F. A. P. Garcia

Optimisation of the enzymatic synthesis of n-octyl oleate with immobilised lipase in the absence of solvents

The enzymatic synthesis of n-octyl oleate by direct esterification of the oleic acid and the octanol in a solvent-free medium was previously shown to be efficiently catalysed by a lipase from Rhizomucor miehei covalently linked to a graft copolymer, the partially hydrolysed poly(ethylene)-g co-hydroxyethyl methacrylate (PE-g co-HEMA). In this work we went further towards an optimisation of the production of n-octyl oleate taking into account several parameters that affect the catalytic activity of the preparation. The physical characteristics of the support, such as the particle size and the degree of hydrolysis of the copolymer, the amount of lipase used in the method of immobilisation, the water content of the reaction mixture and the operational conditions of reaction, in particular the temperature, were evaluated in order to achieve not only high activities but also a good stability of the preparation.

Effects of additives on the activity of a covalently immobilised lipase in organic media

Lipase from Mucor miehei was covalently immobilised onto the graft copolymer poly(ethylene)-g.co-hydroxyethyl methacrylate (PE-g.co-HEMA), partially hydrolysed, via a spacer arm of 1,6-diaminohexane activated with glutaraldehyde. To improve the lipolytic activity of the immobilised lipase (for the synthesis of isoamyl-caprylate, as a model), the effect of several additives was investigated. Polyethylene glycol (PEG), glutaraldehyde, organic solvents and buffers, were added during the immobilisation procedure and their effects are reported and compared with the behaviour of the lipolytic preparation without pre-treatment. An increase of 40-100% in the activity was obtained when small quantities of PEG 2000 and glutaraldehyde (used also as an activator of the spacer arm) were added. The activity had a maximum when the pH of the lipase attachment solution was 7.2 and buffered with phosphate. The effect of the aggregation level of biocatalyst particles on the amount of water retained, as well as the effect of the immobilisation on solid supports on the stability to organic solvents, is also reported.

Lipase immobilisation on to polymeric membranes

Lipase (EC 3.1.1.3) from Candida rugosa was covalently immobilised on to cellulose, cellulose derivatives (cellulose acetate and cellulose phthalate) and cellulose composite membranes using activating agents such as sodium periodate or carbodiimide. Other non-cellulosic polymeric membranes (nylon, polyurethane, chitosan and hydroxyethyl methacrylate-co-methyl methacrylate) were also prepared and used for lipase immobilisation. The results obtained showed that the expressed activities are of the same order of magnitude for similar enzyme loadings when compared with those obtained from literature.

Physical Characterization Of Porous Materials And Correlation With The Activity Of Immobilized Enzyme In Organic Medium

A series of commonly used porous supports was characterized by determination of particle size distribution, porosity, surface area (total and distributions with pore diameters) and skeletal density. The performance of immobilized α-chymotrypsin catalyzed dipeptide synthesis in an acetonitrile medium was correlated with these physical properties. At high enzyme loading, when internal mass transfer limitations are expected to occur, the activity can be correlated with the support characteristic parameter. This is a combination of physical properties such as particle size, porosity, and volumetric porosity, which influence the substrate diffusion rate. At low enzyme loading the important parameter is the accessible surface area, which will determine how the enzyme is distributed in the pores of the support. When assessing the effect of the support material on enzymatic activity, the geometric considerations studied here should always be contemplated before making any assumptions about direct effects of suppo...

Applying LDS to Monitor Flocculation in Papermaking

Flocculation of fines and fillers is important in the papermaking industry. To fulfill the need for accurate control of flocculation, laser diffraction spectroscopy (LDS) was selected to supply the floc size distribution. LDS allowed the detection of different flocculation mechanisms depending on the flocculant characteristics. The analysis relied mainly on the collection of two parameters: the size distribution of the flocs, characterized by its median, and their fractal dimension. Floc resistance to shear was assessed and related to the floc structure through the analysis of the fractal dimension. For the lower charge density, flocs grow faster, becoming less compact and, thus, less resistant. LDS proved to be a valuable technique to monitor flocculation processes. However, to obtain significant results, a close control of obscuration in the measuring cell is required.

