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-