DE3842093A1 - SEMIPERMEABLE MEMBRANE MADE OF POLYBENZOXAZOLE FOR THE SEPARATION OF GASES - Google Patents

Abstract

A selectively semipermeable membrane for separating gases is made of polybenzoxazole of general formula (1> <IMAGE> wherein Ar is an aromatic group and R is a divalent aromatic group and n is 2 to 200. The membrane is useful, for example, in separating hydrogen gas from a hydrogen-methane mixed gas or for obtaining an oxygen-rich gas from the air, or in separating carbon dioxide from a carbon dioxide-methane mixed gas.

Description

The invention relates to the separation of a gas from a Gas mixture by contacting the gas mixture with a semipermeable membrane with relatively high permeability for the gas to be separated compared to another Gas or other gases in the mixture and in particular a new semipermeable membrane, which consists of a polybenzoxazole is formed.

Cellulose acetate membranes are as semi-permeable membranes known for the separation of gases, however, are cellulose acetate membranes in many cases not for practical applications suitable mainly because of their low chemical Resilience and heat resistance. Polysulfone membrane are considered semi-permeable on an industrial scale Membrane with improved heat resistance for gas separation manufactured, but they are semipermeable not satisfactory. There were also investigations on polyimide films with the aim of producing semi-permeable Membranes with excellent heat resistance carried out, but the specified semipermeabilities are still insufficient.

Semipermeable membranes made of silicone resins are used as gas separation membranes with high selective permeability to oxygen gas known, but membranes are made of silicone resin for not particularly suitable for industrial applications because of silicone resins insufficient in mechanical strength and are difficult to use with thin foils or films high permeabilities can be deformed.

The object of the present invention is to provide a semipermeable membrane for gas separation, this Membrane high selective permeabilities for specific gases  have excellent mechanical strength, heat resistance, chemical resistance and weather resistance should have, as well as a method for separating a Gases from a gas mixture by contacting the gas mixture with such a selectively semipermeable membrane with high selective permeability for what is to be separated Gas and excellent mechanical strength, heat resistance, chemical resistance and weather resistance.

A semipermeable membrane is used to solve this task for gas separation, the membrane made of a polybenzoxazole is formed, which is represented by the general formula (1) reproduced structure has:

wherein Ar is an aromatic group, R is a divalent aromatic group and n is an integer from 2 to 200.

The invention further relates to a method for separation a gas from a gas mixture of this gas and at least one other gas by contacting the Gas mixture with such a semipermeable membrane relatively high permeability to this gas in comparison to the further gas or gases, wherein the semipermeable membrane made of a polybenzoxazole structure represented by the general formula (1) is formed.

A polybenzoxazole of the general formula (1) is represented by a dehydration and cyclization reaction of a aromatic polyamide of the general formula (2) reproduced structure:

wherein Ar corresponds to the aromatic group in the general formula (1), R is a divalent aromatic group and n is an integer from 2 to 200.

An aromatic polyamide of the general formula (2) can by reacting a suitable aromatic diamine with an aromatic dicarboxylic acid or its dihalide or diesters can be obtained.

Some such aromatic polyamides of the general formula (2) and polybenzoxazoles of the general formula (1) shown in GB 21 88 936A and GB 21 91 496A.

The polybenzoxazoles used according to the invention have high mechanical strength and excellent heat resistance, chemical resistance, moisture resistance and weather resistance and they can be in easier Formed into foils or films. Polybenzoxazole membrane according to the invention have rather high permeabilities towards different types of industrial major gases including hydrogen gas and oxygen gas. For example, the permeability of a polybenzoxazole membrane according to the invention towards hydrogen gas about 10 to 100 times the permeability of one known as a heat-resistant, semi-permeable membrane, polyimide membrane.

The invention makes it possible to do so in an efficient manner Separate hydrogen gas from a mixed gas that from a Petroleum refining process is submitted and z. B. methane gas  contains together with hydrogen gas. It is also possible to get an oxygen-rich gas from air.

Preferred embodiments are explained in more detail below:

An aromatic polyamide of the general formula (2) can produced by one of the following two procedures will:

The first approach uses an aromatic diamine of the general formula (3):

wherein Ar is the aromatic group in the general formulas (1) and (2) and each -OH group is in the ortho position with regard to one of the -NH₂ groups.

The aromatic diamine is treated with a dicarboxylic acid general formula (4), a dicarboxylic acid dihalide general formula (5) or a dicarboxylic acid diester of general formula (6) implemented:

wherein R represents a divalent aromatic group:

wherein R represents a divalent aromatic group and X represents a halogen atom;

wherein R represents a divalent aromatic group and R 'represents an alkyl group or a phenyl group.

