Determination of the water content of crude oil by thermometric titration

The water content of crude oil needs to be accurately and conveniently determined. A thermometric titration method in which triethyl orthoformate and water react stoichiometrically and then absorb heat has been developed to determine the water content of crude oil. Triethyl orthoformate solution was used as the titrant; a mixture of cyclohexane, isopropanol, and xylene was used as the solvent; and dodecylbenzene sulfonic acid was used as the catalyst. The optimized method has a water mass range of 5 to 300 mg. The upper limit of water mass (300 mg) was greater than those of Karl Fischer coulometric titration (KFCT) and azeotropic distillation-KFCT (AD-KFCT). Real-time calibration by alternatively measuring the sample and a standard and modifying the result by the neighboring recovery was used to reduce the effect of the shift of the calibration curve. The effect of the types of catalysts and titrants was investigated. When the certified reference materials of light or heavy crude oil for water content were measured, the relative standard deviation and absolute value of the relative error of the results were ≤ 1.2% and ≤ 3.9%, respectively. The repeatability and accuracy were better than those of the distillation, KFCT, and AD-KFCT. The present method can determine the water content of commercial crude oil with good accuracy and convenience, and thus has the potential to be an international standard method.