Selective hydrogenation of styrene oxide to 2-phenyl ethanol over polyurea supported Pd–Cu catalyst in supercritical carbon dioxide

2-Phenyl ethanol (2-PEA) is an important chemical which finds several applications in perfumes, deodorants, soaps and detergents. It is prepared by different polluting and dangerous routes. The current work is concerned with production of 2-PEA by hydrogenation of styrene oxide using polyurea encapsulated catalysts (EnCat) in methanol and supercritical carbon dioxide (scCO₂). Bimetallic Pd–Cu catalyst encapsulated with polyurea, Pd–Cu EnCat, is the best catalyst. The epoxide ring in styrene oxide is selectively hydrogenated to give 2-PEA in scCO₂ without formation of any isomerization or deoxygenated products, which are formed in methanol. A complete conversion of styrene oxide with 100% selectivity to 2-PEA was obtained without addition of any promoter. Effects of various parameters were studied and a bifunctional site Langmuir–Hinshelwood–Hougen–Watson kinetic model was found to be in good agreement with the experimental data. The process is clean and green.     

The reversibility of the adsorption of methane–methyl mercaptan mixtures in nanoporous carbon

The results of extensive molecular dynamics simulations and theoretical considerations of the adsorption of methane–methyl mercaptan mixtures in slit-shaped carbon nanopores are presented. We observe significant mobility of both methane and mercaptan molecules within the pore volume, between pores, and between adsorbed and gas phases for a wide range of temperatures and pressures. Although mercaptans adsorb preferentially relative to methane, the process remains reversible, provided non-oxidizing conditions are maintained. A mercaptan/methane ratio of the order of 200 ppm in the adsorbed phase is sufficient for the gas phase to have a mercaptan concentration above the human threshold for detection. The reversibility of the adsorption process and low concentration of mercaptans makes it unlikely that these would be harmful for adsorbed natural gas storage systems.     

Probing structure–heterogeneous nucleation efficiency relationship of mesoporous particles in polylactic acid microcellular foaming by supercritical carbon dioxide

Heterogeneous nucleating agents that can improve cell morphology of polymer foams have been studied extensively, however, the exact relationship among particle structure, surface modification and nucleating efficiency still remain elusive. Previously, we demonstrated that mesoporous structure benefited nucleating efficiency by comparing solid silica particles and mesoporous particles (MCM-41). Herein, the feasibility of using another type of mesoporous particles, namely, SBA-15 as a nucleating agent for polymer foaming was investigated, but surface modification issue was emphasized. Results reveal that SBA-15 particles show excellent nucleation performance on polylactic acid foaming, and such nucleating effect are dependent on the surface modification. The surface modification using fluorinated silane significantly decreases nucleation energy barrier, and thus shows the highest nucleation efficiency. This work provides a comprehensive insight into structure–nucleating efficiency relationship for mesoporous particles, and highlights the importance of surface modification as a structural factor to optimize the design of effective nucleating agents for polymer foaming.     

Electron paramagnetic resonance of color centers in nanoporous glasses impregnated with copper β-diketonatewith the use of supercritical carbon dioxide

The spectral properties of nanoporous glasses containing Cu²⁺ ions, which are introduced into glass pores in the form of organometallic compound of copper -diketonate dissolved in supercritical CO₂, are investigated for the first time. The analysis of the EPR and optical absorption spectra demonstrates that Cu²⁺ ions are located in octahedral sites with symmetry D_4h. It is revealed that the intensity of the EPR spectrum decreases by one order of magnitude after annealing of the glass at a temperature of 200°C, which correlates with the temperature of decomposition of copper -diketonate molecules (250°C) with the formation of CuO or metallic copper. This process is accompanied by a change in the spectrum shape and the spin-Hamiltonian parameters, even though these parameters also correspond to the octahedral environment with symmetry D^4hIt is assumed that the remaining Cu²⁺ ions form new complexes with fragments of decomposed molecules. According to the optical data, the inference is made that high-temperature annealing leads to the formation of copper metal nanoparticles in the glass.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Bagratashvili, Bogomolova, Jachkin, Krasilnikova, Rybaltovskii, Tsypina, Chutko.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part II. Foaming of poly(ɛ-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone fluid mixtures and formation of tubular foams via solution extrusion

