Chongpin Huang

Efficient dehydration of fructose to 5-hydroxymethylfurfural catalyzed by a recyclable sulfonated organic heteropolyacid salt

The dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) with room temperature ionic liquids (ILs) is a way of producing liquid fuels from renewable resources, but separation of products and IL is energy intensive. In this work, a heteropolyacid salt of an IL-forming cation functionalized with a propanesulfonate group, 1-(3-sulfonicacid)propyl-3-methyl imidazolium phosphotungstate ([MIMPS](3)PW(12)O(40)), was used as a catalyst-rather than as a solvent-in the conversion of fructose to 5-HMF. The maximum yield of 5-HMF was 99.1% at 120°C after 2h using sec-butanol as solvent, and the catalyst was separated from the reaction mixture by a simple process at the end of the reaction and reused six times without loss of activity.

Efficient dehydration of glucose to 5-hydroxymethylfurfural catalyzed by the ionic liquid,1-hydroxyethyl-3-methylimidazolium tetrafluoroborate.

The dehydration of fructose or glucose to 5-hydroxymethylfurfural (5-HMF) using room temperature ionic liquids (ILs) as a solvent is a promising method for producing liquid fuels from renewable resources. The IL, 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ([C(2)OHMIM]BF(4)), was used a catalyst-rather than as a solvent-in the conversion of fructose or glucose to 5-HMF. With glucose, the yield of 5-HMF reached as high as 67.3% after 1h at 180°C in dimethylsulfoxide (DMSO) as solvent. The catalyst was separated from the reaction mixture by distilling solvent and reused six times without loss of activity. Furthermore, a kinetic analysis was carried out to illustrate the formation of 5-HMF, and the values of the activation energy and the pre-exponential factor for the reaction were 55.77 kJ mol(-1) and 1.6 × 10(4)min(-1) respectively.

Microwave-assisted conversion of microcrystalline cellulose to 5-hydroxymethylfurfural catalyzed by ionic liquids

Ionic liquid (IL) has been widely investigated in 5-HMF production from biomass. However, most of studies employed IL as reaction solvent which requires a large amount of IL. In the present study, IL was utilized as catalyst in the conversion of microcrystalline cellulose (MCC) to 5-HMF under microwave irradiation (MI) in N,N-dimethylacetamide (DMAc) containing LiCl. 1,1,3,3-tetramethylguanidine (TMG)-based ILs, including 1,1,3,3-tetramethylguanidine tetrafluoroborate ([TMG][BF4]) and 1,1,3,3-tetramethylguanidine lactate ([TMG]L) which were commonly used in the absorption of SO2 and CO2 from flue gas, were synthesized and applied in the conversion of MCC to 5-HMF for the first time. Of the catalysts employed, [TMG]BF4 showed high catalytic activity in 5-HMF production from MCC. The condition including the ratio of IL to MCC, temperature and time for MCC conversion was optimized using Central Composite Design (CCD) and Response Surface Methodology (RSM). The highest 5-HMF yield of 28.63% was achieved with the optimal condition.

Lactic acid production from glucose over polymer catalysts in aqueous alkaline solution under mild conditions

Methods for the transformation of carbohydrates into tactic acid (LA), which is a versatile platform chemical, have been widely investigated. These methods typically employ harsh reaction conditions, especially when water is used as a solvent. In the present study, a one-pot route that uses polymerizates of imidazole and epichlorohydrin ([IMEP]Cl) as catalysts to convert glucose to LA in water was described. The highest LA yield of 63% (mol%) was achieved with 99% glucose conversion at 100 degrees C in 50 mM NaOH solution. Compared to previous reports, the process has lower reaction temperatures and lower concentration of alkaline. A possible reaction mechanism was proposed that the coordination between the weak Lewis acid centers of the polymer with the electronegative oxygens on the intermediates efficiently facilitated the rate determining step during the reaction. This route allows for facile catalyst recovery and recycling white providing a new strategy for carbohydrate conversion.

One-pot conversion of disaccharide into 5-hydroxymethylfurfural catalyzed by imidazole ionic liquid

Conversion of carbohydrate into 5-hydroxymethylfurfural (5- HMF), a versatile, key renewable platform compound is regarded as an important transformation in biomass-derived carbohydrate chemistry. A variety of ILs, not only acidic but also alkaline ILs, were synthesized and used as catalyst in the production of 5-HMF from disaccharide. Several factors including reaction temperature, IL dosage, solvent and reaction time,were found to influence the yield of 5-HMF from cellobiose. Of the ILs tested, hydroxy-functionalized ionic liquid (IL), 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ([AEMIM]BF4) showed the highest catalytic activity and selectivity. 5-HMF yield of 68.71% from sucrose was obtained after 6 hrs at 160 °C. At the same condition with cellobiose as substrate, 5-HMF yield was 24.73%. In addition, 5-HMF also exhibited good stablity in this reaction system. Moreover, a kinetic analysis was carried out in both acidic and alkaline IL-catalyzed system, suggesting main side reaction in the conversion of fructose catalyzed by acidic and alkaline IL was polymerization of fructose and 5-HMF degradation, respectively.

