THE EFFECT OF ASPHALTENES, NAPHTHENIC ACIDS AND POLYMERIC INHIBITORS ON THE POUR POINT OF PARAFFINS SOLUTIONS
Geiza E. Oliveira 1, Cláudia. R. E. Mansur 1, Renata V. Pires 1, Leonardo B. Passos 1, Dellyo R. S. Alvares 2, Gaspar González 2 e Elizabete F. Lucas 1
1 Instituto de Macromoléculas da Universidade Federal do Rio de Janeiro (IMA/UFRJ). Centro de Tecnologia, Bloco J, Ilha do Fundão, Caixa Postal: 68525, CEP: 21945-970, Rio de Janeiro, RJ.
2 Centro de Pesquisas da PETROBRAS (CENPES). Ilha do Fundão, Q.7, CEP: 21949-900, Rio de Janeiro, RJ. Tel: (21) 3865-6898, e-mail: gaspar@cenpes.petrobras.com.br
Precipitation of n-paraffins produces wax deposits that, depending on the crude oil, may contain branched-chain paraffins, asphaltenes, naphthenic acids and resins. These other fractions may be trapped or occluded in the deposits or incorporated to the crystals during the wax formation. In this latter case important differences may occur in the pattern of wax formation and deposition.
In this work the influence of asphaltenes and naphthenic acids on wax appearance temperature (WAT), pour point and wax crystals morphology was estimated for solutions of a commercial paraffin dissolved in a mixture of solvents. Also the performance of inhibitors (ODIs) obtained by modification of ethylene-vinyl acetate copolymers Asphaltenes reduced the pour point and this effect increased with the increase in the asphaltenes concentration, indicating that asphaltenes interact with the paraffins to form particles with a different interaction profile. The observation of the wax crystals using optical microscopy revealed that in the absence of additives plate or a needle-like structure; whereas when asphaltenes were incorporated, the particles were smaller and less well defined. At higher asphaltenes concentrations dark particles whose surface resembled asphaltenes were also observed. Naphthenic acids caused a small increase in the pour point and when both fractions, asphaltenes and naphthenic acids, were added together synergistic effects were not observed. The ODI’s that presented the higher solubility in the solvents mixture presented the best results as pour point, depressant showing that besides possessing hydrocarbon chains to co-crystallize with the waxes, the inhibitors must also present an adequate solubility in the system.