2003 Volume 82 Issue 2 Pages 103-110
Inorganic solid particles accumulated in the reactor of NEDOL bituminous coal liquefaction process were analyzed after their separation into larger and smaller particles than 106μm by SEM, XRD and solid-state 29 Si NMR. The larger particles than 106μm were extracted with HCl and aqua regia to observe residual core particle and to analyze the extracted inorganic substance by atomic adsorption and ICP.
The larger particles were found to carry silica and kaolinite core, and layered shells of Fe1-xS, CaCO3 of which cations were confirmed to be present in the extract. The smaller particles of uniform structure consisted principally of SiO2, Fe1-xS with small amount of Al2O3. Solid-state 29 Si NMR indicated variety of silicate compounds from siloxane (-60ppm) to quartz (-101ppm) in the particles. It is noted that the low temperature ashing provided similar kinds of ash particles to those found in the reactor, however there was no core-shell structured coagulation of particles, or quartz in the ash. Liquefaction conditions are very influential on the chemical species and their morphologies, suggesting the signifi-cant reactivity and deformability of the inorganic substances in the coal under liquefaction conditions.
Based on the above observation, accumulated particles in the reactor are produced by the following schemes.
1) Core-shell particle larger than 106μm is produced through deposition and adhesion of very fine Fe1-xS, CaCO3, SiO2 and siloxane particles to form the shell layer on the silica or kaolinite cores.
2) Core particles of SiO2 or quartz are produced through degradation of kaolinite or decomposition of siloxane. High crystallinity of SiO2 may be obtained through hydrothermal reaction under liquefaction conditions.
3) Uniform particles grow through deposition and adhesion of the fine particles of high reactivity such as CaCO3, SiO2 or Fe1-xS under liquefaction conditions.
4) Molecular forms of inorganic substances in coal are converted under liquefaction conditions into fine oxides, sulfides and carbonates, which have high reactivity or deformability for their adhesion, even fusing or crystallizing through hydrothermal reactions. Such a very fine particle, especially of SiO2 is a characteristic of the deposited solid in the liquefaction of Tanitoharm coal. They are assumed to be derived from kaolinite through its degradation and siloxane through its hydrolysis. Such a scheme of deposit formation appears contrast to that of brown coal which is basically derived from ion-exchangeable calcium ion.
