The coupling reaction of propylene and CO2 to form propylene carbonate (PC) was promoted by an ionic liquid (IL) covalently bound to polyethylene glycol (PEG). The supported ionic liquid, which has both acidic and basic components, proved to be an active catalyst for PC synthesis under mild conditions. The effects of different cations and anions, reaction temperature, CO2 pressure, and reaction time were investigated. It was demonstrated that the acid group in the catalyst plays an important role in the reaction. With this system, a high PC yield (95%) was achieved under mild conditions (3.0 MPa, 120°C and 4 h) without a co-solvent. In addition, the catalyst was readily recovered and reused. Based on the experimental results, a plausible mechanism for the catalyst was proposed.
A solvothermal method has been successfully used to prepare nanostructured hydroxyapatite (HA) hollow spheres with average diameters of about 500 nm and shell thicknesses of about 100 nm in a glycerin/water mixed solvent. Transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM) images show that the shells of the HA hollow spheres are actually composed of nanosheets with thicknesses of about 10 nm. By tuning the glycerin/water volume ratio, two other kinds of HA solid spheres with average diameters of about 6 or 20 μm were assembled from nanoflakes. The properties of the different kinds of spheres as drug delivery carriers were evaluated. Ibuprofen (IBU) was chosen as the model drug to load into the HA samples. The nanostructured HA samples showed a slow and sustained release of IBU. The HA hollow spheres exhibited a higher drug loading capacity and more favorable release properties than the HA solid spheres and thus are very promising for controlled drug release applications.
The effect of iridium and iron impregnation of HZSM-5 zeolite on the methanol to propylene reaction (MTP) was investigated. The selectivities of propylene and other hydrocarbons, and the conversion of methanol were compared by performing MTP in a small pilot plant. The results indicate that HZSM-5 zeolite modified by iron and iridium increased propylene selectivity by 6.3% and 8%, respectively. The selectivity of propylene was higher for Ir/H-ZSM-5 than for Fe/H-ZSM-5, where Fe/H-ZSM-5 was more stable than Ir/H-ZSM-5. Analytic techniques, including X-ray diffraction, BET surface area, temperature-programmed desorption of ammonia, and inductively coupled plasma atomic emission spectroscopy, were used to characterize the modified zeolites as well as the parent zeolites.
Cordierite monoliths coated with Pd-Fe/α-Al2O3 catalysts were prepared at various calcination temperatures and characterized by thermogravimetry, temperature-programmed reduction, transmission electron microscopy, diffuse reflectance infrared Fourier transformation spectroscopy and X-ray diffraction. The performance of the catalytic monoliths for the synthesis of dimethyl oxalate (DMO) through a CO coupling reaction was evaluated. Monolithic catalysts with calcination temperatures ranging from 473 K to 673 K exhibited excellent dispersion of Pd, good CO adsorption properties, and excellent performance for the coupling reaction. The optimized monolithic catalyst exhibited a much higher Pd efficiency (denoted as DMO (g)·Pd (g)-1·h-1) (733 h-1) than that of the granular catalyst (60.2 h-1), which can be attributed to its honeycomb structure and the large pore sizes in the α-Al2O3 washcoat which was accompanied with an even distribution of the active component in the coating layer along the monoliths channels.
A sensitive and selective preconcentration method using solid-phase extraction (SPE) disk made from oxidized multiwalled carbon nanotubes (OMWCNTs), has been developed for the determination of aniline derivatives, such as 2-nitroaniline (2-NA), 4-nitroaniline (4-NA), and 2,4-dichloroaniline (2,4-DCA) in water samples. Anilines were extracted onto OMWCNT disk and then determined by high performance liquid chromatography (HPLC) with UV detector. Several parameters on the recovery of the analytes were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 8 using 200 mL of validation solution containing 2 μg of anilines and 10 mL of acetonitrile/ethanol (8/2, v/v) as an eluent. Relative standard deviations for five determinations were 7.5% (2-NA), 6.5% (4-NA) and 3.8% (2,4-DCA) under optimum conditions. The linear range of calibration curves were 0.5 ng·mL-1 to 15 ng·mL-1 for each analyte with good correlation coefficients. The detection limits (3S/N) of 2-NA, 4-NA and 2,4-DCA were 30 pg·mL-1, 31 pg·mL-1 and 26 pg·mL-1, respectively. Our method was successfully applied to the determination of aniline compounds in river water sample with high precision and accuracy.
The dehydration processes of trisodium citrate (Na3C6H5O7) hydrates were investigated using thermogravimetry (TG), differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). It was found that the temperature of dehydration of trisodium citrate dihydrate was at 430.99 K. For trisodium citrate pentahydrate, there is a two-step dehydration process and the endothermal peaks appear at 337.23 K and 433.83 K, respectively. During the first step of dehydration process, the structure of trisodium citrate pentahydrate changed into the structure of trisodium citrate dihydrate. In addition, the kinetics of dehydration for trisoidum citrate hydrates was also investigated using TG data. According to the activation energies of dehydration calculated by Ozawa equation, it was found that the dehydration mechanisms of the two hydrates were different.
Cellulose samples with molecular weights ranging from 8.39 × 104 to 11.00 × 104 g/mol were obtained from wheat straw. The dewaxed wheat straw was pretreated with aqueous hydrochloric acid followed by delignification using an environmentally benign poly(ethyleneglycol)/salt aqueous biphasic system. The yield of cellulose was in the range of 48.9%–55.5% and the cellulose contained 1.2%–3.2% hemicelluloses, and 0.97%–3.47% lignin. All the isolated cellulose samples could be directly dissolved in a 6 wt-% NaOH/4 wt-% urea aqueous solution through a precooling-thawing process to form a homogenous solution. The separation process was investigated and the obtained cellulose and its solution were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray apparatus, and X-ray diffraction. The results revealed that aqueous soluble cellulose can be directly prepared from wheat straw by this method and this study opens a novel pathway to prepare cellulosic materials from agricultural waste.
