Design Of Organosilica Nanotubes Hybrid Catalysts Based On Organosulfonic Acid And Their Application In Biodiesel Production

Over the recent years, the researcher focused in Green Chemistry tends to explore andinvestigate eco-friendly and commercially visble catalyst systems. Sulfonic acids groupsfunctionalized silica materials which possess high Br nsted acid strength are applied widely.However, it often suffer from serious mass-transport limitation and severe deactivation whencatalyzes biomass conversion. Therefore, a series of arenesulfonic acids (Ar-SO3H)functionalized ethane-or benzene-bridged organosilica nanotubes were demonstrated for thefirst time. Their acid catalytic performances towards biodiesel production from esterificationof palmitic acid and transesterification of yellow horn (or Xanthoceras sorbifolia Bunge) seedoil with methanol under refluxing temperature (65oC) and atmospheric pressure wereinvestigated.1. A series of arenesulfonic acids (Ar-SO3H) functionalized ethane-bridged organosilicananotubes (Si(Et)Si-Ar-SO3H NTs) were developed by preparation process including theco-hydrolysis and-condensation of ethane-bridged organosilica with2-(4-chlorosulfonylphenyl)ethyl trimethoxysilane (CSPTMS) combined with hydrothermaltreatment with the aid of triblock copolymer surfactant. The structure, morphology and textualproperties of the materials were well characterized by solid-state NMR measurements,transmission electron microscopy, and nitrogen physisorption measurement. Additionally,acid-base titration and an ICP-OES method were employed to evaluate the acid property ofthe hybrid catalysts. The influence of different sulfonic acid group loading on catalyticperformance of catalylsts was evaluated by esterification of palmitic acid. As sulfonic acidgroup loading of10mol%, morphology and catalytic activity of the hybrid catalysts are better.We found that10mol%is the optimum loading, and a various of sulfonic acid-basedcatalysts with sulfonic acid group loading of10mol%(Si(Et)Si-Pr-SO3H NTs andSBA-15-SO3H-10) was prepared. Difference of catalytic performances ofSi(Et)Si-Ar-SO3H10NTs, Si(Et)Si-Pr-SO3H NTs10, SBA-15-Ar-SO3H10andAmberlyst-15were tested by esterification of palmitic acid and transesterification of yellowhorn seed oil, we found that Si(Et)Si-Ar-SO3H-10NTs exhibits the highest catalytic activityamong all tested catalysts. For the Si(Et)Si-Ar-SO3H10NTs NTs-catalyzed palmitic acidesterification reaction, the yield of MP reaches99.9%over period of3h. For theSi(Et)Si-Ar-SO3H10NTs-catalyzed yellow horn seed oil transesterification reaction, theyields of MP, MS, MO and ML reaches60.6,65.5,64.3and60.2%, respectively, after thereaction proceeded for24h; The excellent catalytic activity of as-prepared Si(Et)Si-Ar-SO3H10NTs is explained in terms of high Br nsted acid strength, excellenttextual property and better hydrophobicity.2. Arenesulfonic acids functionalized benzene-bridged organosilica nanotubes(Si(Ph)Si-Ar-SO3H10NTs) were developed by using one-step co-condensation technique inthe presence of triblock copolymer surfactant (P123).We use2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS) as arenesulfonic acids group precursor and benzene-bridgedorganosilica as silica precursor in the preparation process. The morphology porosity,structure and compositional properties of the materials were well characterized by TEM,nitrogen physisorption measurement and solid-state NMR. It is concluded that arenesulfonicacids group with benzene-bridged organosilica combined by covalent bonds. Additionally,acid-base titration and an ICP-OES were employed to evaluate the acid capacity of the hybridcatalysts. The catalytic activity of the hybrid catalysts was evaluated by esterification ofpalmitic acid and transesterification of yellow horn seed oil. The experimental resultsindicated that Si(Ph)Si-Ar-SO3H-10NTs exhibits the highest catalytic activity. It can be seenthat the tested catalysts follow the activity order Si(Ph)Si-Ar-SO3H10NTs Si(Et)Si-Ar-SO3H10NTs P123free Si(Ph)Si-Ar-SO3H10Si(Et)Si-Pr-SO3H10NTs SBA-15-Ar-SO3H10Amberlyst-15. It is dut to the fact that Si(Ph)Si-Ar-SO3H10NTsexhibits more hydrophobic property and better textural property than Si(Et)Si-Ar-SO3H10NTs. We also studied the formation mechanism of organosilica nanotubes. The excellentcatalytic activity of Si(Ph)Si-Ar-SO3H10NTs in esterification and transesterificationremained unchanged almost after it has been reused for three times. The recyclableexperiment demonstrates the sulfonic acid groups are strongly bonded to the silica/carbonframework and remain available as acid sites. The prepared hybrid catalysts therefore havepromising potential for working as the efficient and stable solid acid catalystsin production ofbiodiesel.