Mohamed Ghoul

Mechanisms for the selective rejection of solutes in nanofiltration membranes

Two tight nanofiltration membranes of 100 and 400 Da were tested at different operating conditions. The results show that the selective properties of nanofiltration membranes come from a combination of several physicochemical mechanisms. Mass transport is mainly diffusive in the 100 Da membrane, while two mechanisms of segregation exist in the 400 Da membrane. Large molecules are retained at the membrane surface by electrostatic and steric interactions and small, weakly charged ions can enter the pores. In these pores, the segregation is due to surface forces (electrostatic and friction) and the solvent can transfer by a convective mechanism.

Effect of different biochemical parameters on the enzymatic synthesis of fructose oleate

Enzymatic synthesis of sugar ester was performed using an immobilized Candida antartica lipase, fructose and oleic acid methyl ester as substrates and 2-methyl 2-butanol as a solvent. The influence of the molar ratio sugar/acyl donor, methanol concentration and temperature on the performance of the transesterification reaction were studied. When the molar ratio was adjusted only at the beginning of the reaction, the highest concentration of fructose oleate (16 g l−1) was obtained at a ratio of 1:5. When this ratio was kept constant throughout the duration of the reaction (by adding an excess of fructose or by continuous methyl-oleate feeding), 34 g l−1 and 39 g l−1, respectively, of fructose oleate were obtained at a molar ratio of about 1:8. The influence of methanol, which was a byproduct of the reaction, was also investigated. Results indicated that this compound was a strong inhibitor of Candida antartica lipase activity. The increase of temperature from 60 to 80 °C led to an increase of sugar ester concentration. However, the stability of the enzyme decreased as the temperature rose. At 80 °C, more than 90% of the initial activity was lost while at 60 °C, at the same time, only 30% was lost.

Enzymatic-catalyzed synthesis of alkylglycosides in monophasic and biphasic systems. I. The transglycosylation reaction

Enzymatic synthesis of butylgalactoside via the transglycosylation reaction of lactose was carried out using β-galactosidase from Aspergillus oryzae. Reactions were performed in monophasic (butanol phase) and biphasic systems (emulsified aqueous in butanol phase). The results indicated that water content was an essential parameter of this reaction. In the case of the monophasic system, addition of water led to a significant increase of product concentration. The highest concentration was obtained at 17% (v/v) of water. Conversely, in the case of the biphasic system, increasing the aqueous/butanol phase ratio (v/v) provoked a decrease of the final butylgalactoside concentration. In this system, the reaction performance was lower than that in the monophasic system. Lactose favorably influenced the reaction synthesis. However, at high concentrations, it led to a drastic decrease of the product concentration.

Optimization of butylgalactoside synthesis by β-galactosidase from Aspergillus oryzae

Response surface methodology (RSM) was used to optimize the enzymatic synthesis of butylgalactoside from lactose catalyzed by β-galactosidase from Aspergillus oryzae. The empirical models developed by using RSM were adequate to describe relationships between the operating conditions (temperature, water-to-butanol volume ratio, lactose concentration, enzyme concentration) and the responses (butylgalactoside concentration, conversion yield). Based on contour plots and canonical analysis, optimal conditions for maximizing butylgalactoside concentration were: temperature (45°C), water-to-butanol volume ratio (44%), lactose concentration (134 g/l), and enzyme concentration (1.5 g/l). Experimental data indicated that up to 24 g/l were produced at the optimum point. Maximum conversion yield of 79.5% was obtained at: temperature (46°C), water-to-butanol volume ratio (18%), lactose concentration (10 g/l), and enzyme concentration (1.5 g/l). The models were verified experimentally. Synthesis at a large scale was successful.

Enzymic synthesis of fructose monooleate in a reduced pressure pilot scale reactor using various acyl donors

Enzymic synthesis of fructose esters was studied under reduced pressure. Different acyl donors were tested, and immobilized Candida antarctica lipase was used as biocatalyst. Influences of pressure, nature of the acyl donor, molar ratio sugar/acyl donor were investigated. Pressure had the greatest influence. At 200 mbar, more than 90% of fructose was acylated compared to 50% under atmospheric pressure. This is explained by the evaporation of reaction by-product (methanol or water) that shifted the equilibrium. C. antarctica lipase catalyzed sugar ester synthesis very efficiently using rapeseed oil as acyl donor. Moreover, synthesis performed with an equimolar mixture of both substrates gave promising results. Although the reaction rate was slower than synthesis performed with an excess of fatty acid, fructose monooleate concentration was still high (44 g l−1 instead of 56 g l−1) and the residual acyl donor concentration was very low. Downstream processes for the recovery of pure fructose monooleate were simplified in this case.

Enzymatic-catalyzed synthesis of alkylglycosides in monophasic and biphasic systems. II. The reverse hydrolysis reaction

Abstract The β-glucosidase catalyzed synthesis of butylglucoside through the condensation of glucose and butanol was carried out in monophasic and biphasic systems. Water was indispensable for the enzyme activity. In the case of the monophasic system, product concentration increased with the increase of water content, but at high levels of water the equilibrium shifted towards hydrolysis and therefore the butylglucoside concentration decreased. An optimal water content of about 8–13% (v/v) was found. However, in the case of biphasic system, the increase of the aqueous/butanol phase ratio (v/v) was accompanied by a decrease of the butylglucoside concentration. An analysis of the causes of the equilibrium shift is given.

Extended Kalman filtering technique for the on-line control of OKT3 hybridoma cultures

Extended Kalman Filter (EKF) is used for the on-line estimation of viable cell and monoclonal antibody (MAb) concentrations during batch and fed batch cultures of the OKT3 hybridoma cell line. A kinetic model and an experimental system are presented. The practicability of EKF is demonstrated under both cultivation modes using glucose and ammonia as observation variables. For the same process duration, the concentration of viable cells and antibodies are twice as high in the fed batch as in the batch culture.