WO2000010694A1

WO2000010694A1 - Symplex membrane

Info

Publication number: WO2000010694A1
Application number: PCT/EP1999/005737
Authority: WO
Inventors: Heiko Thielking; Erik-Andreas Klohr; Wolfgang Koch; Hans-Hartmut Schwarz; Susanne Knop; Werner-Michael Kulicke; Horst Dautzenberg
Original assignee: Wolff Walsrode Ag; DAUTZENBERG, Karin; Michael, Antje
Priority date: 1998-08-20
Filing date: 1999-08-09
Publication date: 2000-03-02
Also published as: AU5511799A; EP1115475A1; JP2002523527A; DE19837673A1

Abstract

A symplex membrane, containing polyanions as anionic constituentsformed from at least one cellulose ether containing sulphoalkyl groups. The invention also relates to the use of said symplex membrane to separate water or steam from organic substances and mixtures of substances.

Description

Symplex membrane

The invention relates to an improved symplex membrane which contains polyanions formed from at least one cellulose ether containing sulfoalkyl groups as the anionic component and to the use of this symplex membrane for separating water or water vapor from organic substances and substance mixtures.

Symplex membranes are understood to mean sheet-like associations of at least one polyelectrolyte (polyanions or polycations) and a low-molecular or polymeric counterion, in which the positively or negatively charged groups of the polyelectrolyte are crosslinked with the opposite charge of the corresponding counterions via a salt bridge.

The use of such membranes for such separation tasks (pervaporation, ultrafiltration etc.) is described in detail in the literature (R. Rautenbauch. Membrane Process, Springer Verlag 1996, page 15, R. Rautenbach, R. Albrecht Membrane Separation Process - Ultrafiltration and Reverse Osmosis, Otto Salle Verlag, Frankfurt 1981, pages 1 1-21). Non-porous membranes are used especially for material separation processes using pervaporation or ultrafiltration in the vacuum range. For the drainage of organic solvents such as alcohols. Ketones and aldehydes are described in principle suitable membranes in US Pat. No. 3,546,142, US Pat. No. 3,549,016, DE-PS 3526 755, DE-PS 3518871, EP-PS 96339.

However, the systems described have some disadvantages for practical use. The quality of a membrane basically depends on the separation factor, the filtrate flow density to be achieved, the mechanical and chemical stability. The systems described are characterized either by a high separation factor or by a high filtrate flow density, but not a combination of these properties that meets practical requirements. Improvements in the direction of a high filtrate current density and a high separation factor have been achieved by using hydrophilic polyelectrolytes, for example based on ion complexes (J. Membrane Science, 32 (1987) 207). However, these membranes always had good water solubility and therefore insufficient resistance.

A further advance was achieved by using a cellulose ester, cellulose sulfate, as the polyanion (DD 270 012, DD 290 589, DD 292 846, DE 42 ^" 29 530). The membranes produced therefrom show an improved

Flow with medium separation performance. However, these systems were not able to establish themselves on the market for pervaporation or for ultrafiltration, since the cellulose sulfate used in these patents is not available in sufficient quantity and quality.

Many attempts have been made with other polysaccharides (salts of alginic acid, chitosan salts, cationic cellulose derivatives, ammonium or pyridinium ions) (DE-OS-3600333, Prog. Polym. Sci. 14 (1989) 91), especially also with cellulose derivatives ( DD-PS 152 287) but these did not lead to comparable or improved results.

The invention is therefore based on the object of providing an improved symplex membrane which has a high mechanical and chemical stability, consists of material which is available in sufficient quantity and quality, allows simple and reproducible production of membranes and achieves the desired separation performance.

This object was surprisingly achieved by a symplex membrane which contains polyanions formed from at least one cellulose ether containing sulfoalkyl groups as the anionic component. According to the invention

Cellulose ethers containing sulfoalkyl groups, preferably sulfoethyl cellulose, sulfo- propyl cellulose or mixed ethers of cellulose, which are etherified with sulfoethyl and sulfopropyl groups. The use of sulfoethyl cellulose is particularly preferred. In a further embodiment according to the invention, derivatives of sulfoethyl cellulose or sulfopropyl cellulose can be used as the cellulose ethers containing sulfoalkyl groups, which derivatives are additionally substituted by carboxymethyl,

Methyl, hydroxyethyl, ethyl or hydroxypropyl groups with a molar degree of substitution MS <1 are substituted.

As the polymeric or low molecular weight cationic compounds according to the ^"in the art for this purpose, the compounds described are generally applicable.

