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K M Thomas - One of the best experts on this subject based on the ideXlab platform.
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adsorption of gases and vapors on nanoporous ni2 4 4 bipyridine 3 no3 4 metal organic framework materials templated with methanol and ethanol structural effects in adsorption kinetics
Journal of the American Chemical Society, 2004Co-Authors: A J Fletcher, Edmund J Cussen, Matthew J Rosseinsky, Darren Bradshaw, K M ThomasAbstract:Desolvation of Ni2(4,4‘-bipyridine)3(NO3)4·2CH3OH and Ni2(4,4‘-bipyridine)3(NO3)4·2C2H5OH give flexible metal−organic porous structures M and E, respectively, which have the same stoichiometry, but subtly different structures. This study combines measurements of the thermodynamics and kinetics of carbon dioxide, methanol, and ethanol sorption on adsorbents M and E over a range of temperatures with adsorbent structural characterization at different adsorbate (guest) loadings. The adsorption kinetics for methanol and ethanol adsorption on porous structure E obey a Linear Driving Force (LDF) mass transfer model for adsorption at low surface coverage. The corresponding adsorption kinetics for porous structure M follow a double exponential (DE) model, which is consistent with two different barriers for diffusion through the windows and along the pores in the structure. The former is a high-energy barrier due to the opening of the windows in the structure, required to allow adsorption to occur, while the latter...
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adsorption kinetics and size exclusion properties of probe molecules for the selective porosity in a carbon molecular sieve used for air separation
Journal of Physical Chemistry B, 2001Co-Authors: K M ThomasAbstract:The adsorption characteristics of a series of planar (ethylene, benzene, and pyridine) and tetrahedral (methane, chloromethane, dichloromethane, chloroform, and carbon tetrachloride) molecules on a carbon molecular sieve used for air separation (CMS A) were investigated over a range of temperatures as a function of pressure, to study the selective porosity. The size-exclusion characteristics of planar and tetrahedral molecules indicate that the selective porosity behaves as though it has spherical-shaped structural characteristics and, therefore, two minimum dimensions need to be considered in relation to size exclusion. The partial exclusion of the probe molecule adsorptives from the microporous structure for sizes >360 pm allowed the selective and nonselective microporosity and the meso/macroporosity to be quantified. Adsorption kinetics obey a Linear-Driving-Force mass transfer, combined barrier resistance/diffusion, or Fickian kinetic models depending on the adsorptive and experimental conditions. Com...
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adsorption dynamics of gases and vapors on the nanoporous metal organic framework material ni2 4 4 bipyridine 3 no3 4 guest modification of host sorption behavior
Journal of the American Chemical Society, 2001Co-Authors: A J Fletcher, Edmund J Cussen, Timothy J Prior, Matthew J Rosseinsky, Cameron J Kepert, K M ThomasAbstract:This study combines measurements of the thermodynamics and kinetics of guest sorption with powder X-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at different adsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxide and ethanol and methanol vapors on Ni2(4,4'-bipyridine)3(NO3)4 were studied over a range of temperatures as a function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at approximately 10-20% of the total pore volume and at approximately 70% of total pore volume for methanol adsorption. The adsorption kinetics obey a Linear Driving Force (LDF) mass transfer model for adsorption at low surface coverage. At high surface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model. The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantly slower than those observed either before or after the step. X-ray diffraction studies at various methanol loadings showed that the host structure disordered initially but underwent a structural change in the region of the isotherm step. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced by adsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuir isotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanol adsorption on Ni2(4,4'-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the space group remaining unchanged during adsorption. The activation energies and preexponential factors for methanol and ethanol adsorption were calculated for each pressure increment at which the Linear Driving Force model was obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicating a compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structural changes and interactions and the adsorption mechanism. The paper contains the first evidence of specific interactions between guests and functional groups leading to structural change in flexible porous coordination polymer frameworks.
