Mass transfer limitations in binderless ZSM-5 zeolite granules during adsorption of flavour compounds from aqueous streams

BACKGROUND: Recently, a new process concept has been proposed to selectively adsorb wort off-flavours, i.e. aldehydes, from alcohol-free beers with hydrophobic zeolites. RESULTS: In this work, we investigated the uptake of a mixture of wort flavour compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, furfural, and methional), from a model solution onto binderless hydrophobic ZSM-5 zeolite granules in order to quantify mass transfer parameters and identify bottlenecks. Subsequently, the homogenous solid diffusion model was employed to regress the effective diffusion coefficients for each molecule and experimental condition, which ranged between 10⁻¹⁵ and 10⁻¹³ m² s⁻¹, indicating strong intraparticle mass transfer limitation. Furthermore, it was found that the effective diffusion coefficient is inversely correlated to the molecules' hydrophobicity, expressed as the logD value and its isotherm affinity constant. CONCLUSION: These results give valuable insight to design and improve the adsorbent material and an off-flavour removal unit at industrial scale.