Understanding wax appearance temperature in light crude oils by DSC,NMR, and HT-GC

The wax precipitated from oil mixtures primarily consists of C18 to C36 (macro crystalline waxes) or C30 to C60 (micro crystalline waxes), both made of aligned paraffinic and naphthenic molecules. Paraffins have significant impact on wax deposition characteristics as paraffin waxes react and respond easily to temperature changes due to its straight chain structure. In this paper, 12 light crudes of different origin were analyzed by DSC. Method was standardized for the determination of WAT in light crudes and these were found to have WAT ranging from 10 to 30°C. Wax content is proportional to enthalpy of crystallization (ΔH) and the ΔH ranges from 3 to 9 J/g. WAT and wax content do not follow the same trend which is understandable as these parameters depends not only on the concentration and molecular weight of the waxes but also on the chemical nature of both waxy and non waxy part of the crude oil. To understand the trend in WAT, these crudes were also analyzed for paraffinic carbon (Cp), Saturates and CH₂/CH₃ ratio by NMR spectroscopy and carbon number distribution by HT-GC. It was observed that WAT correlates fairly well with CH₂/CH₃ ratio which is in an indicator of normal paraffin content as WAT depends primarily on the nature / type of paraffins. The anomalies can be explained through carbon–wise n-paraffin content by HT-GC.