Evaluation of the correlation between wax type and structure/behavior of the pour point depressant

Abstract

Knowledge of the lowest temperature at which a particular petroleum type is still able to flow (pour point) is important for its marketability. High pour point temperatures make transport and refining more difficult and thus can reduce demand and price. Polymer additives are an alternative to reduce the crude oil pour point. However, the relation between the type of oil and efficacy of a given additive remains obscure. We studied two model systems: one composed of commercial paraffin in toluene; and the other containing paraffins obtained in the laboratory from the distilled fraction of a crude oil, also dissolved in toluene. As pour point depressants (PPD), three samples of poly(ethylene-co-vinyl acetate) were used to determine the pour point and wax appearance temperature (WAT). The samples' behavior was also studied by rheology. The results showed that the content of linear paraffin chains with sizes larger than C30 significantly influenced the efficacy of the additives, not only in relation to the pour point, but also the viscosity of the model system below the WAT. Besides this, mixtures of the commercial waxes showed a practically linear pour point relation with the composition for the pure systems. Such linear behavior was not observed for the efficacy of the additive, which was significantly affected by the presence of a small quantity of chains with higher molar mass. Experiments conducted with the series of waxes extracted from the crude oil showed that the pour point was not influenced by linear paraffin when their concentrations were below 3wt%. In turn, in the fractions with higher concentrations of n-paraffins than this, the additive was only effective in the samples with more than half their chains having sizes under C28.