Two acidic samples, A and B, were isolated from Cerro Negro extraheavy crude oil. Sample A has a relatively low number average molecular weight (M n = 480 Da), low aromaticity (f a = 15.2%), and low γ (6.8 m Nm-1, toluene−0.1 N HCl), whereas for B, these values were M n = 1200 Da, f a = 20%, and γ = 14.8 m Nm-1. These values could be compared to those for Cerro Negro asphaltenes under the same conditions (M n = 5000, in toluene by VPO, f a = 47%, γ = 20.9 m Nm-1).

In the case of the hydrodesulfurization (HDS) processes one of the best catalysts currently available is that based on MoS 2 and WS 2 . A very significant increase in their activity can be achieved by adding Co or Ni as a promoter. In the present report we have used probe aberration corrected STEM (scanning transmission electron microscopy) for the first time to characterize Co doped MoS 2 /WS 2 nanowire catalysts (supported on Al 2 O 3 substrates). The high-resolution imaging reveals clearly the location of Co in the individual catalysts. This has not been possible to date with other experimental techniques because of the insufficient image contrast and/or resolution. On the basis of the HAADF-STEM images, we built two models for the CoÀMoÀS and CoÀWÀS catalysts to illustrate the different morphologies found in the catalysts. With this study it is now possible to better locate, identify, and understand the role of promoters in the design and functioning of catalysts. KEYWORDS: hydrodesulfurization (HDS), MoS 2 and WS 2 based catalysts, Co doped MoS 2 /WS 2 nanowires, probe aberration corrected STEM

The stability of water-in-diluted-crude-oil emulsions is found to depend upon the water-phase salinity and the water-oil ratio for different asphaltene and demulsifier concentrations. It is reported that the most stable emulsions are formed when one of the phase volumes largely exceeds the other and that the minimum stability is found at the formulation for which the emulsion inversion takes place. For asphaltene concentrations over 500 ppm, this occurs at a volumetric fraction between 0.3 and 0.7 and, in this range, the higher the waterphase content, the lower the required demulsifier concentration. It is also determined that there is an optimum value of the demulsifier concentration that promotes the fastest separation. At a fixed asphaltene concentration, an increase in salinity generally leads to a lower demulsifier requirement. Finally, at higher asphaltene concentrations, simultaneous increases in salinity and demulsifier concentration are required to attain an optimal rate of emulsion breaking.

The objective is to understand the effects of organic acid and amine additives on the performance of commercial demulsifiers in breaking water-in-crude-oil (W/O) emulsions, according to the proportional regime test developed in previous articles. Both hydrophilic (ethylamine and acetic acid) and hydrophobic (hexanoic acid and hexylamine) species were tested, and all were found to exhibit different effects. The water-soluble species have essentially no effect, despite a change in aqueous phase pH. Hexanoic acid was found to increase the stability of the W/O emulsions, whereas the hexylamine was found to reduce it. Explanations of the effect of these additives on the interfacial formulation are proposed.