Process for purification of dimethyl sulphoxide (DMSO)

Details Process for purification of dimethyl sulphoxide (DMSO) Process for purification of dimethyl sulphoxide (DMSO)

1998-05-14

2001-05-22

Therkorn, Ernest G. (Department: 1723)

Liquid purification or separation

Processes

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

C210S660000, C210S681000, C568S037000

Reexamination Certificate

active

06235198

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the purification of dimethyl sulphoxide (DMSO) and to the DMSO thus purified.
BACKGROUND OF THE INVENTION
The DMSO currently available on the market is a product which is already of good purity. Its commercial specifications are generally:
purity
≧99.7% by
chromatography
acidity
≦0.04 mg KOH/g by
potentiometry
crystallization
≦18.1° C.
point
visual appearance
≦clear
water content
≦0.15%
colour (APHA)
≦10
Patent FR 2 014 385 describes a process for the preparation of purified DMSO using an ion exchange resin. In both examples of this patent a strongly basic resin of the Amberlite IR-A 400 or Merck III type is employed to treat dimethyl sulphide/DMSO/10% sulphuric acid ternary mixtures. In fact, in this known process the purification seems to be essentially brought about by a fractional distillation of an aqueous solution of DMSO treated beforehand with an anion exchanger.
Analyses of trace metals have now been performed on a number of samples of commercial DMSO from various sources. These analyses are reported in Table 1.
The sodium, iron, potassium, calcium, chromium, copper, nickel and zinc concentrations were measured using ICP (plasma torch—atomic emission spectrometry, Perkin Elmer instrument, Optima 3000 model) and are expressed in ppb (1 ppb=1 part by weight per thousand million=1 &mgr;g per kg).
The list of the metallic elements which appears in Table 1 is not exhaustive in respect of the metallic elements present in these samples.
TABLE 1
Metal cations
Sample
Na
Fe
K
Ca
Cr
Cu
Ni
Zn
1
40
13
60
20
2
10
8
10
2
39
60
3
13
13
<2
18
3
3
30
40
3
20
12
<2
15
3
4
30
40
3
14
13
<2
15
3
5
30
<1
20
25
<2
<2
<3
<3
6
70
90
65
55
15
2
25
60
Detection
2
1
3
2
2
2
3
3
limit
For some applications, as for example in electronics or in pharmacy, the DMSOs analysed above contain too many metallic impurities. A DMSO containing less than 10 ppb of each alkali and alkaline-earth metal and metal contaminant would generally be necessary for most of the uses in the abovementioned two technical fields.
DESCRIPTION OF THE INVENTION
The objective of the present invention is to find a process for purification of commercial DMSO which is already of good purity, the latter being nevertheless insufficient for some applications.
Ion exchange by making use of resins is a technique which is widely employed in the case of aqueous media and particularly allows deionized water to be obtained. The exchange of anions in a liquid DMSO medium of low water content has already been carried out by Alan M. Phipps, Anal. Chem. 40(12) pp. 1769-1773, 1968, with the aim of measuring the quantities of anions bound to the resin in experimental conditions approaching thermodynamic equilibrium.
The subject-matter of the invention is now a process for purification of dimethyl sulphoxide in order to decrease its content of alkali and alkaline-earth metal and metal cations, characterized in that it consists essentially in placing the DMSO to be purified in contact with at least two cation exchange resins at least one of which is a resin of sulphonic type, it being possible for the other (or the others) to be of chelating type.
A DMSO of low water content is advantageously treated, this content being preferably lower than or equal to 0.15% by weight relative to the total weight.
In accordance with the present invention any cation M
n+
(n having a value from 1 to 4) is retained and exchanged with H
+
protons or NH
4
+
cations originating from the resins employed in the acidic form or in the ammonium form.
A highly efficient purification of virtually anhydrous DMSO can be obtained by the combined use of a resin of chelating type which possesses, for example, aminophosphonic or iminodiacetic groups, which is effective for exchanging iron and metals with a multiple charge (M
n+
, n=2, 3 and 4) and a resin of sulphonic type, which is effective for exchanging sodium and single-charge ions.
The cationic resins employed are preferably based on a polystyrene-divinylbenzene copolymer. These resins, in fact, have a backbone which withstands chemical attacks and in particular, they do not dissolve in DMSO.
The contact of the DMSO to be purified with the resins takes place at a temperature ranging from 18.45° C. (melting point of DMSO) to 120° C. (heat stability limit temperature of the resins). This temperature is advantageously between 19 and 80° C., preferably between 20 and 50° C.
The DMSO to be purified may be placed in contact with a mixture of the various resins or successively with each of the various resins.
The operation may be carried out noncontinuously (batchwise) or continuously in the conditions and equipment which are well known to a person skilled in the art. The separation of the purified DMSO from the resins can take place using any suitable known means, especially by filtration, percolation or centrifuging.
Iron and sodium have been adopted as tracer elements and indicators of the general content of alkali and alkaline-earth metal and metal cations, to define the quality of the DMSO capable of being obtained purified by the process according to the invention.
This purified DMSO is characterized in that it has an Fe cation content lower than or equal to 1 ppb and an Na cation content lower than or equal to 2 ppb, the respective limits of detection of the analysis method using plasma torch—atomic emission spectrometry.


REFERENCES:
patent: 5990356 (1999-11-01), Commarieu
patent: 6020530 (2000-02-01), Commarieu
patent: 6123850 (2000-09-01), Commarieu
Alan M. Phipps, “Anion Exchange in Dimethyl Sulfoxide”,Analytical Chemistry40(12) :1769-1773 (1968).
Copy of French Search Report dated Jan. 28, 1998.
Derwent Abstract of WO9629334 Sep. 26,1996.
UK Search Report dated Jul. 30, 1998.
Chaudron, Chimie Analytique 53(5):310-314 (1971) [Includes English Abstract].

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