Influence of dehydrating agents on the oxidative carbonylation of methanol for dimethyl carbonate synthesis over a Cu/Y-zeolite catalyst

The influence of the dehydration by metal oxides on the synthesis of dimethyl carbonate(DMC) via oxidative carbonylation of methanol was studied. A Cu/Y-zeolite catalyst was prepared by the ion exchange method from CuCl_2·2 H_2O and the commercial NH_4-form of the Y type zeolite. The catalyst was characterized by X-ray fluorescence(XRF), N_2 adsorption(BET method), X-ray diffraction(XRD), and temperature-programmed desorption of ammonia(NH_3-TPD) to evaluate its Cu and Cl content, surface area, structure, and acidity. Reaction tests were carried out using an autoclave(batch reactor) for 18 h at 403 K and 5.5 MPa(2CH_3OH + 1/2O_2+CO?(CH_3O)_2CO + H_2O). The influence of various dehydrating agents(ZnO, MgO, and CaO) was examined with the aim of increasing the methanol conversion(X_(MeOH), MeOH conversion). The MeOH conversion increased upon addition of metal oxides in the order CaO MgO ZnO, with the DMC selectivity(SDMC) following the order MgO CaO ZnO. The catalysts and dehydrating agents were characterized before and after the oxidative carbonylation of methanol by thermogravimetric and differential thermogravimetric(TG/DTG), and XRD to confirm that the dehydration reaction occurred via the metal oxide(MO + H_2O → M(OH)_2). The MeOH conversion increased from 8.7% to 14.6% and DMC selectivity increased from 39.0% to 53.1%, when using the dehydrating agent CaO.     

Nanoplatelet reinforcement of cavity cell walls in polymer foams using carbon dioxide supercritical fluid

Reinforcing the cavity cell walls of polymer foams using nanoparticles can offer a new era for the property‐structure‐processing field in the development of functionalized ultra‐light components and devices manufactured from foam. When the nanoparticles are exfoliated in polymers, the viscosity substantially increases and thus mixing or foaming usually becomes almost impossible. We use CO₂ supercritical fluid (CO₂ SCF) for the mixing and foaming of poly(ethylene‐vinyl acetate) copolymer (EVA) with montmorillonite (MMT) nanoplatelets. The in situ evaporation of CO₂ induces robust cavity cells of the EVA/MMT nanocomposite foam in a stable form of spherical shapes, which are seldom achieved by other methods. As the bubble grows and becomes stabilized in CO₂ SCF, the exfoliated MMT nanoparticles are aligned at the cell walls by the Gibbs adsorption principle to minimize the surface energy at the gas–liquid interface and increase the rupture strength of the cavity walls. It is demonstrated that the developed methodology can be successfully used for foaming EVA containing high vinyl acetate (VA) content (>40%). Since EVA is too soft to construct cell walls of foam using conventional methods, the applicability of the developed methodology is extensively broadened for superior adhesion and compatibility with other materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46615.     

Reduced damage to carbon nanotubes during ultrasound-assisted dispersion as a result of supercritical-fluid treatment

A pre-treatment method of carbon nanotubes for ultrasound-assisted dispersion in a solution is reported. Compared to untreated nanotubes, supercritical-fluid (SCF)-treated carbon nanotubes were easily dispersed in an aqueous surfactant solution by using ultrasonication. The nanotubes are found to be less damaged and less shortened, which was confirmed by Raman spectroscopy and dynamic light scattering, respectively. Supercritical ethane was more effective than supercritical CO₂ in treating the carbon nanotubes.     

Correlation of low frequency noise characteristics with the interfacial charge exchange reaction at graphene devices

Graphene based low noise amplifier has been studied actively because the noise characteristics of graphene devices are known to be superior to those of silicon devices. However, 1/f noise characteristics of graphene grown by chemical vapor deposition (CVD) may increase by an order of magnitude when measured before the charge exchange reaction at the interface of the graphene and substrate is saturated. Based on the close correlation between the level of low frequency noise signal and fast charge exchange reaction (in milliseconds), the conductivity fluctuation of graphene caused by the interfacial charge exchange reaction may be the source of the increased low frequency noise. This result suggests that the current assessment of noise characteristics is too optimistic for graphene and that the defect density of CVD graphene needs to be further reduced to minimize the charge exchange reaction.     

Luminescence and structure of Eu2+-doped Ba2CaMg2Si6O17

Eu²⁺-activated Ba₂CaMg₂Si₆O₁₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction measurement. The photoluminescence excitation and emission spectra were investigated. The phosphor presents blue-emitting luminescence. The crystallographic sites of Eu²⁺ ions in Ba₂CaMg₂Si₆O₁₇ host were discussed on the base of luminescence properties and the crystal structure. The lightly Eu²⁺-doped sample shows one luminescence center for the Eu²⁺ ions on Ba²⁺ sites, while there are two luminescence centers for the Eu²⁺ ions on both the Ba and Ca sites in heavily Eu²⁺-doped sample. The dependence of luminescence intensity on temperatures and the activation energy (ΔE) for the thermal quenching were reported. The phosphor shows an excellent thermal stability on temperature quenching because of the special layered structure of Ba²⁺ ions in the interlayer between SiO₄ layers.     

