A Comparison of Static Bed and Moving Bed Chromatography

Abstract

An analysis of static and moving bed perfect column chromatography is carried out for the separation of a binary mixture having constant separation factor isotherms. It is shown that the carrier requirements are identical for both methods of operation. The model does not provide information on the length of the moving bed column, but shows that the length of the static bed column can be made vanishingly small by reducing the duration of feed intervals. Furthermore, separating the feed bands only partially can - lead to a substantial reduction in the length of the static column at fixed separation rates.     

Pure and Binary Adsorption Equilibria of Methane and Carbon Dioxide on Silicalite

Abstract

For the separation of CH₄ and CO₂ from landfill gas, pure and binary adsorption behavior of these gases were studied up to 5 atmosphere pressure at 40, 70, and 100°C for silicalite as the adsorbent. Pure and binary adsorption isotherms were determined experimentally and compared to predicted isotherms by several equilibrium models, as well as the other available data in the literature. Experimental binary isotherms at different concentrations were determined by using three concentration pulse methods (CPM). HT–CPM (Harlick‐Tezel CPM) was observed to be the best one to describe the behavior of this binary system. Equilibrium phase diagrams and separation factors were obtained from the experimental binary isotherms. For this system, the integral thermodynamic consistency tests were also shown and discussed.     

Synthesis of butyl acrylate in a fixed‐bed adsorptive reactor over Amberlyst 15

The butyl acrylate synthesis from the esterification reaction of acrylic acid with 1‐butanol in a fixed‐bed adsorptive reactor packed with Amberlyst 15 ion exchange resin was evaluated. Adsorption experiments were carried out with nonreactive pairs at two temperatures (323 and 363 K). The experimental results were used to obtain multicomponent adsorption equilibrium isotherms of Langmuir type. Reactive adsorption experiments using different feed molar ratios and flow rates were performed, at 363 K, and used to validate a mathematical model developed to describe the dynamic behavior of the fixed‐bed adsorptive reactor for the butyl acrylate synthesis. Due to the simultaneous reaction and separation steps, it was possible to obtain a butyl acrylate maximum concentration 38% higher than the equilibrium concentration (for an equimolar reactants ratio solution as feed at a flow rate of 0.9 mL min^?1 and 363 K) showing that sorption‐enhanced reaction technologies are very promising for butyl acrylate synthesis. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1263–1274, 2015     

Adsorption separation of raffinose from sucrose by activated carbon: Equilibrium,kinetics and dynamic breakthrough

Separation of oligosaccharides with a varied number of monosaccharides is an important issue in food chemistry. Raffinose, a functional oligosaccharide, has attracted increasing attentions due to its strong proliferative effect on bacteria. Industrially, cottonseed meal is an important resource for producing raffinose; however, raffinose extracted from the cottonseed meal contains a significant amount of sucrose that debases raffinose’s quality. In this work, an adsorptive separation of raffinose and sucrose on activated carbon was reported. Adsorption isotherms, adsorption kinetics and dynamic column adsorption–desorption were investigated. The activated carbon chosen has a significantly higher adsorption capacity of raffinose (0.60~0.65 g/g) than sucrose (0.35~0.40 g/g) at the equilibrium concentration studied (~35 g/L) and temperature from 293 K to 333 K. Adsorption isotherms and kinetics were fitted by the Freundlich isotherm model and the pseudo-second-order model, respectively. The effect of flow-rate and initial feed concentration on dynamic adsorption were investigated; meanwhile, the separation performance was further confirmed from dynamic desorption using aqueous ethanol of 20% as eluant. Remarkably, raffinose with purity over 90% and recovery of 79.2% could be obtained by the adsorption–desorption cycle using an aqueous feed solution containing 20 g/L of raffinose and 6 g/L of sucrose.     

Ion Rejection in Single and Binary Mixed Electrolyte Systems by Nanofiltration: Effect of Feed Concentration

Abstract

The objectives of this work were to investigate and compare the separation behavior of ions in single and binary mixed electrolyte systems by NF70, with emphasis on the effect of feed concentration. Experimental results showed that the anion rejection is lower in the binary mixed system compared to the single salt system. Anion rejection decreases with the enhancement of feed concentration of co‐existing electrolyte. As for cation rejection, Na⁺ rejection in the mixed electrolyte system is generally greater than that in the single NaCl system; whereas the separation performance of Ca²⁺ at high feed concentrations shows the opposite trend, and cannot be explained by the Donnan theory. Several possible mechanisms have been evaluated. Finally, the Spiegler‐Kedem equation was used and parameters were calculated.     

