Interest of a chemometric approach in understanding the retention behaviour of three columns in hydrophilic interaction liquid chromatography: application to the separation of glycerol carbonate, glycerol and urea.

A chemometric approach was used to study the retention behaviour of glycerol, urea and glycerol carbonate in hydrophilic interaction liquid chromatography (HILIC). First, a simplex method was developed to optimize the sensitivity of an evaporative light scattering detector. A mixture design was then applied to model retention factors as a function of the mobile phase content in acetonitrile, water and methanol on three columns: Atlantis HILIC Silica, ZIC-HILIC and Monochrom diol. Atlantis HILIC Silica exhibits predominantly hydrophobic interactions, while retention on the other two columns is mainly ruled by hydrophilic interactions. Finally, a desirability function is applied on the resolution factors. The use of this function enables the compositions of eluent phases to be determined in order to achieve separation between the three chemicals. Monochrom diol proved to be the most efficient column.

Kinetic modelling of the degradation of the alpha-tocopherol in biodiesel-rape methyl ester.

The aim of this work was to study the influence of three major factors (light, atmospheric oxygen, temperature) responsible for the degradation of tocopherols. The evolution of alpha-tocopherol contents was analysed by high-performance liquid chromatography. Taguchi's experimental design was applied to establish a mathematical model of alpha-tocopherols degradation in function of the studied parameters especially in a domain of temperature between 50 degrees C and 150 degrees C. The results show that the major factor is the temperature, especially above 100 degrees C. Light is a negligible factor, meaning that degradation is mainly due to an autoxidation phenomenon. Moreover, only interactions between temperature and atmospheric oxygen have been observed especially above 100 degrees C. The mathematical model was validated for a temperature of 75 degrees C and permits to calculate a predictive speed of degradation in this domain.

Purification of sugar beet vinasse - adsorption of polyphenolic and dark colored compounds on different commercial activated carbons.

The adsorption on activated carbons of dark colored compounds contained in sugar beet vinasse was studied. Four commercial activated carbons with different properties (particle size, residual acidity and microporous properties) were respectively checked for efficiency at two temperature levels (25 degrees C and 40 degrees C) and at four pH levels (2,3.5,7,10). The adsorption of organic molecules was determined by quantifying the amounts of total polyphenolic compounds and total organic carbon. The results showed that the adsorption capacity of dark colored compounds was enhanced by the decrease in both temperature and pH values of the solution. In this study, it is shown that this capacity depends on activated carbon characteristics which can be classified in the following order: particle size>residual acidity>microporous volume. Three models (Langmuir, Freundlich and Dubinin-Radushkevich) were tested from experimental data and compared. The Langmuir model provided the best correlation on all the activated carbons studied.

Removal of lead (II) ions from synthetic and real effluents using immobilized Pinus sylvestris sawdust: adsorption on a fixed-bed column.

The purpose of this work was to evaluate the potential of Pinus sylvestris sawdust, in a continuous flow removal of lead (II) ions from synthetic and industrial aqueous effluents. The kinetic parameters obtained in a batch process were used to scale-up the process on a mini-column and to choose the breakthrough model. The column experimental data concerning the volumes treated were correlated using the bed depth service time model. These experimental data closely fitted the bed depth service time model at 10% of the breakthrough curve. The results from the bed depth service time model on the mini-column were then used to design a pilot plant adsorption unit. The performance of the pilot plant column accurately agreed with that obtained from the mini-column. The experiments carried out in a dynamic reactor allowed to bring out the influence of various parameters on the efficiency of the P. sylvestris sawdust. In addition, the process was checked for the treatment of industrial aqueous effluents on a pilot plant scale and the results were in accordance with those obtained from synthetic effluents.

Removal of Cd(II) and Pb(II) ions, from aqueous solutions, by adsorption onto sawdust of Pinus sylvestris.

Fixation of heavy metal ions (Cd(II) and Pb(II)) onto sawdust of Pinus sylvestris is presented in this paper. Batch experiments were conducted to study the main parameters such as adsorbent concentration, initial adsorbate concentration, contact time, kinetic, pH solution, and stirring velocity on the sorption of Cd(II) and Pb(II) by sawdust of P. sylvestris. Kinetic aspects are studied in order to develop a model which can describe the process of adsorption on sawdust. The equilibrium of a solution between liquid and solid phases is described by Langmuir model. Scanning electronic microscopy (SEM) coupled with energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) shows that the process is controlled by a porous diffusion with ion-exchange. The capacity of the metal ions to bind onto the biomass was 96% for Cd(II), and 98% for Pb(II). The sorption followed a pseudo-second-order kinetics. The adsorption of these heavy metals ions increased with the pH and reached a maximum at a 5.5 value. From these results, it can be concluded that the sawdust of P. sylvestris could be a good adsorbent for the metal ions coming from aqueous solutions. Moreover, this material could also be used for purification of water before rejection into the natural environment.

Modelling of influential parameters on a continuous evaporation process by Doehlert shells.

The modelling of the parameters that influence the continuous evaporation of an alcoholic extract was considered using Doehlert matrices. The work was performed with a wiped falling film evaporator that allowed us to study the influence of the pressure, temperature, feed flow and dry matter of the feed solution on the dry matter contents of the resulting concentrate, and the productivity of the process. The Doehlert shells were used to model the influential parameters. The pattern obtained from the experimental results was checked allowing for some dysfunction in the unit. The evaporator was modified and a new model applied; the experimental results were then in agreement with the equations. The model was finally determined and successfully checked in order to obtain an 8% dry matter concentrate with the best productivity; the results fit in with the industrial constraints of subsequent processes.