This paper reports on the foaming of poly(ɛ-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone mixtures. Experiments were carried out in specially designed molds with porous metal surfaces and fluid circulation features to generate foams with uniform dimensions at 60, 70 and 80 °C at pressures in the range 7–28 MPa. Depending upon the conditions, foams with pores in the range from 5 to 200 μm were generated. Adding acetone to carbon dioxide improved the uniformity of the pores compared to foams formed by carbon dioxide alone. In addition, a unique high-pressure solution extrusion system was designed and used to form porous tubular constructs by piston-extrusion of a solution from a high-pressure dissolution chamber through an annular die into a second chamber maintained at controlled pressure/temperature and fluid conditions. Long uniform porous tubular constructs with 6 mm ID and 1 mm wall thickness were generated with glassy polymers like poly(methyl methacrylate) by extruding solutions composed of 50 wt% polymer + 50 wt% acetone, or 25 wt% polymer + 10% acetone + 65% carbon dioxide at 70 °C and 28 MPa. Pores were in the 50 μm range. The feasibility of forming similar tubular constructs were demonstrated with poly(ɛ-caprolactone-co-lactide) as well. Tubular foams of the copolymer with interconnected pores with pore sizes in the 50 μm range were generated by extrusion of the copolymer solution composed of 25 wt% polymer + 10 wt% acetone + 65 wt% carbon dioxide at 70 °C and 28 MPa. Reducing the acetone content in the solution led to a reduction of pore sizes. Comparisons with the foaming behavior of the homopolymer poly(ɛ-caprolactone) that were carried out in the molds with porous metal plates show that the foaming behavior of the copolymer is more akin to the foaming behavior of the caprolactone homopolymer component.     

The deactivation study of Co–Ru–Zr catalyst depending on supports in the dry reforming of carbon dioxide

Carbon dioxide reforming of methane was performed over Co–Ru–Zr catalyst (0.4 wt% Ru added, calcined at 400 °C) with different supports (SiO₂, γ-Al₂O₃ and MgO) in order to study their deactivation. The Co–Ru–Zr/γ-Al₂O₃ showed the highest activity at first, but severe deactivation was observed due to carbon deposition. Co–Ru–Zr/MgO exhibited low activity because of its low specific surface area. However, the high conversions could be obtained in Co–Ru–Zr/SiO₂, and activity was kept almost constantly for 500 h reaction. The characteristics of the catalysts, before and after the reaction, were investigated employing BET, XRD, TPR, TGA-DTA and TEM.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part II. Foaming of poly(?-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone fluid mixtures and formation of tubular foams via solution extrusion

This paper reports on the foaming of poly(?-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone mixtures. Experiments were carried out in specially designed molds with porous metal surfaces and fluid circulation features to generate foams with uniform dimensions at 60, 70 and 80 °C at pressures in the range 7-28 MPa. Depending upon the conditions, foams with pores in the range from 5 to 200 μm were generated. Adding acetone to carbon dioxide improved the uniformity of the pores compared to foams formed by carbon dioxide alone. In addition, a unique high-pressure solution extrusion system was designed and used to form porous tubular constructs by piston-extrusion of a solution from a high-pressure dissolution chamber through an annular die into a second chamber maintained at controlled pressure/temperature and fluid conditions. Long uniform porous tubular constructs with 6 mm ID and 1 mm wall thickness were generated with glassy polymers like poly(methyl methacrylate) by extruding solutions composed of 50 wt% polymer + 50 wt% acetone, or 25 wt% polymer + 10% acetone + 65% carbon dioxide at 70 °C and 28 MPa. Pores were in the 50 μm range. The feasibility of forming similar tubular constructs were demonstrated with poly(?-caprolactone-co-lactide) as well. Tubular foams of the copolymer with interconnected pores with pore sizes in the 50 μm range were generated by extrusion of the copolymer solution composed of 25 wt% polymer + 10 wt% acetone + 65 wt% carbon dioxide at 70 °C and 28 MPa. Reducing the acetone content in the solution led to a reduction of pore sizes. Comparisons with the foaming behavior of the homopolymer poly(?-caprolactone) that were carried out in the molds with porous metal plates show that the foaming behavior of the copolymer is more akin to the foaming behavior of the caprolactone homopolymer component.     