Continuous separation of glucose and fructose at high concentration using two-section simulated moving bed process

A two-section simulated moving bed (SMB) modified from a three-section SMB [Barker et al., 1975] was applied to the separation of an aqueous mixture of glucose and fructose at high concentration up to 500 kg/m³. Dowex 50W-X12 resin of Ca⁺⁺ form was used as an adsorbent and water as an isocratic eluent. The equilibrium isotherms in terms of a quadratic expression and a plug flow model with mass transfer effect were used to predict both the products and on-concentrations in the two-section SMB process. The two-section SMB process suggested in this work was successful in obtaining high fructose corn syrup (fructose with 55-90% w/w) at the high concentration of 500 kg/m³.     

Equilibrium Analysis of Cyclic Adsorption Processes: CO2 Working Capacities with NaY

Abstract

The most common application of adsorption is via pressure swing adsorption. In this type of design, the feed and regeneration temperatures are kept approximately equal, whereas the feed pressure is higher than the regeneration pressure. By exploiting the difference in the amount adsorbed at a higher pressure to the amount adsorbed at a lower pressure, a working capacity is realized. Therefore, by examining the expected (ideal) working capacity of an adsorbent, a performance characteristic can be analyzed for a pressure swing adsorption process (PSA). For this work, feed pressures up to 2.0 atm CO₂ and feed temperatures from 20°C to 200°C were investigated. These limits were chosen due to the nature of the target process: CO₂ removal from flue gas.

Carbon dioxide adsorption isotherms were determined in a constant volume system at 23°C, 45°C, 65°C, 104°C, 146°C, and 198°C, for pressures between 0.001 and 2.5 atm CO₂ with NaY zeolite. These data were fit with the temperature dependent form of the Toth isotherm. Henry's Law constants and the heat of adsorption at the limit of zero coverage were also determined using the concentration pulse method. Comparison of the Henry's Law constants derived from the Toth isotherm, and those obtained with the concentration pulse method provided excellent agreement.

By using the Toth isotherm, expected working capacity contour plots were constructed for PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and PTSA (Pressure Temperature Swing Adsorption) cycles. The largest expected working capacities were obtained when the bed was operated under a high‐pressure gradient PSA cycle, or a high thermal and pressure gradient PTSA cycle. The results also showed that certain TSA and PSA cycle conditions would result with higher expected working capacities as the feed temperature increases.     

An innovative approach for sorptive separation of amphiphilic biomolecules applying high hydrostatic pressure

An innovative approach to separate amphiphilic biomolecules in a fixed bed adsorption experimental set-up is discussed and experimental results are presented. High hydrostatic pressure of up to 360 MPa is utilized to control the sorption equilibrium. Major advantages of this approach are that no auxiliary substances are required for the separation that have to be removed afterwards. Furthermore, of the two physical parameters pressure and temperature that can be used to control reaction or sorption equilibria, pressure is the less harmful one towards the activity of biomolecules.To realize this approach, interdisciplinary researches were necessary. The surfaces of different silica gels were chemically modified in order to synthesize adsorbents with the desired properties. Two high pressure devices were designed and built. One is an circulation plant to investigate equilibrium states. It was utilized to record adsorption isotherms under a pressure of up to 300 MPa. The second one is a semi-continuous set-up for a fixed bed reactor. It was hydrodynamically characterized and afterwards used to look into breakthrough curves and separation cycles. The adsorption capacity of the tailor made adsorbents and its pressure dependency was examined via these plants in equilibrium (isotherm) and dynamic (breakthrough) experiments. Therefore, the nonionic surfactant Triton X-100 was applied as a model substance for e.g. glycolipids, which are within the scope of the separation method.During these experiments a surface modification was identified that showed a high adsorption capacity under high pressure conditions. At the same time at ambient pressure, which represents the desorption condition, it had nearly none adsorption capacity. Furthermore, the adsorption isotherms (taken at room temperature) become more favourable with increasing pressure, indicating an increasing affinity towards the applied surfactant. Experimental data were analyzed utilizing the Langmuir, Frumkin, and Temkin isotherm models. It was found that the best fit could be achieved with the Temkin-type isotherm. The dynamic experiments matched the findings from the isotherms. With increasing pressure the breakthrough of the surfactant through the fixed bed arrangement occurred later.Full separation cycles including adsorption (breakthrough), washing, desorption, and regeneration proofed that the surfactant can be regained and hence the method is feasible. In the first step up to 75% of the initial concentration could be desorbed. The process was then optimized and it was found that there is an optimum pressure for the system examined. If the goal is to maximize the regained concentration, the best adsorption pressure is around 300 MPa. For an optimal efficiency, defined as amount of pressure desorbed substance in relation to unbound and removed compounds in the washing step, the adsorption pressure should be closer to 200 MPa. An influence of the utilized adsorbent's silica structure was discovered as well and a best pore size is suggested.     