However, it has been shown that the best results, in particular the highest mechanical stability, are achieved if the cellulose ether is crosslinked with a polydiallyl dimethylammonium chloride (PDADMAC). Good results are also achieved by crosslinking with chitin, chitosan, preferably in acid solution with a pH <4.7, or derivatives of chitin or chitosan.

To produce the symplex membrane, the cellulose ether solution containing anionic sulfoalkyl groups, preferably sulfoethyl cellulose solution. applied in a uniform layer thickness to a polymeric support and surrounded with the cationic crosslinking agent, for example by spreading the cellulose ether solution with a doctor on the polymeric support and then spreading the cationic crosslinking agent with a second doctor over the first layer. Alternatively, a polymeric carrier is passed sequentially through the cellulose ether solution and the cationic crosslinking agent. The cationic crosslinking agent penetrates the cellulose ether solution from the outside.

Layer and leads to networking there.

As a rule, the symplex membrane is applied to a liquid-permeable carrier for practical use to further improve the mechanical stability. The usual materials, in particular polyacrylonitrile, polyetherimide, polyvinylidene fluoride, polysulfone, polyhydrogenation as porous membrane or polyester, polypropylene as fleece can be used as polymeric carrier for the symplex membrane according to the invention. For small or experimental apparatus, filter paper is also used instead of a polymeric carrier.

In a further production process, the cellulose ether solution is applied in a uniform layer to a degreased glass plate. The coated glass plate is then immersed in the crosslinking bath in which the symplex membrane is formed. After removal from the crosslinking bath and thorough rinsing with water, the symplex membrane is transferred from the glass plate to a polymeric support or also to a PE film as an intermediate support.

The symplex membranes according to the invention can be produced with good mechanical stability, are stable with respect to aqueous systems and organic solvents, and are notable for a high separation factor combined with a high filtrate flow density.

They are therefore particularly suitable for the separation of water or steam from organic substances and mixtures of substances.

The following experiments and examples are intended to illustrate the present invention without restricting it to them:

Determination of the charge density

The charge density of the samples, which can be used to calculate average degrees of substitution (DS value), was determined using polyelectrolyte titration. An oppositely charged polyelectrolyte with a known charge density is added to the solution of the polyelectrolyte. The charges of the titrant neutralize the charges of the sample, the charge zero point denotes the end point of the titration. It was detected using a particle charge detector (PCD).

Determination of the average molecular weights

The average molar masses of the samples used were determined by means of size exclusion chromatography (GPC). It is a chromatographic method in which the particles are separated according to their hydrodynamic volume, which is roughly related to their molecular weight. There is a connection between the time of elution and the molecular weight.

The molecular weights were determined in part by means of relative and absolute GPC. In the case of the relative GPC, a calibration line was created on the basis of pullulin standard samples of known molar mass. With the absolute GPC, there is no need to determine one

Calibration line. A stray light detector was connected online behind the GPC.

Determination of the intrinsic viscosity

The limit viscosity number measurements were carried out in a 0.1 M NaNO ₃ solution as solvent at 25 ° C. using an Ubbelohde capillary viscometer. A series of dilutions was made and the flow time through the capillary of each solution and the solvent was determined. The evaluation was made according to the Huggins equation.

Determination of the symplex membrane thickness

The thickness of the symplex membranes is decisive for the manageability. It was measured with a mechanical thickness measuring device (Ikon from Zeiss, Jena). The measurements were taken ten times at different locations in the

Repeated symplex membrane and then formed the arithmetic mean. Determination of the degree of swelling

The symplex membranes swell to different extents in different solvents. The degree of swelling SD was determined from the mass of the symplex membrane before and after the swelling process using the following equation:

^ swollen dry) I AA dry

Determination of stability to solvents

The stability of the symplex membranes in different solvents or salt solutions was tested. As a measure of the stability ST, the masses of the symplex membrane were related to each other before and after a storage period in the corresponding solvent.

Determination of symplex membrane performance parameters

In a conventional pervaporation apparatus (CELFA AG, Switzerland) alcohol / water mixtures were dewatered by means of pervaporation using the symplex membranes described. A membrane area of 17 cm was available. Filter paper was used as a support for the membrane. Water-isopropanol mixtures of various compositions were measured at 50 ° C. The permeate was condensed with liquid nitrogen in a cold trap. The composition of feed and permeate were determined using

Density measurements (DMA 48, company Paar KG, Austria) determined.

J = filtrate current density kg / h * m ~ alpha = separation factor, calculated according to: alpha = F / P, where P = (conc. Alcohol / conc. Water) in the permeate

F = (conc. Alcohol / conc. Water) in the solution to be dewatered example 1

A sulfoethyl cellulose with an average degree of substitution of DS = 0.29 and an intrinsic viscosity [η] = 524 ml / g was dissolved with stirring at room temperature in deionized water to give a 3% solution. The average molar mass of the sample used was 1.2-10 ⁶ g / mol.

