Eduardo A. Borges da Silva

Application of the Nernst–Planck approach to lead ion exchange in Ca-loaded Pelvetia canaliculata

Ca-loaded Pelvetia canaliculata biomass was used to remove Pb(2+) in aqueous solution from batch and continuous systems. The physicochemical characterization of algae Pelvetia particles by potentiometric titration and FTIR analysis has shown a gel structure with two major binding groups - carboxylic (2.8 mmol g(-1)) and hydroxyl (0.8 mmol g(-1)), with an affinity constant distribution for hydrogen ions well described by a Quasi-Gaussian distribution. Equilibrium adsorption (pH 3 and 5) and desorption (eluents: HNO(3) and CaCl(2)) experiments were performed, showing that the biosorption mechanism was attributed to ion exchange among calcium, lead and hydrogen ions with stoichiometry 1:1 (Ca:Pb) and 1:2 (Ca:H and Pb:H). The uptake capacity of lead ions decreased with pH, suggesting that there is a competition between H(+) and Pb(2+) for the same binding sites. A mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity constants alpha(Ca)(H)=9+/-1 and alpha(Ca)(Pb)=44+/-5, revealing a higher affinity of the biomass towards lead ions. Adsorption (initial solution pH 4.5 and 2.5) and desorption (0.3M HNO(3)) kinetics were performed in batch and continuous systems. A mass transfer model using the Nernst-Planck approximation for the ionic flux of each counter-ion was used for the prediction of the ions profiles in batch systems and packed bed columns. The intraparticle effective diffusion constants were determined as 3.73x10(-7)cm(2)s(-1) for H(+), 7.56x10(-8)cm(2)s(-1) for Pb(2+) and 6.37x10(-8)cm(2)s(-1) for Ca(2+).

Lignin as Source of Fine Chemicals: Vanillin and Syringaldehyde

The sustainability of processes to integrate in biochemical and thermochemical platforms is a key factor for the success of lignocellulose-based biorefineries. Production and separation of high added-value compounds from renewable resources are emergent areas of science and technology with relevance to both scientific and industrial communities. Lignin is one of the raw materials with high potential due to its chemistry and proprieties. One of the routes is the production of aromatic aldehydes, vanillin, and syringaldehyde, toward environmental friendly processes as oxidation with O2, including separation of products by membrane and ion exchange processes. In this chapter, the types, availability, and characteristics of lignins are described, as well as the current trends of some industrial producers and processors. A concise yet comprehensive revision of the literature on lignin oxidation research focusing vanillin and syringaldehyde is provided. Separation processes for recovery of the aldehydes are included closing with a design of reaction and separation integrated process for aldehydes production from lignin.

Glucose isomerization in simulated moving bed reactor by Glucose isomerase

Studies were carried out on the production of high-fructose syrup by Simulated Moving Bed (SMB) technology. A mathematical model and numerical methodology were used to predict the behavior and performance of the simulated moving bed reactors and to verify some important aspects for application of this technology in the isomerization process. The developed algorithm used the strategy that considered equivalences between simulated moving bed reactors and true moving bed reactors. The kinetic parameters of the enzymatic reaction were obtained experimentally using discontinuous reactors by the Lineweaver-Burk technique. Mass transfer effects in the reaction conversion using the immobilized enzyme glucose isomerase were investigated. In the SMB reactive system, the operational variable flow rate of feed stream was evaluated to determine its influence on system performance. Results showed that there were some flow rate values at which greater purities could be obtained.

Production of lactobionic acid and sorbitol from lactose/fructose substrate using GFOR/GL enzymes from Zymomonas mobilis cells: A kinetic study

In this work, we have investigated the kinetics of the biotechnological production of lactobionic acid (LBA) and sorbitol by the catalytic action of glucose-fructose oxidoreductase (GFOR) and glucono-δ-lactonase (GL) enzymes. The cells of bacterium Zymomonas mobilis ATCC 29191 containing this enzymatic complex were submitted to permeabilization and reticulation procedures. The effect of the concentration of substrates on the rate of product formation using a mobilized cell system was investigated. The application of higher fructose concentration seems to not affect the initial rate of formation of the bionic acid. Under conditions of low initial concentration of lactose, the experimental kinetic data of the bi-substrate reaction were modelled by assuming a rate equation of the classical ping-pong mechanism. The found kinetic parameters displayed a low affinity of the GFOR enzyme for both substrates. The enzymatic system did not exhibit normal Michaelis-Menten kinetics in response to a change of concentration of lactose, when fructose was held constant, presenting a sigmoid relationship between initial velocity and substrate concentration. A rate equation based on Hill kinetics was used to describe the kinetic behaviour of this enzyme-substituted reaction at higher lactose concentrations. The results from batch experiments using immobilized cells within Ca-alginate beads revealed that there is no pronounced occurrence of mass transfer limitations on LBA production for beads with 1.2 mm in average diameter. This discussion aids for defining the best operating conditions to maximize the productivity for LBA and sorbitol in this bioconversion and also for reducing the complexity of downstream separation processes.

Analysis of the Behavior of the Simulated Moving Bed Reactor in the Sucrose Inversion Process

Abstract The simulated moving bed reactor (SMBR) is a device in which reaction and separation processes take place simultaneously. The separation of products allows higher conversion and high‐purity product can be also obtained. In this work, a mathematical model has been presented to predict the behavior of the SMBR in the sucrose inversion process. For this process, the triangular region which defines operating conditions to recover high‐purity products in SMBR has been obtained using two modeling strategies. The set of partial differencing equations is solved by finite volume method. The influence of some operation conditions on the reactor performance is analysed for the sucrose inversion process.