Search

U ovom radu proučavana je primena mehanohemije u sintezi prekursora aktivnih katalizatora reakcije transesterifikacije suncokretovog ulja. Ispitivan je uticaj različitih metoda sinteze – mehanohemijske, sa i bez dodatka vode i, radi poređenja, taložne – na osobine dobijenog prekursora CaZn2(OH)6·2H2O. Smeša prahova Ca(OH)2 i ZnO u molskom odnosu od 1:2 je podvrgnuta mlevenju u planetarnom mlinu tokom vremenskog perioda od 7 h, uz dodatak stehiometrijski potrebne količine vode, kao i bez dodatka vode. Izvršena je i sinteza prekursora katalizatora koprecipitacijom Ca(OH)2 i ZnO u vodenom rastvoru KOH radi poređenja. Prekursorski prahovi dobijeni u sve tri sinteze su višefazni, a njihova aktivacija izvršena je na temperaturi od 700 °C, čime su prevedeni u mešoviti oksid CaO·ZnO. Nakon kalcinacije, katalizatori su primenjeni u sintezi metil estara masnih kiselina (MEMK) suncokretovog ulja. Izvršena je i detaljna fizičko-hemijska karakterizaciju pripremljenih prahova, pre i posle kalcinacije: strukturna karakterizacija dobijenih prahova urađena je metodom rendgenske strukturne analize (XRD), dok je morfološka karakterizacija prahova nakon žarenja urađena skenirajućom elektronskom mikroskopijom (SEM/EDS). Takođe, primenjivana je i termijska analiza (TGA/DSC), i infracrvena (IC) spektroskopija radi dobijanja dodatnih informacija o strukturi i sastavu katalizatora. Kako pomenuti katalizatori daju različite prinose u reakciji transesterifikacije triglicerida sa metanolom, utvrđena je bitna povezanost između baznosti katalizatora pripremljenih različitim metodama i katalitičke efikasnosti. Mehanohemijska sinteza se, u odnosu na konvencionalnu koprecipitaciju, pokazala kao jednostavnija metoda koja ne uključuje rastvarač i dodatak alkalija koje mogu ometati uvid u stvarnu katalitičku aktivnost, a ujedno i kao efikasnija metoda za dobijanje aktivnih prekursora mešovitih oksida. Pored Ca(OH)2, kao polazni prah korišćen je i CaO, dobijen nakon žarenja Ca(OH)2 na 700 °C, kao i neg, The use of mechanochemical synthesis to obtain active catalyst precursors and testing their activity in transesterification of sunflower oil with methanol was investigated. The effect of different methods for preparation of catalytic precursor (CaZn2(OH)6·2H2O) – mechanochemical, with or without the addition of water and coprecipitation were investigated. A powder mixture of Ca(OH)2 and ZnO, with the molar ratio of 1:2, with, as well as without stoichiometrically required addition of water were milled in a planetary ball mill for a period of 7 hours. The classical coprecipitation procedure of Ca(OH)2 and ZnO powders in KOH solution was also performed for comparison. Precursor powders obtained after above mentioned procedures were multiphase, and their activation was carried out at temperature of 700 °C, in order to convert them to CaO·ZnO mixed oxide. After calcination, the catalytic activity was tested in the synthesis of fatty acid methyl esters (FAME) from sunflower oil. Structural characterization of obtained powders was done by X-ray diffraction (XRD) analysis, while morphology was observed by scanning electron microscopy (SEM/EDS). Thermal analysis (TG / DSC) was also applied, as well as infrared spectroscopy (IR) in order to obtain additional information on the structure and composition of the catalysts. The difference in the activity of mechanochemically synthesized catalysts and catalyst prepared by coprecipitation procedure could be related to the difference in their basicity. Mechanochemical synthesis has an advantage over the coprecipitation due to its relative simplicity – solid phase reactions without usage of solvents or precipitants which can interfere with catalytic activity. Using CaO, obtained after calcination of Ca(OH)2 at 700 °C, and lime as a starting powders was investigated in order to reduce the amount of carbonates present in the synthesized precursors. Influence of promoter (K2CO3) added to starting mixture of lime and ZnO for mechanochem

