CO Molar Ratio Research Articles

Mechanistic Aspects of Pyrophosphorylation Reactions from Model Studies

Pyrophosphorylation reactions that mimic pyrophosphorylases have been studied by utilizing nitrophenol as substrate and bistrimethylenediamine cobalt(III) pyrophosphate as the pyrophosphorylating agent. Significant pyrophosphorylation was noted for reactions of 1:1 molar ratio of Co(III)tn2 to PPi (i.e., [Co(III)tn2 PPi] in solution) and nitrophenol. The rate of pyrophosphorylation was significantly reduced for reaction solutions that were 2:1 in molar ratio of Co(III)tn2 to PPi, (i.e., [(Co(III)tn2)2PPi] in solution) and nitrophenol. No appreciable pyrophosphorylation was noted for the pyrophosphate complex, which has a 3:1 molar ratio of Co(III)tn2 to PPi (i.e., [(Co(III)tn2)3PPi] in solution) when reacted with equimolar amounts of nitrophenol. Specific mechanistic features and the possible roles metal ions play in pyrophosphorylase enzymes are highlighted from the results of both ultraviolet–visible (UV-vis) and 31P-nuclear magnetic resonance (NMR) studies.

Performance evaluation for dual circulating fluidized-bed steam gasifier of biomass using quasi-equilibrium three-stage gasification model

The effects of gasification temperature ( T G ) and steam to fuel ratio ( γ) on product gas composition and yield were experimentally investigated for steam gasification of pine woodchips in a bench-scale circulating fluidized-bed (CFB) gasifier with external heat supplier. To evaluate process performance in a dual circulating fluidized-bed (DFB) with heat carrier (silica sand), a quasi-equilibrium three-stage gasification (qETG) model was developed and validated with experimental data of biomass steam gasification. The model was divided into three stages including biomass pyrolysis, char–gas reactions, and gas-phase reactions. Carbonic and methane formation ratios were considered at the pyrolysis stage under the assumption of spontaneous decomposition. At the second and third stages, char–gas and gas-phase equilibrium reactions were corrected by two empirical equations concerning the steam participation ratio and the non-equilibrium factor, respectively. Using the qETG model, parametric study on T G and γ was performed to predict final gas composition, carbon conversion, char residue, gas yield, lower heating value, additional fuel ratio, solid circulation ratio, heat recovery and H 2 to CO molar ratio. Focusing on the solid circulation ratio and H 2/CO molar ratio, several effective operating conditions were suggested from the contour of performance criteria.

Growth of single and double walled carbon nanotubes over Co/V/MgO catalysts

High quality single walled carbon nanotubes (SWCNTs) and double walled carbon nanotubes (DWCNTs) were synthesized on Co/V/MgO catalysts by catalytic decomposition of CH 4 in H 2. Raman spectroscopy data revealed that the diameters of as-prepared SWCNTs are 1.28 and 0.73 nm. The diameter value of DWCNTs from Raman analysis also showed a narrow diameter distribution. Using field emission transmission electron microscopy (TEM), it was found that the diameter of carbon nanotubes can be controlled mainly by adjusting the molar ratio of Co–V versus the MgO support. The structure properties of catalysts were examined by X-ray diffraction (XRD). The formation of C 7V 8 may play an important role in preserving carbon in the catalyst particle and favoring the dissociation balance of CH 4.

Effect of Operating Conditions for Higher Alcohols Synthesis from Synthesis Gas over Alkali-Modified Co-Rh-Mo Trimetallic Catalyst Supported on Multi-Walled Carbon Nanotubes

The effects of operating conditions on the higher alcohols synthesis reaction from synthesis gas were studied in a single-pass tubular downflow fixed-bed reactor, using sulfided K-promoted trimetallic Co-Rh-Mo catalyst supported on multi-walled carbon nanotubes (MWCNTs). The p CO conversion increased monotonically with increasing reaction temperature (from 275 to 350°C) and pressure (from 800 to 1400 psi), while decreasing monotonically with increasing GHSV (from 2.4 to 4.2 m3 (STP)/(kg of cat./h)). To maximize the ethanol STY and selectivity, the optimum operating conditions were determined as 330°C, 1320 psi, and 3.8 m3 (STP)/kg of cat./h). Maximum ethanol STY and selectivity were obtained using gas with H2 to CO molar ratio around 1.25.

