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Dear colleagues, we are extremely honoured to present to you the Proceedings of the international conference 19th Ružička Days, which was successfully held on September 21–23, 2022, in Vukovar, Croatia, in the hometown town of our famous Croatian scientist and first Nobel laureate, professor Leopold (Lavoslav) Ružička. The main goals of the Conference were to promote excellence, originality and innovation of interdisciplinary scientific research as well as the practical application of the obtained results through collaboration with industry, emphasizing thus the recognizable slogan of the Ružička Days conference: "Today Science – Tomorrow Industry". In addition, the Conference gave the opportunity for meetings, exchanging the ideas, opinions, experiences and cooperation among participants from different working surroundings. It is also important to point out that since 2008, within the international conference Ružička Days, Meeting of Young Chemists has also been held, where high school students, with the help of their mentors, present papers in the field of chemistry, with the aim to direct students and young people to the technical and natural sciences, especially chemistry. In its seventh issue (2011, 2013, 2015, 2017, 2019, 2021) the Proceedings publishes scientific and professional full papers of high quality in the following sections: Chemical analysis and synthesis (10), Chemical and biochemical engineering (3), Food technology and biotechnology (4), Chemistry in agriculture and forestry (1), Environmental protection (9) and 8th Meeting of Young Chemists (3). Full-length papers were subjected to an international review procedure done by eminent experts from the corresponding fields, to whom we express our gratitude, but they were not subjected to linguistic proofreading. On behalf of the Scientific and Organizing Committee of the 19th Ružička Days we cordially thank all the authors, reviewers, participants, lecturers, organizers, especially the international organizers EuCheMS and EHEDG, auspices and sponsors, and all the others who, in any way, supported the Conference and contributed to the preparation of the Proceedings, especially to our highly skilled and committed associates, who have put a lot of effort in the preparation of these Proceedings. At the very end, special thanks to our young, future scientists and their mentors who are faithful participants of the Meeting of Young Chemists of the Ružička Days conference. Enjoy the extremely interesting scientific and professional papers contained in these Proceedings, until the next 20th jubilee of Ružička Days in 2024! We are looking forward to meeting you again in Vukovar! Yours sincerely, Chief Editors Jurislav Babić Vesna Ocelić Bulatović Dajana Kučić Grgić

The ultrasound irradiation during crystallization (i.e. sonocrystallization) is increasingly used due to the numerous advantages that this operation provides. However, for process design and control it is of enormous importance to define the influence of process conditions on nucleation kinetics of particular substance. In this work the influence of ultrasound amplitude on nucleation kinetics of borax decahydrate were systematically investigated in laboratory scale stirred crystallizer of 2, 7 dm3. The tests were performed at four amplitudes of ultrasonic power, A, in the range of 0 to 30 %, and at four cooling rates, b, from 4 to 10 °C h-1 measuring the metastable zone width and power consumption. The experimental results showed narrowing of the metastable zone width by increasing ultrasound amplitude and decreasing cooling rate. Finally, the functional dependence of the metastable zone width on these variables was derived (∆Tmax = K A-0.739 b0.3525). It was found that in all systems the value of the apparent order of nucleation is the same, while the nucleation rate constant increases with the ultrasound amplitude, i.e. with the power dissipated to the system. It was also found that the nucleation started by the primary nucleation mechanism at all examined conditions, while its rate is considerably affected by the ultrasound amplitude and the cooling rate. Nevertheless, granulometric properties of crystals obtained at 20 % amplitude show close values of mean volume diameter and its standard deviation regardless of the cooling rate. In addition, these values are significantly lower than those obtained in the silent system at 0 % amplitude.

The sorption of copper ions on zeolite NaX is a heterogeneous process, and as such dependent on hydrodynamics in a batch reactor. Therefore, this work aimed to study the effect of mixing speed (N/NJS ratio values, i.e. impeller speed/minimum impeller speed for complete suspension) on the kinetics and power consumption of the process examined.The experiments were carried out in a glass batch reactor of nonstandard configuration (D/dT=0.6, C/H=0.1), equipped with baffles and the SBT impeller. A transient multiphase computational fluid dynamics model was developed to gain valuable insight into complex flow kinetics. The Blanchard model, Mixed surface reaction and diffusion-controlled sorption kinetic model, and Weber-Morris model were used for the kinetic analysis of the experimental kinetic data.According to and RMSE values, the reaction is kinetic controlled in all experiments performed.

The sorption of copper ions on zeolite NaX is a heterogeneous process, and as such dependent on hydrodynamics in a batch reactor. Therefore, this work aimed to study the effect of mixing speed (N/NJS ratio values, i.e. impeller speed/minimum impeller speed for complete suspension) on the kinetics and power consumption of the process examined. The experiments were carried out in a glass batch reactor of nonstandard configuration (D/dT = 0.6, C/H = 0.1), equipped with baffles and the SBT impeller. A transient multiphase computational fluid dynamics model was developed to gain valuable insight into complex flow kinetics. The Ritchie model, Mixed surface reaction and diffusion-controlled sorption kinetic model, and Weber-Morris model were used for the kinetic analysis of the experimental kinetic data. According to τ and AARD values, the reaction is kinetic controlled in all experiments performed.

In order to define the kinetics of nucleation and crystal growth, supersaturation as a driving force of crystallization needs to be determined over process time since it is the driving force of crystallization. Before selecting of an appropriate analytical method for bulk supersaturation measurement, it is necessary to examine its sensitivity [1]. In this work, application of ion-selective electrode (ISE) and refractometer during batch cooling crystallization was analysed. Their calibration, unlike as is commonly done at a constant temperature, was performed here under crystallization process conditions in terms of cooling rate. The refractive index, n, and electrode potential, E, (Na-ISE - Ag/AgCl) of borax solutions of known concentrations, c, cooled at a rate of 6 °C h-1, were measured at certain temperatures, T, in the range from 30 °C to 5 °C. The parameters of the calibration equation for the refractometric (n = K1·ca·Tb) and the potentiometric method (E = K2·cd·Tg) for examined temperatures and solution concentrations were derived. For the blind probe concentration measurement, refractometry was found to be more accurate while potentiometry showed greater precision. However, when deciding on a particular method, it should be borne in mind that the refractometer is calibrated only once, while ISE calibration is required frequently [2, 3]. [1] M. Barrett, M. McNamaraa, H. X. Hao, P. Barrett, B. Glennon, Chem. Eng. Res. Des. 88 (2010) 1108-1119. [2] A. Čelan, I. Milanović, M. Ćosić, N. Kuzmanić, Chem. Eng. Technol. 44 (2021) 11. [3] M. Ćosić, A. Čelan, I. Pehnec, N. Kuzmanić, Chem. Eng. Comm. (207) 6 (2019) 847-860.

