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International audience; A detailed knowledge of the light ions interaction processes with matter is of great interest in basic and applied physics. As an example, particle therapy and space radioprotection require highly accurate fragmentation cross-section measurements to develop shielding materials and estimate acute and late health risks for manned missions in space and for treatment planning in particle therapy. The Fragmentation of Ions Relevant for Space and Therapy experiment at the Helmholtz Center for Heavy Ion research (GSI) was designed and built by an international collaboration from France, Germany, Italy, and Spain for studying the collisions of a C12 ion beam with thin targets. The collaboration's main purpose is to provide the double-differential cross-section measurement of carbon-ion fragmentation at energies that are relevant for both tumor therapy and space radiation protection applications. Fragmentation cross sections of light ions impinging on a wide range of thin targets are also essential to validate the nuclear models implemented in MC simulations that, in such an energy range, fail to reproduce the data with the required accuracy. This paper presents the single differential carbon-ion fragmentation cross sections on a thin gold target, measured as a function of the fragment angle and kinetic energy in the forward angular region (θ≲6∘), aiming to provide useful data for the benchmarking of the simulation softwares used in light ions fragmentation applications. The C12 ions used in the measurement were accelerated at the energy of 400 MeV/nucleon by the SIS (heavy ion synchrotron) GSI facility.

Monolithic materials are novel and attractive supports to be used as stationary phase in chromatographic columns to be used in downstream processes. As microporous membranes, they operate in convective mode which is useful to overcome the diffusive limitations of conventional packed bed columns. In this work, the adsorption and elution of human IgG onto convective interaction media (CIM) Protein A monolithic columns has been studied. Complete chromatography cycles, including adsorption, washing and elution, have been experimentally performed at severa l operating conditions and the results are discussed in detail. The frontal analysis of characteristic points (FACP) approach has been successfully applied for the first time for monolithic media to determine the dynamic binding isotherm for human IgG. Elution was performed over several operating conditions to determine the effect of pH and flow rate on the total recovery of IgG, and on the concentration of the eluted fraction.

Plasmin is protein of the fibrinolityc system, obtained by activation of plasminogen, which is of interest for ophthalmology applications. It can be used as a treatment for diabetic rethinopaty, macular pukers, but also as a facilitator for vitreoctomy since it has the properties to hydrolize a variety of glycoproteins by degrading the links between these components of the vitreoretinal interface and the inner limiting membrane. The purification of plasminogen from blood is conventionally performed with bead-based affinity chromatography, by exploiting the affinity between plasminogen and L-lysine. However, due to its low concentration, which is about 0.2 g/L in human blood, with a single step affinity purification from serum or plasma it is not possible to obtain high levels of purity and a sufficient amount of protein. In this work we describe several strategies that have been investigated in order to improve the affinity chromatography step which is performed with lysine affinity membranes. The affinity membranes were obtained by immobilization of L-lysine on regenerated cellulose membrane supports and characterized in terms of ligand density, binding capacity and selectivity. The effect of operating parameters like flow rate, type of blood source (serum, plasma or Cohn fractions) and elution conditions on the activity of plasmin conversion have been investigated in detail. The comparison with a chromatography column packed with a commercial lysine affinity beads demonstrated the superior performance of the affinity membranes and the feasibility of the proposed process.

The solubility of gaseous mixtures of CO2 and C2H6 in cross-linked poly(ethylene oxide) (XLPEO) has been 11 modeled over a wide range of temperatures, pressures, and compositions with the Sanchez−Lacombe lattice fluid equation of 12 state (LF EoS). The model binary gas−polymer parameters have been determined from pure gas solubility data and kept 13 constant with temperature and composition. Multicomponent solubility is then calculated with no additional adjustable 14 parameters, using a fully predictive procedure. The LF EoS model describes well the mixed gas solubility behavior data over wide 15 ranges of temperature (from −20 to 35 °C), pressure (0−20 atm), and composition. The model also allows representation of the 16 solubility selectivity behavior of XLPEO at different conditions, permitting an a priori determination that ethane solubility is 17 significantly enhanced by the presence of CO2, with a consequent reduction in CO2/C2H6 solubility selectivity relative to the 18 pure gas value. In this regard, the behavior of this rubbery polymer is opposite that of many glassy systems, in which competitive 19 sorption is often dominant, and the solubility of the less soluble gas (i.e., C2H6 in this case) is decreased by the presence of CO2, 20 and the CO2 solubility selectivity is enhanced with respect to the pure gas value.

