Verónica Bucalá

Use of a heterogeneous two-dimensional model to improve the primary steam reformer performance

The reforming units are basically furnaces containing burners (which provide a large amount of heat by fuel combustion) and tubes packed with supported nickel catalyst. Due to the high heat input through the reformer tube wall and the endothermic reforming reactions, the catalyst tubes are exposed to significant axial and radial temperature gradients. For this reason, a two-dimensional mathematical model that takes into account the diffusion reaction phenomena inside the particles rigorously has been used to represent the reactor. Strong radial temperature gradients in the reformer tube have been found, particularly close to the reactor entrance. These temperature differences cause significant variations in the methane reaction rate along the radial position, being the catalyst close to the reforming tube center poorly used. For this reason, the reforming tube diameter and the catalyst activity distribution were modified to use the catalyst more efficiently. The tube diameter has an important influence on the reformer performance, considerable higher conversions and reactor capacities per tube (i.e. closer equilibrium approaches) have been observed for the tubes with smaller diameters. The catalyst activity distribution also strongly impacts the reactor operation. The use of two catalysts of different activity, adequately distributed along the axial and radial directions, allowed to significantly decrease the maximum tube wall temperature and simultaneously minimize the reactor volume fraction packed with the catalyst of higher activity.

Fundamental Study of Thermal Treatment of Soil

Morphological and chemical changes exhibited by different types of soils heated to different final temperatures are reported. Beds of soils were heated (in a helium atmosphere) from ∼20°C to final temperatures, ranging from between 200 to 900°C, simulating ex situ thermal treatments in a nonoxidizing media. Structural changes exhibited by the soil samples during the treatments were analyzed by SEM, measurement of surface area, and measurement of particle porosity. The soil chemical transformations were quantified by means of soil weight loss, light gases yields, and carbon conversion. Soils with low organic matter content do not undergo important structural and chemical changes during the thermal treatment. On the other hand, soils with high organic carbon content suffer significant chemical modifications and, as a consequence, noticeable structural transformations. Indeed, for thermal treatments of about 900°C, weight losses as high as 22 wt%, final surface area of one order of magnitude higher than its original value (untreated soil), and changes of porosity as high as 27% were found for soils of high organic matter content. Simple mathematical equations are proposed to predict the soil weight loss and particle porosity as a function of the treatment temperature. The models provide a good fit to the experimental data.

Population balance discretization for growth, attrition, aggregation, breakage and nucleation

Abstract This paper presents a new discretization method to solve one-dimensional population balance equations (PBE) for batch and unsteady/steady-state continuous perfectly mixed systems. The numerical technique is valid for any size change mechanism (i.e., growth, aggregation, attrition, breakage and nucleation occurring alone or in combination) and different discretization grids. The developed strategy is based on the moving pivot technique of Kumar and Ramkrishna and the cell-average method of Kumar et al. A novel contribution is proposed to numerically handle the growth and attrition terms, for which a new representation of the number density function within each size class is developed. This method allows describing the number particle fluxes through the class interfaces accurately by preserving two sectional population moments. By comparing the numerical particle size distributions with analytical solutions of one-dimensional PBEs (including different size change mechanisms and particle-size dependent kinetics), the accuracy of the proposed numerical method was proved.

New alginic acid-atenolol microparticles for inhalatory drug targeting.

The inhalatory route allows drug delivery for local or systemic treatments in a noninvasively way. The current tendency of inhalable systems is oriented to dry powder inhalers due to their advantages in terms of stability and efficiency. In this work, microparticles of atenolol (AT, basic antihypertensive drug) and alginic acid (AA, acid biocompatible polyelectrolyte) were obtained by spray drying. Several formulations, varying the relative composition AT/AA and the total solid content of the atomized dispersions, were tested. The powders were characterized by: Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry and Powder X-ray Diffraction, while also the following properties were measured: drug load efficiency, flow properties, particles size and density, moisture content, hygroscopicity and morphology. The ionic interaction between AA and AT was demonstrated, then the new chemical entity could improve the drug targeting to the respiratory membrane and increase its time residence due to the mucoadhesive properties of the AA polymeric chains. Powders exhibited high load efficiencies, low moisture contents, adequate mean aerodynamic diameters and high cumulative fraction of respirable particles (lower than 10 μm).