Mehaničko miješanje se primjenjuje u čitavom nizu proizvodnih procesa. Potpuno razumijevanje ove operacije počiva na poznavanju hidrodinamičkih uvjeta koji vladaju u miješalici temeljem kojih je moguće provedbu miješanja i optimirati. Ukoliko se miješanje provodi dvama miješalima, hidrodinamika u promatranom sustavu postaje znatno kompleksnija u odnosu na sustave s jednim miješalom. Cilj ovog rada je bio sagledati utjecaj udaljenosti dvaju miješala od dna posude (C/D) na karakteristične parametre miješanja u miješalici volumena 14.15 dm3. Miješanje se provodilo korištenjem dvaju turbinskih miješala s lopaticama nagnutim pod kutom od 45° (PBT) čija je međusobna udaljenost (S/D) zadržana konstantnom. U radu je eksperimentalno određeno vrijeme homogenizacije, Ntm, mjerenjem vremena do ustaljenja potencijala otopine nakon injektiranja trasera. Pri odabranim brzinama vrtnje miješala mjeren je i zakretni moment na osovini miješala kako bi se odredio utrošak snage. Numerički model je razvijen u računalnom programu ANSYS™ Fluent v17.2. Isti je korišten za prikaz specifičnih tokova fluida, kao i kontura rasipanja privedene energije unutar miješalice. Ovakav kvantitativan i kvalitativan opis miješanja omogućava potpuniju analizu utjecaja miješanja na pojedine stupnjeve provedbe separacijskih procesa, prije svega šaržne kristalizacije za koju je i razvijen.

Povijest razvoja kemijske industrije na splitskom području neminovno se povezuje s poviješću proizvodnje cementa koja se ovdje odvija u kontinuitetu dulje od 150 godina. Početak intenzivnije industrijalizacije hrvatskog, a time i ovog područja, odvijao se pod ingerencijom Austrijskog carstva, a potom i Austro-Ugarske Monarhije. To razdoblje u Hrvatskoj obilježeno je i ukidanjem kasnofeudalnih odnosa 1848., čime se stvaraju preduvjeti za afirmaciju kapitalističkih privrednih odnosa. Relativno uspješan početak proizvodnje cementa u Austrijskom carstvu (1842.) i sve veća popularnost cementa kao građevnog materijala iniciraju diljem Carstva opsežna ispitivanja vezana uz pronalazak što kvalitetnije cementne sirovine – lapora, kao i podizanje novih pogona za proizvodnju cementa. Tehnologija proizvodnje cementa ubrzo se proširuje i u hrvatske krajeve. Pokreće se proizvodnja na otoku Sv. Andrija pored Rovinja 1852., da bi se potom oko 1865. započelo i s proizvodnjom u Dalmaciji

Generally, crystallization is one of the oldest separation operations in chemical engineering. Owing to the fact that it is conducted at relatively low temperatures, it is also one of the most inexpensive ones. A major advantage of crystallization is that it allows generation of a product of specific properties, but only if the process is controlled properly. Certainly, crystallization will depend on physical and chemical characteristics of the crystallizing substance, but since it lays upon the laws by which transport phenomena is governed, crystallization may significantly depend on the process conditions as well. Since crystallization takes place in suspensions, it is often conducted batch-wise in stirred vessels. Until now, many experiments carried out in single and dual impeller batch crystallizers indicate that mixing parameters can have a major impact on borax decahydrate crystallization kinetics and consequently the product properties (Čelan et al., 2018). Most of these investigations are conducted at the just suspended impeller speed in order to explore how transport phenomena reflects on the characteristics of the final product when the process is performed at optimal energy consumption. In the last years, there has been an increase of interest in the application of ultrasound for the control of crystallization process due to more demanding requirements for crystal purity and defined crystal morphology. Several theories were proposed in order to explain the mechanism by which ultrasound affects crystallization, but an exact one still has not been accurately determined. However, it is known that its influence relies upon the phenomenon of ultrasonic cavitation (Kim and Suslick, 2018). By one of the proposed theories, this event generates high local temperatures (Suslick et al., 1990), some suggest that implosion of the bubble causes the rise of the local pressure values, and other imply that ultrasound cavitation causes segregation of the mixture thus inducing nucleation (Grossier et al., 2007). In any case, previous studies have shown that sonication during crystallization can affect induction time and metastable zone width, the mechanism and rate of nucleation but also the kinetics of crystal growth (Jambrak et al., 2014 ; Kuijpers et al., 2002 ; Lyczko et al., 2002). Sonication also increases the repeatability which is one of its key advantages in comparison to conventional crystallization. Investigation on the influence of ultrasound on crystallization are usually carried in unmixed or in systems mixed by magnetic stirrer. But in crystallizers larger than 0, 5 L, neither ultrasound nor magnetic stirrer are powerful enough to suspend growing crystals and ensure conditions for undisturbed crystal growth. Unlike the majority of papers concerning the topic of sonocrystallization, experiments here were conducted in a mechanically stirred batch cooling crystallizer. The research at hand deals with the investigation of an influence of ultrasound amplitude on nucleation kinetics of borax decahydrate whose applications are so versatile that it can be found in almost all industries. Crystallization has been conducted in a 3 L batch cooling crystallizer. Mother liquor of borax decahydrate has been saturated at 30 °C and it has been cooled down linearly at the rate of 6 °C/h. Cooling profile was controlled by Lauda Proline RP855 C X Edition thermostat. Crystallizer was a baffled, flat bottom vessel in which liquid height was equal to crystallizer diameter, H=dT. Impeller used in this investigation was a straight blade turbine (SBT) which generated radial fluid flow pattern in the vessel. Impeller diameter was equal to 1/3 of the vessel diameter, D=1/3 dT and it was mounted on a shaft at the off-bottom clearance, C, which equaled C/D=1. During the entire process, both mechanical stirring and ultrasound irradiation were simultaneously applied. Ultrasound irradiation was applied by using the Hielscher UP400St homogenizer with a H22L2D sonotrode. All experiments were conducted at the impeller speed which ensured the state of complete suspension (N=NJS). The said impeller speed was determined by Zwieterings 1-2 seconds criterion for all four ultrasound amplitudes applied, A=0, 20, 25 and 30 %. It was essential to determine the change of supersaturation during process time, which is the driving force of the process. Supersaturation was determined based on the values of concentration of mother liquor which was measured off-line by using the potentiometric method. Metastable 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. Characteristics of the final product of crystallization, namely crystal size distribution, were determined by laser diffraction using the Horiba LA-300 particle size analyzer. In order to assess the energy requirements of the process, power consumption was determined and it was expressed per unit mass of suspension, P/m. Power consumed by stirring was determined by measuring torque imparted on the shaft (Lightnin Labmaster L1U10F mixer) while the power pertaining to ultrasound irradiation was determined by calorimetric measurements. Obtained results showed that an increase of ultrasound amplitude decreases the metastable zone width and that nucleation commences at lower supersaturation. By using the Mersmanns nucleation criterion, i.e. by plotting the dimensionless supersaturation vs. dimensionless solubility diagram it was found that nucleation started by heterogeneous mechanism and that the rate of nucleation decreased as the ultrasound amplitude grew. An increase of the amplitude also reflected on the properties of the final product. Mean crystal size was larger in the system without ultrasound. Although there was no significant change in mean crystal size in the systems where ultrasound was applied, it was found that the crystal size distribution shifts from bimodal to monomodal as the amplitude rises. The data on power consumption showed that it increases with amplitude but also that the share of the power consumed by ultrasound irradiation is tenfold higher than the one related to stirring. It can be concluded that sonocrystallization is a good choice if monomodal crystal size distribution with high repeatability is required. But with the results of power consumption in mind, if crystal characteristics are not that important, it would be more appropriate to conduct conventional crystallization since its energy requirements are significantly lower.