In this work, different new affinity membranes are considered for the capturing step of a monoclonal antibody production process. The membranes with immobilized protein A and synthetic ligands, have been extensively tested with pure IgG solutions and with a cell culture supernatant containing IgG1. The effects of flow rate and IgG concentration in the feed on the separation performances like binding capacity, selectivity and process yield have been studied in detail. The behaviour and efficiency of the different affinity membranes will be presented and will be also compared with data available for protein A chromatography beads. A model simulation study of the relevant kinetic and transport phenomena led to the development of a mathematical model capable to describe the separation process based on affinity membrane. Model validation has been successfully performed using the experimental data available for the different membrane tested.

Downstream processes for the purification of biological products are often the cost determining production steps. Affinity technology is widely used for the primary capture stage, based on chromatographic beads. In the last decades, significant attention has been devoted to affinity chromatography using microporous membranes as chromatographic supports. Membrane chromatography can overcome the limitation associated to conventional packed-bed columns, such as high pressure drops and slow mass transfer. This work is focused on the purification of Immunoglobulin G (IgG) via affinity membranes. A new support, Sartoepoxy Protein A membranes (Sartorius, Göettingen, Germany) has been tested in detail in dynamic experiments, using pure solutions of polyclonal IgG as well as the supernatant of a fermentation broth containing monoclonal IgG. All the relevant parameters, namely the dynamic binding capacity, process yield and recovery have been evaluated. The influence of several operating parameters on the adsorption and elution performances has been studied to determine the optimal process conditions. A mathematical model including convection, diffusion and multi-component adsorption is proposed to simulate the adsorption, washing and elution steps; the model also considers the possible effects of dead end volumes and flow distribution. Results of the simulation have been compared with the experimental data, giving a good description of the global process.

It is well known that the sorption and transport properties of high free volume glassy polymers do vary significantly with time due to physical ageing that lowers the overall free volume and consequently gas permeability. In this work we perform a series of tests in which the ageing of polymeric membrane films based on a polymer of intrinsic microporosity (PIM-1) and TZ-PIM (PIM containing tetrazole unit) is induced with high temperature treatments under vacuum. The solubility and diffusivity values of CO2 and CH4 are measured at different pressures up to 32 atm and at 50°C within a pressure decay equipment on membranes 1) as cast; 2) thermally pre-treated at 120, 140 and 160°C. The effect of thermal treatment is more evident on the diffusivity than on the solubility coefficient, in both types of membranes. In particular the diffusivity of both gases decreases with increasing heat treatment temperature. Trends of diffusivity with concentration are also thoroughly inspected.

Mixed gas sorption of CO2/CH4 in TZ-PIM (PIM containing tetrazole unit) was characterized at three different temperatures 25°C, 35°C and 50°C and three molar fraction of CO2, 11.3% CO2, 30.7% CO2 and 50.3% CO2 up to a pressure of 35 atm. Pressure decay equipped with gas chromatograph was used for the experiment. Solubility selectivity of TZ-PIM for CO2/CH4 mixture is higher than solubility selectivity of PIM-1. This is due to the tetrazole group which improves the solubility of CO2 while leaving unaffected the solubility of CH4. Solubility coefficient for both gases decreases with increasing temperature.

