DD292846A5 - USE OF SYMPLEXMEMBRANES FOR PERVAPORATION - Google Patents

Abstract

The invention relates to the use of symplex membranes for pervaporation. The membranes used are coated and formed on the basis of aqueous solutions of sodium cellulose sulfate as polyanion and linear or branched poly (dimethyldiallylammonium chloride) as a polycation to form films of 0.1 to 0.3 mm thickness. These symplex membranes, in spite of their porous morphological structure, can be advantageously used to dewater organic solvents, especially aliphatic alcohols, by pervaporation, achieving excellent performance parameters. Cellulose sulfate; Poly (dimethyldiallylammonium chloride); Use; pervaporation; Drainage; Solvent; Water content; Performance parameters; Separation factor; Filtratstromdichte}

Description

Field of application of the invention

The invention relates to the use of symplex membranes for pervaporation, which are preferably used in the chemical industry, food industry and biotechnology for dehydration of organic solvents - which are inert to the release agent -, preferably of alcohols.

Characteristic of the known state of the art

It is well known that non-porous membranes must be used for material separation processes by means of pervaporation. Corresponding, especially for dehydration of organic solvents such as alcohols, ketones and aldehyde J? suitable membranes are in

DE-PS 3526755, DE-PS 3410155, DE-PS 3518871, DE-PS 3536007, DE-PS 3529175, DE-PS 3532022, DE-PS 3304956, DE-PS 3220613, DE-PS 3441190,

EP-PS 96339

described.

The described systems have the known disadvantage that either in the presence of high separation factors too low Filtratstromdichten or in the presence of high filtrate flow densities to low separation factors can be achieved. This deficiency could hitherto only be improved by the use of hydrophilic polyelectrolytes as separation medium,

However, so far only anionic systems (DE-OS 3615325t J. Membrane Science, 32 (1987) 207) were used, which are associated with the significant drawback that membranes produced therefrom due to their water solubility are not durable and their technical usefulness therefore in a Variety of cases, especially at

Drainage problems, not given. In DE-OS 3600333 membranes are described which consist of polymers whose main chain is a glycosidic skeleton

and cationic groups and / or anionic groups, at least a part of which forms a salt with counteranions and / or countercations.

They are membranes of the ionized polysaccharide type, their salts of alginic acid, alginic acid derivatives, chitosan and salts of anionic or cationic cellulose derivatives being preferred because of their film formability, and in a plurality of cases additionally ions of mono- or divalent metal salts because of their crosslinking effect.

As further counterions ammonium and pyridinium ions are mentioned which derive from amines or nitrogen-containing heterocyclic compounds, but these are not polymeric compounds.

Allegedly, the respective counterions suitable for membrane formation may also be polyions, mention being made of ionic complexes between alginic acid and polyethyleneimine, chitosan and polyacrylic acid, and alginic acid and chitosan. However, a disclosure of the preparation of such ionic complexes and the effects that can be achieved in mass separation processes is not present.

To conceivable ion complexes au ' There are no indications at all based on cellulosic substances.

In DE-OS 3 801 690, membranes are described, through which water or water vapor selectively permeates and which are based on a polyion complex formed by association between an anionic and a cationic polymer on the surface of the membrane and / or in the membrane. Polyanions used here are exclusively polyacrylic acid or salts thereof and as polycation polymers based on primary, secondary, tertiary or quaternary amines with the nitrogen atom in the main chain.

The separation achievable with such membranes largely correspond to those of other types already known. Interestingly, membranes based on anionic polysaccharides are considered unsuitable for various reasons.

Embodiments for producing membranes, both as flat membranes and as microcapsules, from polycation-polyanion complexes (so-called symplexes) using anionic and cationic polyelectrolytes are described in DE-OS 2412092, DD-PS 152287, DD-PS 270012 A1.Prog.Polym.Sci. 14 (1989) 91; ActaChim.Hungarica 117 (1984) 67.

Thus, DD-PS 152287 describes membranes prepared from the anionic polyelectrolytes carboxymethylcellulose and cellulose sulfate (CS) or mixtures thereof and poly (dimethyldiallylammonium chloride) (PDMDAAC) as a polycation. Since such symplex membranes have a porous morphological structure, they are exclusively suitable for ultrafiltration and microfiltration purposes.

For this reason, the Symplexmembranen described in DD-PS 270012 and DE-OS 2412092 are used only for ultrafiltration purposes.

