Adsorption of pyruvic and succinic acid by amine-functionalized SBA-15 for the purification of succinic acid from fermentation broth

In this study, mesoporous silica SBA-15 was functionalized with primary, secondary, and tertiary aminofunctional silanes onto the channel walls using a postsynthesis method as a first attempt to purify succinic acid from a fermentation broth. Ordered mesostructures of pristine and functionalized SBA-15 were evaluated using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N₂ adsorption/desorption isotherms. ¹³C and ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) with ¹H cross-polarization (CP-MAS) and thermogravimetric analysis (TGA) revealed that amino-functional silanes were covalently bound to the active layer of pore walls. The distribution and accessibility of amine groups were characterized by scanning transmission electron microscopy (STEM), elemental analysis, and conductivity measurements. Adsorption isotherms were analyzed using the Sips model, simultaneously obtaining the temperature dependence of isotherms derived from the isosteric heats of adsorption. Pyruvic acid had higher adsorption capacities than succinic acid on amine-functionalized SBA-15, resulting in the selective adsorption of pyruvic acid from binary acid solution. In particular, SBA-15 functionalized with primary amino silane obtained higher selectivity on pyruvic acid compared to that of other amine-functionalized SBA-15. The adsorption capacities of pyruvic acid at equilibrium are dependent on the basicity and distribution of amino silanes. The isosteric heats between 10 and 100 kJ/mol and desorption energy between 1 and 10 kJ/mol revealed that the adsorption of pyruvic and succinic acid originated from the formation of an acid-amine complex via hydrogen bonding. It is proposed that the amine functionalization of ordered mesoporous solids provides a simple and effective method of separating or purifying useful carboxylic acids.