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Adsorbent monoliths are gaining increasing interest in gas phase separation processes, but have rarely been studied for liquid phase separations. In this work, we investigate an activated carbon monolith for the recovery of biobutanol from model liquid mixtures as well as compare the obtained column dynamics with the adsorption of biobutanol from gas mixtures. Single solute adsorption isotherms of acetone, n-butanol and ethanol revealed the carbon’s larger affinity for n-butanol (0.11 g/g adsorbed at 2 wt%), while dynamic separations on a fixed-bed of crushed monolith granules proved its capability to effectively separate an aqueous mixture of these three fermentation products. In contrast, liquid phase breakthrough experiments of n-butanol on the monolith column were marked by almost instantaneous detection of adsorbate at the outlet (< 5 min.) and broad tailing of the concentration curve. Measures to improve inlet flow distribution or increasing temperature to enhance mass transfer were unsuccessful. In contrast, using the same inlet flow distributors, a sharp breakthrough profile could be obtained in vapor phase, while the gas contact time (17 s) was much lower than in liquid phase (1300 s). A comparison of characteristic mass transfer times of the adsorption process highlighted the important role of the external film resistance in liquid compared to vapor phase adsorption.

[EN] Isobutanol is a promising renewable platform chemical, produced via fermentation. In the conventional downstream processing, isobutanol is recovered from the fermentation broth via evaporation or gas-stripping, followed by purification via distillation. Alternatively, an adsorptive separation can be used to recover isobutanol from the generated vapor mixture, however this has remained unexplored in the literature. In this work, we investigate the use of a hydrophobic all-silica beta zeolite (Si-BEA) to recover isobutanol from model vapor mixtures via adsorption. The Si-BEA zeolite shows a high selectivity for isobutanol over water (? = 35) and ethanol (? = 10) and excellent mass transfer properties under dynamic conditions. Sharp isobutanol breakthrough profiles were obtained, leading to a fraction of unused bed of only 6% at a gas residence time of only 0.6 s. The adsorbed isobutanol could be fully desorbed via thermal regeneration and an isothermal purge allows to remove co-adsorbed ethanol and water. The results of this work thus show the promising properties of Si-BEA for the recovery of renewable isobutanol from vapor mixtures., Julien Cousin-Saint-Remi is grateful to the FWO for financial support (grant number 12P2217N and 1512118N).

While many studies have focused on the adsorptive recovery of bioethanol and biobutanol produced via fermentation, few articles have been published on the recovery of renewable isobutanol via adsorption. We have screened over 32 materials for their capacity to recover isobutanol from a dilute mixture. From this screening, we identified two promising activated carbons (F300 and F400) and two polystyrene-divinylbenzene resins (XAD-16 and L-493) with a high isobutanol capacities (0.45 g/g XAD-16, 0.38 g/g L-493, and 0.25 g/g F300 and F400). These materials were further characterized (Ar, vapor, and liquid isotherms), and the effect of different typical fermentation components on the batch uptake of isobutanol was investigated. For the F300 carbon and L-493 resin, only a small decrease in the uptake of isobutanol was observed in the presence of fermentation compounds (0.17 g/g F300, 0.26 g/g L-493). Subsequently, we investigated the separation of an isobutanol/ethanol mixture on a packed column of F300 and L-493.For both materials, the high capacity for isobutanol is retained in dynamic conditions. Therefore, in this work, two promising materials (L-493 and F300) emerge as interesting candidates for the adsorptive recovery of isobutanol.

We report the use of 3D-printed ZIF-8 adsorbent monoliths for the recovery of biobutanol from model fermentation mixtures. Two ZIF-8 monoliths, obtained by layer-by-layer printing, with different fiber thickness (250 and 600 μm), front channel size (350 μm × 350 μm and 760 μm × 760 μm), and side channel size (

Increasing energy prices, global warming, and concerns for environmental pollution has been pushing the chemical industry to look for alternatives for traditional, fossil-based chemical feedstocks. Important platform molecules are alcohols, which can be produced from renewable feedstocks via fermentation. The implementation of these fermentation processes to produce chemicals leads to important challenges regarding the downstream purification. Adsorption-based purification technologies are alternatives for traditional energy-intensive distillation processes. The well-defined pore structure of zeolites makes them ideal candidates for the removal of alcohols from these complex fermentation mixtures, which contain cells and cell debris, acids, sugars, lipids, and proteins. The following chapter covers important aspects in the adsorption mechanism of alcohols and water in (mainly) hydrophobic zeolite pores, such as cluster formation and hydrogen bonding. These effects inevitably also play a role when looking at the diffusion of alcohols inside the zeolite pores. Finally, this chapter will cover some examples of studies where hydrophobic zeolites have been used to recover bio-alcohols, such as biobutanol and bioethanol, from model solutions or fermentation broths via fixed-bed separations.

[EN] A vapor phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanolethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape selective all-silica zeolites CHA and LTA were prepared and evaluated via single component isotherms and breakthrough experiments. These zeolites show an opposite selectivity; adsorption of ethanol was favorable on all-silica CHA, while the LTA topology had clear preference for butanol. The molecular sieving properties of both zeolites allowed to easily eliminate acetone from the mixture. The molecular interaction mechanisms were studied by density functional theory (DFT) simulations. Effect of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior was investigated. Desorption profiles were studied to maximize butanol purity and recovery. The combination of LTA with CHA type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows to obtain butanol in unpreceded purity and recovery. A butanol purity of 99.7 mole% could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes., S.V.D.P. and J.F.M.D. are grateful to FWO Vlaanderen for financial support (G025614N). M.P., L.Y.S., S.V. and F.R. gratefully acknowledge financial support of Spanish Government (MAT2015-71842P and Severo Ochoa SEV-2012-0267). The authors thank to A. Vidal and T. Blasco for performing NMR measurements and discussion.

