NCUT Natural Resources Canada, Devon, AB T9G lA8, Canada ydrocracking and hydrotreating of heavy petroleum fractions or of hydrocarbon liquids that require desulfurization and/or H denitrification is one of today's major and now quite mature technologies. The reactions of hydrocracking, hydrodesulfurization (HDS) or hydrodenitrification (HDN) are usually carried out at relatively high temperatures (350'C to 45OOC) and high hydrogen pressures of up to 15 or 20 MPa. In most of these processes, a solid catalyst is present or is formed in the course of the reaction, so that the reaction system is always in a gas-liquid or gas-liquid-solid regime. In many cases, mass transfer can be the controlling rate mechanism in the reactor. In designing such reactors, or in the analysis of their performance, the ability to predict the hydrodynamic behaviour and the gas-liquid mass-transfer rate is necessary. One essential parameter for this analysis is a knowledge of gas-liquid interfacial tension values. The surface tension plays a major role in determining bubble sizes and bubble hydrodynamics, and therefore the interfacial transport area.There is another area in which knowledge of the gas-liquid interfacial tension is very important -the recovery of petroleum from reservoir formations. In the normal petroleum reservoir, oil trapping occurs at varying temperatures and at high pressures due to capillary forces resulting from surface tension. Particularly in secondary recovery, in which gas injection may be used, surface tension is a critical parameter. The variation of surface tension with temperature is well-known, and has been found to be essentially linear except in the vicinity of the critical point. The effects of pressure on surface tension are less easily predicted, and conflicting results have been reported. A significant reduction in surface tension has been found to occur at lower temperatures as gas pressure increases. However, the combined effect of high temperature and high pressure on the interfacial tension of hydrocarbon oils in contact with a gas with a high content of hydrogen or methane appears to require further investigation. The primary objective of this study was to make such surface tension measurements a t hydrocracking or hydrotreating conditions, if possible. Because no apparatus appeared to have been developed capable of such measurements a t these extreme 'Author to whom correspondence may be addressed. E-mail address: dscott@ eremail. uwaterlwxaAn apparatus for the measurement of surface tensions of organic liquids in contact with a gas has been developed which is capable of operation to 400°C and to 14 MPa. It is based on the maximum bubble pressure technique, modified for hydrocarbon oils at high pressures and temperatures. Accuracy of measurement is of the order of *3% for non-aqueous systems for values down to 5 mN/m. Only a 20 to 30 mL liquid sample is required, and small gas volumes. In practice, it was found that measurements with most organic liquids could only be made to a maximum of about ...

A maximum bubble pressure apparatus, described in a previous publication, has been used at pressures to 13.9 MPa (2000 psig) and temperature to 623 K (350°C) to measure the static surface tension of several alkanes and paraffinic petroleum fractions, and two types of Alberta bitumens in contact with hydrogen, helium and hydrogen/methane mixtures. With hydrogen, the surface tensions of alkanes or mixtures of alkanes were nearly independent of pressure, whereas with helium surface tension increased significantly. With hydrogen/methane mixtures, the surface tension decreased in value as pressure increased, with the effect increasing at the higher methane concentrations. For the two bitumens used, the surface tension with hydrogen showed a 10–15% increase as pressure increased at constant temperature. Some discussion is also given concerning methods of predicting the effects of pressure and temperature in hydrogen/hydrocarbon systems.