The products of the addition type polymerization of the derivatives of norbornene represent a group of polymers of high permeability and high free volume. These polymers show solubility-controlled permeation, in which the influence of diffusivity is minor as compared to that of solubility. In this work, the sorption of methane, nitrogen, carbon dioxide, alkane and alkene vapors in poly(exo,endo-3,4-bis(trimethylsilyl)tricyclononene) has been studied at 35.0 ºC with the differential pressure decay technique up to the absolute pressure of ca. 10 atm.

The predictive calculation of the solubility of low molecular weight penetrants in glassy polymers (pure polymers, blends and nano-composites) can be performer based on the knowledge of polymer density, by using the results of the Non-Equilibrium Thermodynamics of Glassy Polymers. Different examples are presented for gases, vapors, liquids and gas mixtures. For swelling penetrants, in the case of bulk rheology relatively slow with respect to the diffusion process, the polymer density varies with time during sorption; consequently the concentration assigned as boundary condition as well as the chemical potential gradient inside the polymer both vary with time. That gives rise to different non-Fickian transport behaviors (anomalous diffusion, two-stage sorption,…) which can be well interpreted by using simple relationships for the polymer bulk rheology. Different examples support the conclusion.

Sorption of pure methane, carbon dioxide and their binary mixtures in two glassy polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP), and the first polymer of intrinsic microporosity (PIM-1), has been studied experimentally and theoretically, at 35.0 ºC. Measurements were obtained on a newly designed pressure decay sorption apparatus which allowed to measure sorption isotherms at constant partial pressure of one component of the gas mixture. Results indicate the presence of a competition for available polymer matrix sites, which is not surprising due to the nature of physical sorption in glassy matrices.

Hydrogen permeation experiments were performed to evaluate the influence of water vapor on hydrogen permeability in 80e20% by weight PdeAg membranes of 2.5 micrometer thickness. In particular, hydrogen flux was measured in pure hydrogen permeation tests as well as in experiments with binary mixtures containing also nitrogen or water vapor, that were performed at temperatures ranging from 473 to 723 K and at a transmembrane pressure differences up to about 3 bar. The membranes, supplied by NGK Insulator Ltd., Japan, showed a very high hydrogen permeance and lifetime, as well as virtually infinite selectivity (exceeding 10000 for H2eN2 mixtures). The experiments in hydrogenenitrogen mixtures were carried out at different temperatures, hydrogen concentrations and feed flow rates and confirmed the existence of a non-negligible concentration polarization phenomenon in the experimental module. The gas phase mass transport and the module fluid dynamics were thus analyzed and the dimensionless numbers characterizing these processes were evaluated at the different operative conditions; a linear correlation was found to hold between Sherwood and Pe´ clet numbers. Interestingly, the hydrogen permeate fluxes measured with feeds containing H2eH2O mixtures resulted always lower than those obtained for the nitrogenehydrogen mixtures performed at the same hydrogen mole fraction and operative conditions: in particular, the hydrogen flux depletion increased with decreasing temperature and/or increasing the concentration of water vapor. All the experimental evidences suggest a clear interaction between water vapor and metallic layer, causing a lower hydrogen adsorption capacity of the membrane surface. That phenomenon is reversible, since the original permeance of the membrane was restored once the water vapor was removed from the feed, and is apparently due to a competitive H2/H2O adsorption on the PdeAg surface. The hydrogen flux depletion was then modeled by considering the simultaneous effects of gas phase resistance and competitive adsorption on the surface, obtaining a rather good agreement between experimental data and calculated results.