While in most adsorptive separations different mixture components tend to compete for different adsorption sites, we report the existence of cooperative effects in the adsorption of alcohols (ethanol and 1-butanol) from the vapor phase on ZIF-8. The presence of these molecules in binary mixtures leads to an increase in their equilibrium capacities, compared to the pure component isotherms. These effects were first observed when predicting the mixture equilibrium capacities using the ideal adsorbed solution theory (IAST) and were also observed via grand canonical Monte Carlo (GC MC) simulations. GC MC simulations showed that the interaction between adsorbate molecules leads to the cooperative effect predicted by IAST. The predicted cooperative adsorption could be confirmed via breakthrough experiments. In these experiments, a "roll-up" of 1-butanol was observed during the regeneration of a ZIF-8 packed column. A dynamic breakthrough model employing IAST was developed and used to explain the effect of the adsorption equilibrium on the dynamic breakthrough profiles.

The vapor phase adsorption of butanol from ABE fermentation at the head space of the fermenter is an interesting route for the efficient recovery of biobutanol. The presence of gases such as carbon dioxide that are produced during the fermentation process causes a stripping of valuable compounds from the aqueous into the vapor phase. This work studies the effect of the presence of carbon dioxide on the adsorption of butanol at a molecular level. With this aim in mind Monte Carlo simulations were employed to study the adsorption of mixtures containing carbon dioxide, butanol and ethanol. Molecular models for butanol and ethanol that reproduce experimental properties of the molecules such as polarity, vapor–liquid coexistence or liquid density have been developed. Pure component isotherms and heats of adsorption have been computed and compared to experimental data to check the accuracy of the interacting parameters. Adsorption of butanol/ethanol mixtures has been studied in absence and presence of CO2 on two representative materials, a pure silica LTA zeolite and a hydrophobic metal–organic framework ZIF-8. To get a better understanding of the molecular mechanism that governs the adsorption of the targeted mixture in the selected materials, the distribution of the molecules inside the structures was analyzed. The combination of these features allows obtaining a deeper understanding of the process and to identify the role of carbon dioxide in the butanol purification process.

The adsorptive vapour phase separation of 1-butanol from a synthetic ABE (acetone, 1-butanol, ethanol) mixture has been studied for the first time on a set of unidirectional small pore pure silica zeolites with ITW, MTF, RTH and STT structures with different pore size and topology. With this systematic approach, we provide insight into the structural and surface properties that can improve the vapour phase recovery of biobutanol. The influence of operation parameters, such as the temperature (40–80 °C), the total flow, and presence/absence of humidity and CO have been studied. For this application, adsorbents need to possess pore openings with one of their dimensions larger than 4.1 Å and cavities with diameters above 7 Å. Si-STT zeolite presents a remarkable selectivity towards 1-butanol, which is not affected by the presence of water or CO in the mixture or by an increase in the temperature. Si-STT results an excellent and robust adsorbent for this separation at conditions close to those of the headspace of the ABE fermenter, achieving purities of 90–93% at recoveries between 90 and 96%., The authors want to thank the Spanish Ministry of Science and Innovation and the Spanish Agency of Research for their funding via Project RTI2018-101784-B-I00. The Generalitat Valenciana, Conselleria d’Innovació, Universitats, Ciència y Societat Digital is acknowledged for their funding via project Prometeo/2021/077. EP-B acknowledges the Spanish Ministry of Education and Professional Training for the grant FPU15/01602 and the additional funding for the stay EST18/00213.

Bio-butanol is an attractive substitute for fossil-based fuels and platform chemicals. It can be produced from renewable resources by the so-called acetone-butanol-ethanol (ABE) fermentation. However, this process severely suffers from product inhibition, leading to low productivities and low final mixture concentrations (typically < 20g/l). Product inhibition can be relieved by combining the fermentation with a gas stripping process. Although butanol is efficiently stripped from the fermentation medium, it still exists within the stripping gas as a mixture with acetone, ethanol and water, requiring further purification. This is conventionally performed via distillation. Unfortunately, this distillation process requires a large amount of energy, making the butanol production process uneconomical. Among the alternatives for the traditional distillation, adsorption on porous materials has been identified as the most energy-efficient technique1. From that perspective, we studied different microporous zeolites that allow a full recovery and purification of the produced butanol from the stripping gas via adsorption. These zeolites were characterised by measuring (static) batch adsorption isotherms and performing (dynamic) fixed-bed separation experiments using vapor mixtures. An all-silica zeolite (ITQ-29) with a LTA topology showed to have a high adsorption capacity for butanol. Fixed-bed experiments revealed the high selectivity of this material for butanol over acetone, ethanol and water. Two other zeolites, Si-CHA and SAPO-34, both possessing a CHA topology, were also studied on their selectivity for the different vapor phase components. The small pore size of these zeolites led to the exclusion of acetone and butanol, whereas ethanol and water could adsorb. The all-silica, apolar Si-CHA zeolite showed a higher selectivity towards ethanol compared to the more polar SAPO-34 zeolite. Since a small amount of ethanol and water co-adsorbed on ITQ-29, these zeolites were used to further purify the butanol adsorbed on ITQ-29. During the regeneration phase of ITQ-29, an adsorption column containing a CHA-type zeolite was placed in series to further purify the desorbing butanol. Using this combined adsorption/regeneration process, 99% of the butanol adsorbed on ITQ-29 could be recovered at a purity of > 99.5 mole%. (1) Qureshi, N.; Hughes, S.; Maddox, I.; Cotta, M. Bioprocess Biosyst. Eng. 2005, 27 (4), 215–222.