2Ie of the invention

The aim of the invention is the use of prepared by a technically simple process symplex membranes for pervaporation, which are suitable for dehydration of organic solvents which are inert to the release agent -, preferably of alcohols, especially aliphatic alcohols, and are particularly advantageous technological and have economic effects.

Explanation of the essence of the invention

The object of the invention is the use of Symplexmembranen for pervaporation, for dehydration of organic solvents - which are inert to the release agent -, preferably of alcohols, especially aliphatic C ₂ - to C _e -alcohols, using a conventional Pervaporationsopparatur, wherein the Symplexmembranen used by particularly advantageous effects, especially in terms of achievable performance parameters, distinguished.

According to the invention, the object is surprisingly achieved in that by dehydration of organic solvents - which are inert to the release agent - preferably alcohols, in particular aliphatic C ₂ - to C ₆ alcohols, by pervaporation, a mixture of one or more hydrous organic solvents, in particular hydrous C ₂ - to C ₆ alcohols, in the "feed" space of a two-chamber system of a conventional pervaporation apparatus, which is separated by a pervaporation membrane in the form of the present invention to be used Symplexmembran from Permeatraum, and wherein in the permeate a adjusted and maintained such partial vapor pressure of the water that the water to be removed from the aqueous solvent or l.ösungsmittelgemisch enters vaporous in the permeate space and is removed therefrom.

According to the invention, the pervaporation membrane used is in each case a symplex membrane based on sodium cellulose sulfate (CS) as polyanion and poly (dimethyldiallylammonium chloride) (PDMDAAC) as polycation, which is prepared from an aqueous solution I of 1 to 10% by weight in% of a CS, with an average degree of substitution of 0, 12 to 1.5 and a relative viscosity (ΕΤΑ ,, ι) - related to an aqueous solution of 1 mass in% at 20 ° C - from 300 to 250OmPa s, and an aqueous solution II of 10 to 40 parts by mass in% linear PDMDAAC with an ETA ,,, 1.8 to 3.7 mPa · s - relative to a 1% Masseantnil in PDMDAAC containing 1N aqueous NaCl solution at 3O ⁰ C or a branched PDMDAAC, z. Example of one prepared according to EP-PS 0264710, miteinerETA "i of 2.5 to 4.0 mPa · s-based on a 1 wt% in% PDMDAAC containing 1N aqueous NaCl solution at 309 ⁰ C-, in the interface between the solutions I and Il was formed into a planar membrane by the tempered to 10 to 60 ° C solution I by means of a suitable device, for. B. by means of an equally tempered doctor device on an equally tempered suitable surface such. As a glass plate, or- to achieve better mechanical strength - on a suitable support material, such as paper, textile or a support membrane, streaked to a film of a wet film thickness of 0.1 to 0.3 mm, this then tempered with the solution I solution Il overlaid in the same way and left the resulting planar structure on the substrate or the support material for 10 to 60min at a temperature of 10 to 60 ° C for membrane formation, the resulting membrane then, to remove excess CS and PDMDAAC, in one Water bath of 10 to 5O ⁰ C, 1 to 50 h watered and then dried in air at least until sufficient mechanical handling.

Are used in this membrane preparation aqueous PDMDAAC solutions containing NaCl up to 5 parts by mass in%,

Thus, the achievable strength values of non-reinforced membranes are positively influenced in a known manner.

The said symplex membranes are surprisingly, despite their porous morphological structure for drainage

of organic solvents - which are inert to the release agent -, preferably of alcohols, in particular aliphatic C ₂ - to C _e -alcohols suitable by means of pervaporation, and are characterized by such

Use also by various surprising and beneficial effects. So z. B. in the case of dehydration of said alcohols one hand, the maximum allowable Water output concentration even up to 95 parts by mass in% be -wobei those used for pervaporation Surprisingly, Symplexmembrans remain stable - and on the other hand, the dewatering process up to the recovery of

anhydrous alcohol, especially in ethanol.

Furthermore, according to the invention for the dewatering of said solutions by means of pervaporation vorwendeten

Symplexmembranen thereby compared to the best known Pervaporationsmembranen - at approximately the same Operating conditions with regard to water outlet concentration and temperature of the solution to be dehydrated and the Filtratraumdruckes - better performance parameters. So z. In dehydration of ethanol and a starting water concentration of 50 parts by mass in%

achieved at least by a factor of 2 higher filtrate current density at comparable separation factors.