Tvornica Jugovinil službeno započinje s radom 1949. puštanjem u rad pogona Elektrolize. Taj pogon osiguravao je klorovodik neophodan pri sintezi vinil-klorid monomera iz kalcijevog karbida. Prve količine poli(vinil-klorida) u Jugovinilu proizvedene su 1950. postupkom emulzijske polimerizacije, a početkom 1960. započinje i proizvodnja suspenzijskog PVC praha. Uz proizvodnju PVC-a započelo se ubrzo i s preradom tog polimera. Početkom 1992. godine tvornica mijenja naziv u Adriachem. Dolazi do njenog razdvajanja na dva dijela. Proizvodnja PVC-a ulazi u sustav INA-e kao INAVINIL, dok prerada pod nazivom Adriachem ostaje pravnim sljednikom Jugovinila. U veljači 2000. obustavljena je proizvodnja PVC-a na ovoj lokaciji. Adriachem je nastavio s preradom PVC-a, ali zbog financijskih problema i on se početkom 2012. zatvara.

Ovo enciklopedijsko poglavlje razmatra temeljne postavke i povijesni razvoj kemijskog inženjerstva kao tehničke znanosti koja se bavi istraživanjem i razvojem postupaka pretvorbe tvari i energije, kao i dimenzioniranjem, izvedbom i radom uređaja kojima se provode te pretvorbe, uvažavajući pritom osnovna načela održivoga razvoja.

Taguchi's approach to experimental design was applied to determine the effect of some process parameters on the sorption of copper ions onto zeolite NaX. The impact of solute concentration (c), temperature (T), contact time (t), impeller speed (n) and anion type (A) on the amount of copper retained on the zeolite, in a batch stirred reactor, was investigated. Optimum experimental conditions and influence of controllable factors were determined using larger-the-better approach. The applied method showed that the optimal copper removal is achieved at the lowest solute concentration, when sulphate anions were used, at the highest impeller speed and temperature used and after 45 min. The influence of controllable factors in descending order is c > n > A > T > t. Also, the impact of anion type, solute concentration and temperature on the process equilibrium was examined. The experimental data were modelled using Langmuir, Freundlich and Sips isotherms and their goodness-of-fit was analysed. Thermodynamic parameters such as G0, H0, and S0 were also determined. According to the thermodynamic parameters copper sorption on zeolite NaX was a spontaneous and endothermic process for all anions used.

In front of you are the Proceedings of the International Conference 17th Ružička days: „Today Science – Tomorrow Industry“ that was held in Vukovar, Croatia at September 19-21, 2018. The main goal of this interdisciplinary conference is to promote excellence in science and engineering as well as application of up-to-date research results and technological achievements in industry. In its fifth issue (2011, 2013, 2015, 2017, 2019) the Proceedings continues with publishing of quality scientific and professional full papers in sections Chemical Analysis and Synthesis (2), Chemical and Biochemical Engineering (3), Food Technology and Biotechnology (4), Medical Chemistry and Pharmacy (2), Environmental Protection (9) and Meeting of Young Chemists (4). All the papers were thoroughly reviewed from respectable evaluators, to whom we express our gratitude. We are also thankful to all the authors and participants of the Ružička days, and to all that support and contribute in its organization; especially our international coorganizers EuCheMS, EFFoST and EHEDG, the members of organizing and scientific committee, plenary and invited lecturers, sponsors, and of course our highly skilled and committed associates, which put a lot of effort in preparation of this book.

Širina metastabilne zone predstavlja bitan parametar za procjenu dominantnog nukleacijskog mehanizma te za određivanje brzine nukleacije. Granica ove zone predstavlja koncentracijske i temperaturne uvjete pri kojima započinje nukleacija, a koja uzrokuje promjene fizikalnih karakteristika sustava, između ostalih i zamućenje matične otopine. Stoga se često početak nukleacije detektira upravo vizualnom metodom temeljenom na promatranju stanja kristalizirajućeg sustava. Međutim, korištenje ove metode ograničeno je na laboratorijske kristalizatore s prozirnom stijenkom, dok je u industrijskim neprozirnim kristalizatorima potrebno primijeniti neku od tzv. in situ metoda među koje se svrstava i turbidimetrijska metoda. U ovom radu sagledana je mogućnost primjene turbidimetrijske metode za određivanje širine metastabilne zone boraksa u šaržnom kristalizatoru s hlađenjem. Ispitivanja su provedena u kristalizatoru volumena 2, 14 dm 3 opremljenom razbijalima virova te radijalnim turbinskim miješalom čija je brzina vrtnje bila konstantna (N = 300 o./min). Kako bi se dobio što potpuniji uvid u o osjetljivost primijenjene metode, ispitivanja su se provodila u otopinama boraksa zasićenim u temperaturnom području od 35 do 17 °C te hlađenim istom linearnom brzinom. Također, početak nukleacije u sustavu određivan je i vizualnom te potenciometrijskom metodom. Rezultati mjerenja ukazali su na vrlo visoku osjetljivost turbidimetrijske metode u odnosu na ostale korištene metode.

