Analysis of long term catalytic performance for isobutane alkylation catalyzed by NMA–AlCl_3 based ionic liquid analog

Isobutane alkylation with 2-butene to produce high-quality gasoline was catalyzed by Nmethylacetamide(NMA)-AlCl_3 based ionic liquid(IL) analog with a NMA/AlCl3 molar ratio of 0.75 and CuCl modification,which was marked as CuCl-modified 0.75 NMA-1.0 AlCl_3.The long-term experiment was carried out in the autoclave operated in continuous mode to investigate the distribution of alkylate under different experimental nodes.The result indicated that the long-term alkylation was divided into three stages:rising,stable,and descending regions.C8 selectivity and molar ratio of trimethylpentanes(TMPs) to dimethylhexanes(DMHs) reached the highest level in the stable region,and research octane number(RON) of alkylate was as high as 97.Anionic Al species([AlbCl_7]~-,[A1 CuC15]-) and cationic Al species([AlCl_2 L]~+) from IL analog as two active Lewis acidic species played a catalytic role in the long-term alkylation,whereas the neutral Al species did not participate into the alkylation.Moreover,the structure of CuCl-modified 0.75 NMA-1.0 AlCl_3 was destroyed after the deactivation,and CuCl was enriched in the CD_2 Cl_2-insoluble substance,resulting in a decreasing TMP/DMH ratio.The catalytic lifetime of IL analog was similar with CuCl-modified 0.55 Et_3 NHCl-1.0 AlCl_3 IL,but IL analog had a lower cost.     

Experimental solid–liquid equilibria and solid formation kinetics for carbon dioxide in methane for LNG processing

In cryogenic liquefaction processes, CO₂ poses a solid-formation risk even in trace concentrations. We present solid–fluid equilibrium (SFE) data for CO₂ in liquid methane at CO₂ concentrations from (52 to 500) ppm, extending the available data and indicating that models tuned to existing data over predict the solubility of CO₂ at LNG storage temperatures (~112 K) by nearly a factor of 3. The new data are used to improve the SFE model in the ThermoFAST software package. The formation kinetics of CO₂ solids in liquid methane are elucidated at conditions relevant to cryogenic gas processing. Repeated, ramped-temperature formation measurements provide a statistical basis for quantifying solidification risk. Nucleation rates extracted from the ramped-temperature data, consistent with those measured at fixed temperature, were used to extract parameters describing CO₂ solid formation in methane. These results significantly improve the ability to predict CO₂ solid formation risk in cryogenic natural gas processing.     

Process intensification and waste minimization in liquid–liquid–liquid phase transfer catalyzed selective synthesis of mandelic acid

Conversion of biphasic reactions into triphasic reactions can lead to process intensification, waste minimization and selectivity enhancement. Unlike liquid–liquid (L–L) PTC, the Liquid–Liquid–Liquid phase transfer catalysis (L–L–L PTC) offers high order of intensification of rates of reaction and catalyst reuse. The rate of reaction is remarkably enhanced by the catalyst-rich middle phase, which is the main reaction phase. Separation of catalyst can be done easily and the separated catalyst can be reused several times by using L–L–L PTC. This leads to waste minimization and other benefits of Green Chemistry. Mandelic acid and its derivatives are used for their dual activities as antibacterial and anti-aging agents. In this work, mandelic acid was produced by L–L–L PTC reaction of dichlorocarbene with benzaldehyde. Dichlorocarbene was generated in situ by the reaction of chloroform and sodium hydroxide in the presence of poly ethylene glycol (PEG) 4000 as the catalyst. The selectivity to mandelic acid was 98%. The reaction mechanism and kinetics model were established to validate the experimental data.     

Membrane contactors for intensified post combustion carbon dioxide capture by gas–liquid absorption in MEA: A parametric study

Post combustion carbon dioxide capture raises tremendous chemical engineering challenges. For the first generation of industrial installations, gas liquid absorption in chemical solvents is classically considered to be the best available technology. Two major bottlenecks have however to be solved in order to achieve technico-economical targets: decrease the energy requirement of the process (e.g. through novel solvents or heat integration approaches) and decrease the size of the installation (through process intensification).     

