Unravelling the influence of carbon dioxide on the adsorptive recovery of butanol from fermentation broth using ITQ-29 and ZIF-8

Abstract

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.

Macroscopic and Microscopic View of Competitive and Cooperative Adsorption of Alcohol Mixtures on ZIF-8

“…Periodic boundary conditions were applied. The molecular models for 1-butanol and ethanol were validated in previous work . Both molecules were defined as flexible models.…”

“…The molecular models for 1-butanol and ethanol were validated in previous work. 24 Both molecules were defined as flexible models. Each CH x group from the aliphatic chain was considered as a single interaction center.…”

“…19−29 Monte Carlo (MC) simulations, using the ambient pressure structure of ZIF-8, were able to accurately describe the experimental adsorption isotherms. [24][25][26]30,31 They, moreover, indicated that the flexibility of the framework has little influence on the adsorption equilibrium of alcohols on ZIF-8. [24][25][26]30,31 Instead, the adsorption mechanism seems to follow that of a polar component adsorbing into hydrophobic pores.…”

“…[24][25][26]30,31 They, moreover, indicated that the flexibility of the framework has little influence on the adsorption equilibrium of alcohols on ZIF-8. [24][25][26]30,31 Instead, the adsorption mechanism seems to follow that of a polar component adsorbing into hydrophobic pores. 21,27,30,32 Although the pure component equilibrium of linear alcohols on ZIF-8 has been well studied, 21,27,30,32 studies on the mixture adsorption equilibrium of alcohols are limited to binary alcohol/water mixtures.…”

“…However, X-ray diffraction results showed that the structure of ZIF-8 when loaded with 1-butanol is very similar to its empty, ambient pressure structure . On the other hand, molecular simulations have been used to gain microscopic insights into this adsorption phenomenon on ZIF-8. − Monte Carlo (MC) simulations, using the ambient pressure structure of ZIF-8, were able to accurately describe the experimental adsorption isotherms. − ,, They, moreover, indicated that the flexibility of the framework has little influence on the adsorption equilibrium of alcohols on ZIF-8. − ,, Instead, the adsorption mechanism seems to follow that of a polar component adsorbing into hydrophobic pores. ,,, Although the pure component equilibrium of linear alcohols on ZIF-8 has been well studied, ,,, studies on the mixture adsorption equilibrium of alcohols are limited to binary alcohol/water mixtures. , …”