José M. Loureiro

Residence time distribution of inert and linearly adsorbed species in a fixed bed containing “large-pore” supports: applications in separation engineering

Abstract Large-pore materials are used in various chemical engineering applications as catalysts, HPLC packings, ceramic membranes. In such supports, mass transfer due to intraparticle convection has to be taken into account. This paper shows how intraparticle convection affects residence time distribution of inert and linearly adsorbed species in fixed-bed processes. The concept is further illustrated with examples from gas—solid systems and liquid—solid systems (HPLC) showing how the column efficiency (measured by HETP in separation engineering) is improved by the use of large-pore supports.

Importance of intraparticle convection in the performance of chromatographic processes

Abstract Large-pore materials are used in separation engineering as high-performance liquid chromatographic packings and adsorbents; however, they find also many applications in reaction engineering as catalyst supports and ceramic membrane reactors and in biotechnology as supports for mammalian cell cultures or biomass growth. In these large-pore materials, mass transport by intraparticle forced convection should be considered in process analysis. A brief historical survey of research work concerned with intraparticle forced convection is given, showing that the concept to be retained is that of effective diffusivity augmented by convection. The behaviour of the height equivalent to a theoretical plate as a function of bed superficial velocity is explained on the basis of the above concept. Analogies between slab and spherical particle geometries are discussed.

Separation of 1,1'-bi-2-naphthol enantiomers by continuous chromatography in simulated moving bed

Abstract The chromatographic separation of 1,1′-bi-2-naphthol enantiomers with 3,5-dinitrobenzoyl phenylglycine bonded to silica gel stationary phases is studied. Continuous chromatography in simulated moving bed (SMB) is analyzed by modeling, simulation and operation of a SMB pilot unit Licosep 12–26 from Separex (France). A model for the prediction of the cyclic steady-state performance of the SMB is developed based on the analogy with the true moving bed (TMB). The model assumes axial dispersion flow for the liquid phase, linear driving force (LDF) approximation for intraparticle mass transfer rate and takes into account multicomponent adsorption equilibria. The SMB package allows the simulation of the pilot unit. The effect of operating variables (switching time, extract and feed flow rates, section length) and number of mass transfer units on the SMB performance is analyzed. The SMB performance is characterized by purity, recovery, solvent consumption and adsorbent productivity. The package also allows the simulation of the dynamic evolution of internal profiles for the transient operation of a TMB. The operation of the SMB pilot unit was carried out for the separation of racemic mixtures of bi-naphthol enantiomers. Using a 8-column configuration purities as high as 94.5% of the more retained species in the extract and 98.9% of the less retained species in the raffinate were obtained.

Adsorption of H2, CO2, CH4, CO, N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H2O, CO2, CH4, CO, N2, and H2 on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.

Gold recovery with ion exchange used resins

In this paper one strong acidic, one strong basic and one weak basic ion-exchange resins, considered as exhausted in an industrial demineralizing plant, are screened for gold recovery from cyanide solutions. Based on the observed ability for the recovery and on the ease of regeneration, the weak base anion exchanger Purolite A-100 is selected. This spent resin is stable until 60°C and, after regeneration, conserves its physical properties as compared with a new one. Equilibrium data for the resin are determined, proving the very high capacity of the resin for gold (∼500 mg Au/g dry resin) and modeled by the Freundlich and mass action isotherm models. A kinetic experiment is conducted in a batch adsorber and modeled with an equivalent Ficks diffusivity using the linear driving force approximation, showing that the film resistance to mass transfer controls the operation. Finally, a fixed bed adsorber is saturated with gold aurocyanide and regenerated with a potassium hydroxide solution. The model used for the simulation of both steps incorporates axial dispersion and the same equivalence for the ionic diffusivity. During the elution process, precipitation of dihydrated potassium aurocyanide occurs inside the resin, increasing the intraparticle resistance to mass transfer. The model is able to reasonably represent the experimental elution results when a large internal resistance to mass transfer is used. A 25-fold concentration of the initial gold solution is obtained in this saturation/elution process, albeit the precipitation, showing the feasibility of the method for the recovery of gold, increasing the useful life of the resins and decreasing pollution. The anionic Purolite A-100 resin showed also a significant capacity for removing silver, although less than for gold, probably because silver cyanide complexes occupy, on the average, more than one ion exchange site in the resin.

Color removal with natural adsorbents: modeling, simulation and experimental

The adsorption in some natural materials containing chitin namely, Squid (Loligo vulgaris) and Sepia (Sepia officinalis) pens, and Anodonta (Anodonta cygnea) shells for color removal from textile wastewaters was studied. A reactive and a direct green dyestuff, the Cibacron green T3G-E (CI reactive green 12) and the Solophenyl green BLE 155% (CI direct green 26) from CIBA, respectively, were selected for this study. Continuous experiments in a packed column at 20°C with the natural materials showed a large internal resistance to mass transfer. In order to improve the adsorbents performances, the materials were submitted to chemical treatment (demineralization and/or deproteinization). Isotherms at 20°C were determined for all systems and compared with the ones using the materials after chemical treatment. These results were fitted by both Langmuir and Freundlich models. The determined parameters showed that equilibrium adsorption capacities increased at least five times. These results and the mathematical simulation of the column runs showed that there are improvements both in equilibrium and kinetic data. The adsorbents physical and chemical properties before and after chemical treatment were briefly characterized in order to investigate the changes responsible for those improvements. Biodegradation of the direct dyestuff was observed during the column operation using both the Anodonta shell and Sepia pen. For these two systems the chemical treatment of the materials did not improve the color removal. Biodegradation was included in the developed model and the influence of the model parameters on the system behavior was analyzed.

