 ° C overnight.

EXAMPLE III

From the same polymer solution as in Example II, a film was poured onto a glass plate, after which the solvent was evaporated in a nitrogen atmosphere at room temperature (25 ° C) for 2 days. The clear solid homogeneous film was then removed by immersion in water. After this, the film was dried in an oven at 200 ° C overnight.

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EXAMPLE IV

15.4 g of the polymer, as described in Example II, was dissolved in 84.5 ml of formic acid at room temperature and then filtered through a 5 µm filter. The solution was then poured onto a glass plate and immersed in a water bath at 25 ° C. An asymmetric polytriazole membrane was obtained with a non-porous and a porous layer. The thickness of the membrane was about 50 µm.

EXAMPLE V

10.5 g of 4-phenyl-1,2,4-polytriazole with an inherent viscosity of 0.8 dl / g were dissolved in 60.1 ml of a mixture of formic acid and water in a weight ratio of 96.4. The solution was then poured onto a glass plate and then immersed in a water bath at 25 ° C.

Hereby a strong asymmetric film with a dense non-porous top layer and a porous bottom layer was obtained.

EXAMPLE VI

11.1 g of the polymer described in Example V was dissolved in 60 ml of formic acid. The solution was then poured onto a glass plate and immersed in a coagulation bath consisting of a formic acid-water mixture in which the weight ratio of formic acid and water in the mixture was 9: 1. The temperature of the coagulation bath was 25 ° C. The membranes obtained had an asymmetric structure with a dense top layer and a porous bottom layer.

EXAMPLE VII

15.5 g of the polymer described in Example V was dissolved in 85.0 ml of formic acid. This solution was then poured onto a glass plate and then transferred to an atmosphere saturated with formic acid vapor and water vapor. These conditions were obtained by passing a stream of nitrogen through an azeotrope mixture of formic acid and water, which was refluxed. 1 hour after the treatment, the membrane was transferred in an atmosphere of saturated water vapor. Finally, the membrane was immersed in water, after which an isotropic porous film with an average pore size of 8 µm was obtained after drying.

EXAMPLE VIII

The isotropic membrane obtained in Example II was placed in a terminal ("dead-end") permeation cell.

On the supply side, pure gas was supplied at a pressure of 4 bar. On the permeate side, the flow rate of the transmitted gas was measured using a soap film capillary with a radius of 0.5 mm. The flux was measured at 41 ° C using nitrogen, oxygen, methane, helium and carbon dioxide, respectively. The results are shown in the table below.

permeability gas __ (Barrer) * _ 15 nitrogen 0.15 methane 0.07 oxygen 1.4 carbon dioxide 4.0 helium_12.3_ 20 * 1 Barrer - 10 cm ^ cm / cm ^ .sec.cmHg.

The selectivities as defined by the quotient of the permeabilities can be obtained from the results of the table. The following selectivities were found: 02 / N2: 9.3 CO2 / CH4: 57.1

He / N2: 82.0

EXAMPLE IX

The same membrane as described in Example VIII was placed in a "dead-end" permeation cell. The cell was transferred to an oven, raising the temperature to 200 ° C. The fluxes of the gases were measured as shown in Example VIII.

fc; , - 12 - permeability gas_ (Barrer) _ oxygen 10.0 nitrogen 2.5 5 helium_100_

The following selectivities were observed: O2 / N2: 4.0

He / N2: 40.0

EXAMPLE X

The same membrane as described in Example VIII

was transferred into a cross-flow permeation cell. A mixture of CO2 and CH4 with the composition of 12% CO2 and 88% CH4 was used as the feed stream. The flow was pressurized to 2 bar. The permeation rate was monitored by measuring the pressure increase in a pre-evacuated calibrated volume on the permeate side. The selectivity was measured by gas chromatography, which was connected to the permeator. Then the real selectivity was measured, defined by the quotient of the molar ratios of both components in the permeate divided by the molar ratios in the feed stream. The test was conducted at a temperature of 20 ° C. The permeate obtained in this way had a molar percentage of 89% CO2, which corresponds to a selectivity factor of 60.

EXAMPLE XI

The asymmetric polytriazole membrane described under example IV was applied to a dead-end permeation cell. The permeation cell was transferred to an oven at 100 ° C. The permeability of He and N2 was measured at 4 bar. The fluxes of helium and nitrogen were found to be 1.14 cm / sec.cmHg and 0.16 cm / sec.cmHg, respectively. This corresponds to a selectivity factor of 71.

EXAMPLE XII

A homogeneous membrane, as described in Example 35 VIII, was transferred to a dead-end pervaporation cell, into which t-13-y was stirred. This mixture was used to separate an ethanol / water mixture at 70 ° C in which the ethanol and water components of the mixture were present in a 1: 1 weight ratio. The supply side was kept at atmospheric pressure, while a vacuum was applied on the permeate side. The permeate was condensed in a "cold trap" which was cooled with liquid nitrogen. The composition of the permeate was determined by gas chromatography, which showed that water selectively permeates through the membrane.

EXAMPLE XIII

An asymmetric membrane, as defined in example VI, was applied to a so-called Amicon deaddencing ultrafiltration cell. On the supply side, water was supplied at a pressure of 3 bar. The water passed through was collected and the flux was measured. A flux through the asymmetric membrane at 3 bar of 3.5 l / m 2 .h was measured.

EXAMPLE XIV

A homogeneous membrane, as described in Example II, was transferred to an oven at 275 ° C for 30 days before being used in the permeation cell, as described in Example VIII. The same experimental conditions were used as in Example 25 VIII. The results obtained with this membrane were the same as those in Example VIII with a membrane that was not subjected to such initial treatment.

It is to be understood that the above examples are illustrative of the present invention only and in no way limit the scope of the invention thereto.

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Claims (12)

2. Semi-permeable membranes according to claim 1, characterized in that the membranes are flat, tubular or exist as hollow fibers. Semi-permeable membranes according to claim 1 or 2, 15, characterized in that the membranes are arranged on a porous support. Semi-permeable membranes according to claim 3, characterized in that the porous support is metal, glass, a ceramic material or a plastic. Semi-permeable membranes according to claims 1-4, characterized in that the membranes are resistant to temperatures up to 500 ° C. 6. Semi-permeable membranes according to claims 1-5, characterized in that the membranes are resistant to the usual organic solvents - with the exception of formic acid. 7. Semi-permeable membranes according to claims 1-6, characterized in that the membranes are suitable for use for gas / vapor separation, liquid / vapor separation, vapor / vapor separation, gas / gas separation, microfiltration, ultrafiltration, or reverse osmosis. 8. Process for the preparation of the semipermeable membranes according to claims 1-7, characterized in that a poly (phenylene) triazole of the formula of the formula sheet, wherein R 1, R 2, R 3, R 4 and R 5 having the meanings defined in claim 1, it is dissolved in a suitable solvent in an amount of 1-50% by weight, after which the resulting solution is subjected to a phase inversion in techniek i ': "· h - 15 - * technique such as removal of the solvent by evaporation or replacement of the solvent with a non-solvent. 9. Process according to claim 8, characterized in that formic acid is used as the solvent. A method according to claim 8 or 9, characterized in that the polymer solution is applied to a suitable support, after which the resulting membrane is separated or not from the support. Method according to claim 8 or 9, characterized in that a porous support is used as the support, in which case the membrane is not separated from the support. 12. A method according to claim 11, characterized in that the porous carrier is metal, glass, a ceramic material or a plastic. Method according to claim 8 or 9, characterized in that the polymer solution is spun into a hollow fiber in a manner known per se. ε ·. · '; 3rd.