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adsorption of gases on a carbon molecular sieve used for air separation Linear adsorptives as probes for kinetic selectivity
Langmuir, 1998Co-Authors: C R Reid, K M ThomasAbstract:The adsorption of oxygen, nitrogen, and a series of gases/vapors with Linear structures (carbon monoxide, carbon dioxide, nitrous oxide, acetylene and carbon disulfide) on a carbon molecular sieve typical of the materials used for air separation were studied over a range of temperatures as a function of pressure in order to understand further the mechanism of air separation. The ratios of the rate constants (kO2/kN2) were typically 25 for the carbon molecular sieve used thereby demonstrating the molecular sieving characteristics. The adsorption kinetics obey a Linear Driving Force (LDF) mass transfer model for most of the gases and experimental conditions studied. However there were deviations from the LDF model for carbon dioxide and nitrous oxide. In the case of the former, the kinetic models ranged from LDF through a combined barrier resistance/diffusion model to Fickian diffusion depending on the experimental conditions. The adsorption rate constants increase exponentially with increasing surface cove...
Alirio E Rodrigues - One of the best experts on this subject based on the ideXlab platform.
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carbon dioxide nitrogen separation through adsorption on activated carbon in a fixed bed
Chemical Engineering Journal, 2011Co-Authors: Tirzha L P Dantas, Francisco Murilo Tavares De Luna, I J Silva, Diana C S Azevedo, Carlos A Grande, Alirio E Rodrigues, Regina De Fatima Peralta Muniz MoreiraAbstract:Abstract The reduction of carbon dioxide emissions from flue gases can be achieved using post-combustion capture technologies such as adsorption. In this paper, we report experimental data for the fixed-bed adsorption of carbon dioxide and nitrogen on activated carbon. The breakthrough curves were obtained at different temperatures – 301–306, 323, 373 and 423 K – using CO2/N2 mixtures. XPS and FTIR measurements were used to identify chemical changes in the adsorbent after CO2 adsorption. A model based on the Linear Driving Force (LDF) approximation for the mass transfer was used, considering the energy and momentum balances, to satisfactorily reproduce the breakthrough curves.
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adsorption of carbon dioxide onto activated carbon and nitrogen enriched activated carbon surface changes equilibrium and modeling of fixed bed adsorption
Separation Science and Technology, 2009Co-Authors: Tirzha L P Dantas, Francisco Murilo Tavares De Luna, I J Silva, Diana C S Azevedo, Alirio E Rodrigues, Suelen M Amorim, Regina De Fatima Peralta Muniz MoreiraAbstract:It has been reported that the CO2 adsorption capacity of the N-enriched activated carbon can increase or decrease. In this study a commercial activated carbon was functionalized with 3-chloropropylamine hydrochloride and its adsorption characteristics in a fixed-bed column were investigated. The N-enriched activated carbon presented lower BET surface area than the original activated carbon suggesting that the nitrogen incorporation partially blocks the access of N2 to the small pores. Although the surface basicity has increased it is not accomplished by an increase of the capacity of the adsorption of the N-enriched activated carbon. The breakthrough curves in a fixed bed column were obtained at different temperatures (301 K, 323 K, 373 K, and 423 K) and a total pressure of 1.01 bar using CO2 diluted in helium at two feed concentrations—10% and 20% (v/v). A model based on the Linear Driving Force (LDF) model for mass transfer was used to estimate the overall mass transfer coefficient and reproduced the br...
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simulation of true moving bed adsorptive reactor detailed particle model and Linear Driving Force approximations
Chemical Engineering Science, 2007Co-Authors: Pedro Sa Gomes, Celina Pinto Leao, Alirio E RodriguesAbstract:Abstract A new true moving bed (TMB) adsorptive reactor model with a detailed particle approach is presented introducing the formulation of the mass balance for the solid phase in counter-current moving systems. The system studied here is the enzymatic inversion of sucrose into fructose and glucose and subsequent separation of glucose/fructose; the reaction occurs both in the outer fluid phase and inside particles. Model equations include film mass transfer, intra-particle diffusion resistance, axial dispersion for the outer fluid phase, plug flow of the solid phase and Linear adsorption equilibrium of glucose/fructose. This new model is compared with previous LDF-type approximations for reactive systems and applied to pure separative TMB process. The numerical solution of model equations is obtained for transient and steady state with commercial and public domain packages (gPROMS and COLNEW). The influence of the particle size and reaction rate constant is analyzed in the ( γ 2 × γ 3 ) reactive/separation region.