Thermogravimetric investigation of the oxidation of the ZrB2-SiO2 composite in the temperature range 800–1300°C

The kinetics and mechanism of high-temperature oxidation of the components of the ZrB₂-SiO₂ system are investigated using thermogravimetric and X-ray powder diffraction analyses. It is shown that the interaction between solid components of the ZrB₂-SiO₂ system, atmospheric oxygen, and the glass-forming melt can be adequately described by the equations of the formal kinetics of heterogeneous processes. The previously revealed effect of encapsulation of a high-melting compound by the glass-forming melt is confirmed. This effect manifests itself in the fact that, upon introduction of a silicon-containing component, the increment of the weight of a sample decreases as a result of the oxidation and the weight losses in the form of gaseous products decrease to almost zero.     

A numerical study of capillary pressure–saturation relationship for supercritical carbon dioxide (CO2) injection in deep saline aquifer

Carbon capture and sequestration (CCS) is expected to play a major role in reducing greenhouse gas in the atmosphere. It is applied using different methods including geological, oceanic and mineral sequestration. Geological sequestration refers to storing of CO₂ in underground geological formations including deep saline aquifers (DSAs). This process induces multiphase fluid flow and solute transport behaviour besides some geochemical reactions between the fluids and minerals in the geological formation. In this work, a series of numerical simulations are carried out to investigate the injection and transport behaviour of supercritical CO₂ in DSAs as a two-phase flow in porous media in addition to studying the influence of different parameters such as time scale, temperature, pressure, permeability and geochemical condition on the supercritical CO₂ injection in underground domains. In contrast to most works which are focussed on determining mass fraction of CO₂, this paper focuses on determining CO₂ gas saturation (i.e., volume fraction) at various time scales, temperatures and pressure conditions taking into consideration the effects of porosity/permeability, heterogeneity and capillarity for CO₂–water system. A series of numerical simulations is carried out to illustrate how the saturation, capillary pressure and the amount of dissolved CO₂ change with the change of injection process, hydrostatic pressure and geothermal gradient. For example, the obtained results are used to correlate how increase in the mean permeability of the geological formation allows greater injectivity and mobility of CO₂ which should lead to increase in CO₂ dissolution into the resident brine in the subsurface.     

Experimental-stochastic investigation of the combustion cyclic variability in HSDI diesel engine using ethanol–diesel fuel blends

An experimental investigation is conducted to evaluate the combustion characteristics of a fully instrumented, high-speed, direct injection (HSDI), standard ‘Hydra’ diesel engine, at various loads when using ethanol–diesel fuel blends up to 15% by vol. ethanol. In each test, combustion chamber and fuel injection pressure diagrams of many consecutive cycles were obtained using a specially developed, high-speed, data acquisition and processing system. Following a performance and exhaust emissions investigation and a heat release analysis of the measured cylinder pressure diagrams reported by the authors, the present work focuses on the cycle-by-cycle combustion variation (cyclic variability) as reflected in the pressure indicator diagrams, by analyzing for the maximum pressure, maximum pressure rate, (gross) indicated mean effective pressure, and dynamic injection timing and ignition delay. These parameters were analyzed using stochastic analysis techniques for averages, standard deviations, coefficients of variation, probability density functions, auto-correlations, power spectra and cross-correlation coefficients. Thus, any cause and effect relationship between cyclic pressure variations and the injection system or the kind of fuel used can be revealed, given the concern for the low cetane number of ethanol blends promoting cyclic variability that can lead to degraded performance and emissions characteristics.     

