Anabela Leitão

Adsorption of phenylalanine onto polymeric resins: equilibrium, kinetics and operation of a parametric pumping unit

Abstract Adsorption of d, l -Phenylalanine onto polymeric adsorbents (Amberlite XAD-4 and XAD-16; Sephabeads SP206 and SP207) was studied. Adsorption equilibrium isotherms were measured by batch equilibration at 15 and 40°C, showing the possibility of using a parametric pumping technique for aminoacid purification/recovery. Dynamic studies in a laboratory adsorption column Amicon Column (22 × 500 mm) were carried out to further screen adsorbents and obtain mass transfer parameters to be used in the modeling, simulation and operation of the pilot parametric pumping unit. The pilot plant includes a Amicon Columnn (90 × 1000 mm) and is completely automated. A package for the simulation of this cyclic operation was developed. Simulated and experimental results using Sephabeads SP206 (Mitsubishi Kasei Corporation, Japan) are in good agreement.

Studies on the impregnation step of the Merox process

Abstract Laboratory studies for the determination of equilibrium data and effective diffusivities of Merox solutions in activated carbon were carried out in batch, CSTR and fixed-bed adsorbers. Simulation of the impregnation step of an industrial Merox unit was then performed. The fixed-bed plant was modelled by a heterogeneous model with pore diffusion in particles and was solved numerically either by using the package PDECOL or the method of characteristics.

Studies on the Merox process: kinetics of N-butyl mercaptan oxidation

The Merox process is industrially used to convert mercaptans from petroleum distillates to disulfides by oxidation with air in the presence of alkaline solution and a supported catalyst. The kinetics of n-butyl mercaptan oxidation was studied as a basis for understanding the Merox process. All kinetic experiments were carried out in a constant pressure reactor. The system involves four phases: the organic phase (n-heptane) containing n-butyl mercaptan, the gas phase (air), the aqueous phase (sodium hydroxide for mercaptan extraction) and the catalyst. Kinetics was studied in the presence of the Merox catalyst alone and then in the presence of activated carbon alone. The information was then used to analyse kinetic experiments in which a supported catalyst was used.

Modeling of biodegradation/adsorption combined processes in fixed-bed biofilm reactors: Effects of the intraparticle convective flow

Abstract A mathematical model for a fixed-bed biofilm reactor is developed in this work, in order to investigate the roles of reaction, adsorption and mass transfer on substrate consumption. Mass transfer throughout the biofilm and support is described by simultaneous Fickian diffusion and convective flow. Numerical solutions were obtained for phenol biodegradation by finite element collocation methods. In terms of substrate removal and production of a good effluent quality, the results show the beneficial role introduced by adsorption in a biodegradation process, as well as the beneficial effects of the convective flow through both the biofilm and support, particularly when a higher intraparticle convective velocity is assumed to occur through the biofilm.

Binary Adsorption of Phenol and m-Cresol Mixtures onto a Polymeric Adsorbent

Adsorption processes are gaining interest as methods of purifying industrial effluents. Most industries discharge effluents containing several components. The adsorption of phenol and m-cresol mixtures from aqueous solutions onto a macroporous polymeric adsorbent, Duolite ES-861, was investigated experimentally in a fixed-bed adsorber for different flowrates, feed concentrations and bed initial conditions (clean or pre-saturated).The experimental results are presented in this work, where the major objective is placed on the modelling of these fixed bed adsorption experiments using an extended Langmuir isotherm equation for two components, based on single component equilibrium data obtained for phenol and m-cresol.The model presented in this paper takes into account axial dispersion of the liquid phase, film diffusion and intraparticle mass transfer and successfully simulates the adsorption behaviour of the phenol and m-cresol mixtures.

Dynamic behaviour of a fixed-bed biofilm reactor: analysis of the role of the intraparticle convective flow under biofilm growth

Abstract The influence of the intraparticle convective flow on the dynamic response of a fixed-bed biofilm reactor is evaluated theoretically for a stepwise increase in substrate concentration in the feed line. Dimensionless transient mass balance equations for the substrate within the bulk liquid, biofilm and support phases are derived considering a substrate inhibition kinetic model (Haldane equation) and biofilm growth. Governing equations are simultaneously solved for phenol biodegradation by finite element collocation methods to yield the bed response, in terms of dimensionless phenol concentration at outlet against a reduced time (breakthrough curves), for two different bulk flow rates. The results reported in this study, for different intraparticle velocities, show that the major beneficial effect of the intraparticle convective flow on the production of a good effluent quality is expressed by the occurrence of later breakthrough curves, due to the improvement of intraparticle mass transfer by convection, particularly when higher diffusional limitations are present inside the biofilm and support. Thus, bioreactors must be operated under such conditions that liquid flow occurs within biofilms.

Modeling and simulation of protein adsorption in permeable chromatographic packings: a double linear driving force model

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.

The simulation of solid—liquid adsorption in activated carbon columns using estimates of intraparticle kinetic parameters obtained from continuous stirred tank reactor experiments

Abstract A kinetic model, based on pore and surface diffusion and accounting for the energetic and structural heterogeneity of the adsorbent, was applied to the dynamics of fixed-bed adsorption of a dye product onto activated carbon particles. Model simulations, using parameters derived from independent equilibrium and kinetic studies, were found to predict the experimental data in a satisfactory manner.

Fixed-bed reactor for gasoline sweetening: Kinetics of mercaptan oxidation and simulation of the Merox reactor unit

Abstract The kinetic study of mercaptans oxidation was extended to the oxidation of n-hexyl mercaptan in n-heptane and to the sweetening of a typical light gasoline. The simulation of a typical industrial Merox reactor was then performed. The fixed-bed reactor was modelled by using a one-dimensional heterogeneous plug-flow model. Both the steady-state and transient behaviour were studied, as well as the influence of the real distribution of Merox catalyst inside particles and along the bed on the simulation results.

Adsorptive processes using “large-pore” materials: analysis of a criterion for equivalence of diffusion—convection, “apparent” diffusion and “extended” linear driving force models

Abstract The intraparticle diffusion—convection model is applied to simulate adsorptive processes using “large-pore” adsorbent particles. In this work, we analyse the feasibility of a criterion for the equivalence of this difficult and computation time consuming model to simpler models: the “apparent” diffusion model and an “extended” linear driving force (LDF) model. It is shown that the “extended” LDF model predicts reasonably well adsorption breakthrough curves in fixed beds, for different equilibrium isotherms, using a λ (intraparticle Peclet number) dependent “augmented” overall mass transfer coefficient between bulk fluid particles.