Jinxia Zhou

Ag/Al2O3 for glycerol hydrogenolysis to 1,2-propanediol: activity, selectivity and deactivation

A series of γ-Al2O3 supported silver catalysts (Ag/Al2O3) prepared with various Ag loadings and calcination temperatures were used to convert glycerol to 1,2-propanediol. A catalyst with 2 mmol Ag per gram Al2O3 and calcined at 400–500 °C presented the highest activity (glycerol conversion 46 mol%) and selectivity (96 mol%) at 220 °C, glycerol/Ag (molar ratio) = 100/2, 1.5 MPa initial H2 pressure and 10 h. Optimal prereduction, elevated reaction temperature and hydrogen pressure promote the activity, but the selectivity deteriorates at higher reaction temperatures. Excessive water is detrimental to the performance. Catalyst deactivation was observed, mainly due to Ag sintering under reducing environment. The spent catalyst could be calcined to fully recover the activity.

Etherification of glycerol with isobutene on sulfonated graphene: reaction and separation

A sulfonated graphene catalyst (SG) prepared by grafting sulfonic acid-containing aryl radicals onto the two-dimensional surface of graphene was used for the etherification of glycerol with isobutene, and a reaction–extraction process was developed for easy realization of product isolation and catalyst recycling. With its ultra thin two-dimensional open substrate, stable sulfonic acid sites, amphiphilic properties and light texture, SG exhibited excellent catalytic performance in the etherification reaction. At 60–70 °C with 4 wt% catalyst loading and a molar ratio of isobutene/glycerol 4, a nearly complete conversion of glycerol in 7 h and a selectivity of more than 90 mol% to desired multi-butyl glycerol ethers were achieved. Moreover, undesired oligomerization of isobutene was successfully suppressed. When extracted with fresh glycerol, the mixture after reaction was successfully layered to two phases, with a transparent liquid containing no less than 96 wt% di- and tri-butyl glycerol ethers in the top phase as a product and a black mixture consisting of glycerol and SG in the bottom phase which can be used to start a new run with fresh isobutene addition. During six consecutive reaction–extraction cycles the catalyst maintained its robust performance.

An ionic liquid–organics–water ternary biphasic system enhances the 5-hydroxymethylfurfural yield in catalytic conversion of glucose at high concentrations

Increasing the glucose loading in the 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ionic liquid containing a dissolved CrCl3 catalyst system led to excessive formation of humins and a serious decrease in the 5-hydroxymethylfurfural (5-HMF) yield. A biphasic system containing glycol dimethyl ether (GDE) as the extraction phase, and [BMIM]Cl/CrCl3/glucose in combination with a partitioned amount of GDE and an appropriate amount of water as the reaction phase was found to be highly efficient for the reaction; CrCl3 catalyzed the formation of 5-HMF in 64.5 mol% yield from a very high glucose concentration (80 wt% with respect to the ionic liquid) at 108 °C. This 5-HMF yield in the [BMIM]Cl–GDE–H2O ternary biphasic system nearly doubled that obtained in the single [BMIM]Cl/CrCl3/glucose reaction phase. Importantly, the GDE phase contained about 56% of the generated 5-HMF without detectable contamination by the ionic liquid or carbohydrates. GDE served multiple functions: as a hydrogen-bond acceptor, it exhibited excellent extraction performance for 5-HMF; due to its low boiling point and suitable solubility saturation point in the ionic liquid, a sustained GDE bubbling phenomenon in the ionic liquid phase was observed that promoted the rate of inter-phase mass-transfer of 5-HMF in reactions; and GDE mediated the [BMIM]Cl phase to a reduced viscosity. In addition, an appropriate amount of water in the ternary system promoted the extraction efficiency of 5-HMF and also lowered the viscosity of [BMIM]Cl/glucose. The ionic liquid–organics–water ternary biphasic system has been demonstrated for high 5-HMF productivity and separation efficiency.

A biodiesel additive: etherification of 5-hydroxymethylfurfural with isobutene to tert-butoxymethylfurfural

Biodiesel is a sustainable and environmentally compatible diesel fuel substitute that presents certain limitations, particularly low-temperature flow properties, which are attributable to its long fatty chain structure. Branched alkyl derivates such as tertiary butyl ethers are efficient biodiesel additives for improved cold flow behaviour of biodiesel. In this study, tert-butoxymethylfurfural (tBMF) is synthesised as a biodiesel additive through etherification of 5-hydroxymethylfurfural (5-HMF), a non-edible biomass-derived building block, with isobutene (IB) on a series of acid zeolites and liquid acids. The catalytic activity and selectivity of a zeolite catalyst involve not only optimisation of the number and strength of its acidic sites and adsorption properties but also promotion of its internal pore space. Efficient solvent systems did not include extremely weakly polar or strongly polar solvents but included moderately polar solvents, such as glycol dimethyl ether which presents suitable hydrophilic/hydrophobic properties. The HY zeolite with a SiO2/Al2O3 mole ratio of 12 in combination with glycol dimethyl ether solvent exhibited an excellent tBMF selectivity of 94 mol% with 59 mol% 5-HMF conversion after 3 h of reaction at 60 °C. Side reactions of 5-HMF dimerisation and the IB oligomerisation were minimal under mild reaction conditions. The activity of the deactivated catalyst was fully recovered by calcination in air, and a detailed deactivation mechanism was proposed.

Enhancement of mass transfer through bubbling effect during extraction and reaction in biphasic systems containing ionic liquid

Separation of a compound from an ionic liquid through extraction usually results in a low mass transfer rate because of the high viscosity of the ionic liquid and the large density difference between the ionic liquid and organics even under strong stirring. An improved interface mass transfer during extraction or biphasic reaction was realized by creating a bubbling effect in a biphasic system containing an ionic liquid. In a model biphasic system containing 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as the solvent phase and methyl isobutyl ketone (MIBK) as the extraction phase, the bubbling reagents partitioned in the [BMIM]Cl phase, such as methanol, ethanol and acetonitrile, exhibit dynamic equilibrium between the two phases through constant gasification from and dissolution into the [BMIM]Cl phase. Bubbling increases the interface area and dynamically enhances the turbulence of the mixture; both phenomena are beneficial for fast transfer of 5-hydroxymethylfurfural from the ionic liquid phase to the extraction phase. The organic solvents suitable as bubbling reagents were identified, and the key parameters in establishing bubbling biphasic systems were determined.