Organic ion exchangers

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.). 

This reaction was studied in the gaseous phase at 120°C with a sulfo-nated organic ion exchanger as catalyst (p. 27), under both the competitive system (Villa) (2 esters + 1 alcohol) and the system (VUIb) (1 ester + 2 alcohols)... 

Processes larger volumes of waste than regenerable, organic ion exchange resins. 

Natural organic ion exchangers Some common natural organic ion exchangers are... 

However, there also some disadvantages. Specifically, the limited radiation and thermal stability set limits to the usage of synthetic organic ion-exchange resins. Regarding temperature, 150 °C is the maximum temperature that cation-exchange resins can withstand, whereas 70 °C is the limit for anion-exchange resins. Consequently, hot streams to be treated have to be cooled below these temperatures. 

It is possible that a pretreatment step is required for organic ion-exchange materials before immobilization, although it is not definitely the case. The immobilization matrices currently used are cement, bitumen, and some polymers. 

However, there are also some disadvantages. First of all, the final waste has a very high volume compared to the initial one. Grinding before cementation may partially solve this problem. Furthermore, when organic ion-exchange materials are stored via cementation, swelling of the resin beads may occur in contact with water, which may lead to cracking of the cement. So, the cementation of such material should be preceded by an appropriate pretreatment step. 

Compare the advantages and disadvantages of zeolites with those of synthetic organic ion-exchange resins in the context of water treatment. 

It has been reported that solid acids and oxides or salts of different metals can catalyse the vapour phase hydration of acetylene. Most typical are phosphoric acid and phosphates of bivalent metals, such as Zn or Cd. Organic ion exchangers and synthetic zeolites exchanged for Zn2+, Cd2+, Hg2+ and Cu2+ ions were also employed. A survey of inorganic catalysts [254] or of organic ion exchangers [283] catalysing the hydration of acetylene or its derivatives can be found in literature. 

Dysprosium occurs in apatite, euxenile. gadolinite. and xenotime. All of these minerals also are processed for their yttrium content. With liquid-liquid organic and solid-resin organic ion-exchange techniques, the separation of dysprosium from yttrium is favorable. 

Primary sources of the element are bastnasite and monazite, which contain from 4 to 8% praseodymium. Plant capacity involving liquid-liquid or solid-liquid organic ion-exchange processes for recovering the element is in excess of 100.000 pounds PreOn annually. Metallic praseodymium is obtained by electrolysis of Pr O] in a molten fluoride electrolyte, or by a calcium reduction of PrFj or PrCls in a sealed-bomb reaction. 

Terbium occurs in apatite and xenotime and is derived from these minerals as a minor coproduct in the processing of yttrium. Processing involves organic ion-exchange or solvent extraction operations. Elemental terbium is produced by calcium reduction of anhydrous TbH in a reactor under an inert atmosphere. Both the oxides and the metal aie available at 99.9% purity. 

Another ion-exchange application of natural zeolites is the removal of radioactive ions from waste-water [7,17,18,20,57,70,71], Chabazite, clinoptilolite, and mordenite selectively exchange radioactive Cs+ and Sr2+ from solutions [5,7,17,18,20,57,70,71], In addition, the high temperature, because of the activity of these radionuclides, and the effect of gamma radiation do not affect the performance of natural zeolites, which is the case for organic ion-exchange resins [72],... 

Ion-exchange polymeric resins are the most important types of exchangers currently in use [113-123], The first, totally organic ion-exchange resin was synthesized in 1935 by Adams and Holmer, when they produced a phenol-formaldehyde cation-exchange resin and an amine-formaldehyde anion-exchange resin, both obtained with the help of condensation polymerization reactions [113], In 1944, D Alelio synthesized styrene-based polymeric resins, which could be modified to obtain both cationic- and anionic-exchange resins. The majority of the resins commercially applied currently are of this type, for example, Amberlite IR-20, Lewatit S-100, Permutit Q, Duolite, C-20, Dowex-50, and Nalcite HCR. 

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