The influence of catalysis by mineral matter in determining the composition of shale oil produced by retorting is uncertain. This is investigated using, as test reactions, the isomerization of 1-octene and cyclopropane and the cracking of octene and isopropylbenzene. Measurements have been made with two spent shales, with the same shales after combustion, and with comparable kaolinite and montmorillonite clay minerals. For most of the reactions studied the order of catalytic activity is kaolinite > montmorillonite > combusted shale > spent shale. The low activity of the latter probably reflects its residual carbon content, which prevents the test compounds making contact with the surface of the minerals in it. The activity of the clay minerals and combusted shale for the isomerization of 1-octene to other n-octenes is great. Significant conversion is observed at temperatures as low as 126 °C. The following criterion for catalysis by mineral matter during retorting is suggested. If the n-olefins present in the shale oil are predominantly of the n-terminal type (i.e. 1-olefins) then catalysis by clay minerals is excluded. This seems to be the most usual situation in practice. For clay mineral catalysis to be inferred, the n-olefins of each carbon number should be near equilibrium and some branched olefins should also be evident.
- mineral matter in coal