Hercilio Rivas

Asphaltenes and resins from the Orinoco basin

Abstract Elemental analyses, molecular weights (by vapour pressure osmometry and gel permeation chromatography), 13 C and 1 H nuclear magnetic resonance precipitation and interfacial studies are reported for asphaltenes and resins from crude oils from the Orinoco basin. No major structural differences were found between coprecipitated resins and those remaining in the maltenes. The high number average molecular weights ( − M n ) of asphaltenes (by v.p.o.) in benzene, 15000-7500, were reduced to ≈2000 after methylation or when measured in pyridine. The results from structural studies indicate the presence of a large number of aliphatic rings in the asphaltenes.

Isolation and characterization of natural surfactants from extra heavy crude oils, asphaltenes and maltenes. Interpretation of their interfacial tension-pH behaviour in terms of ion pair formation

Abstract Natural surfactants (NS) have been isolated from extra heavy crude oils and from their asphaltene and maltene fractions. The elemental analyses and molecular weight (Mw) properties and the molecular weight distribution (MWD), as well as the interfacial tension (γ) behaviour (toluene solutions) with pH have been measured. The NS of crude oils (NSC) and those from asphaltenes (NSA) presented properties similar to those of asphaltenes (high Mw, low H C ratio, heteroatom content and γ-pH behaviour) whereas the NS isolated from maltenes (NSM) resembled neither asphaltenes nor resins. The γ-pH behaviour of the crude oil systems were not reproduced by their fractions (asphaltenes, maltenes, NSC, NSA or NSM). A chemical equilibrium, based on ion pairs formed between carboxylic acids and amines, is proposed to account for the observed γ-pH changes.

Interfacial rheological studies of extra-heavy crude oils and asphaltenes: Role of the dispersion effect of resins in the adsorption of asphaltenes at the interface of water-in-crude oil emulsions☆

Abstract The interfacial behaviour of a crude oil and an asphaltene system has been studied by a planar rheological method. System S1 was a 30% (v/v) xylene dilution of extra-heavy Cerro Negro crude oil; the aqueous phase was tridistilled water or an NACl solution (2% (w/v)). System S2 was a 3.21% (w/v) dilution of Cerro Negro asphaltene in xylene; aqueous phase as for system S1. These systems were studied under creep in the pH range 1.6–9.5. The elasticity (E0 and E1) and viscosity (η1 and ηN) surface moduli were obtained from creep compliance measurements. Viscoelastic as well as elastic behaviour was observed. The interfacial rheological behaviour of asphaltene and crude oil systems was found to be very different in the presence and absence of salt. The high values of the moduli, leading to the high stability of water-in-oil emulsions, was attributed to flocculation of asphaltene-resin micelles at the interface. In the absence of resins, asphaltenes were not dispersed and their adsorption at the interface could lead to precipitation and multilayer formation.

Flow characteristics of concentrated emulsions of very viscous oil in water

This article advances ideas and presents experiments on the flow characteristics of concentrated emulsions of Venezuelan bitumen in water plus surfactant. These emulsions are studied under a variety of flow conditions, namely, between rotating cylinders, in a colloid mill, and in pipes. The ideas advanced here concern the modeling of the highly viscous bitumen drops as solid spheres and their fracture under contact forces between neighboring drops, as in comminution, rather than break‐up by hydrodynamic forces. Further, we observe and discuss the local inversion of an emulsion due to local increases of the bitumen fraction induced by flow and the conditions that lead to slip flow, in which the drag is reduced by the formation of a lubricating layer of water at the wall. We believe that the results presented here unveil mechanisms that take place in the pumping and pipelining of oil‐in‐water emulsions and therefore contribute to the understanding of the dynamic stability of these systems.

ISOLATION AND CHARACTERIZATION OF NATURAL SURFACTANTS PRESENT IN EXTRA HEAVY CRUDE OILS

ABSTRACT Natural surfactants have been Isolated from two Venezuelan crudes using a novel procedure. These compounds were analysed and their interfacial tension against pH were measured. The results were compared with those obtained for resins and asphaltenes Isolated from the crudes by conventional methods.

Creep compliance-time behavior and stability of bitumen in water emulsions

The effect of bitumen concentration, presence of electrolytes, storage temperature, mean droplet diameter, and distribution and the length of the ethylene oxide chain in nonionic surfactants, on the viscoelastic parameters of bitumen in water emulsions, was investigated. Viscoelastic parameters were derived from the creep compliance-time response of the emulsions at a constant stress. All the emulsions exhibited an increase in the instantaneous elastic modulus and in the Newtonian viscosity, when the mean droplet diameter was decreased at constant bitumen fraction, or when the bitumen fraction was increased at constant mean droplet diameter. In all cases studied, the storage temperature and the presence of a magnesium nitrate in the aqueous phase, promoted a decrease in the values of the viscoelastic parameters. Results are explained based on the interaction between the hydrophilic chains of the surfactant molecules adsorbed on adjacent bitumen droplets. Emulsion stability, measured, as a function of the ...

SURFACTANT-OIL-WATER SYSTEMS NEAR THE AFFINITY INVERSION. PART X: EMULSIONS MADE WITH ANIONIC-NONIONIC SURFACTANT MIXTURES.

Anionic and nonionic surfactants exhibit opposite changes in hydrophilicity with a change of temperature. This antagonism can be harnessed by the use of mixtures. The phase behavior and emulsion type are mapped on a temperature water-oil/ratio diagram for different anionic-nonionic mixtures. It is shown that the mixing can result in insensitivity to temperature of different kinds of emulsions.