[Che-student-staff-list] Dhairya Mehta Dissertation Defense on Friday, August 15th, at 1:00 p.m. in G124

[Field, Catherine A]

This e-mail is to announce that Dhairya Mehta will be defending his dissertation, Kinetic Studies of Model Reactions to Transform Biomass into Fuels, on Friday, August 15th, at 1:00p.m. in FRNY G124. The dissertation is being directed by Dr. Ribeiro, and the abstract is below. All are welcome to attend.

Abstract:
Second-generation biofuels utilizing lignocellulosic biomass are considered to be a promising alternative to fossil-based fuels. Lignocellulosic biomass is structurally diverse and therefore requires detailed understanding of the thermal depolymerization and catalytic hydrodeoxygenation reactions to optimize the overall process. This dissertation describes experimental work using model compounds to elucidate the role of bimetallic catalysts and control of the reaction operating parameters such as temperature and hydrogen pressure to maximize energy recovery in the liquid product from biomass resources.

Fast-hydropyrolysis of biomass followed by in-line catalytic hydrodeoxygenation has been shown to have the potential to produce hydrocarbon fuels using hydrogen as a co-feed. The objective of the research project was to identify and quantify the primary products of fast hydropyrolysis as well as to establish the effect of temperature on the overall product distribution. A torch igniter, typically used in rocket engines, was modified to design a reactor that is able to continuously feed biomass at a gram per minute scale and complete the entire process from fast hydropyrolysis to condensation of bio-oil in less than about 70 ms at 3.6 MPa hydrogen pressure. The identification and quantification of products with molecular weight higher than the monomer (levoglucosan) at 70 ms residence time compared to their absence in reactors with residence time of 2-3 s indicate that levoglucosan is not the sole primary product of cellulose pyrolysis. Thus a portion of levoglucosan is a result of dimer (cellobiosan) and trimer (cellotriosan) degradation.

Catalytic hydrodeoxygenation is used to selectively remove oxygen as water and thus transform the oxygenated organic compounds to fungible hydrocarbon fuels. Furfural and dihydroeugenol were the chosen model compounds to represent the cellulose and lignin fractions of biomass. Discerning the role of catalyst descriptors and hydrogen pressure were the main goals of this study. A bimetallic catalyst system comprising platinum as a hydrogenation function and molybdenum as an oxophilic promoter supported on multi-walled carbon nanotubes (MWCNT) was used to achieve 100% hydrodeoxygenation of dihydroeugenol resulting in >96% yield of C9 aromatic and saturated hydrocarbons. At 0.1 MPa hydrogen pressure, direct deoxygenation of the phenolic hydroxyl group to produce propylbenzene was the dominant pathway, whereas at higher hydrogen pressures (0.7 and 2.4 MPa), aromatic ring hydrogenation followed by dehydration took precedence yielding propylcyclohexane as the major product. In the case of furfural, increasing the hydrogen pressure from 0.1 to 1.9 MPa resulted in an increase of C5 product selectivity from ~25% to ~80% at a conversion of 18%.  Scanning transmission electron microscopy combined with electron energy loss spectroscopic analysis on the 5%Pt-2.5%Mo/MWCNT revealed that 77% of nanoparticles were bimetallic Pt-Mo. X-ray absorption spectroscopy also confirmed the presence of Pt-Mo alloy and that Mo was partially reduced with an average oxidation state between 0 and +4. Combination of results from catalyst characterization and kinetic studies over a series of Pt-Mo catalysts suggest that the overall site time yield was proportional to Pt loading, whereas the selectivity toward C-O scission products increased as the relative Mo to Pt ratio increased.


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