Cation production process

There are a number of descriptive terms for smectite products based on geographic source, exehangeable cations, production process, and end use application. 

The standard cation—anion process has been modified in many systems to reduce the use of cosdy regenerants and the production of waste. Modifications include the use of decarbonators, weak acid and weak base resins. Several different approaches to demineralization using these processes are shown in Figure 1. 

The ionic liquid process has a number of advantages over traditional cationic polymerization processes such as the Cosden process, which employs a liquid-phase aluminium(III) chloride catalyst to polymerize butene feedstocks [30]. The separation and removal of the product from the ionic liquid phase as the reaction proceeds allows the polymer to be obtained simply and in a highly pure state. Indeed, the polymer contains so little of the ionic liquid that an aqueous wash step can be dispensed with. This separation also means that further reaction (e.g., isomerization) of the polymer s unsaturated ot-terminus is minimized. In addition to the ease of isolation of the desired product, the ionic liquid is not destroyed by any aqueous washing procedure and so can be reused in subsequent polymerization reactions, resulting in a reduction of operating costs. The ionic liquid technology does not require massive capital investment and is reported to be easily retrofitted to existing Cosden process plants. 

In most of the hitherto known cationic domino processes another cationic process follows, representing the category of the so-called homo-domino reactions. In the last step, the final carbocation is stabilized either by the elimination of a proton or by the addition of another nucleophile, furnishing the desired product. Nonetheless, a few intriguing examples have been revealed in which a succession... 

The induction of steric effects by the pore walls was first demonstrated with heterogeneous catalysts, prepared from metal carbonyl clusters such as Rh6(CO)16, Ru3(CO)12, or Ir4(CO)12, which were synthesized in situ after a cation exchange process under CO in the large pores of zeolites such as HY, NaY, or 13X.25,26 The zeolite-entrapped carbonyl clusters are stable towards oxidation-reduction cycles this is in sharp contrast to the behavior of the same clusters supported on non-porous inorganic oxides. At high temperatures these metal carbonyl clusters aggregate to small metal particles, whose size is restricted by the dimensions of the zeolitic framework. Moreover, for a number of reactions, the size of the pores controls the size of the products formed thus a higher selectivity to the lower hydrocarbons has been reported for the Fischer Tropsch reaction. 

The original process used aqueous tetraethylammonium ethylsulfate as the electrolyte, a lead cathode, and a lead-silver alloy anode. The Mark II process, commercialized in the mid-1970s, uses an emulsion of acrylonitrile in aqueous sodium phosphate containing a salt of the hexamethylene-bis-(ethyldibutylammonium) cation. The process was invented in 1959 by M. M. Baizer at Monsanto Corporation, St. Louis, MO. It was commercialized in 1965 and has been continuously improved ever since. The process is also operated in Japan by Asahi Chemical Industry Company. In 1990, the world production of adiponitrile by this process was over 200,000 tonnes per year. 

Campbell has studied the separation of technetium by extraction with tributyl phosphate from a mixture of fission products cooled for 200 days. Nearly complete separation of pertechnetate is achieved by extraction from 2 N sulfuric acid using a 45 % solution of tributyl phosphate in kerosene. Ruthenium interferes with the separation and is difficult to remove without loss of technetium other radioisotopes can be removed by a cation-exchange process. However, this separation procedure has not been widely applied because of the adverse influence of nitrate. 

Methylbenzenes lose a proton from a methyl group to form a benzyl radical. In aqueous M-percbloric acid this reaction is fast with a rate constant in the range 10 lO s and the process is not reversible [24]. The process becomes slower as the number of methyl substituents increases, Hexaethylbenzene radical cation is relatively stable. When the benzyl radical is formed, further reactions lead to the development of a complex esr spectrum. Anodic oxidation of hexamethylbenzene in trifluoroacetic acid at concentrations greater than 1 O M yields the radical-cation I by the process shown in Scheme 6.1 [14], Preparative scale, anodic oxidation of methylbenzenes leads to the benzyl carbonium ion by oxidation of the benzyl radicals formed from the substrate radical-cation. Products isolated result from further reactions of this carbonium ion. 

The processes of cation production by weathering or ion exchange cannot be differentiated by ion-budget calculations, but they may be distinguished on the basis of kinetics. In early experiments to investigate the role of sediments as buffers, sequential additions of sulfuric acid to well-mixed sediment slurries produced rapid increases in soluble Ca2+ that reached stable concentrations within 24 h (53, 54). The rapid production of cations suggested that the dominant process was ion exchange... 

On the basis of mass balance calculations through the first 3 years of acid additions (17), only 33% of the added acid resulted in a decrease in lake alkalinity. A second 33% was neutralized by in-lake (IAG) processes, of which sulfate reduction accounted for slightly more than half and cation production for slightly less than half. Approximately 33% of the total sulfate load (wet and dry deposition, and acid additions) was lost via outflow. Therefore, about half of the added acid remained in the water column two thirds of it was unreacted and one third was neutralized by base cations. 

