Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2013
Student: NALAN ÖZBAY
Supervisor: NURAY OKTAR
Abstract:Biodiesel, a mixture of methyl esters of fatty acids is produced via transesterification of vegetable oils with methanol or ethanol. Recently it has been recommended as an alternative to diesel fuel which resulted in its elevated production. Glycerol is a major by-product in transesterification process constituting 10% of total biodiesel production. Evaluation of this by-product by conversion to valuable products such as tert-ethers will enable feasible biodiesel production. Use of tertiary ethers of glycerol as motor vehicle fuel/fuel additive is one of the most important methods of evaluation. The main purpose of this study that was performed as a doctoral dissertation, synthesis of glycerol tert-ethers to use as a high octane and cetane numbered fuel/fuel additive by the etherification reaction of tert-butyl alcohol (TBA) and glycerol which is the by-product of biodiesel. In the studies which were performed in the context of the doctoral thesis, tertiary ethers of glycerol were synthesized in batch and continuous systems. Tert-ethers of glycerol were synthesized at constant molar ratio (TBA/G), at different reaction temperatures (90-200°C), in the presence of different catalysts (Amberlyst-15, Amberlyst-16, Amberlyst-35, Lewatit K2629, Relite EXC8D, Nafion SAC-13, H-Beta and H-Mordenite). At 90°C reaction temperature, the highest conversion of glycerol (91%) and di-ether selectivity (36%) were reached in the presence of Amberlyst-15 catalyst in batch reactor. In continuous system, the reaction pressure (1atm-5atm) and the effects of mass transfer resistance were investigated. At Low reaction pressure, by dehydrating of TBA, it was observed that formation of i-butene (IB) increased and also formated IB gas bubles decreased the mass transfer limitations. According to this, it was observed that conversion of glycerol was higher at atmospheric pressure. Additionally, by adding water adsorbed zeolites (Zeolite 4A and Zeolite 5A) to the reaction medium in continuous system, increasing of glycerol conversion and di-ether selectivity were provided in the study. Also, by adding zeolites to the non-catalysed reaction medium, reactant conversion and product selectivities were analyzed. It was observed that Zeolite 4A and Zeolite 5A were give no activity at the non-catalysed reaction medium. In the study, etherification reactions of glycerol with different alcohols (ethanol and methanol) and IB were investigated. In the reactions of glycerol with ethanol and methanol, glycerol conversion obtained in trace amounts (about %1*10-5) were found completely as mono-ethers. All of the products obtained from the conversion of glycerin mono-ethers, respectively. At the reaction of glycerol with IB which are insoluble in each other, glycerol conversion was obtained as 0.4%. In the study, acidic characterized different silica (Aerosil 200, Siral 30 ve Siral 40) supported catalysts were prepared and their characterization studies, (Hammett acidity determination, DRIFTs analysis to get information about the surface acidic groups, BET surface area measurements and thermogravimetric analysis (TGA) in order to examine the thermal behavior of the catalysts) were performed. Activities of these prepared catalysts were tested in continuous system for the etherification reaction of glycerol with tert butyl alcohol. The highest activity was observed in Siral 40 supported catalysts. It was observed that glycerol conversion increased with increasing temperature. No side reaction was observed at high reaction temperatures. Regarding the effect of the impregnated acids on conversion, it was obtained that glycerol conversions were higher in the presence of H2SO4 treated catalysts. It was observed that the main products were mono-ethers, formation of di-ethers are in second sequence, and formation of tri-ether was not observed. In both acidification process, the highest di-ether selectivity (%12) was achieved at 175°C reaction temperature over Siral 40 supported H2SO4 treated catalyst. Over (NH4)2SO4 containing Siral 40 supported catalysts di-ether selectivity was observed as %10. In the final stage, a process that allows the production of biodiesel during the production of glycerol ethers (one-pot synthesis) has been developed. According to this process, glycerol ethers have been produced by putting vegetable oil, methanol and TBA were put into the reaction medium at the same time in the presence of acid (Amberlyst-15) and base (NaOH) catalysts. During one-pot synthesis, analysis of the produced glycerol ethers were made by using GC and GC/MS according to EN 14103 standard. When the results were analyzed, it was seen that ester contents of the fuel mixtures prepared by one-pot synthesis method were close to the ester content of pure biodiesel or higher. When cetane numbers were compared, it was also observed that the cetane numbers of the fuel mixture prepared by one-pot synthesis method were higher than the cetane number of pure biodiesel. Another advantage of one-pot synthesis method is that iodine value of synthesized glycerol ethers are lower than pure biodiesel. The obtained results shows that the one-pot synthesis is industrial and economically promising.