WO2013124190A1

WO2013124190A1 - Method for processing water by means of membrane distillation using a siloxane copolymer membrane

Info

Publication number: WO2013124190A1
Application number: PCT/EP2013/052820
Authority: WO
Inventors: Tobias Halbach; Peter Ball; Erich Schaffer
Original assignee: Wacker Chemie Ag
Priority date: 2012-02-23
Filing date: 2013-02-13
Publication date: 2013-08-29
Also published as: DE102012202792A1

Abstract

The invention relates to a method for processing water by means of membrane distillation, wherein a membrane M made of porous silicone material is used.

Description

METHOD FOR THE PROCESSING OF WATER BY MEANS OF MEMBRANE STILLATION WITH A SILOXANE-COPOLYMER MEMBRANE

The invention relates to a process for the treatment of water by means of membrane distillation, in which a membrane M made of porous silicone material is used.

Common methods of desalination are

Distillation method, reverse osmosis or the

Membrane distillation.

Membrane distillation is a process in which a mixture is separated by means of a porous membrane with a temperature gradient or difference. The membrane pores must not be wetted. By the

Temperature difference between the retentate and the

Permeate side results in a vapor pressure difference, which is the driving force in the membrane distillation.

In the case of an aqueous solution, a hydrophobic, porous membrane must be used. In an aqueous NaCl solution, only the water has a significant vapor pressure, so that only water permeates through the membrane. Prerequisite, however, is a sufficiently small pore diameter, so that no drops of water can pass through. As M. Khayet et al. in Journal of Membrane Science 285 (2006) 4-29, are microporous membranes based on

Polypropylene, polyethylene, polytetrafluoroethylene and

Polyvinylidene fluoride suitable due to their hydrophobicity to desalt water by membrane distillation,

In US 4545862, for example, the use of a

Microporous polytetrafluoroethylene membrane for desalination described. Membranes based on PTFE must be subjected to an elaborate stretching process for pore formation.

Microporous polyolefin membranes, e.g. made of polyethylene or polypropylene are not permanently resistant to oxidation and may lose their hydrophobic properties after oxidation.

The use of a microporous membrane based on

Silicone block copolymers for desalting water are not described in the literature.

In US 2006076294 A, a membrane for desalination

described with a polydimethylsiloxane layer

is coated.

DE 1297552 B describes a method and a device for drinking water production which uses steam-permeable diaphragm tubes made of silicone rubber.

The invention relates to a process for the treatment of water by means of membrane distillation, in which a membrane M made of porous silicone material is used. It has been shown that a membrane M of porous

Silicone material is ideal for the membrane distillation of water.

An advantage over common hydrophobic, microporous

Membranes based on PTFE is the simple production of the membrane by filming a solution, the pore formation, for example, by an evaporation-induced

Phase separation process, on elaborate stretching process can be waived. Compared to polyols inmembranen silicone membranes are characterized by their Oxdidationsstabilität and their intrinsic hydrophobicity.

Preferred is the use of porous membranes M with a uniform pore distribution along the cross section.

Particularly preferred is the use of microporous membranes M, with pore sizes of 0.1 μπι to 20 pm.

The membranes M preferably have an isotropic

10 pore distribution.

The free volume in the membranes M is preferably at least 5% by volume, more preferably at least 20% by volume, in particular at least 35% by volume and at most 90% by volume, 15 particularly preferably at most 80% by volume in particular not more than 75% by volume, relative to the volume of membrane M.

The porous membranes M are preferred from the

Silicone compound S produced.

^'20

The membranes M are preferably produced in one

Method in which

in a first step, a solution or suspension

Silicone compound S is formed from a mixture of solvent LI and solvent L2,

in a second step, the solution or suspension is brought into a mold,

in a third step solvent LI is removed from the solution or suspension until the solubility of the

30 silicone compound S in a mixture of solvent LI and

Solvent L2 is below, with one at

Silicone compound S rich phase A and one on Silicon compound S poor phase B forms and thus the

Structure formation by the phase A takes place and

in a fourth step, the solvent L2 and residues of the solvent LI are removed.

Preferably, the silicone compound gels or precipitates in the third step, and thereby the porous membrane M is obtained from the phase A. The pores are formed by the phase B. The process is much simpler and cheaper than the corresponding processes known from the literature.

A silicone compound S, which has a sufficient

mechanical strength after the structural formation of phase A has, is particularly suitable. That the trained

Cavities must remain stable after removal of the solvent L2 and residues of solvent 1. This can be done by crosslinking the silicone compound S via intermolecular interactions, such as. e.g. about ionic

Interactions, hydrogen bonds, or van der Waals interactions.

Very particularly preferred is the crosslinking via

Hydrogen bonds, such as those in organopolysiloxane-polyurea copolymers, which are sold by Wacker Chemie AG under the brand GENIOMER ^® occur. The silicone compounds S can also be crosslinked.

The networking can be done separately or simultaneously with the

Structure formation of the porous membranes M out

Silicon compound S take place.