Good examples of aromatic diamines of the general formula (3) for the purposes of the invention are:
Bis (3-amino-4-hydroxyphenyl) methane,
1-phenyl-1,1-bis (3-amino-4-hydroxyphenyl) ethane,
1-trifluoromethyl-1,1-bis (3-amino-4-hydroxyphenyl) ethane,
1-phenyl-1,1-bis (3-amino-4-hydroxyphenyl) trifluoroethane,
2,2-bis (3-amino-4-hydroxyphenyl) propane,
2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane,
4,4'-diamino-3,3'-dihydroxybiphenyl,
Bis (3-amino-4-hydroxyphenyl) ketone,
Bis (3-amino-4-hydroxyphenyl) ether,
Bis (3-amino-4-hydroxyphenyl) sulfide,
Bis (3-amino-4-hydroxyphenyl) sulfone,
2,5-diamino-3,6-dihydroxyphenzene and
2,6-diamino-3,5-dihydroxybenzene.

Preferred examples of dicarboxylic acids of the general formula (4) are:
Isophthalic acid, terephthalic acid, 4,4'-bipehnyldicarboxylic acid, biphenyl ether-4,4'-dicarboxylic acid, benzophenone-4,4'-ciarboxylic acid, benzosulfone-4,4'-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, diphenylmethane-4,4 ' -dicarboxylic acid, 4,4'-isopropylidenediphenyl-1,1'-dicarboxylic acid and 4,4'-hexafluoroisopropylidenediphenyl-1,1'-dicarboxylic acid.

Preferred examples of dicarboxylic acid dihalides general formula (5) are chlorides of those listed above ten carboxylic acids, and good examples of dicarboxylic acid diesters of the general formula (6) are diphenyl esters of previously listed ten carboxylic acids.  

It is possible to combine two or more of the dicarboxylic acids, To use dicarboxylic acid dihalides or dicarboxylic acid diesters, to thus copolymerize an aromatic Get polyamide.

In the case of the implementation of an aromatic diamine of the general Formula (3) with a dicarboxylic acid is the reaction in a suitable organic solvent such as e.g. B. N, N-dimethylformamide, N, N-dimethylacetamide or N-methyl-2- pyrrolidone at a temperature in the range of room temperature carried out to the boiling point of the solvent used. If a dicarboxylic acid dihalide is used, the reaction is also in a similar organic Solvent at a temperature in the range of -10 ° C up to 50 ° C. In the case of using a dicarboxylic acid diester the reaction will also be in a similar organic solvents at a temperature in the range from 50 ° C to 300 ° C.

The second procedure uses an aromatic diamine of the general formula (7) used

wherein Ar is the aromatic group of the general formulas (1) and (2) R¹ is a monovalent organosilicon group, R² is a hydrogen atom or a monovalent organosilicon group and each -NHR¹ group in the ortho position with respect to one of the -OR² groups.

The aromatic diamine (7) with a dicarboxylic acid dihalide of the general formula (5) in an organic Solvent implemented.  

Preferred examples of aromatic diamines of the general formula (7) are:
2,2-bis (3-trimethylsilylamino-4-trimethylsiloxyphenyl) hexafluoropropane and 2,2-bis (3-triethylsilylamino-4-triethyl siloxyphenyl) hexafluoropropane. Good examples of dicarboxylic acid dihalides are the dichlorides listed for the first procedure.

There are no organic solvents special restrictions and there can be a wide selection be taken under z. E.g. amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and pyridine, Sulfone solvents such as dimethyl sulfoxide and tetramethyl sulfone, aromatic solvents such as benzene, toluene, Anisole, diphenyl ether, nitrobenzene, benzonitrile, cresol and phenol and halogenated hydrocarbons such as chloroform, Trichloroethane and carbon tetrachloride.

The reaction between an aromatic diamine of the general Formula (7) and a dicarboxylic acid dihalide general formula (5) is selected in an organic Solvent under practically non-aqueous conditions at a temperature in the range of -10 ° C to Reflux temperature of the solvent used carried out. The reaction time is from several minutes to to several hours. The molecular weight of this The reaction formed aromatic polyamide largely depends of the ratio of the dicarboxylic acid dihalide to that aromatic diamine and it is advantageous to equimolar Amounts of these reactants to make one relatively high molecular weight aromatic polyamide to use.  