The evaluation of the mixed gas solubility in glassy polymers is of fundamental importance in several applications such as in the development gas separation membranes. For rubbery polymers the usual equation of state (EoS) models, in their multicomponent version, can be applied to calculate multiple gas solubility in the equilibrium phases; for the case of glassy polymers, a different thermodynamic tool has to be used. The general approach called Non Equilibrium Thermodynamics of Glassy Polymers (NET-GP) [1], coupled to the Lattice Fluid (LF) model for the representation of substances [2], was showed to be able to predict the solubility of gases and vapors in glassy polymers at various pressures based on pure component parameters. The approach is here applied to the modeling of multicomponent gas solubility in a glassy polymeric matrix, to predict the solubility of CH4/CO2 mixtures in Poly(phenyleneoxide) (PPO), C2H4/CO2 and N2O/CO2 in poly(methylmetacrylate) (PMMA), at various pressures, for which experimental data are available. The data show that the solubility of mixed gases differ significantly from the corresponding pure component values: the N2O content in the PMMA is lowered by the increase of CO2 partial pressure; the same effect is observed for the CO2/CH4 pair in PPO. The NELF model is able to predict the experimental behavior observed for mixed gases solubility in both systems; the agreement is indeed remarkable in both cases in the whole pressure range investigated. The present approach allows also to estimate predictively the mixed gas solubility-selectivity of N2/CO2, CO2/CH4 and H2/CO2 mixtures in several glassy polymers including polyimides such as Matrimid, allowing to detect significant deviations from the ideal selectivity behavior and estimate the selectivity of membrane materials.

In this work, an atomistic approach is employed to simulate pvT data of polymers at high temperature (in the rubbery region), by using a molecular dynamics tool. Data are then regressed with the desired EoS to obtain the polymer characteristic parameters, which are used to evaluate the gas solubility in the polymer with NET-GP model.

The enhancement of gas and vapor transport rates induced by the addition of fumed silica nano-particles to fluorinated glassy polymers and PTMSP is interpreted and quantitatively modeled considering the additional free volume created by incorporation of filler. That effect can be evaluated accurately from gas solubility data, using the NELF model. The solubility of CH4 and CO2 in matrices of Teflon AF1600, AF2400 and PTMSP, filled with variable amounts of fumed silica nano-particles, was measured at 35°C; the solubility of n-C4 and n-C5 vapors, as well as their diffusivity and the dilation induced in the same polymer matrices were also measured at 25°C. The fractional free volume (FFV) values, estimated on the basis of CH4 solubility data, were used to predict the solubility of the other penetrants inspected, with excellent agreement with experimental data. In addition, a single empirical correlation can be drawn, for both AF1600 and AF2400-based mixed matrices, between the infinite dilution diffusivity of vapors and the FFV value calculated from solubility data. Similarly, a simple correlation valid for both matrices is obtained as well for the dependence of diffusivity on penetrant concentration. Finally, use of the NELF model allows also to give an estimate of the swelling induced by the sorption process on the basis of virtually one simple data point of gas solubility.

The sorption and diffusion properties of methanol vapor in membranes of equivalent weight 860 gpol/(mol(SO3H) were investigated at different activities and at temperatures between 35 and 65°C. The solubility isotherms can be well represented by a BET-type of equation as a function of the penetrant activity. The molar uptake of methanol, at fixed activity, is compared to that of water in the same membrane and thermal range. The diffusivity increases with temperature and shows a maximum with concentration, similarly to what observed in the case of water vapor diffusion.

A theoretical model is proposed to describe hydrogen permeation in palladium and silver-palladium membranes in presence of a non-inert gas as CO; it is known indeed that hydrogen flux through palladium-based membranes drastically decreases when H2 is fed in mixtures containing carbon monoxide due to the interaction of the latter gas with the membrane surface. To model this process, the adsorption step of the well known approach suggested by Ward and Dao has been modified by considering the competitive adsorption of the different non-inert molecules on the metal interface. In particular, the competitive adsorption of CO and H2 has been examined accounting for the spectrum of information available for CO adsorption on palladium, as well as for hydrogen in palladium and palladium-silver alloys. A validation of the model proposed has been performed through a comparison between several literature data and model calculations, over a rather broad range of operative conditions, obtaining a quite good agreement with the use of a limited number of adjustable parameters. The data available in the open literature indeed allow an estimation of the parameters involved in the model so that only one quantity, namely the change of CO heat of adsorption with carbon monoxide surface coverage, needed to be adjusted to obtain a satisfactory representation of the system behaviour. The model, is able to describe quantitatively the hydrogen permeation in Pd and Pd/Ag membranes in the presence of carbon monoxide and can be profitably used for predictive purposes and as a tool for membrane modules design; furthermore it represents a solid base to describe adequately the effects of other non-inert molecules on hydrogen permeation in Pd based membranes.

