ON EXCHANGE RESINS

Lithium-ethylamine reduction at one or both double bonds of carvone, and of carvenone (58) to carvomenthone only, is reported.The effect of solvent on the lithium or potassium amide-reduction of p-cymene to menthenes and menthadienes has been examined.Hydrogenation of carvone (Vol. 4, p. 32), using palladium-polysaccharide exchange resin, favours endocyclic over exocyclic double-bond reduction, more so than with Pd-C or Pd-BaS04, whereas platinum or rhodium on exchange resins exhibit no special selectivity.Optimum conditions for the catalytic hydrogenation of thymol, and the catalytic dehydrogenation of menthol, to menthone have been determined.Cathodic reduction of carvomenthone (to... 

Zeohtes also have considerable application as catalysts. Iron in the +3 oxidation state is introduced by ion-exchange methods [103]. However, attempted adsorption of Fe " " ions causes complete breakdown of the structure with any retained iron being in the +3 state. Dehydration of the zeolite causes non-reversible reduction of the iron. Adsorption of Fe salts on ion-exchange resins of the sulphonated styrene-divinyl benzene and quaternary ammonium types has httle effect on the iron resonances and indicates very weak binding of the ions to the resin [104]. Spin-relaxation effects and temperature-dependent paramagnetic hyperfine structure have been recorded and interpreted in detail for Fe ions adsorbed on exchange resins [105, 106], and a number of other recent papers have shown interest in this new field [107]. 

Cadmium salts, like some other ions, form a colored chelate with glyoxal bis-(2-hydroxyanil) (see page 401). By masking and selective adsorption on exchange resins, the test becomes specific for cadmium. ... 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

The ratio of reactants had to be controlled very closely to suppress these impurities. Recovery of the acrylamide product from the acid process was the most expensive and difficult part of the process. Large scale production depended on two different methods. If soHd crystalline monomer was desired, the acrylamide sulfate was neutralized with ammonia to yield ammonium sulfate. The acrylamide crystallized on cooling, leaving ammonium sulfate, which had to be disposed of in some way. The second method of purification involved ion exclusion (68), which utilized a sulfonic acid ion-exchange resin and produced a dilute solution of acrylamide in water. A dilute sulfuric acid waste stream was again produced, and, in either case, the waste stream represented a... 

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

PhenoHc-based resins have almost disappeared. A few other resin types are available commercially but have not made a significant impact. Inorganic materials retain importance in a number of areas where synthetic organic ion-exchange resins are not normally used. Only the latter are discussed here. This article places emphasis on the styrenic and acryHc resins that are made as small beads. Other forms of synthetic ion-exchange materials such as membranes, papers, fibers (qv), foams (qv), and Hquid extractants are not included (see Extraction, liquid-liquid Membrane technology Paper.). 

Radiation Stability. Numerous studies have been undertaken to define the effect of radiation on all types of ion-exchange resins. As... 

Historically the United States was a primary exporter of ion-exchange resin. As of 1994, the United States imports substantially more than it exports. Because compliance with tightening environmental regulations in the United States impacts on the cost of manufacture, offshore resin is most often lower in price. 

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