Björn Sivik

Concentration polarization and fouling

Abstract Concentration polarization is often the reason for the serious limitation of the membrane processes due to its negative influence on the transmembrane flux. Many theoretical studies on this polarization phenomena have resulted in mathematical models for concentration polarization. In most of them, solutions are sought for the coupled nonlinear system of the equations of continuity and motion. Each of these solutions makes use of some assumptions in order to simplify the equations which represent the phenomenon. Different kinds of flow systems have been constructed in order to reduce the concentration polarization. The aim of these flow systems has mainly been to improve the mass transport from the membrane surface back to the bulk solution. Fouling often is a result of concentration polarization, but can also have other reasons. The attention that was drawn to fouling ten to fifteen years ago mostly consisted of recognizing the fact as such and to roughly identify the foulant. Later, efforts to avoid the negative effects have basically followed the paths of altering the composition of the feed solution by a pretreatment to change or get rid of the foulant, to change the hydrodynamics of the membrane module or to alter the membrane itself. However, unveiling the basic mechanisms of fouling attracted little attention until the late seventies when for example fouling of an RO sea water desalination membrane could be subdivided into four consecutive steps. Also, studies of the chemistry and physics of fouling have being performed on whey lately and revealed in closer detail some of the responsible phenomena.

Membrane Characterization by the Contact Angle Technique: II. Characterization of UF-Membranes and Comparison between the Captive Bubble and Sessile Drop as Methods to obtain Water Contact Angles

Several commercial UF-membranes are characterized by water contact angles. Two different methods of contact angle measurements, the sessile drop and the captive bubble methods, are compared. Differences in results between the two methods occur for the DDS GR 61 membrane; otherwise the methods give rather consistent results. The advancing and the receding contact angles are measured for the UF-membranes. All membranes show considerable contact angle hysteresis. The cellulose acetate and the polyacrylonitrile membranes show less hysteresis than the polysulfone and the polyolefine membranes. The order of hydrophobicity according to advancing contact angle is polyolefine > polysulfone > cellulose acetate > polyacrylonitrile. The contact angle data are compared with Hansens solubility data. Some correlation between θr and δtotal can be seen. θa correlates to the hydrogen and the polar part of the solubility parameter.

Contact angles of ultrafiltration membranes and their possible correlation to membrane performance

The captive bubble method was used to describe the wetting characteristics of a number of commercial ultrafiltration (UF) membranes. The membranes belonged to one of two homologous (same material, different cut-off) series made by the same manufacturer. One series was made of polysulphone and the other one of cellulose triacetate. The porosimetric characteristics of the membranes have also been measured. The combined data were used to explain the fouling behaviour of the membranes upon ultrafiltration of solutions containing dextran, whey protein concentrate and silicate sols. The cellulose triacetate series is characterized by lower receding contact angle and smaller contact angle hysteresis and shows better flux behaviour (permeate flux during UF and pure water flux recovery at the end of UF) than the polysulphone series. Within the same series the mean permeability pore size shows a better correlation with membrane flux behaviour than with contact angle hysteresis.

Solubility of three monoterpenes, their mixtures and eucalyptus leaf oils in dense carbon dioxide

The solubility of 1,8-cineole, alpha-pinene, limonene, their mixtures and the extract of eucalyptus leaf oils in supercritical carbon dioxide were determined using the dynamic method at 80, 100, 150, and 250 bar and 40 and 60 degreesC for each pressure. The results showed an increase in the solubility of all oils with an increase in pressure and a decrease with temperature. The mixtures of both pure blends as well as the eucalyptus oil extracts exhibited lower solubility than the pure single oil components in the same conditions. The oil of E. radiata exhibited a better separation of 1,8-cineole at 80 bar and 60 degreesC

Effect of fast CO2 pressure changes on the yield of lovage (Levisticum officinale Koch.) and celery (Apium graveolens L.) extracts

The effect of pressure alterations on the yield of CO2, extracts from different anatomical parts of lovage (Levisticum officinale Koch.) and celery (Apium graveolens L.) was studied. It was found that by applying frequent pressure changes in the extraction vessel it is possible to increase the rate of the isolation of CO2 soluble materials from lovage seeds and leaves, lovage and celery roots. However, after passing a sufficient amount of the supercritical solvent, the yields were similar both for constant and pulsing extraction pressures. The composition of the extracts was analyzed by gas chromatography and mass spectrometry and it was found that the phthalides were very important constituents in the extracts from all the anatomical parts of lovage, while linoleic acid was the most abundant component in the celery root extracts

