Xiaoxiang Han

Syntheses of novel halogen-free Brønsted–Lewis acidic ionic liquid catalysts and their applications for synthesis of methyl caprylate

A series of benign halogen-free ionic liquid (IL) catalysts were synthesized by combining the Bronsted acidic ionic liquid [HSO3-pmim]+HSO4− with ZnO in different composition ratios. The IL catalysts, which possess both Bronsted and Lewis acidities, were employed as acidic catalysts for the esterification of n-caprylic acid to methyl caprylate. The [HSO3-pmim]+(1/2Zn2+)SO42−, prepared by cooperating equimolar amounts of Bronsted and Lewis acid sites, was found to exhibit an optimal catalytic performance and excellent durability. This is attributed to a synergy of Bronsted and Lewis acidities manifested by the catalyst. The response surface methodology (RSM) based on the Box–Behnken design (BBD) was utilized to explore the effects of different experimental variables (viz. catalyst amount, methanol to caprylic acid molar ratio, temperature, and reaction time) on the esterification reaction. Analysis of variance (ANOVA) was also employed to study the interactions between variables and their effects on the catalytic process. Accordingly, the deduced optimal reaction conditions led to a high methyl caprylate yield of 95.4%, in good agreement with experimental results and those predicted by the BBD model. Moreover, a kinetic study performed under optimal reaction conditions revealed an apparent reaction order of 1.70 and an active energy of 33.66 kJ mol−1.

Highly nitrogen-doped mesoscopic carbons as efficient metal-free electrocatalysts for oxygen reduction reactions

A facile method was developed for the synthesis of metal-free, highly N-doped (>7 wt%) mesoscopic carbons (NMCs), which were fabricated by first preparing carbon–silicate (C–Si) composites by co-condensation method using a melamine-formaldehyde resin oligomer as the primary nitrogen and carbon source, and P123 triblock copolymer surfactant and sodium silicate as the soft and hard template, respectively, under microwave irradiation conditions, followed by carbonization and silica-template removal. The NMCs were found to exhibit superior electrocatalytic activity, long-term stability, and excellent tolerance over methanol crossover effect. Such NMCs derived from organic–inorganic hybrids assisted by microwave heating not only possess high surface areas and active quaternary and pyridinic-N species that are favourable for ORR, as verified by DFT calculations, but also render large-scale production and practical applications as cost-effective electrode materials.

Transesterification of soybean oil to biodiesel by tin-based Brønsted-Lewis acidic ionic liquid catalysts

A series of Brønsted-Lewis acidic ionic liquid (BLAIL) catalysts consisting of sulfonated ionic liquid [SO3H-pmim]Cl and Sn(II) chloride have been synthesized and exploited for catalytic transesterification of soybean oil with methanol to biodiesel. The structural and chemical properties of these [SO3H-pmim]Cl-xSnCl2 (x=0-0.8) catalysts were characterized by different analytical and spectroscopic techniques, such as FT-IR, TGA, and NMR. In particular, their acid properties were studied by solid-state 31P NMR using trimethylphosphine oxide as the probe molecule. The BLAIL catalysts were found highly efficient for transesterification reaction due to the introduction of Lewis acidity by SnCl2 in the initially Brønsted acidic [SO3H-pmim]Cl catalyst. The effects of three independent process variables on biodiesel yield were optimized by response surface methodology (RSM). Consequently, an excellent biodiesel yield of 98.6% was achieved under optimized reaction conditions over the BLAIL catalyst with SnCl2 loading (x) of 0.7.

Production of biodiesel catalyzed by Candida rugosa lipase at interface of w/o microemulsion system

The synthesis between palmitic acid and methanol was carried out in a w/o reverse microemulsion prepared from the mixture of dodecylbenzenesulfonic acid (DBSA)/isooctane/water. Box-Behnken design was adopted to evaluate the effect of significant factors on the methyl palmitate yield and response surface methodology (RSM), which was employed to optimize the process parameters in the esterification. The conditions that showed optimal results for methyl palmitate preparation were: 3.33 w0 ([H2O]/[surfactant]), 4.2 h reaction time, 5:1 methanol/acid molar ratio, and 130 mg g-1 lipase ([lipase]/[acid]) concentration. The following verification experiment obtained a result of 97% in almost total agreement with the expected value (98%). The kinetic constants of the model were determined by experiments at 40 °C with initial concentrations of 0.025-0.25 mol L-1 palmitic acid and 0.025-0.3 mol L-1 methanol in the microemulsion system. The kinetic studies showed that the reaction obeyed the Ping-Pong bi-bi mechanism with inhibition by methanol.