U okviru ove doktorske disertacije istraživana je metanoliza otpadne svinjske masti u prisistvu KOH, CaO ili negašenog kreča na umerenim temperaturama (ispod tačke ključanja metanola) i molskom odnosu metanol:masna sirovina, 6:1. Radi poređenja i doprinosa boljem razumevanju samog procesa, pored otpadne svinjske masti, kao izvori TAG korišćene su još i komercijalna „čista“ svinjska mast i „čista“ svinjska mast koja je termički tretirana pod uslovima procesa pečenja svinjskog mesa. Metanoliza je izvođena u šaržnom reaktoru sa mešanjem u prisustvu homogenog (KOH) i čvrstog katalizatora u obliku praška (komercijalni CaO i negašeni kreč) i protočnom reaktoru sa nepokretnim slojem čestica negašenog kreča. Dobijeni proizvodi sinteze su prečišćavani poznatim postupcima: „pranje“ vodom i tretman sa natrijum–karbonatom i metanolom. Finalnom proizvodu su određena svojstva od značaja za njegovu primenu kao dizel goriva. Realizovanim istraživanjima ostvareni su svi postavljeni cilјevi doktorske disertacije u pogledu mehanizma i kinetike sinteze MEMK u prisustvu različitih katalizatora, karakterizacije finalnih proizvoda i razvoja tehnološkog postupka za dobijanje biodizela iz otpadne svinjske masti. Kinetika reakcije metanolize zavisi od vrste masne sirovine, vrste katalizatora i temperature. Reakcija metanolize u prisustvu KOH je kontrolisana samo hemijskom reakcijom, dok je u prisustvu čvrstog katalizatora limitirana prenosom mase TAG u njenom početku, a zatim hemijskom reakcijom. Kinetika metanolize otpadne svinjske masti u prisustvu KOH najbolje se opisuje jedno–parametarskim modelom nepovratne reakcije pseudo–prvog reda, dok se kinetika heterogeno katalizovane reakcije dobro opisuje tro–parametarskim modelom koji uključuje promenljivi red reakcije u odnosu na TAG i prvi red u odnosu na MEMK. Konstanta brzine nepovratne reakcije pseudo–prvog reda u prisustvu KOH se povećava sa povećanjem stepena nezasićenosti masnih sirovina sledećim redom: termički tretirana svinjska mast, In this doctoral dissertation the methanolysis of waste lard from piglet roasting in the presence of KOH, CaO or quicklime at moderate temperatures (below the boiling point of methanol) and the molar ratio of methanol:fatty feedstockof 6:1. For comparison and contribution to a better understanding of the process, in addition to the waste lard, TGA used as sources are also commercial "clean" pork lard and "clean" pork lard that is thermally treated under the piglet roasting. The methanolysis was carried out in a batch stirred reactor in the presence of homogeneous (KOH) and solid powdered catalysts (commercial CaO and quicklime) and a flow packed–bed tubular reactor filled with bits (2.0–3.15 mm). The products were purified by the known methods: washing with water and the treatment with sodium carbonate and methanol. Certain properties of the final products, important for their use as an alternative fuel, were determined. All goals of the doctoral dissertation regarding the mechanism and kinetics of the synthesis of fatty acid methyl esters (FAMEs) in the presence of various catalysts, characterization of final products and the development of the technological process for obtaining biodiesel from waste lard were achieved. The kinetics of waste lard methanolysis depends on the type of fatty feedstock, the type of catalyst and temperature. The methanolysis reaction in the presence of KOH is controlled only by the chemical reaction while it in the presence of the solid catalyst is limited by the mass transfer of triacylglycerols (TAGs) at its beginning, and then by the chemical reaction. The kinetics of waste lard methanolysis in the presence of KOH is describes by the one–parameter model of an irreversible pseudo–first order reaction, while the kinetics of heterogeneously catalyzed reaction is well described by a three–parameter model that includes the variable reaction order with respect to TAG, and the first order with respect to to FAMEs. The rate constant of irreve

