Miriam Maria de Resende

Distribution of suspended particles in a Taylor–Poiseuille vortex flow reactor

Vortex flow reactors (VFRs) are specially suited to work with shear-sensitive particles, due to the gentle and efficient stirring characteristics of Taylor vortices. For heterogeneous VFRs, the distribution of the solid phase must be accounted for in detail. This work presents residence-time distributions (RTDs) of agarose gel particles (Φ av =214 μm), suspended in different liquid solutions. Reactor porosity was 90%. The mass transfer coefficients of a lumped-parameter model of the reactor are estimated from residence time distributions of a tracer. The VFR has radius ratio η=0.664 and aspect ratio Γ=14.9. Axial flow rates were selected to provide a mean residence time of 1850 s, adequate for many applications. Minimum rotation rates of the inner cylinder were imposed by suspended particles homogeneity criteria. The VFR operational region was: 0.0645<Re ax <0.592 and 98<Re θ <3820, corresponding to very high values of the ratio Re θ /Re ax (between 5293 and 6236). Under these conditions, the vortices were stationary, and circumvented by a by-pass stream. The results indicate that the gel particles are unevenly distributed in the vortex core and by-pass regions. Mean residence times for the particles are substantially greater than for the liquid. The mathematical model presented in this paper can accommodate this behavior, using a partition coefficient for the solid phase.

ESTIMATION OF MASS TRANSFER PARAMETERS IN A TAYLOR-COUETTE- POISEUILLE HETEROGENEOUS REACTOR

A bench-scale, continuous vortex flow reactor (VFR), with a radius ratio, h, equal to 0.48 and an aspect ratio, G, equal to 11.19 was studied. This reactor may be used in the enzymatic hydrolysis of polypeptides obtained from sweet cheese whey with enzymes immobilized on agarose gel. Operational conditions were 2410 < Req < 11793 and 30-min residence time for glycerol-water, 14% w/w, 27oC (Reax = 1.1) and for water, 38oC (Reax = 1.5). Residence time distributions (RTDs) were obtained after pulse injections of different tracers (including dyed solid particles). Mass transfer coefficients of a lumped-parameter model of the reactor were estimated from these data. Model fitting to experimental data was accurate. Working conditions were selected so that transport properties of the fluids would be similar to the ones in the actual process at the final stages of whey hydrolysis.

Simulating a ceramic membrane bioreactor for the production of penicillin: an example of the importance of consistent initialization for solving DAE systems

Abstract Computer simulation of membrane bioreactors may give rise to numerical divergence when their operational strategy includes sudden changes in the culture medium. The mathematical model of this type of bioreactor is a system of differential–algebraic equations (DAE). This work illustrates the importance of defining consistent initial conditions for this system. The membrane bioreactor presented here is used for the cultivation of Penicillium chrysogenum , immobilized on the upper face of a flat, porous, ceramic membrane. Substrate comes from the medium stream flowing parallel to the membrane lower face. The cells are preserved from shear–stress damage and are kept in direct contact with air. To enhance penicillin production, the medium is diluted at the end of the trophophase. A consistent set of (new) initial conditions has to be selected at this moment; otherwise, the numerical solvers will not converge. Tests are performed using the codes dassl and radau , with almost identical results.

Production of omega-3 polyunsaturated fatty acids through hydrolysis of fish oil by Candida rugosa lipase immobilized and stabilized on different supports

Abstract This paper describes the fish oil hydrolysis performed to obtain Omega-3 fatty acids using Candida rugosa lipase (CRL) immobilized and stabilized on different supports. The enzyme was successfully immobilized, presenting higher thermal stability than the free enzyme. Besides, the cationic derivatives were more stable than the others derivatives and free enzyme in methanol, propanol and cyclohexane. Reactions of fish oil hydrolysis were carried out in organic aqueous medium using 10 U of biocatalyst per gram of oil, at 37 °C. After 96 h, the CRL immobilized on cyanogen bromide agarose rendered the lower fish oil hydrolysis, producing 218 μM of Omega-3, which was 1.1-fold more than the hydrolysis catalyzed by free enzyme, while the ionic derivatives rendered the highest fish oil hydrolysis producing 582 and 577 μM of Omega-3 using the carboxymethyl and sulfopropyl derivatives, respectively. The carboxymethyl and the sulfopropyl derivatives resulted in a 2.9-fold increase in the hydrolysis of fish oil, making these derivatives attractive for industrial applications.

