Kinetic of copper ion exchange onto iminodiacetic resin

The internal porosity and swelling/shrinking of a chelating iminodiacetic type ion exchange resin have been experimentally studied during the uptake of copper onto it. The swelling of the particle could be analyzed with a modified model on th basis of the unreacted core model (UCM), including the influence of chemical equilibrium. The ion exchange kinetic results in batch experiments are used with the UCM to calculate the effect of pH on the internal diffusion coefficients. Results from shallow bed experiments with mixed internal and external diffusion controls have shown the applicability of the above model to analyze ion exchange with low external velocities.     

Simplified Predictions of Breakthrough Fronts for Constant-Pattern Adsorption and Ion Exchange

Abstract

The loading cycle of many (perhaps most) commercial adsorption and ion exchange operations involves a favorable isotherm. Concentration fronts for favorable isotherms approach a constant pattern for long bed lengths, and most industrial adsorption and ion exchange operations use sufficiently deep beds that the constant-pattern conditions are approached. Once a constant pattern is established, the region around the front can be analyzed using conventional methods developed for continuous absorption/stripping operations, but the location of the feed and withdrawal points must be assumed to move down the bed at the same rate at which the front moves. Using this approach, the constant-pattern front can be calculated for any shape of constant-pattern isotherm. The dimensionless distance in the bed is expressed in terms of transfer units, and the shape of the front can be evaluated graphically even when the relations can not be integrated analytically. This procedure is illustrated for binary ion exchange isotherms. In the simplest cases, exchange of ions with like charge, the integration can be performed analytically. For other cases, numerical and graphical solutions are illustrated.     

Electric field-associated deformation of polyelectrolyte gel near a phase transition point

The influence of de electric fields on sodium acrylate—acrylamide copolymer gel near a phase transition point in acetone—water mixtures containing NaOH was studied. In the mixtures free of NaOH, the shrunken-state gel near a phase transition point was not influenced by dc electric fields, while the swollen-state gel near it shrank from its part facing to the positive electrode in dc electric fields. In the presence of NaOH, unprecedented swelling of the shrunken-state gel has been observed. The swollen-state gel showed swelling or shrinking in the field. The type of deformation was determined by the concentration of NaOH. The drift of mobile ions played a role in the deformation. The shrinking occurred through the conformational change of polymer network caused by the drift. The swelling was observed by the change of the osmotic pressure based upon the ion concentration difference between the inside and the outside of a gel.     

EXTRACTION OF Cd(II) FROM AQUEOUS NITRATE SOLUTION BY THERMOSENSITIVE GEL CROSSLINKED WITH 2,6-DI(3-VINYLBENZYL-1,2,4- TRIAZOL-5-YL)PYRIDINE (BTP)

A poly-N-isopropylacrylamide (poly-NIPA) gel crosslinked with 2,6-di(3-vinylbenzyl-1,2,4-triazol-5-yl)pyridine (BTP) was prepared by the ultrasonic polymerization technique and the extraction of Cd(II) from an aqueous nitrate solution was tested. The BTP-NIPA gel showed phase transition phenomena, in which the gel was shrunken at temperature higher than the phase transition temperature (304 K) and swollen at less than 304 K. The extraction capacity of Cd(II) was affected by the phase transition phenomena and was decreased by the structural change of gel from the shrinking state to the swelling one. This is attributable to the configurational change of nitrogen donors in BTP, which occurs by the structural change of gel. When the extraction mechanism is assumed as the formation of a complex ion, Cd(BTP)²⁺ and its nitrate complex, Cd(BTP)(NO₃)⁺ at both the shrinking and swelling states, the equilibrium constant for the complex formation of Cd(BTP)²⁺ at the shrinking state corresponds to about 2.5 times of that at the swelling state. These results suggest that the extractability of Cd(II) can be controlled by the configurational change of nitrogen donors with the phase transition of BTP-NIPA gel.     

IONIC GEL EXTRACTION IN AN ELECTRIC FIELD

This paper reports the successful synthesis of an ionic gel with good swelling property and high sensitivity to the electric field. This gel shrinks rapidly as an electric field with a low supply voltage is applied across it, and the overall shrinking process can be completed in 15 minutes. The gel would swell again when the the electric field is removed. A theoretical analysis and experimental study have been carried out on the kinetics of swelling and shrinking of the disk shape gels. The modeling of kinetics of swelling and shrinking of the disk gels is in good accordance with the experimental results.     