U ovoj disertaciji ispitivana je sinteza metil estara masnih kiselina (MEMK), odnosno biodizela u reakciji metanolize triglicerida (TG) u prisustvu čvrstog katalizatora. Sinteza katalizatora izvršena je mehanohemijskim putem polazeći od CaO i ZnO prahova uz dodatak vode, kako bi se dobio prekursor CaZn2(OH)6·2H2O, koji se ţarenjem na 700 °C prevodi u smešu oksida CaO∙ZnO. Nakon detaljne karakterizacije, CaO∙ZnO katalizator korišćen je u reakciji metanolize rafinisanog suncokretovog i korišćenog biljnog ulja (KBU) koja je izvedena u šarţnim uslovima. U cilju odreĎivanja parametara koji u potpunosti definišu brzinu metanolize i ukazuju na osnovne otpore od kojih ona zavisi, analiziran je uticaj temperature, molarnog odnosa metanol:ulje, mase katalizatora i intenziteta mešanja na brzinu procesa. UtvrĎeno je da brzina procesa zavisi od otpora prenosu mase TG do površine katalizatora i otpora hemijskoj reakciji na površini katalizatora, koji su definisani kao recipročna vrednost ukupnog zapreminskog koeficijenta prenosa mase, , i konstante brzine reakcije pseudo prvog reda, . Ovi kinetički parametri odreĎuju vrednost prividne konstante brzine koja se menja sa napredovanjem procesa metanolize, odnosno sa promenom stepena konverzije TG. Brzina procesa je na taj način opisana kinetičkim modelom nepovratne reakcije prvog reda sa promenljivom prividnom konstantom brzine koja uzima u obzir i prenos mase TG i brzinu hemijske reakcije izmeĎu TG i metanola. UtvrĎeno je da ukupan zapreminski koeficijent prenosa mase, , zavisi od specifične meĎufazne površine, kao i da se moţe predstaviti kao funkcija stepena konverzije TG. Ova pretpostavka se bazira na uočenom efektu da se dostizanjem odreĎene kritične konverzije TG nakon stvaranja prvih količina monoglicerida (MG), diglicerida (DG) i MEMK, brzina prenosa mase znatnije uvećava i postaje veća od brzine hemijske reakcije na površini katalizatora. Tada reakcija na površini katalizatora počinje da kontroliše brzinu ukupnog procesa..., The synthesis of fatty acid methyl esters (FAME), i.e. biodiesel, in the methanolysis of triglycerides (TG) in the presence of solid catalyst was studied. Heterogeneous catalyst was synthesized by mechanochemical treatment of CaO and ZnO powder mixture with the addition of water required for the formation of corresponding mixed hydroxides, CaZn2(OH)6·2H2O, followed by calcination at 700 °C in air to obtain CaO∙ZnO composite powder. After detailed characterization CaO∙ZnO catalyst was used in methanolysis of refined sunflower as well as used vegetable oil (UVO) in the batch conditions. Influence of temperature, agitation speed, catalyst amount and methanol to oil molar ratio on the rate of reaction was analyzed in order to determine parameters that completely define the rate of methanolysis and indicate the basic resistances on which it depends. It was revealed that the rate of the process depends on the two resistances – mass transfer of triglycerides to the catalyst surface and chemical reaction on the catalyst surface, which are defined as reciprocal value of , the overall triglyceride volumetric mass transfer coefficient and , the effective pseudo-first order reaction rate constant. These kinetic parameters actually determine the value of the apparent reaction rate constant, , which changes with the progression of the methanolysis process, i.e. with the change of triglyceride conversion. The rate of the process is thus described with the simple kinetic model of irreversible pseudo-first order reaction with the variable apparent rate constant, which takes into account both the triglycerides mass transfer and chemical reaction between TG and methanol. The overall volumetric mass transfer coefficient, , was found to depend on interfacial area between the oil and methanol, and can be presented as the function of TG conversion. This assumption is based on the observed effect that when critical conversion of TG is achieved, after formation of small amounts of MG, DG an

