| Producing furfural from agricultural and forestry waste biomass is an effective way to realize resourceful utilization of hemicellulose. However, furfural industry is one the of trades with serious environmental pollution. End of pipe control and treatment measures have little effect on reducing pollution of furfural industry. Recent furfural manufacturing-process optimization investigations have made progress on improving furfural yield, avoiding the use of super-heated steam and realizing waste recycling, but the challenges associated with producing furfural in an ecofriendly pathway continue to be of great importance for the sustainable growth of furfural industry. The furfural wastewater has the characteristic of high concentration of organism and high acidity, so it’s difficult to treat. Facts proved that neither end of pipe treatment nor process optimization could improve the environmental performance of furfural industry without any change in the main production process. Novel ecofriendly catalytic processes for furfural production are badly needed in order to minimize the carbon footprint.Given this, from the viewpoint of pollution prevention, this paper focused on the development of green production process for furfural production to reduce or eliminate the emission of pollutants from the source. The emission of pollutants was reduced by increasing furfural yield and utilization ratio of raw materials-the most effective, most direct and most economical way to reduce the emission of pollutants; the furfural wastewater which was very difficult to treat was avoided by applying anhydrous reaction medium and avoiding the use of superheated steam; the emission of waste was reduced by increasing the reaction rate with highly effective catalyst and the recycling of the reaction solvent and catalyst. This dissertation mainly contains four sections as follow:1. Three solid acids (H3PW12O40, Amberlyst-5and NKC-9) were used as catalysts for producing furfural from xylose, xylan and lignocellulosic biomass in [BMIM]Cl under microwave irradiation. Amongst these catalysts, H3PW12O40exhibited the best catalytic activity, it performed a furfural yield up to93.7%from xylan at433K for10min. The furfural yields obtained from untreated biomass catalyzed by different solid acids were in the range of11.6-26.8%. Lewis and Br(?)nsted sites were both responsible for catalyzing the dehydration of xylose to produce furfural, and furfural selectivity increased with increasing in the Br(?)nsted to Lewis acid site ratio of the catalysts. Furfural was stable in [BMIM]C1when other organics were absent under heterogeneous catalysts. All the reactions in this reaction system exhibited the heterogeneous nature.[BMIM]C1could be recycled and reused with stable solvent capacity for multiple runs (5x) after furfural was extracted with ethyl acetate.2. To further increase the reaction rate of furfural production, the catalyzed conversion of xylan into furfural in [BMIM]C1was studied by using metal chlorides as catalysts under microwave irradiation. In general, trivalent chlorides showed particularly strong effect on producing furfural under this reaction condition, divalent chloride had a medium effect, and monovalent ones were weakest in this work. The role of metal chloride was supposed to display a different catalytic pathway than H+ion for furfural production, and both Cl-ion and metal cations were all responsible for this reaction. Amongst these catalysts, AlC13·6H2O resulted in the highest furfural yield of84.8%from xylan at443K for10sec. For xylose, a highest furfural yield of82.2%was obtained at433K. The effect of AlC13·6H2O on the conversion efficiency of untreated lignocellulosic biomass was also investigated, the yields of furfural from corncob, grass and pine wood catalyzed by AICl3·6H2O in [BMIM]Cl were in the range of17.1-33.6%. Furfural was stable in [BMIM]Cl in the presence of AlC13·6H2O when other organics were absent.[BMIM]Cl and AlCl3·6H2O could be recycled for four runs with stable catalytic activity.3. To further reduce the ecotoxicity of the reaction solvent, and to increase the viability of the reaction system for industrial applications, the use of deep eutectic solvents (DESs) as reaction solvent with the addition of trivalent metal chloride for furfural production was conducted by conventional heating (oil bath). The effects of types of catalyst, reaction temperature, reaction time and types of reaction system on furfural production were investigated. ChCl-citric acid or ChCl-oxalic acid acted as both reaction medium and Br(?)nsted acid catalyst. Compared with water, ChCl-oxalic acid and ChCl-citric acid had advantage in terms of xylose and xylan conversion into furfural at relatively low temperature (e.g.<373K). Both monophasic route (DES as medium, without organic solvent as extractant) and biphasic route (with methyl isobutyl ketone as extractant for in situ extraction of furfural) were proposed. With ChCl-citric acid, the highest furfural yields obtained from xylose and xylan in monophasic approach were59.3%and54.2%respectively at413K, and these values increased to73.1%and68.6%when applying biphasic system for the reaction. For ChCl-oxalic acid, moderate furfural yields (14-44%) were obtained under very mild conditions (353-373K) in monophasic reaction system in the presence of AICl3·6H2O, and furfural yields obtained in biphasic approach from xylose and xylan were60.4%and55.5%, respectively. Moreover, the two DESs and AlC13·6H2O could be reused with stable catalytic effect for five successive runs in the biphasic systems.4. An efficient and simple one-pot monophasic reaction system with small carbon footprint for converting xylose, xylan and corncob into furfural was developed by using FeCl3·6H2O as catalyst in y-valerolactone (an ideal sustainable solvent derived from lignocelluloses) by conventional heating (oil bath). A surprisingly high furfural yield of79.6%from untreated corncob was achieved at458K for100min. The degradation of furfural was unremarkable in GVL in the absence of other organic compounds. Contrary to what was generally believed, the addition of water, reduced the rate of the reactions, but showed positive effect on preventing the furfural from degradation in γ-valerolactone. Besides, the C6sugars (glucose and cellulose) afforded11.4-24.5%furfural yields when employing this catalytic approach. |
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