With decreasing water outlet concentration, these beneficial effects continue to increase, so that z. B. at a

Water output concentration of 10 parts by mass in% at least a factor of 5 higher filtrate current density

achieved at comparable separation factors.

embodiments

- all percentages mean mass shares in%

as sodium cellulose sulfate (CS), a product prepared in a manner known per se from cotton linters, having a cuoxam DP of 1400, was used

- The solutions used, as well as the doctor device and the coating material used in each case were adjusted to the same temperature

In a conventional pervaporation apparatus, alcohol and water mixtures were dewatered by means of pervaporation using the described symplex membranes and, on the other hand, using comparative membranes, and the following membrane performance parameters were determined, which are summarized in Table 1 for the dehydration of alcohol / water mixtures and in which:

• J »= filtrate current density in kg / h · m ²

• 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 dehydrated

example 1

A tempered to 20 ° C, 2% aqueous CS solution with a DS = 0.40 and a ΕΤΑ ,, ι = 55OmPa · s - based on a 1% aqueous solution at 20 ⁰ C - was by means of a Doctor blade device to a 0.2 mm thick film streaked on a glass plate backing, which then in the same manner with a 20% aqueous solution of a linear PDMDAAC with a ΕΤΑ ,, ι = 2.8 mPa · s - based on a 1% PDMDAAC 1N aqueous NaCl solution was coated at 3O ⁰ C overlaid. After standing for 30 minutes at 20 ° C in air, the pad with the membrane formed thereon 48h in a water bath of 2O ⁰ C was watered and the membrane then dried at 20 ° C in the air to constant mass. Using the membrane obtained different, heated to 5O ⁰ C, mixtures of alcohol and water in a conventional pervaporation apparatus were dehydrated at a Permeatraumdruck of 0.67 kPa by means of pervaporation. Performance parameters:

Mixture of 50% ethanol / 50% water: J _v = 8.9; alpha = 19 Mixture of 80% ethanol / 20% water: J _v = 4.0; alpha = 54 mixture of 90% ethanol / 10% water: J _v = 1,6; alpha = 93 mixture of 18.8% ethanol / 15.1% water / 4.1% n-propanol /

15.9% i-butanol / 46.1% i-pentanol: J, = 2.3; alpha = 205

Example 2 The procedure was as in Example 1, but a CS solution with a DS = 0.45 and an ETA ₁ ,, = 495 mPa used. Performance parameters: Mixture of 50% ethanol / 50% water: J _v = 7.6; alpha = 21 Example 3 The procedure was as in Example 1, over to produce a composite membrane in place of the glass plate pad Filter paper (basis weight = 90g / m ² ) used as a substrate connecting with the membrane. Because the obtained Compositmembran incurred directly with a sufficient mechanical strength, could on the described in Example 1

final drying process can be omitted.

Performance parameters: Mixture of 90% ethanol / 10% water: J _v = 1.5; alpha - = 85 Example 4 The procedure was as in Example 1, but a branched PDMDAAC (prepared according to EP-PS 0264710) with a

ΕΤΑ ,, ι = 3.08 mPa s - based on a 1% PDMDAAC containing 1N aqueous NaCl solution at 30 ⁰ C - used.

Performance parameters: Mixture of 90% ethanol / 10% water: Jy = 1.4; alpha = 91 Example 5

The procedure was as follows, but using a CS solution with a DS = 0.41 and a ΕΤΑ ,, ι = 212OmPa · s.

Performance parameters:

Mixture of 90% Etha.iol / 10% water: J, = 1.1; alpha = 67

Example 6 (comparative example)

To carry out the pervaporation, a chitosan membrane crosslinked with formaldehyde and prepared according to DE-OS 3600333 was used as a pervaporation membrane, the temperature to be separated ethanol / water mixture at 6O ⁰ C and maintained in the permeate <jm a pressure of 0.04 kPa.

Performance paramaters:

Mixture of 50% ethanol / 50% water: J _v = 4.4; alpha = 18

Example 7 (comparative example)

For carrying out the pervaporation procedure was as in Example β, but an N-acylated chitosan membrane prepared according to DE-OS 3600333 used as Pervaporationsmembran.

Leisiungsparameter:

Mixture of 50% ethanol / 50% water; J _v = 4.1; alpha = 17

Example 8 (Comparative Example)

The pervaporation was carried out as in Example 6, but using a sodium alginate membrane prepared according to DE-OS 3600333 as a pervaporation membrane.

