| Abstract | U ovom radu ispitivano je kako brzina hlađenja matične otopine utječe na rast kristala dinatrijevog tetraborat dekahidrata (boraksa) tijekom sonokristalizacije. Ispitivanja su se provodila u šaržnom kristalizatoru laboratorijskog mjerila s pregradama i radijalnim turbinskim miješalom čija je brzina vrtnje bila jednaka potrebnoj za postizanje stanja potpune suspenzije kristala (N JS = 324 o min -1 ). Ultrazvučno djelovanje na otopinu provodilo se pomoću homogenizatora, frekvencije 24 kHz i snage 400 W, kontinuirano pri 20 % amplitudi. Kristalizacija se provodila iz matične otopine zasićene pri 30 °C hlađenjem do temperature od 10 °C pri brzinama od 4, 6, 8, 10 °C h -1 . Kako bi se dobio uvid u utjecaj ultrazvuka na navedeni proces također se provodila i kristalizacija bez njegovog djelovanja pri istovjetnim procesnim uvjetima (N JS = 324 o min -1 , T z = 30 °C) i brzini hlađenja od 6 °C h -1 . Tijekom eksperimenta, nakon nuleacije, provodila se analiza kristala u matičnoj otopini metodom laserske difrakcije te se istodobno određivala i koncentracija matične otopine refraktometrijskom metodom. Iz rezultata provedenih analiza sagledane su promjene raspodjele veličina kristala, srednjeg volumnog promjera kristala i njegove standardne devijacije te specifične površine kristala tijekom procesnog vremena pri svim ispitivanim uvjetima. Produkti kristalizacije pri navedenim procesnim uvjetima su također podvrgnuti granulometrijskoj analizi prosijavanjem te je analiziran i njihov oblik. Za sve ispitivane uvjete određen je i utrošak snage privedene sustavu tijekom miješanja i ultrazvučnog djelovanja. Iz rezultata je uočeno da se u procesu sonokristalizacije bez obzira na brzinu hlađenja matične otopine svojstva kristala ne mijenjaju bitno s obzirom na raspodjelu veličina i njihovu srednju veličinu. Najveći utjecaj brzine hlađenja odrazio se na promjenu specifične površine kristala koja je pak posljedica sekundarne nukleacije u sustavu. S druge strane, kad se usporede rezultati provedenih analiza u sustavima sa ultrazvukom sa sustavom bez ultrazvuka može se zaključiti da utjecaj ultrazvučnog djelovanja na svojstva kristala značajno nadmašuje utjecaj brzine hlađenja. |
| Abstract (english) | In this work, the influence of the cooling rate of the mother liquor on the growth of crystals of disodium tetraborate decahydrate (borax) during sonocrystallization was studied. The test was carried out in a batch laboratory crystallizer equipped with a radial turbine with four blades whose rotation speed was equal to that required to achieve a state of complete crystal suspension (N JS = 324 rpm). Ultrasonic irradiation of the solution was carried out with a homogenizer with a frequency of 24 kHz and a power of 400 W, continuously at 20% of the amplitude. Crystallization was carried out from a mother liquor saturated at 30 °C by cooling to a temperature of 10 °C at rates of 4, 6, 8, 10 °C h -1 . In order to gain insight into the influence of ultrasound on the process, crystallization was performed without ultrasound, under the same process conditions (N JS = 324 rpm, Tz = 30 °C) at a cooling rate of 6 °C h -1 . During the experiment, after nucleation, crystals in the mother liquor were analyzed by laser diffraction method and at the same time, concentration of the mother liquor was determined using the refractometric method. Changes were observed in crystal size distribution, mean volume diameter of the crystals and its standard deviation, as well as the specific surface area of the crystals during process time. The obtained products were subjected to sieve analysis, and the shape of the crystals was also analyzed. For all investigated process conditions, the power supplied to the systems by mixing and ultrasonic radiation was determined. From the results, it was observed that during the sonocrystallization process, regardless of the cooling rate of the mother liquor, the properties of the crystals do not change significantly with regard to the size distribution and their average size. The greatest influence of the cooling rate was reflected on the change in the crystal specific surface area, which is a consequence of secondary nucleation in the systems. On the other hand, comparing the results obtained in systems with and without ultrasound, it can be concluded that the influence of ultrasound on crystal properties significantly exceeds the influence of the cooling rate. |
