Kinetics of CO2 gas bubbling for the separation of residual solvent from waste solids: Effects of bubble size

Solvent loss in the residual solids has been considered as a major challenge during the solvent extraction processes of unconventional oil ores (oil sands, asphalt rocks, etc.) or similar liquid-solid extraction. Meanwhile, the residual solvent in the solvent-extracted solids also causes serious environmental problems. The gas (CO2) bubbling process is proved to be an effective method for the removal and recovery of residual solvents from solvent-extracted solids. Herein, the kinetic model of the solvent removal by the gas bubbling has been built after considering the bubbling process as quasi vapor-liquid equilibrium. It is found that the solvent removal by gas bubbling matches well with the first-order kinetic model. Based on the fitting of gas bubbling experimental data under different water volumes, the quasi Henry's constant and separation rate constant were obtained. At this time, all the related parameters of gas bubbling kinetic model were determined. Then the effect of bubble size on the gas bubbling kinetics was systematically analyzed, a potential strengthening method of connecting micronano bubbles and large bubbles is proposed for improving the solvent removal from the residual solids. Finally, the molecular dynamic (MD) simulation and gas bubbling experiments combined with large bubbles and micro-nano bubbles prove micro-nano could well accelerate the solvent removal in the residual solids. This work provides the fundamental basis for the industrialization of the gas bubbling process for the solvent removal from residual solids, which also provides a new idea for the treatment of environmental problems, such as the treatment of solvent-containing waste solids.