DE4437869B4 - Surfactant-containing membranes for pervaporation, process for their preparation and use of a surfactant-containing membrane - Google Patents

Abstract

surfactant Membrane for pervaporation with a polyelectrolyte-surfactant complex with a water-soluble macromolecular compound (polyelectrolyte), characterized that it the polyelectrolyte is an anionic cellulose derivative and the surfactant is a cationic surfactant.

Description

The The invention relates to a surfactant-containing membrane for pervaporation with a Polyelectrolyte-surfactant complex with a macromolecular compound (Polyelectrolyte), a process for their preparation and the use a surfactant-containing membrane.

A Surfactant-containing membrane of this type is known (US Pat. No. 4,927,540). This is a coating for membranes for one Substance separation according to the principle of reverse osmosis known, i. the There provided coating for one already for reverse osmosis suitable membrane can be used with an ionic complex, about the performance the support membrane or to improve the existing membrane. After application a first ionic layer is in the known membrane a oppositely charged second component applied to the Goal to the already existing salt-retaining properties too strengthen so that one Improvement of salt retention from Z. B. 91.5% to 98.2% is achieved.

When Support membranes in the known membrane cellulose acetates used in different ways. These support membranes are in their structure asymmetric and possess a nonporous, separating active Layer at the top, which already has reverse osmosis separation properties having. In the known membrane, the support membrane has a coating which consists of a so-called ionic complex, which consists of a first cationic compound (more precisely: first compound with cationic Groups) and a second anionic compound (more precisely: second Compound with anionic groups) is constructed.

For the separation liquid Mixtures of substances in which distillative separation is difficult achieve, for example in azeotropes, that poses as pervaporation (evaporation through membranes) called membrane process one Alternative, for the dense membranes needed Be after the solution-diffusion mechanism function. The chemical character of the membrane determines which Type of components preferably permeated. Thus strongly hydrophilic membrane materials favor water transport and are therefore used for dewatering organic mixtures used. In the case of a hydrophobic membrane material, the one diffuses organic component, the strongest interacts with the membrane polymer.

For such Separation already exist numerous organophilic membranes, the made from a variety of polymers and modified polymers WUR the. A comprehensive overview of the behavior of such polymer membranes, J.Neel in R.Y.M. Huang: pervaporation Membrane Separation Processes, Elsevier 1991, Chap. 1. Condition for one good release effect is a swelling of the membrane polymer, i. a selective uptake of the organic component to be separated. Often But the polymer application finds its natural limit by the solubility in organic systems. This can be done by chemical crosslinking the membrane polymer are counteracted. At the same time sink but the material flow densities in some technically uninteresting orders of magnitude down.

It are already pervaporation membranes of polyelectrolyte complexes known over high throughput rates and good selectivity even at low working temperatures feature, See Polymer Bulletin 25 (1991) 95 and DE-A-42 29 530; EP-A-0 587 071.

at These polyelectrolyte complexes are reaction products of oppositely charged macromolecular ions. As a result of the hydrophilic character of these polyions are membranes of polyelectrolyte complexes though for the drainage organic solvent well suited. However, they show pure organic mixtures only a minor one or no separation effect.

In DD-A-270 012 the formation of a membrane of cellulose sulfate and a surfactant, which is a precipitation process of the polyelectrolyte in an aqueous solution of a cationic surfactant. This is a porous membrane for the Ultrafiltration obtained, their separation efficiency under proportions however completely is inadequate and that of half even about any related technical Has relevance.

Polyelectrolyte-surfactant ion complexes (PEL-TS complexes) have also been described. The complex formation can be carried out between cationic polymers and anionic surfactants, between anionic polyelectrolytes and cation surfactants as well as with polyampholytes and polypeptides. A Comprehensive literature review by Dawydoff, Linow and Philipp in Acta Polymerica 38 (1987) 307-312, 461-466, 509-515. However, such PEL-TS complexes have not yet been used for separation purposes.

task The present invention is one after the solution-diffusion mechanism provide a functioning membrane with which it is possible organic liquid mixtures to separate with high efficiency and / or organic components aqueous mixtures separate.

Is solved this task with regard to the membrane in that it is in the polyelectrolyte to an anionic cellulose derivative and in the surfactant is a cationic surfactant.

