| Along with the gradual fossil resources being exhausted, biomass is regarded asfeedstock to produce high value-added fine chemicals, which is the most abundant renewableresource on the earth. Such technology named as biorefinery is the necessary rout to realizesustainable development of chemical industry in the future. And the alkyl glucosidesproducted from biomass as raw material possess much more excellent surfactant propertiesthan any other kind surfactant, especially in the terms of ecological security. Therefore, thesynthesis of alkyl glucoside directly from biomass will be of promising application values inits industry.Our work is aimed at study the glycosidation of glucose or starch into some alkylglucosides, including methyl-, ethyl-, butyl-, octyl-and dodecyl-glucosides, in the presence ofa kind of Nano-magnetic solid superacid noted as SO42/ZrO2-TiO2-Fe3O4, which is based ona magnetic core of Fe3O4doped with TiO2. And the according contents are shown as follows:(1) Firstly, Nano-magnetic solid superacids were prepared by introducing magneticsubstrates by chemical co-precipitation method, which were charactered using various kind ofmethods including FT-IR, XRD, TG, BET, NH3-TPD, SEM, TEM and VSM. The calcinationtemperature has great influence on acidity and aicd strength of these solid acids. With theincrease of the calcination temperature, the specific surface area resulted is quickly decreasedto generate Br nsted acid sites from Lewis acid sites. Moreover, the formation of sulfate ion(SO42-) bonded to the solid acid surface is chelating double ligand. The solid acid calcined at550oC is proved to be the strongest one among the solid acids synthesized in this work, whichalso presents the superparamagnetic property. When the calcination temperature is enhancedover700oC, the aicd strength of the solid acid is reduced dramatically. It may lead to destroythe binding of sulfate species with solid surface of catalysts, and this bonding is usuallyrelated with the superacid property of the solid acid.(2) Next, the catalytic activity has been investigated in the glycosidation of glucose innear-critical methanol. The yield of methyl glucoside could achieve84.6%after2h catalyzedby SZT-550solid superacid at140oC, and the catalyst loading is50wt%. Compared withother acids, such as HCl, C-SO3H, H3PW12O40and SO42-/ZrO2, solid superacid SZT-550hasshown more excellent catalytic activity and stability in the glycosidation reaction. Due to theintroduction of Fe3O4nanoparticles, SZT-550solid superacid was endowed withsuperparamagnetism, thus it could be easily separeted from the reaction system by a simplemagnetic field in as high as97.5%. Moreover, the activity of solid superacid could beregenerated completely after recalcinated.(3) In order to study the catalytic activity in the glycosidation of starchs in near-criticalmethanol, the experiments were carried out under the conditions shown as follows: solid-liquid ratio was0.05g/mL, catalyst amount was50wt%, the temperature was150oCand the reaction time was2.5h, the yield of methyl glucoside reached up to95.2%. It isanticipated that the solid superacid has a good prospect in the synthesis of alkyl glucoside.Reuse of the SZT solid superacid with various Zr/Ti molar ratios calcined at550oC for theconversion of starch to methyl glucoside. The results show that the solid acid after thereasonably combination of ZrO2and TiO2may effectively alleviate the deactivation rate of theSZT solid acid.(4) Finally, the efficient conversion of glucose into ethyl-, butyl-, octyl-and dodecylglucoside via SZT-550solid superacid under similiar reaction conditions, whose yields were74.2%,68.9%,84.7%and76.5%, respectively, after purification through silica gel columnchromatography. And these reactions were resulted in excellent catalytic activity andselectivity. The analysis of ESI-MS shows that the products are almost alkyl monoglycoside.The alkyl glucosides obtained above were detected in regard to their surface properties, suchas surface tension, emulsification and foaming power. It was found that n-octyl glucoside andn-dodecyl glucosides had good emulsifying and foaming properties.In a word, the solid superacid SZT-550is found as an effective catalyst to promote thetransformation of glucose and starch in the hot-compressed alcohol phase, which may providea new method for the green production of alkyl glucosides. |
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