Production of jet-range biofuels from 2,3-butanediol
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Wang, Thomas
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Abstract
In the transition from our current energy mix still dominated by fossil fuels to an increasingly carbon-neutral energy mix, the energy consumption in the transportation sector is a focal point. In air transport, the most viable current technology for decarbon-ization is through synthetic biofuels. An important route is the jet-fuel synthesis from fermented bio-alcohols using a short-chain olefin intermediate. This thesis examines such a route involving synthesis of jet-range biofuels from 2,3-butanediol (BDO) through a butene intermediate. The thesis first examines the deactivation mechanism of the bifunctional catalysts converting BDO to butene. This is then followed by an exami-nation of the oligomerization of butene with two zeolite catalysts at a range of condi-tions to optimize production in the jet range.
The bifunctional catalysts converting 2,3-butanediol to butene are ZSM-5 zeolite (framework type MFI, with 3-D interlinked 10-MR channels) supports with supported copper nanoparticles (Cu/ZSM-5). Zeolites, microporous and crystalline aluminosilicate materials, possess acid sites that can catalyze reactions including the dehydration of al-cohols and hydrocarbon interconversion such as oligomerization and cracking. The con-version from BDO to butene proceeds through the dehydration of the BDO to carbonyl intermediates including methyl ethyl ketone (MEK) and isobutyl aldehyde (IBA). These carbonyl intermediates are then hydrogenated to butanol isomers which undergo another dehydration to produce butene isomers. The zeolite support provides the acid site that catalyze the dehydration steps, but can also produce non-volatile carbonaceous deposits (“coke”). These deposits can induce deactivation of heterogeneous catalysts through routes such as blocking access to pores or active sites. Supported metal catalysts can also deactivate through the growth in size of the metal particles, thus reducing the sur-face area of the active metal. The first chapter of this work examines these two deacti-vation mechanisms among others for the conversion of BDO to butenes and explore de-activation-resistant designs, to achieve longer catalyst lifetimes for butene production from the bio-alcohol.
The production of jet-range biofuels from the bio-derived butene involves the ol-igomerization of butene isomers to jet-range olefins before a well-established hydro-genation procedure. The oligomerization of butenes can be performed with a variety of catalysts, but solid acids are preferable because the coke-induced deactivation is less detrimental to the poisoning of metal active sites found in catalysts with active sites such as nickel (II) involving coordination chemistry. Among solid acids, the confine-ment effect zeolite micropores and easier regeneration make zeolites the preferred cata-lyst. The second chapter of this work examines the effects of temperature, pressure, and butene feed rate on the oligomerization of butene catalyzed by HZSM-5 and Hβ zeolites. The chosen temperature, pressure, and feed rate ranges are selected to reflect conditions typical of what can produce mixtures that are close to jet-range.
Chapter 1 introduces the fundamentals of zeolite catalysts and supported-metal catalysts, their preparation and applications, the development of Cu/ZSM-5 catalysts, the uses of various acidic zeolites in alkene oligomerization, provides an introduction in catalyst deactivation through coke formation and metal particle growth, and defines the jet fuel specifications this work aims to achieve.
Chapter 2 describes the two experimental setups each used for the conversion of 2,3-butanediol to butene and the oligomerization of butene.
Chapter 3 examines the deactivation behavior of Cu/ZSM-5 catalysts. The deac-tivation was able to be attributed to mainly a combination of sintering and the reduction in copper site accessibility via coking, with pore filling and support aging found to be negligible. Mesoporous supports from treatment with NaOH and CsOH solutions re-spectively were used to prepare new Cu/ZSM-5 catalysts with superior performance due to more accessible copper and lower coke formation, with the catalyst with CsOH-treated support being the most resistant to deactivation.
Chapter 4 explores the effects of temperature, pressure, and butene feed rate on the oligomerization of butene catalyzed by HZSM-5 and Hβ zeolites. The weight-average molecular weight of the oligomer product were found to peak at certain temper-ature and pressure conditions especially at lower feed butene feed rates, due to increas-ing cracking at higher temperatures and lower diffusion rates at higher pressures. Long-term performance at jet-fuel-producing conditions for both catalysts were vary stable given the 3D channel structure of the catalysts and the relatively low coke formation for the long time on stream.
Chapter 5 summarizes the conclusions of chapters 3 and 4 and outlines future research directions based on the findings of this work.
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2024-12-06
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