Part I: TheoryBased on the concept of reactions in a continuum, a mathematical model has been developed to simulate coal liquefaction kinetics. In an excess hydrogen donor environment, the rate-limiting reactions are considered to be irreversible cracking reactions involving cleavage of carbon and oxygen linkages. Concurrent evolution of a wide spectrum of products, with an initial rapid formation of species of high carbon and oxygen contents, followed by progressively slower reactions leading to lower carbon and oxygen content species is predicted. Simple lumping functions are employed to obtain conventional lumped pseudocomponents (preasphaltenes, asphaltenes, and oils). Parameter analysis has been carried out. SCOPEIn reactions that involve numerous species it is often not practical to develop kinetic models that describe the behavior of all the participating species. It is convenient to group together various species and treat them as pseudocomponents. Models based on such an approach have been termed lumped kinetic models. The success of such a model depends upon the kinetic similarity of the species present in a lump. The numerous product species obtained upon liquefaction of coal are usually lumped together into several groups based on solubility criteria. For example, the fraction of coal liquefaction product that is soluble in benzene but not soluble in pentane is given the name asphaltenes.The lumped models based on such pseudocomponents are essentially correlative in nature and have very little scope for generalization. Hence they cannot be used to predict the liquefaction behavior of coals other than the one used in developing the model. Thus there is a need for a fundamental model that can describe the processes occurring during liquefaction of coal. This work presents one such approach to a fundamental model based on the concept of reactions in a continuum (Aris and Gavalas, 1966). Such a concept is likely to be valid in the presence of a numerous species where the concentrations and kinetic rate constants of the species present in the mixture can be specified by continuous distribution functions. The distribution, which is a statistical measure of composition and reactivity of the species present in the mixture, will depend upon one or more state variables chosen to identify the structure and functionalities of the species present in the mixture. This paper attempts to generalize the reactions that occur during liquefaction of coal, using the continuum approach. CONCLUSIONS AND SIGNIFICANCEA fundamental model based on the concept of reactions in a continuum has been developed to simulate the rate processes occurring during liquefaction of coal. The reaction mixture has been described ,in terms of two state variables, the number of carbon atoms and ronment of excess available hydrogen the rate-limiting reactions can be considered as thermal cracking reac-
Carbon deactivation of a 0.5 wt % Ru/7-AI203 surface-impregnated catalyst was studied by using a Berty continuous-stirred, gas-solid reactor (CSGSR)-gas chromatograph setup. The experimental variables were as follows: temperature, 473-573 K; pressure, 2-6 atm; weight hourly space velocity, 0.85, 16.5 h_1; H2/CO feed ratio, 3 and 2; and synthesis time, 0.5-5 h. Carbon deposited in a synthesis run was measured by integrating the methane evolution profile during catalyst reduction at 723 K in H2. Significant amounts of carbon were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C2-C4 hydrocarbons showed a maximum during the initial stages of deactivation. The kinetic data could be correlated by assuming both hydrogen-assisted CO dissociation and hydrogenation of surface carbon to be rate determining. The turnover numbers for methanation (NCHf) and carbon deposition (A/C/FJ are given by eq 3 and 4.
Carbonyl sulfide and methyl mercaptan were interacted with anhydrous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), di-2-propanolamine (DIPA), methyldiethanolamine
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...
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