Date

2014

Author

Ozanırk, Firat

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Triethyl citrate (Ethyl citrate, TEC) is an environmentally friendly substance with a non-toxic structure, it does not give any harm or allergic effect on human beings. Therefore, it is widely used in food industry as a food additive, in pharmaceutical and toy industry as non-toxic plasticizers. Triethyl citrate is also used in cosmetics due to its anti-bacterial properties. The triethyl citrate is synthesized via the esterification of the citric acid with ethyl alcohol which is an equilibrium limited reaction. The synthesis of the triethyl citrate is commercially carried out in batch or continuously stirred reactors in the presence of a liquid catalyst. Besides, distillation columns are likely to be used in the triethyl citrate production systems to obtain pure triethyl citrate. In this study, it is aimed to increase the triethyl citrate percentage in the product by the removal of the water from the reaction mixture by Pervaporation Membrane Reactor (PVMR), Vapor Permeation Membrane Reactor (VPMR) and Reactive vi Adsorption (RA) systems. Additionally, the batch reactor experiments were carried out to compare its results with the proposed esterification processes. Quantitative and qualitative analysis of all reactants and products were accomplished by high pressure liquid chromatograph (HPLC) and Karl Fischer analysis method. In batch reactor experiments, the parameters that affect the esterification kinetics were investigated. For this purpose the effect of the temperature (75, 90 and 100 0C), initial molar ratio of the ethyl alcohol to citric acid (5/1 and 10/1), catalyst loading (0, 3, 5, 7 and 10 wt% of total mixture) and catalyst type (Amberlyst-15 and Sulfuric Acid) on the esterification were tested. According to experiments, the selectivity of the TEC in all various esters was increased with increasing catalyst loading, initial molar ratio of the reactants (alcohol to acid) and temperature. In the experiments TEC selectivity changed between 0.05 and 0.49. The highest TEC selectivity, 0.49, was obtained from the batch (RUN 76) at the 18th hour of the experiment which had 5/1 initial mole ratio of the reactants (alcohol to acid), at 100 0C and 0.8 wt% sulfuric acid catalyst loading. Pervaporation membrane reactor (PVMR) experiments were carried out at 90 0C. In the experiments, 5/1 initial reactant molar ratio of the reactants (alcohol to acid) was used. In PVMR different catalyst loading amounts and different membrane types were tested. According to PVMR experiments, the Optimized Silica membrane showed to have higher stability than HybSi membrane in the reactive mixture. However after several tests, both membranes were irreversibly blocked by reactive mixture. According to PVMR results, the highest TEC selectivity, 0.81, was obtained in the RUN 39. In the VPMR experiments, the effect of the temperature (90 and 100 0C), alcohol to acid initial molar ratio (5/1, 7/1 and 10/1), membrane length (25 and 50 cm) and catalyst type (Amberlyst-15 and Sulfuric acid) on the esterification of the citric acid and ethyl alcohol were tested. In experiments, the hydrophilic Hybsi membranes were used. According to VPMR experiments, the selectivity of the triethyl citrate in all various esters at the end of the test changed between 0.87 and 0.94. By using vapor permeation technique, not only the blocking of the membrane was prevented, but also higher TEC selectivities were obtained. vii In the reactive adsorption (RA) system, the effect of the catalyst loading (0.3 0.8 and 1 wt% H2SO4 of the total mixture), alcohol to acid initial molar ratio (5/1 and 10/1) and temperature (100 and 115 0C) on the esterification were investigated. In the reactive adsorption system the zeolite 3A were used to remove the water from the reaction mixture. The vapor phase adsorption was used for removing the water from the reaction mixture. At the end of the reactive adsorption experiments the TEC selectivities were changed between 0.91 and 0.96. Finally, the experiments showed that the selectivity of the TEC was increased by reaction temperature, initial mole ratio of the reactants (alcohol/acid) and catalyst loading. Moreover, the TEC selectivity was increased above the batch reactor results by the integration of a water removal unit to the synthesis system.

Subject Keywords

Esterification., Citrates., Citric acid., Adsorption., Membrane reactors.

URI

http://etd.lib.metu.edu.tr/upload/12617600/index.pdf
https://hdl.handle.net/11511/23726

Collections

Graduate School of Natural and Applied Sciences, Thesis