Tunable ceria–zirconia support for nickel–cobalt catalyst in the enhancement of methane dry reforming with carbon dioxide

Ceria–zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel–cobalt (Ni–Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H₂ = 32%; CO = 44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47 wt.%.     

Tensile strength of a water-setting (hydration-hardening) zirconium dioxide based concrete in the 300–2300 k range

Conclusions During primary heating of the modified zirconium dioxide-based water-setting concrete (TsGBM), after attaining the desired temperature level, _tns increases up to approximately 1h if the temperature is below 2000 K (due to sintering of the finely dispersed barium aluminate separated during the decomposition of the crystallohydrates and due to the transformation of the concrete into a two-phase ceramic) and up to approximately 5 h if the temperature exceeds 2000 K (owing to sintering of the particles of the electromelted zirconium dioxide filler) and, thereafter, it remains constant:the level of the stationary strength of TsGBM decreases monotonically with increasing temperature from 3.5 N/mm² (under normal conditions) up to 0.25 N/mm² (at a temperature exceeding 2100 K) and corresponds to the strength of a granular and porous zirconium dioxide ceramic;up to 1200 K, the stationary strength of the concrete is determined by the quantity and the crystallohydrates of barium aluminate and their bond strength; up to 2100 K, it is determined by the degree of sintering and the intrinsic strength of barium aluminate; and above 2100 K, it owes to the formation and the strength of the zirconium dioxide-zirconium dioxide type bonds.Translated from Ogneupory, No. 5, pp. 4–8, May, 1991.The authors gratefully acknowledge the help rendered by T. A. Melekhin and T. A. Evdokimov in carrying out specimen preparation and Yu. I. Chubarov in the operation of the testing unit.     

Identification of bioactive compounds with GC–Q-TOF–MS in the extracts from Clinacanthus nutans using subcritical carbon dioxide extraction

Subcritical carbon dioxide Soxhlet extraction of biologically active compounds from Clincanthus nutans was investigated by full factorial design to identify and optimize the factors (particle size and co-solvent) affecting extract yield, antioxidant activity, total phenolic content, total flavonoid content, and α-glucosidase inhibitory activity. An average of 3.103% yield, 98.90% antioxidant activity, 49.40 mg/g (GAE) TPC, 43.76 mg/g (RE), and 88.58% AGI activity can be achieved using the optimum levels of independent variables. The GC-Q-TOF MS identification of optimized extract shown that different classes of phytoconstituents were successfully separated by CO₂-Soxhlet to produce potential antioxidant and α-glucosidase inhibitory activity.     

An improvement on Martin–Hou equation of state for more precise prediction in the liquid region

A modified Martin–Hou (M–H) equation of state (EOS) for the accurate representation of thermodynamic property data of some pure substances in liquid phase is presented in this work. The improvement is achieved by substituting a new parameter η into the original M–H EOS. Eighteen pure substances are chosen to construct the dependency relationship of η on reduced temperature T_r and acentric factor ω. Furthermore, to verify the effectiveness and improvement of the modified M–H EOS, the calculated values of the saturated vapor and liquid molar volumes are compared with the literature data in the reduced temperature ranging from approximately 0.6 to 1.0. The results show that the modified M–H EOS perform a good prediction in gaseous phase for pure substances with the average absolute deviation (AAD) generally less than 1%, and more precise liquid molar volume values can be obtained with the modified equation. In liquid phase, the AAD of the modified M–H EOS is 3.71%, which is much lower than 6.16% of the original M–H EOS.     

