Mariana Altenhofen da Silva

A Review of Drying Models Including Shrinkage Effects

ABSTRACT This article presents a review of the different strategies used in the literature to model drying processes in which material shrinkage occurs. An analysis is provided of the different drying theories, the different approaches to deal with the shrinkage phenomenon, and the numerical methods used. It is common practice to directly apply the transfer models applicable for non-shrinking situations to the shrinking cases and to adopt a separate procedure to account for shrinkage. In addition, the use of effective transfer coefficients also abounds in the literature. Thus, coupling between the transfer processes and mechanical interactions is rarely considered.

Ascorbic Acid Thermal Degradation during Hot Air Drying of Camu-Camu (Myrciaria dubia [H.B.K.] McVaugh) Slices at Different Air Temperatures

Abstract Air drying of camu-camu slices was performed in order to estimate the effect of air temperature on the kinetics of ascorbic acid thermal degradation. Moisture variation during the air drying process was monitored gravimetrically by weighing the trays at predetermined time intervals. The experimental points were adjusted by Ficks diffusion model and by the Page empirical model. The effective diffusion coefficient (Deff) ranged from 8.48 × 10−10 to 1.34 × 10−9 m2/s.The ascorbic acid content was evaluated in samples taken during the drying process using Iodine titration, and the results modeled by the Weibull equation. Concerning ascorbic acid retention the best drying condition required air at 50°C. The ascorbic acid retention was 78%, when the moisture content of the product reached 10% (wet basis).

Synthesis and application of natural polymeric plasticizer obtained through polyesterification of rice fatty acid

This study includes the synthesis of a new natural plasticizer obtained through esterification reaction of rice fatty acid and polyols, its physicochemical characterization and its preliminary application in polyvinyl chloride (PVC). Monopropylene glycol, octanol and diethylene glycol were used as polyols for esterification reaction. Catalyst Fascat ® 4100, was also added. Viscosity, acidity and hydroxyl index, moisture content, molar mass, chemical composition (by FTIR) and color were determined to characterize the natural plasticizer synthesized. The results were compared with a commercial plasticizer (DOA: di-octyl adipate) derived from petrochemical source and synthesized in laboratory. According to the results, except from color, the natural plasticizer presented similar properties of commercially available plasticizers, such as DOA. Mechanical tests indicated that the addition of the natural plasticizer to PVC films resulted in a significant increase on its elongation at break (371.2%) compared to pure PVC film, indicating a possible application for this plasticizer.

Influence of Drying Conditions on Physical Properties of Alginate Films

The effect of drying conditions of the film-forming solution on thickness, moisture content, water vapor permeability, and tensile properties of alginate films were investigated. A long period of constant rate was observed in all conditions and the model proposed by Wang and Singh was able to adjust the drying data. As expected, there was a clear effect of temperature on drying kinetics; that is, increasing the drying temperature decreased the drying time. Considerable glycerol losses were observed when alginate gel was oven dried at temperatures above 40°C. Compared to other drying conditions, films oven dried at 60°C were thinner, had lower moisture content, and were less flexible.

Volatiles identification in pineapple submitted to drying in an ethanolic atmosphere.

Pineapple slices were dried under normal and modified atmosphere in a lab-scale tunnel dryer. The atmosphere was modified by addition of 0.5% ethanol v/v to the air stream using two different temperatures and two different air velocities. A manual solid-phase micro-extractor coupled to a gas chromatographer/mass spectrometer (SPME-GC-MS) was used to determine the volatiles composition in fresh and dried pineapple samples. Important volatile compounds of pineapple aroma were detected in fresh as well as dried samples. The modified atmosphere promoted more rapid water evaporation and better retention of the volatile compounds upon drying.

Drying behavior of binary mixtures of solids

Abstract In this work, a model system zeolite NaY and kaolin (both from Aldrich®), and mixtures (1:4, 2:3, 3:2, 4:1) were studied. True and bulk densities, porosity, and specific surface area were determined for single solids and mixtures. Physical properties of mixtures were calculated from the mixing rule using mass fraction of each solid in the mixture. Calculated and experimental values presented perfect agreement for true density and specific surface area. For bulk density and porosity the mixing rule works well if the volumetric fraction is used, since the mixtures do not follow the mass proportion due to the different particle size distribution. The mixtures present the drying curves between those of the single solids according to their mass proportion. The results show that it is possible to use the mixing rule to evaluate some physical properties as well as the sorption isotherms and drying curves of binary mixtures of solids.

Capillary Pressure Determination from Sorption Isotherms for Mixtures of Porous Solids

Abstract Capillary pressure and relative permeability are important parameters for characterization of the draining of fluid phases in porous media. In this work, capillary pressure and relative permeability were evaluated in porous solids with distinct morphological properties, namely NaY zeolite, kaolin, and alumina as well as their binary mixtures in the compositions of 20, 40, 60, and 80% in mass fraction. The objective of the present work was to verify the influence of the composition of the solid mixture and the structural characteristics of the components on capillary pressure and relative permeability. Capillary pressure as a function of saturation of the material was determined from moisture desorption isotherms. The results showed that structural characteristics greatly influence capillary pressure and permeability. The obtained capillary pressure in microporous materials was higher than that in macroporous and mesoporosous materials at the same saturation. It was verified that when microporous materials were present in the mixture, the capillary pressure of the binary mixtures tended to approach the capillary pressure of the microporous materials, since micropores control the adsorption and desorption processes.

Lipid productivity in the fed-batch growth of Desmodesmus green microalgae from sugarcane vinasse

The technological potential of biodiesel from microalgae depends on the growth characteristics and lipid accumulation of these microorganisms. In this sense, the use of wastewater becomes an alternative biomass production as compared to traditional methods of photoautotrophic culture. The use of microalgae in the wastewater treatment has been studied as an alternative to conventional decontamination processes. Green microalgae Desmodesmus subspicatus has shown high cell viability in effluents, tolerating changes in temperature and pH. Vinasse is the main wastewater from sugarcane processing generated by ethanol fermentation-distillation, which presents high organic matter (non-volatile molecules with high molecular weight) and salts. Several strategies have been propose to improve the accumulation of lipids in the microalgal biomass, such as nutrient limitation and temperature. As the accumulation of intracellular lipids is dependent on biomass accumulation, fed-batch strategies can become attractive. In this sense, the study aimed to evaluated lipid productivity in the fed-batch growth of green microalgae Desmodesmus subspicatus from sugarcane vinasse. The experiments were set up a heterotrophic stirred bioreactor with 3 L of sugarcane vinasse, aeration of 1 VVM (volume of air per volume of liquid per minute) and 25°C. Lipid extraction using CO2-SC was conducted in a semi-continuous supercritical fluid extraction apparatus. Results of fed-batch cultivation indicate duplication biomass during fed-batch time (9 hours), with lipid content in the biomass around 15%. Thus, it was lipid productivity of 360 mg L-1day-1, similar value of simple batch experiments of our research group, suggesting the technical feasibility of fed-batch microalgae growth from this wastewater.