Separation of Water and Nitric Acid with Porous Hydrophobic Membrane by Air Gap Membrane Distillation (AGMD)

Abstract

This study investigates the effect of operation parameters on the separation of nitric acid‐water mixture using air gap membrane distillation (AGMD). Porous hydrophobic PTFE membrane was used. The performance was evaluated based on the permeate flux and the nitric acid selectivity. Operating parameters such as feed solution temperature, feed concentration, flow rate, and air gap width were varied. Nitric acid selectivity was found to increase with the increase in feed solution temperature, feed concentration, flow rate, and air gap width. Permeate flux increased, when the feed temperature and the flow rate were increased. The effect of recirculation of the feed solution was also studied. With the recirculation mode, at different initial solution volumes, it was observed that the nitric acid concentration in the feed and the permeate, increased. The rate of flux decline was greater, when the initial feed solution volume was lower.     

Pervaporation of Aqueous Ethanol Mixtures through Poly(Dimethyl Siloxane) Membranes

Abstract

The separation of ethanol/water mixtures by pervaporation with a poly (dimethyl siloxane) membrane has been studied. The membrane exhibited ethanol selectivity during all process runs. Investigations focused on the effects of temperature and permeate-side pressure on membrane transport with dilute ethanol feed solutions. An increase in temperature increased the flux exponentially but had little effect on selectivity. As the permeate-side pressure was increased, the flux decreased. Selectivity did not change appreciably over the pressure range evaluated. Studies also analyzed the effect of feed concentration on flux and selectivity. Flux increased and selectivity decreased as the ethanol feed concentration increased. The permeate concentration profile is superior to a standard vapor–liquid equilibrium curve at low ethanol feed concentrations.     

Experimental study of a simulated counter-current adsorption system-V. Comparison of resin and zeolite absorbents for fructose-glucose separation at high concentration

The operation of a simulated counter-current adsorption process for separation of fructose-glucose mixtures has been studied experimentally at high concentration under conditions similar to those employed in the commercial process with both CaY zeolite and Duolite resin as the adsorbent. The overall performance of the system is similar for both adsorbents although the flow conditions required to achieve separation are significantly different. At high concentration the equilibrium isotherms deviate somewhat from linearity and this has an important effect on the concentration profile (and therefore the performance) of the counter-current unit. The equilibrium stage model, with due correction for the concentration dependence of the apparent distribution coefficients, is shown to provide a good representation of the system behaviour.     

Solvent Extraction of Transuranium Elements

Abstract

Steady-state and unsteady-state digital computer programs, processed on an IBM 7072 computer, were used to obtain the concentration profiles for hydrochloric acid, curium, americium, and europium for a 16-stage liquid-liquid extraction process which is the final purification step in the production of curium 244. The equilibrium data were in the form of empirical equations which were suitable for the computer solutions.

The steady-state program, a trial-and-error procedure based on a mass balance and an equilibrium and efficiency condition written for each stage, was used to investigate the effect of changing the system variables on the separation.

The unsteady-state program is based on mass balances and an equilibrium condition for each stage and was used to obtain the unsteady-state buildup of the transuranium concentration profiles for a step change in the transuranium feed concentrations.     

Ultrapurification of Aromatic Hydrocarbons through Liquid-Liquid Extraction with Sulfuric Acid

Abstract

Sulfuric acid is shown to be a selective extractant that will successfully remove trace amounts of anthracene from cyclohexane solutions of phenanthrene; high yields of ultrapure phenanthrene were obtained easily and inexpensively. The method also appears to be successful in the purification of 2-phenylnaphthalene. The effects of acid concentration, hydrocarbon concentration, phase volume, and contact time have been investigated; in general, nonconstant distribution coefficients were obtained, indicating that equilibrium is not established during the separation time. Spectrophotometric studies of the sulfuric acid layer suggest that while protonation may be the initial step in the extraction, slow sulfonation of the hydrocarbon is the ultimate cause of the inability to attain equilibrium rapidly.     