The porous membranes M have vapor permeabilities which are significantly higher than the compact silicone films of the prior art. Furthermore, liquids, such as For example, water through the porous membranes M only at higher pressure through the porous membranes M.

Suitable as silicone compound S are in principle all

silicone-containing polymers which fulfill the stated properties.

The silicone compounds S which can be used are preferably copolymers, where all silicone copolymers known from the literature can be used as silicone compounds S. Examples of such silicone copolymers include the groups of the silicone carbonate, silicone imide, silicone imidazole, silicone urethane, silicone amide, silicone polysulfone, silicone polyether sulfone, silicone polyurea, and the like Silicone polyoxalyldiamine copolymers.

Particularly preferred is the use of

Organopolysiloxane / polyurea / polyurethane / polyamide or

Polyoxalyldiamine copolymers of the general formula (III)

wherein the structural element E is selected from the general formulas (IVa ~ f)

R ^H 0

(ivd) -N Y N-

R ^H oo R ^H

(IVe)

-NCOYOCN ~

wherein the structural element F is selected from the general formulas (Va-f)

R ^H 0

-N- -C-

(Vd)

in which

R substituted or unsubstituted coals, which may be interrupted by oxygen or nitrogen,

RH has hydrogen, or the meaning of R,

X is an alkylene radical having 1 to 20 carbon atoms in which non-adjacent methylene units are represented by groups

-O- may be replaced, or an arylene radical having 6 to 22

Carbon atoms,

Y is a bivalent, optionally substituted by fluorine or chlorine hydrocarbon radical having 1 to 20

Carbon atoms,

D is optionally substituted by fluorine, chlorine, Ci-Cg-alkyl or

C] _- Cg-alkyl ester substituted alkylene radical having 1 to 700

Carbon atoms in which not adjacent to each other Methylene units may be replaced by groups -O-, -COO-, -OCO-, or -OCOO-, or arylene radical having 6 to 22

Carbon atoms,

B, B ^{1 is} a reactive or non-reactive end group which is covalently bonded to the polymer,

m is an integer from 1 to 4000,

n is an integer from 1 to 4000,

g is an integer of at least 1,

h is an integer from 0 to 40,

an integer from 0 to 30 and

3 is an integer greater than 0.

Preferably, R is monovalent

Hydrocarbon este having 1 to 18 carbon atoms, which are optionally substituted by halogen atoms, amino groups, ether groups, ester groups, epoxy groups, mercapto, Cyanogru'ppen or (poly) glycol radicals, the latter being composed of oxyethylene and / or oxypropylene units, more preferably Alkyl radicals with 1 to 12

Carbon atoms, especially the methyl radical,

However, radical R can also be divalent radicals which, for example, link together two silyl groups. Examples of radicals R are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, 1-n-butyl, 2-n-butyl, iso-butyl, tert. Butyl, n-pentyl, iso-pentyl, neo-pentyl, tert. - pentyl radical; Hexyl radicals, such as the n-hexyl radical; Heptyl radicals, such as the n-heptyl radical; Octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as the 2, 2, -trimethylpentyl radical; Nonyl radicals, such as the n-nonyl radical; Decyl radicals, such as the n-decyl radical; Dodecyl radicals, such as the n-dodecyl radical; Octadecyl radicals, such as the n-octadecyl radical; Cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl radicals; Aryl radicals such as phenyl, naphthyl, anthryl and phenanthryl res; Alkaryl radicals, such as o-, m-, p-tolyl radicals; Xylyl radicals and ethylphenyl radicals; and aralkyl radicals, such as the benzyl radical, the α- and the β-phenylethyl radical.

Examples of substituted radicals R are methoxyethyl,

Ethoxyethyl and ethoxyethoxyethyl or chloropropyl and trifluoropropyl.

Examples of divalent radicals R are the ethylene radical,

Polyisobutylenediyl radicals, and propanediyl-terminated

Polypropylene glycol residues.

The radical R ^H is preferably hydrogen or the radicals specified for R above.

Radicals Y are optionally halogen atoms, such as fluorine or chlorine, substituted hydrocarbon radicals having 3 to 13 carbon atoms, in particular the 1,6-hexamethylene radical, the 1,4-cyclohexylene radical, the methylenebis (cyclohexylene ) Rest, the 3-methylene ~ 3, 5, 5-trimethylcyclohexylenrest, the phenylene and the

Naphthylene radical, the m-Tetramethylxylylenrest and the

Methylene bis (4-phenylene) radical.