Evaluation of process conditions in the performance of yeast on alcoholic fermentation

ABSTRACT This work studied the resistance of Saccharomyces cerevisiae Y904 to ethanol on an alcoholic fermentation process operated in fed-batch. The effect of temperature, inoculum size and substrate concentration on fermentation yield, productivity and residual sugars concentration was studied by a central composite design (CCD). Based on the CCD study, it was determined the optimum values of 240, 35 g/L, and 26°C for total reducing sugars, inoculum concentration and temperature, respectively. This set of conditions experimentally enabled a productivity of 6.0 g/L h, a yield of 93% and an alcohol content of 113.6 g/L, after 10 h of fermentation. When yeast cells were adapted at 4°C, the inoculum pH adjusted to 2.5 and sugarcane broth used as substrate, a 94% yield and a 10.1 g/L. h productivity were achieved.

Sucrose hydrolysis by invertase immobilized on Duolite A-568 employing a packed-bed reactor

ABSTRACT The conversion of sucrose to a highly concentrated commercial syrup by immobilized invertase by combining the processes of adsorption and cross-linking using Duolite A-568 as the carrier was studied. Central Composite Design (CCD) was used to assess the effect of glutaraldehyde concentration and cross-linking reaction time on immobilized enzyme activity throughout the hydrolysis of sucrose in a batch reactor. Cross-linking optimization allowed us to find the optimum conditions for activity with a glutaraldehyde concentration of 0.6 g · L−1 and a cross-linking time of 6 h. The temperature and pH that maximized the activity of the immobilized biocatalyst in the cross-linking process were 50°C and 4.0, respectively. Cross-linking allows the biocatalyst to be active at higher temperatures and lower pH. High-sucrose conversions to invert sugar using a continuous fixed-bed reactor were obtained. The immobilized biocatalyst also demonstrated greater thermal stability at low temperatures.

DETERMINAÇÃO DA DENSIDADE DE CORRENTE LIMITE E AVALIAÇÃO DA REMOÇÃO DE CROMO (VI) DE EFLUENTES SINTÉTICOS CONTAMINADOS ATRAVÉS DE UMA CÉLULA DE ELETRODIÁLISE COM E SEM A APLICAÇÃO DE CORRENTE

A eletrodialise e um processo de separacao eletroquimica onde os ions sao removidos da solucao diluida atraves de membranas de troca ionica por meio de uma voltagem de corrente direta. Um parâmetro conhecido por densidade de corrente limite pode reduzir consideravelmente a eficiencia desse processo atraves de um fenomeno conhecido por polarizacao por concentracao das membranas. Este trabalho teve por objetivo determinar a maxima corrente a ser utilizada na unidade sem que ocorra a polarizacao das membranas ionicas; bem como avaliar a remocao de Cr (VI) de solucoes sinteticas que simulam a concentracao de cromo presente em efluentes industriais, com e sem aplicacao de corrente. Foi utilizada uma unidade experimental com tres tanques de armazenagem e uma a celula eletrolitica PCCell ED 64 0 02 com dois compartimentos . As solucoes foram agua destilada, solucao de dicromato de potassio em varias concentracoes e solucao Na2SO4 0,25 M.. De acordo com os resultados encontrados, a maxima densidade da corrente limite a ser utilizada e aproximadamente 0,03 A e, em relacao a remocao do ion Cr2O7 2que contem o cromo na forma Cr 6+ pode-se notar que tanto com a aplicacao de corrente como sem a aplicacao de corrente o sistema de eletrodialise e eficiente, mas com aplicacao de corrente o tempo necessario para atingir os limites legais de lancamento em corpo hidrico e menor. Alem disso, observou-se que a corrente pode ser utilizada como um fator de limpeza das membranas ionicas.