A 4% solution of a PDADMAC sample with an average molecular weight of 100,000 g / mol was prepared under the same conditions.

The sulfoethyl cellulose solution was applied to a glass plate at a layer height of 500 μm and the entire glass plate was then placed in the PDADMAC solution. After 1 hour, the symplex membrane formed was removed from the solution, rinsed thoroughly with water, transferred to a PE film and dried at room temperature.

When dry, the symplex membrane is slightly cloudy. It is very stable and can be handled well without tearing. An elastic modulus of 3733 MPa with an elongation at break of 3.6% was determined for the mechanical stability.

The symplex membrane formed can be described with the following parameters:

The thickness of the symplex membrane was 12 μm, the degree of swelling was 289%. In the cleaning phase, excess polycation components of approx. 12% by weight are flushed out of the symplex membrane, and then there are no more changes in weight. Analogous behavior was observed in CaCl- _> and NaCl solutions. The separation performance of the symplex membrane in relation to the separation of isopropanol / water is one

Mixture of 20% water and 80% alcohol at J _v = 2.5 kg / h * m ^2, alpha = 365 mixture of 15% water and 85% alcohol at J _v = 1, 6 kg / h * m ^2, alpha = 880

Example 2

A sulfoethyl cellulose with an average degree of substitution of DS "= 0.36 and an intrinsic viscosity [η] = 482 ml / g was added with stirring

Room temperature dissolved in deionized water to a 3% solution. The average molar mass of the sample used was 7.1-10 ⁵ g / mol.

A 4% solution of a PDADMAC sample was prepared under the same conditions. The sample used has an average molecular weight of 100,000 g / mol.

The sulfoethyl cellulose solution was spread on a glass plate in a layer thickness of 500 μm and the entire glass plate was placed in the PDADMAC solution. After 1 hour, the symplex membrane formed was removed from the solution, rinsed thoroughly with water, transferred to a PE film and added

Room temperature dried.

When dry, the symplex membrane is slightly cloudy. It is very stable and can be handled well without tearing.

The symplex membrane formed can be described with the following parameters:

The thickness of the symplex membrane was 20 μm, the degree of swelling was 139%. In the cleaning phase, excess polycation components of approx. 6% by weight are flushed out of the symplex membrane, and then there is no change in weight. Analogous behavior was observed in CaCl ₂ and NaCl solutions. The separation performance of the symplex membrane in relation to the separation of isopropanol / water is one

Mixture of 20% water and 80% alcohol at J _v = 1.67 kg / h * m ² , alpha = 593

Mixture of 15% water and 85% alcohol at J _v - 1.24 kg / h * m ² , alpha = 587

Example 3

With a sulfoethyl cellulose that has an average degree of substitution of

DS = 0.35 and an intrinsic viscosity [η] = 432 ml / g, a 4% solution was prepared with stirring at room temperature in deionized water. The average molar mass of the sample used was 5.5-10 ⁵ g / mol.

A 4% solution of a PDADMAC sample with an average molecular weight vpn

100,000 g / mol was produced under the same conditions.

The sulfoethyl cellulose solution was applied in a layer height of 500 μm on a glass plate and the glass plate was then placed in the PDADMAC solution. After 1 hour, the one that had formed in the meantime

Symplex membrane removed from the solution, rinsed thoroughly with deionized water, transferred to a PE film and dried at room temperature.

When dried, the symplex membrane is slightly cloudy. It is very stable and can be handled well without tearing.

The symplex membrane formed can be described with the following parameters:

The thickness of the symplex membrane was 19 μm, the degree of swelling was 152%. In the cleaning phase, excess polycation components of approx. 8% by weight flushed out of the symplex membrane, then no change in weight occurs. Analogous behavior was observed in CaCl2 and NaCl solutions.

The separation performance of the symplex membrane in relation to the separation of isopropanol / water is one

Mixture of 20% water and 80% alcohol at J _v = 2.02 kg / h * m ² , alpha = 446 Mixture of 15% water and 85% alcohol at J _v = 1.52 kg / h * m ² , alpha = 676

Example 4

As Example 3: Instead of the 4% sulfoethyl cellulose solution, a 3% sulfoethyl cellulose solution was used.

The symplex membrane formed can be described with the following parameters'

The thickness of the symplex membrane was 13 μm, the degree of swelling was 183%. In the cleaning phase, excess polycation components of approx. 10% by weight are flushed out of the symplex membrane, and then there is no change in weight. Analogous behavior was observed in CaCl ₂ and NaCl solutions.

