Kinetic modeling of mechanisms of industrially important organic reactions in gas and liquid phase

This dissertation is based on 5 articles which deal with reaction mechanisms of the following selected industrially important organic reactions: 1. dehydrocyclization of n-butylbenzene to produce naphthalene 2. dehydrocyclization of 1-(p-tolyl)-2-methylbutane (MB) to produce 2,6-dimethylnaphthalene 3. esterification of neopentyl glycol (NPG) with different carboxylic acids to produce monoesters 4. skeletal isomerization of 1-pentene to produce 2-methyl-1-butene and 2-methyl-2-butene The results of initial- and integral-rate experiments of n-butylbenzene dehydrocyclization over selfmade chromia/alumina catalyst were applied when investigating reaction 2. Reaction 2 was performed using commercial chromia/alumina of different acidity, platina on silica and vanadium/calcium/alumina as catalysts. On all catalysts used for the dehydrocyclization, major reactions were fragmentation of MB and 1-(p-tolyl)-2-methylbutenes (MBes), dehydrogenation of MB, double bond transfer, hydrogenation and 1,6-cyclization of MBes. Minor reactions were 1,5-cyclization of MBes and methyl group fragmentation of 1,6- cyclization products. Esterification reactions of NPG were performed using three different carboxylic acids: propionic, isobutyric and 2-ethylhexanoic acid. Commercial heterogeneous gellular (Dowex 50WX2), macroreticular (Amberlyst 15) type resins and homogeneous para-toluene sulfonic acid were used as catalysts. At first NPG reacted with carboxylic acids to form corresponding monoester and water. Then monoester esterified with carboxylic acid to form corresponding diester. In disproportionation reaction two monoester molecules formed NPG and corresponding diester. All these three reactions can attain equilibrium. Concerning esterification, water was removed from the reactor in order to prevent backward reaction. Skeletal isomerization experiments of 1-pentene were performed over HZSM-22 catalyst. Isomerization reactions of three different kind were detected: double bond, cis-trans and skeletal isomerization. Minor side reaction were dimerization and fragmentation. Monomolecular and bimolecular reaction mechanisms for skeletal isomerization explained experimental results almost equally well. Pseudohomogeneous kinetic parameters of reactions 1 and 2 were estimated by usual least squares fitting. Concerning reactions 3 and 4 kinetic parameters were estimated by the leastsquares method, but also the possible cross-correlation and identifiability of parameters were determined using Markov chain Monte Carlo (MCMC) method. Finally using MCMC method, the estimation of model parameters and predictions were performed according to the Bayesian paradigm. According to the fitting results suggested reaction mechanisms explained experimental results rather well. When the possible cross-correlation and identifiability of parameters (Reactions 3 and 4) were determined using MCMC method, the parameters identified well, and no pathological cross-correlation could be seen between any parameter pair.

Liquid-phase alcohol promoted methanol synthesis from CO2 and H2

Methanol is an important and versatile compound with various uses as a fuel and a feedstock chemical. Methanol is also a potential chemical energy carrier. Due to the fluctuating nature of renewable energy sources such as wind or solar, storage of energy is required to balance the varying supply and demand. Excess electrical energy generated at peak periods can be stored by using the energy in the production of chemical compounds. The conventional industrial production of methanol is based on the gas-phase synthesis from synthesis gas generated from fossil sources, primarily natural gas. Methanol can also be produced by hydrogenation of CO2. The production of methanol from CO2 captured from emission sources or even directly from the atmosphere would allow sustainable production based on a nearly limitless carbon source, while helping to reduce the increasing CO2 concentration in the atmosphere. Hydrogen for synthesis can be produced by electrolysis of water utilizing renewable electricity. A new liquid-phase methanol synthesis process has been proposed. In this process, a conventional methanol synthesis catalyst is mixed in suspension with a liquid alcohol solvent. The alcohol acts as a catalytic solvent by enabling a new reaction route, potentially allowing the synthesis of methanol at lower temperatures and pressures compared to conventional processes. For this thesis, the alcohol promoted liquid phase methanol synthesis process was tested at laboratory scale. Batch and semibatch reaction experiments were performed in an autoclave reactor, using a conventional Cu/ZnO catalyst and ethanol and 2-butanol as the alcoholic solvents. Experiments were performed at the pressure range of 30-60 bar and at temperatures of 160-200 °C. The productivity of methanol was found to increase with increasing pressure and temperature. In the studied process conditions a maximum volumetric productivity of 1.9 g of methanol per liter of solvent per hour was obtained, while the maximum catalyst specific productivity was found to be 40.2 g of methanol per kg of catalyst per hour. The productivity values are low compared to both industrial synthesis and to gas-phase synthesis from CO2. However, the reaction temperatures and pressures employed were lower compared to gas-phase processes. While the productivity is not high enough for large-scale industrial operation, the milder reaction conditions and simple operation could prove useful for small-scale operations. Finally, a preliminary design for an alcohol promoted, liquid-phase methanol synthesis process was created using the data obtained from the experiments. The demonstration scale process was scaled to an electrolyzer unit producing 1 Nm3 of hydrogen per hour. This Master’s thesis is closely connected to LUT REFLEX-platform.