Performance parameters:

Mixture of 90% ethanol / 10% water; J »= 0.3; alpha = 89

Example 9 (Comparative Example)

For carrying out the pervaporation, the procedure was as in Example 6, but a lithium alginate membrane prepared according to DE-OS 3600333 was used as a pervaporation membrane.

Le stungsparameter!:

Mixture of 90% ethanol / 10% water; J _v = 0.3 alpha = 95

A comparison of Examples 1 and 2 shown in Table 1 with 6 and 7 shows that in the separation of ethanol / water mixtures 50/50% solution of the invention leads to a higher by about a factor of 2 filtrate current density, with comparable separation factors.

An example of the examples 1.3 (composite membrane) and 4 with 8 and 9 shows that in the separation of ethanol / water mixtures 90/10%, the solution according to the invention to an approximately higher by a factor of 5 filtrate current density, at comparable separation factors , leads.

The above-stated increase factor is in reality even higher, since the pervaporation was carried out in the comparative examples at a temperature higher by 10 ^° C.

Example 5 is not directly comparable with the other examples mentioned above, since a very high-purity CS was used as a membrane constituent.

Table 1

Summary of membrane performance parameters for dehydration of alcohol-water mixtures

Ex. Ethanol / water (%) alpha 4.4 19 80/20 I 4.0 54 90/10 alpha Ethanol / water / :; PermeatraumdruckO, 67kPa 4.1 21 n-propanol / i-butanol / 8.9 J _v alpha jv 93 i-pentanol (%) 50/50 7.6 18.8 / 15.1 / 4.1 / 15.9 / 1.6 85 46.1 jv 60 ^° C; Permeatraumdruck0,04kPa) 91 Jv alpha (T = 5O ⁰ C 18 1.5 67 1 Comparative Examples (T = 17 1.4 2,3205 2. β 1.1 3 7 4 8th 89 5 9 95 0.3 0.3

Claims (2)

1. Use of symplex membranes for pervaporation for dehydration of organic solvents - which are inert to the release agent - to which a mixture of one or more aqueous solvents, in the "feed" space of a two-chamber system of a conventional Pervoporationsapparatur is passed through a pervaporation membrane is separated from the permeate space, and wherein in the permeate space such a partial vapor pressure of the water is adjusted and maintained that the water to be removed from the aqueous solvent or solvent mixture enters the permeate space in vapor form and is removed therefrom, characterized in that in each case a membrane based on sodium cellulose sulfate (CS) as polyanion and poly (dimethyldiallylammonium chloride) (PDMDAAC) from polycation is used as Pervoporationsmembran from an aqueous solution I from 1 to 10 parts by weight in% of a CS, with an average Substitution degree of 0.20 to 1.5 and a relative viscosity (ETA _re i) - based on an aqueous solution of 1 mass in% at 20 ^c C from 300 to 250OmPa · s, and an aqueous solution II from 10 to 40 Mass fractions in% of a linear PDMDAAC with an ETA _re | from 1.8 to 3.7 mPa · s-based on a 1 wt% in% PDMDAAC containing 1N aqueous NaCl solution at 30 ° C or a branched PDMDAAC, for example one prepared according to EP-PS 0264710, with an ETA _re i from 2.5 to 4, OmPa · s - based on a 1 wt% in% PDMDAAC containing 1N aqueous NaCl solution at 3O ⁰ C-, was formed in the interface between the solutions I and II to a planar membrane by the on 10 to 6O ⁰ C tempered solution I by means of a suitable device, for. B. by means of an equally tempered doctor device on an equally tempered suitable surface such. As a glass plate, or-to achieve better mechanical strength - struck on a suitable support material, such as paper, textile or a support membrane, to a film of a wet film thickness of 0.1 to 0.3mm, this then with the solution tempered as solution I. Covered in the same way and left the resulting planar structure on the substrate or the support material for 10 to 60 min at a temperature of 10 to 60 ⁰ C for membrane formation, the resulting membrane then, to remove excess CS and PDMDAAC, in A water bath of 10 to 50 ⁰ C, 1 to 50h watered and then dried in air at least until sufficient mechanical handling. 2. Use according to claim 1, characterized in that the symplex membranes are preferably used for dehydration of alcohols, in particular aliphatic C ₂ - to C ₆ -alcohols, by means of pervaporation.