Coupling reaction of carbon dioxide and epoxides efficiently catalyzed by one-component aluminum–salen complex under solvent-free conditions

Four novel bifunctional aluminum–salen complexes (2a, 2b, 2c, and 2d) containing both Lewis acidic metal center and Lewis base quaternary phosphonium salt sites within one molecule and an aluminum–salen complex with a neutral tert-butyl group (2f) for comparison were synthesized and characterized by UV–vis, IR, ¹H, ¹³C, ²⁷Al NMR spectroscopy and Elemental analysis (EA). Their catalytic efficiencies as single-component catalysts toward the coupling reaction of carbon dioxide and propylene oxide were evaluated. These complexes exhibit catalytic activity in the order 2d > 2a > 2b > 2c ? 2f. ²⁷Al NMR spectra reveal the existence of five- and six-coordinated metal centers in the aluminum–salen complexes bearing a quaternary phosphonium salt group, whereas only five-coordinate aluminum species were found in the aluminum–salen complex with a neutral tert-butyl group. This indicates the importance of the six-coordinate aluminum center in enhancing the catalytic activity as well as an intramolecular cooperative effect in bifunctional aluminum–salen complexes 2a–d. The effects of reaction variables on the catalytic performance were investigated in detail. These new catalysts are highly stable to moisture and air and robust to impurities in the coupling reaction.     

Electrogenerative formation of ferric ions in a sulfur dioxide–sulfuric acid solution; Graphite catalysed sulfur dioxide oxidation

The electrogenerative oxidation of ferrous ions in 3m sulfuric acid, containing sulfur dioxide and subsequent sulfur dioxide oxidation, were studied in connection with potential regenerable sulfur dioxide remediation processes. The presence of sulfur dioxide in the feed stream did not affect cell performance. Oxidation of sulfur dioxide in the electrogenerative reactor took place when high ferrous to ferric ion conversions were obtained. Low cost graphite and iron ions served as an effective mediating system for promoting electron transfer to sulfur dioxide in strong acid solutions. In contrast, the homogenous reaction between iron(iii) and sulfur dioxide is relatively slow. In a separate batch reactor, the heterogeneous iron(iii) and sulfur dioxide reaction was found to be graphite catalysed, accounting for sulfur dioxide conversion observed in the electrogenerative reactor. Ferrous ion presence should be minimized, because it inhibits the desired catalysed reaction.     

Volumetric expansion and vapour–liquid equilibria of α-methylstyrene and cumene with carbon dioxide at elevated pressure

Volumetric expansion data and vapour-liquid equilibria (VLE) for α-methylstyrene (AMS) with CO₂ are reported at temperatures of 308 and 323 K and pressures approaching the mixture critical point. Similar data are reported for the mixture of carbon dioxide and cumene at a temperature of 323 K. It is shown that the volumetric expansion data for the various systems coincide when plotted as a function of the solubility of CO₂ in the liquid phase. A procedure is described for calculating the molar volume of the liquid phase from the phase compositions and volumetric expansion data. The experimental VLE data are correlated with the Peng-Robinson (PR) equation of state and the interaction parameter for each binary system is obtained by regression. The interaction parameter is subsequently used to predict the liquid molar volume for each binary system. The use of a single interaction parameter with the PR equation of state provides a satisfactory correlation of the liquid molar volume.     

Chiral induction in anion–anion electron transfer in aqueous solution catalyzed by a chiral cation

The oxidation of cobalt(II) chelate complexes [CoY]²⁻, where Y=edta (ethylenediaminetetraacetate), pdta (1,2-propanediaminetetraacetate) and cydta (trans-1,2-cyclohexanediaminetetraacetate), by [Co(mal)₃]³⁻ (mal=malonate) was catalyzed by chiral [Co(en)₃]³⁺ to yield optically active products with the enantiomeric excesses which increase with increasing concentration of chiral [Co(en)₃]³⁺. Substituents on the ethylenediamine backbone of [CoY]²⁻ had significant effects on the sign and the magnitude in the stereoselectivity. The results are interpreted in terms of a chiral induction mechanism in which the ion pair between [CoY]²⁻ and chiral [Co(en)₃]³⁺ is stereoselectively oxidized by [Co(mal)₃]³⁻. A model is proposed for the relative orientation of oxidant, reductant, and catalysis complexes.     

