Fast batch to continuous transposition : application to the extraction of andrographolide from plants

Abstract

The objective of this study is to propose a fast development method for batch to continuous processes transposition. This method is based on transient regime experiments analysis and is applied to a solid liquid extraction. The application under consideration is the extraction of an active principle from plant in a non-sinusoidal pulsed column. Typically, the proposed signal is composed of two different periods: in one hand, a classical sinusoidal pulsation step used to mix the liquid and solid phases in the active part of the column and allow an optimal mass transfer and, in a second hand, an impulsion phase, used generally for the transport of solid. The extraction is carried out in a disc and doughnut column of 54 mm in diameter, and 3.5 m in height. Liquid and solid are flowing cocurrently and downwardly. This technological improvement has been implemented to solve the difficulties due to the important heterogeneity of the matter: part tends to float and other to sink, which always leads to a definitive flooding in classical operations. The effects of the solid flow rate and of the solvent characteristics on the hydrodynamic behavior of the column are studied. The mean residence time and the total solid holdup are calculated by using transient regime mass balance on experiments. These experiments allow pointing out and quantifying opposite effects of the operating parameters. Mass transfer experiments have been performed and the results fit calculated values obtained by coupling the hydrodynamic with batch extraction results. Despite of the simplification made, this validates the fast development method proposed to help the batch to continuous transposition.