Separations Technology最新文献

The optimum angles of inclination for maximum separation, maximum production rate and minimum column length in a flat-plate thermal-diffusion column have been determined. Considerable improvement in performance is obtainable if the column is tilted at the optimum angle, instead of being placed vertically, so that the convection strength can be properly reduced and controlled, resulting in suppressing the undesirable remixing effect while still preserving the desirable cascading effect.

The effect of humidity on the adsorption and desorption of methyl iodide was investigated in a TEDA (triethylenediamine)-impregnated activated carbon bed. The amounts of chemisorption and physical adsorption of methyl iodide were measured in different humidity levels for base and TEDA-impregnated activated carbons. The physical adsorption of methyl iodide in the presence of water vapor was fitted with the potential theory-based Dubinin-Radushkevich equation. The significant amount of chemisorption even in high humidity conditions confirmed the effectiveness of TEDA-impregnation for trapping methyl iodide permanently.

The experimental adsorption and desorption rate data for pure propylene, pure propane, and propylene-propane mixtures on 13 X molecular sieves are presented for different temperatures and compositions; these rate data were efficiently determined using the differential sorption bed system described by Liapis et al. (Liapis et al. (1992) Rates and equilibria of adsorption and desorption of propane and propylene on 13 X molecular sieves determined experimentally using a differential sorption bed system. Sep. Technol. 2, 141–154). Propylene is the most preferentially adsorbed component, and the desorption rates of propylene and propane are slower than the adsorption rates. Mathematical models were constructed and solved, and it was found that the two-component model could provide a quantitative measure of the interactions between propylene and propane, and could describe the behavior of binary adsorption kinetics including the overshoot of the equilibrium loading by the less preferentially adsorbed propane. The theoretical results indicate that the desorption rates are not described by the same intracrystalline diffusion coefficients as the adsorption rates.

Experiments on fixed-bed adsorption of 1-butanol vapor, p-xylene vapor and their mixtures with high silica zeolites (HSZ) were conducted. For the cases of single-component adsorption, the adsorption equilibria obey the Langmuir equation, and the presence of water vapor was found to reduce the amount of adsorption. On the other hand, water vapor showed no effect on adsorption kinetics. For binary adsorption of 1-butanol and p-xylene with HSZ of Y- and Mordenite-type, depending upon the relative concentration of the two species, either species may be preferentially adsorbed. No simple expression was found to represent the equilibrium data. In contrast, the Langmuir equation was found to represent the binary equilibrium data of HSZ of the ZSM-5 type. Further, the dynamics of the fixed-bed adsorption may be predicted with use of the extended mass-transfer-zone method.

The removal of formaldehyde from aqueous solutions of 2-butyne-1,4-diol (BD), which are prepared from ethynylation of acetylene with aqueous formaldehyde, was successfully accomplished by a number of approaches: reaction with sodium bisulfite and removal of the resultant ionic product with an anion exchange resin in a fixed bed system or using an anion exchange resin bed in bisulfite form; reactive distillation with methanol and ethylene glycol in the presence of cation exchange resin as catalyst to give the corresponding acetals; internal acetalization with BD in the presence of cation exchange resin as catalyst; Cannizzaro's reaction with sodium hydroxide; and aldol type condensation in the presence of sodium hydroxide. Residual concentrations of formaldehyde as low as 20 ppm could be achieved through more than one of the methods mentioned above.

The mechanism of cake formation in constant pressure filtrations of submicron particles is studied by analysing the forces exerted on the depositing particles. The Brownian dynamic method is used to trace the loci of slurry particles and to simulate the packing structure of submicron particles in filtrations. The major factors affecting the particle packing, such as frictional drag, van der Waals' force, electrostatic force, and Brownian force, etc., are discussed. The most compact cake is found when the frictional drag and Brownian force are of the same order of magnitude. A numerical program is designed to estimate the variations of local cake properties during a course of constant pressure filtration. The calculated results of average cake porosity and average specific filtration resistance agree very well with the experimental data.

The distribution coefficients, K_D, were measured for the extraction of butyric acid, valeric acid, and caproic acid with tributylphosphate from an aqueous waste stream. The measurements were also carried out in the presence of salts such as sodium sulphate and sodium chloride. The results presented are expected to aid process environmental engineers.