Crude oils are intricate mixtures of hydrocarbon compounds; different physicochemical characterizations must be performed to get to know their complexity. A series of four typical Mexican Crude Oils (MCOs) with densities ranging from 30 to 9 °API was characterized through different physical, spectroscopic, and thermal methods. The four types of MCOs were also fractionated into saturates, aromatics, resins, and asphaltenes (SARA) through high-performance liquid chromatography (HPLC). The fractions obtained were subsequently characterized through different physicochemical techniques such as Fourier transform infrared (FTIR) spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). VPO led to determining the average molar mass of each MCO fraction to be compared to those of the different Mexican petroleums. It was clearly observed that the molar mass of the resin and asphaltene fractions increases when crude oil gets heavier than saturate and aromatic components. The thermal stability of the series of MCOs was evaluated by TGA observing that the decomposition temperature increases with the average molecular mass of the crude oil. The original heavy crude oil and its fractions were studied through differential scanning calorimetry (DSC); the study of heat effects associated to phase transitions was monitored for each fraction, resulting into the Wax dissolution temperature (WDT) and the Wax precipitation temperature (WPT) of the four MCOs investigated. It was established that the different molecular features of crude oils may be clearly correlated to their average molar mass.

This work presents a theoretical study of the effects of different molecular weights of a triblock co-polymer ethylene oxide/propylene oxide/ethylene oxide, bifunctionalized with ethalamine, on the coalescence of water drops imbibed in a crude oil environment. The polymer/crude oil/water (PCW) time evolution of the emulsion was simulated using the framework of the dissipative particle dynamics (DPD) technique. The bead-bead interactions of the molecular components were calculated using the correlation between the solubility parameter, χ ij , of the Flory-Huggins theory and the conservative force parameter, a ij . The solubility parameter was obtained from atomic molecular models of prototype molecules of saturates, aromatics, resins, asphaltenes, and the triblock co-polymer, through the blend methodology. The dynamic evolution of coarse-grain mesomolecules was carried out in cells of 20 Â 20 Â 20 DPD unit length with periodic boundary conditions. The composition of the emulsion was chosen to be similar to a Mexican heavy crude oil: asphaltenes, 11.9%; resins, 11.8%; aromatics, 42.7%; saturates, 29.6%; polymer, 4%; and two water drops of 3 DPD length units in radius. Finally, a drastic change in the coalescence of water molecules is observed for a short co-polymer length with respect to long co-polymer lengths.

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A series of copolymers derived from styrene (S), n-butyl acrylate (BuA), and vinyl acetate (VA) monomers were prepared by emulsion polymerization to improve some physical properties of Mexican crude oils (MCOs). Once obtained, the copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, size-exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Later, they were dissolved in toluene and were added to both light and heavy MCOs; the pour point temperature and apparent viscosity of these mixtures were carefully evaluated. Results indicate that styrene and vinyl acetate (SVA) copolymers show a good pour point depressant performance for both types of crude oils. The apparent viscosity dependence on temperature for light and heavy crude oils, mixed with copolymers, was also established. It was observed that, in general, the addition of copolymers decreases the apparent viscosity of both light and heavy crude oils above 35 °C.

The rheological behavior of dilute solutions from different terpolymers was investigated over a wide range of temperatures (20−45 °C) and shear rates (0.1−300 s−1). The investigation focuses on the effect of three co-monomer contents, their molecular weight, the terpolymer, and the viscosity−temperature relationship of a Mexican crude oil (MCO). Terpolymers with different contents of styrene (S), n-butylacrylate (BA), and vinyl acetate (VA) were synthesized through semi-continuous emulsion polymerization. The composition of the terpolymers was evaluated by nuclear magnetic resonance (NMR) spectroscopy. The average molecular weight and polydispersity of the polymers were determined through size-exclusion chromatography (SEC). Both the untreated crude oil and the one treated with a solution of terpolymer exhibited non-Newtonian behavior. The results confirm that the viscosity of crude oil is reduced when the terpolymers have a high percentage of S and small amounts of BA or VA. The molecular weight of terpolymers plays a fundamental role in their performance as viscosity reducers.

A series of multibranched block copolymers was synthesized by means of anionic ring opening polymerization (AROP) techniques, using different alkoxide salts obtained from molecules that present different numbers of alcohol functions as initiators. Propylene oxide (PO) and ethylene oxide (EO) were polymerized in two steps, with the intent of obtaining multibranched block copolymers (PO/EO) with demulsifying activity in petroleum. The characterization of the polymers was done by means of size exclusion chromatography (SEC), Fourier transformed infrared spectroscopy (FTIR), carbon-13 nuclear magnetic resonance ( 13 C NMR), and thermogravimetric analysis (TGA). A theoretical study by semiempirical AM1/NDDO has been carried out in order to explain the growth of multiple branches from the initiators during the early stages of the anionic polymerization. These simulations revealed complex patterns of polymer growth and increasing polydispersities when initiators with a greater number of active sites were employed to start the reactions. Afterward, the water removal efficiency, as a function of the number of copolymer branches, was evaluated through bottle tests in two crude oils: a heavy crude oil with 12.71°API and an extra-heavy crude oil with 9.68°API, with a water content of 47 and 39 vol %, respectively. A complex and nonlinear behavior of the water removal, as a function of the number of the block copolymer branches, was observed.

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