Selective hydrogenation of phenol in supercritical carbon dioxide

Liquid phase hydrogenation of phenol over Pt/C catalysts was investigated under conventional conditions and supercritical carbon dioxide (scCO2). The equivalent ration of hydrogen to phenol shows a significant effect on the product selectivity. Hydrogenation of phenol in different solvents was also studied, the experimental results show that polarity of solvents influences the yield of cyclohexanone remarkably, scCO2 has the highest one. Catalytic hydrogenation of phenol in scCO2 or sub-sc…     

Supercritical CO2: an effective medium for the chemo-enzymatic synthesis of block copolymers?

In this review, we describe the combination of enzymatic polymerisation and controlled free radical polymerisation in supercritical carbon dioxide. This combination facilitates the preparation of a range of block and graft copolymers, some of which cannot easily be obtained by conventional polymer synthesis. Biocatalysis in polymer science provides significant new opportunities and will open up a very broad range of new polymeric materials.     

Preparation of yolk-shell sulfur/carbon nanocomposite via an organic solvent route for lithium–sulfur batteries

A yolk-shell sulfur/carbon (S/C) composite for the cathode of lithium–sulfur batteries was successfully prepared by an accessible method with tetrahydrofuran as solvent. The as-prepared composites are characterized by thermal gravimetric, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption and desorption. In this composite, sulfur particle is encapsulated in the carbon shell even entering into the micropores of carbon Bp2000. The electrochemical performance of the S/C composites is evaluated. The results indicate that the S/C composite with 50 wt% sulfur content shows good reversibility, excellent rate capability, and slow degradation. It delivers an initial capacity of 784.4 mAh g^?1 (based on sulfur weight) and preserves at 598.3 mAh g^?1 after 195 cycles at 1C. It achieves a high-capacity retention of 76.27 % from the 5th to 200th cycle, and as high as 91.19 % during the latter 150 cycles. The improvement is mainly attributed to the favorable structure of the S/C composite, in which the carbon cannot only facilitate transport of electrons and Li⁺ ions but also trap polysulfides and retard the shuttle effect during charge/discharge process.     

High-pressure densities and P–T–x–y diagrams for carbon dioxide+linalool and carbon dioxide+limonene

Liquid and vapor densities for carbon dioxide+linalool, and carbon dioxide+limonene were measured by using a system consisting of two vibrating tube densimeters. The P–T–x–y diagrams and saturated liquid and vapor densities for these two binary mixtures were determined at 313, 323 and 333 K, respectively, as well as at pressures up to 11 MPa. The density of the saturated CO₂ phase increased with increasing pressure. At higher pressure, the density of the liquid phase decreased with increasing pressure, corresponding to an increasing amount of carbon dioxide.     

Nickelocene/lithium aluminium hydride-a “homogeneous raney nickel” for catalytic hydrogenation

Nickelocene/lithium aluminum hydride in THF has been found to be an active homogeneous catalyst for catalytic hydrogenation. The reaction behaviour Is very similar to Raney nickel.     

Is nitrate really an inert electrolyte? A brief review

It has been common practice to use sodium or potassium nitrate as a supposedly inert background electrolyte or for adjustment of ionic strength, but nitrate forms sufficiently stable complexes with many metals for its use to result in erroneous values for stability constants. This note surveys the effects.     

High-pressure phase equilibria for the carbon dioxide–2-methyl-1-butanol,carbon dioxide–2-methyl-2-butanol,carbon dioxide–2-methyl-1-butanol–water,and carbon dioxide–2-methyl-2-butanol–water systems

High-pressure vapor–liquid equilibria for the binary carbon dioxide–2-methyl-1-butanol and carbon dioxide–2-methyl-2-butanol systems were measured at 313.2 K. The phase equilibrium apparatus used in this work is of the circulation type in which the coexisting phases are recirculated, on-line sampled, and analyzed. The critical pressure and corresponding mole fraction of carbon dioxide for the binary carbon dioxide–2-methyl-1-butanol system at 313.2 K were found to be 8.36 MPa and 0.980, respectively. The critical point of the binary carbon dioxide–2-methyl-2-butanol was also found 8.15 MPa and 0.970 mole fraction of carbon dioxide. In addition, the phase equilibria of the ternary carbon dioxide–2-methyl-1-butanol–water and carbon dioxide–2-methyl-2-butanol–water systems were measured at 313.2 K and several pressures. These ternary systems showed the liquid–liquid–vapor phase behavior over the range of pressure up to their critical point. The binary equilibrium data were all reasonably well correlated with the Redlich–Kwong (RK), Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), and Patel–Teja (PT) equations of state with eight different mixing rules the van der Waals, Panagiotopoulos–Reid (P&R), and six Huron–Vidal type mixing rules with UNIQUAC parameters.     

