Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Comparative Assessment of Separation Methods of Organic Acids Produced with Fermentation

The aim of this study is to compare the processes which use for separation organic acids from aqueous solutions. The processes which compared in this study were extraction, adsorption and ion-exchange.

The organic acids used in this study are lactic acid and citric acid. Lactic acid is a monohydroxy carboxylic acid, and citric acid is a trihydroxy carboxylic acid. In the extraction of these acids were used two different extractants. The first of these extractants was tridodecylamine that is a long chain tertiary amine. The second was Amberlite LA-2 which is a mixed secondary amine. These extractants were diluted with different solvents which have different chemical structures. Solvents used for this aim are 1-octanol, methyl isobutyl ketone (MIBK), isooctane, toluene and cyclohexane.

The adsorbent used in adsorption process is active carbon. Amberlite IRA-67 is a weakly basic ion exchange resin that was used for ion exchage process.

In the experimental section, aqueous acid solution at 10% (w/w) concentration were prepared. In the extraction of organic acids, the aim was to investigate the effects of the type of amines, the concentration of amines, nature of solvents and solvent mixtures and initial acid concentrations. For this purpose, the extractants were prepared in five different concentrations in five different solvents. These concentrations were 0.22, 0.52, 0.94, 1.57 and 2.62 mol/L for TDA and 0.32, 0.74; 1.33; 2.22 and 3.70 for Amberlite LA-2. Prepared amine- solvent and aqueous acid solutions were mixed at equal volumes (1:1), and extraction was performed in a thermostated shaker for 4 hours. Then the distribution coefficients and loading factors calculated from experimental results were presented. The results of the extraction experiments, the distribution coefficient depends on the amine concentration. The distribution coefficient increases with increasing amine concentration for all diluents. The best solvent for both acids was 1-octanol and the best extractant for both acids was Amberlite LA-2 in this study.

In the adsorption experiments, active carbon was used as an adsorbent. In the first stage, for determining the period to achieve the adsorbent’s equilibrium state, seven identical acid and active carbon mixtures were prepared, were placed in the shaker and started to mix. After that, every 30 minutes one sample’s aqueous phase was analyzed. So, the period of the achieving to the equilibrium state of active carbon was found as 180 minutes for both acids. Then, the effects of different active carbon amount on adsorption and initial acid concentrations on adsorption were investigated. The results of adsorption experiments, the removal of acid percentages were increased with increasing adsorbent amount.

In the experiment of ion exchange, the processes which were done for adsorption, were repeated. So, the period of the achieving to the equilibrium state of Amberlite IRA-67 was found as 120 minutes for both acids. The results of ion exchange experiments were the same as adsorption process’ results.

Ion-exchange and adsorption processes were compared as their value of percentage of removal acid. The result of the comparison; Amberlite IRA-67 was better than active carbon.

Langmuir and Freundlich isotherms were calculated as well. It was observed that lactic acid was in compliance with both isotherms. On the other hand adsorption of citric acid on active carbon was not in accordance with Freundlich isotherm.