CFD Simulation of Two-phase and Three-phase Flows in Internal-loop Airlift

Airlift reactors are pneumatically agitated reactors that have been widely used in chemical, petrochemical, and bioprocess industries, such as fermentation and wastewater treatment. Computational Fluid Dynamics (CFD) has become more popular approach for design, scale-up and performance evaluation of such reactors. In the present work numerical simulations for internal-loop airlift reactors were performed using the transient Eulerian model with CFD package, ANSYS Fluent 12.1. The turbulence in the liquid phase is described using κ- ε the model. Global hydrodynamic parameters like gas holdup, gas velocity and liquid velocity have been investigated for a range of superficial gas velocities, both with 2D and 3D simulations. Moreover, the study of geometry and scale influence on the reactor have been considered. The results suggest that both, geometry and scale have significant effects on the hydrodynamic parameters, which may have substantial effects on the reactor performance. Grid refinement and time-step size effect have been discussed. Numerical calculations with gas-liquid-solid three-phase flow system have been carried out to investigate the effect of solid loading, solid particle size and solid density on the hydrodynamic characteristics of internal loop airlift reactor with different superficial gas velocities. It was observed that averaged gas holdup is significantly decreased with increasing slurry concentration. Simulations show that the riser gas holdup decreases with increase in solid particle diameter. In addition, it was found that the averaged solid holdup increases in the riser section with the increase of solid density. These produced results reveal that CFD have excellent potential to simulate two-phase and three-phase flow system.

Sisäisten donorien vaikutus Polypropeeni Ziegler-Natta katalyytissä

Tässä työssä tutkittiin erilaisten sisäisten donorien vaikutusta polypropeenin ominaisuuksiin käytettäessä Ziegler-Natta-katalyyttiä, joka valmistettiin Borealiksen aiemmin kehittämällä kaksifaasimenetelmällä. Tällä uudella menetelmällä katalyytti voidaan valmistaa ilman lisättyä sisäistä donoria ja kantajaa. Katalyyttihiukkaset saadaan kaksifaasisysteemin ansiosta muodoltaan pyöreiksi. Työn kokeellisessa osassa valmistettiin erilaisia Mg-komplekseja, jossa sisäinen donori muodostuu in-situ alkoholin ja karboksyylihappokloridin reagoidessa keskenään. Katalyyttisynteesissä Mg-kompleksi reagoi TiCl4:n kanssa. Saatujen katalyyttien ominaisuuksia testattiin polymeroimalla niillä propeenia 70 °C:ssa tunnin ajan. Polymeerien ominaisuuksia tutkittiin useiden eri karakterisointimenetelmien avulla. Lisäksi tutkittiin mahdollisuutta valmistaa katalyytti, joka ei sisältäisi ftalaattia. Työssä havaittiin, että katalyytin valmistusmenetelmä on käyttökelpoinen myös muilla sisäisillä donoreilla kuin referenssinä käytetyllä DOP:lla. Kaksiliuosfaasi-systeemi saatiin aikaan myös kahdella muulla työssä tutkitulla sisäisellä donorilla. Lisäksi faasitasapainokokeissa kahden liuosfaasin systeemi saatiin aikaan sisäisellä donorilla, joka ei sisältänyt ftalaattia. Kyseisellä katalyytillä havaittiin olevan muista katalyyteistä poikkeavia ominaisuuksia. Esimerkiksi se antoi matalamman isotaktisuuden kuin referenssikatalyytti ja se saattaisikin soveltua matalan isotaktisuuden pehmeille tuotteille. Työssä kokeiltiin yhdellä uudella katalyytillä myös eteenin polymerointia, sillä katalyytin donoripitoisuus oli hyvin matala. Katalyytin aktiivisuus eteenipolymeroinnissa oli varsin hyvä.

