Phenolic compounds can be found in industrial or agricultural waste, such as waste water from olive mills. Because of the environmental problem caused by this residue from olive oil production, the aim of this work was to model the effect of salts on the solubility of four phenolic compounds. For this purpose, the solubilities of gallic acid, protocatechuic acid, vanillic acid and vanillin have been measured in various chloride solutions at constant temperature. The Clegg-Simonson-Pitzer activity coefficient, together with the dissociation constant obtained from the literature, has been used to represent the equilibrium solid-liquid data. Good agreement (3.4%) between the experimental and calculated values for solubility was obtained.

No abstract

The kinetic of the reaction of sand with aqueous NaOH corresponding to the ratio Si02/Na20 = 2 was studied in a pressure vessel at 22OOC and 2.7 MPa. Since the kinetic curves could not be obtained directly from the experimental data, a new method is proposed to plot the entire kinetic graph from experimental data. An analytical expression of the type Q = A [I -exp(-Bt)] describes the system perfectly. The constants A and B were calculated for a silica sample having a narrow granulometric distribution (range i.e. 300-315 pn). The value ofA is found to be almost constant, between 0.95 to 0.99 and B ranges from 0.03 to 0.14 when [OH-] increases from 0.5 to 12.5 mol/L. The kinetic order with respect to O K is equal to 0.470 f 0.013 and the kinetic constant at 220°C is 3.933 x lod g/m2 .s. ~~On a etudie la cinetique de la reaction du sable avec du NaOH aqueux correspondant au rapport SiO,/N%O = 2 dans un reservoir sous pression a 22OOC et 2,7 Mpa. Etant donne que les courbes de cinetique n'ont pas pu &tre obtenues directement des donnees experimentales, une nouvelle methode est proposee pour tracer le diagramme cinetique au complet au moyen des donnees experimentales. Une expression analytique du type a = A Keywords: solid-fluid reaction, sand, sodium hydroxide, silica dissolution, sodium silicate.he study of non-catalytic reactions involving a fluid and T a solid is of a growing interest in chemistry (in applications such as leaching, silica descaling, metal corrosion). There are several difficulties when the measurements of the kinetics of the transfer of material from the solid to the dissolved phase are made. Some difficulties occur because the reaction products can be insoluble precipitates which may adhere to the reagent surface and induce reaction-blockage. Furthermore, differences of reactivity are also observed if the solid is covered with an amorphous layer such as silica, or an oxide layer, such as may occur for some metals.The solid can also be comprised of an aggregate of phases which have different physical and chemical properties, such as a phosphate ore where the apparent reactivity is the sum of the reactions of each phase. On the other hand, the rate of solid dissolution depends markedly on the solid morphology, as well as on its porosity. If the external form of the grains is irregular, the study of surface kinetics becomes more complicated. The presence of asperities, which have a better contact with the fluid, leads to a faster surface reaction.The great variety of cases which may occur explains the various forms of kinetic curves. Studying the weight loss or change in solution concentration during the dissolution of many solids, Barret (1973) found that the general form of the kinetic curves can be sigmoidic, parabolic, linear, logarithmic, exponential, etc.Sigmoidal dissolution curves show an induction period, which corresponds to a very slow starting of the reaction during an initial time, most commonly called "induction time". Such curves were observed by Cornell and Giovanoli (1 993) during t...

No abstract

No abstract