Examples of divalent hydrocarbon radicals Y are alkylene radicals, such as the methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, tert. Butylene, n-

Pentylene, iso-pentylene, neo-pentylene, tert. Pentylene radical, hexylene radicals, such as the n-hexylene radical, heptylene radicals, such as the n-heptylene radical, octylene radicals, such as the n-octylene radical and iso- Octylene radicals such as the 2, 2, 4-trimethylpentylene radical, nonylene radicals such as the n-nonylene radical, decylene radicals such as the n-decylene radical, dodecylene radicals such as the n-dodecylenes;

Cycloalkylene radicals, such as cyclopentylene, cyclohexylene,

Cycloheptylenreste, and Methylcyclohexylenreste, like the

Methylene-bis- (4-cyclohexylene) - and the 3-methylene-3, 5, 5-trimethylcyclohexylenrest; Arylene radicals, such as the phenylene and the naphthylene radical; Alkarylene radicals, such as o-, m-, p-tolylene radicals, xylylene radicals, such as the m-tetramethylxylylene radical, and

Ethylphenylenreste; Aralkylenreste, such as the benzylene radical, the α- and the ß-phenylethylene radical and the methylene bis (4-phenylene) radical.

Preferably, radical X is alkylene radicals having 1 to 20 carbon atoms, which may be interrupted by oxygen atoms, particularly preferably alkylene radicals having 1 to 10 carbon atoms, which may be interrupted by oxygen atoms, particularly preferably n-propylene, isobutylene, 2-0xabutylene and methylene residues.

Examples of radicals X are the examples given for radical Y and optionally substituted alkylene radicals in which the carbon chain can be interrupted by oxygen atoms, such as, for example, 2-0xabutylene radical.

The remainder B is preferably a

Hydrogen atom, a radical OCN-Y-NH-CO-, a radical

H ₂ NY-NH-CO-, a radical R ³ ₃ Si (0-SiR ³ ₂ ) _n ^~ or a radical R ³ ₃ Si- <0-SiR ³ ₂ ) _n -XE-.

The radical B 'is preferably the radicals indicated for B. The radicals D are preferably divalent polyether radicals and alkylene radicals, particularly preferably divalent polypropyleneglycol radicals and also alkylene radicals having at least 2 and at most 20 carbon atoms, such as the ethylene radical, the 2-methylpentylene and the butylene radical, in particular Polypropylene glycol radicals having 2 to 600 carbon atoms and the ethylene and the 2-methylpentylenrest. n is preferably a number of at least 3, in particular at least 10 and preferably at most 800, in particular at most 400. m is preferably the ranges specified for n. Preferably, g is a number of at most 100, more preferably from 10 to 60.

H is preferably a number of at most 10, more preferably of 0 or 1, in particular 0. j is preferably a number of at most 400, particularly preferably 1 to 100, in particular 1 to 20.

I preferably has a number of at most 10, particularly preferably 0 or 1, in particular 0.

The systems described herein can be cured by any method known to those skilled in the art.

These systems optionally include other typical ones

Additives, e.g. functional silanes.

Suitable as silicone compounds S are next to all

literature-known silicone copolymers, which in addition to the silicone Proportion of organic polymer units, eg polyimides,

Polyurethanes, polysulfones, polyimidazoles, polyamides possess.

In addition to the silicone compounds S

in addition, other polymeric compounds are used. The porous membranes M produced in the process preferably comprise at least 50%, particularly preferably at least 80%, in particular at least 90%, more preferably at least 95%, of the silicone compounds S.

The solvent LI is more easily removable from the solution or suspension prepared in the first step

Silicone compound S as the solvent L2. The

Removability refers in particular to lighter ones

Evaporate or extract.

The term solvent LI includes all organic and inorganic compounds which dissolve silicone compound S at most temperatures. This term preferably includes all compounds which, under otherwise identical conditions, such as, for example, B, pressure and temperature, can dissolve the silicone compound S to a greater extent than the solvent L2.

That the maximum achievable concentration of

Silicone compound S in the solvent LI is preferably higher than the maximum achievable concentration of the silicone compound S in the solvent L2.

The maximum achievable concentration of the silicone compound S is preferably by the factor 2, particularly preferably by the

Factor 10, but especially by a factor of 100 in the

Solvent LI higher than in the solvent L2. The term solvent LI additionally includes relatively high molecular weight compounds, such as liquid polymers.

Depending on the solvent LI and silicone compound S, increased pressures may also contribute to the solubility.

Preference is given to solvents LI in which the

silicone-containing polymers at 20 ° C and 1 bar to at least 10 wt .-%, more preferably at least 15 wt .-% and in particular at least 20 wt .-% solve.

Depending on the solvent and polymer, increased pressures may also contribute to low solubility. The term solvent L2 additionally encompasses also relatively high molecular weight compounds, such as, for example, liquid polymers.

Preference is given to solvents L2 in which the

silicone-containing polymers at 20 ° C and 1 bar to at most 20 wt .-%, more preferably at most 10 wt .-% and in particular at most 1 wt .-% solve.

The solvent LI and the solvent L2 may each consist of one or more components.

Preferably, the solvent LI or all components of the solvent LI at 20 ° C and 1 bar has a higher

Vapor pressure on as the solvent L2 or all constituents of the solvent L2,

Preferably, the boiling point of the solvent LI or all components of the solvent LI at 1 bar at least 30 °, more preferably at least 40 °, in particular at least 50 ° lower than the boiling point of the solvent L2 or all components of the solvent L

If, in the first step, a suspension of the silicone compound S is formed in a mixture of solvent LI and solvent L2, this indicates an incipient phase separation, which can be partially prevented by stirring.