Mass Transfer Mechanisms in the Fixed‐Bed Ion‐exchange Process for Dilute Colloidal Silica Manufacture

The ion exchange behavior of the H⁺ form C‐100 Purolite resin for the production of colloidal silica from dilute sodium silicate solutions has been investigated. The exchange isotherm has been found to be almost irreversible. The effective resin diffusion coefficient has been found to be 2.84 × 10^–10 m² s^–1 using a shrinking core model for the batch uptake experiments. Fixed bed experiments for different column heights and feed flow rates were performed. Numerical solution of the governing equations showed that the process is initially controlled by film diffusion and consequently by resin diffusion. Axial dispersion had to be taken into account. A simple power law correlation has been determined that relates the fluid Peclet number to the Reynolds number. It is presumed that some sort of resin ‘deactivation’ due to intraparticle microgel formation is responsible for the sluggish end part of the breakthrough curves.     

膨胀床吸附层析技术基础性能研究进展

膨胀床吸附层析技术兼有流化床和填充床层析的优点,不需预先除去料液中的颗粒而可以直接从料液中吸附目标产物。但该技术还不成熟,操作还有很大的不确定性,为了解其基础性能,掌握其膨胀和吸附机制,本文从膨胀床流体力学性能、吸附性能、吸附剂与细胞和细胞碎片之间的相互作用等方面,对近年来国内外膨胀床基础性能的研究进行了综述。     

膨胀床吸附层析技术基础性能研究进展

膨胀床吸附层析技术兼有流化床和填充床层析的优点,不需预先除去料液中的颗粒而可以直接从料液中吸附目标产物。但该技术还不成熟,操作还有很大的不确定性,只有了解其基础性能从而掌握它的膨胀和吸附机制,才能使它真正发挥作用。从膨胀床流体力学性能、吸附性能、吸附剂与细胞和细胞碎片之间的相互作用以及基础性能的其他方面,对近年来国内外膨胀床基础性能的研究进行了综述。     

A fundamental CFD study of the gas–solid flow field in fluidized bed polymerization reactors

A Eulerian–Eulerian model incorporating the kinetic theory of granular flow was applied to describe the gas–solid two-phase flow in fluidized bed polymerization reactors. The model parameters were examined, and the model was validated by comparing the simulation result with the classical calculated data. The effects of distributor shape, solid particle size, operational gas velocity and feed manner on the flow behavior in the reactor were also investigated numerically. The results show that with the increase of solid particle diameter, the bubble numbers decrease and the bubble size increases, resulting in a smaller bed expansion ratio. Bed expansion ratio increases with increasing the gas inlet velocity. Moreover, the final fluidized qualities are almost the same for the plane distributor case and the triangle distributor case. There exists a tempestuous wiggle from side to side in the bed at the continuous feed manner, which could not be obtained at a batch feed manner.     

Effect of attrition on particle size distribution and SO2 capture in fluidized bed combustion under high CO2 partial pressure conditions

In both pressurized and oxygen-enriched fluidized bed combustion the partial pressure of CO₂ in the reactor becomes high, which affects SO₂ capture by limestone. Both of these technologies are also applicable to decreasing greenhouse gas emissions; the first one by increasing the efficiency of electric energy production and the latter by enabling capture of carbon dioxide for storage.Attrition increases the reaction rate by removing the sulphated layer on the particle, thus reducing the diffusion resistance. In the well-known solution for the shrinking core model the reaction time can be presented as the sum of the contributions of the kinetics and diffusion. It is shown that the effect of attrition can be expressed as an auxiliary term in this expression. A method to extract the diffusivity of the product layer from the SO₂ response in a bench-scale fluidized bed test using a limestone sample with a wide particle size distribution is presented. Based on a population balance model, a method to estimate the particle-size-dependent attrition rate from measured particle size distributions of the feed and bed material is illustrated for a 71-MW_e pressurized power plant. In addition attrition and its effect on the optimization of the limestone particle size for sulphur capture in oxygen-enriched combustion are discussed.     

Modelling and numerical simulation of liquid–solid circulating fluidized bed system for protein purification

A novel liquid–solid circulating fluidized bed (LSCFB) was modelled for protein recovery from the feed broth. A typical LSCFB system consists of downer and riser, integrating two different operations simultaneously. A general purpose, extensible, and dynamic model was written based on the tanks-in-series framework. The model allowed adjusting the degree of backmixing in each phase for both columns. The model was validated with previously published data on extraction of bovine serum albumin (BSA) as model protein. Detailed dynamic analysis was performed on the protein recovery operation. The interaction between the riser and downer were captured. Parametric studies on protein recovery in LSCFB system were carried out using the validated model to better understand the system behaviour. Simulation results have shown that both production rate and overall recovery increased with solids circulation rate, superficial liquid velocity in the downer and riser, and feed solution concentration. The model was flexible and could use various forms of ion exchange kinetics and could simulate different hydrodynamic behaviours. It was useful to gain insight into protein recovery processes. The general nature of the model made it useful to study other protein recovery operations for plant and animal proteins. It could also be useful for further multi-objective optimization studies to optimize the LSCFB system.     

