Acidic cation-exchange resins

Acidic Cation-Exchange Resins. Brmnsted acid catalytic activity is responsible for the successful use of acidic cation-exchange resins, which are also soHd acids. Cation-exchange catalysts are used in esterification, acetal synthesis, ester alcoholysis, acetal alcoholysis, alcohol dehydration, ester hydrolysis, and sucrose inversion. The soHd acid type permits simplified procedures when high boiling and viscous compounds are involved because the catalyst can be separated from the products by simple filtration. Unsaturated acids and alcohols that can polymerise in the presence of proton acids can thus be esterified directiy and without polymerisation. 

In many industrial appHcations, strong acid cation-exchange resins are used in the hydrogen form to process Hquids containing low concentrations of salts. 

Methyl Isopropenyl Ketone. Methyl isopropenyl ketone [814-78-8] (3-methyl-3-buten-2-one) is a colorless, lachrymatory Hquid, which like methyl vinyl ketone readily polymerizes on exposure to heat and light. Methyl isopropenyl ketone is produced by the condensation of methyl ethyl ketone and formaldehyde over an acid cation-exchange resin at 130°C and 1.5 MPa (218 psi) (274). Other methods are possible (275—280). Methyl isopropenyl ketone can be used as a comonomer which promotes photochemical degradation in polymeric materials. It is commercially available in North America (281). 

The choice of catalyst is based primarily on economic effects and product purity requirements. More recentiy, the handling of waste associated with the choice of catalyst has become an important factor in the economic evaluation. Catalysts that produce less waste and more easily handled waste by-products are strongly preferred by alkylphenol producers. Some commonly used catalysts are sulfuric acid, boron trifluoride, aluminum phenoxide, methanesulfonic acid, toluene—xylene sulfonic acid, cationic-exchange resin, acidic clays, and modified zeoHtes. 

Weakly acidic cation-exchange resins have carboxylic groups (COOH) as the exchange sites. When operated on the hydrogen cycle, the weakly acidic resins are capable of removing only those cations equivalent to the amount of alkalinity present in the water, and most efficiently the hardness (calcium and magnesium) associated with alkalinity, according to these reactions ... 

Where dealkalization by acid cation exchange resin is employed, a small risk exists of contamination from acid breakthrough. A failure in the neutralization process may lead to acidic treated water entering the FW system, which reduces the FW pH and results in localized acid corrosion. 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

Tanaka, K., Chikara, H., Hu, W., and Hasebe, K., Separation of carboxylic acids on a weakly acidic cation-exchange resin by ion-exclusion chromatography, /. Chromatogr. A, 850, 187, 1999. 

The hydrolysis of sucrose catalyzed by the strongly acidic cation-exchange resin Amberlite 200C in RH form was chosen as a model reaction to compare the use of stirred tank and continuous-flow reactors [47-49], Scheme 10.6. 

Acidic cation-exchange resins, 12 191 Acidic corrosion, in industrial water treatment, 26 130-131 Acidic donors, 10 421 Acidic extractants, of rare-earth elements, 14 641-642... 

Strong-acid catalysts, in phenolic resin polymerization, 73 760-761 Strong acid cation-exchange resins, 74 381-382... 

The ion-exchange resins used as etherification catalysts are strongly acidic cation-exchange resins. These materials consist typically of polystyrene chains that have been linked with divinylbenzene (DVB), the amount of which determines the degree of crosslinking and regulates the rigidity of the structure schematically presented in Fig. 10.3 [24],... 

In order to study further the favorable aspects of in situ acid catalyzed hydrolysis, experiments were performed at different temperatures so as to evaluate the dependence of rate on temperature. Solutions of aldlcarb were passed through a jacketed column around which water at 30, 40, or 50°C was circulating. The ion exchange bed (5 cm x 0.70 cm) contained 2.0 g of Bio-Rad AG MP-50 strong acid cation exchange resin (iT ", 100-200 mesh), and the solution flow rate was approximately 1.0 ml/mln. The percent of Initial aldlcarb remaining at the end of the column for each temperature decreased from 76% at 30 C to 56% at 40 C and 35% at 50°C. Future temperature studies will be done in order to evaluate the practicality of temperature control in a detoxification filter unit. 

However, this method possesses several disadvantages such as long reaction time and complicated work-up procedure. For example, in the case of Sc(OTf)3-catalyzed reaction, the treatment required 72 h to get completed at the ambient temperature. After that a pure product was isolated from the reaction mixture by the capture of the solid phase by using strongly acidic cation exchange resin, followed by washing of the solvent and final treatment of resin with 2 M methanolic ammonia. 

In the first experiment, Amberlyst-15, a strongly acidic cation exchange resin, was used as a catalyst to synthesize mesityl oxide, the precursor of MIBK, from acetone without hydrogenation. The effects of acetone feed rate, reboiler duty and reaction temperature on the mesityl oxide productivity and product distribution were investigated. Preliminary results of this experiment are outlined in Table 1. 

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