Imaging Particulate Two-Phase Flow in Liquid Suspensions with Electric Impedance Tomography

Different approaches have been followed to model the hydraulic transport of particles, ranging from pure empirical correlations to general models based on fundamental principles. However, these models suffer from uncertainties associated with the parameters in the constitutive equations and scarcity of experimental data in the literature. Nonintrusive techniques such as electric impedance tomography (EIT) can be used to circumvent the difficulties associated with sampling techniques. EIT is an imaging technique for the phase distribution in a two-phase flow field, allowing reconstructing the resistivity/conductivity distribution gradients from electrical data in a medium subjected to arbitrary excitations. Our best efforts were concentrated on the development of a new EIT system that is analogue based, portable, low-cost, and capable of providing high-quality sharp images when used to characterize the flow of particle suspensions. A voltage source was used, rather than a more complex and costly current source, since it provided the EIT system with a more precise and flexible current output. The data acquisition system consists of 16 electrodes equally spaced in the boundary of a tube and a custom dedicated electronic apparatus. The software supplies results in the form of two-dimensional reconstructed images that allow mapping the phase distribution inside the tube.

Immobilization of lipase from Mucor miehei onto poly(ethylene) based graft copolymers

Lipase from Mucor miehei was immobilized covalently onto hydrolyzed poly(ethylene)-g.co-hydroxyethyl methacrylate (PE-HEMA). This hydrolysis of the copolymer was achieved using 0.1 M NaOH over different periods of time, under controlled conditions. The graft copolymers and their hydrolyzed equivalents were characterized by scanning electron microscopy (SEM) and by differential scanning calorimetry analysis (DSC). Water sorption studies were undertaken to provide a measure of relative hydrophobicity of the samples.The lipase immobilization reaction was studied in order to assess the effects of controlling various important parameters. These include the nature of the buffering medium, the time over which the immobilization was allowed to occur, the concentration of the activating and coupling agent used (CMC) and the concentration of enzyme employed during attempts at effective immobilization. The immobilized lipase was used in the hydrolysis of triolein (glycerol trioleate). From this study, the apparent K...

CFD simulation of a turbulent fiber suspension flow - a modified near-wall treatment

Turbulent Eucalyptus fiber suspension flow in pipes was studied numerically using commercial CFD software. A pseudo-homogeneous approach was proposed to predict the flow behavior of pulp fiber suspensions for medium consistencies and for Reynolds numbers ranging from 4.7÷65.3·103. Viscosity was introduced into the model as a function of shear rate to represent the non-Newtonian behavior of the pulp suspension. Additionally, the existence of a water annulus was considered at the pipe wall, surrounding the flow core, where viscosity is equal to the water viscosity. The near-wall treatment was modified considering an expression for the logarithmic velocity profile in the boundary layer, similar to the one suggested by Jäsberg (2007). The final model could reproduce the drag-reduction effect resulting from the presence of fibers in the flow. Moreover, the numerical results show that a better fit for pressure drop is obtained when the modified near-wall treatment is used and the Jäsberg adjustable parameters are adapted to take into account the flow conditions.

Evaluation of Polyelectrolyte Performance on PCC Flocculation Using the LDS Technique

Flocculation of precipitated calcium carbonate induced by polyelectrolytes was monitored using light diffraction scattering (LDS), which can supply the complete kinetic curve for the flocculation process. Cationic polyacrylamides of very high molecular weight with different charge densities and degrees of branching were tested. The effects of the charge density, degree of branching, and concentration of the flocculant on the flocculation process, as well as on floc resistance and reflocculation capacity, were investigated. Moreover, floc structure was evaluated through the calculation of the fractal dimension using the scattering matrix. The study demonstrates the benefit of using LDS for the evaluation, in a single test, of flocculant performance in the different stages of flocculation: aggregation, stabilization, deflocculation, and reflocculation.

Evaluation of the Performance of Dual Polyelectrolyte Systems on the Re-Flocculation Ability of Calcium Carbonate Aggregates in Turbulent Environment

Flocculation can be used in turbulent environments resulting in floc breakage due to shearing. The degree of re-flocculation relates directly to product quality and process efficiency. This study aimed at looking for alternatives to improve the re-flocculation ability of aggregates when polyelectrolytes (PEL) are used as flocculation agents. Moreover, because branched PEL have proved previously to lead to high flocculation efficiencies, the work presented focus on the improvement of the re-flocculation ability of branched PEL. Thus, a selection of branched polymers were used primarily as flocculation aid and after flocs break up a linear polymer was added to the system in order to improve re-flocculation. Different mixtures were tested with the objective to try to induce, during re-flocculation, complementary flocculation mechanisms, favoring the patching mechanism. Re-flocculation improved significantly with this strategy. Laser Diffraction Spectroscopy was used to monitor the flocculation and re-flocculation processes supplying information about the floc size and structure. Since inorganic materials, namely bentonite, have been widely used to improve the re-flocculation capacity of polyelectrolytes, the results of using dual polyelectrolyte systems were compared with the effect of adding bentonite to the system.