Studies on low-carbon aromatics and jet fuel synthesis

概要

At present, traditional jet fuels and low-carbon aromatics are mainly delivered from traditional petrochemical industries, with the fossil resource decreasing and the serious pollution caused by fossil fuel combustion, the jet fuels and low-carbon aromatics synthesis by petroleum-free method attracted more and more attention. Besides, the development of petrochemical industries leads to serious of environmental problems such as global warming. Using recyclable raw materials to produce high value-added products instead of traditional petrochemical industrial, such as jet fuel and low-carbon aromatics, which is makes more sense to reduce carbon emissions.

Isobutyl alcohol, biological isobutyl alcohol as a new generation biomass energy can be produced through biomass fermentation from non-food crops such as cellulose, CO2. The utilization of bio-isobutyl alcohol to produce the jet-range hydrocarbons, which is a new promising process route that maybe can instead of traditional petrochemical industrial route.

CO2, as the main greenhouse gas, the method to effectively reduce CO2 emissions have attracted widespread attention. CO2 as raw materials was hydrogenated into low- carbon aromatics seems to be an efficient and replaceable solution for low-carbon aromatics synthesis, which meets the requirements of the sustainable process and carbon emission.

Thus, our work focuses on new catalysts exploits, new catalytic reaction process develops, and new reactor designs in low-carbon aromatics and jet fuel synthesis in the thesis: (1) Catalytic isobutyl alcohol oligomerization to generate liquid fuels over H-Y, SAPO-34, H-MOR zeolite and Al-MCM-41 catalysts (Chapter 1); (2) Various dealuminum methods of zeolite Beta to generate the jet fuels by converting isobutyl alcohol (Chapter 2) ; (3) Multifunctional catalyst composed of Na-Fe@C and hollow H-ZSM-5 for directly converting CO2 to low-carbon aromatics (Chapter 3).

In chapter 1, It presents an new catalytic process for the direct conversion of isobutyl alcohol into jet-range hydrocarbons. A series of catalysts such as H-Y, SAPO-34, H- MOR zeolite and Al-MCM-41 was developed and applied in direct isobutyl alcohol conversion to liquid fuels, especially H-MOR shows the best reactivity, achieving 94% conversion of isobutyl alcohol and 63% selectivity C5+ liquid fuels, the reaction system was discussed and was considered to be a two-step process i) isobutyl alcohol dehydration reaction via a typical acid catalysis, ii) a polymerization reaction of small molecules into large ones, the present work shows that the pore size and acid property of the zeolite are the two main factors controlling this catalytic dehydration and oligomerization reaction. This work offers a new and efficient method to generate the liquid fuels from isobutyl alcohol directly.

Chapter 2 shows that Beta zeolite by different dealuminum methods shows the different pore size and acid property for direct conversion of isobutyl alcohol into jet- range hydrocarbons. The Beta was treated by the HCl or the EDTA to dealuminate, it shows the different dealuminum process by the strong acid and weak acid, the extra- framework Al was can be partly removed by HCl treatment, which cause the pores of the zeolite Beta become smoother, and the acid property was manipulated by this treatment. Consequently, isobutyl alcohol can be quantitatively oligomerized over the dealuminated zeolite Beta with the selectivity of C8-16 exceeding 50% at a conversion of 98%. The present work provides a possible way to develop a promising catalyst for generating jet fuels by catalytic oligomerization from isobutyl alcohol.

In chapter 3, we report a Multifunctional catalyst composed of Na-Fe@C and hollow H-ZSM-5 for directly converting CO2 to low-carbon aromatics. A carbon encapsulated iron catalyst with Na modification (Na-Fe@C) was prepared using Fe-based metal- organic frameworks (Fe-MOFs) as precursors. Benefiting from the periodic structure of Fe-MOFs, highly dispersed Fe3O4 nanoparticles encapsulated by a few graphene- like carbon layers were obtained after pyrolysis of Fe-MOFs under N2 atmosphere. After combining Na-Fe@C with the NaOH treated H-ZSM-5, the alkenes produced from Na-Fe@C can be converted to aromatics via the dehydrogenation and cyclization reactions on the acidic sites of H-ZSM-5. Surprisingly, the STY of aromatics (203.8 gCH2 kgcat-1 h-1) obtained from the multifunctional catalyst composed of Na-Fe@C and hollow H-ZSM-5. Furthermore, the driving force in the tandem process was also clarified, the interplay between the two catalyst components facilitated the dehydrogenation and cyclization reactions of the intermediate alkenes, which was beneficial for the aromatics synthesis. This work offers a simple and effective strategy to synthesize low-carbon aromatics from CO2 under mild conditions directly.

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