MedWorm: Chemistry

Xvi-sibee: the xvi brazilian symposium of electrochemistry and electroanalytical chemistry

Journal of the Brazilian Chemical Society — Sat, 05 Jul 2008 15:35:21 +0100

(Source: Journal of the Brazilian Chemical Society)

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Experimental study of fluidized bed agglomeration of acerola powder

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

The aim of this work was to study the main effects of acerola powder on fluidized bed agglomeration. A 2(4-1) fractional factoring design was used to evaluate the main operating conditions (fluidizing air temperature, fluidizing air velocity, atomizing air flow and height of nozzle in the bed). The mechanical and physicochemical product changes were determined by analysis of particle diameter, moisture content, wetting time and bed porosity. The particle enlargement by agglomeration occurred when the relative humidity in the bed increased and, thus, the moisture of the product increased. However, the excessive increase in relative humidity resulted in a decrease in yield, caused by caking and product incrustation. The consolidation of small granules resulted in an increase in the instant properties, decreasing the wetting time and increasing the solubility in a short period of agitation. (Source: Brazilian Journal of Chemical Engineering)

Simultaneous heat and mass transfer in packed bed brying of seeds having a mucilage coating

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

The simultaneous heat and mass transfer between fluid phase and seeds having a mucilaginous coating was studied during packed bed drying. To describe the process, a two-phase model approach was employed, in which the effects of bed shrinkage and nonconstant physical properties were considered. The model took into account bed contraction by employing moving coordinates. Equations relating shrinkage and structural parameters of the packed bed with moisture content, required in the drying model, were developed from experimental results in thick-layer bed drying. The model verification was based on a comparison between experimental and predicted data on moisture content and temperature along the bed. Parametric studies showed that the application of correlations capable of incorporating changes in bed properties gives better data simulation. By experimental-theoretical analysis, the importance of shrinkage for a more accurate interpretation of heat and mass transfer phenomena in the drying of porous media composed of mucilaginous seeds is corroborated. (Source: Brazilian Journal of Chemical Engineering)

Characteristics of flow in wet conical spouted beds of unequal-sized spherical particles

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

Interparticle forces, developed in wet spouted beds composed of a mixture of spherical particles with different size distributions, intensify particle segregation mechanisms interfering in gas distribution inside the bed and, consequently, in the spouting flow characteristics. Therefore, this paper is aimed at describing the effect of interparticle forces on the air-solid flow distribution in conical spouted beds of unequal-sized particles coated by a thin glycerol film. Experimental results show that both the minimum spouting airflow rate and the minimum spouting pressure drop decrease as the amount of glycerol added to the bed increases. In addition, simulated results of the annular air velocity along the bed height showed that, at the base of the column, the radial component of the inertial force is high enough to break liquid bridges between particles and carry these particles out along the spout. Moreover, as the glycerol concentration increases, the spout diameter increases along the bed height. Such changes in the air-solid flow can maintain the spouting regime for higher glycerol concentrations as shown by experimental data. (Source: Brazilian Journal of Chemical Engineering)

Mass transfer inside oblate spheroidal solids: modelling and simulation

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

A numerical solution of the unsteady diffusion equation describing mass transfer inside oblate spheroids, considering a constant diffusion coefficient and the convective boundary condition, is presented. The diffusion equation written in the oblate spheroidal coordinate system was used for a two-dimensional case. The finite-volume method was employed to discretize the basic equation. The linear equation set was solved iteratively using the Gauss-Seidel method. As applications, the effects of the Fourier number, the Biot number and the aspect ratio of the body on the drying rate and moisture content during the process are presented. To validate the methodology, results obtained in this work are compared with analytical results of the moisture content encountered in the literature and good agreement was obtained. The results show that the model is consistent and it may be used to solve cases such as those that include disks and spheres and/or those with variable properties with small modifications. (Source: Brazilian Journal of Chemical Engineering)

Modelling and automation of the process of phosphate ion removal from waste waters

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

Phosphate removal from waste waters has become an environmental necessity, since these phosphates stimulate the growth of aquatic plants and planktons and contribute to the eutrophication process in general. The physicochemical methods of phosphate ion removal are the most effective and reliable. This paper presents studies on the process of phosphate ion removal from waste waters resulting from the fertiliser industrys use of the method of co-precipitation with iron salts and with calcium hydroxide as the neutralizing agent. The optimal process conditions were established as those that allow achievement of a maximum degree of separation of the phosphate ions. The precipitate resulting from the co-precipitation process was analysed for chemical composition and establishment of thermal and structural stability, and the aim was also to establish in which form the phosphate ions in the formed precipitate can be found. Based on these considerations, the experimental data obtained in the process of phosphate ion removal from waste waters were analysed mathematically and the equations for the dependence of the degree of phosphate separation and residual concentration versus the main parameters of the process were formulated. In this paper an automated scheme for the phosphate ion removal from waste waters by co-precipitation is presented. (Source: Brazilian Journal of Chemical Engineering)

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Production of enantiomerically pure d-phenylglycine using pseudomonas aeruginosa 10145 as biocatalyst

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

Different bacterial strains were screened to detect nitrilase and/or nitrile hidratase/amidase activities towards benzonitrile, to be used as biocatalyst to produce enantiomerically pure non-proteinogenic amino acids using amino nitriles as starting material. The best biocatalyst found was Pseudomonas aeruginosa 10145, which showed high enzyme activities. Whole cells were used as catalyst for the transformation of 2-phenyl-2-amino-acetonitrile for the corresponding D-phenylglycine. The percentage conversion was followed by chiral HPLC. After 1 hour reaction 18% of 2-phenyl-2-amino-acetonitrile was converted into D-phenylglycine with an enantiomeric excess of over 95%. When an inducer was added to the media, an increase in nitrile hydrolyzing activities was detected, hence leading to total conversion of (R)-2-phenyl-2-amino-acetonitrile to the corresponding amino acid in 30 min reaction. The isolated yield of the target product was 50% and its characterization was performed by polarimetry, chiral HPLC, IR-FT spectroscopy and GC-MS. (Source: Brazilian Journal of Chemical Engineering)

Editorial: announcement

Brazilian Journal of Chemical Engineering — Sat, 05 Jul 2008 15:34:48 +0100

(Source: Brazilian Journal of Chemical Engineering)

Lithium manganese(ii) diaquaborophosphate monohydrate

Acta Crystallographica Section E — Sat, 05 Jul 2008 13:15:59 +0100

The title compound, LiMn(H2O)2[BP2O8]·H2O, is built up of an open framework of helical borophosphate ribbons interconnected by MnO4(H2O)2 octahedra, forming one-dimensional channels along [001] occupied by Li+ cations and disordered H2O molecules (site occupancy 0.5). The Li cations reside in two partially occupied sites [occupancies = 0.42 (3) and 0.289 (13)] near the helices. (Source: Acta Crystallographica Section E)

A new spin on sorting nanotubes

Chemistry World | Latest News — Sat, 05 Jul 2008 06:21:44 +0100

A technique that separates semiconducting and metallic nanotubes could pave the way for progress in nanoelectronics (Source: Chemistry World | Latest News)

Creating a second genetic code

Chemistry World | Latest News — Sat, 05 Jul 2008 06:21:44 +0100

Scientists have created artificial DNA strands that could form a new biological data storage system (Source: Chemistry World | Latest News)

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Diethyl [2,2,2-trifluoro-1-phenylsulfonylamino-1-(trifluoromethyl)ethyl]phosphonate