Selective inhibition of paraffin deposition under high flow rate as a function of the crude oil paraffin type and content by fluorescence depolarization: polypropylene and high-density polyethylene

High-density polyethylene (HDPE) and polypropylene (PP) were studied to identify tailor-made materials for walls of pipelines and ducts for crude paraffinic oil that inhibit paraffin depositions. The interfacial interaction was investigated from 50 to 70 degrees C and as a function of the n-C(36)H(74) paraffin concentration added to the paraffinic crude oil. The static and the dynamic interfacial tensions were observed, respectively, by traditional contact angle measurements and by fluorescence depolarization of the natural fluorescent probes of the crude oil, flowing at a high rate. The static interaction showed a low dependence on the n-paraffin content for both surfaces. For PP, it decreased slightly as the n-paraffin concentration increased, evidencing an increase in the liquid-liquid interaction. The dynamic interfacial tension with PP clearly decreased as temperature and n-paraffin concentration increased, the latter effect being attributed to the PP methyl groups hindering the interaction between the n-paraffin and the PP main chain. For the flow on HDPE, the interaction proved to be highly dependent on the n-paraffin concentration and temperature. It increased as n-paraffin was added and temperature decreased. The former effect is attributed to the alignment of the n-paraffin chains within the high rate flowing liquid and the similar molecular geometry of the n-paraffin and the linear polymer surface (almost without branches), which increases the number of sites available for interaction. PP proved to be more suitable for transportation of crude oil rich in paraffins with more than 36 carbon atoms, while HDPE was more suitable for those with smaller paraffinic chains.