Continuous reaction mixture model for coal liquefaction kinetics

Abstract

Nomenclature Axx(f) = rms spectrum defined as the square root of the amplitude of the power spectral density at frequency f E = time-averaged emulsion phase fraction f = frequency, Hz R = rms of pressure signal, kPa V = the mean of capacitance probe signal measured during a period of several minutes, V V , = capacitance probe response to 100% void, V V, = the most probable signal amplitude obtained from a capacitance probe response to hydrodynamics dominated by the emulsion phase, V Greek Letters z = time-averaged bed voidage to = emulsion-phase void fraction Literature Cited Potter, 0. E.; Whitehead, A. B. Chem. Eng. Sci. 1979, 34, Nguyen, H. V.; Whltehead, A. B.; Potter, 0. E. AIChE J . 1977, 23, 913. Nicastro. M. T. M.S. Thesis, Department of Mechanical Engineering, Massachusetts Institute of Technology, 1982. Sadasivan, N.; Barreteau, D.; Laguerie, C. Powder Techno/. 1980, 26, 67. Sitnai, 0. Chem. Eng. Sci. 1982, 37, 1059. Svoboda, K.; Cermak, J.; Hartman, M.; Drahos, J.; Selucky, K. Ind. Eng. Werther, J.; Molerus, 0. Int. J. Multiphase Flow 1973, 1 , 123. Whitehead, A. 8.; Dent. D. C.; McAdam, J. C. H. Powder Techno/. 1977, 18, 27, 388. 1163. Chem. Process Des. Dev. 1983, 22, 514. 231.The complex reactions taking place in the coal liquefaction process have been described in terms of a continuous reaction mixture with the molecular weight as a single state variable. A kinetic model, based on this approximation as well as on simple fission of molecules, in which the reactivity of coal is described by a reaction rate function k , and the reactions between the product species by a reaction rate function k,, has been developed. The resulting new mathematical model, glving the amount of coal undissolved and the molecular weight distribution of the species produced at a given time in a batch reactor, is amenable to the solution of an integrodifferential equation. With simple reaction rate functions, referred to as rate kernels, a very fast converging iterative type of numerical solution has been used. Available kinetlc data, which include molecular weight distributlons for liquefaction products from a subbituminous coal at 427 O C , have been successfully correlated with the simple dimensionless rate kernel, k , = lOy'(yy'), where y and y' are the scaled molecular weights of the reactant and lighter product, respectively, and are shown to be insensitive to the nature of the function k,, even for the shortest reacting time of 10 min.Thus these data yield no information on coal reactivity, whereas the overall reactivity of the product species falls off as the cube of its molecular weight. Stable species having molecular weights of naphthalene, disubstituted naphthalenes by CH, and OH, and species with up to five aromatic rings are unreactive and do accumulate.It is shown that the vertical concentration profiles observed at the steady state in systems in which the jetsam has a minimum fluidization velocity comparable to that of the flotsam cannot be explained solely on the basis of settling of jetsam particles relati...

Continuous‐Mixture kinetics of thermolytic extraction of coal in supercritical fluid

“…Our data for the MWDs, as well as that of Syamlal and Wittmann (1985) and Franz et at. (1981), show that multiple, overlapping peaks appear in the product distribution.…”

Continuous-mixture kinetics of coal thermolysis in supercritical fluid. [Quarterly technical progress report, August--October 1992]

“…The linkages between monomeric units are methylene, ethylene, and ether bridges. Our data for the molecular weight distribution (MWD), as well as Syamlal and Wittmann (1985), show that multiple, overlapping peaks may appear in the product distribution. Oil shale extraction likewise yields multipeak IvIWDs (Tahiti et al, 1988).…”