Mixture of 20% water and 80% alcohol at J _v = 2, 10 kg / h * m ² , alpha = 679

Mixture of 15% water and 85% alcohol at J _v = 1.49 kg / h * m ² . alpha = 1492 mixture of 11% water and 89% alcohol at J _v = 0.97 kg / h * m ² . alpha = 2570 Example 5

As Example 3: Instead of the 4% sulfoethyl cellulose solution, a 5% sulfoethyl cellulose solution was used.

The symplex membrane formed can be described with the following parameters:

The thickness of the symplex membrane was 25 μm, the degree of swelling was 139%. In the cleaning phase, excess polycation components of approx. 6% by weight are flushed out of the symplex membrane, and then there is no change in weight. Analogous behavior was observed in CaCl ₂ and NaCl solutions.

Mixture of 20% water and 80% alcohol at J _v = 1.44 kg / h * m ² , alpha = 797 Mixture of 15% water and 85% alcohol at J _v = 1.14 kg / h * m ² . alpha = 1115 mixture of 14% water and 86% alcohol at J _v = 0.84 kg / h * m ² , alpha = 151 1

Example 6

A porous polyacrylonitrile base was made using the hanging meniscus method with a sulfoethyl cellulose, which had an average degree of substitution of DS = 0.35 and an intrinsic viscosity [η] = 432 ml / g. coated. The casting solution had a concentration of 2%. The middle

Molar mass of the sample used was 5.5-10 ⁵ g / mol.

A 20% solution of a PDADMAC sample with an average molecular weight of 100,000 g / mol was prepared with stirring at room temperature in deionized water and used for crosslinking. The separation performance of the symplex membrane in relation to the separation of isopropanol / water is one

Mixture of 20% water and 80% alcohol at J _v = 1.47 kg / h * m ² , alpha = 1009 Mixture of 18% water and 82% alcohol at J _v = 1.35 kg / h * m ² , alpha = 1843

Comparative Examples

Commercially available carboxymethyl cellulose samples with average degrees of substitution of DS = 0.82-0.95 and viscosities in 2% solution in

Range of V2 = 5 - 40,000 mPas with stirring at room temperature dissolved in deionized water so that 1 - 10% solutions were formed.

The procedure was carried out under the conditions from Example 1. However, no mechanically stable symplex membranes could be obtained.

Comparative data

In the patent specification DD 292 846 there are separation performances for symplex membranes. which were manufactured in accordance with DE-OS 3600 333 or DD 292 846, compiled:

Mixture of 20% water and 80% alcohol at J _v = 4.0 kg / h * m ² , alpha = 54 Mixture of 10% water and 90% alcohol at J _v = 1.6 kg / h * m ² , alpha = 93 mixture of 10% water and 90% alcohol at J _v = 1.5 kg / h * m ² . alpha = 85

Mixture of 10% water and 80% alcohol at J _v = 1.4 kg / h * m ² , alpha = 91 Mixture of 10% water and 90% alcohol at J _v = 1.1 kg / h * m ² , alpha = 67 mixture of 10% water and 90% alcohol at J _v = 0.3 kg / h * m ² , alpha = 89 mixture of 10% water and 90% alcohol at J _v = 0.3 kg / h * m ² , alpha = 95 A comparison with the data from Examples 1 to 6 shows that the symplex membranes according to the invention bring about a significantly improved separation factor at a comparable filtrate current density.

Claims

claims

1. Symplex membrane containing polyanions formed from at least one cellulose ether containing sulfoalkyl groups as the anionic component.

2. Symplex membrane according to claim 1, characterized in that sulfoethyl cellulose containing sulfoethyl cellulose, sulfopropyl cellulose or mixed ethers of cellulose etherified with sulfoethyl and sulfopropyl groups are used as the cellulose ethers containing sulfoalkyl groups.

3. Symplex membrane according to claim 1, characterized in that the sulfoalkyl group-containing cellulose ether derivatives of sulfoethyl cellulose or sulfopropyl cellulose are used which are additionally substituted by carboxymethyl, methyl, hydroxyethyl, ethyl or hydroxypropyl groups with a molar degree of substitution MS <1 .

4. Symplex membrane according to claims 1 to 3, characterized in that the cationic component is chitin, chitosan or derivatives of chitin or chitosan or in particular a polydiallyl dimethylammonium chloride.

5. Use of the symplex membrane according to one of claims 1 to 4 for the separation of water or water vapor from organic substances and mixtures of substances.