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PhD Defense: Jason Gulbinski, “Phosphorus-Containing Zeolites for Biofuel Production”.

Date/Time: 

Friday, June 3, 2022 - 9:00am

Location: 

Lederle 201 and Zoom

Details: 

Chair:  Wei Fan

 

Abstract:

Fossil fuel consumption has led to an ever-growing climate change crisis. Despite the danger, fossil fuel consumption continues to increase by 2% a year, not only for transportation fuels but due to the large variety of specialty chemicals derived from oil, including plastics and synthetic fibers. One of the largest fractions of specialty chemicals is p-xylene, a monomer of polyethylene terephthalate. It is used in plastics and synthetic fibers, with a demand of over 50 million tons in 2021 and expected to increase by 5% a year through 2026. Therefore, a sustainable method of p-xylene production is highly desired.

p-Xylene can be produced renewably through the Diels-Adler cycloaddition of lignocellulosic biomass- derived 2,5-dimethylfuran (DMF) with ethylene from bio-ethanol and subsequent dehydration over a solid acid catalyst. However, industry standard catalysts such as aluminosilicate zeolites achieve a selectivity of only 75%, with loss in selectivity to side products and coking. Therefore, a new class of catalysts is necessary which can selectively catalyze DMF and ethylene to p-xylene, as well other products from lignocellulosic biomass. Recently, phosphoric acid-containing aluminum-free zeolites, called P-zeosils, such as dealuminated zeolite P-BEA have shown high selectivity to p-xylene over 95%. However, the active site structure and structure-property relationships which lead to high selectivity are unknown.

Herein, the behavior of phosphoric acid in p-xylene production from DMF and ethylene without siliceous zeolite support and with the interaction between phosphoric acid and siliceous zeolite support is investigated. Phosphoric acid without silica support is active in the p-xylene reaction, and in the presence of silica support, the phosphoric acid will preferentially adsorb on the support in-situ, leading to higher selectivity than phosphoric acid without support. However, when phosphoric acid is impregnated, dried, and calcined on the silica support prior to reaction, the P-zeosil achieves the highest selectivity to p-xylene. The effect of Si/P ratio and calcination temperature on the impregnated P-zeosils are further investigated through X-ray diffraction (XRD), nitrogen adsorption and 31P solid state magic angle spinning nuclear magnetic resonance (MAS NMR). The active sites in reaction are likely Brønsted acid sites (BAS), and the BAS is determined through titration and temperature-programmed reaction of a basic probe molecule, t-butylamine (TBA). Good agreement was found between initial reaction rates in DMF conversion and the BAS density. Water can hydrolyze oligomerized P structures, and a method for hydrolyzing oligomeric P structures at higher temperatures are investigated. Understanding the active site structure of P-BEA and other P-zeosils is crucial for their future industrial use in renewably relevant reactions.

 
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