Predicting
the asphaltene stability in crude oils from different
production streams is very useful in the petroleum industry because
it allows avoiding serious problems caused by formation of solid deposits
during oil flow. That prediction can be carried out by applying the
solubility parameter (δ) of each oil, as calculated by the asphaltene
precipitation onset value, obtained by titration with n-heptane. However, many crude oils do not have a well-defined precipitation
onset point, which can be overcome by adding a crude oil assumed as
the standard. This article analyzes the influence of a crude oil (called
APS) on the precipitation onset of two other petroleum samples (called
APA and APB). For this purpose, the asphaltene fractions C3I and C5I
were extracted from APS, and the influence of the addition of this
crude oil as well as its asphaltenes fractions in samples of oils
APA and APB was evaluated by tests involving titration of n-heptane with detection by near-infrared spectroscopy (NIR).
The calculation of the solubility parameters of the oils without well-defined
precipitation onset, by adding the oil with well-defined precipitation
onset, led to varied errors in function of the type of oil in question.
The smallest errors were obtained when using, as the solubility parameter
of the mixture (δM), the solubility parameter of
the solvent system at the precipitation onset of the asphaltene C3I
fraction (extracted from the crude oil assumed as the standard) in
toluene, determined by titration with n-heptane.
One of the methods to prevent wax precipitation, during petroleum production, transport, and refining, is the use of polymer additives that can reduce the oil pour point. However, no single additive work for all types of crude oil and this relation is not yet well known. In this study, a family of polymers based on poly(ethylene-co-vinyl acetate), containing hydroxyl groups and long pendant hydrocarbon chains (from C6 to C18), were synthesized and characterized by H 1 nuclear magnetic resonance and solubility test. Four crude oil samples containing different amounts and size distribution of the wax were used. The additive's action is favored by higher contents of iso + cycloalkanes and lower contents of n-paraffins with larger chain sizes. The presence of the CH 3 COO group in the copolymers promoted the lowering of the pour point, supported by a low OH concentration and the presence of a long pendant hydrocarbon chain: the best results were obtained with C10 and C12 chain lengths.
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