Tailoring zeolite morphology by Charge Density Mismatch for aromatics processing

• The CDM concept was used to synthesize nano-crystalline UZM-5 and UZM-14.
• UZM-5 has a surface topology favorable for liquid-phase alkylation.
• The morphology of UZM-14 zeolite was found to be effective for aromatic transalkylation.
• Morphological properties critical to alkylation and transalkylation performance were identified.

Nano-crystalline zeolites UZM-5 and UZM-14 were synthesized via the Charge Density Mismatch (CDM) approach and were shown to have distinct morphologies that significantly impact aromatic alkylation and transalkylation reactions. UZM-5 has surface structure features and thin plate morphologies favorable for catalyzing the alkylation of benzene with ethene. The alkylation activity depends on the crystallinity and morphology, which affect acidity and access to surface cups and internal pores. Nano-crystalline mordenite, UZM-14, was characterized in terms of crystallite length in the direction of the 12-MR channels, mesoporosity, and accessibility of acid sites. Aromatics transalkylation performance was shown to correlate with mesoporosity and crystallite length along the pore direction. This was rationalized in terms of decreased diffusion path length in the micropores and improved accessibility of feed molecules to acid sites in the interior of the zeolite crystals.

Control over zeolite crystallization comes by first preventing it by employing a Charge Density Mismatch tetraethylammonium (TEA+) aluminosilicate solution that cannot crystallize and then perturbing it with crystallization agents such as Na+ and TMA+ to yield nano-crystalline UZM-5 (UFI) and UZM-14 (MOR) that are excellent alkylation and transalkylation catalysts, respectively.Figure optionsDownload high-quality image (103 K)Download as PowerPoint slide