Vapor—liquid equilibrium studies for the carbon dioxide—methanol system

Experimental vapor—liquid equilibrium measurements of carbon dioxide and methanol have been conducted from 230 K (−43.15°C) to 330 K (56.85°C) at pressures to the very vicinity of the critical states. The consistency of the data sets are examined and compared to literature values.Unlike the methane—methanol system, which exhibits two liquid phases at low temperatures, the carbon dioxide—methanol system exhibits complete liquid phase miscibility. Accordingly, the effects of critical behavior on the vapor liquid equilibria behavior begin to manifest themselves at much lower pressures.     

On the necessity of organic solvent extraction for carbon isotopic analysis of α-cellulose: implications for environmental reconstructions

α-cellulose is widely used as a target substance for isotope ratio analysis in environmental reconstructions. Its preparation includes three basic steps: organic solvent extraction, delignification and alkaline hydrolysis. Recent works have suggested omission of the first step. We have made a detailed comparison in carbon isotope ratio of α-cellulose with or without organic solvent extraction using 32 consecutive tree ring and 30 subfossil peat samples. These samples were exposed to three different chemical treatments: with organic solvent extraction as the first step (Cell_OE), without organic solvent extraction (Cell_NOE), and with organic solvent extraction as the final step (Cell_NOE/OE). The third treatment is used to test if organic extractives can be completely removed or if their solubility in organic solvents has been altered by delignification and alkaline hydrolysis. In tree rings and peat, δ¹³C_{C ell NOE} was always significantly different from δ¹³C_{C ell OE}, but the trends were not the same. In tree rings, δ¹³C_{C ell NOE} was always more negative than δ¹³C_{C ell OE} by ?0.31 ～ ?0.01‰. In contrast, δ¹³C_{C ell NOE} in peat could be more negative or more positive than δ¹³C_{C ell OE} by ?3.08 ～ 0.27‰. The third chemical treatment resulted in different patterns. For tree rings, δ¹³C_{C ell NOE/OE} was still more negative than δ¹³C_{C ell OE} by ?0.36 ～ ?0.08‰. However, the differences between δ¹³C_{C ell NOE/OE} and δ¹³C_{C ell OE} for peat varied in a more narrow range from ?0.58 to 0.61‰, compared to the differences between δ¹³C_{C ell NOE} and δ¹³C_{C ell OE}. These results exposed a complex chemical evolution behaviour and an incomplete removal of lipids during delignification and alkaline hydrolysis. The mean value, long-term trend and seesaw patterns for a tree ring or peat Cell_NOE series were significantly different from those for a Cell_OE series, indicating that omission of organic solvent extraction will lead to a biased inference of past environmental conditions.     

Supercritical carbon dioxide extraction and gas chromatography–mass spectrometry analysis of Gymnema sylvestre R.Br. roots

Supercritical fluid extraction (SFE) achieves a wide range of applications since the past decade as a sustainable green technology. The present study investigates the process for producing high yield by supercritical carbon dioxide (Sc-CO₂) extraction form Gymnema sylvestre R.Br. roots. The effect of temperature and pressure on the percentage of accumulative yield is demonstrated. It is found that the highest yield is obtained at the temperature of 60°C and the pressure of 10?MPa. A proper review showed that there is a lack in the study of Sc-CO₂ extraction of this plant especially for optimization of SFE process which makes this study useful and valuable. For more benefit, the extract which achieves highest percentage is subjected to gas chromatography–mass spectrometry to study its chemical composition and detect the active principle compounds which present with high concentration and expected to be responsible of the pharmaceutical properties of the extract.     

Carbon dioxide catalytic conversion to nano carbon material on the iron–nickel catalysts using CVD-IP method

The over-consumption of fossil fuels resulted in the large quantity emission of carbon dioxide(CO2), which was the main reason for the climate change and more extreme weathers. Hence, it is extremely pressing to explore efficient and sustainable approaches for the carbon-neutral pathway of CO2 utilization and recycling. In our recent works with this context, we developed successfully a novel chemical vapor deposition integrated process(CVD-IP) technology to converting robustly CO2 into the value-added solid-form carbon materials.The monometallic Fe Ni0–Al2O3(FNi0) and bimetallic Fe Nix–Al2O3(FNi2, FNi4, FNi8 and FNi20) samples were synthesized and effective for this new approach. The catalyst labeled FNi8 gave the better performance, exhibited the single pass solid carbon yield of 30%. These results illustrated alternative promising cases for the CO2 capture utilization storage(CCUS), by means of the CO2 catalytic conversion into the solid-form nano carbon materials.     

