MECHANISM AND MOLECULAR DYNAMICS OF SUCCESSIVE SOLVOLYTIC EXTRACTION IN SIMPLE AND THERMOCHEMICAL DISSOCIATIVE SEQUENTIAL EXTRACTIONS UNDER AMBIENT PRESSURE CONDITIONS AND ROLE OF MOLECULAR ENTANGLEMENTS AND DISAGGREGATIONS

摘要

Assam coal was subjected to solvent extraction studies using 40 solvents belonging to different class, group and functionality. Boiling point of a solvent was found to have no relation with extractability of coal at atmospheric pressure, excepting within the same class, group and functionality of solvents. Boiling point should not be used for classifying the coal extractability, rather chemical nature of solvent should be used. Cetene (high boiling α-olefin), anthracene oil, liquid paraffin (through thermochemical dissociative extraction) and ethylenediamine (simple extraction) were found to give good extraction yields from Assam coal. Successive extraction of coal was possible only using anthracene oil or ethylenediamine. Chemical interaction of these solvents with coal which renders the enhanced amount of coal extractable through stepwise extractions has been discussed. Mechanism and molecular dynamics of solvent extraction of coal in AO, α-olefins etc. has been explained. This is a novel finding in coal chemistry. Stepwise extraction could cut short the total extraction time in anthracene oil. Anthracene oil and high boiling α-olefins extractions result in molecular fluidization of coal macromolecules under ambient pressure. Successive extractions of coal in low boiling solvents ( < 250℃) did not modify on the highest extraction yield of coal in the solvent used in the sequence, whereas in case of successuve chemical dissociative extractions it did. Swelling studies helped in the studies of the action of solvents on coal. Coal macromolecules have intertwined, intermeshed and entangled with each other to form almost macromolecular knots which inhibit the extraction and solubilisation of coal molecules without actually being chemically disengaged and dissociated. Role of molecular entanglements and disaggregation of coal macromolecules from these entanglements (involved in the three dimensional network structure of coal macromolecules) by the successive sequential attack of chemically different organic solvents has been explained for the first time. Coal consists of 5 different types of macromolecules having a range of different structural units and molecular sizes.