Abstract
This article is divided into two parts. In the first part, the authors present a comparison of the major techniques for the measurement of the molecular weight of macromolecules. The bibliographic results are gathered in several tables. In the second part, a comparative ebulliometer for the measurement of the number average molecular weight (Mn) of heavy crude oil fractions is described. The high efficiency of the apparatus is demonstrated with a preliminary study of atmospheric distillation residues and resins. The measurement of molecular weights up to 2000 g/mol is possible in less than 4 hours with an uncertainty of about 2%.
Highlights
The average molecular weights of a crude oil and of its fractions are fundamental data, which are required in the petroleum industry to develop descriptive and predictive compositional thermodynamic models
We used three atmospheric distillation residue (DV1, DV2, DV3) samples as well as the corresponding cuts obtained by SARA (Saturates, Aromatics, Resins, Asphaltenes) fractionation
The measurement lasts less than 4 hours, so the initial objectives were successfully attained
Summary
The average molecular weights of a crude oil and of its fractions are fundamental data, which are required in the petroleum industry to develop descriptive and predictive compositional thermodynamic models. The equipment generally used in this industry to measure such values are the vapor pressure osmometers (VPO or industrial tonometers). These osmometers often cannot give results with an accuracy better than about 10% for average molecular weights above 1000 g/mol. In every case, the analysis requires either time or money and significant analytical and technical expertise. These methods can be used only in an analytical center dedicated to research
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