Višefazni reakcioni procesi predstavljaju ključne stupnjeve u proizvodnji dizel goriva, obnovljivih i mineralnih. U savremenim rafinerijama proces hidrotritinga zauzima značajno mesto pri čemu se odvija u prisustvu čvrstog katalizatora. Glavni ciljevi procesa hidrotritinga u preradi nafte su uklanjanje sumpora, stabilizacija proizvoda i uklanjanje drugih neželjenih primesa. Hidrodesulfurizacija gasnog ulja se odvija u reaktoru sa nepokretnim slojem katalizatora uz prisustvo vodonika na povišenom pritisku (uobičajeno do 60 bar-a) i temperaturi (633 K). U ovoj disertaciji razvijen je deterministički matematički model reaktora za simulaciju procesa. Model čine diferencijalni bilansi toplote i hemijskih vrsta, kao i odgovarajuće kinetičke jednačine za reakcije desulfurizacije. Sistem diferencijalnih jednačina koje čine model je rešavan primenom programa napisanog u MATLAB-u. Višefazni reakcioni proces sinteze biodizela je modelovan i simuliran za nekatalitičku etanolizu i metanolizu triglicerida na povišenom pritisku i temperaturi. Raspodela faza i ravnoteža za sistem para – tečnost i para – tečnost – tečnost metanola i etanola sa trioleinom je ispitivana sa ciljem određivanja parametara koji omogućavaju visoku konverziju ulja. Simlacija ravnoteže faza korišćenjem RK-Aspen jednačine stanja u UniSim softveru pokazala je veoma dobro slaganje sa eksperimentalnim podacima. Rezultati simulacija ukazuju na važan uticaj na reakcioni mehanizam i na ukupnu kinetiku procesa u sub-kritičnoj oblasti (T < 270 ◦C na 200 bar-a) s obzirom da u početnoj fazi reakcije egzistiraju dve faze, što uzrokuje lošiji kontakt između reaktanata. U slučaju postojanja jedne reakcione faze (T > 270 ◦C na 200 bar-a) inicijalno visoka brzina reakcije je limitirana na visokim konverzijama zbog porasta stepena odigravanja povratne reakcije. Matematički model nekatalitičke sinteze biodizela je tretiran kao kompleksna uzastopno – paralelna povratna reakcija. Kinetički parametri su određeni primenom standar, Multiphase reaction processes constitute key steps in manufacturing of diesel fuels, both renewable and mineral. In modern refineries there is a major role for the hydrotreating processes that operate under high pressure in the presence of a solid catalyst. The main role of hydrotreating within the petroleum refining is the removal of sulphur compounds, the stabilization of the product and the removal of other undesirable impurities. Hydrodesulphurization of gas oil takes place in a reactor with a fixed bed catalyst in the presence of hydrogen at elevated pressure (normally up to 60 bar) and temperature (633 K). In this thesis, a mathematical model of a deterministic type was developed and used to simulate the hydrotreating reactor operation. The model consists of differential balance equations of heat and chemical species, and the corresponding kinetic equations for the reactions of hydrodesulphurization of sulphur compounds. The system of differential equations that constitute the mathematical model was solved using the MATLAB software package. Multiphase reactions for biodiesel synthesis were modeled and simulated for non-catalytic methanolysis and ethanolysis of triglycerides under high pressure and at elevated temperature. The vapour–liquid or vapour–liquid–liquid equilibrium and phase distribution of methanol and ethanol with triolein were investigated in order to determine the range of pressure and temperature required for high oil conversion. Simulation of phase equilibrium using RK-Aspen EOS and UniSim software were found to correlate well with the experimental data. Simulation results show the important influence of the phase equilibrium on the reaction mechanism and overall kinetics under subcritical conditions (T < 270 ◦C at 200 bar) since the two liquid phases exist at the beginning of reaction, thereby limiting the contact between the reactants. In case of single reaction phase (T > 270 ◦C at 200 bar) the initially high reaction rate is limited at high