The inventive membrane is opposite extraordinary organic media stable, as it arises as a reaction product of poly or surfactant ions and as a "salt-like" compound through purely organic components is hardly attacked. In addition, the membrane according to the invention has only over a small thickness, so that it possible with her is, high rivers even at low process temperatures to ensure.

The inventive membrane thus represents a type of membrane that allows the special hydrophobic properties of surfactants in the separation process of pervaporation exploit.

The inventive membrane is formed by forming a polyelectrolyte-surfactant complex. By combining a water-soluble Polyelectrolyte with a water-soluble cationic surfactant is a thin membrane insoluble in water and organic liquids formed, which surprisingly despite the hydrophilic polyelectrolyte no drainage properties has more, but in particular to permeate organic components leaves.

These according to the invention, membrane receives by an interface reaction an aqueous solution of a anionic or cationic macromolecular compound with a also dissolved in water, oppositely charged ionic surfactant. The surfactant solution should have a high solids content.

The inventive membrane can be obtained on two procedures. So you can, for example to prepare the polyelectrolyte surfactant complex separately by an aqueous solution, in particular one higher viscous solution, a polyelectrolyte with an aqueous surfactant solution, in particular a concentrated surfactant solution, overcoated. After a certain reaction time, the resulting water is watered Membrane to remove adherent, unreacted reactants. Subsequently you can dry in air at room temperature. The obtained Membrane is for ready for pervaporation use. To improve the mechanical Stability is transferred the polyelectrolyte-surfactant membrane, in particular in the so-called Trans ferverfahren, on a porous backing and only then dry. This gives a composite membrane composite.

you However, a layer of a film of the polyelectrolyte can first be used on a base. Then you cover this polyelectrolyte film either in the wet state or after drying with the surfactant solution and thus produces the polyelectrolyte-surfactant complex.

It is according to the invention thus possible to form membranes from polyelectrolytes and ionic surfactants the after solution-diffusion mechanism function.

The membranes according to the invention represent organophilic membranes that are primarily formed by electrostatic interactions, but also held together by hydrophobic interactions and a high chemical stability especially opposite organic liquids exhibit. Thus, according to the invention a new type of membrane is provided which has excellent filtrate flow performance with at the same time excellent separation factor.

The inventive membrane is preferably prepared according to the following general procedure, as the polyelectrolyte, a water-soluble anionic cellulose derivative and as a surfactant, a cationic surfactant is used.

A 1 to 10%, preferably 2 to 6% aqueous solution of a Natriumcellulosesulfates with egg nem degree of substitution of 0.3 to 0.8, optionally after filtration and / or deaeration, at room temperature by application to a flat surface of glass, metal, plastic, fabric, non-woven or paper, the documents may be dense or permeable, deformed to a 0.1 to 1 mm, preferably 0.2 to 0.5 mm thick film. This film of the polyelectrolyte is overcoated with the aqueous solution of the ionic surfactant. The surfactant concentration is between 10 and 50%, the coating thickness between 0.1 and 1 mm. The upper stratification with the surfactant solution can be carried out successively but also simultaneously. After a reaction time of 0.5 to 30 minutes, a treatment with water to remove the unreacted reactants. The polyelectrolyte-surfactant complex membrane formed can then be dried in air, or the drying is carried out after being passed on a porous support layer, or it is dried immediately after preparation on a porous pad, in both latter cases a composite membrane arises.

The The invention is explained in more detail below with reference to the examples.

example 1

On a glass substrate is a film of an aqueous cellulose sulfate solution with a drawing strength of 0.2 mm drawn. The concentration of the cellulose sulfate solution is 5% by mass. Thereafter, with an aqueous solution of Surfactants N-Dodecylpyridiniumchlorid overlaid. The surfactant concentration is 20% by mass, the coating thickness 0.3 mm. After a reaction time of 15 min, the resulting Membrane repeatedly treated with water and wet on a porous one Support made of polyvinylidene fluoride (PVDF). Subsequently, will dried at room temperature in air.