In heterogeneous solid-liquid systems mixing needs to ensure complete solid suspension and optimal hydrodynamic conditions regarding product properties and power consumption. In order to find optimal hydrodynamic conditions for copper exchange on zeolite NaX under isothermal conditions (303 K) Taguchi L8 (4 1 2 3 ) method was used. Experiments were carried out in a glass reactor, V = 1.3 dm 3 . Suspension height, H = 0.12 m was equal to reactor diameter, d T . Mixing was performed using pitched blade turbine with four blades (D = 0.05 m). Size of zeolite particles used was in the range from 0.063 - 0.071 mm. Solutions containing copper were prepared by dissolving Cu(NO 3 ) 2 ·3H 2 O or CuCl 2 ·2H 2 O. In the first part of this work the impeller speed that ensures the state of complete suspension (N JS ) was determined by Zwietering’s visual method 1 s at 0.33 impeller off-bottom clearances (C/H) and zeolite mass m = 6.5 g in a reactor with and without baffles. Also, at all examined mixing conditions torque was measured by Lightnin LabMaster LB2 and the power consumption was determined as well. The N JS obtained was used as one of four factors for Taguchi L8 statistical method. Along with N JS , as factors, presence and absence of baffles in the reactor, blade angle of pitched blade turbine (30° and 70°) and two different solutions containing copper, were used. For experimental results obtained, Signal to Noise ratio (S/N – larger the better) were calculated and used to evaluate optimal experimental conditions. Results of Taguchi analysis showed that the most influential factor is anion (copper solution), then blade angle, impeller speed and presence of baffles as last. At optimal conditions kinetic experiment was performed and data obtained were tested with two kinetic models: Morris-Weber (diffusion based model) and Ritchie (reaction based model).

Highlights • The effect of impeller off-bottom clearance and zeolite mass concentration was investigated. • Critical impeller speed increases with impeller position and zeolite mass concentration. • Rate of copper exchange is affected by impeller position and zeolite mass concentration. • Amount of copper exchanged is affected only by zeolite mass concentration.

In the last few decades, an interest in batch crystallization had increased significantly due to the numerous advantages of this separation method. Even though the number of scientific papers dedicated to the subject is continuously increasing, only a few of them deal with the impact of mixing on the process of crystallization. Additionally, the number of those researches in which mixing is performed by dual or even a multi-impeller system is almost negligible. Since mixing ensures favorable conditions for mass and energy transfer, an impact of this operation on every aspect of a crystallization process should be investigated. For this reason, the aim of this work was to find how the off-bottom clearance influences mechanism and crystal growth kinetics. Batch crystallization of disodium tetraborate (borax) by controlled cooling was conducted in a crystallizer of 15 dm 3 , which was equipped with four baffles. Saturated solution was prepared at 30°C and was cooled at the rate of 6 °C/h. Since liquid height to vessel diameter ratio (H/d T ) equaled 1.3, mixing was performed by using two impellers of a standard diameter (D/d T =0.33). Radial SBT impeller was mounted above an axial PBT impeller on a single shaft (PBT-SBT dual impeller system). Impeller spacing (S/D) was kept constant and equal to S/D=1 while the off-bottom clearance was varied in the range of 0.2 to 1.3. Impeller speed, at which crystallization was conducted, ensured the state of a complete suspension (N/N JS =1). Solution concentration was monitored continuously by Na-ion selective electrode. Linear crystal size over process time was determined by microscopic analysis of the slurry samples with Motic Images Advanced 3.2 software. In order to explain obtained results, it was also necessary to analyze the fluid flow generated by impellers. For this purpose, the overall fluid flow pattern was photographed according to the method developed by S. Ibrahim and A. W. Nienow. Results of this investigation indicate that the change of off-bottom clearance reflects on the values of linear crystal size over process time and consequently on the crystal growth kinetics. It was found that the overall crystal growth coefficient, k g , increases with an increase of impeller off-bottom clearance. A deviation from this trend is only present when the flow generated by the lower impeller is transformed due to the vicinity of the crystallizer bottom. An analysis of numerical values of the order of overall crystal growth process, g, did not imply a regular dependence of this parameter on the off-bottom clearance. To determine the crystal growth mechanism, a model proposed by Mersmann was used. By this model, in all tested conditions, crystal growth was integration limited.

Utrošak snage pri provedbi miješanja može značajno ovisiti o geometrijskim karakteristikama sustava, posebno miješala. U ovom radu sagledan je utjecaj veličine i pozicije miješala na utrošak snage miješanja pri provedbi šaržne prekristalizacije boraksa. Ispitivanja su provedena u kristalizatoru volumena 15 dm3 u kojem je omjer visine stupca kapljevine i promjera kristalizatora iznosio 1.3. Zbog navedenog omjera miješanje se provelo dvama aksijalnim turbinskim miješalima s ravnim lopaticama nagnutim pod kutom od 45° (PBT tip miješala). Utjecaj veličine miješala na utrošak snage ispitivan je primjenom miješala različitih promjera, dok je pozicija miješala sagledavana kroz udaljenost donjeg miješala od dna te kroz razmak između miješala. Iz rezultata je uočeno da utrošak snage značajno ovisi o primijenjenim parametrima miješanja. S obzirom da se utrošak sagledavao pri postizanju stanja potpune suspenzije kristala, dobiveni rezultati mogli su se objasniti tek uvidom u strukturu toka kapljevine. U tu svrhu izvršeno je fotografiranje tokova te je analizom slike određen tok kapljevine kojeg razvija pojedino miješalo. Ovisno o veličini i poziciji miješala na slikama je uočeno preklapanje nastalih tokova. Na osnovu provedenih ispitivanja utvrđeno da je utrošak snage direktna posljedica strukture sveukupnog toka kapljevine, ali i mjera međudjelovanja tokova dvaju miješala. Za suspendiranje kristala boraksa potom je predložena optimalna geometrija dvaju aksijalnih miješala.

The aim of this work was to experimentally investigate the influence of impeller off-bottom clearance on crystal growth kinetics of disodium tetraborate decahydrate (borax) in a dual-impeller batch cooling crystallizer. Examinations were carried out in a crystallizer of 15 dm3 with liquid height to crystallizer diameter ratio (H/dT) of 1.3. In this research, two pitched blade turbines (PBT) with diameter D/dT=0.33, were mounted on the same shaft with a constant spacing between impellers (s/D=1.0). Mixing was performed at the impeller speed which ensured the state of complete suspension in the system (N=NJS). The impeller off-bottom clearance (C/D) was varied from 0.2 to 1.3. Crystallization was carried out by a controlled cooling of the solution saturated at 30°C. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over time were determined by optical microscope and image analysis software. Experimental results indicate that impeller off-bottom clearance influences the change of crystal size over process time. But, regardless of the impeller off-bottom clearance, crystal growth is integration limited. The value of an order of crystal growth rate changes insignificantly with C/D ratio, while the crystal growth rate constant is affected by the change in hydrodynamics. Obtained results are a consequence of the hydrodynamic conditions in the dual- impeller crystallizer. In order to analyze the overall fluid flow pattern, in which an interaction of the flows generated by each of the impellers occurred, photographs of the flows were taken and simulations by VisiMix 2000 Turbulent were made. Taking into account the values of kinetic parameters of crystal growth, characteristic of obtained crystals, power consumption and the overall fluid flow pattern, it is possible to define the impact of impeller off- bottom clearance on borax crystal growth kinetics.

