Dynamic Procedure for Solid/Vapor and Liquid/Vapor Equilibria of Heavy Alkanes

Vapour and sublimation pressures are fundamental data required in petroleum industries to develop thermodynamics models, molecular modelling or ab initio calculations. Our laboratory has a long tradition in low pressure measurements particularly in the low pressure range (down to 1 Pa) using a static apparatus and down to 10-4 Pa using a gas saturation apparatus. In the present study we have studied vaporisation and sublimation pressures of 3 paraffins using an apparatus based on the saturation of an inert gas followed by a chromatographical analysis. The originality of this apparatus consists in the use of a standard compound along with the sample and its completely automatic operation. Both compounds are simultaneously swept by the inert gas into a cold capillary column where they are trapped. The 2 compounds are then eluted by heating the column and detected by an FID. The present apparatus is totally automatic as all the valves are controlled by the GC output. It allows sublimation and vapor pressures measurements in the range between 10-4 Pa and 1 kPa with the following uncertainty: 5% for pressure between 10-4 Pa to 10 Pa 2% for pressure between 10 Pa to 1 kPa During the conference we will present the apparatus, the experimental results obtained for the 3 n-alkanes, the comparison with literature data when available.