A continuous esterification of malonic acid with citronellol using packed bed reactor: Investigation of parameter and kinetics study

A continuous packed bed immobilized lipase reactor was used in the synthesis of citronellyl malonate. Biocatalyst Candida rugosa lipases which were immobilized on Amberlite MB-1 support were employed to synthesize citronellyl malonate. Investigations on the effect of different citronellol and malonic acid concentration and feed flow rate on the conversion were being conducted. Full conversion of acid to product was achieved at high concentration of citronellol (50 mmol/L) and reached a steady state after 180 min of reaction time. Maximum conversion of acid was found at a ratio of 1:3 acids to alcohol concentration. An inhibition effect was observed when a high concentration of malonic acid was used in the system. A higher feed flow rate into the packed bed reactor system had increased the conversion to 90%. An investigation on the kinetics was conducted and an ordered bi bi mechanism with dead end complex of malonic acid was found to fit the initial rate data.     

Adsorption of Phenol from Aqueous Systems onto Spent Oil Shale

Abstract

To evaluate its ability to remove phenol from aqueous solution, Jordanian “spent” oil shale, an abundant natural resource, has been used in an experimental adsorption study. Equilibrium of the system has been determined at three temperatures: 30, 40, and 55C. The resulting experimental equilibrium isotherms are well represented by Frendlich, Langmuir, and Redlich-Peterson isotherms. The relevant parameters for these isotherms, as regressed from the experimental equilibrium data, are presented. Effects of solution pH (in the range of 3–11), in addition to effects of three inorganic salts (KI, KCl, and NaCl, each at 0.1, 0.01, and 0.005 M), on the equilibrium isotherms have been experimentally investigated. The effects of pH in the presence of KI and NaCl were also investigated for a possible interaction between salts and solution pH. The initial concentration of phenol in the aqueous system studied ranges from 10 to 200 ppm. Experimental results show that while an acidic solution has no effect on the adsorption capacity of spent oil shale to phenol, a highly basic solution reduces its adsorbability. No sound effect was observed for the inorganic salts studied on the adsorption of phenol on spent oil shale. The experimental results show that there is no interaction between the pH of solution and the presence of salts. In spite of its ability to remove phenol, spent oil shale showed a very low equilibrium capacity (of an order of magnitude of 1 mg/g). Should the adsorption capacity of the shale be improved (by different treatment processes, such as grafting, surface conditioning), results of this study will find a direct practical implication in serving as “raw” reference data for comparison purposes. salts. The experimental results show that there is a certain degree of coupling between the pH of a solution and the presence of KI salt. Other salts have shown no interaction with the solution pH. The experimental results are explained in terms of the degree of ionization of the adsorbate which is controlled by the pH of the solution.     

Binary adsorption behaviour of methane and nitrogen gases

Separation of methane and nitrogen gases is critical in the upgrading of LFG (Landfill gas), natural gas and coal bed gas in order to have a commercial heating value for methane. From an environmental point of view, methane capture from landfill gas is essential to prevent greenhouse gas emissions. Adsorption could be a beneficial process to capture low purity methane from a landfill site that is nearing the end of its lifecycle and produce high purity methane. In this work, Ceca 13X zeolite and Alcan Activated Alumina AA 320-AP have been studied for their potential for this separation and compared with Silicalite in literature. Pure and mixture adsorption isotherms were determined at 40 and 100?°C for these adsorbents by constant volume method and concentration pulse chromatographic technique, respectively. Mixture adsorption isotherms for the binary system of methane and nitrogen gases at 40 and 100?°C and 1 atmosphere total pressure have been determined by VV?CCPM (Van der Vlist and Van der Meijden Concentration Pulse Method). The application of Extended Langmuir model for this binary system have also been discussed and compared to the experimental results. Results show that equilibrium separation factor for silicalite is larger than zeolite Ceca 13X and Alcan activated alumina AA320-AP. Both Silicalite and Ceca 13X find application in the bulk separation of methane from nitrogen when y _CH4?>?0.4, especially in LFG, coal bed gas and natural gas.     