This membrane was subjected to a pervaporation test. The feed used was a mixture of 20% ethanol and 80% water or 20% isopropanol and 80% water. The working temperature was 15 ° C and 30 ° C, the pressure in the permeate space was in the range of 1 to 5 mbar. The pervaporation results are summarized in the following table. Table 1 Temperature Feed concentration Permeate concentration Flow

Example 2

METHANOL/CYCLOHEXAN

For the separation of methanol / cyclohexane or ethanol / cyclohexane by means of pervaporation, the membrane type described in Example 1 was used. The working temperatures were 30 ° C and 50 ° C, the pressure in the permeate space was 0.4 to 1.8 mbar. Table 2 Temperature Feed concentration Permeate concentration Flow

METHANOL / CYCLOHEXANE

Example 3

The cellulose sulfate film was prepared as in Example 1. For overcoating, the surfactant N-benzyl-N-dodecyl-N-bis (2-hydroxyethyl) ammonium chloride was used. Its concentration was 20% by mass, the coating thickness 0.3 mm and the reaction time 15 min. After washing, the membrane was transferred to a porous polyacrylonitrile underlayer and dried in air. Pervaporation was carried out at 50 ° C. with ethanol / cyclohexane or methanol / cyclohexane at a pressure in the permeate space of 0.7 to 1.6 mbar. Table 3 Temperature Feed concentration Permeate concentration Flow

Example 4

• a) Benzethoniumchlorid (BEC)
• b) Methylbenzethoniumchlorid (M-BEC)
• c) Hexadecyl-trimethylammoniumchlorid (HDAC)
• d) Hexadecyl-pyridiniumchlorid (HDPC)
• e) Dodecylcarbamyl-methyl-dimethylbenzylammoniumchlorid (Quartolan)

According to the procedure described in Example 1, further cationic surfactants were reacted with cellulose sulfate as the polyelectrolyte component:

• a) Benzethonium chloride (BEC)
• b) Methylbenzethonium chloride (M-BEC)
• c) hexadecyltrimethylammonium chloride (HDAC)
• d) hexadecylpyridinium chloride (HDPC)
• e) Dodecylcarbamylmethyldimethylbenzylammonium chloride (Quartolan)

METHANOL/CYCLOHEXAN

The pervaporation results are summarized in the table, the working temperature was in all cases 50 ° C, at a Permeatraumdruck of 0.4 to 1.8 mbar. Table 4 Surfactant Feed Conc. Permeate Concentration Flow

METHANOL / CYCLOHEXANE

Example 5

Membranes of cellulose sulfate and the surfactants N-dodecylpyridinium chloride (N-DPC), benzethonium chloride (BEC) and hexadecyl-pyridinium chloride (HDPC) were prepared according to Example 1. The pervaporation experiments were carried out with a mixture of 2% methanol and 98% pentane at a working temperature of 30 ° C. The pressure in the permeate space was in the range of 0.6 to 1.2 mbar. Table 5 Surfactant Feed Conc. Permeate Concentration Flow

Claims (7)

Surfactant-containing membrane for pervaporation with a polyelectrolyte-surfactant complex with a water-soluble macromolecular compound (polyelectrolyte), characterized in that it is at the Po lyelektrolyt to an anionic cellulose derivative and the surfactant is a cationic surfactant. Membrane according to claim 1, characterized in that that she from a layer of the polyelectrolyte and a layer of composed of the cationic surfactant, the two layers connected at their common boundary layer by reaction are. Membrane according to claim 2, characterized in that that the Polyelektrolytschicht and the surfactant layer each have a thickness of 0.1 to 1.0 mm, in particular from 0.2 to 0.5 mm. Membrane according to one of claims 1 to 3, obtainable thereby, that he a) produces a film of the polyelectrolyte, if necessary on a plane Underlay, and with an aqueous solution of the Overlaid cationic surfactant or b) an aqueous solution the polyelectrolyte with an aqueous solution of layered with cationic surfactant, c) react, d) treated with water, e) if necessary, transferred to a porous pad and f) dries. Membrane according to claim 4, obtainable thereby, that he a 1 to 10% by mass, in particular 2 to 6% by mass, polyelectrolyte solution and / or a 10 to 50% by mass surfactant solution used and / or allowed to react for 0.5 to 30 min. Process for producing a membrane according to one the claims 1 to 3, characterized in that a) make a movie the polyelectrolyte produced, optionally on a flat surface, and with an aqueous solution of Overlaid cationic surfactant or b) an aqueous solution the polyelectrolyte with an aqueous solution of layered with cationic surfactant, c) react, d) treated with water, e) if necessary, transferred to a porous pad and f) dries. Use of a surfactant-containing membrane after a the claims 1 to 5 for pervaporation.