Effect Of Solvent Treatment On Swelling And Diffusion Properties Of Low-order Coal

Liquid phase diffusion in coal particles,which mainly depends on the structure and propeities of coal,is an important factor affecting the direct liquefaction of coal and thermal dissolution process of coal.In order to investigate the effect of coal macromolecule relaxation and small molecular phase separation on the liquid phase diffusion in coal particles,Xilingele lignite(XL),Shenfu sub-bituminous coal(SF)and their treated coals,which prepared by soxhlet extraction with THF solvent,room temperature extraction with CS2/NMP mixed solvent and thermal dissolution with tolutene and tolutene/methanol mixed solvent at high temperature,respectively,were used as experimental samples.The swelling behavior and swelling kinetics of the two kinds of coal were investigated.Further,the liquid phase diffusion properties of two kinds of raw coal and pretreated coal were studied by the method of dissolution-out of probe.The results show that the swelling temperature significantly affects the equilibrium swelling ratios of raw coal and treated coal,and the higher temperature coal was swellened,the greater the swelling ratio.Ethanolamine aqueous solution is a very effective swelling solvent of XL coal,which equilibrium swelling ratio can reach the equilibrium swelling ratio of SF coal in pyridine solvent.Solvent extraction and high temperature thermal dissolution can loosen the coal macromolecule structure to a certain extent and lead to rearrangement of noncovalent bond crosslinking,thus the treated coal showed different the swelling behaviors.Although the swelling process of coal and treated coal follows Fickian diffusion,which is mainly controlled by solvent diffusion,but the solvent treatment reduces the swelling activation energy of coal to varying degrees.The pore size and porosity of the XL treated coal were significantly increased by comparison with those of the coal.The pore structure of the SF treated coal was close to that of the raw coal,and the diameter and porosity of the treated coal were not changed obviously.The diffusion kinetics studies showed that the diffusion coefficient of the liquid phase in the coal is mainly affected by the pore structure andthe degree of coal macromolecule relaxation,and the solvent treatment can relax the coal macromolecule structure to varying degrees,so that the effective diffusion coefficients of most treated coal are greater than that of raw coal.