An aromatic polyamide of the general formula (2) can in a simple manner in a corresponding polybenzoxazole of the general formula (1) can be converted by the Polyamide from a dehydration and cyclization reaction is subjected. This reaction is accomplished by heating the Polyamides in a non-oxidizing gas atmosphere at a Temperature in the range of about 100 ° C to about 500 ° C during a sufficient period of time, which is several seconds lasts up to several ten hours. Optional can the polyamide in the presence of a dehydrating agent such as B. polyphosphoric acid for the expiry of Dehydration and cyclization reaction in one relatively low temperature. Is also it possible to carry out the reaction temperature Lower reaction under reduced pressure.

As can be seen from the previous description, can in the polybenzoxazoles used in the invention the aromatic group Ar in the general formula following Have meaning:

where A

means
and the divalent aromatic group R may be a phenylene group, biphenylene group, naphthylene group or the group

A gas separation membrane according to the invention can thereby be produced be that first a membrane or a film of a aromatic polyamide of the general formula (2) according to a conventional method and then the polyamide film into a polybenzoxazole film or a film the heat treatment or heat treatment described above is converted. If the desired membrane in foil form is present, the polyamide film is melt-pressed, for example, Melt extrusion or casting made from the solution. Polyamides of the general formula (2) are numerous Types of organic solvents soluble. If the desired membrane is in the form of a tube, the Polyamide film e.g. B. by melt spinning or by wet or dry spinning from a solution.

For the semipermeabilities of the polybenzoxazole membranes according to the invention, the "gas permeation coefficient", P, and the "selectivity", γ , are given in the following examples as representative parameters:

The gas permeability coefficient is an index which the rate of permeation of a specific gas through the semi-permeable membrane and it is through given the following formula:

where V is the volume (at normal temperature and pressure) of the gas that has passed through the membrane, t is the thickness of the membrane, A is the area of the membrane, T is the permeation time and P is the gas pressure.

A large value for the coefficient P shows that the gas passes through the membrane at high speed.

When using the semi-permeable membrane to separate a mixture of two types of gases, the selectivity, γ , of the membrane is the ratio of the rate of permeation of the gas which passes relatively easily through the membrane to the rate of permeation of the other gas which does not easily pass through the membrane Are defined. Selectivity can be measured directly by bringing a known mixture of two gases into contact with the membrane and analyzing the gas mixture that has passed through the membrane. Alternatively, the selectivity can be determined approximately by measuring the permeation rate of each of the two gases through the same membrane and comparing the permeation rates of the respective gases with one another. If the selectivity of a membrane for an H₂ / CH₄ mixture z. B. 200, this means that hydrogen gas in the mixture passes through this membrane at a rate which is 200 times as high as the permeation rate of the methane gas in the mixture through this membrane.

The following examples illustrate the invention explained.

example 1

1.638 g (2.5 mmol) were placed in a 50 ml three-necked flask. 2,2-bis (3-trimethylsilylamino-4-trimethylsiloxyphenyl) - hexafluoropropane in 5 ml of dimethylacetamide by stirring dissolved in a nitrogen gas atmosphere. The solution was frozen using a dry ice acetone bath and then 1.073 g (2.5 mmol) of hexafluoroisopropylidene biphenyl-4,4'-dicarboxylic acid dichloride entered into the flask.  The dry ice bath was then exchanged for an ice bath and it started with a gentle stir, to gradually melt the frozen solution. Stirring was continued for 5 hours while maintaining the nitrogen gas atmosphere continued in the flask. After that was the reaction liquid into a large amount of water for precipitation cast in a polymer.

The basic molar viscosity number of the polymer obtained was 0.79 dl / g (0.5 g / dl in dimethylacetamide at 30 ° C). By IR spectral analysis and elemental analysis was confirmed that the polymer is a polyamide with the structure of the following Formula was:

This polyamide was dissolved in N-methyl-2-pyrrolidone and the solution was sprayed onto a glass plate, then became the solvent to form a film evaporates. The polyamide film was then in a nitrogen gas flow heated to 280-300 ° C for 10 h. As a result the polyamide film turned into a transparent one and very tough film around. Through IR spectral analysis and elemental analysis it was confirmed that by the heat treatment obtained film a polybenzoxazole with the structure was the following formula:  

Table 1 shows the heat resistance values of this Polybenzoxazole and two other polybenzoxazoles, which were produced in the following examples, and the Table 2 shows the mechanical properties of the same Polybenzoxazoles. Table 3 shows the gas permeation coefficients of the polybenzoxazole film obtained in each example for oxygen, carbon dioxide, carbon monoxide, methane, Nitrogen and hydrogen, and Table 4 shows the Selectivities of any polybenzoxazole film as a gas separation membrane for the separation of methane and hydrogen or carbon monoxide or the separation of nitrogen and oxygen.