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modeling and simulation of protein adsorption in permeable chromatographic packings a double Linear Driving Force model
Biochemical Engineering Journal, 1999Co-Authors: Anabela Leitao, Alirio E RodriguesAbstract:Permeable large-pore packings have many applications, particularly in perfusion chromatography for bioseparations. The major objectives of this paper are: (i) to develop a double Linear Driving Force (LDF) model based on Linear Driving Force approximations inside throughpores and microparticles to simulate dynamic nonLinear adsorption in columns having spherical permeable chromatographic packings with a bidisperse pore structure; and (ii) to analyze the performance of this simple model to simulate breakthrough and elution curves for bovine serum albumin adsorption on POROS Q/M large-pore particles (PerSeptive Biosystems, Cambridge, MA, USA), in comparison with a more realistic and difficult model (intraparticle diffusion/convection model) which is also presented in this paper. Model results obtained for several values of the intraparticle Peclet number, λ, resulting from the convective flow in the throughpores show the very reasonable performance of the double LDF model in simulating breakthrough and elution curves of proteins, particularly for higher values of λ. This finding is of relevance due to the remarkable saving in computation time afforded with the double LDF model.
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Linear Driving Force approximation in cyclic adsorption processes simple results from system dynamics based on frequency response analysis
Chemical Engineering and Processing, 1998Co-Authors: Alirio E Rodrigues, Madalena M DiasAbstract:The Linear Driving Force (LDF) approximation for cyclic adsorptive processes is discussed on the basis of model equivalence with the homogeneous diffusion model (HDM), the pore diffusion model (PDM) and the intraparticle diffusion and convection model (IDCM). Model equivalence is based on the frequency response of the adsorbent particle, namely on the equality of the amplitude ratio and the phase-lag functions. The analysis of the continuous stirred tank adsorber (CSTA) and of the plug flow adsorber (PFA) is addressed.
Steven M. Cramer - One of the best experts on this subject based on the ideXlab platform.
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comparison of Linear gradient and displacement separations in ion exchange systems
Biotechnology and Bioengineering, 2002Co-Authors: V Natarajan, Sanchayita Ghose, Steven M. CramerAbstract:The Linear gradient mode of chromatography is the most widely employed mode of operation in ion-exchange chromatographic separations. However, in recent years, the displacement mode has received considerable attention because of its promise of high throughput and high resolution. To enable a comparison of these two modes of chromatography, it is essential to identify the optimum operating conditions for each. We employed an iterative algorithm to carry out the necessary optimization. The Steric Mass Action model of ion-exchange chromatography is used in concert with the solid-film Linear-Driving Force model to describe the chromatographic behavior of the solutes in these systems. The performances of displacement and gradient modes of chromatography are compared for different types of separation problems. It turns out that for “easy” separations, both the modes are equally effective. However, for challenging separations, the displacement mode is superior to the gradient mode. Our results shed significant light on the performance of gradient and displacement modes in protein ion-exchange systems. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 365–375, 2002.
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optimization of ion exchange displacement separations ii comparison of displacement separations on various ion exchange resins
Journal of Chromatography A, 2000Co-Authors: Venkatesh Natarajan, Steven M. CramerAbstract:A variety of stationary-phase materials are currently available for the chromatographic purification of biomolecules. However, the effect of various resin characteristics on the performance of displacement chromatography has not been studied in depth. In Part I, a novel iterative scheme was presented for the rapid optimization of displacement separations in ion-exchange systems. In this article, the optimization scheme is employed to identify the optimum operating conditions for displacement separations on various ion-exchange resin materials. In addition, the effect of different classes of separation problems (e.g., diverging, converging or parallel affinity lines) on the performance of displacement separations is also presented. The solid film Linear Driving Force model is employed in concert with the Steric Mass Action isotherm to describe the chromatographic behavior in these systems. The results presented in this article provide insight into the effects of resin capacity and efficiency as well as the type of separation problem on the performance of various ion-exchange displacement systems.
