51314-4117-Evolution of Oil Organic Acids Using a Laboratorial Distillation Unit

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Product Number: 51314-4117-SG

ISBN: 4117 2014 CP

Author: Flora Machado

Publication Date: 2014

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The presence of organic acids in petroleum and their effects are clearly described in the relevant literature mainly by the term "naphthenic acid corrosion". Traditionally the structure of naphthenic acids includes the presence of at least one ring with six saturated carbon atoms. Currently this term also includes linear acids. Naphthenic acid content is usually represented by total acid number (TAN) which is reported in mgKOH.g-1 of sample. Studies suggest that corrosion rate is not directly related to TAN values but depends on the structure of acid species present in the oil the operation temperature and sulfur content among others. These acids exist in relatively low concentrations in oil. Depending on the boiling point of these compounds these acids can be concentrated in certain cuts during the distillation process and can cause non-watery corrosion under high temperatures. Short-chain acids — mainly from one to four carbon atoms — are concentrated in the system at the top of refining towers worsening corrosion of watery solutions in these systems. Thus this study aims at quantifying and specifying acids from one to four carbon atoms which reach the top of the distillation column during the distillation of Brazilian oils. It also investigates the possible degradation process during distillation of acid species with higher molecular weight. Methodology of this study comprises the process of distillation of oils from different sources in a laboratorial manual distillation unit adapted for capturing acids at the top of column. The crudes their cuts and the residue generated after compliance with standard ASTM D2892 were subject to quantitative acidity investigation. Through the acid capture system a watery extract was produced. From this extract formic acetic propionic and butyric acids were quantitatively analyzed through ion chromatography. Through acidity mass balance the study verified that initial acidity in oil was generally higher than that of cuts and residue after distillation which suggests acidity loss through thermal degradation of naphthenic acids. The analyses of extracts obtained at the top of the column showed significant contents of short-chain organic acids.