Effect of Operating Conditions for Higher Alcohols Synthesis from Synthesis Gas over Alkali-Modified Co-Rh-Mo Trimetallic Catalyst Supported on Multi-Walled Carbon Nanotubes

The effects of operating conditions on the higher alcohols synthesis reaction from synthesis gas were studied in a single-pass tubular downflow fixed-bed reactor, using sulfided K-promoted trimetallic Co-Rh-Mo catalyst supported on multi-walled carbon nanotubes (MWCNTs). The p CO conversion increased monotonically with increasing reaction temperature (from 275 to 350°C) and pressure (from 800 to 1400 psi), while decreasing monotonically with increasing GHSV (from 2.4 to 4.2 m3 (STP)/(kg of cat./h)). To maximize the ethanol STY and selectivity, the optimum operating conditions were determined as 330°C, 1320 psi, and 3.8 m3 (STP)/kg of cat./h). Maximum ethanol STY and selectivity were obtained using gas with H2 to CO molar ratio around 1.25.

Biogas reforming over La-NiMgAl catalysts derived from hydrotalcite-like structure: Influence of calcination temperature

Hydrotalcite-like compound with general formula [M(II)1 − xM(III)x(OH)2]x+(An−x/n) · mH2O, where An− is the compensation anion, has been used as precursor of active catalysts for biogas reforming. This precursor was calcined at six different temperatures between 250 and 750 °C and the resulting catalysts were tested in order to evaluate the influence of the calcination temperature on the catalytic activity and stability. XRD characterization showed that from 250 °C the hydrotalcite structure is no longer detected, leading to Mg(Ni,Al)O solid solutions, where no peaks related to lanthanum appear. An increase on the calcination temperature increased the grain size and cell parameter value. 50 h-catalytic tests were carried out at 700 °C, CH4:CO2 molar ratio of 1:1 and a mass/feed alimentation ratio (W/F) of 0.4 mg min cm− 3. Used catalysts were characterized by temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and Raman spectroscopy in order to obtain information about coke deposition. Catalytic tests highlighted the great influence of calcination temperature over catalytic activity and stability, having found that, as a general trend, calcination temperatures below 750 °C decrease both the stability and catalytic activity, with the exception of the catalyst calcined at 550 °C, where a higher activity was achieved but with a comparatively low stability.

Deactivation Studies of Alkali-Promoted Trimetallic Co−Rh−Mo Sulfide Catalysts for Higher Alcohols Synthesis from Synthesis Gas

Multiwalled carbon nanotubes (MWCNTs) and activated carbon (AC)-supported K (9 wt %)-promoted trimetallic Co (4.5 wt %)−Rh (1.5 wt %)−Mo(15 wt %) catalysts are used to study the long-term deactivation for continuous 720 h of higher alcohols synthesis (HAS). The fresh catalysts are extensively characterized in both oxide and sulfide phases, together with the spent catalysts. The catalysts are tested for the synthesis of higher alcohols from synthesis gas under similar conditions of 330 °C, 9.1 MPa (1320 psig), and 3.8 m3 (STP)/((kg of cat.)/h), using a H2:CO molar ratio of 1.25. The alkali-promoted trimetallic Co−Rh−Mo catalyst supported on MWCNTs has shown two different deactivation steps: loss of sulfur from the surface and sintering of the catalyst species located on the outer surfaces of the carbon nanotubes. After regeneration, the total activity recovery (∼10%) over this catalyst is close to the total activity loss during the first deactivation step. The percentage CO conversion decreased from 58% to...