Recycle optimization in non-linear productive chromatography—I Mixing recycle with fresh feed

This paper examines the chromatographic separation of two solutes interacting non-linearly with the sorbent, when only partial separation is achieved at the column outlet, and an intermediate cut of the effluent is recycled. It is shown that, for given feed composition and column size, there is an optimum of the amount of fresh feed injected per cycle; alternately, for given feed composition and amount treated per cycle, there is an optimal column length. This optimum is such that interferences of concentration fronts are minimized in the column. The process is analysed using the “equilibrium theory”, which neglects hydrodynamic dispersion and mass-transfer resistances. Complete analytical solutions are given in the optimal situation, for the case of mass-action law equilibria with unity exponents (Langmuir type equilibrium).The theoretical predictions are compared to experimental results for the separation of Na⁺ from K⁺ by H⁺ eluent in chloride solutions, on a commercial cation-exchanger. The results are also compared to “classical” chromatography (without recycle), and to “two-way” chromatography, presented in a previous paper[1]. With respect to “classical chromatography”, for a given product purity, the optimal recycle process is shown to improve product richness (i.e. concentration of product with respect to solvent) and all performance criteria (eluent consumption, sorbent immobilization, productivity). With respect to “two-way” chromatography, it improves sorbent immobilization and productivity, but yields a poorer Na⁺ product, thus uses more eluent.     

Study of the Fixed‐Bed Adsorption Behavior of Phenylalanine on Solvent Impregnated Resins,Part III

Abstract

The implementation of the SIR technique for the amino acid separation from diluted aqueous solutions in a fixed‐bed column is presented and a mathematical model for the prediction of the adosrption behavior is developed. Independently determined equilibrium and kinetic parameters are used for the calculation of the breakthrough curves. Fixed‐bed parameters, such as axial dispersion and bed porosity, are determined experimently and compared with correlations. Analysis of the Biot and Bodenstein number reveal that the mass transfer through the film liquid around the particles, as well as the axial dispersion in the column, could be neglected at the studied experimental conditions. A simplified mathematical model was found to give the best prediction to the experimental breakthrough curves over a wide range of feed concentrations and flow rates.     

Affinity Dialysis–A Method of Continuous,Rapid Metal Ion Separation Using Dialysis Membranes and Selective,Water-Soluble Polymers as Extractants

Abstract

A membrane process utilizing dialysis and selective complexation by water-soluble polymers has been developed. This process, termed affinity dialysis, has been shown to selectively extract and concentrate both cations and anions in a manner similar to ion exchange or solvent extraction. The selective removal of calcium from sodium with selectivity of about 30, removal of chromate ion from dilute streams, and separation of transition metal ions such as Cu/Fe and Cu/Zn have all been successfully demonstrated. Effects of different polymers, polymer concentration, temperature, and flow rates have been studied. The effect of increased polymer concentration is to increase product concentration if appropriate changes in feed, polymer solution, and strip flow rates are made. A continuous polymer solution recycle and regeneration system has been constructed and operated with Cu/Zn and chromate/chloride feed streams. Removal of over 95% of the desired ion in one pass and concentration factors of product over effluent in excess of 100 have been achieved at feed flow rates of 24 gal/d. Product concentrations of greater than 3% from as little as 400 ppm feed have been demonstrated in a continuous process. In addition, the degree of polymer loss to the effluent stream has been shown to be less than 0.01%/d for a typical system. Metal removal from typical feeds is about 0.9 g/m² per 1000 ppm metal in the feed. It is expected that this technique may be useful in the separation of organic and biological materials, as well as for ionic species     

Adsorption of Ibuprofen and Atenolol at Trace Concentration on Activated Carbon

Abstract

Adsorption isotherms of atenolol and ibuprofen onto activated carbon (AC) at trace concentration in water (initial concentration, 80 μg/L – equilibrium concentration as low as 0.13 μg/L) are presented in this paper. Their adsorption was studied considering two ACs (F400 and Picabiol) showing different textural and chemical characteristics. Experiments were performed in buffered ultrapure water with and without humic acids to evaluate their influence on adsorption. It was found that adsorption was not in agreement with expectations based either on the log K_ow or log D values of the target compounds. Adsorption mechanisms were discussed and the experimental isotherms were modelled.