Process for solvent extraction and extraction unit therefor, as well as in-line device comprising such extraction units, in particular with solvent recovery

摘要

A solvent extraction process and unit (1a) are used to determine a constituent to be extracted from a sample. The sample is boiled in the extraction unit, together with the solvent, while a liquid extraction is carried out. A vapour extraction above the liquid level of the extraction solvent is then carried out. The evaporated extraction solvent which condenses at the water cooler (5) is later collected in an overflow unit (7) with a collecting chamber (13) and flows outwards into a solvent collecting container (10) for recovery purposes. Such a level reduction of the solvent may also be carried out to effet a change from liquid to vapour extraction. It is known to keep open the outlet (8) of the overflow unit by means of an outer regulating valve and a timing programmer until the desired solvent level is reached by a continuous sinking process. The discharged amounts of extraction solvent are however not reproducible, they may prematurely evaporate and the extracted constituent in the residual amount may vary. The sample container (2) is heated in an inaccurate manner, so that different heat transfer rates lead to different dripping speeds of the condensate. In order to prevent higher error rates of the residual liquid level from setting in, to avoid a premature removal of the sample containers or the admixture of additional extraction solvent, the collecting chamber (13) of the overflow unit, which may be filled with a constant, predetermined volume, is emptied in a quantified manner. The collecting chamber (13) is filled with the generated condensate and emptied several times successively. As it may be rapidly emptied by pressure medium supply or suction effect, known, quantified amounts of solvent are discharged in a predetermined time, so that the resulting residual amounts may be accurately predetermined. This extraction unit is particularly suitable in an in-line apparatus for handling potentially explosive extraction solvents, for example for determining the fat content of a sample.