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2).

Effect of hydrodynamics on ion exchange kinetics in a batch reactor is still not properly studied despite the fact that proper mixing parameters may considerably improve the process of solid suspension and influence the hydrodynamic layer thickness responsible for the mass rate transfer. For this reason the aim of this work was to analyse the influence of hydrodynamic conditions generated by different impeller diameters on the maximum amount of copper exchange onto zeolite NaX and exchange kinetics as well. Investigations were carried out in a 2.1 dm3 baffled batch reactor at the state of complete suspension. Mixing was conducted using straight blade turbine (4-SBT) which impeller to tank diameter ratio (D/T) were varied in the range from 0.46 to 0.68. Solution containing Cu2+ was prepared by dissolving the appropriate weight of Cu(NO3)2∙3H2O. The initial concentration (7 mmol/L) was checked by Perkin Elmer Lambda 25 UV/VIS spectrophotometer. Zeolite NaX was crushed and sieved to obtain particles in the range from 0.071 – 0.09 mm. In the first part of the examination just suspended impeller speed, NJS, was determine for different impeller diameters and mass of zeolite (10.5, 13.125, 15.75 and 18.345 g) according to the Zwietering criterion. For all examined conditions power consumption was determined as well. In the second part of examination the influence of hydrodynamic on the kinetics of copper exchange on zeolite were analysed. Kinetics experiments were carried out at just suspended impeller speed (NJS) for all impellers and solid/liquid ratios used, while solution temperature was kept constant. Obtained experimental kinetics data were fitted using Elovich and Blanchard model [1-2]. The obtained results showed that just suspended impeller speed decreases as impeller diameter increases. The increase in zeolite mass causing the slight increase of NJS which is more pronounced in the systems with smaller impeller. Power consumption, at the state at complete suspension, generally decreases as impeller diameter increases. Kinetics results indicated that amount of copper ion sorbed increases sharply with the time in the initial stage and then gradually until the equilibrium is reached for all hydrodynamics conditions examined. Considering the relationship between amount of copper exchanged and power consumption at the state of complete suspension it is possible to suggest more viable (D/T) ratio for the examined process.

Utjecaj operacije miješanja na proces šaržne kristalizacije često se zanemaruje, premda ona utječe gotovo na svaki segment tog procesa. Pri odabiru optimalne konfiguracije kristalizatora, veličine koje mogu pri tome mogu pružiti veoma korisne informacije su vrijeme homogenizacije, brzina nukleacije kao i utrošena snaga miješanja. Svi eksperimenti u ovom radu provođeni su u kristalizatoru s kontroliranim hlađenjem volumena 15 dm 3 te omjera visine stupca matične otopine boraksa i promjera kristalizatora 1, 3, što je omogućilo uvođenje drugog miješala na zajedničku osovinu. Cilj je bio sagledati kako različite konfiguracije jednog i dvaju turbinskih miješala mogu utjecati na gore navedene parametre. Vrijeme homogenizacije je određivano potenciometrijskom metodom korištenjem Na-ion selekivne elektrode, dok je brzina nukleacije određivana iz podataka o prezasićenosti matične otopine primjenom Mersmannovog kriterija. Utrošak snage miješanja je kontinuirano praćen tijekom eksperimenta mjerenjem zakretnog momenta. Dobiveni rezultati ukazuju na to da se geometrijske i hidrodinamičke karakteritike ovakvih sustava značajno odražavaju na vrijeme homogenizacije, širinu metastabilne zone te brzinu nukleacije. S obzirom na navedeno, odgovarajućim odabirom konfiguracije dvaju miješala moguće je direktno utjecati na karakteristike finalnog produkta procesa šaržne kristalizacije.

Mnoge operacije u kemijskoj industriji u velikoj mjeri ovise o uspješno provedenom miješanju. Koliko će ono biti uspješno moguće je procijeniti kroz nekoliko parametara, pa tako i kroz poznavanje vrijednosti snage miješanja. Snaga miješanja predstavlja energiju preko miješala dovedenu u sustav. Njezina vrijednost, između ostalog, utječe i na veličine važne pri provedbi procesa kristalizacije kao što su stupanj izmješanosti te koeficijent prijenosa tvari. U ovom istraživanju, šaržna kristalizacija boraksa je provedena u sustavu volumena 15 dm3 pri čemu je omjer visine stupca matične otopine i promjera kristalizatora (H/T) iznosio 1.3. Miješanje se provodilo uporabom dvaju radijalnih turbinskih miješala (tzv. 4-SBT tip miješala) pri onoj brzini vrtnje koja je osiguravala stanje potpune suspenzije (N = NJS). U sustavu su kontinuirano praćene koncentracija matične otopine (uz uporabu Na-ion selektivne elektrode) te zakretni moment (korištenjem mjerila zakretnog momenta Himmelstein and Co.). Ispitan je utjecaj veličine miješala – D/dT (promjer miješala/promjer miješalice), utjecaj udaljenosti donjeg miješala od dna – c/D te međusobni razmak dvaju miješala – s/D na vrijednost snage miješanja. Snaga miješanja je izračunata iz izmjerenih vrijdnosti zakretnog momenta te je izražena kao snaga utrošena po jedinici mase suspenzije – P/m. Rezultati su pokazali kako utrošak snage izrazito ovisi kako o veličini tako i o položaju miješala unutar kristalizatora. Obzirom da je udio troškova vezanih uz utrošak snage miješanja u ukupnim troškovima proizvodnje znatan, nužno je razmotriti alternativne konfiguracije miješala kako bi se proizveo produkt zadovoljavajućih karakteristika uz minimalne troškove proizvodnje.