The transition of the solution or suspension to the silicone molding can be done in different ways. If e.g. a homogeneous solution of silicone compound S is present, in the third step in the phase separation first a suspension can be formed, from which then a first gel body

arises, which is characterized by the further removal of the

Solvent LI or solvent L2 can be converted to a stable porous membrane M of silicone compound S.

If a suspension already exists in the first step, the gel structure from the suspension of the silicone compound S can be formed in the third step in the phase separation. This is faster in most cases than when starting with homogeneous

Solutions of silicone compound S.

Preferably, after the third step, at most 30% by weight, particularly preferably at most 20% by weight, in particular at most 10% by weight, of the solvent LI used in the first step are present in phases A and B.

The solvent LI can in the third step through all

Technically known options are removed from the casting solution. Preferably, the removal of the solvent LI is by evaporation or extraction. Examples of preferred technical processes are evaporation by convection, forced convection, heating or

evaporate in a humid atmosphere or extract by

Solvent exchange or washing with a volatile solvent.

The method must always be chosen so that a production of the porous membranes M in an acceptable

Period, however, the structure can also be formed.

The rate of evaporation is preferably chosen so that the liquid-liquid phase separation does not occur under thermodynamic equilibrium conditions, otherwise no porous structures are formed.

The solvent L2 does not always have to be inert.

Optionally, the polymer is in the solvent L2

swellable. Preference is given to solvents L2 which are a

Adsorption of preferably not less than 10 wt .-%, particularly preferably not less than 50 wt .-% possess.

The appropriate choice of the solvent L2 is important, as this decides whether the structure is retained after the phase separation or not.

The solvent L2 can in the fourth step on all the

Experts familiar methods to remove species from the molding, examples include extraction, evaporation, a successive solvent exchange or simply washing out the

Solvent L2. The solution or suspension of silicone compound S can be prepared in many ways. In a preferred

Ausführungsforra the invention, silicone compound S is dissolved in the solvent LI and the solvent L2 is added. In a particularly preferred embodiment of the invention, the polymer is dissolved in a solvent mixture of LI and L2.

The solubilities of the silicone compound S in solvent LI are familiar to the person skilled in the art, or if no data are found, can be easily determined by solubility studies. The appropriate solvent L2 can be quickly found in a few experiments, e.g. in simple

Turbidimetric titrations. For this purpose, as long as a second solvent is added to a homogeneous polymer solution until a

Failure of the polymer is observed.

Since the solubilities of silicone compound S greatly differ, solvent LI for a particular silicone compound S may be solvent L2 for another silicone compound S at the same time.

Preferred organic solvents LI or solvent L2 are hydrocarbons, halogenated hydrocarbons, ethers, alcohols, aldehydes, ketones, acids, anhydrides, esters, N-containing solvents and S-containing solvents.

Examples of common hydrocarbons are pentane, hexane, dimethyl butane, heptane, hex-1-ene, hexa-1, 5-diene, cyclohexane, turpentine, benzene, isopropylbenzene, xylene, toluene, benzene, naphthalene, and terahydronaphthalene, examples of common halogenated Hydrocarbons are fluoroform,

Perfluoroheptane, methylene chloride, chloroform,

Carbon tetrachloride, 1, 2-dichloroethane, 1, 1, 1-trichloroethane, Tetrachloroethene, trichloroethene, pentyl chloride, bromoform, 1,2-dibromoethane, methylene iodide, fluorobenzene, chlorobenzene and 1,2-dichlorobenzene, examples of common ethers are diethyl ether, butyl ethyl ether, anisole, diphenyl ether, ethylene oxide,

Tetrahydrofuran, furan, triethylene glycol and 1,4-dioxane.

Examples of common alcohols are methanol, ethanol,

Propanol, butanol, octanol, cyclohexanol, benzyl alcohol,

Ethylene glycol, ethylene glycol monomethyl ether, propylene glycol, butyl glycol, glycerol, glycerol, phenol and m-cresol,

Examples of common aldehydes are acetaldehyde and

Butyraldehyde. Examples of common ketones are acetone, diisobutyl ketone, butan-2-one, cyclohexanone and acetophenone. Common examples of acids are formic acid and acetic acid. Common examples of anhydrides are acetic anhydride and maleic anhydride. Common examples of esters are

Acetic acid methyl ester, ethyl acetate,

Butyl acetate, phenyl acetate, glycerol triacetate, diethyl oxalate, dioctyl sebacate, methyl benzoate, dibutyl phthalate, DBE ^® (DuPont de nemours) and

Phosphoric acid tricresyl ester. Common examples of

nitrogen-containing solvents are nitromethane, nitrobenzene, butyronitrile, acetonitrile, benzonitrile, malononitrile,

Hexylamine, aminoethanol, N, N-diethylaminoethanol, aniline, pyridine, N, N-dimethylaniline, N, N-dimethylformamide, N-methylpiperazine and 3-hydroxypropionitrile. Common examples of sulfur-containing solvents are carbon disulfide, methanethiol, dimethyl sulfone, dimethyl sulfoxide and thiophene. Common examples of inorganic solvents are water, ammonia, hydrazine, sulfur dioxide, silicon tetrachloride and titanium tetrachloride.