The primary capture of monoclonal antibodies by Protein A affinity-chromatography packed beds is the preferred method used in the biotech industry. However, this operation suffers from several limitations such as high material and operational costs, diffusion as the primary transport phenomenon, and difficulties associated with packing and scale-up. The employment of convective-based chromatographic media could help to circumvent these operational limitations due to an appreciable decrease in pressure drops, increased mass transport rates, ease of packing, and overall reduced processing times. The work presented here characterizes the transport phenomena and adsorption of IgG in a commercially available convective interaction media (CIM) Protein A monolithic column. The moment analysis was used to determine the interstitial porosity and axial dispersion coefficient for several tracers covering a large range of molecular weights. The frontal analysis of characteristic points (FACP) approach has been successfully applied for the first time for monolithic media to determine the dynamic binding isotherm for human IgG. Elution was performed over several operating conditions to determine the effect of pH and flow rate on the total recovery of IgG, and concentration of the eluted fraction. A complete chromatographic model was used to fit the data for each section of the FACP assay. The chromatographic model accounts for all mass transport and intrinsic rate parameters of the solute including axial convection, longitudinal dispersion, adsorption and desorption rates at the surface of the solid phase, and the extra-column effects associated with the mixing volumes and delay times of the circuit. The model was used to simultaneously fit the IgG effluent data for all of the operating conditions investigated in order to determine the kinetic parameters associated with breakthrough and elution steps. The model showed a good agreement with the experimental data, elucidating both the predictive capability of the model and the reliability of the experimentally determined mass transfer parameters.

Membrane affinity chromatography is an innovative technique that stands out among the cutting edge bioseparation technologies. Membrane chromatography separations are not limited by diffusion, as it is the case for the majority of chromatographic resins, and therefore are exceptionally well suited for purifying large bio-molecules such as immunoglobulin G. The modelling of such processes is of particular interesting view of the implementation of this technique for large scale applications. Indeed, the development of accurate and predictive models for membrane chromatographic operations is an imperative need that is not yet completely resolved. In this work we present and validate an effective mathematical model for membrane affinity chromatography. The model includes convection, dispersion and an appropriate set of kinetic equations to simulate the adsorption, washing and elution steps. The model also considers the extra column contributions to band spreading due to dead end volumes and mixing effects. Model validation is achieved by comparing simulation results with an extensive set of experimental data obtained using different affinity membranes; the experimental system considered is the primary capture of IgG from a cell culture supernatant. The good agreement of the model predictions with experimental data for the different supports considered demonstrates the accuracy of the model to describe all the relevant transport mechanisms involved. A comparison with other mathematical models taken from the literature is presented underlying the theoretical differences. Furthermore, the different models are used in order to generate simulations that scale-up membrane chromatographic modules. This study highlights the advantages in the predictive capabilities when using the proposed model.

Membrane affinity chromatography is an innovative technique that is receiving increasing attention by the biotechnology industry. Membrane chromatography is not limited by diffusion as the process based on resin beads, since the main transport mechanism is due to convection through the porous structure; therefore it is particularly suitable for purifying large bio-molecules such as IgG. In the present work the purification of immunoglobulin G using novel affinity membranes endowed with improved performance is discussed. The membrane adsorbers studied derive from the functionalization of epoxy membranes with natural and synthetic affinity ligands that show high specificity towards IgG. The resulting affinity membranes are fully characterized in complete adsorption, washing and elution affinity cycles. The separation performance of each affinity support has been determined by feeding both pure IgG solutions and a cell culture supernatant. The relevant process parameters, like maximum adsorption capacity, affinity equilibrium constant and selectivity, are compared for the different affinity membranes tested, as well as for available commercial membrane adsorbers. Exam of the impact of the improved affinity materials on industrial scale applications is also addressed. The experimental data collected have been used also for the validation of a simulation model proposed. The model developed is based on species mass balance equation over the membrane column, coupled with a suitable kinetic equation which represents the interaction between the IgG target molecule and the ligand immobilized on the porous support. Model simulations are in good agreement with the experimental affinity cycles, demonstrating the accuracy of the model to describe the transport phenomena in the column and the adsorption binding mechanism. On the basis of parameter values obtained for pure IgG solutions the model is able to predict the behaviour observed with a cell culture supernatant.