Mittausmenetelmien kehittaminen kuplakolonnille

Kuplakolonnireaktoreiden CFD-mallinnus on talla hetkella voimakkaasti kehittyva tutkimusalue. Kaksifaasivirtauksen luotettava simulointi ja mallintaminen on haastavaa kuplakolonnireaktorissa tapahtuvien ilmioiden monimutkaisuuden vuoksi. Reaktorin kayttaytymiseen vaikuttavat tekijat, kuten kolonnin hydrodynamiikka ja aineensiirto, tulee tuntea hyvin ennen mallien tekoa. Tassa tyossa on kokeellisesti tutkittu erilaisten mittausmenetelmien soveltuvuutta kuplakolonnin hydrodynamiikan tutkimiseen. Mittausmenetelmissa on keskitytty erityisesti CFD-mallien vaatimiin paikallisiin mittauksiin. Lisaksi tyossa on arvioitu mittausmenetelmien soveltuvuutta j a luotettavuutta CFD-mallien validointiin. Tyon kirjallisuusosassa on perehdytty kuplakolonnireaktorin hydrodynaamiseen kayttaytymiseen ja siihen vaikuttaviin tekijoihin. Naita ovat mm. reaktorityypit, kaasun dispergointi, virtaustyypit ja -alueet, kaasun tilavuusosuus, kaasukuplan koko ja kuplan nousunopeus. Mittauksia tehtiin kahdessa erikokoisessa kuplakolonnissa, joista pienemman halkaisija oli 0,078 m ja suuremman 0,182 m. Molempien kolonnien nestepinnan korkeus oli 4,62 m. Mittaukset tehtiin vesijohtovedella ja epaorgaanisella prosessiliuoksella. Hydrodynaamisista ominaisuuksista mitattiin kaasun tilavuusosuus, kaasukuplan koko seka kaasukuplan nousunopeus. Kaasun tilavuusosuusmittaukset tehtiin paaasiassa paine-eromittauksella ja joissakin tapauksissa pinnanmittausmenetelmalla. Kuplakoko- ja kuplan nousunopeusmittaukset tehtiin suumopeusvideokameralla ja laser Doppler-anemometrilla. Mittauksissa kaytettiin kahdeksaa erilaista kaasunjakolaitetta, joilla selvitettiin kaasunjakolaitteen ominaisuuksien vaikutusta kolonnin hydrodynamiikkaan. Tuloksista havaittiin, etta nestefaasin ominaisuuksilla oli suuri vaikutus kolonnin hydrodynaamiseen kayttaytymiseen. En kaasunjakolaitteilla vesijohtovedella mitatut hydrodynaamiset ominaisuudet eivat poikenneet paljoa toisistaan, kun taas prosessiliuoksella kaasunjakolaitteiden valille saatiin huomattavat erot. Mittausmenetelmista laser Doppler-anemometri ei kaytettavissa olleella optiikalla soveltunut kaasukuplien mittaamiseen. Kuplat olivat menetelmalle liian suuria. Suumopeusvideokamerallaja paine-eromittauksella paastiin hyviin tuloksiin.