Four forms of the basic IAG model (27, 46) are described here to predict rates of recovery of LRL alkalinity. The models are described in order of increasing complexity and realism, reflecting the inclusion of IAG contributions from more biogeochemical processes (4,17). As previously discussed, chemical budgets from the first 3 years of acidification indicated that the main processes controlling IAG are sulfate reduction and cation production by ion exchange (in order of importance). Effects of nitrate and ammonium retention roughly cancel each other (in terms of net alkalinity production) (17). 

Results of the four models (Figure 9a) illustrate the effect on predicted recovery rates of including various alkalinity-generating processes. Models 1 and 2 probably yield upper and lower limits of the time required to recover to the preacidification alkalinity level. Model 3 probably yields an underestimate of recovery time, in that it does not consider the need to neutralize acidified surficial sediments (and restore base cations on sediment-exchange sites that have been lost during the last years of acid loading). Model 4 probably yields the most accurate estimate of recovery time, but it does not provide a functional relationship for the cation-production term. Based on Model 4, the north basin will reach 50% of the preexperimental alkalinity concentrations in 3-5 years and 90% in 8 years. Complete recovery is predicted to occur in 12.5-15 years. 

Mass-balance calculations for the first 3 years of acid additions indicate that the principal IAG processes are sulfate reduction and cation production. Specifically, one-third of the total sulfate input (added acid and deposition) was neutralized by in-lake processes. Increased sulfate reduction consumed slightly more than one-sixth and production of cations neutralized somewhat less than one-sixth of the acid added. Of the remaining sulfate, one-third was lost by outflow, and one-third decreased lake alkalinity. Laboratory determinations suggest that sediment-exchange processes occurring in only the top 2 cm of surficial sediments can account for the observed increase in water-column cations. Acidification of the near-surface sediments (with partial loss of exchangeable cations) will slow recovery because of the need to exchange the sediment-bound H+ and neutralize it by other processes. Reactor-based models that include the primary IAG processes predict that... 

Several of these dimerizations have quantum yields greater than unity, particularly when the oxidation potential of the dimer is either higher than that of the monomer or, at least, when the two oxidation potentials lie close to each other [114,115,120]. These observations, once again, support the involvement of radical cation chain processes, which seem to operate, whenever the electron transfer from the starting material to the product radical cation is efficient. 

There are two general types of fragmentation reactions. In one type the radical cation fragments to a neutral molecule and a new radical cation. This process is especially favorable when the neutral product is a small, stable molecule. For example, the loss of water from the molecular ion of alcohols is very facile. For this reason the M+ peak is very small for primary and secondary alcohols, and it is usually undetectable for... 

It is well known that ACN reacts with active metals (Li, Ca) to form polymers [48], These polymers are products of condensation reactions in which ACIST radical anions are formed by the electron transfer from the active metal and attack, nucleophilically, more solvent molecules. Species such as CH3C=N(CH3)C=N are probably intermediates in this polymerization. ACN does not react on noble metal electrodes in the same way as with active metals. For instance, well-re-solved Li UPD peaks characterize the voltammograms of noble metal electrodes in ACN/Li salt solutions. This reflects a stability of the Li ad-layers that are formed at potentials above Li deposition potentials. Hence, the cathodic limit of noble metal electrodes in ACN solutions is the cation reduction process (either TAA or active metal cations). As discussed in the previous sections, with TAA-based solutions it is possible that the electrode surfaces remain bare. When the cations are metallic (e.g., Li+), it is expected that the electrode surfaces become covered with surface films originating from atmospheric contaminants reduction if the electrodes are polarized below 1.5 V (Li/Li+). As Mann found [13], in the presence of Na salts the polarization of metal electrodes in ACN solutions to sodium deposition potentials leads to solvent decomposition, with evolution of H2, CH4 and sodium cyanide (due to reaction with metallic sodium). 

A continuing problem with the cation exchange process as used in production operations is that it has not been sufficiently selective and therefore allows considerable carryover of the MSE salt constituents and impurities with the plutonium and americium. This isn t serious with plutonium since plutonium can be subsequently purified by anion exchange. For americium, however, the subsequent recovery process is oxalate precipitation which is less selective and carries some of the impurities into the final product. 

Recovery of actinides at the RFP with an organic phosphorous bidentate extractant has been proposed. A conceptual production flow sheet is shown in Figure 3. The bidentate reagent, dihexyl-N, N-diethylcarbamoylmethylenephosphonate (DHDECMP), is especially attractive since it can recover actinides from MSE residues containing aluminum. The cation exchange process is unable to effect actinide purification when aluminum is present. (DHDECMP extracts actinides and lanthanides, but does not extract common RFP contaminants, e.g., aluminum. No lanthanides are used in process streams at RFP.)... 

---