ENGLISH VERSION

ZESZYT 373

Modeling of ultrasound-assisted solid-liquid extraction
zeszyt 373, ss. 10

The solid-liquid extraction is one of the most difficult problem for modeling among diffusion processes. In the case of ultrasound-assisted extraction the diffusion models with the power of ultrasonic field in their structure was applied only in a few studies.

The aim of this work was to work out the mathematical model for describing multicomponent mass transfer which takes into account the influence of ultrasonic field on yield of periodic extraction.

The research was conducted for two model raw materials, which differ in morphological building, i.e. sage leaves (Salvia officinalis L.) and lovage roots (Levisticum officinalis). Water and 90% aqueous ethanol solution were used as solvents. During ultrasound assisted extraction, ultrasonic processor Sonics VCX 750 was used. The following parameters of ultrasonic field were applied: frequency – 20 kHz, intensity 3.2 W·cm-2, 6.8 W·cm-2 and 11.2 W·cm-2 and times: from 5 minutes to 75 minutes. The temperature of extraction was stabilized by circulating water bath at three levels: 30, 40 and 50ºC. A coefficient of saturation, concentration of solute in extracts and yield of extraction was assigned. For select parameters of ultrasonic treatment the content of essential oils, O-dihydroxyphenols and flavonoids was determined. 
There was positive effect of ultrasonic field on solute extraction from plant materials. The developed and verified model of ultrasound-assisted extraction formulates in complex way relationship between main process parameters, i.e. the influence of time and intensity of acoustic field on final solute concentration. Analysis of extraction parameters which was obtained on the basis of the developed model points out that ultrasonic field intensifies both stages of extraction, i.e. stage of washing and stage of slow extraction. The positive influence of ultrasound on the first stage of extraction consists in destroying cell structure and releasing solute to solvent. The visible and measurable effect of this phenomenon is a clear increase in the apparent washing coefficient under ultrasounds. The positive effect of ultrasound on the second stage of extraction is manifested in initializing eddy diffusion, which rises diffusion mass transfer in extraction system. Experimental verification confirms that the developed model is useful for mechanism and efficiency evaluation of ultrasound-assisted extraction.