Thermodynamic Studies On L-lysine Solvent Reaction Extraction

L-lysine is a typical alkalescent amino acid, which is widely used in foodstuff, feed, curative industry. In recent years, it is found can be used as basic material to synthesize biodegradable compound. Now, L-lysine is produced by zymotechnics and its technique is mature, but the down-stream processing such as separation and purification are still weak. The technology of using solvent reaction method extracting amino appeal widely attention and become a research hot point.But the study of using this method to separate and purify L-lysine is not complete and the mechanism of extracting alkalescent amino is not reported. In the paper, the mechanism of solvent chemical extraction of L-lysine and thermodynamic solubility of L-lysine in water were studied.(1) Solubility data of L-lysine in pure water in different temperature were measured, the data were correlated with Xti and Wilson equation, the results show both equations can describe the solubility characters. Based on characteristic of correlating thermodynamic model parameters, some modification was made in Standard Genetic Algorithm (SGA) and a Modified Genetic Algorithm (MSA) was proposed. Correlating results show the MGA can calculate quicker than SGA, which is a good optimizing method for thermodynamic model parameter correlating. Solubility data of L-lysine in different pH value were measured and a solubility model was deduced and established. The calculated results by proposed solubility model are well coincided with experiment data, which show the proposed solubility model reveal the relationship between L-lysine solubility and temperature.(2) The experiment equipment and method of measuring distribution ratio was established, and the distribution ratio of extracting L-lysine with di-(2-ethylhexyl) phosphoric acid was measured. The experiment result shows: when pH is lower than 1.5, the distribution ratio is small, when pH is higher than 2.0, the distribution ratio increase with the concentration and pH value and decrease with the raise of temperature, which show the reaction between L-lysine and di-(2-ethylhexyl) phosphoric acid is a heat-release reaction.(3) Relation between L-lysine's ion form in water and pH was analyzed. When pH value is smaller than 3.5, there are two kind positive ion in water, each combines di-(2-ethylhexyl) phosphoric acid respective. Infrared Spectra of did-(2-ethylhexyl) phosphoric acid/L-lysine complex is not related with pH value ,which prove only one charge positive ion combine with did-(2-ethylhexyl) phosphoric acid and two charge positive ion does not take part in reaction. Based on the reaction mechanism, the calculating model of distribution ratio was deduced, and good results were obtained. One L-lysine is extracted by forming a complex with two dimeric P204 molecules. The reaction equilibrium constant is 0.0061071/mol.