Studies On Reactive Extraction Of Pyridine Carboxylic Acids Using Trialkylamine

With the development of the modern industry, the separation of polar organic species from diluent solution has become a widespread problem. As a highly effective and highly selective mothod for separating polar organic species, reactive exrraction has been received great attention.Amphoteric compounds, which contain two typical functional groups of Lewis acidic and Lewis basic groups, possess of particular physical, chemical and biological properties. They are widely used in the fields of chemical engineering, biological engineering, and pharmaceutical engineering etc. In the present thesis, reactive extractions of a kind of amphoteric compounds, namely pyridine carboxylic acids including picolinic acid, nicotinic acid and iso-nicotinic acid, using trialkylamine (7301) and 7301/tributylphosphate (TBP) as extractants, were systematically studied. The effects of concentration of extractants, diluents, equilibrium and initial concentration of pyridine carboxylic acids on distribution coefficient (D) were discussed. The mechanisms of 7301 reacting with pyridine carboxylic acids were deduced by Fourier Transformation infrared spectrometry. Also expressions of equilibrium D were proposed and the parameters of the apparent extraction equilibrium constants (K) were calculated by fitting experimental data. The key factors those affect extraction equilibrium were revealed.The polar n-octanol was a suitable diluent for extracting pyridine carboxylic acids with 7301 as extractant. D increased first and then decreased with the increase of concentrations of 7301 and there was a maximum when the concentration of 7301 is 0.4218mol/L. As pH increasing, D also increased first and then decreased, and was shown with a maximum in a pH range in which neutral (or zwitterion) and anionic pyridine carboxylic acids dominated. D was also found to be reduced with increasing initial concentrations of pyridine carboxylic acids.The interaction mechanisms between 7301 in n-octanol and pyridine carboxylic acids were validated by Infrared spectroscopic analysis. Pyridine carboxylic acids could complex with n-octanol through hydrogen-bonding, thus accelerated the transfer of pyridine carboxylic acids into organic phases to react with 7301.7301 mainly reacted with neutral (or zwitterion) and anionic pyridine carboxylic acids, and formed a type of ion-pair complexes. The equilibrium pH has no influence on the type of complexes.Based on the experimental results, simultaneously taking physical extraction and chemical extraction into account, expressions of D were proposed, and the apparent extraction equilibrium constants (K) were obtained by fitting experimental data. The results indicated that the precision of proposed model was satisfying.The apparent basicity of extractant, the polarity of diluents and the characteristic parameters of solutes (i.e. pKa and logP) were of great influences on extraction equilibrium. The relationships of them with logK were also presented in the thesis. It indicated that the differences of pKa and logP were the key factors which caused D to be different among picolinic acid, nictonic acid and iso-nicotinic acid.In addition, equilibrium studies of pyridine carboxylic acids extracted by a series mixtures of 7301 and TBP in n-octanol were also carried out. It was observed with obvious synergistic effect between 7301 and TBP. Concentrations of 7301 and TBP played important roles on extraction equilibrium. The maximum D values were also found to be in the pH range that neutral (or zwitterion) and anionic pyridine carboxylic acids dominated. It existed optimal ratio of 7301 to TBP at which the much higher D values were obtained. As the same as processes of pyridine carboxylic acids extracted by 7301, D values of the mixtures also decreased with the increasing initial concentrations of pyridine carboxylic acids. IR analysis indicated that there were three types of reaction during extraction processes, namely,7301 reacting with pyridine carboxylic acids to form binary complexes, TBP reacting with pyridine carboxylic acids to form binary complexes, and 7301 and TBP co-reacting with pyridine carboxylic acids to form ternary complexes.