Uusien polyuretaanimateriaalien kehittäminen

Polyuretaanielastomeerit ovat jaksottaisia sekapolymeerejä, jotka muodostuvat vuoroittaisista joustavien ketjujen segmenteistä ja hyvin polaarisista kovista segmenteistä. Kemiallinen rakenne ja ominaisuudet riippuvat käytetyistä reaktiokomponenteista. Pehmeän segmentin muodostaa polyoli ja kovan segmentin muodostaa yleensä di-isosyanaatti ja ketjunjatkaja. Polyuretaanielastomeerien valmistus tapahtuu valamalla, jolloin reaktiokomponentit ovat nestemäisiä. Työssä tutkittiin kahta perusmateriaalia ja yhden lisäaineen vaikutusta niiden ominaisuuksiin. Erityisesti kiinnitettiin huomiota dynaamisiin ja mekaanisiin ominaisuuksiin ja verrattiin aineita keskenään. Käytettyjä karakterisointimenetelmiä olivat kontaktikulmamittaukset, DMTA-mittaukset, dynaaminen rasittaminen pyörityslaitteella, elektronimikroskopia, hydrolyysitesti, vetotesti ja kulutustesti. Tutkittujen materiaalien pääasiallinen käyttökohde on pyörä- tai telapinnoitteena. Työn aikana kehitettiin pyörityslaite, jolla voitiin tutkia pinnoitemateriaalin käyttäytymistä halutuissa rasitusolosuhteissa. Lisäaineen vaikutus dynaamisiin ominaisuuksiin oli negatiivinen tai olematon, sillä DMTA-testien perusteella lisäaine kasvatti materiaalien häviötekijää (tan d). Pyöritystestien perusteella lisäaineella ei ollut vaikutusta hystereesiin eli pinnoitemateriaalin lämpenemiseen testin aikana. Uusi tutkittu materiaali osoittautui dynaamisissa kokeissa paremmaksi kuin vanha tuotantomateriaali. Lisäaine kasvatti molempien tutkittujen aineiden pintaenergiaa kontaktikulmamittausten perusteella. Tuotantoaineen vetomurtolujuus kasvoi lisäaineen vaikutuksesta, mutta uuden aineen vetomurtolujuus pieneni. Lisäaineella oli lievä hydrolyysiltä suojaava vaikutus tutkituilla perusaineilla. Uusi tutkittu perusmateriaali sieti hydrolyysiä paremmin kuin tuotantomateriaali, koska sen valmistuksessa käytettiin polyeetteripolyolia ja tuotantomateriaalissa polyesteripolyolia.

Hydrodynamics and Heat Transfer in an Airlift Reactor

Työn teoriaosassa esitetään kirjallisuudessa esiintyviä teoreettisia ja kokeellisia yhtälöitä nesteen nopeuden, kaasun tilavuusosuuden, painehäviön ja lämmönsiirron laskemiseksi. Lisäksi käsitellään airlift-reaktoreiden toimintaa, rakennetta ja teollisia sovelluksia, sekä sekoitusta ja geometrian vaikutusta airlift-reaktoreiden hydrodynaamisiin ominaisuuksiin. Kokeellisessa osassa kuvataan käytetty koelaitteisto ja mittausmenetelmät sekä esitetään saadut koetulokset. Koelaitteisto on viidellä nousuputkella varustettu ulkoisen kierron airlift-reaktori. Kokeellisessa osassa pyritään ratkaisemaan tällaisessa reaktorissa mahdollisesti esiintyviä ongelmia, kuten "slug flown" muodostuminen nousuputkissa sekä fluidien epätasainen jakautuminen nousuputkiin. Lisäksi tutkitaan erilaisten muuttujien, kuten kaasun tilavuusvirran, nesteen viskositeetin, suutinkoon ja nesteen jakoputken rakenteen, vaikutusta kaasun tilavuusosuuteen ja nesteen nopeuteen nousuputkissa. Nesteen nopeudet mitataan merkkiainemenetelmällä ja kaasun tilavuusosuudet manometrimenetelmällä. Lämmönsiirtoa tutkitaan mittaamalla lämpötilaeroja nousuputkissa NiCr-Ni –termoelementeillä. Mittaustulosten perusteella muokataan korrelaatiot kaasun tilavuusosuudelle ja nesteen tyhjäputkinopeudelle. Korrelaatioista lasketut tulokset sopivat kohtuullisen hyvin yhteen mitattujen tulosten kanssa. "Slug flown" ei todettu muodostuvan ongelmaksi 2.5 mPa s pienemmillä viskositeetin arvoilla 2 metriä pitkissä ja 19 mm halkaisijaltaan olevissa putkissa. Lisäksi todettiin, että kaasu- ja nestefaasien jakautumisongelmat voidaan ratkaista rakenteellisesti.

