Impact of stimultaneous application of mechanical stirring and ultrasound irradiation on nucleation kinetics of borax decahydrate : diploma thesis

Osnovni zadatak ovog rada bio je ispitati utjecaj istovremenog miješanja i ultrazvučnog djelovanja na kinetiku nukleacije boraksa u šaržnom kristalizatoru s kontroliranim hlađenjem. Ispitivanja su se provodila u kristalizatoru laboratorijskog mjerila volumena 2,65 dm 3 , gdje je matična otopine zasićena pri 30 °C hlađena brzinom od 6 °C h -1 . Tijekom cijelog procesnog vremena, na matičnu otopinu je istovremeno djelovano ultrazvukom i mehaničkim miješanjem. Detaljno se sagledavao utjecaj amplitude ultrazvuka, A=0, 20, 25 i 30 %, dok je brzina vrtnje miješala odgovarala minimalnoj brzini vrtnje potrebnoj za postizanje stanja potpune suspenzije (N=N JS ). U okviru ovog rada bilo je potrebno odrediti promjenu koncentracije matične otopine potenciometrijskom metodom off-line, kao i promjenu apsolutne prezasićenosti tijekom procesnog vremena pri sve četiri primjenjene amplitude ultrazvuka. Određena je i širina metastabilne zone općeprihvaćenom vizualnom metodom. Na temelju dobivenih rezultata, primjenom Mersmannova nukleacijskog kriterija, određen je dominantni nukleacijski mehanizam, a potom su izračunate i uspoređene brzine nukleacije pri svim ispitivanim uvjetima. Primjenom granulometrijske analize prosijavanjem detaljno su sagledane karakteristike konačnog produkta kristalizacije. Kako bi se odredili energetski zahtjevi provedenih ispitivanja određena je snaga miješanja suspenzije te snaga ultrazvuka, obje izražene privedenom snagom po jediničnoj masi suspenzije, P/m. Konačno, na temelju dobivenih rezultata, preporučeni su optimalni uvjeti provedbe procesa.The essential task of this research was to investigate the effect of simultaneous mixing and ultrasound impact on kinetics of borax nucleation in a batch crystallizer with controlled cooling. Experiments were done in a laboratory scale crystallizer, where the volume of mother liquor saturated at 30 °C was 2,65 dm 3 . The applied cooling speed was 6 °C h -1 . During the entire process, both mechanical stirring and ultrasound irradiation were simultaneously applied. All experiments were conducted at that impeller speed which ensured the state of complete suspension (N=N JS ), while the effect of four different ultrasound amplitudes, A=0, 20, 25 and 30%, was closely monitored. It was essential to determine the change of mother liquor concentration, which was done off-line by using the potentiometric method. Also, for all four ultrasound amplitudes applied, the change of absolute supersaturation during process time was monitored. Metastabile zone width was determined by using a widely accepted visual method. Based on that data, a dominant nucleation mechanism was determined by Mersmann’s nucleation criteria. Furthermore, for all experimental conditions tested, nucleation rates were calculated and compared. The characteristics of the final product of crystallization were analyzed in detail by sieving. In order to assess the energetic requirements of the experiment, the mechanical mixing power of the suspension as well as the power of ultrasound irradiation were determined and expressed as the power consumed per unit mass of suspension, P/m. Finally based on given results, the optimal process conditions for combined use of mehanical stirring and ultrasound irradiation were suggested