Two liquid-solid reactions, in which the morphology of the solid changes as the reactions proceeds, were examined. One is the NA conversion in oil by decarboxylation on metal oxides and carbonates, and the other is the Kraft pulping in which lignin removal by delignification reaction. In the study of the NA conversion, CaO was chosen as the catalyst for the kinetic study from the tested catalysts based on NA conversion. Two reaction mixtures, carrier oil plus commercial naphthenic acids and heavy vacuum gas oil (HVGO) from Athabasca bitumen, were applied in the kinetic study. The influence of TAN, temperature, and catalyst loading on the NA conversion and decarboxylation were studied systematically. The results showed that the removal rate of TAN and the decarboxylation of NA were both independent of the concentration of NA over the range studied, and significantly dependent on reaction temperature. The data from analyzing the spent catalyst demonstrated that calcium naphthenate was an intermediate of the decarboxylation reaction of NA, and the decomposition of calcium naphthenate was a rate-determining step. In the study on the delignification of the Kraft pulping, a new mechanism was proposed for the heterogeneous delignification reaction during the Kraft pulping process. In particular, the chemical reaction mechanism took into account the heterogeneous nature of Kraft pulping. Lignin reacted in parallel with sodium hydroxide and sodium sulfide. The mechanism consists of three key kinetic steps: (1) adsorption of hydroxide and hydrosulfide ions on lignin; (2) surface reaction on the solid surface to produce degraded lignin products; and (3) desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than the reactions occurring in the liquid phase. A kinetic model has, thus, been developed based on the proposed mechanism. The derived kinetic model showed that the mechanism could be employed to predict the pulping behavior under a variety of conditions with good accuracy. / Chemical Engineering

Most metal ions have negative impacts on pulp mill operations. The concentrations of metal ions on pulp fibers and in washwaters rise significantly with increased wastewater recycling. The development of technology to remove these metal ions requires an understanding of how metal ions are bound to pulp components. It is also desirable to predict distribution of metal ions between the pulp fibers and the washwaters. The adsorption isotherms for eight metal ions (Ca, Ba, Mn, Zn, Pb, Cd, Ni, Na) were measured on bleached and unbleached (brownstock) kraft pulps at neutral pH and temperatures ranging from 25 to 75��C. On bleached pulps, the metal ion adsorption increased rapidly with increasing metal ion concentration in solution and then leveled off. At neutral pH, the adsorption on bleached pulp was stoichiometric to the carboxylate sites, whereas the adsorption on unbleached pulp was not, especially at high metal ion concentration in solution and low temperature. The pH isotherms specify the adsorption isotherms of sodium and calcium on wood pulps as pH ranging from 2.5 to 11.0. The pH isotherms on bleached pulp with only COOH functional groups (pK[subscript a] of 3.77) were saturated at pH 4 and above, whereas those on brownstock pulp with both COOH and PhOH (pK[subscript a] of 10) functional groups increased in two steps, at pH 4 and 8. The brownstock pulp is heterogeneous material. Therefore, only the empirical Freundlich model was applied to the data. To predict the metal ion adsorption on bleached pulps, two fundamental equilibrium models were developed: the multi-component ion exchange and the Donnan equilibrium models. The ion-exchange model better predicts the metal adsorption at neutral pH, whereas the Donnan equilibrium model more accurately predicts the pH isotherms. The adsorption kinetics of Ba����� and Ni����� were measured on wood pulps as a function of mixing speed, initial metal ion concentration, and temperature. The adsorption of metal ions reached equilibrium rapidly. The intraparticle diffusion model, based on first principle with a linear relationship assumption between adsorbed and free metal ion concentration, satisfactorily predicted the adsorption kinetics at low metal ion concentration in solution. / Graduation date: 2001

No description available.

No description available.

No description available.

No description available.

see pdf

No description available.

No description available.

No description available.