Lipase-catalyzed alcoholysis of cod liver oil in supercritical carbon dioxide

Enzymatic alcoholysis of cod liver oil, with an immobilized lipase, was carried out in supercritical carbon dioxide. The enzyme was catalytically active under the experimental conditions used. The reaction medium was investigated to preferentially extract ethyl esters, synthesized during the course of the experiment, from the unconverted cod liver oil substrate and side-products. The effect of pressure changes on the amount of tri-, di-, and monoglycerides and ethyl esters, present in both the extract and the remaining lipid residue, was determined. Furthermore, the fatty acid compositions of the lipid classes were analyzed, and the relative amounts of both eicosapentaenoic acid and docosahexaenoic acid to palmitic acid were determined. The results show that it is possible to preferentially extract the synthesized ethyl esters at low pressures. The extract collected at 9 MPa contained 64 g ethyl esters/100 g extract, while the total amount of all other lipid classes detected was 19 g/100 g extract. As the pressure was increased, the relative amount of the other lipid classes detected in the extract, especially triglycerides, was enhanced. The relative amounts of both eicosapentaenoic acid and docosahexaenoic acid to palmitic acid increased for some lipid classes in the extract. This increase was most pronounced for the monoglyceride lipid class. The integration of biocatalysis and product fractionation, applied in this study, suggests that the potential for biocatalysis in industrial processes is considerably wider than had been thought.

Supercritical fluid extraction of borage (Borago officinalis L.) seeds with pure CO2 and its mixture with caprylic acid methyl ester

The influence of different pressures of CO2 and the addition of caprylic acid methyl ester as an entrainer was studied for the extraction process of borage seed. The increase of CO2 pressure from 100 to 350 bar resulted in the increase in extract yield from 0.14 to 24.29% (w/w) while the changes in the extract composition were not so considerable. The highest solubility of pure caprylic acid methyl ester in dense CO2 was determined at 100 and 300 bar (approximately 1 g of ester in 1 g of CO2). The addition of this entrainer increased the yield of pure extract up to 47.8 times at 100 bar, 2.4 times at 200 and 300 bar. Due to the high solubility of caprylic acid methyl ester at the lower (100 bar) pressure it is easy to separate the entrainer, which constituted only 4.22% of the total borage seed extract

Process parameters influencing ethanolysis of cod liver oil in supercritical carbon dioxide

Abstract Production of ethyl esters from ethanol and cod liver oil by an immobilized lipase (E.C. 3.1.1.3), Candida antarctica , in supercritical carbon dioxide is described. The effects of process parameters, such as density of the reaction/extraction medium, flow rate of the carbon dioxide, and ethanol substrate, were investigated. Further, the possibility of separating nutritionally valuable fatty acid ethyl esters during the process was evaluated. The results revealed that a high flow rate of ethanol influenced the purity of the product rather than promoting the enzyme reaction. Increasing the carbon dioxide flow rate did not strongly affect the extraction rate of ethyl esters, which suggests that internal diffusion/enzyme kinetics limit the efficiency of the process investigated. Additionally, the first fractions of the extracts obtained were enriched in short saturated fatty acid ethyl esters, whereas the last fractions contained a higher proportion of long unsaturated fatty acid ethyl esters.

Alcoholysis and glyceride synthesis with immobilized lipase on controlled-pore glass of varying hydrophobicity in supercritical carbon dioxide

Lipases from Humicola lanuginosa and Candida antarctica lipase B were adsorbed onto methylated controlled-glass beads with varying degrees of hydrophobicity. The effect of support hydrophobicity on the amount of lipase adsorbed was studied. The immobilized lipases were examined for their activity in an alcoholysis reaction of cod liver oil with ethanol in supercritical carbon dioxide. Furthermore, the activity of the immobilized Humicola lanuginosa lipase in glyceride synthesis in supercritical carbon dioxide was studied. For both lipases investigated, the amount adsorbed decreased with decreasing hydrophobicity of the support; moreover, for Humicola lanuginosa lipase, the lipolytic activity was found to depend largely on the substrate and the hydrophobicity of the immobilization support. In the alcoholysis reaction, a highly hydrophobic carrier enhanced lipase activity whereas in glyceride synthesis, the reverse effect was observed. For Candida antarctica lipase, the support hydrophobicity did not affect the activity of the lipase. In addition, the results showed that the lipid class composition of the reaction mixture reflected the lipolytic activity of the lipases immobilized on the different supports tested.

Gelatinization of cassava, potato and wheat starches in supercritical carbon dioxide

The gelatinization of cassava, potato and wheat starches in supercritical carbon dioxide was investigated using light microscope. The starch was placed in a stainless steel chamber at atmospheric pressure and high CO2 pressures, 8 and 30 MPa as well as at 8 MPa N-2 and the gelatinization degree observed by light microscopy. The results showed that both pressure and supercritical fluid affected the gelatinization degree. Cassava and potato starches showed a lowering of the gelatinization temperatures at 8 MPa and an increasing at 30 MPa as compared with the gelatinization degree at atmospheric pressure. For wheat starch, the decrease in the gelatinization temperature occurred in the same direction as the pressure increased, in comparison with the atmospheric pressure conditions. However, between the two applied pressures, there was a larger increase of the gelatinization temperature at 30 MPa than at 8 MPa. The effect of hydrostatic pressure component of the CO2 was evaluated by using N-2 at 8 MPa. The replacement of CO2 by N-2 at 8 MPa increased the gelatinization temperature for all the studied starches compared with the atmospheric conditions