The Engineering Procedure for Calculating the Plant for Betulin Extraction from Birch Bark

Abstract

The analysis of the current state of the process of betulin extraction from birch bark has shown the relevance of the implementation of periodic extraction technology using toluene as a solvent at small enterprises of the timber industry complex. This article presents the scheme of an extraction plant consisting of an extractor, an evaporator, a condenser, a florentine flask, an extract collector, as well as the principle of the plant operation. The extraction process is carried out in two stages: when the raw material is at rest in relation to toluene and when the raw material is extracted by continuous feeding of fresh extractant. The engineering procedure for calculating the extractor has been developed, allowing to determine its overall dimensions (diameter and height) and the duration of individual stages of the extraction process. The duration of the first stage has been calculated by solving Fick’s differential equation of mass conductivity under boundary conditions of the first kind. The duration of the second stage has been calculated considering the fact that betulin extract is continuously withdrawn from the extractor and fresh extractant is injected. In the latter case, the betulin content in the extractant varies not only in time, but also with the height of the extractor. The developed mathematical description and subsequent modeling made it possible to obtain the calculated curves of betulin distribution in birch bark at different points in time, as well as to compare the experimental and calculated data on the kinetics of the average betulin content in birch bark and toluene for each stage. Meanwhile, the kinetic curves of the average betulin content in birch bark at the second stage are presented for different heights of the extractor. It has been established that the optimal duration of the first stage is 20 min, and with the continuous feeding of fresh extractant with a flow rate of 22.5 kg/h at the second stage, the process speed increases by 6 times. This significantly reduces the total extraction time under the specified process parameters. The necessity for the introduction of the third stage (the stabilization period of the betulin content over the layer height and the cross– section of particles) has been shown.