Heterogeneous amino acid-based tungstophosphoric acids as efficient and recyclable catalysts for selective oxidation of benzyl alcohol

A series of organic-inorganic composite catalysts, prepared by modifying tungstophosphoric acid (TPA; H3PW12O40) with different amino acids such as phenylalanine (Phe), alanine (Ala), and glycine (Gly) were synthesized. The physicochemical and acidic properties of these (MH)xH3−xPW12O40 (M=Phe, Ala, and Gly; x=1–3) composite materials were characterized by a variety of different analytical and spectroscopic techniques, namely TGA, XRD, FT-IR, XPS, and NMR, and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H2O2). Among them, the [PheH]H2PW12O40 catalyst exhibited the best oxidative activity with an excellent BzOH conversion of 99.0% and a desirable benzaldehyde (BzH) selectivity of 99.6%. Further kinetic studies and model analysis by response surface methodology (RSM) revealed that the oxidation of BzOH with H2O2 follows a second-order reaction with an activation energy of 56.7 kJ·mol−1 under optimized experimental variables: BzOH/H2O2 molar ratio=1 : 1.5 mol/mol, amount of catalyst=6.1 wt%, reaction time (x3)=3.8 h, and amount of water (x4)=30.2 mL.

Ionic Liquid–Silicotungstic Acid Composites as Efficient and Recyclable Catalysts for the Selective Esterification of Glycerol with Lauric Acid to Monolaurin

The synthesis of glycerol monolaurate (GML) by the esterification of glycerol (GL) with lauric acid (LA) over a series of propyl sulfonic acid‐functionalized ionic liquids (SAFILs)‐modified silicotungstic acid (STA; H4SiW12O40) composite catalysts has been investigated. The synthesized organic–inorganic hybrid catalysts were characterized by different physicochemical techniques. In particular, their acidic properties were studied by solid‐state 31P magic angle spinning (MAS) NMR spectroscopy by using adsorbed trimethylphosphine oxide (TMPO) as a probe. The effects of key reaction parameters, such as glycerol/lauric acid molar ratio, amount of catalyst, reaction time, and reaction temperature on LA conversion and GML product yield were elucidated and optimized with response surface methodology (RSM). The N,N‐dimethyl(benzyl)ammonium propyl sulfobetaine (DMBPS)‐modified STA [DMBPSH]H3SiW12O40 exhibited the optimal catalytic activity and was exploited for process optimization. A highest GML yield of 79.1 % was achieved with the optimized reaction conditions. The high catalytic activity of these hybrid catalysts were attributed to strong acidity, low transport resistance, and their “pseudoliquid” characteristics. A kinetic study was made based on a second‐order irreversible model of the esterification reaction, which resulted in an activation energy of 39.49 kJ mol−1 for [DMBPSH]H3SiW12O40 under optimized reaction conditions.

Optimization of process variables in the synthesis of butyl butyrate using amino acid-functionalized heteropolyacids as catalysts

Abstract Response surface methodology was successfully applied to optimize esterification of butanol with butyric acids over amino acid-functionalized heteropolyacids, namely, [GlyH]xH3-xPW12O40 (x=1.0–3.0). A series of catalysts were prepared by incorporating tungstophosphoric acid (TPA) with varied amounts of glycine (Gly). The [GlyH]1.0H2.0PW12O40 catalyst was found to exhibit the best activity with an optimal butyl butyrate yield of 97.9%, which was in excellent agreement with the predicted value by the Box-Behnken design (BBD) model. These superior esterification activities observed for the organic TPA salt catalysts might be due to their highly acidic nature, weak molecular transport resistance, and “pseudoliquid” catalysis modes. Furthermore, the catalytic activity of [GlyH]1.0H2.0PW12O40 catalyst was observed to have no appreciable change in the conversion after five consecutive runs. A kinetic study for the esterification was also performed under optimal reaction conditions. The results revealed that the reaction followed second-order kinetics, and the activation energy was found to be 81.90 kJ/mol.

Optimization of Process Variables in the Synthesis of Isoamyl Isovalerate Using Sulfonated Organic Heteropolyacid Salts as Catalysts

Based on single factor experiments, a three level, four variable central composite designs were carried out to establish a quadratic regression model for the catalytic synthesis of isoamyl isovalerate over sulfonated organic heteropolyacid salts as a function of molar ratio of alcohol to acid, reaction time, the amount of water-carrying agent and the amount of catalyst. The optimum conditions were obtained as follows: n (isoamyl alcohol): n (isovaleric acid) = 1.1:1, amount of catalyst was 6.4% of acid, reaction time 2 h and water-carrying agent 10 mL. Under these conditions, the yield of isoamyl isovalerate reached 97.5%. The ionic liquid could be reused six times without noticeable drop in activity. Under optimum conditions, catalysts showed a superior catalytic efficiency and reusability due to better superacidity, lower molecular transport resistance and self-separation characteristics.

Optimized microemulsion production of biodiesel over lipase-catalyzed transesterification of soybean oil by response surface methodology

Abstract Production of biodiesel in water/oil (w/o) microemulsion system through a lipase-catalyzed (lipase from porcine pancreas) methanolysis of soybean oil was investigated. The independent factors were researched and response surface methodology (RSM) based on the Box-Behnken design was used to optimize the significant reaction variables, including w0 (defined as the molar ratio of water to surfactant), lipase concentration, reaction time and substrate molar ratio. Results indicated that the optimal conditions for biodiesel preparation were: w0 3.6, lipase concentration 4.3% (based on oil weight, g), reaction time 17 h and molar ratio (methanol/oil) 10.5. The actual fatty acid methyl ester yield (96.8%) coincided with the optimum predicted value (97.5%) under the optimal conditions. Fatty acid methyl ester synthesized in microemulsions directly which may provided a potential way to produce biodiesel microemulsion.