Magnetic and electromagnetic properties of composites of iron oxide and Co–B alloy prepared by chemical reduction

Magnetic and electromagnetic properties were investigated on the composites of iron oxide and Co–B alloy, which were prepared by a modified chemical reduction method. The composites are characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The complex electromagnetic parameters (permittivity ε r= ε r′+j ε r″ and permeability μ r= μ r′+j μ r″) of paraffin mixed composite samples (paraffin:composites=1:1 in mass ratio) were measured in the frequency range 2–18 GHz by vector network analyzer. The measured real part ( ε r′) and imaginary part ( ε r″) of the relative permittivity show two resonant peaks in the range of 2–18 GHz. The imaginary parts of relative permeability ( μ r″) of all samples exhibited one broad resonant peak over the 2–8 GHz range. The μ r″ of samples with higher molar ratio of Co to Fe (C and D) shows negative values within 13–18 GHz, which exhibit resonant and antiresonant permeabilities simultaneously. Calculation results indicated that the reflection loss values of the composites and paraffin wax mixtures are less than −10 dB with frequency width of about 6 GHz at the matching thickness.

Synthesis of SnO 2 nanorods from aqueous solution: The effect of preparation conditions on the formed patterns

SnO 2 nanorods were deposited on the Si substrates in an aqueous solution containing both SnCl 4 and CO(NH 2) 2. It is found that different self-assembled patterns of SnO 2 nanorods can be obtained by changing the deposition conditions such as the molar ratio of CO(NH 2) 2 to SnCl 4 and the pretreatment of the substrate. Scattered SnO 2 nanorods, for example, can be changed into flower-like patterns when the molar ratio of CO(NH 2) 2 to SnCl 4 is raised, and well-aligned nanorod arrays can be formed when the pretreatment of the substrate is changed. In addition, some interesting patterns, e.g. tree-like patterns, can also be observed.

Polymorph control of calcium carbonate by reactive crystallization using microbubble technique

In this study, we used the minute gas–liquid interfaces around CO 2/NH 3 microbubbles as new reaction fields where the crystal nucleation progresses and developed a crystallization technique to control the polymorphism of calcium carbonate (CaCO 3). In the regions around the gas–liquid interfaces of CO 2/NH 3 microbubbles, Ca 2+ and CO 3 2− ion concentrations can be adjusted because of the characteristic of the electric charge on the bubble surface and the decrease in CO 2 concentration based on unit bubble caused by minimization of bubble size, and because of the pH difference between local pH at the gas–liquid interface and overall pH in the bulk liquid caused by mixing of NH 3 with CO 2; hence, the polymorph change of CaCO 3 is expected to occur. CaCO 3 was crystallized at 298 K by a semi-batch type reaction in which CO 2/NH 3/N 2 bubbles were continuously supplied to an aqueous Ca(NO 3) 2 solution using a self-supporting bubble generator. The solution pH during crystallization was maintained at a constant level of 6.9–12.0 by adding HNO 3 and NH 4OH solution. The average bubble size ( d bbl) was varied in the range of 40–1000 μm by controlling the N 2 flow rate, and the molar ratio of CO 2/NH 3 ( α C O 2 /N H 3 ) was set at a specified value of 0.20–1.00 at a constant CO 2 flow rate. The following results were obtained by varying solution pH, d bbl, and α C O 2 /N H 3 : at a constant d bbl of 40 μm and α C O 2 /N H 3 of 0.20, vaterite and calcite were major products at a solution pH lower than 9.0 and at a solution pH greater than 11.0, respectively, while aragonite was crystallized predominantly in the solution pH range of 9.7–10.5; at a constant solution pH of 9.7 the crystallization of aragonite was accelerated remarkably with a decrease in α C O 2 /N H 3 and d bbl.

