Rapid Determination of Total Acid Content of Oils Resulting from Sub/Supercritical Water Liquefaction of Lignite by Headspace Gas Chromatography

This paper reports a headspace gas chromatographic method (HS-GC) for the rapid determination of the total acid content of oils resulting from sub/supercritical water liquefaction of lignite. Acids in the oil react with added bicarbonate solution to release carbon dioxide (CO2), which is quantitatively measured by GC. The reaction goes to completion in less than 10 min at 60 degrees C. Use of larger samples of oil, to increase the sensitivity of the method, results in reduced CO2 formation. This effect can be minimized if the volume ratio of bicarbonate solution to sample is greater than 10. Three replicates of the method had a relative standard deviation of less than 6.0%; the limit of quantification (LOQ) was 3.95 mu mol; and the recovery ranged from 94 to 105%. The present method is simple, rapid, and practical. It is suitable for total acid content testing in the samples from the liquefaction of lignite or possibly other related materials.