Affinity chromatography represents one of the most important and widely used unit operation in the biotechnology industry. Traditional packed bead columns suffer from several limitations such as high pressure drop, slow mass transfer through the diffusive pores and strong dependence of the binding capacity on flow rate. One possible alternative to overcome these drawbacks is represented by convective media columns packed with affinity membrane or monoliths. To promote their application in large scale processes, it is imperative to have a reliable simulation tool suitable to predict the process performance at all scales. This work presents and validates an effective model for convective affinity chromatography processes. The model accounts for axial convection, longitudinal dispersion in the micro-porous matrix and affinity binding, and includes also extra-column effects associated to mixing volumes and delay times of the circuit. The mathematical description takes into account all the different chromatographic steps: adsorption, washing and elution. Model validation is accomplished by comparing simulation results with an extensive set of experimental data obtained using affinity membranes and monoliths. The good agreement with experimental data for the different supports considered, demonstrates the model accuracy in describing all the relevant transport mechanisms involved. The simulation model was able to predict the chromatographic cycle of IgG capture from a cell culture supernatant based on data obtained for pure IgG solutions. Furthermore, a proper study of the model parameters for the two convective media is addressed, elucidating the main operative differences between the membrane and monolithic columns for protein affinity chromatography.

Affinity chromatography with Protein A packed bed columns is the current standard for the primary capture of monoclonal antibodies. However traditional packed bead columns suffer from several limitations such as high pressure drop, slow mass transfer through the diffusive pores and strong dependence of the binding capacity on flow rate. One possible alternative to overcome these drawbacks is represented by convective media columns packed with membrane and monolithic materials. Complete affinity cycles have been performed using different innovative affinity membranes and monolithic columns that were characterized for adsorption of pure immunoglobulin G. The most promising materials were tested under a broad range of operating conditions to investigate the effects of operating parameters, like feed concentration and flow rate, on separation performance. Material selectivity was evaluated during the purification of IgG1 from a cell culture supernatant. A critical evaluation between the two convective media used as a support will be presented. However, to promote the application of convective materials in large scale processes, it is imperative to develop a reliable simulation tool able to describe the process performance in a predictive way. An effective model for the description of convective affinity chromatography processes will be presented. The model considers all the relevant mass transport and kinetic phenomena involved with convective media materials, namely axial convection, longitudinal dispersion in the micro-porous matrix and affinity binding, together with extra-column effects in terms of mixing volumes and delay time. The mathematical description takes into account all the different chromatographic steps: adsorption, washing and elution. Model validation has been performed by comparing simulation results with an extensive set of experimental data for both membranes and monolithic columns. Simulations reveal a good agreement with experimental data for all the chromatographic steps, both in the case of membranes and monoliths considered, demonstrating the model accuracy for the description of the transport phenomena in the column and the adsorption binding mechanism. Furthermore, a proper study of the model parameters for the two convective media is addressed, elucidating the main operative differences between the membrane and monolithic columns for protein affinity chromatography.