As higher molecular weight solvent LI or solvent L2, all non-reactive polymers can be used. Preference is given to liquid non-reactive polymers available in industrial quantities at the processing temperature

used. Examples of such solvents LI and solvent L2 include i.a. Polydimethylsiloxanes with non-reactive

End groups, for example trimethylsilyl terminated linear silicones, phenylsiloxanes, cyclic siloxanes, e.g. Cyclohexadimethylsiloxane or cyclodecadimethylsiloxane. Further examples of such solvents LI or solvent L2 include polypropylene oxides, polyethylene oxides, polyamides,

Polyvinyl acetates, polyisobutenes, polyacrylates, polybutadienes, polyisoprenes and copolymers of the listed substance groups. Particularly preferred solvents LI are for silicone

Copolymers as Silicone Compound S Alcohols, e.g. Isopropanol. Particularly preferred solvents LI are for silicones e.g. Toluene, xylene, benzines (boiling point higher than 80 ° C), pentane or hexane.

Particularly preferred solvents L2 are for silicone copolymers as silicone compound S e.g. Toluene,

Polyethylene glycols, polypropylene glycols, triethylene glycol, ^DBE® , glycerol or NMP. The silicone compounds S can also be in ternary

Solvent mixtures are dissolved. A common example of a tertiary solvent mixture may be e.g. a mixture of a solvent LI and two solvents L2.

An example of a ternary solvent mixture is isopropanol (solvent LI), N-methylpiperazine

(Solvent L2) and dimethylformamide (solvent L2). The silicone compounds S and may also be in Solvent mixtures of more than one solvent LI and more than two solvents L2 are dissolved.

The proportions between solvent LI and

Solvents L2 can vary within a wide range.

Preferably, at least 2, in particular at least 10 parts by weight of solvent L2 and at most 5000, in particular at most 1000 parts by weight of solvent L2 are used in the first step for 100 parts by weight of solvent LI.

The solution or suspension prepared in the first step preferably contains up to 95% by weight, more preferably up to 80% by weight, particularly preferably up to 60% by weight, of solvent LI and solvent L2.

The solution or suspension prepared in the first step preferably contains at least 1% by weight, particularly preferably at least 10% by weight, in particular at least 15% by weight and at most 70% by weight, particularly preferably at most 40% by weight, in particular at most 25% by weight of silicone compound S,

Preferably, the solution or suspension is brought in the second step at temperatures of at least 0 ° C, more preferably at least 10 ° C, in particular at least 20 ° C and at most 60 ° C, more preferably at most 50 ° C in a mold.

In one embodiment of the invention, further additives are added to the solution or suspension. Typical additives are inorganic salts and polymers. Common inorganic salts are LiF, NaF, KF, LiCl, NaCl, KCl, MgCl ₂ , CaCl ₂ , ZnCl ₂ and CdCl ₂ . The added additives may remain in the porous membrane M after preparation or be extracted or washed out with other solvents. It is also possible to incorporate mixtures of different additives into the solution or suspension. The

Concentration of the additives in the polymer solution is preferably at least 0.01% by weight, more preferably at least 0.1% by weight, in particular at least 1% by weight of ° C and at most 15% by weight, particularly preferably at most 5% by weight .-%. Thus, in a particularly preferred embodiment of the invention, 1 to 3% by weight LiCl and 2 to 5% by weight NaCl are added to the solution or suspension. The solutions or suspensions may also be used in

Formulations contain conventional additives and additives. To call here would be u.a. Leveling agents, surface-active substances, adhesion promoters, light stabilizers such as UV absorbers and / or radical scavengers, thixotropic agents and other solids and fillers. To generate the respectively desired

Property profiles of the moldings such additives are preferred.

In a likewise preferred embodiment of the invention, the porous membranes M still contain a proportion

Particles. A list of suitable particles can be found in EP 1940940.

In a likewise preferred embodiment of the invention, the porous membranes M also contain active reinforcing agents

Particle. Examples of reinforcing particles are fumed or precipitated silica with treated or untreated surfaces. The solutions or suspensions have, based on the total weight, preferably a content of particles of 0-20% by weight, more preferably 0-10% by weight and most preferably 0-5% by weight.

The polymer solutions may have one or more

contain different particle types, for example

Silica and aluminophosphate. To produce the porous membrane M, the solutions or suspensions are preferably applied or spun onto a substrate in the second step. The applied to substrates solutions or suspensions are preferred to

Membrane films M further processed while the spun

Solutions or suspensions are preferably processed to porous membranes M in the form of hoses and hollow fibers.

