Robert P. Fishwick

Explaining mass transfer observations in multiphase stirred reactors: particle-liquid slip velocity measurements using PEPT

Abstract Solid–liquid mass transfer coefficients were determined using the technique of dissolving a sparingly soluble solid, salicylic acid loaded onto silica, in water. Mass transfer was found to be dependent on various particle characteristics. Of particular interest is the influence of the particle-liquid density difference. It is suggested that the change in mass transfer coefficient with these parameters is related, to some extent, with the particle-liquid slip velocity. The technique of positron emission particle tracking (PEPT) has been used in parallel with the mass transfer measurements in order to study the effect of different operating conditions on the liquid flow patterns and the particle-liquid slip velocities. Using PEPT, time-averaged slip velocities were determined by simple subtraction of the data from a neutrally buoyant particle. In this way, important information about solid–liquid behaviour and zones of poor mass transfer in stirred vessels is revealed.

Effect of gassing rate on solid-liquid mass transfer coefficients and particle slip velocities in stirred tank reactors

Abstract While solid–liquid dispersion in mechanically agitated vessels has been widely investigated, the suspension of particles with simultaneous gas dispersion is, however, less well understood. A consideration of the gassing rate is of particular importance when designing “dead-end” batch reactors. Solid–liquid mass transfer coefficients were determined using the technique of dissolving a sparingly soluble solid, salicylic acid loaded onto silica gel, in water. Mass transfer was found to be dependent on a variety of geometric, physical and hydrodynamic properties; with the significant exception of agitation speed the influence of the latter properties was independent of gas dispersion. Flow visualisation with positron emission particle tracking has been used alongside the mass transfer measurements to study the effects of gas injection on the liquid flow patterns and the solid–liquid slip velocities. Time-averaged relative slip velocities were determined by simple subtraction of the data obtained using a neutrally buoyant particle. Gas dispersion was found to affect the particle–liquid slip velocity, explaining the mass transfer coefficient trends observed. While only a small diameter vessel has been used it does point to considerable non-uniformity of mass transfer in larger vessels.

Experimental Optimization of Catalytic Process In-Situ for Heavy Oil and Bitumen Upgrading

The worldwide conventional crude-oil demand is on the rise, and because of the rising prices, unconventional oils are becoming more economically attractive to extract and refine. However, technological innovation is needed if heavier oil supplies are to be exploited further. Toe-to-heel air injection (THAI) and its catalytic add-on processes (CAPRI) combine in-situ combustion with catalytic upgrading using an annular catalyst packed around the horizontal producer well. These techniques offer potentially higher recovery levels and lower environmental impact than alternative technologies (e.g., steam-based techniques). An experimental study is reported concerning the optimization of catalyst type and operating conditions for use in the THAI-CAPRI process. The feed oil was supplied from the Whitesands THAI-pilot trial. Experiments were carried out using microreactors containing 10 g of catalyst, with oil flow of 1 mL/min and gas flow of 0.5 L/min, under different temperatures, pressures, and gas environments. Catalysts tested included alumina-supported CoMo, NiMo, and ZnO/CuO. It was found that there was a trade-off in operation temperature between upgrading performance and catalyst lifetime. At a pressure of 20 bar, operation at 500C led to an average of 6.1API upgrading of THAI oil to 18.9API, but catalyst lifetime was limited to 1.5 hours. Operation at 420C was found to be a suitable compromise, with upgrading by an average of 1.6API, and sometimes up to 3API, with catalyst lifetime extended to 77.5 hours. Coke deposition occurred within the first few hours of the reaction, such that the catalyst pore space became blocked. However, upgrading continued, suggesting that thermal reactions or reactions catalysed by hydrogen transfer from the coke itself play a part in the upgrading reaction mechanism. The CAPRI process was relatively insensitive to changes in reaction-gas medium, gas-flow rate, and pressure, suggesting that the dissolution of hydrogen or methane from the gas phase does not play a key role in the upgrading reactions. By careful control of the temperature and oil-flow rate in the in-situ CAPRI process, additional upgrading compared with the THAI process alone may be effected, resulting in a more-valuable produced oil, which is easier to transport.