A modified Gray-King assay method for small oil shale samples

A precise method for the assay of oil shales requiring only 10 g of shale per assay has been developed by modifying the Gray-King technique for the carbonization assay of coals. The precision of the method is illustrated by results obtained for a Queensland (Julia Creek) oil shale. Twelve sub-samples were assayed at 520 °C to give a mean oil yield of 6.77% with a standard deviation of 0.09%. At 500 °C the mean oil yield was 6.73% and the standard deviation 0.10%. Repetitive assays by the Fischer method yielded a mean oil value of 5.71% with a standard deviation of 0.06%. Significant departures from the Gray-King method include the use of an inert carrier gas to remove the pyrolysis products as they are formed, a more efficient condensate trapping system and an accurate method of measuring the water content. Separation of the water from the oil is the most critical part of the assay. Repeatable results can be obtained when boiling times are extended and the water retained on the condenser walls is collected. Assays can be conducted on the same-sized samples as used for chemical analysis, so that correlations can be attempted with greater confidence.