Parafinas

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Melting and glass transitions in paraffinic and naphthenic oils
NRCC-47736 Masson, J-F.; Polomark, G.M.; Bundalo-Perc, S.; Collins, P.

A version of this document is published in / Une version de ce document se trouve dans : Thermochimica Acta, v. 440, no. 2, Jan. 15, 2006, pp. 132140 Doi: 10.1016/j.tca.2005.11.001

Meltingand glass transitions in paraffinic and naphthenic oils J-F. Masson*, G. M. Polomark, S. Bundalo-Perc, P. Collins Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario, Canada, K1A OR6. *To whom correspondence should be addressed. Phone: (613) 993-2144. Fax (613) 952-8102. e-mail: jean-francois.masson@nrc.gc.ca

Abstract Naphthenic and paraffinic oils wereanalyzed by modulated differential scanning calorimetry (MDSC). The results showed several improvements in the analysis of

thermal properties when compared with standard DSC. The glass transition temperature (Tg), the enthalpy relaxation at Tg, and the melting endotherms could be deconvoluted, and reversible melting could be identified. This allowed for an easier interpretation of the thermalproperties of the oils. With MDSC, the Tgs in mineral oils were found to coincide with endothermic enthalpy relaxation, which is generally regarded as a melting endotherm with standard DSC. A decrease in heat capacity after Tg was attributed to the existence of rigid amorphous material. From Δcp at Tg and the oil molecular weight, the number of repeat units in the oil chains was estimated at lessthan 20. The Tg of a hypothetical pure aromatic oil was found to be similar to that for petroleum asphaltenes, and that for a naphthenic oil of infinite molecular weight to be similar to that of petroleum resins.

Keywords: differential scanning calorimetry (DSC); modulated differential scanning calorimetry (MDSC); hydrocarbons; naphthenic oils; paraffinic oils; bitumen; cold crystallization;enthalpy relaxation; melting; glass transition temperature.

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1. Introduction Mineral oils and paraffinic waxes are of great technological and economic interest, partly because crystalline waxes can lead to an array of difficulties. For

instance, the crystallization of paraffins can lead to the clogging of pipelines during the transportationof paraffinic crude oils [1]; in roadway bitumens, crystallization may reduce the adhesion to aggregates [2]. Waxes also affect viscosity [3], thus limiting the use of oils in many applications. Since the late 60’s and early 70’s, thermal analysis, and differential scanning calorimetry (DSC) in particular, has been used to characterize petroleum products (readers familiar with petroleumderivatives, but unfamiliar with DSC, are referred to the Glossary). DSC was used to study the glass transition temperature (Tg) and

crystallization in bitumen [4, 5], oils [6] and waxes [7]. Noel and Corbett [5] first established that the Tg of bitumen depended on its source and that “waxy” and “nonwaxy” bitumens could be distinguished based on the DSC profiles. Upon heating, “waxy” bitumens were foundto show exothermic cold crystallization and endothermic melting, both of which were reported to arise from the lighter bitumen fraction, the saturates. Giavarini and Pochetti [7] later observed two endotherms in paraffinic waxes, whereas they observed a single broad endotherm in microcrystalline (non-paraffinic) waxes. It is thus generally considered that endotherms in petroleum products arisefrom paraffins, or alkanes. However, it was recently demonstrated that the endotherm size in DSC is not necessarily proportional to the saturates content [8] and that the ordering of aromatic rings may also contribute to the endotherm [9].

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DSC is commonly used to determine crystallinity because it is rapid and more convenient than wet...