Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-08-17
2003-07-22
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S353000, C528S171000, C528S172000, C528S173000, C528S174000, C528S176000, C528S183000, C528S185000, C528S188000, C528S220000, C528S229000, C528S350000, C204S157760, C204S157810, C204S157870, C204S450000
Reexamination Certificate
active
06596838
ABSTRACT:
DESCRIPTION
The invention relates to a semi-permeable membrane separation process and device in which the said membranes comprise sulphonated polyimides.
The present invention also relates to the use of sulphonated polyimide membranes in separation processes and devices using semi-permeable membranes.
In a general manner, the technical field of the invention can be described as that of industrial processes, in particular separation processes using semi-permeable membranes.
The first characteristic of the membranes used in these processes is that they favour the movement of certain species. The membrane is therefore considered to have a certain selectivity which, associated with the permeation flow, allows the performance of the membranes to be defined.
Amongst semi-permeable membranes, ion exchange membranes or ionic membranes are very widespread and very widely used.
They are used, in particular, in processes that use an electrical field to favour the transfer and the separation of different species of ion, such as electro-dialysis, electro-osmosis or in electrochemical cells used in the treatment of various effluents, in this latter case, the membranes then act as separators between the anodic and cathodic compartments.
Two types of ion exchange membranes are mainly distinguished:
anionic membranes, which are only permeable to anions and whose functional group is, for example, a quaternary ammonium group.
cationic membranes, which are only permeable to cations and whose functional group is, for example, an acid group.
The properties of the membranes, which determine the general properties of the processes and the devices which are used in them, are mainly permselectivity, selectivity, ionic conductivity, electrical resistance and mechanical strength.
Permselectivity, or the cation—anion transfer restriction factor, is one of the fundamental properties of an ion exchange membrane. It is characterised by the value of the transfer number of the mobile ion or counter ion (in other words, the ion which should normally pass through the membrane; in the case of a cationic membrane, the counter ion is thus the cation) in the membrane.
By definition, the transference number for a perfectly permselective membrane is equal to one. In fact, it is more accurate to measure the increase in the transference number value in the membrane compared to its value in solution. The permselectivity of a membrane is therefore actually defined by:
Ps
=
t
~
-
t
1
-
t
where {overscore (t)} is the transference number of the counter ion in the membrane and t is the transference number of the said ion in the solution.
The permselectivity of a membrane must be as high as possible; the permselectivity of most membranes is generally greater than 80%.
Selectivity is defined in a more or less analogous manner, as being the transference restriction factor between two ions with the same polarity. This selectivity must also, preferably, be as high as possible.
The ionic conductivity of the membrane, expressed by &sgr; in S.cm
−1
, must be as high as possible and depends, amongst other things, on the structure of the membrane (swelling, concentration in groups of exchangers and physical structure).
The electrical resistance of the membrane must be as low as possible, in such a way that it does not lead to too high consumption of energy; the electrical resistance is, for a given conductivity, proportional to the thickness of the membrane.
The mechanical strength of the membrane must also be high in order to resist any pressure differences and stresses that may occur during the manufacture of the devices.
Other important properties are the temperature resistance, which must be as high as possible, in order to make it possible to treat media at high temperature, and the resistance to extremes of pH, in other words, very basic or very acidic and/or very oxidising media.
In the conditions of use corresponding to extremely acidic pHs or in very oxidising media, the operational life of the membranes can be very limited.
It has been observed that the membranes presently available for semi-permeable separation processes or devices do not meet all of the criteria and requirements mentioned above while, at the same time, being at an acceptable cost. In particular, membranes that can operate in extreme pH media, for example, very acidic and/or very oxidising media, are certainly known, but they do not meet one or all of the other criteria defined above and they are very expensive.
The document FR-A-2 050 251 describes sulphonated polyimides and their use as cationic membranes in electro-dialysis. However, these polymers, due the process used for their preparation, are completely statistical polymers with a random structure whose properties, such as conductivity, are completely uncontrolled and difficult to master. As a result, these polymers are unsuitable for applications in any separation process and do not meet, in fact, any of the criteria defined above.
There is therefore a need for a semi-permeable membrane separation process and device in which the said membranes meet all of the criteria mentioned above and which have improved performance compared to existing membranes.
Furthermore, there is also a need for a process and a device whose membranes are not expensive to manufacture and whose resistance in extremely acidic pH media and/or very oxidising media is excellent.
The aim of the invention is to provide a semi-permeable membrane separation process and device in which the membranes meet the requirements mentioned above, and which do not have the demerits, disadvantages, defects or limitations of the processes and devices of the prior art and which overcome the problems of the prior art.
This aim and others are achieved according to the invention by a semi-permeable membrane separation process in which the said membrane(s) comprise a sulphonated polyimide that has the following general formula (I):
In which the groups C
1
and C
2
may be identical or different, and each represent a tetravalent group comprising at lease one aromatic carbon ring, which may be substituted, having 6 to 10 carbon atoms and/or a heterocyclic ring with an aromatic character, which may be substituted, having 5 to 10 atoms and comprising one or several heteroatoms chosen from the group S, N and O: C
1
and C
2
each form, with the neighbouring imide groups, rings with 5 or 6 atoms.
The groups Ar
1
and Ar
2
may be identical or different, and each represent a divalent group comprising at least one aromatic carbon ring, which may be substituted, having 6 to 10 carbon atoms and/or a heterocyclic ring with an aromatic character, which may be substituted, having 5 to 10 atoms and comprising one or several heteroatoms chosen from the group S, N and O: at least one of the said aromatic carbon and/or heterocyclic rings of Ar
2
being, in addition, substituted with at least one sulphonic acid group. In the formula (I), each of the groups R
1
and R
2
represent NH
3
, or a group with the formula:
Where C
3
is a divalent group comprising at least one aromatic carbon ring, which may be substituted, having 6 to 10 carbon atoms and/or a heterocyclic ring with an aromatic character, which may be substituted, having 5 to 10 atoms and comprising one or several heteroatoms from the group S, N and O; C
3
forming, with the neighbouring imide group, a 5 or 6 atom ring.
In addition, in the formula (I) above:
m represents a whole number, preferably between 2 and 20, and even more preferably, between 2 and 10
n represents a whole number, preferably between 2 and 30, and even more preferably, between 2 and 20
o represents a whole number, preferably between 2 and 10, and even more preferably, between 2 and 6.
The copolymer used in the process according to the invention may be defined as being a sequenced or block copolymer comprising two types of structures.
The molecular weight of the polyimide according to the invention is generally between 10 000 and 100 000, and preferably between 20 000 and 80 000.
The equivalent molecular weight of the polyimide acc
Mercier Regis
Pinery Michel
Pourcelly Gerald
Commissariat A l'Energie Atomique
Hampton-Hightower P.
Pearne & Gordon LLP
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