The substrates preferably contain one or more substances from the group comprising metals, metal oxides, polymers or glass. The substrates are basically none

bound geometric shape. Preferably, however, the use of substrates in the form of plates, films, textile surface substrates, woven or preferably nonwoven nets or particularly preferably in the form of nonwoven webs are used.

Substrates based on polymers contain, for example, polyamides, polyimides, polyetherimides, polycarbonates,

Polybenzimidazoles, polyethersulfones, polyesters, polysulfones, polytetrafluoroethylenes, polyurethanes, polyvinylchlorides,

Cellulose acetates, polyvinylidene fluorides, polyether glycols, polyethylene terephthalate (PET), polyaryl ether ketones,

Polyacrylonitrile, polymethyl methacrylates, polyphenylene oxides, Polycarbonates, polyethylenes or polypropylenes. Preference is given to polymers having a glass transition temperature Tg of at least 80 ° C. Contain substrates based on glass

For example, quartz glass, lead glass, float glass or soda-lime glass.

Preferred mesh or nonwoven substrates include glass, carbon, aramid, polyester, polyethylene, polypropylene,

Polyethylene / polypropylene copolymer or

Polyethylene terephthalate fibers.

The layer thickness of the substrates is preferably> 1 μκι, more preferably> 50 μτη, most preferably> ■ 100 μπη and preferably <2 mm, more preferably <600 μπι, most preferably <400 pm. Most preferred ranges for the layer thickness of the substrates are those of

above-mentioned values.

The thickness of the porous membrane M of silicone compound S is determined primarily by the amount of solution or suspension. As in the process according to the invention preferably a

Evaporation or extraction step takes place, thinner moldings are preferred. All technically known forms of the order of the solution or suspension on substrates can be used for the preparation of the porous membranes M.

The application of the solution or suspension to the substrate is effected preferably by means of a doctor blade

Meniscus coating, casting, spraying, dipping, screen printing,

Gravure printing, transfer coating, gravure coating or spin on disk. Thus applied solutions or suspensions have μτη film thicknesses of preferably _^> 10, more preferably _> 100 μηι, in particular _> 200 μιτι and preferably <10,000 μπι, more preferably <5,000 μκι, in particular <1000 μηι

produced. Most preferred ranges for the film thicknesses are the ranges formulated from the above values.

Preferably, from the solutions or suspensions formed in the third step, the solvent LI and preferably thereafter in the fourth step the solvent L2 and residues of solvent LI are removed by evaporation,

The evaporation is preferably carried out at temperatures of at least 10 ° C, more preferably at least 20 ° C and at most 150 ° C, particularly preferably at most 200 ° C,

The evaporation can be carried out at any pressure, e.g. at negative pressure, at overpressure or at normal pressure. The evaporation can also take place under defined humid conditions. Depending on the temperature are relative

Humidities in the range of 0.5 to 99% are particularly preferred.

As already mentioned, the evaporation step can also be carried out under defined solvent atmospheres, for example H ₂ O steam, alcohol-steam. The saturation content of the atmosphere can be varied within a wide range, eg between 0% (dry atmosphere) to 100% {complete saturation at the process temperature). This can be the

Evaporation rate of the solvent LI or the inclusion of a solvent or solvent L2 from the atmosphere, vary within a wide range.

The preferred duration of evaporation can be determined for the respective system in a few experiments. Preferably, the evaporation is at least 0.1 second to several hours. The indication of a precise evaporation time can not be given because the determination must be made individually for each system and for each solution or suspension, In a likewise preferred embodiment of the invention, the solvent L2 and residues of solvent LI are removed by extraction in the fourth step.

The extraction is preferably carried out with a further solvent which does not destroy the porous structure formed, but is readily miscible with the solvent L2. Particularly preferred is the use of water as

Extractant. The extraction is preferred

Temperatures between 20 ° C and 100 ° C instead. The preferred duration of the extraction can be determined for the respective system in a few experiments. The duration of the extraction is preferably at least 1 second to several hours. The process can also be repeated several times. Both the evaporation time and the

Evaporation conditions affect the porous structures in terms of pore size, pore size and overall porosity.

If preferred for the intended treatment of water, an anisotropic pore distribution in the membrane M can be achieved by the choice of process parameters.

The treatment of water can be desalination of example

To be brackish or seawater.

The invention is for all common applications in the field

Water treatment available, such as desalination, the treatment of waste water or biological or

nuclear components of contaminated water,

Preferably, the membrane M is used for the production of drinking water, water for irrigation of crops or for the purification of contaminated water. Particularly preferred is the membrane M for the production of

Drinking water and used to produce water for irrigation of crops. The untreated water, in particular salt water, can be treated directly by using the membrane M, so that the treated water can be used directly as drinking water or for irrigating crops.

The use of a membrane distillation step is sufficient to achieve sufficient purity.

The use of multi-stage membrane distillation can be used if very high purities are to be achieved,

The untreated water, especially salt water can

Additives such. B, for the prevention of encrustation, to

Corrosion protection, anti-fouling aids or additives may be added for disinfection.