Peak resolution in linear chromatography : effects of intraparticle convection

Abstract The quantitative relationship between separation performance and intraparticle convection in large-pore, permeable supports for chromatography is examined. A model for linear chromatography is used in the analysis for particles that contain both throughpores where diffusive and convective transport occur and purely diffusive micropores. The key concept is that of a convection-augmented intraparticle diffusivity, which depends only on the intraparticle Peclet number, λ. The separation performance is expressed in terms of both resolution and peak profiles at the column outlet. It is shown that, for given operating conditions, the separation enhancement obtained for intraparticle convection is dependent on the relative importance of throughpore and micropore diffusion rates. In the absence of micropore resistances, the resolution is always increased by intraparticle convection. The latter, however, is shown to have no effect on the separation performance when micropore diffusional resistances are dominant. Relationships necessary to assess the importance of these effects for linear chromatography conditions are provided.

Application of statistical experimental methodology to optimize reactive dye decolourization by commercial laccase.

Three-level Box-Behnken factorial design with three factors (pH, temperature and enzyme concentration) combined with response surface methodology (RSM) was applied to optimize the dye degradation of reactive red 239 (RR239), reactive yellow 15 (RY15) and reactive blue 114 (RB114) dyes by commercial laccase. Mathematical models were developed for each dye showing the effect of each factor and their interactions on colour removal. The model predicted for RY15 that a decolourization above 90% (after 24h) could be obtained when the enzyme concentration, temperature and pH were set at 109.8U/L, 39.2 degrees C and 6.6, respectively; whilst for RB114 and RR239 the temperature and enzyme concentration did not affect the decolourization (>90%) in the considered range and optimum pH value was found at 5.5-7.0 and 7.0-7.5, respectively. These predicted values were also experimentally validated. Average final values of responses were in good agreement with calculated values, thus confirming the reliability of the models of RY15, RB114 and RR239 decolourization.

Modeling, simulation and operation of a simulated moving bed for continuous chromatographic separation of 1,1′-bi-2-naphthol enantiomers

Abstract The objective of this paper is to study the separation of enantiomers of 1,1′-bi-2-naphthol in 3,5-dinitrobenzoyl phenylglycine bonded to silica gel, using heptane–isopropanol (72:28) as eluent by simulated moving bed chromatography (SMB). A model for the prediction of the cyclic steady state performance of the SMB, based on the analogy with the true moving bed, is developed assuming axial dispersion flow, linear driving force approximation for intraparticle mass transfer and multicomponent adsorption equilibria. The SMB package allows the simulation of the pilot unit. The effect of several operating parameters on the SMB performance is analyzed. The performance is characterized by purity, recovery, solvent consumption and adsorbent productivity. The package is an important tool for learning and training operators, allowing the choice of best operating conditions. The operation of the SMB pilot unit was carried out for the separation of racemic mixtures using a 8-column configuration. Purities and recoveries higher than 95% in the extract and raffinate were obtained. Model and experimental results are compared and the package is also used to predict the steady state internal profiles for the SMB operation in good agreement with experimental results.

Separation of enantiomers of a chiral epoxide by simulated moving bed chromatography

Abstract The paper deals with chiral separation by simulated moving bed (SMB) chromatography. The separation of chiral epoxide enantiomers in microcrystalline cellulose triacetate using methanol as eluent is considered as illustrative example. The use of microcrystalline cellulose triacetate for the chromatographic separation of enantiomers is first reviewed and a methodology for obtaining basic data (adsorption equilibrium isotherms, axial dispersion and mass transfer coefficient) is discussed. A model for the prediction of the cyclic steady-state performance of the SMB, based on the analogy with the true moving bed, is developed assuming multicomponent adsorption equilibria, axial dispersion flow and linear driving force approximation to describe the intraparticle mass transfer rate. The simulation package is used to predict the effect of operating variables on the process performance and to define the regions for enantiomer separation. A simple optimization procedure is proposed for choosing the best SMB operating conditions. This procedure is extensively tested for the separation of chiral epoxide enantiomers. The experimental operation of a SMB pilot unit was carried out for this system. Purities and recoveries higher than 90% were obtained for both extract and raffinate, using a 420 ml inventory of stationary phase. The SMB pilot allows the continuous resolution of 52 g of racemic mixture per day and per liter of bed, with a solvent consumption of 0.4 l of mobile phase per gram of racemic mixture processed. The simulation package is also used to predict the steady-state internal concentration profiles for the SMB operation with reasonable agreement with experimental results.