Fischer-Tropsch Slurry Bubble Column Reactor Modeling

The literature part of the work reviews overall Fischer-Tropsch process, Fischer-Tropsch reactors and catalysts. Fundamentals of Fischer-Tropsch modeling are also presented. The emphasis is on the reactor unit. Comparison of the reactors and the catalysts is carried out to choose the suitable reactor setup for the modeling work. The effects of the operation conditions are also investigated. Slurry bubble column reactor model operating with cobalt catalyst is developed by taking into account the mass transfer of the reacting components (CO and H2) and the consumption of the reactants in the liquid phase. The effect of hydrostatic pressure and the change in total mole flow rate in gas phase are taken into account in calculation of the solubilities. The hydrodynamics, reaction kinetics and product composition are determined according to literature. The cooling system and furthermore the required heat transfer area and number of cooling tubes are also determined. The model is implemented in Matlab software. Commercial scale reactor setup is modeled and the behavior of the model is investigated. The possible inaccuraries are evaluated and the suggestions for the future work are presented. The model is also integrated to Aspen Plus process simulation software, which enables the usage of the model in more extensive Fischer-Tropsch process simulations. Commercial scale reactor of diameter of 7 m and height of 30 m was modeled. The capacity of the reactor was calculated to be about 9 800 barrels/day with CO conversion of 75 %. The behavior of the model was realistic and results were in the right range. The highest uncertainty to model was estimated to be caused by the determination of the kinetic rate.

Use of the Optical Cantilever Microphone in Photoacoustic Spectroscopy

A novel cantilever pressure sensor was developed in the Department of Physics at the University of Turku in order to solve the sensitivity problems which are encountered when condenser microphones are used in photoacoustic spectroscopy. The cantilever pressure sensor, combined with a laser interferometer for the measurement of the cantilever movements, proved to be highly sensitive. The original aim of this work was to integrate the sensor in a photoacoustic gas detector working in a differential measurement scheme. The integration was made successfully into three prototypes. In addition, the cantilever was also integrated in the photoacoustic FTIR measurement schemes of gas-, liquid-, and solid-phase samples. A theoretical model for the signal generation in each measurement scheme was created and the optimal celldesign discussed. The sensitivity and selectivity of the differential method were evaluated when a blackbody radiator and a mechanical chopper were used with CO₂, CH4, CO, and C2H4 gases. The detection limits were in the sub-ppm level for all four gases with only a 1.3 second integration time and the cross interference was well below one percent for all gas combinations other than those between hydrocarbons. Sensitivity with other infrared sources was compared using ethylene as an example gas. In the comparison of sensitivity with different infrared sources the electrically modulated blackbody radiator gave a 35 times higher and the CO2-laser a 100 times lower detection limit than the blackbody radiator with a mechanical chopper. As a conclusion, the differential system is well suited to rapid single gas measurements. Gas-phase photoacoustic FTIR spectroscopy gives the best performance, when several components have to be analyzed simultaneously from multicomponent samples. Multicomponent measurements were demonstrated with a sample that contained different concentrations of CO₂, H₂O, CO, and four different hydrocarbons. It required an approximately 10 times longer measurement time to achieve the same detection limit for a single gas as with the differential system. The properties of the photoacoustic FTIR spectroscopy were also compared to conventional transmission FTIR spectroscopy by simulations. Solid- and liquid-phase photoacoustic FTIR spectroscopy has several advantages compared to other techniques and therefore it also has a great variety of applications. A comparison of the signal-to-noise ratio between photoacoustic cells with a cantilever microphone and a condenser microphone was done with standard carbon black, polyethene, and sunflower oil samples. The cell with the cantilever microphone proved to have a 5-10 times higher signal-to-noise ratio than the reference detector, depending on the sample. Cantilever enhanced photoacoustics will be an effective tool for gas detection and analysis of solid- and liquid-phase samples. The preliminary prototypes gave good results in all three measurement schemes that were studied. According to simulations, there are possibilities for further enhancement of the sensitivity, as well as other properties, of each system.