Liquid-phase degradation of HDPE over alkali-treated natural zeolite catalysts

Catalytic performance of alkali-treated natural zeolites was studied in the liquid-phase catalytic degradation of HDPE. Alkali treatment of natural zeolite with a moderate NaOH solution brought about the formation of mesopores and a decrease in acid site density, resulting in a considerable improvement of its catalytic activity. However, alkali treatment with highly concentrated NaOH solutions induced zeolite structure destruction, resulting in lower activity. HDPE conversion and product selectivity of alkali-treated natural zeolites were discussed in terms of their pore structures, acidities and the diffusion properties of large molecules.     

SO2 oxidation over the V2O5/TiO2 SCR catalyst

The effects of V₂O₅ loading of the V₂O₅/TiO₂ SCR catalyst on SO₂ oxidation activity were examined by infrared spectroscopy (DRIFT) and SO₂ oxidation measurement. Vanadium oxide added to the catalyst was found to be well dispersed over the TiO₂ carrier until covered with monolayer V₂O₅. The rate of SO₂ oxidation increased almost linearly with V₂O₅ loading below the monolayer capacity and attained saturation with further increase. The hydroxyl groups bonded to vanadium atoms, V–OH, might be altered by SO₂ oxidation. Both V=O and V–OH groups are likely involved in the adsorption and desorption of SO₂ and SO₃.     

A dynamic mechanical and thermal analysis of unplasticized and plasticized poly(vinyl alcohol)/methylcellulose blends

The miscibility of poly(vinyl alcohol) (PVA)/methylcellulose (MC) blends was investigated over the entire composition range using the dynamic mechanical analyzer (DMA) and the differential scanning calorimeter (DSC). On the basis of the glass transition temperature, determined by DMA, one could conclude that the blends exhibited some miscibility below 80 wt % of MC and a good miscibility above 80 wt % of MC. The highest depressions of the melting and crystallization temperatures of the blends compared to those of PVA, determined via DSC analysis, were observed for MC contents greater than 80 wt %. The miscibility between PVA and MC can be attributed to the hydrogen bonds formed between the two components. The DMA studies showed that water is a good plasticizer for PVA and poly(ethylene glycol) 400 (PEG 400), a good plasticizer for MC. The inclusion of both water and PEG 400 in the blends revealed a synergistic plasticizing effect, which resulted in an increased miscibility between PVA and MC over a greater range of MC compositions (>60 wt %). The elongations of PVA, MC, and their blends were found to increase with the addition of PEG 400, but the tensile strengths to decrease. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1825–1834, 2001     

Preparation and characterization of LDPE/PVA blend films filled with glycerin‐plasticized polyvinyl alcohol

A series of LDPE/PVA blend films were prepared via a twin‐screw extruder, and their morphology, thermal property, oxygen and water vapor permeation, surface properties, and mechanical properties were investigated as a function of the PVA content. During the extrusion process of the blend films, glycerin improved the compatibility and processing conditions between LDPE and PVA. The melting temperature (T_m), melting enthalpy (ΔH_m), crystallinity (%), and thermal stability of the thermal decomposition temperature (T_5%) of the LDPE/PVA blend films decreased with increasing PVA content. The oxygen permeabilities of the blend films decreased from 24.0 to 11.4 cm³·cm (m²·day·atm)^?1 at 23°C. The WVTR increased from 7.8 to 15.0 g(m² day)^?1 and the water uptake increased from 0.13 to 9.31%, respectively. The mechanical properties of blend films were slightly enhanced up to 2% PVA and then decreased. The physical properties of the blend films strongly varied with the chemical structure and morphology depending on the PVA and glycerin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41985.     

Effects of microwave,UV, and O3 on propylene gas degradation via photocatalytic reaction with CVD TiO2 films

A microwave/UV/ozone/TiO₂ photocatalyst hybrid process system, which is a combination of various propylene gas treatment techniques, is evaluated for use as an advanced, efficient technology for air pollution treatment. TiO₂ photocatalyst balls were prepared using low-pressure metal-organic chemical vapor deposition. The microwave/UV/TiO₂ photocatalyst hybrid process exhibited the higher degradation efficiency than the microwave/UV/alumina ball hybrid system. The degradation efficiency increased almost linearly with increasing ozone dose. The lower the propylene inlet concentration was the higher degradation efficiency. The double bond of propylene is broken by ozone and OH, resulting in production of CH₄ and C₂H₆. These two intermediate products are mineralized into CO₂, H₂O, and CO. C₂H₄ and C₃H₈ may be produced from CH₄, whereas C₂H₆ and C₃H₆ are produced by microwave irradiation.