EP0790852A1

EP0790852A1 - Filter material and process for removing components from gas mixtures and liquids

Info

Publication number: EP0790852A1
Application number: EP95937856A
Authority: EP
Inventors: Michael Haubs; Heinz-Joachim Rieger; Jörg von Eysmondt; Wolfgang Sixl; Holger Jung; Marc Schmidt
Original assignee: Hoechst AG; Ticona GmbH
Current assignee: Ticona GmbH
Priority date: 1994-11-08
Filing date: 1995-10-31
Publication date: 1997-08-27
Also published as: KR970706882A; AU695368B2; JPH10509376A; WO1996014130A1; AU3870395A

Abstract

The invention relates to a filter material as well as a process for removing components from gas mixtures and liquids wherein a flow of gas or a liquid is brought into contact with a filter material made of a porous polymer. The porous polymer is formed from homogenous solution by phase inversion. The filter material works selectively and can be used especially for removing ozone, hydrogen peroxide, nitrogen oxides, halogens and organic peroxides from gas flows and liquids.

Description

description

Filter material and method for removing components from gas mixtures and liquids

The invention relates to a filter material for removing components from gas or liquid mixtures and its production.

The removal of unwanted components from liquid or gas mixtures is an important task in many areas of technology and medicine. This task is frequently set in the area of environmental and personal protection.

One way to solve this problem is to sorb the undesired components onto porous bodies, of which activated carbon and zeolites have gained technical importance. However, these materials have the disadvantage that they are subject to wear, often sorb several components at the same time and therefore do not have sufficient selectivity.

The removal of the irritant gas ozone, especially from air, has become increasingly important in recent years. It has recently been found that certain polymers can react very selectively with this gas. However, with a short residence time of the gas, for example in a filter, the filter effectiveness leaves something to be desired.

PCT application WO 93/04223 describes a microporous permselective fiber or film membrane made of polyphenylene sulfide (PPS) which is said to be suitable for mixing gaseous or liquid components from a mixture of To separate components. The mean pore size is given as 0.154 micron. However, the membranes mentioned were only tested for their permeability to nitrogen and water in the examples. The general use is described as the separation of gases, the separation of dissolved from suspended particles in solutions, the separation of dissolved molecules and of suspended solid particles from smaller molecules, for example in ultrafiltration. The known membranes are therefore used for conventional pressure-driven separation processes that are based on a physical separation method. The use as a filter for removing ozone, for example, by chemosorption is not mentioned or mentioned.

The task was therefore to find a material which selectively and completely removes pollutants such as ozone or nitrogen oxides with short residence times.

The object is achieved in that suitable polymers are used for chemosorption.

The invention relates to a filter material based on polymers for removing components from gases and liquids, the polymer base consisting of a porous polymer which was produced from homogeneous solution by phase inversion, and its production.

The term "filter material" includes all forms of a polymer with which it is possible to remove individual components from a mixture by means of chemosorption.

"Polymer-based filter material" means that the filter material contains at least one polymer. It has been shown that these polymers, particularly in special embodiments with a large inner surface, are considerably more effective than those described in the prior art. Here, the large inner surface must be accessible by diffusion in a very short time (compared to the dwell time in the filter) in order to ensure satisfactory removal of the pollutants. Finally, the materials must also be as amorphous as possible in order to allow the mixture to be separated to diffuse through the filter surface into the filter material.

For example, an effective ozone filter should have the following features: it must a) consist of a material that is able to react quickly with ozone, b) have a large inner surface, c) have a morphology that prevents the access of ozone to the inner surface in a short time Time allowed and d) have a sufficiently high diffusion rate of the ozone in the polymer itself.

Of course, these criteria also apply to compounds to be removed other than ozone.

The polymers used according to the invention are converted into a porous form by phase inversion, in which a homogeneous solution is generally advantageous, while at the same time they can easily be converted into a corresponding geometric shape (for example fiber or film or ball) . The porous polymers are then brought into contact with a mixture to be separated, one or more undesirable components being removed from the mixture practically completely and selectively.

"Chemosorption" is understood to mean the ability to bind chemical compounds absorptively, this being predominantly through chemical reactions with the "absorber material" happens. The term "phase inversion" means that the polymer material is brought into a shape which is different from the starting form by means of various types of aggregate states. This can be done by various known methods.