Reagenssin pinta-aktiivisuuden hyödyntäminen sinkin uutossa

Työssä tutkittiin sinkin uutossa käytettävän di(2-etyyliheksyyli)fosforihappo (D2EHPA) -uuttoreagenssin faasikäyttäytymistä ja miten laimentimen koostumus, lämpötila ja orgaanisen faasin sinkkipitoisuus vaikuttavat faasitasapainoon. Laimentimen vaikutuksen havaittiin olevan pientä, kun taas lämpötilan nostaminen yli huoneenlämpötilan leventää faasidiagrammin yksifaasialuetta. Pienet orgaanisen faasin sinkkipitoisuudet eivät juuri vaikuta faasitasapainoon. Sinkin ja D2EHPA:n moolisuhteen ollessa välillä 0,1–0,2 kompleksin rakenne ilmeisesti muuttuu. Sinkkipitoisuuden kasvaessa yksifaasialue muodostuu pienemmillä ammoniakkimäärillä. Suurilla orgaanisen faasin sinkkipitoisuuksilla ja ammoniakkimäärillä muodostuu orgaanisen faasin ja vesifaasin välille kolmas nestefaasi. D2EHPA:n (40 p %) vesipitoisuuden ja viskositeetin pH riippuvuutta tutkittiin, kun laimentimena oli alifaattinen hiilivetyliuotin. Nostettaessa pH yli 3,5:n uuttoreagenssi alkoi muodostaa käänteismisellejä, jolloin orgaanisen faasin vesipitoisuus ja viskositeetti kasvoivat eksponentiaalisesti. Sinkin mukana uuttautuu epäpuhtauksia kuten Al3+, Co2+, Cu2+, Na+, Ni2+, Cl- ja F-. Takaisinuuton kautta epäpuhtaudet joutuvat talteenottoelektrolyysiin, jossa ne voivat vaikuttaa tuotteen laatuun ja laskea virtahyötysuhdetta. Tarkoituksena oli tutkia väheneekö epäpuhtauksien myötäuuttautuminen jollakin tietyllä sinkin latausasteella. Fluoridin ja kuparin uuttautumisen havaittiin vähenevän vasta, kun sinkin pitoisuus orgaanisessa faasissa oli yli 20 g/L lämpötilasta riippumatta. Fluoridi uuttautuu mahdollisesti alumiinikompleksina ja/tai fluorihappona. Koboltin ja nikkelin myötäuuttautumisen havaittiin vähenevän, kun sinkin latausaste oli yli 10 g/L. Natrium ja kloridi eivät myötäuuttautuneet.

Counter-current Washing of Filter Cakes

The main objective of this thesis was to compare the efficiency of counter-current and co-current filter cake washing techniques. Filter cake washing is a common unit operation which is used in the chemical process industry for improving the recovery of the liquid phase or for purifying the solid phase of the filter cake. Counter-current displacement washing is more difficult to arrange and it requires additional process equipment but the advantage of counter-current method is that the consumption of wash water that is required for achieving certain filter cake purity may be considerably decreased when compared to the co-current washing method. This is true especially for materials that are difficult to wash. The literature part of this thesis consists of a review of filter cake washing in general, including the basic principles of co-current and counter-current techniques, and a description of the structure and operation of a horizontal vacuum belt filter, which is the equipment considered in the experimental part of this thesis. Also the most common cake washing models are introduced. The experiments were performed by washing wheat apatite filter cakes in a laboratory scale vacuum filter by using both co-current and counter-current washing methods. The main results of these tests were the washing curves that relate the purity of the filter cake to the amount of wash liquid used. Comparison between the obtained washing curves showed that both washing methods could be efficiently applied for achieving good washing results. The differences between the wash liquid consumptions in the co-current and counter-current washing methods were found to be surprisingly small but this is most probably explained by the relatively good washing characteristics of the apatite cakes. The washing models introduced in the literature part were compared with the results obtained from the experiments and it was found out that the studied cake washing processes could be described

The influence of crystallization conditions on the filtration characteristics of sulphathiazole suspensions