Pervaporation separation of dimethyl carbonate/methanol mixtures with regenerated perfluoro‐ion‐exchange membranes in chlor‐alkali industry

The waste perfluoro‐ion‐exchange membranes (PFIEMs) in chlor‐alkali industry were regenerated and used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) mixtures by pervaporation process. The energy‐dispersive spectrum (EDS) demonstrates that the impurities on the surfaces of waste PFIEMs can be effectively cleared by the regeneration process. The degree of swelling, sorption, and pervaporation properties of the regenerated PFIEMs with different counter ions were investigated. The results indicate that the counter ions of PFIEMs conspicuously influence the degree of swelling, sorption, and pervaporation properties for DMC/MeOH mixtures. The degree of swelling and solubility selectivity both decreases with the alkali metal counter ions in the sequence: Li⁺ > Na⁺ > K⁺ > Cs⁺. The degree of swelling increases with MeOH concentration increasing in feed liquid. The pervaporation measurements illustrate that the permeation flux decreases and the separation factor increases with the rising in ion radius of counter ions. The increase of feed concentration (MeOH) and feed temperature is advantageous to improve permeation flux while at the cost of separation factor decreasing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

BATCH SORPTION BY LIGAND EXCHANGE: DETERMINATION OF INTRAPARTICLE DIFFUSIVITY

A mathematical model has been developed to describe batch sorption by ligand exchange. A ligand is sorbed onto an exchange sorbent from a finite bath. The sorbent particles are uniformly suspended in the fluid bath volume. The transport mechanisms are diffusion through the solid sorbent and external film diffusion. The equilibrium between the solid and fluid phase is described by a Langmuir isotherm. Two approaches are presented for representing the intraparticle mass transfer—diffusion in a pseudohomogeneous solid accompanied by sorption and diffusion through a saturated region to an unreacted shrinking core. The solid diffusion model, consisting of a partial differential equation, has been solved numerically by orthogonal collocation. The shrinking core model, a single ordinary differential equation, has been solved by conventional numerical integration. Both models successfully correlated data on diffusion of ammonia in copper-complexed carboxylic acid type ion exchange resin. The resultant sorbent diffusion coefficient is useful in designing fixed bed continuous ligand exchange columns.     

Continuous monitoring of the swelling behaviour of gel-type reactive polymers and chromatographic media: Some practical applications of the technique

A new technique allowing monitoring of the swelling behaviour of gelatinous polymeric reagents and chromatographic supports is described. It is based up on the application of a continuous flow ‘zero dead volume operating’ reaction system of original design equipped with a potentiometric pickup kinematically attached to the movable piston of the reactor. The latter transduces the polymer bed volume change into an electrical signal that can be conveniently registered on a common laboratory chart recorder. The proposed method provides rapid access to swelling data of the polymer and, moreover, for the first time allows for real-time investigation of swelling dynamics of reactive polymers that are involved in chemical and/or physical process. The practical scope of the technique is illustrated by the results of its application in solid phase peptide synthesis, ion exchange and studies of swelling behaviour of resins and gel-type polymeric reagents.     

Dehydration of tetrahydrofuran by pervaporation using crosslinked PVA/PEI blend membranes

Dense blend membranes were prepared by blending hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(ethyleneimine) (PEI), which were then crosslinked by glutaraldehyde (GA) in a mixture of solvents under the catalysis of hydrochloric acid (HCl) for the dehydration of tetrahydrofuran (THF) by pervaporation. The effect of experimental parameters such as feed water concentration, permeate pressure, and membrane thicknesses on permeate parameters, i.e., flux and selectivity were determined with feed water concentration less than 40 wt %. The membranes were found to have good potential for breaking the azeotrope of 94 wt % THF with a flux of 1.072 and 0.376 kg/m² h for plane PVA/PEI and crosslinked PVA/PEI blend membrane, which exhibited high selectivity of 156 and 579 respectively. Selectivity was found to improve with decreasing feed water concentration and increasing membrane thickness, whereas flux decreased correspondingly. High permeate pressure causes a reduction in both flux and selectivity. These effects were clearly elucidated with the aid of the known relationship among plasticization effect, degree of swelling, permeate pressure, and feed water concentration. These blend membranes were also subjected to sorption studies to evaluate the extent of interaction and degree of swelling in pure as well as binary feed mixtures. Further ion exchange capacity studies were carried out for all the crosslinked and uncrosslinked membranes to determine the total number of interacting groups present in the membranes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1152–1161, 2006     

Modeling of transient heterogeneous two-dimensional catalytic packed bed reactor

A two-dimensional transient catalytic packed bed model, incorporating all transport parameters and resistances, along with boundary conditions based on a catalytic single pellet has been developed. Thermal conduction through the solid phase is included in the model. The overall steady state reactor performances of packed bed reactor using a model proposed in this study are compared with those from different models which are often used for a packed bed reactor. The model presented is very useful in the presence of internal temperature and concentration gradients in the catalyst pellets. The dynamic behavior in feed temperature change is examined during ethane hydrogenolysis. A transient thermal runaway is observed by feed temperature decrease. The sensitivities of the computation to each physical parameter and the effects of some simplifying assumptions in the model are also analyzed. The magnitude and position of hot spot in catalytic packed bed reactor are relatively sensitive to thermal parameters and characteristic parameters of a catalyst pellet.     