The invention further relates to a method for producing this filter material and the use of this material for removing components from gas and liquid mixtures.

According to the present invention, for example, a suitable polymer is dissolved in a solvent, the solution is brought into the desired geometric shape (for example as a fiber, film or ball) and brought into contact with a non-solvent until practically all of the solvent has been replaced by non-solvent. The non-solvent is then removed by drying. Finally, the porous polymer is brought into contact with the mixture of substances in a suitable manner, one or more components of the mixture being selectively removed.

Suitable polymers according to the invention are, for example, those which contain electron-rich aromatic groups, as is the case in polyarylene ethers and thioethers, and which have an average molecular weight M _w of 1,000 to 2,000,000, preferably 10,000 to 500,000 and in particular have 20,000 to 200,000. The molecular weight of soluble polymers is generally determined by means of gel permeation chromatography (GPC).

The terms polyarylene ether and thioether are synonymous with "polyarylene oxide" and "polyarylene sulfide". The commercially available polyphenylene sulfide (PPS) of the formula I and poly (2,6-dimethyl) oxyphenylene (PPO) of the formula II are particularly suitable:

In formula (I), the radicals R are identical or different and mean a hydrogen atom, a C- - C ₈ -alkyl group, a halogen atom or -SO ₃ H or -COOH. Mixtures, including blends, of these polymers have also been found to be effective.

The polyarylene ether can also be blended with one or more other polymers or be a block copolymer.

Blends containing at least one polyarylene ether can be used to remove nitrogen oxides from gases and liquids according to the invention. Suitable blends are, for example, polyarylene ether blends which contain polystyrene homopolymer and / or polystyrene copolymer and / or polyamide and / or polyolefin.

Examples of polyarylene ethers and their preparation are described in "Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A21, B. Elvers (Ed.), VCH, Weinheim-Basel, Cambridge-New York 1992, keyword 'Poly (Phenylene Oxides)' , Page 605-614 ", to which reference is made. Other suitable polymers are polyarylene sulfides.

Polyarylene sulfides, especially polyphenylene sulfide, can be produced on the basis of the reaction of dihalogenated aromatics with sodium sulfide according to EDMONDS and HILL. Polyarylene sulfides and their preparation are described in "Ulimann ^'s Encyclopedia of Industrial Chemistry, Volume A21, B. Elvers, S. Hawkins and G. Schulz (Eds.), VCH, Weinheim-New York 1 992, pp. 463-472) The synthesis of polyarylene sulfides containing sulfone groups, which can also be used, is described in Chimia 28 (9), (1 974) 567, to which reference is also made.

In principle, all those liquids which dissolve the polymer, optionally at elevated temperature, and which are miscible with a suitable non-solvent are suitable as solvents. Dipolar aprotic solvents such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) or dimethylacetamide (DMAc) for polyarylene ethers are particularly suitable, for example. Chlorinated aromatics, for example 2-chloronaphthalene, have also been used successfully.

The concentration of the dissolved polymer is generally 5 to 25%, preferably 10 to 20%. There may also be higher concentrations depending on the application.

All liquids which do not or only slightly dissolve the polymer and are miscible with the solvent of the polymer are suitable as non-solvents. Water or methanol or acetone or mixtures thereof are preferred, as are mixtures of solvents and non-solvents.

The processing of the polymer solution to the desired porous polymer can be carried out, for example, in such a way that membranes, films, fibers, spheres are obtained from the polymer solution by phase inversion by known methods or hollow fibers arise, the geometric dimensions (film thickness, fiber thickness and length, ball diameter) can be varied within wide limits. The precipitation bath in the production of fibers and balls for the precipitation of the polymer solution generally has a temperature of 10 to 80 ° C. The adaptation of these parameters can be optimized for every application.

The porous polymers according to the invention generally have a specific surface area of more than 2 m ² / g, preferably 20 to 400 m / g, measured according to Brunnauer, Emmet and Teller (BET).

In the simplest case, the removal of the non-solvent can be achieved by evaporation, with a heated air stream advantageously being used. However, other known techniques can also be used, for example freeze drying.

For removing components from gases or liquids, e.g. of ozone, the gas mixture or the liquid is brought into contact with the porous polymer. There are a number of ways to do this; the list of examples is not exhaustive.