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optimization of ion exchange displacement separations i validation of an iterative scheme and its use as a methods development tool
Journal of Chromatography A, 2000Co-Authors: Venkatesh Natarajan, Wayne B Bequette, Steven M. CramerAbstract:Displacement chromatography has been demonstrated to be a powerful, high-resolution preparative tool. The performance of displacement systems can be affected by a variety of factors such as the feed load, flow-rate, initial salt concentration and the displacer partition ratio. Thus, the optimization of displacement separations is a uniquely challenging problem. In this manuscript, an iterative optimization scheme has been presented whereby one can identify the optimum operating conditions for displacement separations at a given level of loading on a given resin material. The solid film Linear Driving Force model has been employed in concert with the Steric Mass Action formalism of ion-exchange chromatography to describe the chromatographic behavior in these systems. Simple pulse techniques have been employed to estimate the transport parameters. The iterative scheme has been validated using a rigorous Feasible Sequential Quadratic Programming algorithm. Finally, the utility of the iterative optimization scheme as a methods development tool for displacement separations has been demonstrated for a difficult separation. The results indicate that the use of the optimization scheme leads to significantly better performance than standard rules of thumb.
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modeling shock layers in ion exchange displacement chromatography
Aiche Journal, 1999Co-Authors: Venkatesh Natarajan, Steven M. CramerAbstract:In ideal displacement chromatography (systems with infinite mass-transfer kinetics), various solutes are separated by sharp discontinuities. In real systems, however, the shocks are eroded into shock layers because of the finite rates of mass transfer. The thickness of these shock layers, which can reduce the yields achievable in these systems, depend on the flow rate, particle diameter and the “difficulty” of these separations. The steric mass action formalism of ion-exchange chromatography was used in concert with a solid film Linear Driving Force model to describe the effects of flow rate, particle diameter, and the degree of difficulty of the separation on ion-exchange displacement systems. Simple pulse techniques are employed to estimate the thermodynamic and mass-transfer parameters. The simulations are then compared to experimental results over a range of conditions. The results demonstrate that this relatively simple modeling approach can be employed to describe the behavior of these nonideal displacement systems.
Giorgio Carta - One of the best experts on this subject based on the ideXlab platform.
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Linear Driving Force approximation for intraparticle diffusion and convection in permeable supports
Chemical Engineering Science, 1995Co-Authors: Giorgio CartaAbstract:The objective of the communication is to determine if a Linear-Driving Force (LDF) approximation can be used instead of a more rigorous diffusion-convection on the breakthrough behavior under conditions of nonLinear adsorption with a favorable isotherm. Such an approximation is commonly used in the simulation of fixed-bed adsorption operations and chromatography (Ruthven, 1984). However, its use in simulating process in which intraparticle convection is important has not yet been established
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the Linear Driving Force approximation for cyclic mass transfer in spherical particles
Chemical Engineering Science, 1993Co-Authors: Giorgio CartaAbstract:An approach alternative to that of Alpay and Scott (1992) to obtaining an exact, purely periodic solution of the particle diffusion equation is presented. The solution is obtained via Laplace transform, and the intraparticle concentration profile and instantaneous flux at the surface are expressed as trigonometric series expansions with respect to time
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exact solution and Linear Driving Force approximation for cyclic mass transfer in a bidisperse sorbent
Chemical Engineering Science, 1993Co-Authors: Giorgio CartaAbstract:Abstract A purely periodic analytic solution for cyclic mass transfer in an adsorbent pellet with a bidisperse pore structure is obtained. The solution is used to define the effective rate coefficient, K , for the Linear Driving Force (LDF) approximation for cyclic adsorption and desorption. The results obtained differ from those previously derived using an equivalent solid diffusion model for the pellet with a single diffusional time constant, approaching this limit only when macropore diffusion is dominant. In fact, for rapid-cycling the mass transfer rate cannot be expressed in the terms of a simple Linear combination of the diffusional time constants for the bidisperse pellet independent of cycle time. Thus, in this case, the exact solution must be used to arrive at an appropriate representation of mass transfer rates in cyclic adsorption, which can be used for the simulation of sportive separations.
