Studies On Adsorption Equilibrium And Kinetics For Multi-component Amino Acid Solution

The adsorption equilibrium and fix-bed adsorption were investigated for the solutions of three amino acids, which consist of L-tryptophan, L-tyrosine, and L-phenylalanine, on H+form732cation exchange resins.The three-wavelength spectrophotometry was used to determine the concerntration of three-component mixtures, determined the best wavelength combination which was204nm,206nm,208nm,218nm,222nm and230nm. The adsorption equilibrium of L-tryptophan, L-tyrosine and L-phenylalanine was studied with the Freundlich model. Results showed that equilibrium adsorption capacity of L-tryptophan, L-tyrosine and L-phenylalanine were reduced with the initial pH value decreased from4.5to1.5. The equilibrium adsorption capacity of three-component solutions decreased significantly due to the excess of H+when the initial pH was lower than2.0, reduced with the temperature increase from30℃to45℃, and reduced with the increase in concentration of added glucose and sodium chloride.The adsorption equilibrium isotherms of three-component solutions were represented with the extended Freundlich equation in different temperature and initial pH, meanwhile, the temperature as a variable parameter was introduced into the equation, the final equation would have temperature variable parameters. The extended Freundlich equations, which fitted the experimental data of three-component adsorption equilibrium, were highly significant at a=0.001level under different initial pH and temperatures. The mean relative errors were less than3.3%and the maximum relative error was6.0%. By fitting the adsorption equilibrium data under different temperatures, the multi-temperature adsorption equilibrium models of three-component solutions were as follows: q1=(-0.0002T2+0.0088T+0.61)c1(c1+0.94c2+0.37c3)-0.0001T2+0.0095T-0.74q2=(-0.0009T2+0.050T+0.17)c2(1.1c1+c2+0.39c3)-0.0001T3+0.0091T-0.78q3=(-0.035T2+2.6T-29)c3(3.3c1+3.0c2+c3)0.0005T2-0.037T-0.61In the above model, the subscript1,2and3represented L-phenylalanine, L-tyrosine and L-tryptophan, respectively. Results showed that the mean relative errors of L-phenylalanine, L-tyrosine and L-tryptophan predicted by the modified andextended Freundlich models which had temperature variable parameters were2.5%、1.7%and3.6%in different temperatures, respectively. The maximum relative errorwas7.9%.It is experimentally discussed that the effect of the initial concentrations, theconcentration ratio, the bed height, and the flow rate on breakthrough curves ofthree-component solutions in a fix-bed adsorption. Results showed that thebreakthrough time decreased with increasing the initial concerntration and thebreakthrough curve exhibited the strip-peak. The strongest adsorbate is L-Trp, thesecond is L-Tyr, and the weakest is L-Phe in the adsorption system by changingconcentration ratios. The mass transfer rate increased and breakthrough timedecreased due to increase flow rates which would weak the role of displacement. Thebreakthrough time and the exchange capacity increased with increasing bed heightswhich would enhance the role of displacement.