1 . The porous polymer is produced in the form of small spheres, a column is charged with it and the mixture to be separated is passed through the column, as is known from absorption towers. Instead of the balls, cut or milled fibers (pulp) can sometimes be used with advantage. It is important that the porous polymers are distributed as evenly as possible, so that the latter flows uniformly through the fill and flow channels are avoided.

2. The porous polymer is formed as a flat membrane and operated in the sense of a "dead end" filtration. Multiple membranes can also be used stack on top of each other to render defects within a membrane ineffective.

3. Hollow fiber membranes can also be used, which can also be produced from the polymer solutions in a known manner.

In the latter two cases, the mixture of substances can flow through the membrane (as is known from classic membrane filtration) or can simply be led a sufficiently long distance past the membrane surface.

4. Finally, the membranes can also be used in the form of modules that are known from filtration technology.

The filter material according to the invention, e.g. B. based on polyarylene ether or polyarylene thioether is not only suitable for removing ozone, but also for removing nitrogen oxides (NO _x , x> 1), in particular NO, H ₂ O ₂ , halogens, HNO ₃ or organic peroxides. The removal takes place selectively, for example NO ₂ can be removed from mixtures of nitrogen oxides, for example NO _{2 in} addition to NO.

Examples

® 1) 15 g of poly (2,6-dimethylphenylene oxide), trade name Blendex HPP 820

Manufacturer: General Electric Co., Schenectedy, USA, were at 90 ° C in 85 g

NMP resolved. Part of this solution was drawn out with a doctor blade on a glass plate to form a film with a wet thickness of approximately 200 micrometers

(Glass plate and doctor blade were previously heated to 70 ° C). The coated wet film was immersed in 45 ° C warm water, the resulting one

Membrane separated from the glass plate after 2 minutes and in 24 hours

Water is inserted to remove residual solvent. Then the

Air dried membrane. A circular section with a diameter of 2 cm was clamped in a membrane test cell and flowed through with an air stream which was loaded with 100 ppb ozone, the mean residence time in the membrane being only 2 ms. The air flow passed through the membrane was analyzed for its ozone content (ML 9810 ozone measuring device from Rhode & Schwarz, 63263 Neu-Isenburg, Federal Republic of Germany). The ozone concentration was found to be below the detection limit of 1 ppb. Even after 2 hours, the ozone concentration was below 1 ppb. Ozone is thus completely removed in less than two milliseconds.

2) The experiment from Example 1 was repeated, but instead of

®

Blendex from the polymer blend NORYL from General Electric, USA (it consists of a homogeneously mixed blend of PPO and polystyrene). The same results as in Example 1 were obtained, which means complete removal of ozone with a residence time of 2 ms and a test duration of more than 2 hours.

3) A molding solution was prepared by mixing 80 g of N-methylpyrrolidone and 20 g of polyphenylene oxide, which formed a homogeneous solution at temperatures above 70 ° C. The solution was filtered, heated to 80 ^C C and then through a spinning pipe (90 ° C) to a Naßspinndüse (80 ° C) promoted. The nozzle had 100 holes with a diameter of 0.2 mm. During the spinning, the nozzle was immersed in a precipitation bath made of 35 ° C warm water. The precipitation distance in the precipitation bath was 75 cm. After passing through several washing baths, the monofilament fibers obtained were wound up wet.

A variant of the process is the production of so-called "fiber pulp", which can be obtained by mechanical comminution which takes place directly after the coagulation (in water at room temperature). One on this Pulp so prepared was soaked for several days and then dried at 50 ° C.

4) PPO powder was dissolved in NMP at 90 ° C. The polymer concentration was set at 15%. The Blendex HPP 820 polyphenylene oxide powder used as the starting material had a grain size of 0.2 to 0.5 mm and a specific surface area of 1.1 m ² / g.

The homogeneous polymer solution was placed in a heated dropping funnel and thermostatted to 70.degree. The solution was then added dropwise to a stirred water bath thermostatted to 70 ° C., which served as a precipitation bath. Alternatively, a heated nozzle head can be used to feed the drops into the precipitation bath. The morphology and size of the balls can be varied by selecting the dropping nozzle, the dropping speed and the stirring speed in the precipitation bath.