The enhancement of gas and vapor transport rates induced by the addition of fumed silica nano-particles to fluorinated glassy polymers and PTMSP is experimentally studied and the behaviours is interpreted and quantitatively modeled considering the additional free volume created by incorporation of filler. That effect can be evaluated accurately from gas solubility data, using the NELF model. The solubility of CH4 and CO2 in matrices of Teflon AF1600, AF2400 and PTMSP, filled with variable amounts of fumed silica nano-particles, was measured at 35°C; the solubility of n-C4 and n-C5 vapors, as well as their diffusivity and the dilation induced in the same polymer matrices were also measured at 25°C. The fractional free volume (FFV) values, estimated on the basis of CH4 solubility data, were used to predict the solubility of the other penetrants inspected, with excellent agreement with experimental data. In addition, a single empirical correlation can be drawn, for both AF1600 and AF2400-based mixed matrices, between the infinite dilution diffusivity of vapors and the FFV value calculated from solubility data. Similarly, a simple correlation valid for both matrices is obtained as well for the dependence of diffusivity on penetrant concentration. In parallel the transport in hybrid membranes formed by PTMSP and SiO2 obtained from tetraethoxysilane (TEOS) via sol-gel reaction, with silica content ranging from 10 to 30% was examined following the same approach. In that case the effect of the filler is to decrease the FFV of the polymer matrix thus reducing both solubility and diffusivity. In all cases, use of the NELF model allows also to give an estimate of the swelling induced by the sorption process on the basis of virtually one simple data point of gas solubility.

Alternatives to conventional packed-bed capture and purification of monoclonal antibodies has been the motivation of many studies over the past decade. The work presented here fully characterizes the transport phenomena, affinity-adsorption, and elution of IgG in a commercial convective interaction media (CIM) Protein A monolithic column. The moment analysis method was employed to determine mass transfer parameters, namely axial dispersion, and evaluate the column efficiency through the height equivalent of a theoretical plate (HETP) using several tracer molecules covering a large range of molecular weights. The frontal analysis approach in the staircase mode was successfully applied for the first time in monolithic media to determine the dynamic binding isotherm for human IgG. In addition, elution was performed over a range of operating conditions to determine the critical pH needed to initiate desorption and subsequently the effects of pH and flow rate on the recovery of the bound IgG. A complete chromatographic model was used to fit the data for each section of the separation process. The chromatographic model accounts for all mass transport and intrinsic rate parameters of the solute including axial convection, longitudinal dispersion, adsorption/desorption at the surface of the solid phase, and the extra-column effects associated with the mixing volumes and delay times of the circuit. The model was used to simultaneously fit the IgG effluent data for all of the operating conditions investigated in order to determine the kinetic parameters associated with breakthrough, washing, and elution steps. In particular, a detailed study was performed to investigate different kinetic models and the effect of pH on the elution kinetic parameters. The model showed a good agreement with the experimental data, elucidating both the predictive capability of the model and the reliability of the experimentally determined mass transfer parameters.

Membrane affinity chromatography is one of the processes that are considered as a possible alternative to bead based chromatography. Membrane chromatography is not limited by diffusion as the majority of chromatographic resins and therefore it is particularly suited for purifying large bio-molecules such as high molecular mass proteins and viruses. Nevertheless, in order to promote its applications in up-scaled plants, it is imperative to develop a reliable simulation tool able to describe the process performance in a predictive way. In this work we present a mathematical model that can describe a complete affinity cycle and its chromatographic steps: adsorption, washing and elution. The mathematical formalization takes into account all the relevant mass transport and kinetics phenomena involved in the membrane affinity chromatography process, namely axial convection, longitudinal dispersion in the micro-porous matrix and affinity binding with the specific adsorption site. Further, extra-column effects in terms of mixing volumes and delay time are included in the model. The few relevant fitting parameters were derived from a calibration with an extensive set of experimental affinity cycles performed with pure IgG solutions. The affinity cycles have been carried out using different innovative affinity membranes tested under a broad spectrum of operating conditions. Model validation is then achieved by comparing simulation results with experimental data which have been obtained for the purification of immunoglobulin G from a complex feed as a cell culture supernatant. Model simulations are in good agreement with the experimental affinity cycles both in the case of pure IgG solutions and for the cell culture supernatant considered, demonstrating the accuracy of the model to describe the transport phenomena in the column and the adsorption binding mechanism.