Madalena M. Dias

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.

Gas–liquid flow in a 2D column: Comparison between experimental data and CFD modelling

Abstract Euler/Euler CFD simulations are validated against experimental data acquired in a 2D rectangular column with 2 mm gap thickness. Data was collected using image velocimetry and laser velocimetry techniques, from bubbly to slug flow regimes, including the two hydrodynamic situations of stagnant and flowing liquid. Experimental data profiling was carried out at different axial locations providing a suitable database for CFD modelling. Two-phase flow was simulated by the commercial CFD package CFX 4.2 taking into account the drag force term obtained experimentally and using the lift force based on the Bernoulli effect, as proposed by Ranade (Trans. Inst. Chem. Eng. 75 (1997) 14). Turbulence was modelled by an extra transport equation for bubble-induced turbulence, that allows for the inclusion of experimentally verified anisotropic effects, as proposed by Lopez de Bertodano, Lahey, and Jones (Int. J. Multiphase Flow 20 (1994) 805).

Linear driving force approximation in cyclic adsorption processes: Simple results from system dynamics based on frequency response analysis

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.

A Novel Continuous Industrial Process for Producing Hydroxyapatite Nanoparticles

Fluidinova, a recent start‐up high technology engineering company, has developed and is now commercializing a novel continuous industrial reactor NETmix for the manufacture of high added value products, such as nanomaterials, microemulsions, and pharmaceutical products. Through this technology, Fluidinova, in cooperation with Instituto de Engenharia Biomédica, has developed and patented the industrial process for the synthesis of a new high quality product consisting of hydroxyapatite nanoparticles with extremely high purity and crystallinity to be used as biocompatible nanomaterial for biomedical and pharmaceutical applications, to improve the quality of the already existing hydroxyapatite based medical devices, such as bone grafts, coated implants, and drug delivery systems.

Spray-drying microencapsulation of synergistic antioxidant mushroom extracts and their use as functional food ingredients

In this work, hydroalcoholic extracts of two mushrooms species, Suillus luteus (L.: Fries) (Sl) and Coprinopsis atramentaria (Bull.) (Ca), were studied for their synergistic antioxidant effect and their viability as functional food ingredients tested by incorporation into a food matrix (cottage cheese). In a first step, the individual extracts and a combination of both, showing synergistic effects (Sl:Ca, 1:1), were microencapsulated by spray-drying using maltodextrin as the encapsulating material. The incorporation of free extracts resulted in products with a higher initial antioxidant activity (t0) but declining after 7 days (t7), which was associated with their degradation. However, the cottage cheese enriched with the microencapsulated extracts, that have revealed a lower activity at the initial time, showed an increase at t7. This improvement can be explained by an effective protection provided by the microspheres together with a sustained release. Analyses performed on the studied cottage cheese samples showed the maintenance of the nutritional properties and no colour modifications were noticed.

Validation of a 2D CFD Model for Hydrodynamics' Studies in CIJ Mixers

A 2D model of a confined impinging jets mixer having the same geometry of the mixing chamber of a Reaction Injection Moulding, RIM, machine is introduced for the flow field simulation in a Computational Fluid Dynamics, CFD, code. From the CFD simulations the flow field structures and dynamics are clearly established. In addition, the numerical parameters affecting the 2D model simulations are studied, setting for each parameter a validity range. The 2D model is validated and used in the study of some operational parameters: the Reynolds number, the Froude number and the momentum ratio between the opposed jets. The validation of the CFD simulations is also made by comparison with experimental results. The limitations of the 2D model, for simulating the actual 3D flow field, are assessed; from the 2D/3D comparison, it is clearly shown that the introduced model can predict the main flow field features.

Effect of forced convection on reaction with mole changes in porous catalysts

Abstract The effect of intraparticle forced convection on a heterogeneous reaction within a catalyst pellet is studied. The extended dusty gas model is used to describe mass transport for a first-order, irreversible, isothermal reaction with mole changes within a slab-geometry catalyst pellet. Four dimensionless parameters are introduced and studied: the Thiele modulus, o; the ratio α between the Knudsen and effective diffusivities; the ratio β between the viscous momentum and molecular diffusivity; the normalized external pressure drop Δf. Results show that pressure gradients can exist within the pellet, as a result of the reaction stoichiometry and the external pressure gradient. The effectiveness factor is not only dependent on the Thiele modulus and on the change in moles, but it is also dependent and enhanced by intraparticle forced convection.

Quantification of mixing in RIM using a non-diffusive two-phase flow numerical model

Mixing in RIM is made mainly by advective mechanisms, rather than diffusion. In this paper, the advective mechanisms that enable reducing the mixing scales down to the values required for the complete chemical reaction of the two monomers inside the RIM mixing chamber are identified and studied. From Computational Fluid Dynamics (CFD) simulations of non-diffusive two-phase flow using the Volume-of-Fluid (VOF) model, a linear scale of segregation is determined as a measure of the degree of mixing and the effect of the Reynolds number is studied.

Functionalized textiles with PUU/limonene microcapsules: effect of finishing methods on fragrance release

The majority of the commercially available microencapsulated fragrance systems with interest for textile applications are based on phenol–formaldehyde/melamine–formaldehyde resins. Recognized human health problems concerning formaldehyde emissions led to the use of poly(urethane–urea) (PUU) systems. In this work, fabrics were impregnated with PUU microcapsules containing limonene produced by interfacial polymerization. To aid the microcapsule impregnation, a specific binder was used followed by a drying and thermofixation process. The textiles were then subjected to abrasion and dry cleaning tests. Fragrance release was analysed for different binder to microcapsule ratios. SEM images of the impregnated samples indicate good adhesion of the microcapsules to the fabric fibres, but some capsule breakage was observed. Fragrance release tests were followed by GC–FID–HS and showed good resistance to abrasion tests with 30% of the initial limonene detected after 9000 abrasion cycles. A lower resistance was observed for the dry cleaning tests, although 20% of the limonene was still present after five dry cleaning cycles.

The effect of intraparticle convection on conversion in heterogeneous isothermal fixed-bed reactors with large-pore catalysts for first-order reactions

Abstract Residence time distributions have been largely used in chemical engineering to make diagnosis of the ill-functioning of chemical reactors and to predict conversion in homogeneous isothermal reactors once the kinetic rate of reaction is known. The prediction is unambiguous for first-order reactions. In this paper, the impulse tracer response of isothermal heterogeneous fixed-bed reactors packed with large-pore catalysts, in which intraparticle convection occurs, is derived. From the impulse tracer response, the residence time distribution of the outer phase is calculated and used to predict the steady state conversion in the reactor for first-order reactions. The effect of intraparticle convection, measured by the intraparticle Peclet number λ for a given reaction-catalyst system, i.e. for a set of Damkholer, Thiele, Biot and Peclet numbers (Da, o, Bi m and Pe respectively) is to drive the conversion between the diffusion-controlled and the kinetic-controlled limits. The problem of scaling from batch to continuous packed beds is also addressed.