Resins, separators

The reaction mixture is heated and allowed to reflux, under atmospheric pressure at about 100°C. At this stage valve A is open and valve B is closed. Because the reaction is strongly exothermic initially it may be necessary to use cooling water in the jacket at this stage. The condensation reaction will take a number of hours, e.g. 2-4 hours, since under the acidic conditions the formation of phenol-alcohols is rather slow. When the resin separates from the aqueous phase and the resin reaches the requisite degree of condensation, as indicated by refractive index measurements, the valves are changed over (i.e. valve A is closed and valve B opened) and water present is distilled off. 

On further heating the methylolmelamines condense and a point is reached where hydrophobic resin separates out on cooling. The resinification is strongly dependent on the pH and is at a minimum at about pH 10.0-10.5. An increase or decrease of pH from this value will result in a considerable increase in resinification rates. 

Cation units usually contain a sulphonic acid resin whilst anion resins fall into the two main categories of strongly basic, with quaternary ammonium groupings and weakly basic, with tertiary amine groups. The final unit is the mixed bed in which, by a mixture of cation and anion resins in the same vessel, the effect is achieved of a multiplicity of separate cation and anion units. Resin separation is necessary for regeneration purposes. Considerable improvements in water quality are obtainable by these means. 

In the second half of the 1960s, at the same time but independently, three basically different plastic separators were developed. One was the polyethylene separator [16] already referred to in starter batteries, used only rarely in stationary batteries, but successful in traction batteries. The others were the microporous phenolic resin separator (DARAK) [18] and a microporous PVC separator [19], both of which became accepted as the standard separation for stationary batteries. They distinguish themselves by high porosity (about 70 percent) and thus very low electrical resistance and very low acid displacement, both important criteria for stationary batteries. 

NOTE A practical problem resulting from the rapid reaction kinetics of HQ is that when water containing HQ passes through an MBDl, it turns the resin black, obscuring visual observation of resin separation during regeneration. 

The application of the Chelex 100 resin separation and preconcentration, with the direct use of the resin itself as the final sample for analysis, is an extremely useful technique. The elements demonstrated to be analytically determinable from high salinity waters are cobalt, chromium, copper, iron, manganese, molybdenum, nickel, scandium, thorium, uranium, vanadium, and zinc. The determination of chromium and vanadium by this technique offers significant advantages over methods requiring aqueous final forms, in view of their poor elution reproducibility. The removal of sodium, chloride, and bromide allows the determination of elements with short and intermediate half-lives without radiochemistry, and greatly reduces the radiation dose received by personnel. This procedure was successfully applied in a study of... 

Shinohara et al. [299] have described a procedure based on gas chromatography for the determination of traces of two, three, and five-ring azarenes in seawater. The procedure is based on the concentration of the compounds on Amberlite XAD-2 resin, separation by solvent partition [300], and determination by gas chromatography-mass spectrometry with a selective ion monitor. Detection limits by the flame thermionic detector were 0.5-3.0 ng and those by gas chromatography-mass spectrometry were in the range 0.02-0.5 ng. The preferred solvent for elution from the resin was dichloromethane and the recoveries were mainly in the range 89-94%. 

The results of these analyses are summarized in Table I. The estimated amounts of each compound are given in terms of micrograms per gram of dry resin. In a normal resin separation-concentration procedure, these amounts would be the same, independent of the amount of water passed through the resin. Some peaks could not be identified. 

Clean Water Blank Experiment. This experiment was performed for the purpose of identifying any artifacts that might arise from the resin in the course of normal resin experiments. Four replicate resin blanks were run by the normal resin separation-concentration procedure. Data from this experiment yielded the following conclusions ... 

Influence of unstirred layers near the membrane. Near the membrane there exist unstirred layers which under unfavourable conditions can exert a considerable influence on the fluxes and the membrane potential too. F. Helfferich (57) has drawn the attention to this effect. The thickness of these layers depends on the rate of stirring. Under good stirring conditions the film-thickness amounts to 20 to 1 10-3 cm. Under extreme conditions it can be reduced to 10-4 cm. It is not always possible to eliminate its influence (139). The transport in the films is diffusion-controlled. In some cases the effect of the films can be involved in the calculations. As an example the case of selfdiffusion is given here. A cation-exchange resin separates two solutions of identical chemical composition. The cations on either side are isotopes of the same element. 

Zhu, X. and Jyo, A. (2001) Removal of arsenic(V) by zirconium(IV)-loaded phosphoric acid chelating resin. Separation Science and Technology, 36(14), 3175-89. 