Example 2

To prepare a polyamide, 1.638 g (2.5 mmol) 2,2, -Bis- (3-trimethylsilylamino-4-trimethylsiloxyphenyl) - hexafluoropropane with 0.633 g (2.5 mmol) of 2,5-naphthalenedicarboxylic acid dichloride following the same procedure as in Example 1 implemented.

The intrinsic viscosity of the polymer obtained was 0.60 dl / g (0.5 g / dl in dimethylacetamide at 30 ° C). By Analysis of the polymer confirmed that it was a polyamide with a structure of the following formula:

A film of this polyamide was made using the same procedure as in Example 1 and the film became the same Subject to heat treatment as in Example 1. After When heat treated, the film was transparent and tough. By Analysis of this film confirmed that it was from a Polybenzoxazole with a structure of the following formula:

Example 3

To prepare a polyamide, 1.368 g (2.5 mmol) 2,2-bis (3-trimethylsilylamino-4-trimethylsiloxyphenyl) - propane with 0.7678 g (2.5 mmol) benzophenone-4,4'-dicarboxylic acid dichloride following the same procedure as in Example 1 implemented.

The intrinsic viscosity of the polymers obtained was 1.00 dl / g (0.5 g / dl in dimethylacetamide at 30 ° C). By Analysis confirmed that this polymer was a polyamide with a structure of the following formula:

A film of this polyamide was made using the same procedure as in Example 1 and the film became the same Subject to heat treatment as in Example 1. The heat treated  Film was transparent and tough. Through analysis confirms that the film is made from a polybenzoxazole the structure of the following formula was:

Table 1

Table 2

Table 3

Table 4

Example 4

The aromatic polyamide produced in Example 1 was dissolved in dimethylformamide and the solution was made up one side of a glass pane with a high silicon dioxide content (Vycol glass from Corning Alss Co.), which with a mean pore diameter of 4 nm (40 Å) microscopic porous and thus permeable to gas, applied. The disc had a diameter of 30 mm and a thickness of 1 mm. After evaporation of the solvent, the polyamide film on the glass pane under a nitrogen gas flow heated to 280-300 ° C for 3 h. As a result, the Polyamide film into a film of that produced in Example 1 Converted polybenzoxazole. The thickness of the film was about 1 µm.

The one on the glass pane with a high silicon dioxide content Carried polybenzoxazole film was in a measuring device used for gas permeabilities to increase performance of the film for separating oxygen gas from air (oxygen concentration about 21% by volume) at room temperature determine. The pressure difference between the front of the polybenzoxazole film and the opposite side was adjusted to 1.01 bar (76 cmHg). The composition of the gas passed through the film was determined by gas chromatography analyzed, it was found that the penetrated gas contained about 41 vol .-% oxygen. At In this test, the gas flow rate through the polybenzoxazole film was 38 ml / h.

Claims (9)

1. Semipermeable membrane for the separation of gases, characterized in that the membrane consists of a polybenzoxazole, which has a structure represented by the following general formula (1): wherein Ar is an aromatic group, R is a divalent aromatic group and n is an integer from 2 to 200. 2. Semipermeable membrane according to claim 1, characterized in that Ar in the general formula (1) is where A means. 3. Semipermeable membrane according to claim 2, characterized in that R in the general formula (1) is a phenylene group, biphenylene group, naphthylene group or the group is what means. 4. A method for separating a gas from a gas mixture of this gas and at least one further gas by bringing the gas mixture into contact with a semipermeable membrane with a relatively high permeability to this gas compared to the other gas or gases, characterized in that this membrane consists of a polybenzoxazole is formed, which has a structure represented by the following general formula (1): wherein Ar is an aromatic group, R is a divalent aromatic group and n is an integer from 2 to 200. 5. The method according to claim 4, characterized in that Ar in the general formula (1) is where A means. 6. The method according to claim 5, characterized in that R in the general formula (1) is a phenylene group, biphenylene group, naphthylene group or the group is what means. 7. The method according to claim 4, characterized in that the gas to be separated is hydrogen gas, the gas mixture Includes methane gas. 8. The method according to claim 4, characterized in that the gas to be separated is carbon dioxide gas, the gas mixture Includes methane gas. 9. The method according to claim 4, characterized in that the gas to be separated is oxygen gas, the gas mixture Nitrogen gas.