Katalizatori na osnovi zeolita i bakra kao aktivne komponente imaju izuzetno široku primjenu u procesnom inženjerstvu. Za njihovu uspješnu pripremu nužno je poznavanje utjecaja različitih parametara na brzinu ionske izmjene kao i kinetički model izmjene. Stoga je u ovom radu ispitan utjecaj koncentracije bakra na brzinu ionske izmjene u kinetičkom području te je izvršena usporedba različitih kinetičkih modela s dobivenim eksperimentalnim podacima. Eksperimentalna kinetička ispitivanja provedena su na sustavu bakar - sintetski zeolit NaX u kotlastom reaktoru pri temperaturi od 306 K i pri konstantnoj brzini miješnja (N = 240 okr/min). Otopine bakra različitih koncentracija pripravljene su otapanjem bakrovog (II) nitrata u destiliranoj vodi, dok je srednja veličina čestica korištenog zeolita iznosila 0.08 mm. Analizom eksperimentalnih podataka utvrđeno je da vrijeme potrebno za uspostavu ravnoteže, kao i kapacitet izmjene iona rastu porastom početne koncentracije bakra u otopini. Izmjena iona bakra u početnom periodu je izuzetno brza, nakon čega se može okarakterizirati postupnom do uspostave ravnoteže. Analiza eksperimentalno dobivenih kinetičkih podataka provedena je metodom nelinearne regresije za tri različita kinetička modela: Hoovov, Blanchardov i Ritchiev model. Jako dobro slaganje uočeno je kod sva tri modela s obzirom da svi korišteni modeli pretpostavljaju da je reakcija izmjene bakra na NaX zeolitu reakcija drugog reda tj. da se dva iona natrija zamjenjuju jednim ionom bakra. Tako da i Hoovov i Blanchardov model pokazuju dobro slaganje s eksperimentalnim podacima i tek su neznatno lošiji od Ritchieva modela koji je inače razvijen za proces sorpcije na heterogenoj površini kakvom se i površina zeolita NaX može smatrati.

Jedan od bitnijih čimbenika koji utječe na početak i brzinu nukleacije, a time i na cjelokupan proces kristalizacije je širina metastabilne zone matične otopine. To je zona unutar koje spontana nukleacija još nije moguća, ali čija širina bitno utječe na rast kristala i stabilnost prezasićene otopine. Mogućnost utjecaja na širinu metastabilne zone predstavlja i mogućnost direktnog utjecaja na svojstva kristalnog produkta. S obzirom da s termodinamičkog i kinetičkog aspekta ta zona metastabilnosti nije u potpunosti definirana, u ovom radu je ispitan utjecaj parametara miješanja na njenu širinu i to u procesu kristalizacije dinatrijevog tetraborat dekahidrata (boraksa). Kristalizacija se odvijala u šaržnom kristalizatoru u kojem se matična otopina volumena 15 dm3 , zasićena na 30 °C, hladila brzinom od 6 °C h –1. Omjer visine stupca otopine i promjera kristalizatora (H/dT ) iznosio je 1, 3 što je zahtijevalo uvođenje drugog miješala u sustav tj. uporabu dvaju miješala smještenih na istoj osovini. Primijenjena radijalna turbinska miješala (tzv. 4-SBT tip miješala) svojom brzinom vrtnje osiguravala su u kristalizatoru stanje potpune suspenzije. Eksperimentalna ispitivanja su provedena s različitim promjerima miješala (D/T) te pri različitim omjerima c/D (omjer udaljenosti donjeg miješala od dna posude i promjera miješala), različitim vrijednostima s/D (omjer međusobne udaljenosti miješala i promjera miješala) kao i pri različitim vrijednostima N/NJS (omjer brzine vrtnje miješala i brzine vrtnje koja osigurava stanje potpune suspenzije). Promjena koncentracije matične otopine boraksa kontinuirano je praćena Na-ion selektivnom elektrodom uz uporabu Ag/AgCl elektrode kao referentne elektrode. Rezultati navedenih ispitivanja ukazuju da u šaržnom kristalizatoru s dvama turbinskim miješalima, uz brzinu hlađenja matične otopine, geometrijske karakteristike korištenih miješala, njihova pozicija kao i udaljenost miješala na zajedničkoj osovini te brzina vrtnje miješala imaju značajan utjecaj na vrijednost maksimalne apsolutne prezasićenosti, a samim tim i na vrijednost brzine nukleacije.

U radu je ispitivan utjecaj broja miješala na mehanizam i brzinu nukleacije te kinetiku rasta kristala u procesu šaržne kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) kontroliranim hlađenjem. Miješanje u kristalizatoru, volumena 15 L, provodilo se jednim, odnosno dvama istovjetnim aksijalnim turbinskim miješalima s 4 ravne lopatice nagnute pod kutom od 45° (tzv. PTD miješala). Brzina vrtnje miješala osiguravala je stanje potpune suspenzije u sustavu (N = Njs). Omjer visine stupca matične otopine i promjera kristalizatora (H/T) iznosio je 1.3, dok se ta otopina, zasićena pri temperaturi od 30 °C, hladila brzinom od 6 °C h-1. Promjena koncentracije boraksa tijekom procesnog vremena praćena je uporabom Na-ion selektivne elektrode. Kontinuirano praćenje promjene koncentracije otopine, odnosno prezasićenosti omogućilo je determiniranje širine metastabilne zone ispitivanih sustava. Brzina nukleacije određivana je Mersmannovim kriterijem, dok su podaci o brzini linearnog rasta kristala dobiveni direktnim mjerenjem veličina kristala uzorkovanih tijekom procesa kristalizacije. Pored navedenih mjerenja, u radu je također izvršena i usporedba utroška snage miješanja za ispitivane sustave. Finalni produkti podvrgnuti su granulometrijskoj analizi te je provedena usporedba granulometrijskih parametara kako bi se što detaljnije sagledao utjecaj broja miješala na proces kristalizacije boraksa. Nazočnost drugog miješala u kristalizatoru bitno mijenja tokove fluida u reaktorskom prostoru, a što se direktno odražava i na vrijednosti ispitivanih kinetičkih parametara.

This work gives an insight into the impact of impeller speed in a dual-impeller crystallizer on the process of batch cooling crystallization of disodium tetraborate decahydrate (borax). Experiments were conducted in a 15 L baffled batch cooling reactor with specific geometrical characteristics at linear cooling rate of 6°C/h. Mother liquor mixing was performed using the straight blade turbine (4-SBT) that created a radial flow pattern in the system. Mentioned specific geometrical characteristics primarily relate to the liquid level to vessel diameter ratio (H/dT). Since that ratio was 1.3, an installation of a second impeller was required. The ratio of impeller diameter to vessel diameter, D/dT was 0.33 while the ratio of impeller off-bottom clearance and impeller spacing to the impeller diameter ratios, c/D and s/D respectively, equaled 1. In order to reveal the degree of influence that a dual- impeller system has on the process of crystallization of borax, the same had to be compared to the single-impeller system setup. Considering the fact that the observed system is a solid-liquid suspension, initial experiments were carried out at the recommended impeller speed that ensured the state of a complete suspension (NJS). Further runs included entering the intermedial suspension state since the impeller speed, N to NJS ratio was varied from 1 to 2. This kind of an experimental setup enabled a detailed analysis of the impact of different impeller speed on nucleation and crystal growth kinetic parameters, growth rate, crystal size distribution (CSD) and crystal shape as well. During the process, mother liquor concentration was monitored in-line by the use of a Na ion- selective electrode. Linear crystal growth was determined by the means of optical microscopy where the samples were analyzed using Motic Images Plus 2.0 software. At the end of the process, crystal product was dried and then subjected to sieving to determine the crystal size distribution. To calculate the power consumption at different impeller speeds, data acquisition software was used to monitor and analyze torque values. Results showed that an installation of a second impeller in a system with geometrical characteristics described earlier, leads to a decrease in NJS but with no significant change in power consumption. The effect that an increase in impeller speed in a dual-impeller system has on nucleation kinetic parameters, crystal growth kinetic parameters, growth rate and crystal size distribution is evident. This influence is especially pronounced when it comes to crystal shape of the final product at N/NJS=2 where more than 85% of the final crystal product is regularly shaped. An increase in impeller speed in a dual-impeller system shows an expected increase in power consumption but with no fluctuations in its value over time. Nevertheless, it should be emphasized that these experiments were carried out in laboratory scale and that formation of a new (solid) phase in the system would most likely have to have an impact on the change of power consumption if the same would be implemented in a much larger scale.

