| Since 1980s, energy crisis and the environment pollution due to the excessive use of fossil-based energy resources during the last century, such as petroleum, coal and natural gas, have become great challenges for human beings. Currently, these resources, which are used mainly as transport energy, feedstock for refineries and chemical raw materials, are response to 70%-80% of world’s primary energy consumption and have become important restricting factors of economic development with the decreasing reserves. However, with the enhanced worldwide fuels demand, the increased climate concerns about the use of fossil-based energy carriers and the political commitment, people have recently shifted their focus to the improved utilization of renewable energy resources. Biomass, as the most abundant renewable resource on the earth, have the advantage of converting the carbon dioxide into hydrocarbons through photosynthesis? and can be made into liquid fuels, industrial raw materials and many valuable chemicals through recently developed technologies such as gasification, pyrolysis, and chemical processing. Energy production from biomass will significantly give out less greenhouse gas emissions compared to the use of fossil fuels and have great impact on the world’s energy structure in the future.5-Hydroxymethylfurfural (HMF), a very important biomass derived platform chemical that can be converted into alternative materials to those from fossil resource and other platform chemicals, has been considered as the bridge between the petrochemical industry and the biomass industry, and drawn much attention from people in the last 30 years. HMF can be derived from hexose by losing three molecules of water in an acidic medium. Consequently, different types of acid catalyst have been widely applied in this reaction. However, by-reactions, rehydration of HMF and the formation of soluble polymers and insoluble humins restrict the HMF selectivity in aqueous solutions. Dumesic and co-workers made very successful optimization by using organic solvents such as DMSO and MIBK in a biphasic reaction system. In recent years, more attention has focused on acidic ionic liquids (ILs) for their excellent catalytic performance. But the high cost as well as the complicated and high energy consuming separation processes becomes the barrier to the commercial application. In contrast, heterogeneous catalysts can be easily separated and regenerated which make them more applicative in industrial production. However, most catalytic systems need to be improved due to the low performance, high application cost and the use of environment-unfriendly mediums, which should also be the most important problems to be resolved in front of the industrial production of HMF from biomass.On the other hand, alkylation of bio-derived isobutane and butene in the presence of strong acids leads to the formation of alkylate which composed by mixtures of branched alkanes. Alkylate has a high octane number (-93), a low vapor pressure and a narrow distillation range. Moreover, it contains no olefins, aromatics and sulfur, which make it an excellent blending component for gasoline and the alternative fuel to the fossil-based products. Up to now, HF and H2SO4 are the main catalysts for alkylate production. However, these liquid acids will cause environment hazards during transportation, storage and handling. Besides, HF is a volatile acid with high toxicity while about 70-100 kg of H2SO4 should be consumed for one ton of alkylate. Thus, there has been substantial pressure to develop a more eco-friendly and efficient alkylation process.Zeolites, being non-corrosive solid acidic materials, have been widely studied in different areas. For instance, Garwood and Venuto started the pioneering research on rare earth modified faujasitic zeolites. Later, other zeolites and other solid acidic materials such as heteropolyacids, supported sulfated oxidates and sulfonic acid type ion exchange resin were used in these reactions. However, applications of the most of these catalysts are limited by the harsh conditions required and the unsatisfactory activities. TfOH is a perfluorosulfonic acid of strong acid strength that is stronger than that of H2SO4. Angelis et al. made an efficient alkylation catalyst by connecting TfOH to the surface of silica through chemical bonds. Another perfluorosulfonic material is Nafion resin, which is an extremely stable acid as a substitute of homogeneous acids. But the small surface area (-0.02 m2/g) and the intention to aggregate during the reaction limited its application. To improve this situation, Harmer et al. prepared Nafion modified porous silica to increase the surface area, and successfully improved the catalytic activity of Nafion resin.Therefore in this thesis, a series of perfluorosulfonic solid acid catalysts were synthesized by adopting mesoporous silica materials such as SBA-15, SBA-16 and MCF as supports, and applied in dehydration of fructose and isobutane/butene alkylation. With the view of efficiency and economical- and environment-friendly in mind, triphosphazene-based organic compounds were developed for the HMF production from fructose.(1) Nafion-resin-modified SBA-15, SBA-16 and MCF were synthesized through an impregnation method, and used for fructose dehydration. With the same Nafion loading, the activity of catalysts with 3-D structure, that is SBA-16 and MCF, was better than that of 1-D structure (SBA-15). The strong acid strength, super large pore size and open framework of Nafion/MCF, which enabled Nafion to have a well dispersion in the mesopores in the form of nanoparticles, made it superior to other catalysts. An 89.3% HMF yield with a high selectivity of 95.0 was obtained in DMSO at 90℃ for 2 h. The interactions between the reactant and the solid catalyst, such as electrostatic effects and hydrogen bonds from the polar silanol-rich surface of the MCF, were found to facilitate the dehydration. Based on which a possible mechanism for fructose dehydration to HMF over Nafion-modified MCF solid acid was proposed. Moreover, the recyclability of the Nafion/MCF catalyst and the reaction conditions were systematically studied.(2) Nafion-resin-modified mesoporous silica catalysts were also applied in isobutane/butene alkylation. Better butene conversion was received when Nafion/SBA-16 was used, while Nafion/MCF possessed higher selectivity for C8 products and stability. By changing the active component into small molecule-sized TfOH, both the initial activity and the stability had been significantly improved, which might be due to the better dispersion and availability of active sites as well as the clearer channels for mass transfer. In addition, some primary work has been done on carbon-based FDU-14 and periodic mesoporous organosilicas (PMOs) as alternative supports.(3) To develop clean and efficient catalytic system, triazaheterocyclic compounds with covalent bonded chlorine, hexachlorocyclotriphosphazene (HCCP) and cyanuric chloride (CNC), were found for the first time to have excellent catalytic performance on dehydration of fructose into HMF. And a serial of triazine analogues had also shown their activities in this reaction. High HMF yield was received by HCCP and CNC, which was better than the traditional acid catalysts (HCl and H2SO4) under the same reaction conditions. The high efficiency should be attributed to the active substituents with electron-withdrawing ability, which could have strong interactions with fructose through hydrogen bonds, and to the electropositive center (phosphorous or carbon atom) on the body ring structure. Moreover, O-triphosphazene compounds were considered as the important intermediates during the process, based on which a possible mechanism of dehydration of fructose into HMF was proposed.(4) Triazaheterocyclic compounds, as homogeneous catalysts, could not be easily recycled and reused, thus their mobilization became another part of this thesis. HCCP was widely used as flame retardant and functional modifier in poly-material production. In this work, a serial of phosphazene based poly-nanoparticles through copolymerization of HCCP with 4,4’-sulfonyldiphenol (BPS),4,4’-(hexafluoroisopropylidene) diphenol (BPAF) and 4,4’-(diaminodiphenyl ether) (ODA), respectively. Highly conversion of fructose to HMF was achieved by these materials. For example, HMF was produced with 97.2% yield in 3 wt% fructose solution and 85.9% yield in 30 wt% fructose solution at 90℃ for 0.5 h. Moreover, it was substantially verified that the as-prepared polyphosphazene nanoparticle catalyst bore the following outstanding properties:a) high activity, selectivity, recyclability and stability; b) unique electron-withdrawing polymer backbone activating the P-Cl active sites for a better catalytic performance; c) being environment-friendly without the use of strong proton acid and any metal. The concept of structure-enhanced catalyst opened a new pathway for designing highly active heterogeneous catalytic systems. |
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