Cooling crystallization is one of the most important purification and separation techniques in the chemical and pharmaceutical industry. The product of the cooling crystallization process is always a suspension that contains both the mother liquor and the product crystals, and therefore the first process step following crystallization is usually solid-liquid separation. The properties of the produced crystals, such as their size and shape, can be affected by modifying the conditions during the crystallization process. The filtration characteristics of solid/liquid suspensions, on the other hand, are strongly influenced by the particle properties, as well as the properties of the liquid phase. It is thus obvious that the effect of the changes made to the crystallization parameters can also be seen in the course of the filtration process. Although the relationship between crystallization and filtration is widely recognized, the number of publications where these unit operations have been considered in the same context seems to be surprisingly small. This thesis explores the influence of different crystallization parameters in an unseeded batch cooling crystallization process on the external appearance of the product crystals and on the pressure filtration characteristics of the obtained product suspensions. Crystallization experiments are performed by crystallizing sulphathiazole (C9H9N3O2S2), which is a wellknown antibiotic agent, from different mixtures of water and n-propanol in an unseeded batch crystallizer. The different crystallization parameters that are studied are the composition of the solvent, the cooling rate during the crystallization experiments carried out by using a constant cooling rate throughout the whole batch, the cooling profile, as well as the mixing intensity during the batch. The obtained crystals are characterized by using an automated image analyzer and the crystals are separated from the solvent through constant pressure batch filtration experiments. Separation characteristics of the suspensions are described by means of average specific cake resistance and average filter cake porosity, and the compressibilities of the cakes are also determined. The results show that fairly large differences can be observed between the size and shape of the crystals, and it is also shown experimentally that the changes in the crystal size and shape have a direct impact on the pressure filtration characteristics of the crystal suspensions. The experimental results are utilized to create a procedure that can be used for estimating the filtration characteristics of solid-liquid suspensions according to the particle size and shape data obtained by image analysis. Multilinear partial least squares regression (N-PLS) models are created between the filtration parameters and the particle size and shape data, and the results presented in this thesis show that relatively obvious correlations can be detected with the obtained models.

Effect of hydrodynamics on modelling, monitoring and control of crystallization

Crystallization is a purification method used to obtain crystalline product of a certain crystal size. It is one of the oldest industrial unit processes and commonly used in modern industry due to its good purification capability from rather impure solutions with reasonably low energy consumption. However, the process is extremely challenging to model and control because it involves inhomogeneous mixing and many simultaneous phenomena such as nucleation, crystal growth and agglomeration. All these phenomena are dependent on supersaturation, i.e. the difference between actual liquid phase concentration and solubility. Homogeneous mass and heat transfer in the crystallizer would greatly simplify modelling and control of crystallization processes, such conditions are, however, not the reality, especially in industrial scale processes. Consequently, the hydrodynamics of crystallizers, i.e. the combination of mixing, feed and product removal flows, and recycling of the suspension, needs to be thoroughly investigated. Understanding of hydrodynamics is important in crystallization, especially inlargerscale equipment where uniform flow conditions are difficult to attain. It is also important to understand different size scales of mixing; micro-, meso- and macromixing. Fast processes, like nucleation and chemical reactions, are typically highly dependent on micro- and mesomixing but macromixing, which equalizes the concentrations of all the species within the entire crystallizer, cannot be disregarded. This study investigates the influence of hydrodynamics on crystallization processes. Modelling of crystallizers with the mixed suspension mixed product removal (MSMPR) theory (ideal mixing), computational fluid dynamics (CFD), and a compartmental multiblock model is compared. The importance of proper verification of CFD and multiblock models is demonstrated. In addition, the influence of different hydrodynamic conditions on reactive crystallization process control is studied. Finally, the effect of extreme local supersaturation is studied using power ultrasound to initiate nucleation. The present work shows that mixing and chemical feeding conditions clearly affect induction time and cluster formation, nucleation, growth kinetics, and agglomeration. Consequently, the properties of crystalline end products, e.g. crystal size and crystal habit, can be influenced by management of mixing and feeding conditions. Impurities may have varying impacts on crystallization processes. As an example, manganese ions were shown to replace magnesium ions in the crystal lattice of magnesium sulphate heptahydrate, increasing the crystal growth rate significantly, whereas sodium ions showed no interaction at all. Modelling of continuous crystallization based on MSMPR theory showed that the model is feasible in a small laboratoryscale crystallizer, whereas in larger pilot- and industrial-scale crystallizers hydrodynamic effects should be taken into account. For that reason, CFD and multiblock modelling are shown to be effective tools for modelling crystallization with inhomogeneous mixing. The present work shows also that selection of the measurement point, or points in the case of multiprobe systems, is crucial when process analytical technology (PAT) is used to control larger scale crystallization. The thesis concludes by describing how control of local supersaturation by highly localized ultrasound was successfully applied to induce nucleation and to control polymorphism in reactive crystallization of L-glutamic acid.