The treated water may also contain additives such as e.g. Fertilizers are added.

The membranes M can be used as hollow fibers, flat membranes,

Hoses or concentric hoses be executed.

The membranes M can be installed in all common modules, such as flat membrane modules, plate modules,

Cushion modules, winding modules, spiral wound winding modules,

Pocket Modules, Crossflow Modules, Deadend Modules, Tube Modules, Hollow Fiber Modules and Capillary Modules. The membrane M is preferably in direct contact with

Salt water (retentate side), preferably with elevated

Temperature past the membrane and evaporated through the membrane M. The steam will then be on the other Membrane side (permeate, distillate or fresh water side) condensed. The temperature on the distillate side is lower than that on the retentate side, so that through the

Temperature difference is a sufficient difference in vapor pressure is present, which causes the permeate flow through the membrane M and maintains.

The temperature gradient between untreated water and

Permeate side of the membrane M is 10-90 ° C, preferably 20-80 ° C, particularly preferred are temperature gradients of 40-70 ° C.

The untreated water, in particular salt water is passed over the membrane at elevated temperature in the range of 20-100 ° C, preferably temperatures of 30-100 ° C, more preferably temperatures of 40-90 ° C, the water can also with the help of solar thermal energy or waste heat from other processes such as Cooling circuits are heated.

On the retentate side of the membrane M can additionally

Overpressure can be applied and / or a vacuum (vacuum) can be applied and / or on the permeate side

Purging gas flow can be used.

On the permeate side (distillate side), the membrane M can be directly in contact with the fresh water, or it can

Air gap between membrane and fresh water exist.

The flow on both sides of the membrane M may be laminar or turbulent, preferably turbulent. The Rententat- and

Permeate side can be flowed in cocurrent or countercurrent, as embodiments in the process for the treatment of water by membrane distillation are all known in the art process variants. Particularly suitable is the direct contact merabrane distillation (DCMD), the air gap membrane distillation (AGMD), the sweep gas membrane distillation (SGMD) and the vacuum membrane distillation (VMD). Especially suitable is the direct contact membrane

distillation (DCMD) and the air gap membrane distillation

(AGMD).

The membrane M can be used for mechanical support

Support fabrics or plastic sieves with larger pores than the membrane M are applied. In addition, the membrane can be directly, i. without any backing or protective fabric,

be used.

All the above symbols of the above formulas each have their meanings independently of each other. In all

Formulas is the silicon atom tetravalent. The sum of all

Components of the silicone mixture give 100 wt .-%.

In the following examples, unless otherwise indicated, all amounts and percentages are by weight, all pressures are 0.10 MPa (abs.) And all temperatures are 20 ° C.

Examples

Example 1: Preparation of a casting solution with triethylene glycol

To a solution consisting of 40 g of isopropanol and 10 g of an organopolysiloxane-polyurea copolymer (SLM TPSE 100, Wacker Chemie AG) 15 g of triethylene glycol, boiling point 278 ° C, was added. The entire batch is then dissolved with stirring at room temperature for 16 h.

This gives a slightly cloudy, viscous solution with a

Solid content of 15 wt .-%. Example 2: Preparation of a porous silicone membrane

For the preparation of a porous silicone membrane from the doctoring solution prepared in Example 1, a Rakelsiehgerätes (Coatmaster 509 MC I, Erichson) is used,

When Filmziehrahmen a chambered doctor blade with a film width of 11 cm and a gap height of 400 μπι is used.

The glass plate used as a substrate is fixed by means of a vacuum suction plate. The glass plate is in front of the

Wiping with a clean room towel soaked in ethanol. In this way, possibly, existing

Particle impurities removed.

Subsequently, the Filmziehrahmen is filled with the solution and pulled with a constant film drawing speed of 20 mm / s over the glass plate.

Thereafter, the still liquid wet film is dried at 20 ° C in air for about 16 h. This shows a cloudiness of the film.

This shaped body, which still contains triethylene glycol, is placed in water for about 24 hours to remove the triethylene glycol. Subsequently, the molding is dried for about 30 minutes in air.

This gives a 95 pm thick, opaque membrane. in the

Scanning electron microscope is the homogeneous and uniform

Distribution of approximately 6 μιιι large pores clearly visible. On the surfaces of the membranes are also about 1-4 m large holes can be seen. The total porosity of the film is about 60% by volume.

Example 3 (comparative example not according to the invention)

Production of compact films without porosity For the production of compact films are up to 25 g

Isopropanol 10 g of an organopolysiloxane polyurea

Copolymer (SLM TPSE 100, Wacker Chemie AG) added.

The whole approach will be followed by 16 h

Room temperature dissolved on a vertical shaker.

A clear solution having a solids content of 29% by weight is obtained. -%.

When Filmziehrahmen a chambered doctor blade with a film width of 11 cm and a gap height of 400 μιη is used.

Wiping with a clean room towel soaked in ethanol. In this way, possibly existing

Particle impurities removed. filled and pulled over the glass plate at a constant film drawing speed of 2.5 mm / s.