Sol-Gel Encapsulation as Matrix for Potentiometric Nitrite-Selective Membranes Doped with Chloro (5, 10, 15, 20-Tetraphenylporphyrinato) Cobalt (III)

Organic-inorganic hybrid sol-gel matrices were used as hosts for chloro (5, 10, 15, 20-tetraphenylporphyrinato) cobalt (III) (Co[TPP]Cl), a known ionophore for nitrite. The sol-gel precursor was prepared by the reaction of (3-isocyanopropyl) triethoxysilane with 1,4-butanediol. An appropriate amount of the anion-exchanger, tridodecylmethylammonium chloride (TDMAC) and the plasticizer, tributylphosphate (DBP) were used as membrane additives. On mixing with an acidic catalyst, the sol-state precursors slowly gelled, yielding a membrane in which the active components, Co[TPP]Cl and TDMAC, were encapsulated. The performances of the sol-gel membrane-based electrodes were compared to those of Co[TPP]Cl-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with a molar ratio of Co[TPP]Cl: TDMAC (1 : 0.1) showed reasonable response slopes toward nitrite. The response slopes were typically 53 mV/ decade between 10 −5.4 and 10 −1.0 M. Selectivities toward nitrite over hydrophilic and small anions such as chloride were somewhat inferior to those observed with PVC-based membranes, but selectivities over lipophilic anions were quite similar. Reduced asymmetry potentials due to protein adsorption were found to occur with the sol-gel matrix relative to PVC-based films when the sensors were employed as a detector in flow-through configuration.

Earthworm cast as a promising filter bed material and its methanotrophic contribution to methane removal

The use of biocovers is a promising strategy toward mitigating CH 4 emission from smaller and/or older landfills. In this study, a filter bed material consisting of a mixture of earthworm cast and rice paddy soil in a biocover was evaluated. Although the CH 4 oxidation rate of the enriched paddy soil was 4.9 μg g-dry soil −1 h −1, it was enhanced to 25.1 μg g-dry soil −1 h −1 by adding an earthworm cast with a 3:7 ratio of earthworm cast:soil (wet weight). CO 2 was found as the final oxidation product of CH 4, and the mole ratio of CO 2 production to CH 4 consumption was 0.27. At a moisture content range of 15–40% and a temperature range of 20–40 °C, the CH 4 oxidation rates of the enriched mixture were more than 57% of the maximum rate obtained at 25% moisture content and 25 °C. By denaturing gradient gel electrophoresis analysis employing primers for the universal bacterial 16S rRNA gene, and terminal-restriction fragment length polymorphism analysis using primers for the pmoA gene, the bacterial and methanotrophic communities in the enriched mixture were mainly originate from paddy soil and earthworm cast, respectively. Both type I (mainly Methylocaldum) and type II methanotrophs (mainly Methylocystis) played important roles in CH 4 oxidation in the enriched mixture.

Combined Reforming and Partial Oxidation of CO2-Containing Natural Gas Using an AC Multistage Gliding Arc Discharge System: Effect of Stage Number of Plasma Reactors

The effect of stage number of multistage AC gliding arc discharge reactors on the process performance of the combined reforming and partial oxidation of simulated CO2-containing natural gas having a CH4:C2H6:C3H8:CO2 molar ratio of 70:5:5:20 was investigated. For the experiments with partial oxidation, either pure oxygen or air was used as the oxygen source with a fixed hydrocarbon-to-oxygen molar ratio of 2/1. Without partial oxidation at a constant feed flow rate, all conversions of hydrocarbons, except CO2, greatly increased with increasing number of stages from 1 to 3; but beyond 3 stages, the reactant conversions remained almost unchanged. However, for a constant residence time, only C3H8 conversion gradually increased, whereas the conversions of the other reactants remained almost unchanged. The addition of oxygen was found to significantly enhance the process performance of natural gas reforming. The utilization of air as an oxygen source showed a superior process performance to pure oxygen in terms of reactant conversion and desired product selectivity. The optimum energy consumption of 12.05 × 1024 eV per mole of reactants converted and 9.65 × 1024 eV per mole of hydrogen produced was obtained using air as an oxygen source and 3 stages of plasma reactors at a constant residence time of 4.38 s.

