Column exchange process

Naphthalenedisulfonate-acetonitrile as the only mobile phase with a silica column coated with a crosslinked aminofluorocarbon polymer has proven to be an effective combination for the separation of aliphatic anionic surfactants. Indirect conductivity and photometric detection modes are used to monitor these analytes. The retention of these surfactants is found to depend on both the ionic strength and the organic solvent content of the mobile phase. The mechanism of retention is considered to be a combination of both reverse phase and ion exchange processes. Selective separation of both alkanesulfonates and... 

Pharmacia s Q- and S-Sepharose anion- and cation-exchange resins For the anion-exchange process it was found that two step changes, simultaneous in pH and salt concentration were necessary to carry out the anion-exchange separation. A 0.01 M sodium acetate buffer, pH 5.8, was used forthe starting state orfeed loading buffer. After the whey feed was loaded onto the column, one column volume of this... 

As shown in Illustrative Examples 19.3 and 19.4, often it is not immediately known whether an exchange process is controlled by transport across a boundary layer or by transport in the bulk phase. In Illustrative Example 19.3 we look at the case of resuspension of particles from the polluted sediments of Boston Harbor. We are interested in the question of what fraction of the pollutants sorbed to the particles (such as polychlorinated biphenyls) can diffuse into the open water column while the particles are resuspended due to turbulence produced by tidal currents in the bay. To answer this question we need to assess the possible role of the boundary layer around the particles. 

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... 

Eluants.—Citric acid buffered with ammonium citrate is the first eluant to be used in the separation of rare earths by ion exchange process. It is also the most extensively [85—89] investigated eluant. At low pH the individual rare earths move down the column at different rates. A plot of volume of eluted portion vs. concentration shows typical bell-shaped curves (Fig. 2) with widely spaced maxima characteristic of elution chromatography, although the system makes use of a chelating agent. 

For an experienced analyst who knows the techniques involved, the laboratory time to complete this experiment (excluding time for preparation) is 6-8 hours it will take longer for those new to the procedure. The experiment can be interrupted conveniently before the ion-exchange process (Step 10), after the plutonium is stripped from the column (Step 12), and at the conclusion of the preparation for electrodepositon (Step 14). An alternative procedure is given for a 25-mL sample that skips the concentration Steps 3-8. 

Frequently, IEC separations are carried out at elevated temperatures. This is because the kinetics of the ion-exchange process may be improved dramatically. The efficiency of the column may be increased by a factor of three if the temperature is increased from 30 to 70 °C [371], An additional advantage of an increased column temperature is a decrease in the eluent viscosity and hence a reduced pressure drop over the column. 

Air-cooled heat exchangers are employed on a large scale as condensers of distillation columns or process coolers. The approach temperature-the difference between process outlet temperature and dry-bulb air temperature-is typically of 8 to 14 °C above the temperature of the four consecutive warmest months. By air-... 

The technique employed almost exclusively in the process developed is extraction chromatography (LLC), which is an ideal technique, in view of the column exchange capacities, for the extraction of moderate amounts of material present in a limited volume, or for the recovery of elements present in low concentration in large volumes. The simplicity of the equipment and the low sensitivity of extraction performance to fluctuations in solution throughputs make it a simpler technique for use than liquid-liquid extraction. Moreover, LLC lends itself well to discontinuous operation. In the case of difficult separations, such as Am/Cm separation, LLC offers the advantage of a large number of stages in a simple, compact unit. Since the extraction of the U(VI) present in the Masurca waste in macroconcentration is not economically feasible by LLC, the conventional liquid-liquid technique was adopted. 

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