Thereafter, the still liquid wet film at 80 ° C.

dried for about 3 hours.

This gives a transparent film with a layer thickness of 160 μιη.

Example: Membrane distillation with the produced membranes

The experimental setup consists of two cylindrical chambers of the same diameter, each with a volume of approximately 150 mL. Between the two chambers, the membrane is clamped by means of screwing, so that both chambers are separated by the membrane. The position of the membrane is horizontal. The upper chamber is kept at a constant 80 ° C. by means of a double jacket and is filled with 135 ml of a 3.5% by weight aqueous NaCl solution. The solution is mixed by means of a mechanical stirrer. The lower chamber is tempered by a double jacket to a constant 15 ° C. Experimental conditions: T (upper chamber) = 80 ° C; T (lower chamber) ° C; Stirrer speed = 100 rpm; Test duration = 18 h;

Membrane area = 7.07 cm ²

Water in upper chamber; Water with 3.5 wt .-% NaCl

The sodium content of the distillate was determined by ICP-OES

certainly .

* not according to the invention

** not according to the invention: PTFE membrane from Ningbo Changqi Porous Membrane Technology Co., Ltd., China; Pore size = 0, 2 - 0.5 μπΐ; Thickness = 30 m

The table clearly shows that the

used according to the invention membrane of Example 2 im

Compared to the made of solid material film

Example 3 has a significantly higher distillate flow. Compared to a thinner by a factor of 3 and thus

mechanically less durable PTFE membrane has the

According to the invention used membrane from Example 2 approximately the same distillate flow.

These properties make the membrane used in the invention more efficient than prior art materials.

Claims

claims

1. Process for the treatment of water by means

Membrane distillation using a membrane M of porous silicone material,

2. The method of claim 1, wherein the pore size of

Membrane M from 0, 1 μπι to 20 pm.

3. The method of claim 1 or 2, wherein the free volume in the membrane M is 20 to 80 vol .-%, based on the volume of the membrane M.

4. The method according to claim 1 to 3, wherein the membrane M

is produced in a process in which

in a first step, a solution or suspension of silicone compound S is formed a mixture of solvent LI and solvent L2,

in a second step, the solution or suspension is brought into a mold,

in a third step, solvent LI is removed from the solution or suspension until the solubility of the silicone compound S in the mixture of solvent LI and solvent L2 is exceeded, wherein a rich in silicone compound S phase A and a

Silicon compound S poor phase B is formed and thus the formation of the structure by the phase A occurs and

in a fourth step, the solvent L2 and residues of the solvent LI are removed.

5. The method of claim 4, wherein the silicone compound S is an organopolysiloxane / polyurea / polyurethane / polyamide or polyoxalyldiamine copolymers of the general formula (III),

wherein the structural element E is selected from the general formulas (IVa-f)

OR ^H R ^H O

(ivb) II I II

-0 C N Y N C 0-

R ^H 0 R ^H

(IVc) I

-N- -o II I

N

0 R ^H R ^H O

II I MI

(ivd) -C N Y N C-

R ^H 0 o H

(IVf), II

-N- ~ c- -c-

wherein the structural element F is selected from the general formulas (Va-f) R ^H 0 R ^H

(Va) -YNCN-

R ^H 0 o R ^H

(Vc) -Y- -N- -c II- -c II- -N-

in which

R is substituted or unsubstituted hydrocarbon radicals which may be interrupted by oxygen or nitrogen atoms,

R ^{H is} hydrogen, or has the meaning of R,

-O- may be replaced, or an arylene radical having 6 to 22

Carbon atoms,

Y is a bivalent, optionally fluorine- or chlorine-substituted hydrocarbon of from 1 to 20

Carbon atoms,

D is optionally substituted by fluorine, chlorine, Ci-Cg-alkyl or

Ci-Cg-alkyl ester substituted alkylene radical having 1 to 700

Carbon atoms in which not adjacent to each other Methylene units may be replaced by groups -O-, -COO-, -OCO-, or -OCOO-, or arylene radical having 6 to 22 carbon atoms,

B, Β a reactive or non-reactive end group which is covalently bound to the polymer,

m is an integer from 1 to 4000,

n is an integer from 1 to 4000,

g is an integer of at least 1,

h is an integer from 0 to 40,

i is an integer from 0 to 30 and

j is an integer greater than 0.

6. The method of claim 4 or 5, wherein the solvent L2 and residues of solvent LI are removed by extraction with a further solvent from the solutions or suspensions brought in the fourth step.

7. The method of claim 1 to 6, wherein the treatment of water is selected from desalination, purification of biological or nuclear components.

8. The method according to claim 1 to 7, wherein the membranes M as hollow fibers, flat membranes, hoses or

concentric hoses are executed.

9. The method of claim 1 to 8, wherein the untreated water is passed over the membrane M at temperatures of 20-100 ° C,

10. The method of claim 1 to 9, wherein the

Temperature gradient between untreated water and permeate side of the membrane M is 10-90 ° C.