Countercurrent exchange

About: Countercurrent exchange is a research topic. Over the lifetime, 2255 publications have been published within this topic receiving 28687 citations. The topic is also known as: Countercurrent exchange.

A continuous multicolumn countercurrent solvent gradient purification (MCSGP) process

Abstract: Biomolecules are often purified via solvent gradient batch chromatography Typically suitable smooth linear solvent gradients are applied to obtain the separation between the desired component and hundreds of impurities The desired product is usually intermediate between weakly and strongly adsorbing impurities, and therefore a central cut is required to get the desired pure product The stationary phases used for preparative and industrial separations have a low efficiency due to strong axial dispersion and strong mass transfer resistances Therefore a satisfactory purification often cannot be achieved in a single chromatographic step For large scale productions and for very valuable molecules, countercurrent operation such as the well known SMB process, is needed in order to increase separation efficiency, yield and productivity In this work a novel multicolumn solvent gradient purification process (MCSGP-process) is introduced, which combines two chromatographic separation techniques, which are solvent gradient batch and continuous countercurrent SMB The process consists of several chromatographic columns, which are switched in position opposite to the flow direction Most of the columns are equipped with a gradient pump to adjust the modifier concentration at the column inlet Some columns are interconnected, so that non pure product streams are internally, countercurrently recycled Other columns are short circuited and operate in batch mode As a working example the purification of an industrial stream containing 46% of the hormone Calcitonin is considered It is found that for the required purity the MCSGP unit achieves a yield close to 100% compared to a maximum value of a single column batch chromatography of 66%

Modeling wood gasification in a countercurrent fixed‐bed reactor

Abstract: A one-dimensional, unsteady mathematical model is presented of fixed-bed countercurrent wood gasifiers, which couples heat and mass transport with wood drying and devolatilization, char gasification, and combustion of both char and gas-phase species. The model is used to simulate the structure of the reaction fronts and the gasification behavior of a laboratory-scale plant as the reactor throughput and the air-to-wood (or char) weight ratio are varied. It is observed that a wide zone, acting essentially as a countercurrent heat exchanger, separates combustion/gasification from devolatilization/ drying. Moreover, the former zone presents interesting dynamic patterns driven by the highly variable solid/gas heat transfer rates. For a constant air-to-wood weight ratio, the gasification process is improved by increasing the reactor throughput as a result of higher temperatures, in spite of the simultaneous reduction in the amount of char generated from wood devolatilization. In fact, an increase in the air-to-wood (or char) ratio always lowers the efficiency of the gasification process. Finally, good agreement is obtained between predictions and experiments for the axial temperature profiles and the composition of the producer gas. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2306 –2319, 2004

Countercurrent chromatography : the support-free liquid stationary phase

Abstract: Fundamentals of countercurrent chromatography Operating a CCC machine Solvents systems Centrifugal partition chromatography: the story of a company Centrifugal partition chromatography:an engineering approach Liquid stationary phase retention and resolution in hydrodynamic CCC Special uses of a support-free liquid stationary phase Separataion and purification of natural products (medicinal herbs) by high speed countercurrent chromatography Separation of inorganic compounds - theory, methodology and applications Use of CCC in the pharmaceutical industry Enantioseparations in countercurrent chromatography and centrifugal partition chromatography Supercritical fluids as mobile phases in CCC. Appendix: Commercially available countercurrent chromatographs.

Buoyancy-driven exchange flow through small openings in horizontal partitions

Abstract: This paper describes an experimental study of the phenomenon of buoyancy-driven exchange (countercurrent) flow through openings in a horizontal partition. A density-driven exchange flow was obtained by using brine above the partition and fresh water below the partition. In the first part of the study, flow measurements were made with a single opening, for opening ratios L/D in the range 0.01 to 10.0, where L and D are the length of the openings (in the direction normal to the partition) and the diameter of the opening, respectively. Four different flow regimes are identified as L/D is increased through this range. As a result of the competition between two of these regimes, the exchange flow rate versus L/D relation exhibits a peak. The exchange flow rate was found for all practical purposes, to be independent of viscosity, enabling a universal correlation between Froude number (dimensionless exchange flow rate) and L/D. The second part of the study was an experimental investigation of the same phenomenon, but with two openings in the horizontal partition. Two openings were observed to give rise to three different flow configurations involving both one-way and countercurrent flows within the openings.