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

Abstract

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 m 2 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.

β‐Zeolite‐Assisted Lignin‐First Fractionation in a Flow‐Through Reactor**

“…Mass transfer limitations can affect the overall monomer generation rate and, in general, should be avoided for optimal system operation [33] . Specifically for lignocellulosic biomass and microporous zeolites, the system is prone to internal mass transfer limitations due to the interaction of large lignin macromolecules with microporous solids [34] . In order to ensure absence of internal and external mass transfer limitations during delignification, we have studied the effect of biomass particle size in the delignification rate of birch wood (see the Supporting Information, Section 16) and concluded that there are no diffusional limitations for particles below 150 μm and a solvent flow rate of at least 0.5 mL min −1 .…”

“…The systematic rate‐limiting step analysis suggests that it is necessary to increase both solvolytic and catalytic reaction rates to enhance the phenolic monomer yield. Homogeneous acid addition is known to increase β‐O‐4 bond cleavage through hydrolysis, leading to a higher delignification rate [26,34] . Nevertheless, acid‐catalyzed lignin depolymerization may also lead to more severe lignin recondensation [18] .…”

“… [33] Specifically for lignocellulosic biomass and microporous zeolites, the system is prone to internal mass transfer limitations due to the interaction of large lignin macromolecules with microporous solids. [34] In order to ensure absence of internal and external mass transfer limitations during delignification, we have studied the effect of biomass particle size in the delignification rate of birch wood (see the Supporting Information, Section 16) and concluded that there are no diffusional limitations for particles below 150 μm and a solvent flow rate of at least 0.5 mL min −1 . To rule out mass transfer limitations for the zeolite‐catalyzed reactions, the effect of β‐zeolite particle size was evaluated by comparing the performance of 40–80 μm particles (i. e., reference case) with that of 80–150 μm particles.…”

“…Homogeneous acid addition is known to increase β‐O‐4 bond cleavage through hydrolysis, leading to a higher delignification rate. [ 26 , 34 ] Nevertheless, acid‐catalyzed lignin depolymerization may also lead to more severe lignin recondensation. [18] Thus, we evaluate the co‐addition of a homogeneous acid on the monomer yield.…”

β-Zeolite Assisted Lignin-First Fractionation in a Flow-Through Reactor

“…Mass transfer limitations can affect the overall monomer generation rate and, in general, they should be avoided for optimal system operation [29] . Specifically for lignocellulosic biomass and microporous zeolites, the system is prone for internal mass transfer limitations due to the interaction of large lignin macromolecules with microporous solids [36] . In order to ensure absence of internal and external mass transfer limitations during delignification, we have studied the effect of biomass particle size in the delignification rate of birch wood (See ESI Section 16) and concluded that there are no diffusional limitations for particles below 150 m and a solvent flowrate of at least 0.5 mL/min.…”