Development and Validation of a Reduced Mechanism for Urea-based SNCR Process based on QSS Graph

This paper reports a reduced mechanism used in urea-based SNCR process for NOx control that is developed from the detailed mechanism originally proposed by Rota et al. (Chem. Eng. Sci. 2002, 57, 27−38) consisting of 173 elemental reactions and 31 chemical species. Sensitivity analysis and rate-of-production analysis are first conducted to exclude redundant elemental reactions and species, forming a skeletal mechanism. After that, quasi-steady-state species are identified and a 12-step 16-species reduced mechanism is established. The balance equations for quasi-steady-state species are innovatively solved by means of QSS graph method presented by Lu and Law (J. Phys. Chem. A 2006, 110, 13202−13208) with the avoidance of efficiency compromise stemming from algebraic iterations. The predictions of the reduced mechanism show satisfactory agreement with those of the detailed one over a wide range of operating conditions, including various temperatures, molar ratio of CO(NH2)2/NO and O2 and CO concentrations. T...

Study on a multifunctional energy system producing coking heat, methanol and electricity

A multifunctional energy system (MES) capable of consuming coke oven gas (COG) and coal, and simultaneously producing coking heat, methanol and electricity, was subject to an exergy analyses based on Energy Utilization Diagrams (EUDs). In this system a coal-fired coke oven is adopted to produce coke and COG, where non-coking coal is burned to supply thermal energy to the coking process. The COG and coal gas gasified from coal in a gasifier, were mixed to produce syngas for methanol synthesis. Since COG rich in hydrogen and coal gas rich in CO, the mixture of COG and coal gas can easily adjust the mole ratio of CO to H 2 of syngas instead of the conversional reforming and shift processes. The active component of syngas is firstly converted into methanol and then the rest is introduced to a gas turbine for power generation. As a result, the overall efficiency of the MES system is about 62.3%, and its energy savings ratio is about 15% comparing with individual systems. The paper provides a new approach to use coal more efficiently and cleanly.

Complete oxidation of methane on Co3O4-SnO2 catalysts

Co3O4-SnO2 hybrid oxides were prepared by the coprecipitation method and were used to oxidate methane (CH4) in presence of oxygen. The Co3O4-SnO2 with a molar ratio of Co/(Co + Sn) at 0.75 exhibited the highest catalytic activity among all the Co3O4-SnO2 hybrid oxides. Experimental results showed that the catalysts were considerably stable in the CH4 combustion reaction, and were verified by X-ray photoelectron spectra (XPS). It was found that Co3O4 was the active species, and SnO2 acted as a support or a promoting component in the Co3O4-SnO2 hybrid oxides. The surface area was not a major factor that affected catalytic activity. The hydrogen temperatureprogrammed reduction (H2-TPR) results demonstrated that the interaction between cobalt and tin oxides accelerated the mobility of oxygen species of Co3O4-SnO2, leading to higher catalytic activity.

Magnetic CoFe 2O 4 nanocrystal: A novel and efficient heterogeneous catalyst for aerobic oxidation of cyclohexane

