Catalytic Conversion of Biomass-derived Platform Molecules to Distillate-range Fuels PDF Download

Author: Nathaniel Eagan
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Languages : en
Pages : 0

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Book Description
Current trends in resource consumption and environmental degradation inspire research into the benign transformation of renewable feedstocks to transportation fuels with lower net greenhouse gas emissions. Growing demands in heavier middle-distillate fuels such as diesel and jet fuel particularly motivate the use of carbon-containing feedstocks such as biomass in order to produce liquid fuels substantially similar to those already essential to our economy. Such fuels still require carbon chains larger than those of the monomeric sugars comprising cellulose and hemicellulose, however, thus carbon-carbon bond forming technologies have an important place in the overall biomass-to-distillate landscape. These technologies can be utilized to upgrade platform molecules easily obtainable from biomass. The research discussed here focuses on the use of sorbitol and ethanol platforms, providing promising new directions for their utilization. Sorbitol conversion to distillate fuels first requires a challenging hydrodeoxygenation step focused on producing mono-functional oxygenates. Here this chemistry was promoted by a Co/TiO2 catalyst at yields (56%) competitive with more costly noble-metal catalysts. FT-ICR-MS provided evidence that oligomeric species produced may also act as intermediates in the process. However, this catalyst suffered from irreversible deactivation via oxygenate-promoted Co leaching and sintering which could not be inhibited by the SMSI-stabilization of the catalyst. Pathways by which ethanol can be converted into middle-distillate fuels were then extensively evaluated by considering the fundamental chemistries which can be exploited and how they can be most effectively combined. These processes involve integrating dehydration, hydrogen transfer, olefin oligomerization, aldol condensation, and ketonization in a variety of ways which can overcome the limitations of any one particular technology. From these analyses, promising research directions are recommended. The subsequent focus here is on the use of Guerbet coupling to directly oligomerize ethanol to distillate-range fuels. Cu-doped AlMgO and AlCaO catalysts were first examined for this purpose, with the importance of operating at elevated pressures to promote selective coupling explained. Selective ethanol oligomerization is still challenging with these catalysts, however, given that alcohol selectivities were limited here to ~55% at 20% conversions, and conversions above 30% were difficult to achieve due to inhibition by products of the reaction (e.g. water). Calcium hydroxyapatite (HAP) was then examined as a more selective catalyst for this transformation, though declining selectivities and reaction rates were observed as conversion increased. However, integration of selective ethanol coupling over HAP with bimolecular dehydration shows promise as a novel method to produce diesel-range ethers from biomass-derived sources. Overall a process was developed which can produce these ethers in addition to jet-range paraffins at theoretical yields above 80%. Lastly kinetic modeling was utilized to better understand the limitations and potential of using Guerbet coupling to oligomerize ethanol to distillate-range alcohols. Inhibition effects by water rationalize the aforementioned declining rates and selectivities observed with increasing conversion. In the absence of these phenomena, however, the production of distillate-range alcohols is limited by the underlying kinetics which resemble step-growth oligomerization with the additional stipulation that branched alcohols cannot couple as nucleophiles. The model discussed here suggests that catalysts which promote the electrophilic action of higher alcohols over that of ethanol are promising for promoting linear alcohol formation that cascades into the distillate-range.