When it hit the precipitation bath, the drops of the polymer solution solidified into spherical shapes. By continuously adding fresh, preheated water, suspended beads were discharged from the precipitation bath together with the used precipitation bath solution (water / NMP) via an overflow. The residence time of the beads (granules) in the precipitation bath was about 10 minutes in the present case.

After washing several times with water and drying for several hours at 90 ° C. under reduced pressure (200 mbar), an abrasion-resistant granulate made of PPO was obtained which had a specific surface area of at least 40 m ² / g (BET measurement) and excellent properties as an ozone Had filters. 5) Ozone removal from a gas stream using porous PPO granules or fiber pulp

The materials listed in Tables 1 and 2 were placed in a glass tube 30 cm long and 2.3 cm inside diameter. The ozone-containing gas was then passed through the glass tube at room temperature. The ozone concentration in front of and behind the glass tube was measured using an ozone analyzer (from Fischer, type Ozotron 23, Meckenheim, Federal Republic of Germany). For comparison, non-pretreated PPO (starting material) was subjected to the process. The conditions and the results obtained are shown in Tables 1 and 2 below.

Table 1

Example 5a 5b

Polymer material polyphenylene oxide polyphenylene oxide (Blendex HPP 820) (Blendex HPP 820)

Morphology fiber pulp fiber pulp

(50 μm diameter) (200 μm diameter) spec. Surface area [m ² / g] 300 400

Weight [g] 6.2 3, 1

Bulk volume: 100 cm ³ 30 cm ³

Carrier gas oxygen oxygen rel. Humidity [%] 0 0

Volume flow 100 100 carrier gas [C / h)

Ozone concentration 10000 10000

- entrance [mq / m ³ ] - Example 5a 5b

Ozone concentration 0.0 0.0 - Output [mg / m ³ ] at the end of the experiment

Test duration [h] 3.25 1 spec. Ozone uptake 0.52% 0.32% [g O, / g polymer]

Table 2

Example 5c 5d 5e spec. Ozone uptake 0.34 0.29 0.01 [g 0 ₃ / g polymer]

The results summarized in Tables 1 and 2 show that ozone is virtually completely removed (> 99%) from gas mixtures with very short residence times (ie less than 1 second). In addition, the materials according to the invention are able to remove about 50% of their own weight of ozone.

The comparison, on the other hand, shows that untreated material gives completely inadequate values.

6) Removal of dissolved ozone from water with PPO granules

The PPO granules with a grain size of 1.5 to 2.5 mm used in the example were produced by a phase inversion process according to Example 4.

In addition, the granules were mechanically pre-crushed, washed intensively with acetone and water and then dried at 100 ^° C. for 8 hours. The average grain size of the shredded material was 1 mm, the bulk density 0.2 to 0.25 g / cm ³ .

The ozone filter for use in the liquid phase was produced as follows: the dried, hydrophobic PPO material was filled into a glass tube (2.3 cm inside diameter, 20 cm length) and soaked with a water / ethanol mixture to wet the pores. The remaining ethanol was then displaced by water. A bubble column filled with 1.5 liters of drinking water was gassed with ozone-containing oxygen (20 g O ₃ / m ³ ). The ozonized drinking water was continuously pumped through the ozone filter and back into the bladder column using a gear pump. The ozone concentration was checked indirectly via the redox potential before and after the ozone filter. The conditions and results are shown in Table 3.

Table 3

Example 6a 6b

Polymer material Polyphenylene oxide (PPO) Polyphenylene oxide (PPO)

Morphology Granules Granules medium Grain size [μm] 1000 1 000

Weight [g] 5.9 10

Filter volume [cm ³ ] 25 42

Filter length [cm] 6 10

Filter cross section [cm] 2.3 2.3

Liquid drinking water drinking water

(ozonized) (ozonized)

Volume flow 20 40

(Liquid) [l / h]

Dwell time 4.5 3.8

(Liquid) [sec]

Carrier gas oxygen oxygen

Ozone concentration 20.0 20.0

(in carrier gas) [g / m ³ ]

Redox potential [mV] 200 210

(Drinking water, not ozonized)

Redox potential [mV] 820 (approx. 4 mg / l O ₃ ) 860 (approx. 4 mg / l O ₃ )

(ozonized drinking water, before filter) Example 6a 6b

Redox potential [mV]

(ozonized drinking water, behind filter)

1 h test duration 270 (<0.3 mg / l O ₃ ) 230 (<0.2 mg / l O ₃ )

2 h test duration 250 (<0.3 mg / l O ₃ ) 220 (<0.2 mg / l O ₃ )

4 h test duration 230 (<0.3 mg / l O,) 210 (<0.2 mg / l 0 ₃ )

Total test duration [h] 4

The results in Table 3 also show the effectiveness of the filter for removing ozone in liquid media.