Solid–liquid equilibria for the dimethyl ether + carbon dioxide binary system

A recently built experimental setup was employed for the estimation of the solid–liquid equilibria of alternative refrigerants systems. The behavior of dimethyl ether (DME) + carbon dioxide was measured down to temperatures of 131.6 K. To confirm the reliability of the apparatus, the triple point of the DME was measured. The triple point data measured revealed a good consistency with the literature. The results obtained for the mixtures were corrected by the Rossini method and interpreted by means of the Schröder equation.     

Air-stable P-stereogenic secondary phosphine oxides as chiral monodentate ligands for asymmetric catalytic carboncarbon bond formation

P-Stereogenic secondary phosphine oxides are configurationally stable in the presence of metal ions both in solution and in the solid state. They have the potential to serve as chiral monodentate phosphorus ligands for asymmetric catalysis. In the asymmetric allylic alkylation of 1,3-diphenylprop-2-enyl acetate, ca. 80% ee was achieved using (R_p)-tert-butylphenylphosphine oxide.     

Nickel–cobalt hydroxide catalysts for the cycloaddition of carbon dioxide to epoxides

Research on Chemical Intermediates - Nickel and cobalt bimetallic hydroxides, in which both metal cations present the same oxidation state, were synthesized and characterized by XRD, TGA, TEM, XPS,...     

Inactivity of iridium–triphenylphosphine complexes for catalytic imine hydrogenation: formation of neutral, dihydrido-ortho-metallated species

Reactions of cis,trans,cis-[Ir(H)₂(PPh₃)₂(MeOH)₂]PF₆ in MeOH with the imines Ph(R′)C=NR under 1 atm H₂ precipitate the neutral, Ir(III)-dihydrido complexes [Ir(H)₂{RN=C(R′)(o-C ₆H₄)}(PPh₃)₂], where R = alkyl or benzyl, and R′ = Ph, H, or Me; the dihydrides are well characterized through elemental analysis, NMR and IR data and, in one case, with the imine Ph₂C=NCH₂Ph, an X-ray structure. These products are formed via intermediate ortho-metallated species, exemplified by [Ir(H){PhCH₂N=CPh(o-C ₆H₄)}(PPh₃)₂(MeOH)]PF₆ in the case of the Ph₂C=NCH₂Ph reaction; the intermediate then reacts with H₂ (via net heterolytic cleavage: H₂ → H⁻ + H⁺) to give the neutral dihydride and HPF₆ as co-product. The ‘unique’ imine PhCH=NPh, under the same conditions, does not form a dihydride and instead is readily catalytically hydrogenated to PhCH₂N(H)Ph; remarkably, we have shown previously that this imine is ‘unique’ within the corresponding Rh system in that no catalytic hydrogenation occurs because the amine product ‘poisons’ the Rh centre by coordination through the N-phenyl ring.     

Can 1,3-dimethylcyclobutadiene and carbon dioxide co-exist inside a supramolecular cavity?

The calculated free energy barrier at 175 K between 1,3-dimethylcyclobutadiene and carbon dioxide inside a calixarene host (ωB97XD/6-311G(d,p)+polarizable continuum solvent model) has the low value of ~8-10.5 kcal mol(-1). This value casts doubt on the recently claimed isolation and X-ray structure determination at 175 K of 1,3-dimethylcyclobutadiene and carbon dioxide as separate species inside such a cavity.     

Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide

Three different porous metal organic framework (MOF) materials have been prepared with and without uncoordinated amine functionalities inside the pores. The materials have been characterized and tested as adsorbents for carbon dioxide. At 298 K the materials adsorb significant amount of carbon dioxide, the amine functionalised adsorbents having the highest CO₂ adsorption capacities, the best adsorbing around 14 wt% CO₂ at 1.0 atm CO₂ pressure. At 25 atm CO₂ pressure, up to 60 wt% CO₂ can be adsorbed. At high pressures the CO₂ uptake is mostly dependent on the available surface area and pore volume of the material in question. For one of the iso-structural MOF pairs the introduction of amine functionality increases the differential adsorption enthalpy (from isosteric method) from 30 to around 50 kJ/mole at low CO₂ pressures, while the adsorption enthalpies reach the same level at increase pressures. The high pressure experimental results indicate that MOF based solid adsorbents can have a potential for use in pressure swing adsorption of carbon dioxide at elevated pressures.