Separations Technology最新文献

This work examines the mass transfer resistance associated with the separation of sorbed organic contaminants, tetrachloroethene (PCE) and trichloroethene (TCE), from the Borden sand and Moffett aquifer solids, respectively. The experimental method entails extracting the sorbed solute directly into scintillation fluid. Desorption rate data are interpreted using a pore diffusion model, in spherical coordinates, to determine effective pore diffusivity values (D_p). An apparent increase in observed desorption rates for long-term samples is discussed in the framework of a potential experimental artifact induced by a cosolvent effect. The results from the scintillation fluid extraction method are less reproducible than those from an aqueous purge-and-trap protocol (used previously for the same solute-sorbent systems). However, estimated D_p values were of the same order of magnitude for the two methods. This result suggests that the solvent extraction technique is subject to mass transfer resistances that are similar to those encountered in aqueous systems. The method is tested over a range of temperatures, and results are interpreted with respect to mechanism validation. For a Moffett fraction, temperature dependent results were indicative of an aqueous diffusion mechanism. Corresponding results for a Borden fraction were less certain, but suggested a more severe mass transfer resistance.

We analyze in detail the thermodynamic properties and the kinetic features of adsorption on fractal structures, focusing on those topics that can be useful in practical adsorption-based processes and highlighting the theoretical results that can be applied in the design of suitable separation and sorption conditions. The development and the application of thermodynamically consistent models of adsorption isotherms, encompassing the fractality of the adsorbent and the volume-to-surface effects in microporous fractal structures, are analyzed.

Electrodialysis is an interesting technique developed for recovering and purifying salts and acids from fermentation broths. In this work the concentration process of sodium lactate solutions was analyzed using a two-compartment electrodialytic unit equipped with commercial membranes (Neosepta AMX and CMX, Tokuyama Soda). The influence of several operating parameters on the overall process performance was investigated. For instance, it came out that at low current density values such membranes are able to operate a perfect separation of opposite charges, resulting in a good process performance. Moreover, water transport by electro-osmosis has to be considered, hence lowering the stack performance. Lastly, the reliability of a general mathematical model for this process was tested. The consistency between experiments and model results is fairly good, allowing the use of this model for design and optimization purposes.

Cationic surfactants can be easily recovered by precipitation method. Precipitation can be achieved by the addition of ions of opposite charge to that of the surfactant. The method is simple, rapid and effective.

The separation of finely dispersed oil from oil-water emulsions was carried out in an electroflotation cell which has a set of electrodes, a lead anode and stainless steel screen cathode. The effect of operating parameters on the performance of the batch cell was examined. The parameters investigated are electrical current, oil concentration, flotation time and flocculant agent concentrations. A well-fitted empirical correlation represents the change in percentage oil removal with wide range of operating conditions was obtained. The oil separation reached 65% at optimum conditions; 75% in the presence of NaCl (3.5% by wt. of solution); and 92% with the presence of NaCl and at optimum concentration of flocculant agent. Electrical energy consumption varied from 0.5 to 10.6 KWh/m³ according to experimental conditions. An equation relates the K with I was obtained. The general form of the equation is K = constant (I)ⁿ; where the n values are 0.6 4 and 0.62 for solutions with and without NaCl, respectively. The previous relation is valid only for current values from 0.3 to 1.2 A. The effect of emulsion flow rate on the separation process was determined on continuous scale.

This work presents a stochastic approach, based on Monte Carlo method, to simulate liquid filtration processes through non-woven fibrous materials. The real filter material is represented as a multilayer medium with a network of multiply connected pores. To describe the deposition and resuspension of particles on and from the filter medium, the following four mechanisms were considered: particle capture by sieving, patricle capture by fibers; particle capture by blocked pores; and particle re-entrainment. The particle capture by fibers and blocked pores, and particle re-entrainment depend on the balance between the adhesion and removal forces. The adhesion forces for particles of diameter smaller than 20 μm were determined through the concept of London-Van Der Waals forces. For particles of diameter greater than 20 μm, gravitational forces were considered. Three-dimensional random flow was assumed to stimulate the particles motion through the multilayer medium. The pressure drop across the filter medium was calculated as the sum of the pressure drop across the clean filter plus the pressure drop due to the deposited particles.

A FORTRAN Program was developed to implement the filtration process model. For a wide range of typical filtration conditions, the calculated filter efficiencies predicted the experimental results with a percent difference between 0.5 and 19.3 depending on the particle size. The filter material capacities were predicted with an average discrepancy of 23.0%

The replacement of Br⁻ by trimethylamine for the synthesis of anion exchange adsorbent particles by surface functionalization of polystyrene-divinylbenzene based spherical porous particles was studied experimentally and theoretically. The calculated values of the kinetic parameters indicate that the net rate of the replacement of Br⁻ by trimethylamine is dominated by the kinetic mechanism involving the formation and opening of an epoxide,

A simulated counter-current chromatographic (SCC) separation process is simulated using a dispersed plug flow model with a direct approach. The solution of the governing partial differential equations is solved with a numerical technique based on the method of orthogonal collocation. Mass transfer resistances and axial dispersion are accounted for in the model. This model is used to simulate the separation of praziquantel enantiomers in the SCC system. The model accounts fully the sequential operation of the system. The transient and steady state behaviour of the separation of praziquantel enantiomers by this chromatographic system can be described adequately by this model.

The operation of a continuous countercurrent adsorption system is modelled and optimized. The objective is to maximize the recovery of the less strongly adsorbed species in the raffinate for a specified purity of the product. The optimization is carried out for a system with linear and non-linear isotherms. The optimization results indicate that the optimum values of parameters are significantly different for linear and non-linear isotherms. An optimal choice of operating variables corresponding to a compromise between recovery and purity is also suggested.

Extraction of carboxylic acids, C₂C₆, was carried out with tributylphosphate (TBP) from an aqueous waste stream at pH = 2, 2.5, and at as such pH taken from an environmental process engineering point of view. The effect of the presence of H₂SO₄ and HCl on the distribution coefficients for C₂C₆ carboxylic acids was investigated. The measurements were also carried out in the presence of inorganic salts such as Na₂SO₄ and NaCl.