Sinteza i karakterizacija katalizatora na bazi mešovitih oksida kalcijuma i drugih metala i ispitivanje njihove aktivnosti u procesu heterogeno katalizovane sinteze biodizela

Abstract

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 negašeni kreč, a sve sa ciljem smanjenja količine prisutnih karbonata u sintetisanim prekursorima. Uticaj dodatka promotora (K2CO3) tokom mehanohemijske sinteze na strukturu i katalitičku aktivnost je ispitivan variranjem odnosa K:Ca...

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 mechanochemical synthesis on precursor structure and catalytic activity was examined by varying the ratio of K:Ca...