Formulation and Characterization of Polysaccharide Microparticles for Pulmonary Delivery of Sodium Cromoglycate

ABSTRACTSodium cromoglycate (SC) is an antiasthmatic and antiallergenic drug commonly used for chronic inhalation therapy; however, many daily intakes are required due to the fast drug clearance from airways. For these reasons, SC polymeric particles for inhalatory administration with adequate aerosolization and mucoadhesive properties were designed to prolong the drug residence time in the site of action. Sodium carboxymethylcellulose (CMCNa), sodium hyaluronate, and sodium alginate were selected to co-process SC by spray drying. The influence of these polysaccharides on the spray drying process and powder quality was evaluated (among others, morphology, size, moisture content, hygroscopicity, flowability, densities, liquid sorption, and stability). In vitro aerosolization, drug release, and mucoadhesion performance were also studied. Particularly, a novel method to comparatively evaluate the interaction between formulations and mucin solution (mucoadhesion test) was proposed as a rapid methodology to measure adhesion properties of inhalable particles, being the results as indicative of clearance probability. Among all the studied formulations, the powder based on SC and CMCNa exhibited the best mucoadhesion and aerosolization performance, the highest process yield and adequate moisture content, hygroscopicity, and stability. SC-CMCNa formulation arose as a promising inhalatory system to reduce the daily intakes and to increase the patient compliance.

Impact of feed counterion addition and cyclone type on aerodynamic behavior of alginic-atenolol microparticles produced by spray drying

The inhalatory route has emerged as an interesting non-invasive alternative for drug delivery. This allows both pulmonary (local) and systemic treatments (via alveolar absorption). Further advantages in terms of stability, dose and patient preference have often lead researchers to focus on dry powder inhaler delivery systems. Atenolol is an antihypertensive drug with low oral bioavailability and gastrointestinal side effects. Because atenolol possesses adequate permeation across human epithelial membranes, it has been proposed as a good candidate for inhalatory administration. In a previous work, atenolol was combined with alginic acid (AA) and microparticles were developed using spray-drying (SD) technology. Different AA/atenolol ratios, total feed solid content and operative variables were previously explored. In order to improve particle quality for inhalatory administration and the SD yield, in this work the AA acid groups not neutralized by atenolol were kept either free or neutralized to pH∼7 and two different SD cyclones were used. Particle morphology, flow properties, moisture uptake and in vitro aerosolization behavior at different pressure drops were studied. When the AA acid groups were neutralized, particle size decreased as a consequence of the lower feed viscosity. The SD yield and in vitro particle deposition significantly increased when a high performance cyclone was employed, and even when lactose carrier particles were not used. Although the in vitro particle deposition decreased when the storage relative humidity increased, the developed SD powders showed adequate characteristics to be administered by inhalatory route up to storage relative humidities of about 60%.

Carrier free indomethacin microparticles for dry powder inhalation

Graphical abstract Figure. No Caption available. Abstract The present studies were designed to evaluate inhalatory microparticles carrying indomethacin (IN) for potential local (specific and non‐specific bronchial inflammatory asthma responses) and systemic treatments (joint inflammation, rheumatoid arthritis and osteoarthritis pain) by optimizing microparticle properties, characterizing their lung deposition, drug release, evaluating cytotoxicity and also pharmacological effect in vitro. The acidic groups of IN were complexed with the cationic groups of the polyelectrolyte polylysine in order to increase the drug water compatibility. The polylysine/indomethacin ratio was fixed and the pH was adjusted in different formulations. Microparticles were obtained by spray drying using a relatively high atomization air flowrate (742 L/min) and a high‐performance cyclone in order to optimize the production of microparticles with adequate attributes for inhalatory delivery. The produced microparticles exhibited high process yield and IN loading, volumetric mean diameters smaller than 5 &mgr;m and narrow particle size distributions. According to demonstrated aerosolization performance, the powders were suitable for inhalatory indomethacin local and systemic treatments. Emitted fraction was higher than 90%, the MMAD was around 3 &mgr;m and the GSD lower than 3. The respirable fraction for particles with aerodynamic diameters smaller than 5 &mgr;m was around 29% while for particles with aerodynamic diameters smaller than 3 &mgr;m the value was around 17%. The addition of lactose as carrier worsened the aerodynamic performance of the microparticles. The developed powdered systems got wet and dissolved quickly and presented higher release rates respect to pure IN in simulated lung physiological conditions. Furthermore, the assays performed in RAW 264.7 cell line showed that the microparticles exhibited the same anti‐inflammatory capability as the pure drug. The developed particles did not affect the RAW 264.7 cell viability. In conclusion, a promising powder formulation for DPIs has been developed to treat, locally and systemically, inflammatory diseases.