Cation exchangers operation

Hydrogen cycle A complete course of cation-exchange operation in which the adsorbent is employed in the hydrogen or free acid form. 

The optimisation of this process, performed in the present study, evidences that a sufficiently small regenerant volume, equal to only 12 BV, is able to remove more than 50% of the lead stored in the bed during the service step. Such a partial regeneration, however, allows the fixed bed of NYT to keep outlet Pb concentration below the limit eillowed by law (0.2 mg/1) for about 1700 BV of eluate, thus giving rise to a yield of the cation-exchange operation of about 140, which is a very satisfying performance. 

The later chemical work of Silva et was done with the Berkeley 65 s, 261 isotope, and this longer half-life enabled a rapid cation-exchange operation to be undertaken. The material was loaded on to Dowex 50 resin and eluted with ammonium a-hydroxyisobutyrate. Despite complications caused by the daughter No having a very similar alpha spectrum to Rf, it was concluded that Rf eluted in much the same fraction as Hf and Zr tracers, in contrast to actinide tracers which were not eluted in these conditions. 

Polymeric cation-exchange resins are also used in the separation of fmctose from glucose. The UOP Sarex process has employed both 2eohtic and polymeric resin adsorbents for the production of high fmctose com symp (HFCS). The operating characteristics of these two adsorbents are substantially different and have been compared in terms of fundamental characteristics such as capacity, selectivity, and adsorption kinetics (51). 

Mesityl oxide can also be produced by the direct condensation of acetone at higher temperatures. This reaction can be operated ia the vapor phase over 2iac oxide (182), or 2iac oxide—2irconium oxide (183), or ia the Hquid phase over cation-exchange resia (184) or 2irconium phosphate (185). Other catalysts are known (186). 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

Despite the higher cost compared with ordinary catalysts, such as sulfuric or hydrochloric acid, the cation exchangers present several features that make their use economical. The abiHty to use these agents in a fixed-bed reactor operation makes them attractive for a continuous process (50,51). Cation-exchange catalysts can be used also in continuous stirred tank reactor (CSTR) operation. 

Scott et al. [12] provided some experimental evidence supporting equation (27). The mixture contained uracil, hypoxanthine, guanine and cytosine, each present in the mobile phase at a concentration of 14 mg/1. The column employed was Im long, 1.5 mm I.D., packed with a pellicular cation exchange resin and operated at a flow rate of 0.3 ml/min. 

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 ... 

Cycle A complete course of ion-exchange operation. For instance, a complete cycle of cation exchange would involve regeneration of the resin with acid, rinse to remove excess acid, exhaustion, backwash, and finally regeneration. 

Anion exchange resins are generally lower in their exchange capadty and durability than cation exchange resins and are seldom used for industrial separation. In general, ion exchange as a tool for separation is only used when other steps fail, because of its tedious operation, small capadty and high costs. 

Where hardness removal is required, the simplest pretreatment method for smaller, lower pressure boiler plants (below 200-300 psig) is to use a cation-exchange softener. This removes the calcium and magnesium at source and converts the bulk of temporary hardness salts into sodium bicarbonate (NaHC03), which decomposes to form sodium carbonate (soda ash) but does not scale under normal boiler operating conditions. 

Recovery of phenylalanine from aqueous solutions by cation-exchange resins has been reported by Carta and co-workers (Borst et al., 1997). It might be possible to improve the efficiency of resin treatment by raising the operating temperature, to, say, 65 °C. 

Formation damage caused by clay migration may be observed when the injected brine replaces the connate water during operations such as water-flooding, chemical flooding including alkaline, and surfactant and polymer processes. These effects can be predicted by a physicochemical flow model based on cationic exchange reactions when the salinity decreases [1665]. Other models have also been presented [345,1245]. 

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