The aim of this work was to investigate the influence of fluid flow pattern in the crystallizer created by different impellers on the nucleation mechanism and nucleation rate of disodium tetraborate decahydrate (borax) in the process of batch cooling crystallization. Examinations were performed in the crystallizer of 15 dm3 with liquid level to tank diameter ratio (H/dT) of 1, 3 and diameter ratio impeller to tank (D/dT) of 0, 33. The fluid flow patterns in the crystallizer were generated by axial and radial turbine impellers and by their different dual combinations. Impeller speed ensured the state of complete suspension in the system for all configurations used (N = NJS). Crystallization was carried out by cooling of the mother liquor from the saturation temperature of 30°C by the rate of 6 °C h-1. Concentration of solution was measured in line by the means of Na ion-selective electrode, while the onset of nucleation i.e. metastable zone width was detected from the changes of concentration values. Mechanism and nucleation rate were determined according to Mersmann´s nucleation criterion. In order to gain complete insight into the overall fluid flow in the crystallizer the photographs of the flows were taken and simulations by VisiMix 2000 Turbulent package were made. Power consumption over the process time for all impeller configuration used were measured as well. Obtained results indicated that flow pattern developed by single impeller or by interaction of flows generated by each of impellers in dual impeller system significantly influenced the nucleation mechanism and nucleation rates of borax. Different impeller configurations affect the values of just suspended impeller speed, the final product properties and power consumption as well.

Izložba „Vremeplov laboratorijskih vaga na Kemijsko-tehnološkom fakultetu“ održana je na Kemijsko-tehnološkom fakultetu u sklopu Festivala znanosti u Splitu 2014. godine.

In this work influence of seed surface area and shape factor on granulometric properties of disodium tetraborate decahydrate (borax) obtained by batch cooling crystallization were investigated. In the crystallizer with the volume of 2.14 dm3, mixing was performed by straight blade turbine impeller (abbrev. SBT). In all experiments impeller speed was kept constant (N = 350 rpm) in order to ensure the state of complete suspension in the system. Mother liquor, saturated at temperature of 30 °C, was cooling down at rate of 6 °C h-1. In the first part of the work, unseeded batch cooling crystallization was carried out in order to determine metastable zone width, granulometric properties of crystal product and to define conditions under which seeded crystallization will be performed. Afterwards, the influence of seed surface area and shape factor on the crystal size distribution and agglomeration ratio of final product was investigated. Crystals of borax with needle and plate like morphology, in size range from 45 to 142 m, were used as seed. In order to examine the effect of seed surface area, different masses of crystals of defined size and shape factor were added to the mother liquor. Analysis of crystal size distribution and agglomeration ratio of final crystal product obtained for each examined seed surface area was carried out. Obtained data were compared in details. Seed that results in borax crystal product with a narrower crystal size distribution, larger weight mean diameter and lower agglomeration ratio, could be considered as optimal option.

Razvoj ekološki prihvatljivih i učinkovitih tehnologija proizvodnje vodika bitan je za napredak vodikove ekonomije. Jedna od perspektivnih metoda dobivanja vodika temelji se na reakciji aluminija s vodom. Cilj ovog rada je istražiti mogućnost dobivanja vodika kao energenta uporabom ambalažnog otpada, tj. aluminijskih posudica za prehrambene proizvode u vodenoj otopini natrijevog hidroksida. Ispitan je utjecaj omjera broja molova aluminija i natrijevog hidroksida (0, 1, 0, 15 i 0, 2) kao i temperature reakcije u području od 27 do 57 °C na iskorištenje reakcije dobivanja vodika. Eksperimentalno dobiveni podaci su pokazali da povećanjem omjera broja molova reaktanata kao i radne temperature otopine raste volumen oslobođenog vodika, a time i iskorištenje reakcije. Ispitivanja su pokazala da je obnovljivi aluminij zanimljiva alternativa za proizvodnju vodika.

U radu je ispitivana cijepljena šaržna kristalizacija dinatrijevog tetraborat dekahidrata (boraksa) postupkom kontroliranog hlađenja. Miješanje u kristalizatoru laboratorijskog mjerila (V = 2.14 dm3) izvodilo se s radijalnim turbinskim miješalom s četiri ravne lopatice (tzv. SBT miješalo) čija je brzina vrtnje od 350 o. min-1 osiguravala stanje potpune suspenzije u sustavu. Matična otopina, zasićene pri temperaturi od 30 °C, se hladila brzinom od 6 °C h-1. Ovim radom se nastojao sagledati utjecaj površine dodanog cjepiva na raspodjelu veličina dobivenih kristala, s ciljem određivanja optimalnih uvjeta cijepljenja. U prvom dijelu rada izvršena je necijepljena šaržna kristalizacija kako bi se odredila širina metastabilne zone, granulometrijske karakteristike produkta dobivenog tim postupkom te definirali uvjeti provedbe cijepljene kristalizacije. U drugom dijelu rada razmatran je utjecaj mase i veličine cjepiva na granulometrijska svojstva produkata šaržne kristalizacije. Kao cjepivo korištene su četiri različite mase kristala boraksa igličastog oblika veličina 45 m, 63 m, 84 m i 142 m. Za sve korištene mase određene veličine cjepiva izvršena je granulometrijska analiza finalnog produkata te je provedena usporedba dobivenih rezultata. Kao optimalno cjepivo odabrano je ono koje je rezultiralo kristalima većeg masenog promjera i uže raspodjele veličina. Iz odnosa površina i veličina cjepiva definirana je funkcionalna ovisnost koja omogućuje određivanje optimalne mase cjepiva u području ispitivanih veličina cjepiva. U radu je također sagledan i utjecaj veličine cjepiva na pojavu sekundarne nukleacije i aglomeracije kristala nastalih u ispitivanim uvjetima cijepljene kristalizacije.