Glavni problem za širu primenu metil estara masnih kiselina (biodizela) je njihova visoka cena proizvodnje. Proizvodna cena biodizela bi mogla da se smanji kako smanjenjem cene sirovina (biljnih ulja, životinjskih masti, korišćenih ulja) tako i primenom efikasnijih tehnologija za njegovu proizvodnju. Da bi se tehnologija sinteze biodizela, koja se danas najviše primenjuje u industrijskim uslovima, poboljšala ili eventualno predložila nova, neophodno je da se sam reakcioni sistem jasno definiše. U ovom radu je analizirana sinteza u natkritičnim uslovima, definisana fazna ravnoteža sistema triglicerida i metanola, kao i njihovih proizvoda, metil estara, diglicerida, monoglicerida i glicerola. Metodom doprinosa grupa izračunati su kritični parametri i na osnovu eksperimentalnih podataka rastvorljivosti triglicerida u metanolu u natkritičnim uslovima i njihovom regresijom na više temperature i pritiske, definisan je termodinamički model, koji najbolje opisuje ponašanje analiziranog sistema. Simulacijom u programskom paketu ASPENplus analizirano je ponašanje ovako kompleksnog sistema, ravnoteža i broj faza tokom reakcije metanolize. U zavisnosti od reakcionih uslova, pritiska i temperature, kao i molskog odnosa metanol – ulje, predloženi su kinetički modeli i određeni kinetički parametri reakcije metanolize triglicerida u subkritičnim i natkritičnim uslovima. Ovako definisani kinetički modeli su potvrdili postojanje promene faza, odnosno broja faza u reakcionom sistemu u zavisnosti od temperature i pritiska. Sa definisanim termodinamičkim parametrima i kinetičkim modelom, izvršena je simulacija procesa natkritične proizvodnje biodizela i ovaj postupak sinteze upoređen sa homogeno katalizovanom metanolizom triglicerida. Dobijeni rezultati ukazuju da je proizvodnja biodizela u natkritičnim uslovima konkurentna i realno primenljiva u industrijskim uslovima. Na osnovu detaljne analize i simulacije procesa ukazani su nedostaci postojeće klasične tehnologije zasnovane na prime, The main obstacle for wider application of biodiesel is its relatively high cost. This is still the truth, although the price gap between petroleum based diesel fuel and biodiesel is narrowing due to the recent increase of crude oil prices. The overall cost of biodiesel fuel could be reduced either by the reduction of raw material cost (vegetable oil, animal fat, used vegetable oil) or by the application of more efficient processing technology. For the further development of biodiesel production technology or application of some advance and new technology, it is necessary clearly defined the reaction system. In this study it was detailed defined the phase equilibria for the system triglycerides and methanol as well as for their products (methyl esters, diglycerides, monoglycerides and glycerol). It was calculated the new value for the critical parameters based on group contribution method. Regression of experimental data for solubility of triglycerides in methanol in subcritical conditions and simulation to higher temperature and pressure, it was define the thermodynamic model which truly describe such system (RK-Aspen equation of state). Simulation with ASPENplus software it was defined the behavior of such complex system during the reaction of methanolysis of triglycerides. The phase content and phase transition was clearly described, also. Kinetic model and kinetic parameters of methanolysis reaction in subcritical and supercritical conditions are proposed in dependenc of temperature and pressure and methanol to oil molar ratio. Such defined the kinetic model was matched and have explanation with the phase equilibria of analyzed system (the number of phases for subcritical and supercritical conditions for reaction). Furthermore, with defined therodinamic and kinetic data, it was performed the process design for the supercritical production of biodiesel. The obtained results are comperd with design’s data for the clasicaly production of biodiesel (alkali homgeniou