Browsing by Subject "Coal liquefaction"
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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 Catalyzed and uncatalyzed batch reactions of methanol with coal.(Texas Tech University, 1975-05) Garner, Donald NanceNot availableItem Coal liquefaction with methanol(Texas Tech University, 1986-05) Liu, Chen-lunSmall particles of Texas lignite from the Wilcox formation at Limestone, Texas, were reacted with methanol In a 1-liter batch reactor at three different temperatures (264. 278. and 292 °C). The reaction times varied from 30 minutes to 120 minutes under autogeneous pressure. Additional runs using programmed heating consist of keeping the reaction system at a low temperature (in this case 187 °C for 8 hours) and heating up to the desired temperature was also performed. This allows the selective activation of a particular step in a complicated reaction mixture, helping clarify complicated reaction sequences. To analyze the kinetic data for this reaction system, three reaction models were selected. The first model assumed a single step first order reaction of the organic to solubles. The second assumed two competitive reactions from the original organic content to solubles and residue. The third assume a Gaussian distribution for the activation energy. To find the best set of kinetic parameters that fit the data, the Nelder-Mead Simplex method was selected using a least square approach applied to the conversion to solubles as the objective function. To solve the resulting differential equations for each case, a modified Coats and Redfern approximation was used for the single first order reaction and the Backward Difference Formation of the Gear package was selected for the other case. Analysis of the kinetic data indicated no shifts in the reaction curves; henceforth a sequential reaction model seems to be the prevalent reaction path. The parameters calculated using a first order model as proposed by Hill et al. gives an activation energy of 23.62 Kcal/mole and frequency factor of 5.12x 10^5 min^-1Item 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.)