Correlation between the amount of carbon in shale oils and carbon distribution of oil shales: estimation of carbon recovery by a multiple regression method

Abstract

Solid s ta te C P / M A S 13C N M R spec t roscopy is a very a t t rac t ive m e t h o d for the di rect d e t e r m i n a t i o n of the a roma t i c i ty of solid fuels. T h e r e are m a n y papers repor t ing the appl ica t ion of th is t echn ique to oil shale cha rac te r i za t ion [1,2]. Maciel et al. [I] proposed that aromatic carbon in oil shale kerogen is responsible for the carbonaceous residue in spent shale after retorting [ 3 ]. They also proposed a linear correlation between the percentage of aliphatic carbon in an oil shale and Fischer assay oil yield [4]. This correlation is useful for estimating Fischer assay oil yield from the results of other oil shales having similar characteristics. Problems with this correlation can arise due to depending on sedimentary factors such as geologic age and geographic location. Furthermore, the aromaticity of shale oil obtained by Fischer assay is considered to depend on that of kerogen [ 5 ]. A part of the aromatic carbon seems to contribute to the aromaticity of shale oil. This suggests that the aromaticity of kerogen has to be considered to estimate Fischer assay oil yield. We have recently determined the contents of aliphatic, aromatic and inorganic carbon in oil shales by solid state CP/MAS '3C NMR technique and elementary analysis. Then, from these results, we have estimated the percentage of carbon which formed shale oils by Fischer assay, using a multiple regression method. In this paper, we will define the carbon which is converted to that in shale oil by Fischer assay as 'converted carbon'. Although our experiment is designed to estimate Fischer assay 'carbon' yield rather than Fischer assay oil yield, it is considered valuable in estimating the oil yield because shale oil usually contains about 80 wt.% of organic carbon.