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Analytic solution for volume-overloaded gradient elution chromatography
Journal of Chromatography A, 1992Co-Authors: Giorgio Carta, W.butler StringfieldAbstract:Abstract An analytic solution to a partial differential equation model for gradient elution chromatography is obtained. The model is restricted to Linear isotherms and treats mass transfer effects with the Linear Driving Force approximation. The solution is obtained for periodic, rectangular feed pulses, with an arbitrary gradient shape and type, and is given in the form of a convergent series that allows a direct calculation of the effluent profile and of the average product concentration. Calculations for small feed pulses, show that the solution gives the retention time and peak spreading predicted by the Linear solvent strength theory for reversed phase chromatography, in the limit of Gaussian peaks. For larger feed pulses the solution predicts asymmetric peaks with concentrations exceeding that of the feed sample. The theory developed is succesfully used to predict volume overload effects in gradient elution from isocratic elution data for an experimental system.
A J Fletcher - One of the best experts on this subject based on the ideXlab platform.
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adsorption of gases and vapors on nanoporous ni2 4 4 bipyridine 3 no3 4 metal organic framework materials templated with methanol and ethanol structural effects in adsorption kinetics
Journal of the American Chemical Society, 2004Co-Authors: A J Fletcher, Edmund J Cussen, Matthew J Rosseinsky, Darren Bradshaw, K M ThomasAbstract:Desolvation of Ni2(4,4‘-bipyridine)3(NO3)4·2CH3OH and Ni2(4,4‘-bipyridine)3(NO3)4·2C2H5OH give flexible metal−organic porous structures M and E, respectively, which have the same stoichiometry, but subtly different structures. This study combines measurements of the thermodynamics and kinetics of carbon dioxide, methanol, and ethanol sorption on adsorbents M and E over a range of temperatures with adsorbent structural characterization at different adsorbate (guest) loadings. The adsorption kinetics for methanol and ethanol adsorption on porous structure E obey a Linear Driving Force (LDF) mass transfer model for adsorption at low surface coverage. The corresponding adsorption kinetics for porous structure M follow a double exponential (DE) model, which is consistent with two different barriers for diffusion through the windows and along the pores in the structure. The former is a high-energy barrier due to the opening of the windows in the structure, required to allow adsorption to occur, while the latter...
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adsorption dynamics of gases and vapors on the nanoporous metal organic framework material ni2 4 4 bipyridine 3 no3 4 guest modification of host sorption behavior
Journal of the American Chemical Society, 2001Co-Authors: A J Fletcher, Edmund J Cussen, Timothy J Prior, Matthew J Rosseinsky, Cameron J Kepert, K M ThomasAbstract:This study combines measurements of the thermodynamics and kinetics of guest sorption with powder X-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at different adsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxide and ethanol and methanol vapors on Ni2(4,4'-bipyridine)3(NO3)4 were studied over a range of temperatures as a function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at approximately 10-20% of the total pore volume and at approximately 70% of total pore volume for methanol adsorption. The adsorption kinetics obey a Linear Driving Force (LDF) mass transfer model for adsorption at low surface coverage. At high surface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model. The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantly slower than those observed either before or after the step. X-ray diffraction studies at various methanol loadings showed that the host structure disordered initially but underwent a structural change in the region of the isotherm step. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced by adsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuir isotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanol adsorption on Ni2(4,4'-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the space group remaining unchanged during adsorption. The activation energies and preexponential factors for methanol and ethanol adsorption were calculated for each pressure increment at which the Linear Driving Force model was obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicating a compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structural changes and interactions and the adsorption mechanism. The paper contains the first evidence of specific interactions between guests and functional groups leading to structural change in flexible porous coordination polymer frameworks.