Study Of Selective Conversion Of Carbohydrates

Catalytic conversion of renewable carbohydrates(cellulose, hemicelluloses, etc.) into high value-added platform chemicals is beneficial to decline the dependence of fossil resource for the development of society, and also to alleviate the serious energy and environmental pollution. It is very significant for promoting the sustainable development of our country, and can afford the very important security in terms of energy, resource, and society.In this dissertation, the selective conversion of carbohydrates into platform chemicals in the subcritical biphasic and monophasic solvents has been investigated intensively in the presence or absence of external acid catalysts. And, based on the distribution of products, the possible reaction process has also been proposed, correspondingly. The detailed works are listed as follows:(1) An acidic ionic liquid-methyl isobutyl ketone(MIBK)/H2 O biphasic system has been designed for the catalytic conversion of carbohydrates and delignification of typical agricultural residues, such as bagasse and others. In the system, the carbohydrates(cellulose and hemicelluloses) can be depolymerized in the acidic aqueous solution, resulting in the release of the lignin, which will be extracted into organic phase as the organosolv lignin, and then achieving selective catalytic conversion and delignification of renewable biomass in a “one-pot” process. Moreover, under the optimal conditions, 85.8% of bagasse could be fractionated into 71.4% biochemicals with 76.3% lignin extraction ratio.(2) Efficient synthesis of butyl levulinate(BL) from cellulose in bio-butanol medium has been investigated in the presence of the acidic ionic liquid catalysts. Results showed that acid strength of catalysts, catalyst dosage, reaction temperature, reaction time, and solvent composition had the significant impact on the conversion of cellulose and the yield of target products. 98.4% of cellulose could be converted into 31.1% of BL accompanying with 33.4%, 20.6% and 23.8% of butyl formate(BF), water soluble products(WSP) and biofuel(Biof), respectively, under the optimum conditions consisting of 0.5 mmol [C4H8SO3Hmim]HSO4 dosage and 20 m L solvent intake at the temperature of 180 oC for 45 min.(3) Dehydration of fructose into 5-hydroxymethylfurfural in the subcritical solvents has been tested in the absence of external catalysts. The effect of reaction temperature and reaction time on fructose conversion and product yield has been investigated intensively. The results showed the yield of 5-hydroxymethylfurfural is much lower than the by-products. The mass spectrometry(MS) analysis illustrated that the by-products are the oligosaccharides, which may be formed through the intermolecular dehydration of fructose. In addition to, by comparing the dehydration performance of fructose in different solvents with in water, it is found that the water is the good reaction medium for dehydration of fructose into 5-hydroxymethylfurfural in the absence of any added catalysts.(4) A catalyst-free biphasic system, viz., MIBK/H2 O, has been constructed to convert fructose-based carbohydrates into 5-hydroxymethylfurfural. In the biphasic system, the dehydration of fructose occurs in the aqueous phase through the autocatalytic process; and then, the formed 5-hydroxymethylfurfural will be extracted and protected by MIBK, giving the 73.6% of product yield at the 96.8% of fructose conversion. The system is also feed-tolerant, and the carbohydrates with fructose unit can be converted efficiently with acceptable product yield. Moreover, a simple and efficient purification strategy for as-prepared product, viz., the Na OH neutralization method, has also been tested, achieving more than 99% of recovery with more than 98% of purity, correspondingly. Hence, this catalyst-free biphasic system combined with the Na OH neutralization method can be considered as a reference for producing 5-hydroxymethylfurfural from fructose-based carbohydrates industrially.The as-constructed biphasic or monophasic sytems in the dissertation can act as a guide for utilization of biomass resource, and can also afford the desired pathway for the production of platform chemicals from original biomass or the industrial grade carbohydrates.