Study of the adsorption of the amino acid L-lysine onto microporous materials

Zeolites are aluminosilicate minerals composed of [SiO4]4- and [AlO4]5- tetrahedral units linked through the oxygen atoms creating a regular crystalline structure with microporous cavities that confer a high superficial area. The physico-chemical properties of zeolites depend strongly on the composition of their framework, in particular the hydrophilic/hydrophobic behaviour is affected by the SiO2/Al2O3 ratio (SAR). Moreover, the different shapes and dimensions of the internal channels and cages influence the adsorption selectivity towards host molecules. The ability of zeolites to adsorb biologically active biomolecules such as amino acids is of particular interest in industrial biotechnology due to the fact that these adsorbent materials could be used as solid solvents to stabilize the different charged forms of the amino acids. In addition, these materials can also be employed in enrichment and separation processes of amino acids from complex mixtures. In the present study the adsorption of the amino acid L-lysine onto zeolites L and ZSM-5 from aqueous solutions was evaluated. Zeolites presenting different framework structures were selected in order to evaluate the effect of the intra-crystalline characteristics of the material. Moreover, different SAR values were considered to determine the adsorption behaviour according to this factor.