The effect of impeller blade angle on the nucleation kinetics, crystal growth rate, crystal size distribution and crystal shape of borax decahydrate has been investigated. The importance of blade angle was studied in a laboratory scale unseeded batch cooling crystallizer equipped with four-bladed turbine. The blade angle to the horizontal axis was varied from 30° to 90°. Experiments were performed at constant impeller diameter, off-bottom clearance and impeller speed of 350 rpm which ensured the state of complete suspension in the crystallizer. Obtained results show that the maximum value of the supersaturation, cmax, decreases with increasing impeller blade angle. The nucleation behaviour was estimated according to Mersmann's criteria. In all examined systems the nucleation takes place by heterogeneous nucleation mechanism. Impeller blade angle has also affected the crystal growth. Numerical values of order of crystal growth indicate that the growth of crystals was controlled by combination of diffusion and surface-integration growth mechanism regardless of impeller blade angle. The differences in values of second growth kinetic parameter, that is crystal growth rate constant, point to the different fluid dynamic conditions in the crystallizers caused by impeller blade angle. Namely, the increment of impeller blade angle significantly changes flow pattern in the crystallizer from axial to radial, reflecting on the crystal size distribution and shape of crystal product as well. In this work torque measurements were also performed to evident power consumption in systems with diferrent impeller blade angle. Since the crystallization is process in which a new, solid phase forms from supersaturated solution, a data acquisition software package was used to evident the possible changes of power consumption during the process. It was found that the power consumption per unit mass of suspension increased as blade angle increase. In examined systems this parameter is nearly constant over process time, so they do not change over the process time regardless of the fact that during the process the new solid phase forms.

Podaci o koncentraciji matične otopine predstavljaju bitan parametar za kontrolu i procjenu mehanizma kristalizacijskog procesa. Cilj rada bio je razviti metodu pogodnu za kontinuirano mjerenje koncentracije kristalizirajuće soli tijekom procesa šaržne kristalizacije dinatrijevog tetraborat dekahidrata postupkom kontroliranog hlađenja. Iz navedenog razloga ispitana je mogućnost primjene potenciometrijske metode tj. natrijeve ion-selektivne elektrode. Kako ion- selektivna elektroda ne daje direktno vrijednost koncentracije otopine, njeno korištenje zahtjeva primjenu baždarne krivulje koju, u ovom slučaju, nije moguće izraditi uobičajenim postupkom. Naime, tijekom šaržne kristalizacije hlađenjem temperatura matične otopine se kontinuirano mijenja što zahtijeva određene modifikacije baždarnog postupka. Te modifikacije svode se na definiranje funkcionalne ovisnosti elektrodnog potencijala o koncentraciji i temperaturi matične otopine. Utvrđeno je da se baždarenje elektrode mora izvršiti pri istim procesnim uvjetima pri kojima će se potom provoditi i kristalizacija hidratiziranog dinatrijevog tetraborata. Tu se prvenstveno misli na brzinu hlađenja i volumen matične otopine. U daljnjem dijelu rada potenciometrijska metoda primijenjena je za kontinuirano praćenje promjena koncentracije, odnosno prezasićenosti matične otopine tijekom kristalizacijskog procesa koji se provodio pri različitim uvjetima miješanja. Promjene navedenih veličina prikazane su u ovisnosti o načinu provedbe procesa te su detaljno analizirane. U cilju provjere točnosti potenciometrijske metode koncentracija matične otopine određivana je i volumetrijskom metodom. Utvrđeno je vrlo dobro slaganje primijenjenih metoda.

U radu je ispitano anodno ponašanje Al i Al-In slitine u 2M NaCl otopini. Uzorci su polarizirani anodnim gustoćama struje različitog iznosa (od 20 do 100 mA cm-2) kroz vrijeme od 30 minuta. Tijekom anodne polarizacije snimani su potencijal-vrijeme odgovori, mjeren je volumen izlučenog vodika te određen gubitak mase. Po završetku mjerenja, površine uzoraka mikroskopski su analizirane i fotografirane pri uvećanju od 100 puta. Kod svih primijenjenih anodnih gustoća struje dolazi do istovremenog otapanja uzoraka i izlučivanja vodika. Povećanjem anodne struje linearno se povećava brzina otapanje metala, ali i brzina izlučivanja vodika (pojava negativnog diferencijalnog efekta, NDE). Ustanovljeno je da se legiranjem aluminija malim količinama indija uklanjaju osnovni nedostaci aluminija kao aktivnog anodnog materijala, tj. smanjuje se polarizacija elektrode za čak 0.4 V, smanjuje se NDE te se povećava anodna djelotvornost pri realnim radnim gustoćama struje Al/zrak baterije (i > 80 mA cm-2).

Hidrodinamički uvjeti u kristalizatoru, koji su bitno određeni tipom i veličinom primjenjenog miješala, značajno utječu na svaki pojedini stupanj procesa kristalizacije. U ovom radu ispitivan je utjecaj promjera turbinskog miješala na širinu metastabilne zone,  Cmax, brzinu nukleacije, B, brzinu rasta kristala, G, te raspodjelu veličina dobivenih kristala dinatrijevog tetraborata dekahidrata. Eksperimenti su provođeni u šaržnom kristalizatoru volumena 2 L, koji je sadržavao četiri razbijala virova standardnih dimenzija (b = T/10) uz konstantnu brzinu hlađenja (6 °C/h). Miješanje se provodilo turbinskim miješalom sa četiri ravne lopatice (4-SBT) uz brzinu vrtnje od 100 min-1, s tim što se promjer miješala u odnosu na promjer posude, D/d, mijenjao od 0.46 do 0.68. Širina metastabilne zone određivana je vizualnom metodom tj. promatranjem otopine od temperature zasićenja do temperature na kojoj su uočeni prvi vidljivi nukleusi. Promjena koncentracije otopine boraksa tijekom eksperimenta praćena je uporabom Na-ion selektivne elektrode, dok je rast kristala određivan mikroskopski. U radu je također određivan i utrošak snage korištenih miješala, te je ujedno praćena i promjena tog parametara s procesnim vremenom. Rezultati rada ukazuju da promjer miješala utječe na širinu metastabilne zone. Korištenjem Mersmannovog nukleacijskog kriterija utvrđeno je da je heterogena primarna nukleacija dominantan nukleacijski mehanizam u ispitivanom sustavu, te su za istu izračunate brzine nukleacije za korištene vrijednosti Re-značajke. Promjer miješala također utječe na rast i raspodjelu veličina kristala. Na osnovu rezultata ispitivanja može se zaključiti da je promjer miješala parametar koji bitno utječe na proces šaržne kristalizacije boraksa hlađenjem, te ga svakako treba uzeti u obzir prilikom dizajniranja šaržnog kristalizatora.