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Synthesis, Characterization And Performance Of Solid Acid For The Environmental Friendly Condensation Of Toluene And Formaldehyde

Posted on:2009-03-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:D F JinFull Text:PDF
GTID:1101360245974325Subject:Chemistry
Abstract/Summary:PDF Full Text Request
Liquid acids such as HCl, H2SO4, AlCl3 are used popularly as catalysts in organic synthesis and production of fine chemicals, which causes a series of problems as equipment corrosion, environmental pollution and health hazards. Recently solid acid catalysts have received considerable attention for their lower corrosion, less pollution and ease recycle usage. In this thesis, several solid acid catalysts (heteroploy acids, supported heteroploy acids, zeolite, HPW@USY and SO42-/meso-ZrO2) were prepared and used in condensation between toluene and formaldehyde in order to replace traditional liquid acid catalysts.In the first,H3PW12O40 and H4SiW12)O40 were prepared using microwave assistant method instead of the traditional hydrothermal process that costs long time and high energy. These synthesized catalysts showed higher activity in the condensation reaction between toluene and formaldehyde. It was found that the activity of the heteropoly acids increased with their acidity. The influence of reaction temperature, time and the amount of the phosphotungstic acid were tested in detail, and the best yield of dimethyldiphenylmethane (DMDPMs) reached 81.5% with conversion of HCHO nearly 100%. Then, the possible mechanism of the condensation reaction was proposed as follows: In order to increase the surface area of HPW and decrease its solubility in polar solvents, HPW was supported on different carriers and used in condensation between toluene and formaldehyde. FT-IR, N2-adsorption and XRD characterizations found that both the dispersion of HPW and the acidity of the suppoted HPW depend strongly on the physical properities of the supports and also on the loading amount of HPW. HPW dispersed highly on SiO2 and MCM-41 that possesses a high surface area and large pore diameter. While higher loading amount of HPW would make MCM-41 destroyed. On the surface of the activated carbon, HPW dispersed poorly and bigger HPW particles formed. At the same time, the oxygen-contained groups in the surface of activated carbon would interact with the proton of HPW, which reduced the acid strength of HPW. The activity of the HPW/SiO2 and HPW/MCM-41 were higher than that of pure HPW, and the highest TON of every proton in that of HPW/SiO2 and HPW/MCM-41 reached to 429.1 and 532.2, respectively. However, the maximum TON of every proton in HPW/AC was less than 50.A series of zeolites such as H-X, H-Y, H-beta, H-ZSM-5, H-mordenite and MCM-41 were selected and used in the condensation between toluene and formaldehyde in order to increased the selectivity 4,4'-DMDPM. H-beta zeolite, with a unique pore sized in 0.66 nm and higher proportion of stronger acid site, exhibited the highest activity and stereo-selectivity (86.5%). Characterizations (NH3-TPD-MS and pore structure) disclosed that the catalytic activity of various zeolites depends mainly on its strong acid site and accessibility of the internal pores. Small sized H-beta zeolite was more active due to the enhanced accessibility of its acid site. The best yield of 4,4'-DMDPM reached 71.1% at 140℃. On the basis of calculated molecular sizes of DMDPM isomers and the pore structure parameters of zeolites, the excellent product distribution on zeolite H-beta was illuminated.Under microwave irradiation, HPW was successfully synthesized in situ and encapsulated in the supercage of faujasite type zeolite (USY) in several minutes. XRD show the structure of the zeolitic matrix after encapsulated is retained. But the framework of USY collapsed in the traditional hydrothermal routine. FT-IR and the 31P MAS NMR spectrum found the interaction between phosphorus and aluminum from the zeolitic matrix. As shown by NH3-TPD, the amount of the HPW heteropoly acid increased with the irradiation time. However, the zeolitic matrix would be collapsed for longer irradiated time and formed some room bigger than the supercage that many HPW crystals assembled in to form the cluster. This hybrid solid acid exhibited higher activity and selectivity in the synthesis of 4,4'-DMDPM via toluene and formaldehyde and could be acted as a solid acid catalyst in the aqueous solutions.As the activity of different acids for the condensation between toluene and formaldehyde depended on the proporation of its strong acid site, mesoporous zirconia supported sulfate acid was synthesized via the self-assembly method and characterized via XRD, N2-adsorption and HRTEM. The thermal stability of the prepared mesoporous zirconia supported sulfate acids were checked at different calcination temperature. It was found that the structure of mesoporous zirconia remained under 600℃, but damaged at higher temperature. NH3-TPD found that the catalyst calcined at 500℃has the highest acid amount and this catalyst showed the highest activity in the condensation between toluene and formaldehyde. The conversion of formaldehyde reached 45.7%.
Keywords/Search Tags:Solid acids, Dimethyldiphenylmethane, Toluene, Formaldehyde, Heteropoly acid, Supported phosphotungstic acid, Shape-selective performance, HPW@USY, Mesoporous solid acid materials
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