The effect of carbon source and molar ratio in Fe–Ti–C system on the microstructure and mechanical properties of in situ TiC/Fe composites

The size, distribution, and morphology of TiC particle in Fe–Ti–C system have a great influence on the mechanical properties of TiC/Fe composites. In this work, TiC/Fe composites were fabricated in the Fe–Ti–C system with different carbon source and molar ratio by combustion synthesis and hot-pressing method. Morphology and size of ceramic particles, as well as microstructure, interface bonding and mechanical properties of composites were compared. The results showed that the size of TiC particles decreased with increase of Fe content of Fe–Ti–C systems fabricated by the same carbon source, while the particles change from spherical shapes to cubic shapes which can reduce stress concentration between ceramic particles and matrix. Furthermore, TiC/Fe composites fabricated by 5Fe–Ti-carbon blacks (CBs) system exhibited superior yield strength (1523 MPa) compressive strength (2203 MPa) and microhardness (691.5 HV), caused by the high interface bonding strength and lamellar pearlite matrix which can commendably limit the dislocation slip. By comparison, TiC/Fe composites fabricated by 21Fe–Ti-carbon nanotubes (CNTs) system showed higher fracture strain (25.85%) on account of the ferrite matrix with favorable plastic. This work reveals the influence of carbon source and molar ratio of Fe–Ti–C system on TiC/Fe composites, which is helpful to further improve the properties of TiC/Fe composites.     

Prediction of solubilities of solid solutes in carbon dioxide-expanded organic solvents using the predictive Soave–Redlich–Kwong (PSRK) equation of state

In this study, the solubilities of solid solutes in carbon dioxide (CO₂)-expanded organic solvents are predicted using the predictive Soave–Redlich–Kwong (PSRK) equation of state (EOS). The liquid-phase compositions and volume expansion ratios of CO₂-expanded organic solvents are predicted prior to the solubility predictions. With predicted liquid-phase compositions and volumetric properties, the solubilities of cholesterol in CO₂-expanded acetone, naphthalene in CO₂-expanded toluene, stearic acid in CO₂ expanded ethyl acetate and tetradecanoic acid in CO₂-expanded ethyl acetate are predicted according to their reference solubilities in pure organic solvents. In addition to satisfactory predictions of liquid-phase composition and volume expansion ratios, the PSRK EOS also provides qualitative prediction ability for solubilities of solid solutes in CO₂-expanded organic solvent. This study demonstrated that the PSRK EOS was a simple model with predictive ability for solubility evaluation in preliminary process design and development for supercritical fluid technology using CO₂-expanded organic solvents.     

Compressibility,fugacity, and water-solubility of carbon dioxide in the region 0–36 atm. and 0–100°c

An improved form of the Beattie volume-explicit equation of state for carbon dioxide is described, containing two additional terms. Tables of compressibility, fugacity, and water-solubility of carbon dioxide are presented for the region 0–36 atm. and 0–100°C.     

What scene information is needed for models of colour appearance in the natural world?

Colorimetry is an essential tool in every part of colour. This article looks over our shoulders at the colour research of Maxwell, Wright, Land and Wyszecki to build a framework for colour. Then, the article looks forward to the needs of digital imaging's future. Colour is the fusion of today's imaging technology with our understanding of colour. Molecular physical chemistry describes the light–matter interactions, while human colour is controlled by neurons that compare light from the entire scene, covering a nearly 180° visual angle. This article's question asks about the information required by a future Model of Colour Appearance that is able to predict any scene: all natural scenes and any experimental display.     

Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition–fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide

Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to control the grafting of 2,2,2-trifluoroethyl methacrylate (TFEMA) with ramie fibers in supercritical carbon dioxide (scCO₂). The hydroxyl groups of the ramie fibers were converted to 2-dithiobenzoyl isobutyrate as the RAFT chain transfer agent (cellulose-CTA). Then, the subsequent grafting with TFEMA was mediated by RAFT polymerization in the presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (ECPDB) as the free RAFT chain transfer agent (free CTA). The modified ramie fibers were highly hydrophobic with water contact angles of up to 149°. Size exclusion chromatography showed narrow polydispersity (PDI = 1.28) of the grafted poly(TFEMA) chains. This grafting polymerization process is a novel and environmentally friendly approach for the preparation of functional grafted copolymers utilizing ramie fiber biomass.