Coal liquefaction with methanol

Small 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^-1