Pipelines for heavy crude oils have recurrent clogging situations due to paraffin deposition that may lower production rates and be responsible for leakages. This work evaluates the effect of three polymers on crude oil wettability and on paraffin deposition inhibition: polypropylene (PP), high-density polyethylene (HDPE), and a vinyl acetate copolymer with 28% oxygen content (EVA28). Under static conditions, the interfacial tension between the crude oil and the linings was determined by the contact angle being 12% and 17% higher for EVA28 and HDPE, respectively, than for that of PP. As the crude oil inside the pipelines is flowing at high rates, the dynamic interfacial tension was also observed for high flow rates when molecular effects overtake hydrodynamic ones. For this, the perturbation of intermolecular orientation within the flow, caused by the beginning of deposit formation and by the wettability, was determined using depolarization of the fluorescence induced by laser. Under flow, EVA28 and HDPE caused an increase of interaction with the crude oil of 79% and 43%, respectively, compared to that of PP. HDPE yielded globular wax deposits. The higher tendency of HDPE than PP to form deposits was attributed to the absence of methyl branches in the first. The EVA28 tendency to form deposits was attributed to the oxygen atoms on the surface as well as to its high polycyclic aromatic hydrocarbon sorption. Thus, under a high flow rate, PP is better suited to inhibit wax deposition than HDPE and EVA28.

No abstract

Steady-state fluorescence depolarization has proven, in the past few years, to be a method sensitive to adhesion of thin liquid films flowing without boundaries on solid substrates of different chemical constitutions. This work extends our prior preliminary assessment of the efficiency of the method and the influence of experimental variables. Ten thin films of ethylene glycol (MEG) were mapped over 102 mm2 by polarized laser-induced fluorescence (PLF−FI) while flowing on substrates. The interfacial tension, ΓSL, was varied either by changing the chemical constitution of the substrate (borosilicate, tin dioxide, poly(vinyl alcohol) (PVA), and linear alkylbenzene sulfonate (LAS)) or by addition of tensoactives to MEG (sodium dodecyl sulfate (SDS) and poly(ethylene oxide) (PEO)). Contact angle measurements were employed to classify interfaces according to their static ΓSL, that is, their wetting efficiencies. PLF−FI experimental variables, such as laser power, film thickness, and impinging velocity profile, did not alter the data within the range studied, except for flow rates over 220 cm s-1. Average polarization (P av) increased from 10.5% to 13.5% upon decreasing adhesion by varying the chemical constitution of the solid. When surfactants were dissolved in the liquid flow, polarization ranged from 5.4% to 3.8% while for surfactant as substrate it increased. Simple multivariate principal component analysis (PCA) was applied to downstream polarization averages (P down) for each map. The two principal components accounted for 95.6% of the variance, ordering the maps according to decreasing adhesion and gathering them into three groups:  dissolved surfactants, liquid films flowing at the highest flow rate, and solid surfaces of different chemical composition. Hierarchic cluster analysis (HCA) showed that, as adhesion decreased, similarity among the polarization maps increased.

No abstract