Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
1998-06-17
2001-05-08
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C525S332200, C525S344000
Reexamination Certificate
active
06228896
ABSTRACT:
The present invention relates to a process for the preparation of mechanically and osmotically stable, high-capacity strongly acidic cation exchangers having a particle size of 0.1 mm or larger by sulphonation of gel-like or porous bead polymers with sulphuric acid without the use of inert chlorine-containing swelling agents and/or of comonomers based on acrylonitrile. The literature discloses a large number of investigations which are concerned with the preparation of mechanically and osmotically stable cation exchangers having optimum properties in terms of capacity. According to said literature, industrially useful strongly acidic cation exchangers are prepared mainly by sulphonation of bead-like styrene/divinylbenzene copolymers, the polymer being preswelled with a deficit of an inert swelling agent and subsequently sulphonated and worked up. In particular, 1,2-dichloroethane has proved a particularly useful inert swelling agent. Thus, U.S. Pat. No. 5,248,435 describes a process for the sulphonation of porous styrene/divinylbenzene copolymers with the addition of chlorine-containing swelling agents with a 95% strength sulphuric acid at 80° C. However, owing to its easy ignitability, toxic and carcinogenic properties and the systemic effects and the dangerous decomposition product hydrogen chloride, the use of 1,2-dichloroethane has become critical. The environmentally safe handling of the inert swelling agent requires considerable expensive technological and technical effort.
The gaseous and liquid waste products of the production process are contaminated with dichloroethane since it can be only incompletely recovered from the sulphonation process and traces must be removed from the end product by special treatments. With regard to safety, 1,2-dichloroethane must be utilized or disposed of after use, since improper elimination endangers the environment. This requires downstream expensive environmental technologies, such as incineration in approved chlorine-resistant plants or working up in licenced regeneration plants and circulation procedures, adsorption or stripping.
The route for the preparation of industrially useful strongly acidic cation exchangers having a particle size of 0.1 mm upwards without the use of environmentally unsafe inert swelling agents such as 1,2-dichloroethane, was not pursued in the past as long as the known industrial processes using the inert chlorine-containing swelling agent were regarded as safe. The development with the aim of obtaining industrially useful strongly acidic cation exchangers without inert swelling agents therefore preceded the development phase involving the use of swelling agents.
Cation exchangers which are obtainable by sulphonation of crosslinked bead polymers of monovinylaromatics and polyvinylaromatics, preferably of styrene and divinylbenzene—the amount of crosslinking agent being 3 to 11%—were described in U.S. Pat. No. 2,366,007. In the preparation of these exchangers, the starting materials used were polymers which were obtained by polymerization of the monomers in the presence of small amounts of initiators with slowly increasing temperatures over several days. The sulphonation temperatures were above 100° C. but substantial particle disintegration nevertheless occurred during the hydration.
It is also known to sulphonate styrene/divinylbenzene bead polymers by a treatment with sulphuric acid at 100° C. in the presence of silver sulphate (J. Chem. Soc. 1949, page 3303). The products thus obtained exhibited a low mechanical stability and an unsatisfactory exchange capacity.
Attempts were furthermore made to improve the mechanical stability by carrying out the sulphonation with chlorosulphonic acid in liquid sulphur dioxide (U.S. Pat. No. 2,809,959; DAS (German Published Specification) 1,031,514). However, only partially sulphonated products were obtained by this method. In addition, chlorosulphonic acid and liquid sulphur dioxide are technically not simple to handle.
The application DE-AS (German Published Specification) 974,216 had the same object. Here, before the sulphonation with chlorosulphonic acid, the styrene/divinylbenzene copolymer is subjected to heating to achieve high hardness or the compensation of internal stresses, by heating the polymer for 15 minutes to 180° C. and then cooling it to room temperature over a period of 16 h. The polymers thus prepared are sulphonated by the action of chlorosulphonic acid at temperatures of 50 to 80° C.
DE-AS (German Published Specification) 1,233,143 describes a process having more advantageous reaction conditions, in which polymers of styrene, divinylbenzene, acrylonitrile or methacrylonitrile are used and are sulphonated with 96 to 99.1% strength sulphuric acid at reaction temperatures between 80 and 120° C. This procedure has proved advantageous for degress of crosslinking of the divinylbenzene of 14-29% by weight. The disadvantage of this process is the use of acrylonitrile, which is a hazardous substance and water pollutant and, as with the use of swelling agents, results in expensive safety and environmental measures.
EP 0 009 395 describes the preparation of strongly acidic cationic exchangers for the range of extremely small particles having a particle size of 0.01-1.5 &mgr;m by sulphonation of styrene/divinylbenzene copolymers with sulphuric acid without the addition of inert swelling agents. The preparation of strongly acidic cation exchangers in this particle size range is, except for special applications, of little importance for industrial use, which requires particle sizes of 0.3-1.2 mm. The strongly acidic cation exchangers having the particle size from 0.1 mm upwards cannot be prepared by means of sulphonation without the addition of DCE by the process described.
It is the object of the invention to find a process by means of which mechanically and osmotically stable, high-capacity strongly acidic cation exchangers having a particle size from 0.1 mm upwards can be prepared by sulphonation of gel-like or porous styrene/divinylbenzene copolymers by means of technically convenient sulphonating agents without the use of inert chlorine-containing swelling agents and/or of comonomers based on acrylonitrile.
It has now been found that strongly acidic cation exchangers having the required properties can be prepared, according to the invention, from gel-like or porous styrene/divinylbenzene copolymers, also referred to as bead polymers, whose crosslinker content of divinylbenzene is 1-65% by weight, by sulphonating these for up to 20 hours at temperatures of 125 to 180° C. with a sulphuric acid whose concentration is 80 to 96%. The strongly acidic cation exchanger is then hydrated and washed out by the known methods.
The gel-like or porous three-dimensionally crosslinked copolymers are products which are obtained by bead polymerization of a mixture of the monomers styrene and technical-grade divinylbenzene of commercial composition with or without the addition of inert compositions, such as hydrocarbons having a boiling range between 120-220° C.
It was furthermore found that strongly acidic cation exchangers have similar or better characteristic quality features, as shown in the tables, in comparison with the products produced still conventional processes if, preferably within the limits of the reaction conditions according to the invention,
porous bead polymers are sulphonated at 130-140° C. and
gel-like bead polymers are sulphonated at 160-170° C. with 86-94% strength sulphuric acid for 8-12 hours. The higher temperatures found are required for obtaining a completely smooth particle surface in the case of gel-like bead polymers since, at sulphonation temperatures below 160° C., the surface has characteristic indentations, known as orange peel among those skilled in the art. The bead polymers sulphonated by the process according to the invention are hydrated and worked up by known methods. Mechanically and osmotically stable, high-capacity strongly acidic cation exchangers having a particle size of ≧0.1 mm can be prepared by the process according to the in
Bachmann Reinhard
Feistel Lothar
Seidel Rudiger
Siekiera Karl-Heinz
IAB Ionennaustauscher GmbH Bitterfeld
Lipman Bernard
Norris & McLaughlin & Marcus
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