Magnetic nanocrystalline spinel-type cobalt ferrite complex oxides were prepared by a simple sol–gel auto-combustion method at five different molar ratios of Co II to Fe III (1:4.0, 1:2.8, 1:2.0, 1:1.5, and 1:1.1) and characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR) and transmission electron microscopy (TEM). Their catalytic performance was evaluated in the oxidation of cyclohexane with oxygen as oxidant in the presence of neither solvents nor reducing agents. It has been revealed that the catalysts had high catalytic activities for heterogeneous oxidation of cyclohexane. Especially, when pure CoFe 2O 4 was used as catalyst; excellent results with turnover number of 288 and 92.4% selectivity for cyclohexanone and cyclohexanol was obtained under 1.6 MPa of initial oxygen pressure at 418 K after 6.0 h of reaction. The influences of initial oxygen pressure, reaction temperature, reaction time, and free-radical initiator on the oxidation of cyclohexane over CoFe 2O 4 were investigated. The catalyst can be easily separated by an external magnet and no obvious loss of activity was observed when reused in five consecutive runs. CoFe 2O 4 was proved to be also efficient for oxidation of linear alkanes.

Synthesis Gas Generation by Chemical-Looping Reforming Using Ce-Based Oxygen Carriers Modified with Fe, Cu, and Mn Oxides

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H-2 selectivity at above 800 degrees C. As for the Ce-Fe-O oxygen carrier, methane was converted to synthesis gas at a H-2/CO molar ratio close to 2:1 at a temperature of 800-900 degrees C; however, the methane thermolysis reaction was found on Ce-Cu-O and Ce-Mn-O oxygen carriers at 850-900 degrees C. Among the three kinds of oxygen carriers, Ce-Fe-O presented the best performance for methane CLR. On Ce-Fe-O oxygen carriers, the CO and H-2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce-Fe-O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce-Fe-O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce-Fe-O oxides by X-ray diffraction (XRD) analysis.

Enhanced Kinetics of CO2 Hydrate Formation under Static Conditions

Trapping CO2 in hydrates is one of the new technologies for CO2 capture and storage. One of the primary obstacles to this option is the low formation rate. This work presents the rapid formation of CO2 hydrates with a small amount of cyclopentane (CP). The formation kinetics was investigated in a 474 cm3 nonstirred batch reactor with 100 and 200 cm3 of water. At volume ratios of CP to water between 0.01 and 0.1, the maximum growth rate is 0.32 mol h−1 at CO2 pressures ranging from 1.9 to 3.4 MPa and at 274 K. CO2 hydrates (sI) and CO2 + CP (sII) binary hydrates coexist at the end of hydrate growth. The mole ratio of CO2 entrapped in the sI hydrates to that in the sII binary hydrates is higher with 100 cm3 of water than with 200 cm3 of water. The same trend is also observed for the total amount of CO2 entrapped in the hydrate phase. The growth rate depends not only on the water volume but also on the pressure. The hydrate growth rate and the water conversion reach a maximum at 3.06 MPa and then decrease as...

Hierarchical Three-Dimensional Cobalt Phosphate Microarchitectures: Large-Scale Solvothermal Synthesis, Characterization, and Magnetic and Microwave Absorption Properties

Novel hierarchical cobalt phosphate (alpha- and beta-Co2P2O7) and cobalt hydrogen phosphate hydroxide [Co-11(HPO3)(8)(OH)(6)] three-dimensional (3D) architectures with different morphologies were synthesized under a solvothemal condition. The form and shape of cobalt phosphate can be readily tuned by adjusting experimental parameters of the reaction system. The novel hierarchical alpha-CO2P2O7 microcrystals with basketry-like microstructures were obtained with a molar ratio of Co2+/H3PO4/CH3NH2/HO(CH2)(2)0OH of 1:1.2:1:108, the reaction temperature of 180 degrees C, and the reaction time of 5 days; dumbbell-like beta-Co2P2O7 microspheres were formed with the same reaction temperature and time but the molar ratio of 1: 1.2:1:54, and Co-11(HPO3)(8)(OH)(6) with peony-like nanostructures was prepared with the same molar ratio and reaction time as beta-Co2P2O7 but the reaction temperature of 120 degrees C. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR) technologies, a Quantum Design superconducting quantum interference device (SQUID) magnetometer, and a network analyzer. The formation mechanism of cobalt phosphate microstructures was investigated in detail.