High pressure vapor–liquid equilibrium for the ternary system ethanol/(±)-menthol/carbon dioxide

In this work the phase behavior of the ternary system ethanol/(±)-menthol/CO₂ was studied at the temperatures of 313 and 323 K, in the pressure range 8–10 MPa. Experiments were performed using a high pressure phase equilibrium apparatus with a visual cell. CO₂ is more selective toward ethanol, separation factors ranging from 1.6 to 7.6 at the conditions tested. The pTxy data obtained were correlated with the Peng–Robinson equation of state combined with the Mathias–Klotz–Prausnitz mixing rule. The model gave a good fitting to the data, with a total average absolute deviation of 3.7%, and was able to predict the occurrence of a three-phase region observed experimentally at 313 K and 9 MPa.     

Estimation of solubility of solids in supercritical carbon dioxide

Peng-Robinson equation of state(PR EOS)was chosen for modeling the thermodynamic be-havior of supercritical(SC)-CO_2/Solid systems.The necessary critical constants and acentric factorof the solute were obtained by the Sigmund and Trebble(1992)method based on the molecular weightand boiling temperature,and the vapor pressure of the solute was calculated by its meltingtemperature and heat of fusion.This approach compared very favorably with the conventional corres-ponding state theory,but without using critical constants and vapor pressure of solutes.Four mixingrules were tested for the calculation of solid solubility in SC-CO_2.van der Waals(vdW)mixing rulewith one parameter was considered to be most suitable for the estimation of solubility.A simplecorrelation was developed for the SC-CO_2/solid binary interaction coefficient k_(ij) with the meltingtemperature of pure solutes.The solubilities of solids in SC-CO_2 were estimated for eleven binarysystems at various temperatures,the total absolute average     

Oxidative dehydrogenation of ethylbenzene with carbon dioxide on alkali‐promoted Fe/active carbon catalysts

Well defined Mo²⁺ surface sites of silica-supported catalyst, produced by H2 reduction of the fixed molybdenum tetraallyl precursor, show a characteristic IR signal at 2170 cm^-1 due to adsorbed carbon monoxide. Higher oxidation states of Mo in the same catalyst do not show any signal related to this probe molecule. This revised version was published online in July 2006 with corrections to the Cover Date.     

Desulfurization of liquid hydrocarbon fuels via Cu_2O catalyzed photooxidation coupled with liquid–liquid extraction

By combining the photochemical reaction and liquid–liquid extraction(PODS), we studied desulfurization of model fuel and FCC gasoline. The effects of air flow, illumination time, extractants, volume ratios of extractant/fuel, and catalyst amounts on the desulfurization process of PODS were analyzed in detail. Under the conditions with the air as oxidant(150 ml·min~(-1)), the mixture of DMF–water as extractant(the volume ratio of extractant/oil of 0.5) and photo-irradiation time of 2 h, the sulfur removal rate reached only 42.63% and 39.54% for the model and FCC gasoline, respectively. Under the same conditions, the sulfur removal rate increased significantly up to79% for gasoline in the presence of Cu_2O catalyst(2 g·L~(-1)). The results suggest that the PODS combined with a Cu_2O catalyst seems to be a promising alternative for sulfur removal of gasoline.     

Three-phase catalytic hydrogenation of α-methylstyrene in supercritical carbon dioxide

The three-phase catalytic hydrogenation (TPCH) of α-methylstyrene using supercritical carbon dioxide (scCO₂) in a slurry reactor is reported. Kinetic data are presented for the reaction at 323 K over the range of pressure from 7.0 to 13.0 MPa using a carbon-supported palladium catalyst. The experimental data are fitted to a first-order power-law model. A detailed explanation of the methodology used to isolate the effect of CO₂ on the rate of reaction is presented. Particular attention is given to the phase behaviour of the reaction system and the volumetric expansion of the liquid phase with CO₂. It is shown that scCO₂ significantly enhances the rate of reaction. This effect is attributed to the enhancement of the solubility of hydrogen in the liquid phase.     