Sr-Resin separations can also be set up in a renewable separation-column approach83 as described above for "Tc determinations, and illustrated in Figure 9.6. In this case, the sample was separated and eluted from the column. The advantage of the renewable column approach was that fresh column material could be provided for each separation. The carryover on Sr-Resin columns, described above, is largely due to the resin material. It was shown that automatically replacing the resin material largely eliminated carryover from one sample to the next. 

FIGURE 9.10 Schematic diagram of a multisyringe separation system using solenoid valves rather than a multiposition valve. Normally open and normally closed ports on the solenoid valves are marked with open and closed circles, while the common port is unmarked. System is shown with wash and eluent solutions for Sr determination using a Sr-Resin separation column. 

Most recent studies describing fluidic automation of TRU-Resin separations have been directed to ICP-MS analysis. Evans et al. used a FI system with a TRU-Resin column to concentrate U and Th from a variety of aqueous and biological standard reference materials.131 After the wash step with 2 M HNQ3, these analytes were... 

Several groups have described the use of UTEVA-Resin separations coupled to ICP-MS for actinide analyses (see Table 9.4). UTEVA-Resin contains the extractant dipentyl pen-tylphosphonate (DP[PP]), which is also known as diamylamyl phosphonate (DAAP).31 This extractant retains actinides from nitric acid solutions as nitrato complexes, with increasing uptake as nitric acid concentrations increase (see Figure 9.11). Extraction equilibria for representative species are shown in Equations 9.6 and 9.7, where the bar above a species indicates that it is immobilized on the resin.4... 

The XAD-8 resin separation of hydrophobic and hydrophilic components of WSOM was also employed by Sannigrahi et al. (2006). The 13C-NMR results indicated that WSOM in urban atmospheric particles is mostly aliphatic in nature (-95% C mass) with major contributions from alkyl and oxygenated alkyls (-80%), carboxylic acid (-10%), and aromatic functional groups (-4%). The authors also found that urban aerosol WSOC are only qualitatively similar to aqueous humic material in terms of functional group distribution. 

Allylic alcohols [e.g. citronellol, geraniol (8), and nerol (18)] exhibit strong shielding at the y-carbon and deshielding at the 5-carbon in the 13C n.m.r. upon acylation.127 Cationic exchange resins separate acyclic [e.g. myrcene (12)] from cyclic (e.g. limonene) monoterpenoids.128... 

Two additional problems occurred in these separations. Firstly, the asphaltene samples when applied from cyclohexane solutions as described by McKay (3) were leaving 3%-4% residuum at the column head. Secondly, the solvent series was the same as that used by McKay, differing from that used for resin separations only in that cyclohexane was used as the initial solvent instead of nC5, and benzene/methanol was employed instead of methanol. These modifications are necessary because of the lower solubility of asphaltenes. 

Similar solubility phenomena can also be observed for the resins. The sample for resin separation after removal of asphaltenes is normally applied as a solution in nC5. However, after the removal of the oil, the fractions obtained from the ion exchangers show a marked decline in solubility in the same solvent. Also, if resin separation is done by the SARA method, the tetrahydro-furan fraction is hardly soluble in nC5. This again shows the solubility criterion to be a function of several variables the removal of some of the solubilizing components of the resins renders the remainder insoluble. 

A study of MW distribution for precipitated asphaltenes and the derivation of conclusions about bitumen or asphalt properties from it has severe limitations since this complex mixture exhibits a considerable overlap of GPC curves for all the fractions obtained in a conventional separation procedure. Similarly, the resins separated on clay and the eluted hydrocarbons exhibit overlap, as shown by Figures 5 and 6. Figure 5 demonstrates the GPC profiles of Athabasca asphaltenes (nC5) and resins (Attapulgus clay—total resin eluent)... 

Figure 7. GPC profiles of fractions of Cold Lake resins separated on anion exchange resin (IRA-904) and cation exchange resin (A-15) (a) acid fractions, (b) base fractions column and conditions same as in Figure 6...

Natural waters Sample concentration by cation-exchange resin, separation by ion-exchange resin and complexation with Arsenazo III Spectrophotometry (total uranium) 0.1 fjg/L 80% Paunescu 1986... 

Uchida, T., Nagase, M., Kojimo, I., lida, C A simple decomposition chelating resin separation for the determination of heavy metals in silicates by atomic absorption spectrometry. Anal. Chim. Acta 94, 275 (1977)... 

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