7) A gas mixture of 90 ppm NO ₂ in helium was passed at 25 ° C. over a filter cartridge which was filled with a polyarylene ether (Blendex HPP 820) in the form of a fiber pulp. After passing through the filter cartridge, the gas was analyzed for NO and NO ₂ (chemiluminescence measuring device: type CLD 700 El Ht, Eco Physics AG, Durnten, Switzerland; minimum detection limit 0.1 ppm, linearity + / - 1% of full scale). The results are summarized in Table 4.

The filter effect on NO ₂ occurs immediately. Part of the NO ₂ is converted into NO.

Table 4

Polymer material polyphenylene oxide (Blendex HPP 820)

Morphology fiber pulp (precipitation 1/1 in H _? O, extracted in acetone) spec. Surface area [m ² / g] 180

Sample weight [g] 2

Bulk volume [cm ³ ] 1 1, 6 Polymer material polyphenylene oxide (Blendex HPP 820)

Carrier gas helium rel. Humidity [%] 0

Volume flow 25 carrier gas [l / h]

NO ₂ concentration 900 - input [ppm]

Test duration [h] 2.3 spec. NO ₂ uptake 0.062 [g NO, / g polymer]

Within the test period shown in Table 4, the NO ₂ concentration was always below the detection limit of 0.1 ppm.

Claims

claims

1. Filter material based on polymers for removing components from gases and liquids, characterized in that the polymer base consists of a porous polymer with a specific surface area (BET) of more than 2 m / g.

2. Filter material according to claim 1, characterized in that the surface is 20 to 400 m ² / g.

3. Filter material according to claim 1 or 2, characterized in that the polymer base is a polyarylene sulfide or a polyarylene ether.

4. Filter material according to one or more of claims 1 to 3, characterized in that the polymer base is a polyphenylene sulfide with repeating units of the formula (I)

wherein the radicals R are identical or different and are a hydrogen atom, a C _r C _e alkyl group, a halogen atom or -SO ₃ H or -COOH

5. Filter material according to one or more of claims 1 to 3, characterized in that the polymer base is a poly- [2,6-dimethylphenylene oxide] with repeating units of the formula (II) is.

6. Filter material according to one or more of claims 1 to 5, characterized in that the molecular weight of the polymers is 4,000 to 200,000.

7. A process for producing a porous polymer, characterized in that a polymer based on a polyarylene sulfide or a polyarylene ether is converted from a solution by phase inversion to a porous polymer with a specific surface area (BET) of more than 2 m / g.

8. The method according to claim 7, characterized in that the polymer is dissolved in a solvent, the solution is brought into the desired geometric shape and brought into contact with a non-solvent until practically all of the solvent is replaced by non-solvent and then the non-solvent is removed by drying becomes.

9. The method according to claim 7 or 8, characterized in that the polymer base is a polyarylene sulfide with repeating units of the formula (I)

s-μ (i)

wherein the radicals R are identical or different and are a hydrogen atom, a C ₁ -C ₈ alkyl group, a halogen atom or -SO ₃ H or -COOH.

10. The method according to claim 7 or 8, characterized in that the polymer base is a polyarylene ether with repeating units of the formula (I)

1 1. The method according to any one of claims 7 to 10, characterized in that the molecular weight of the polymer used is 1,000 to 2,000,000.

12. Use of the filter material according to claim 1 for removing components from gases and liquids by chemosorption.

13. Use according to claim 12, characterized in that the gases or liquids to be treated are contacted with the filter material.

14. Use according to claim 12 or 13, characterized in that ozone, hydrogen peroxide, nitrogen oxides NO _x (x> 1), halogens or organic peroxides are removed.