Influence of biodegradation on crude oil acidity and carboxylic acid composition

Quantitative analysis of separated carboxylic acid fractions of 33 crude oi ls from the UK, Italy and California, showed that the carboxylic acid fract ion is a major factor responsible for the acidity in these oils. It was app arent that biodegradation is the main process that produces high concentrat ions of carboxylic acids in these crude oils with the extent of biodegradat ion, as measured from their hydrocarbon compositions, being clearly correla ted with their total acid number (TAN). Although probably not important in influencing oil TAN, the distribution of C-30-C-32 hopanoic acids was also seen to be controlled by biodegradation, increasing in concentration for al l but the most biodegraded oils. Hopanoic acids with the 17 beta (H),21 bet a (H) stereochemistry were found in many of the biodegraded oils, and were thought to be mainly derived from the bacteria that were responsible for th e biodegradation of the oil. This may have implications for the timing and mechanisms of the biodegradation involved. The role of C-0-C-3 alkylphenols in determining oil acidity was investigated and shown not to be a signific ant factor in the sample set studied. However, a number of undegraded oils, with low carboxylic acid contents were seen to have relatively high acidit ies, showing that factors other than biodegradation, possibly related to hi gh sulphur content can control oil acidity in certain oil types. (C) 2000 E lsevier Science Ltd. All rights reserved.