Browsing by Subject "Lignite -- Texas"
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Item Aqueous alkaline liquefaction of Texas lignite(Texas Tech University, 1985-08) Shah, RajivSmall particles of Texas lignite, Wilcox formation, were reacted with 0.5 and 0.25N solutions of sodium hydroxide in a two-liter batch reactor. The reaction times varied from 1 to 8 hours and were carried under an autogeneous pressure. Temperature levels of 100, 130 and 160°C were used. Maximum conversion levels of around 75 to 90% were discovered for these temperature- time combinations. The behavior of the kinetic data for this reaction system pointed to a two-step mechanism for the thermal dissolution of the lignite. A special numerical technique was developed to retrieve the best set of kinetic parameters, for the simplified two-step reaction model, that can represent the experimental data. For the first reaction, an activation energy of around 3000 kcal/mole was found for both a first- and second-order reaction, showing some kind of diffusion-controlled reaction or the breakage of yery weak bonds. The latter hypothesis was selected because the product extracted was found to be soluble in organic solvents in which the original coal was not soluble. Asphaltene yields of up to 10% weight fraction from the soluble fraction were reported. The second step of the reaction had an activation energy of around 16,000 kcal/mole that will represent the reaction of soluble material back to insoluble. Higher extraction yields and asphaltene production was reported for the alkaline concentration, indicating a direct correlation between ionic strength and the amount of lignite reacted. The results presented in this thesis validate the concept of the use of alkaline solutions as the optimal solvent for in-situ lignite liquefaction due to their high extraction yields, low severity operating conditions, and the low cost solvent used.Item Aqueous alkaline liquefaction of Texas lignite under an oxygen atmosphere(Texas Tech University, 1988-05) Garza, Hector ANot availableItem Determination of pyrolysis kinetic parameters of San Miguel (Texas) lignite(Texas Tech University, 1982-08) Jih, Jefferson Shau-tungThe kinetics of San Miguel (Texas) lignite pyrolysis was investigated in range of 650 to 800°C at atmospheric pressure. An experimental system which facilitated the monitoring of the actual sample temperature, collection of gas and tar, and measurement of sample weight loss as a function of time was used. It is found that, in the range investigated, lignite decomposition into gas, tar, and char can be described by three parallel first order reactions. Examination of experimental data indicated that, in the range investigated, the rate of pyrolysis is controlled by intraparticle heat transfer. A simplified kinetic-transport model was used to estimate the individual reaction rate constants and the activation energies. The amount and composition of the pyrolysis gas products were also analyzed. The gas produced consisted mainly of carbon dioxide, carbon monoxide, hydrogen, and some low hydrocarbons. The hydrocarbon products consisted mainly of methane, ethane, ethylene, and trace amounts of C+3 compounds.Item In-situ mining of Texas lignite with sodium carbonate aqueous solution(Texas Tech University, 1986-08) Ouyang, WenNot availableItem Reaction model for the thermal dissolution of Texas lignite(Texas Tech University, 1985-08) Patel, Prakash DA kinetic model for the thermal dissolution of Texas lignite from the Yegua formation at San Miguel, Texas has been proposed. The lignite was liquefied in a 1-liter batch reactor at three different temperatures (350, 360 and 385ºC) using tetralin as a hydrogen-donor solvent. The reaction times varied from 15 minutes to 2 hours under autogeneous pressure. Additional runs using programmed heating were performed. This allowed the activation of a particular step in the reaction sequence by soaking the system at a lower temperature level (240 and 275*0 for 8 hours) and then heating up to the desired temperature. This selective activation helped clarify the overall mechanism of this complicated reaction scheme. Analysis of the kinetic data has indicated no shifts in the reaction curves (conversion versus time), henceforth a sequential reaction model C → 0 where C = Lignite C = Oils seems to be the prevalent reaction path. The kinetic parameters calculated using a first order model as proposed by Hill et al. gives an activation energy of 21 kcal/mol and a frequency factor of 2.5 ^ 10 min. These values were obtained using a nonlinear search that gave the best least square fit for the rate curves. The activation energy for the lower temperature step (soaking) does not vary, but the frequency factors increased by 50%, indicating more frequent molecular collisions. (This phenomenon could be explained by the release of the macromolecules from the lignite matrix due to the lower temperature preheating.)