Graphene–terpyridine complex hybrid porous material for carbon dioxide adsorption

A graphene-based porous material for carbon dioxide sorption was designed and fabricated through an azide–alkyne click reaction between alkynyl group modified graphene oxide (alkynyl-GO) and azido-terpyridine complex. In the preparation of graphene terpyridine complex hybrid porous materials (GTCF), alkynyl-GO sheets were synthesized and used as the building blocks, which were then cross-linked with azido-terpyridine complexes through a copper (I) ion-catalyzed click reaction (Huisgen cycloaddition reaction). The incorporation of the non-planar terpyridine complexes between graphene sheets increases the porosity in the GTCF materials. Meanwhile, three kinds of nitrogen-containing groups (amine, triazole, and terpyridine groups) were introduced or formed during the modification and cross-linking, which offer more basic sites for the acidic gas sorption. Gas sorption analysis shows that the GTCF hybrid porous materials possess high specific surface area and their carbon dioxide capacity could reach up to 11.7 wt.% at 273 K.     

Evaporative liquid jets in gas–liquid–solid flow system

Some aspects of the fundamental characteristics of evaporative liquid jets in gas–liquid–solid flows are studied and some pertinent literature is reviewed. Specifically, two conditions for the solids concentration in the flow are considered, including the dilute phase condition as in pneumatic convey and the dense phase condition as in bubbling or turbulent fluidized beds. Comparisons of the fundamental behavior are made of the gas–solid flow with dispersed non-evaporative as well as with evaporative liquids.For dilute phase conditions, experiments and analyses are conducted to examine the individual phase motion and boundaries of the evaporative region and the jet. Effects of the solids loading and heat capacity, system temperature, gas flow velocity and liquid injection angle on the jet behavior in gas and gas–solid flows are discussed. For dense phase conditions, experiments are conducted to examine the minimum fluidization velocity and solids distribution across the bed under various gases and liquid flow velocities. The electric capacitance tomography is developed for the first time for three-phase real time imaging of the dense gas–solid flow with evaporative liquid jets. The images reflect significantly varied bubbling phenomenon compared to those in gas–solid fluidized beds without evaporative liquid jets.     

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The onestep procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixedbed reactor. Application of supercritical NH₃ as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8–10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via ,unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3propanediol.     

Continuous oxidation of benzyl alcohol in “supercritical” carbon dioxide

Supercritical (dense) carbon dioxide has been applied as solvent for the partial oxidation of benzyl alcohol with molecular oxygen in a fixed-bed reactor. High rate and good selectivity to benzaldehyde (93–97%) has been achieved with 0.5 wt% Pd/alumina or 0.5 wt% Pd/C, at around 100C and 100 bar, using only moderate excess of oxygen. The by-product benzoic acid has an autocatalytic effect on the hydration of benzaldehyde, and the subsequent oxidative dehydrogenation leads to benzoic acid, and benzyl benzoate by esterification. Promotion of Pd by Pb improves the selectivity. No catalyst deactivation or metal leaching has been observed. The method provides reasonable yields at much lower temperature than that applied in conventional gas phase oxidation, showing a potential for the synthesis of thermolabile, water-insoluble aromatic aldehydes.     

Ethylbenzene into styrene with carbon dioxide over modified vanadia–alumina catalysts

Dehydrogenation of ethylbenzene to styrene with carbon dioxide has been investigated using various vanadia–alumina catalysts to exhibit high activity and selectivity. Redox behavior of vanadium oxide played a key role in the dehydrogenation. Among several additives, antimony oxide has been found for improving catalyst stability as well as catalytic activity to produce styrene, revealing that the addition of the antimony oxide leads to the easier redox cycle between fully oxidized and reduced vanadium species.