| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 102 === The global warming has gained increased concerns and the technologies of international energy trends have been changed. It is estimated that fossil energy supplied will be still relied until 2030. Therefore, it is an important for bioenergy to guarantee environmental sustainability. Current liquid biofuel production processes rely on first-generation conversion pathways and comprise two distinct products: bioethanol and biodiesel. World policies have setted some targets on biofuel demand and blending quotas. Futhermore, they also have aided its development by establishing support mechanisms. In the present work, the objectives were to synthesize complete solid acidic catalysts of PDVB-SO3H and PDVB−SO3H−SO2CF3 with different solvents in optimal conditions, reaction mechanisms and efficiencies of esterification/transesterification, and the enhacement of biodiesel production. In addition, several analytic techniques such as XRD, TGA, FE-SEM/EDS, HR-TEM, N2 adsorption, GC-MS, FTIR, ESCA, Contact angle meter, Raman, NMR and XAS (XANES/EXAFS) were also conducted.
Experimentally, the FE-SEM micrographs of the solid acid catalysts synthesized with acetonitrile showed that the resulting products were spherical structures with smooth surface. Since sulfonate groups copolymerized with the S=O double bonds on PDVB surfaces, the particle sizes around 1-2 μm of PDVB increased slightly for the solid acid catalysts. The particles size increased when sulfonate group copolymerized with the double bonds on PDVB surface. Increasing the amount of sulfonate groups, the surfaces of PDVB particles may cover with sulfonate groups and make the resin-like structure formed instead. Solid acid catalysts synthesized with ethyl acetate may have unpolished and rough surfaces of resin-like structures. The TGA curves show two-step weight losses at 240−380 and 470−590℃ respectively, which are assigned to decomposition of sulfonic or trifluoromethanesulfonic groups and to destroy the polymer networks, respectively.
In order to investigate the effects of －SO2CF3 groups on PDVB polymer frameworks, the BET surface area (N2 isotherms) and the corresponding pore size distributions of PDVB-x-SO3H synthesized with acetonitrile and ethyl acetate with different molar ratios of sodium p-styrene sulfonate to DVB were performed. It can be seen that all the pore size distributions of the catalysts are typical isotherms of type-IV, having a steep increase at a relative pressure ranged of 0.6 &;lt; P/P0 &;lt; 0.9, indicating the presence of mesoporosity. It should be noted that an increase in the content of sodium p-styrene sulfonate, the BET surface areas and pore volumes of the catalysts tend to decrease.
FT-IR spectra of PDVB-x-MeCN, PDVB-x-EAC and PDVB-SO3H-SO2CF3 samples at 1,010, 1,035, 1,125, and 1,220 cm-1 respectively, the band around 1,035 cm-1 is notably associated with the presence of a C－S bond on the benzene rings. The specific bands around 1,010, 1,125, and 1,220 cm-1 are associated with the asymmetric and symmetric stretching signals of the O=S=O bonds of a sulfonic group. Moreover, beside the signal of sulfonic groups, an unique peak assigned to C–F (1,289 cm−1) bond was also found on the surface of PDVB-SO3H-SO2CF3 catalysts. The NMR resonance peaks at 113.9 and at 141.4 ppm are attributed to the carbon atoms of =CH2 and C–SO3H, respectively. The aromatic carbons in the ortho- or meta-position of the C–SO2CF3 group are lumped together in a peak centered at 142.8 ppm,
Based on the XPS measurements of solid acid catalysts which exhibit the obvious signals of C, S, O, and F elements, the S 2p and S 2s peaks at 169.1 and 233 eV are assigned to S−O and S=O bonds, respectively. The C 1s peaks around 284.8 and 286.1 eV are associated with C−C and C−S bonds. The F 1s peaks around 690.8 eV is associated with C−F bond confirming the sulfonic and trifluoromethanesulfonic groups functionalized on the polymer network, in good agreement with the results obtained from FT-IR spectra.
Based on the measured results of contact angle analyzer for water with PDVB-x-MeCN, PDVB-x-EAC, and PDVB-SO3H-SO2CF3, all the samples exhibit the excellent hydrophobicity clearly. The superior hydrophobic active site network may be favorable to increase the exposition degree of active sites for the organic reactants in the processes of various catalytic reactions. Catalytic tests show that PDVB-0.5-MeCN and PDVB-SO3H-SO2CF3 exhibit excellent catalytic activities in biomass esterification to biodiesel. The excellent catalytic activity and good recyclability of this work result from their characteristics such as large surface area, strong acid strength, adjustable hydrophobic–oleophilic and stable network which are important for their applications on biodiesel production industries.
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