Highly active tin(IV) phosphate phase transfer catalysts for the production of lactic acid from triose sugars

Lactic acid (LA) is an important intermediate in the fine chemical industry because it is utilized as a building block for the production of biodegradable plastics. In this study, a series of tin phosphate phase transfer catalysts modified with several surfactants have been prepared by a facile one-pot synthesis method and tested for the direct conversion of trioses to LA under hydrothermal conditions. Poly(ethylene glycol) (PEG) was identified as the most promising surfactant, and the product distribution closely depended on the reaction temperature, catalyst loading and substrate concentration. Complete DHA conversion and a good yield of up to 96.1% of LA were obtained at 140 °C after 4 h of reaction time. Pyridine FTIR demonstrated the presence of Bronsted and Lewis acid sites, which play crucial roles in the dehydration of DHA to pyruvaldehyde (PA) and the following isomerization of generated PA to LA. Furthermore, the isomerization of PA to LA was found to be the rate-determining step. A possible reaction mechanism was proposed: 1) the coordination between PEG and the metal ions caused a greater separation of the tin ions from the phosphate anions, making them more potent Lewis acid sites, and 2) the PEG behaved as a phase transfer catalyst during the reaction. This study paves the way for the further design of improved solid acid catalysts for aqueous phase production of LA from carbohydrates.

Siliceous tin phosphates as effective bifunctional catalysts for selective conversion of dihydroxyacetone to lactic acid

Methods to catalytically convert carbohydrates into lactic acid (LA), which is a versatile platform chemical, have been widely investigated. In this study, siliceous tin phosphates were utilized as reusable Bronsted–Lewis acid bifunctional catalysts during the conversion of 1,3-dihydroxyacetone (DHA) to LA under hydrothermal conditions. The product distribution closely depended on the reaction temperature, catalyst loading and substrate concentration. The highest LA yield of 93.8% was achieved with a complete DHA conversion at 140 °C after 5 h. The reaction was facilitated by the vast presence of Bronsted and Lewis acid sites that were confirmed by both pyridine FTIR and NH3-TPD analysis. The incorporation of silica significantly lowered the Sn content and improved the thermal stability of the tin phosphate catalysts. A possible reaction mechanism was proposed in that the Lewis and Bronsted acid sites synergistically catalyzed the conversion of pyruvaldehyde to LA, which was found to be the rate-determining step. The method allows for facile catalyst separation and recycling while expanding the applicability of silica in the field of biomass-to-chemical conversion.

An oniom study of the distribution of skeletal Al atoms and Brønsted acidity in ZSM-23 zeolite

This paper, based on the density functional theory (DFT), mainly studies the distribution of Al in seven nonequivalent T sites as well as the acidity of the corresponding Bronsted acids (B-acids). The distribution of the acid sites in the double-Al models is also investigated. Using ONIOM (B3LYP/6-31g(d,p):AM1) method, substitution energies, proton affinities and frequencies are calculated to characterize the Al distribution and Bronsted acidity. The result shows that T6 is the most destabilized site after substitution, while T7 buried in the framework is the most favorable for Al. Besides, Al4–O4–Si5 and Al2–O1–Si1 are the most readily sites to form B-acids, and the acid strength of Al4–O3–Si3 is the strongest. In the case that there are two B-acid sites on the 10-membered ring, one of the B-acid sites will be most likely to form at the Al4–O4–Si5 site, and the other one forms either at the other Al4–O4–Si5 or at Al2–O1–Si1 site on the opposite side.

Niobium phosphotungstates: excellent solid acid catalysts for the dehydration of fructose to 5-hydroxymethylfurfural under mild conditions

The efficient conversion of carbohydrates to 5-hydroxymethylfurfural (5-HMF) under mild conditions represents a very attractive and promising method of producing important building blocks. In this work, niobium phosphotungstates, with Nb/P molar ratios of 0.6, 1.0, 2.0 and 4.0 (NbPW-06, NbPW-1, NbPW-2, and NbPW-4, respectively) have been prepared by a facile, one-pot, alcohol-mediated thermal process and used for the direct conversion of fructose to 5-HMF. By adding a certain amount of Nb, the surface of the catalyst became enriched in P, and this enrichment was associated with the presence of surface P–OH groups that offered Bronsted acid sites that can activate superficial hydrogen species to facilitate 5-HMF generation. Pyridine-FTIR confirmed the presence of Bronsted and Lewis acid sites, which might play important roles in the dehydration of fructose to 5-HMF. Furthermore, polar aprotic solvents were well-suited for the conversion, and higher yields of 5-HMF were obtained in polar aprotic solvents than in nonpolar solvents. A 5-HMF yield of 96.7% with complete fructose consumption was obtained over NbPW-06 in DMSO at 80 °C after 90 min. In addition, NbPW-06 could be recycled several times without a significant decrease in the catalytic activity. A catalytic mechanism for this reaction was proposed. Moreover, this catalytic system can also be utilized for the dehydration of sucrose and inulin to 5-HMF in satisfactory yields. This study establishes an important platform for the further design of Nb-containing catalysts for the production of 5-HMF from carbohydrates under mild conditions.