Technical Session: Tailoring Zeolites Properties for Separation Processes

Many gas and vapour separation processes require complex infrastructures and/or are very demanding from an energy point of view, which makes the search for more sustainable alternatives highly desirable. Examples of such separations include natural gas upgrading where CO₂ must be removed before being transported, recovery of light olefins from olefin/paraffin mixtures and recovery of bioalcohols from fermentation broths, among others. These separations pose a great challenge and an enormous economic impact, since current technologies that involve cryogenic distillation, amine scrubbing or extraction-evaporation-distillation processes could be replaced by separation units based on the use of porous materials as selective adsorbents.

The particular needs of these separations exemplify how the properties of the adsorbent, particularly zeolites, must be tailored to maximize the production of a separation unit. In this regard, the influence of the porous properties and the chemical composition of the zeolites on the adsorption capacity and separation selectivity will be discussed.

The first case study shows that CO₂ and CH₄ isotherms allow the evaluation of zeolite adsorbents that provide the best CO₂ adsorption capacity and CO₂/CH₄ separation selectivity from a simulated natural gas mixture. Furthermore, changes in the chemical composition of zeolites that modify their polarity have been found to be of paramount importance for achieving effective CO₂/CH₄ separation.

Secondly, the applicability of pure silica zeolites in different processes will be presented. In the case of olefin separations, the complete absence of acid sites prevents pore blocking caused by olefin oligomerization within the porosity of the zeolites. It will be shown how subtle modifications in pore opening can have a significant effect on the selectivity during competitive adsorption and the influence of zeolite framework flexibility in the adsorption behaviour. Medium-pore pure silica zeolites will also be presented as selective adsorbents to separate linear and monobranched from multibranched alkanes in the gasoline range.

Other separations in which pure silica zeolites have shown great promise are vapour phase adsorption recovery processes to isolate biobutanol or isobutanol from vapour mixtures obtained from fermentation media in which the alcohols are diluted in water in very low concentrations. In these cases, the hydrophobicity of pure silica zeolites becomes a key parameter to maximize bioalcohol recovery.

These examples illustrate the parameters governing adsorption processes and the strategies adopted to improve productivity and selectivity during gas separation processes using zeolites as selective adsorbents.

Speakers

SUSANA VALENCIA

KAUST

KAUST Research Centers

KCC Research Groups