Adsorptive removal of harmful organic compound from aqueous solutions

Adsorption is one of the most commonly used methods in water treatment processes. It is attractive due to it easy operation and the availability of a wide variety of commercial adsorbents. This doctoral thesis focuses on investigating and explaining the influence of external phase conditions (temperature, pH, ionic strength, acidity, presence of cosolutes) on adsorption phenomena. In order to cover a wide range of factors and phenomena, case studies were chosen from various fields where adsorption is applied. These include the adsorptive removal of surface active agents (used in cleaning chemicals, for example) from aqueous effluents, the removal of hormones (estradiol) from drinking water, and the adsorption of antibiotics onto silica. The latter can beused to predict the diffusion of antibiotics in the aquatic system if they are released into the environment. Also the adsorption of living cells on functionalized polymers to purify infected water streams was studied. In addition to these examples, the adsorptive separation of harmful compounds from internal water streams within a chemical process was investigated. The model system was removal of fermentation inhibitors from lignocelluloses hydrolyzates. The detoxification of the fermentation broth is an important step in the manufacture of bioethanol from wood, but has not been studied previously in connection with concentrated acid hydrolyzates. New knowledge on adsorption phenomena was generated for all of the applications investigated. In most cases, the results could be explained by combining classical theories for individual phenomena. As an example, it was demonstrated how liquid phase aggregation could explain abnormal-looking adsorption equilibrium data. In addition to the fundamental phenomena, also process performance was of interest. This aspect is often neglected in adsorption studies. It was demonstrated that adsorbents should not be selected for a target application based on their adsorption properties only, but regeneration of the spent adsorbent must be considered. It was found that using a suitable amount of organic co-solvent in the regeneration can significantly improve the productivity of the process.

Safety study of hydrogen peroxide direct synthesis

Kandidaatintyön johdantokappaleessa esitellään vetyperoksidi ja mihin sitä käytetään teollisuudessa. Työssä vertaillaan antrakinoniprosessia ja suoraa prosessia sekä selvitetään nykyisin enemmän vetyperoksidituotantoon käytetyn antrakinoniprosessin ongelmakohdat ja osoitetaan, miksi suora synteesi vetyperoksidin tuotannossa olisi parempi vaihtoehto. Kandidaatintyön käsittelee suurilta osin turvallisuusongelmia, joita esiintyy suoran synteesin yhteydessä. Kirjallisuudesta on etsitty ratkaisuja näihin ongelmiin, kuten membraaniprosessin käyttöä räjähdysvaaran välttämiseksi. Pienemmän reaktorin eli ns. mikroreaktorin käyttö tuo mukanaan monia etuja vetyperoksidin tuotantoon. Tällöin prosessi on turvallisempi ja sitä on helpompi hallita. Mikroreaktorissa voidaan käyttää korkeampia lämpötiloja ja paineita kuin makroreaktorilla ilman, että räjähdysvaara prosessissa kasvaisi. Mikroreaktorin sisällä olevat mikrokanavat luovat turvallisen ympäristön synteesille. Aspen plus – simulointiohjelmalla mallinnettiin ja simulointiin suoran prosessin kriittisiä virtoja mikroreaktorissa. Tarkoituksena oli löytää virrat, joissa kulkee mahdollisesti räjähtävä kaasuseos. Kaasumaiset prosessivirrat ovat kriittisimmät vetyperoksidin suorassa synteesissä, koska ne aiheuttavat todennäköisemmin räjähdyksen kuin nestemäiset prosessivirrat. Kaikkein eniten prosessiturvallisuutta uhkaavat ainevirrat ennen ja jälkeen mikroreaktoria.