Inorganic filtering material modified with organomineral...

Details Inorganic filtering material modified with organomineral... Inorganic filtering material modified with organomineral...

2000-10-04

2003-07-22

Hoey, Betsey Morrison (Department: 1724)

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

C210S490000, C210S500250, C210S500270

Reexamination Certificate

active

06596173

ABSTRACT:

The present invention relates to filtration membranes which are modified by grafting with organominerals and/or minerals, and to a process which is useful for preparing the said membranes.
Membranes have been known for many years for their separating properties. To date they have been widely exploited industrially as replacements for conventional separating techniques, in many sectors of activity, such as in agrifoods, biotechnology and the processing of water and of effluents from the chemical, electronic or nuclear industries.
This technological transfer towards membrane-based separating techniques, especially in the fields of ultrafiltration and microfiltration, is a direct consequence of the understanding of the mechanisms involved and especially the advances in synthetic membranes, in particular with the appearance of a new generation of membranes: inorganic membranes and in particular those consisting of ceramic materials.
These inorganic membranes offer specific advantages over their organic homologues: their mechanical strength as well as their chemical, biological and thermal inertia make them long-lasting and especially allow them to be used under extremely severe conditions.
Illustrations of these inorganic membranes which may be mentioned in particular are microporous membranes made of a metal such as silver or nickel, or of glass, and most particularly carbon membranes, or membranes made of an oxide such as alumina or zirconia.
The technique most commonly used for preparing these ceramic membranes consists in depositing one or more selective layers a few microns in thickness, constituting the filtering layer, onto a macroporous support matrix which provides the mechanical strength. Membranes made of &ggr;-alumina and &agr;-alumina deposited on &agr;-alumina supports, tubular membranes made of zirconia on a carbon support (Carbosep® from the company Orelis) and more recently zirconia membranes on a monolithic support made of metal oxides (Kerasep® from the company Orelis; EP 585 152) have thus been developed. The filtering layer is usually obtained by depositing mineral oxides onto the matrix, followed by a final heat treatment.
In general, the filtration membranes are characterized by the following parameters: their permeability to water and to air, the size distribution of their pores and their retention.
As more particularly regards this last parameter, it is conventionally measured from the rate of retention of the solute under consideration, which is defined by the following equation:
R
=
1
-
Cp
Co
with Cp being the concentration of solute in the permeate and Co being the concentration of solute in the initial solution. Thus, the cutoff threshold of the membrane corresponds to the molecular mass of the smallest solute retained to a level of 90% by the membrane.
The studies carried out in the context of the present invention have the object, specifically, of optimizing the selectivity of inorganic filtration membranes.
It has been demonstrated, unexpectedly, that a modification of the surface of the filtering layer of these inorganic membranes by grafting with organominerals and/or minerals significantly increases their selectivity towards various solutes.
A first subject of the present invention is thus an inorganic filtration membrane, characterized in that it comprises a support made of inorganic material coated with at least one separating membrane layer consisting of particles of metal hydroxide(s) and/or oxide(s), at the surface of which are covalently grafted organomineral and/or mineral units.
The grafting of these organomineral and/or mineral units at the surface of the separating membrane layer advantageously makes it possible to significantly improve its selectivity with regard to solutes.
This grafting is based on the establishment of covalent bonds between the mineral functions of the metal hydroxides and/or oxides in the separating membrane layer and those of the organomineral and/or mineral units.
For the purposes of the present invention, the expression “inorganic filtration membrane” is intended to cover inorganic membranes which can be used for microfiltration, ultrafiltration or nanofiltration.
Microfiltration and ultrafiltration are among the family of membrane-based separating techniques in which the driving force for the transfer is a pressure gradient. The operating principle thus consists in circulating the liquid to be treated under pressure along a membrane which is permeable to solvent but impermeable to the solutes which it is desired to retain.
The distinction between microfiltration and ultrafiltration is purely linked to the size of the elements to be separated. It is generally accepted that microfiltration concerns particles in suspension which are greater than 0.2 &mgr;m in size, while ultrafiltration separates in the range of macromolecules with molecular masses of greater than a few thousand up to colloidal particles 0.2 &mgr;m in diameter.
Generally, microfiltration is conventionally used for the purposes of clarification and sterilization, and ultrafiltration preferentially concerns the separation of macromolecular solutes.
As regards nanofiltration, this more particularly concerns the retention of solutes with a molecular mass of greater than 1000 g/mol.
The organomineral and/or mineral units grafted onto the surface of the separating membrane layer are generally derived from hydrolysable organometallic complexes comprising at least one titanium and/or zirconium atom.
According to one preferred embodiment of the invention, these organometallic complexes are chosen from organotitanates, organozirconates and organozircoaluminates.
As organotitanates which are suitable for the invention, mention may be made most particularly of those of the alkoxy, neoalkoxy and chelate type.
As regards the zirconates, the species concerned are in particular those of the neoalkoxy, chelate or organozircoaluminate type.
The organometallic complexes more preferably concerned are:
organotitanates or organozirconates corresponding to either of the general formulae I and II below:
 in which:
M represents a titanium or zirconium atom,
R represents a group
R
1
and R
2
, which may be identical or different, represent a non-hydrolysable organic radical,
X represents a methylene or CO group,
m and n are equal to 0, 1, 2 or 3 and p is equal to 1 or 2 on condition that the sum of n, p and m is equal to 4 and with
when p is equal to 1,
Z
1
and Z
2
, which may be identical or different, representing
—O—, —OC(O)—, —OC(O)O—, —OP(O)(O—)
2
, —OP(O)(OH)P(O) (O—)
2
, OP(O)(OH)P(O)(O—)
3
, OP(O)(O—)
3
, OS(O)
2
— or OS(O)
2
(—)
3
and
when p is equal to 2,
Z
1
and Z
2
together forming a divalent chain of cyclic structure such as a cyclopyrophosphite;
or an organozircoaluminate corresponding to the general formula III below:
with R representing a (CH
2
)
2
, (CH
2
)
4
or (CH
2
)
12
hydrocarbon-based chain and X representing an NH
2
, SH, OH, COOH or
group.
As regards the substituents R
1
and R
2
of general formulae I and II, they are preferably chosen from alkyl, cycloalkyl, alkoxyalkyl, phenyl and phenylalkyl groups optionally substituted with alkoxy, alkylthio, alkoxycarbonyl or alkylcarbonyl groups, for example.
The following organotitanates or organozirconates are preferably used:
isopropyl tri(N-ethylaminoethylamino)titanate,
neoalkoxytri(N-ethylaminoethylamino)titanate,
neoalkoxytri(neodecanoyl titanate,
isopropyl tri(isostearoyl)titanate,
isopropyl tri(dioctylphosphato)titanate,
trineoalkoxy(dioctylphosphato)titanate,
trineoalkoxy(neodecanoyl)zirconate,
trineoalkoxy(dodecanoyl)benzenesulphonyl-zirconate,
trineoalkoxy(ethylenediaminoethyl)zirconate, and
trineoalkoxy(m-aminophenyl)zirconate.
All of these organomineral compounds react via their hydrolysable group(s), i.e. their alkoxy or carboxyl function(s) for example, with the mineral functions of the separating membrane layer and thus establish covalent bonds at the surface of the said layer.
A subject of the present invention is also an inorganic filtration membrane comprising a support

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