Rationalization for the molecular weight distributions of Coal pyrolysis liquids

Abstract

A model for coal thermal depolymerization is described and used to predict molecular weight distributions (MWD) of primary coal pyrolysis liquids. The model assumes that rupture of kinetically similar bonds in the coal is the preferred pathway for release of oligomers which ultimately become tars or extractables. The analysis provides the liquids MWD as a probability function of finding different oligomers composed of whole integer numbers of monomers and it is in excellent qualitative agreement with measured MWDs of coal pyrolysis liquids. The predicted MWDs are of the form of the gamma distribution function (GDF), and its parameters are interpreted in terms of the postulated chemistry of coal thermal depolymerization. Consequently, successful empirical correlations of experimental data on coal pyrolysis liquids MWDs with the GDF are better understood. Thus a protocol is provided to predict MWDs of pyrolysis liquids from knowledge of coal molecular structure.

Degradation kinetics of polymers in solution: Time-dependence of molecular weight distributions. [Quarterly report, January--March 1996]

“…versatile representation of naturally distributed systems (e.g., Darivakis et al, 1990;Wang et al, 1994), and is chosen to represent the MWDs,…”

Chemical kinetics and transport processes in supercritical fluid extraction of coal. Final report, August 10, 1990--December 30, 1992

“…This MWD varied with time and, according to the model, eventually yielded a mixture of molecules ali having an identical, minimum MW. Darivakis et al (1990) applied probabtlity theory to develop a model for coal thermolysts to showed that a gamma distribution function can successfully fit experimental MWD data. Although the model interpreted the MWDs of pyrolysis products, it did not consider rate expressions for the thermolysis reactions.…”

“…Here we present a rate theory based in part upon the concepts presented by Darivakis et al (1990) and combined with concepts of continuous-mixture kinetics. The model builds on earlier approaches, and introduces the following novel features: • Regular polyaromatic units connected tnto the main structure by two linkages.…”

“…Following Darivakis et al (1990), we assume that the MWD of each group of extractable polyaromatic units is described by a gamma distribution,…”

“…(6-5) and Eq. (6-11 ) leads to the following solution Two types of parameters appear in this model: those in the three gamma functions describing the initial MW distributions of extractable polyaromatic units in coal, and the rate coefficients for the thermolysis of the extractable groups, lt was reported (Darivakis et al, 1990) that the range of a is 1.3-3.0, but the most likely value is 2. In our simulations we fixed a = 2 for the three gamma functions.…”