Mathematical modelling of coal combustion in fluidized beds with sulphur emission control by limestone or dolomite

A model is developed for the combustion of coal in fluidized beds with sulphur emission control by limestone or dolomite. The gas and solid flow analysis is based on multiple gas bubbles of varying sizes which, accompanied by the cloud and wake, rise through the particulate emulsion phase. Solids population balance relating the feed, overflow, and elutriation with the physiocochemical changes of particles in the bed is carried out for coal and sulphur-absorbent respectively. The reactions in the bed are then formulated in terms of the above determined gas velocities and distribution functions for solids. Experimental data from various pilot-plant operations are used to assess the validity of the proposed model. The observed coal conversion and sulphur retention under various operating conditions are in good agreement with the predicted values.     

Stability analysis of perforated plate type single stage suspension fluidized bed without downcomer

The stability of operation of a perforated plate type suspension bed without downcomer was analyzed experimentally and numerically. The effects of the feed rate, the gas flowrate and the opening ratio and hole diameter of the perforated plates on the operating stability of the fluidized bed were examined. A full three-dimensional discrete particle simulation method proposed by Tsuji [1993] was performed to study the formation of a stable suspension fluidized bed. The course and behavior of particles that formed a dense and stable fluidized bed are discussed. Both the experimental and simulation results of this study show that the process of forming a suspension bed can be categorized into (i) an induced stage, (ii) a growing stage, and (iii) a stable stage. The velocity of gas through the orifice directly controls the formation of the bed while the solid flow rate over a considerable range maintains a balanced hold-up in the suspension bed system without downcomers. The existence of a multiplicity of steady states corresponding to different gas flow rates, for the same feed rate and perforated plate type, was observed. Results show that the design of the plate, the particle feed rate and the gas velocity distribution through the hole affect the stability of the fluidized bed. The simulated results agree qualitatively well with experimental observations.     

Operating experience and performance data of an advanced barge-mounted VTE/VC seawater desalination plant

The floating desalination demonstration plant “MEDA” presents an advanced concept to produce fresh water from seawater with low energy consumption. At first step of ts demonstration phase, MEDA was operated at Helgoland in the North-Sea at its design capacity of 5000 m³/day and a performance ratio of 22 to 1 kg/kg. The 24 effect VTE evaporator combined with two vapor compression topping effects operated at a max. feed temperature of 135 °C with sulphuric acid pretreatment. High heat transfer rates were obtained using foamy upflow in double-fluted evaporator tubes without inter-effect pumps. Data were obtained for an alternative pretreatment system for feed make-up using a fluidized bed ion exchanger system operating in the countercurrent mode. Calcium ion content in the feedwater was demonstrably reduced by more than 90 %. This paper presents and analyses the above performance results.     

Novel shrinking–swelling hysteresis in DMSO/THF mixtures of copolymer gels containing sulphonate groups

The swelling volume of copolymer gels made from 2-(acrylamido)-2-methylpropanesulphonic acid (AMPS; electrolyte monomer), N,N-dimethylacrylamide (DMAA; comonomer) and N,N′-methylenebis(acrylamide) (BIS; crosslinker) was measured in mixtures of two organic solvents, dimethyl sulphoxide (DMSO) and tetrahydrofuran (THF) at 25°C. A volume phase transition was observed in the gels having 43·18mol% AMPS with different counterions K⁺, Na⁺ and H⁺, when the THF concentration in the mixture increased beyond a certain value. We observed a swelling-hysteresis between the shrinking and swelling curves, i.e. more DMSO was required to make a shrunk gel start to swell again than to cause the volume shrinking. This hysteresis stems from the formation of ion pairs and/or multiplets in the ionizable gels when the medium polarity is decreased. An excess of DMSO is required to reduce the ionization energy for making the shrunk gel swell again in the DMSO/THF mixture. These aggregates and multiplets do not seem to be entirely removed by the swelling process and act as additional physical crosslinks, so that the DMSO concentration required to induce the shrunk gel to swell becomes higher in the next swelling process, showing another hysteresis. The release of bound water from the solvating layer after shrinkage may be another possible reason for this hysteresis. © 1998 Society of Chemical Industry