Ethane upgrading and ethylene ethane separation with transition metal-exchanged zeolites
Date
2023
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Publisher
University of Delaware
Abstract
The goal of this thesis is to advance new technologies for ethylene production through innovations in microporous catalysts and adsorbents. Worldwide ethylene consumption exceeded 150 million tons in 2017. Ethylene production is conducted industrially via stream cracking of ethane, a highly energy-intensive process due to the high temperature conditions (>750 ºC). Each ton of ethylene produced causes 1-2 tons of CO2 emission, depending on the feedstock. An alternative method of ethylene production with the accessible ethane feedstock is highly desirable and ethane catalytic dehydrogenation is a potentially energy-saving alternative for ethylene production. ☐ At the same time, ethylene/ethane separation is another important industrial process that is performed using cryogenic distillation. The low temperature, high pressure and high equipment cost of cryogenic distillation calls for innovative energy-saving approach that minimizes energy consumption. One of the methods that requires less energy input is the adsorptive separation of ethylene and ethane. ☐ In this thesis, metal-exchanged zeolite materials were synthesized, characterized, and tested for their catalytic and adsorption performance for ethylene synthesis. X-ray and neutron powder diffraction and the subsequent Rietveld refinement were utilized to extract structural information of the zeolite materials and the adsorbed gas molecules. The structural information provides insight that helps understand the guest-host interaction between the adsorbed gas molecules and the zeolite adsorbent. Structure-property relationship was established for the zeolite catalyst/adsorbent materials to understand the performance difference between different metal-exchanged zeolite materials. ☐ In chapter 3, a capillary experimental setup was used for the collection of laboratory-scale X-ray powder diffraction data on dehydrated and reduced metal-exchanged zeolite catalysts. Rietveld refinement was performed on the In-CHA catalyst to locate and identify the exchanged In cation in the In-CHA zeolite catalyst. ☐ In chapter 4, Zn-exchanged CHA and AEI zeolites were synthesized, characterized, and tested for their catalytic performance for ethylene hydrogenation. Rietveld refinement of neutron powder diffraction data shows the Zn sites are almost identical in Zn-CHA and Zn-AEI. Ethylene adsorption structure analysis shows that ethylene adsorbed on Zn-CHA has stronger interaction with the Zn site and is more polarized. Ethylene polarization is explained by the enhanced ethylene H to framework O interactions of ethylene adsorbed on Zn-CHA. The more polarized ethylene adsorption structure also agrees with the higher ethylene hydrogenation activity on Zn-CHA compared to Zn-AEI. ☐ In chapter 5, metal-exchanged KFI zeolites were synthesized, characterized, and tested for their adsorption performance for ethylene and ethane. Analysis of single component adsorption isotherms shows a high ethylene adsorption selectivity for Mn-KFI zeolite. Heats of adsorption calculations also shows more negative (stronger) ethylene heat of adsorption on Mn-KFI. Rietveld refinement confirms the ion exchange positions in metal-exchanged KFI zeolites. We also demonstrated different ethylene adsorption modes in Mn-KFI and Na-KFI, which can help explain their different adsorption properties. ☐ In chapter 6, a summary of novel zeolite synthesis attempts was shown for the synthesis and characterization of high-Al AFI zeolite and the framework Fe-containing CHA zeolite, as potentially good model zeolites for catalysis studies.
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Keywords
Catalysis, Powder diffraction, Rietveld refinement, Separation, Structural analysis, Zeolite