Chemical evaluation of crude oils by programmed thermogravimetric analysis

Abstract

A method for the chemical evaluation of crude oils is described using a thermogravimetric analysis technique. In this method, a heating program is established including constant heating rate steps and two isothermal steps at 350 and 550°C for two minutes each. Following this program, the thermogravimetric curves indicated two distinct weight loss steps. The first was between 25 and 350°C, L + M, and the second was between 350 and 550°C, H. The values of L + M, H and the residual material above 550°C, R, were found to be independent of the heating rate and were characteristic of the crude oil analysed. The method was tested on seventeen crude oils with API gravity values of 42 down to 15.8. At a moderate heating rate (50°C min −1) a test run took only 15 min from which the above characteristic fractions could be estimated. These fractions, in addition to the ratio (L+ M)/H + R) were correlated with the API gravity, and the vanadium and sulphur contents of the corresponding crude oils. Some useful relationships could be obtained.