Inorganic arsenicals, including arsenite (AsIII) and arsenate (AsV), are well-known human carcinogens. Recently, studies have indicated that arsenic triglutathione (As(GS)3) is unstable in an aqueous solution. The present study was designed to evaluate the degradation mechanism of As(GS)3 in an aqueous solution using high-performance liquid chromatography-electrospray ionisation mass spectrometry (HPLC-ESI-MS). Based on the fragments obtained from MS2 and MS3, we identified two new compounds: one was an isomer of glutathione (GSH), and the other was a product from the cleavage of the glutamyl of oxidised glutathione (GSSG). The isomerization of GSH resulted in the loss of its function such as detoxification of many reactive metabolites. The formation of the two new compounds affected the ratio of GSH/GSSG, and thus may affect the antioxidant and detoxification of GSH/GSSG in mammalian cells.
High performance polyvinylidene fluoride (PVDF) flat sheet ultrafiltration (UF) membranes have been prepared by an immersion precipitation phase inversion method using perfluorosulfonic acid (PFSA) as a pore former and as a hydrophilic component of the membranes and polyethylene glycol (
Multiple-effect membrane distillation (MEMD) using a hollow fiber-based air-gap membrane distillation module was experimentally examined for concentrating dilute aqueous hydrochloric acid. The effects of the hot and cold feed-in temperatures, and the feed-in volumetric flow rates on the performance of the MEMD process were studied. The performance was evaluated using the performance ratio (
The objective of this study is to investigate numerically the flow characteristics of falling film on horizontal circular tubes. Numerical simulations are performed using FLUENT for 2D configurations with one and two cylinders. The volume of fluid method is used to track the motion of liquid falling film and the gas-liquid interface. The effect of flow characteristics on heat and transfer coefficient may be remarkable, although it has been neglected in previous studies. The velocity distribution and the film thickness characteristics on the top tube, some special flow characteristics on the bottom tube, intertube flow modes and effect of liquid feeder height on flow characteristics have been studied. Our simulations indicate that 1) the velocity distributions of the upper and lower parts of the tube are not strictly symmetric and non-uniform, 2) the film thickness depends on flow rate and angular distributions, 3) the flow characteristics of the top tube are different from those of the bottom tube, 4) three principal and two intermediate transition modes are distinguished, and 5) the liquid feed height plays an important role on the formation of falling film. The numerical results are in a good agreement with the theoretical values by the Nusselt model and the reported results.
The design of two-stage pusher centrifuges have developed rapidly, but a good understanding of the theory behind their practice is a long-standing problem. To better understand centrifugal filter processes, the computational fluid dynamics (CFD) software program FLUENT has been used to model the three-dimensional geometry and to simulate multiphase flows based on Euler-Euler, moving mesh, dynamic mesh and porous media models. The simulation tangential velocities were a little smaller than those for rigid-body motion. In the stable flow region, the radial velocities were in good agreement with the theoretical data. Additionally, solid concentration distribution were obtained and also showed good agreement with the experimental data. These results show that this simulation method could be an effective tool to optimize the design of the two-stage pusher centrifuge.
Dextran-hyaluronate (Dex-HA) based supermacroporous cryogel scaffolds for soft tissue engineering were prepared by free radical cryo-copolymerization of aqueous solutions containing the dextran methacrylate (Dex-MA) and hyaluronate methacrylate (HA-MA) at various macromonomer concentrations under the freezing condition. It was observed that the suitable total concentration of macromonomers for the preparation of Dex-HA cryogel scaffold with satisfied properties was 5% (w/w) at the HA-MA concentration of 1% (w/v), which was then used to produce the test scaffold. The obtained cryogel scaffold with 5% (w/w) macromonomer solution had high water permeability (5.1 × 10-12 m2) and high porosity (92.4%). The pore diameter examined by scanning electron microscopy (SEM) was in a broad range of 50–135 μm with the mean pore diameter of 91 μm. Furthermore, the cryogel scaffold also had good elastic nature with the elastic modulus of 17.47±1.44 kPa. The culture of 3T3-L1 preadipocyte within the scaffold was investigated and observed by SEM. Cells clustered on the pore walls and grew inside the scaffold indicating the Dex-HA cryogel scaffold could be a promising porous biomaterial for applications in tissue engineering.
A three-stage homogenate extraction was used as a new method for inulin extraction from Jerusalem artichoke tubers. Compared with the results from conventional hot water extraction, the three-stage homogenate extraction gave higher yields and caused less degradation of the inulin. The inulin crude extract was then clarified by a carbonate-precipitation method, during which three variables — the quicklime mass, the reaction temperature and the reaction time were optimized for the main liming process to give the best clarification effect. A Plackett-Burman design, the path of steepest ascent method, a Box-Behnken design and response surface methodology (RSM) were employed in the experimental design. The optimal conditions for the main liming process were determined to be 12.0 g/L, 71.4°C and 8 min. The confirmatory tests proved that the best clarification efficiency (92.74%) was achieved at these conditions and this was approximately equal to the value predicted by the model.
The latest progress and developments in catalysts for the oxidation of cyclohexane are reviewed. Catalytic systems for the oxidation of cyclohexane including metal supported, metal oxides, molecular sieves, metal substituted polyoxometalates, photocatalysts, organocatalysts, Gif systems, metal-organic catalysts and metalloporphyrins are discussed with a particular emphasis on metalloporphyrin catalytic systems. The advantages and disadvantages of these methods are summarized and analyzed. Finally, the development trends in the oxidation technology of cyclohexane are examined.