The gasification of carbon by carbon dioxide at high temperatures and pressures

Presented is the analysis of experimental data on the interaction of carbon with CO₂ + N₂ mixtures at temperatures up to 3400 K and pressures up to 40 atm. The influence of pressure and roles of different stages of the reaction multistage mechanism are determined.     

Adsorption equilibria for hydrogen and carbon dioxide on activated carbon at high pressure up to 30 atm

Equilibrium data for the adsorption of hydrogen, carbon dioxide, and binary mixture of both gases on activated carbon were determined experimentally. Pure component isotherms were presented along with pressures up to 30 atm at 301 K, 323 K and 348 K. Also, the binary equilibria were obtained at various temperatures same above for pressure of 1.5, 10 and 20 atm, respectively. For the pure component system, Freundlich isotherm was shown to be fitted best to the experimental results. However, in the binary system, the ideal adsorption solution (IAS) theory gave good representation of the binary experimental data in high pressure range.     

Comparison of pore structure in Kentucky coals by mercury penetration and carbon dioxide adsorption

For four Kentucky coals, a comparison was made between pore volume distribution evaluated from CO₂ adsorption isotherms calculated from the Cranston-Inkley method and the Medek method. These distributions agree in the micropore range from approximately 0.6–2.0 nm. Most of the pore structure is in the micropore range. For the mercury penetration studies a rectilinear relation is found between penetrated volume and applied pressure from approximately 0.1 MPa (1 atm) up to 345 MPa (3400 atm). Surface areas were calculated from adsorption data by the BET, Langmuir, and Dubinin-Polanyi methods.     

Methanol formation at high pressure by the catalyzed oxidation of natural gas and by the sensitized oxidation of methane

A three part study of the partial oxidation of natural gas or methane to methanol was carried out. In the first part, the effect of reactor wall composition on the homogeneous oxidation of natural gas was determined at a pressure of 30 atm (1 atm=1.01325·10⁵ Pa) and temperatures of 350–400°C. In the second part, the effect of solid catalysts on the oxidation of natural gas was determined in a heterogeneous system at 30 atm and various temperatures. Finally, the effect of various homogeneous 'sensitizers' on the oxidation of pure methane at 10 atm was evaluated.     

Thermodynamic evaluation of the carbon-hydrogen system at high temperatures

A theoretical study of the C-H system reveals that, at high temperatures, many polymeric species have to be taken into account. Free energy functions of the species involved have been calculated to permit the evaluation of the equilibrium compositions of the system in both the heterogeneous and homogeneous regions. Pressures ranging from 0.1 to 10 atm. and carbon to hydrogen ratios from 0.5 to 20 were investigated between 2,000 and 6,000°K. Since the reaction of carbon vapor with hydrogen is highly exothermic, a reaction scheme was also developed whereby the endothermic heat of cracking of various hydrocarbons could be balanced by the former reaction. Several conditions related to a global heat of reaction have been considered.     

A rough-hard-sphere theory for diffusion in supercritical carbon dioxide

A rough-hard-sphere (RHS) theory is found to successfully account for the effects of molecular rotation and dynamically correlated molecular collisions on self-diffusion in carbon dioxide at temperatures from 35 to 100°C and pressures from 70 to 246 atm. The Mathur-Thodos empirical equation finds its molecular basis within the framework of the RHS theory. The theory is also applicable to tracer diffusion of benzene in carbon dioxide at 35–55°C and 91–158 atm, where densities are greater than 0.500 g/cm³. Its failure at lower densities suggests that the molecular dynamics computer result of self-diffusion is inadequate for describing the effect of collective molecular motion encountered in tracer diffusion across the entire density range. Further computer work is recommended which will refine the prediction of tracer diffusion in supercritical fluids using the RHS theory.     

Synthesis of C1-C7 alcohols from synthesis gas with supported cobalt catalysts

Supported cobalt-molybdenum-potassium catalyst was found to be active for the synthesis gas conversion to aliphatic alcohols containing 1 to 7 or more carbon atoms at temperatures from 200 to 300(C and under pressures from 10 to 70 atm. Reduced cobalt was essential for the formation of carbon structure of alcohols and hydrocarbons. Potassium carbonate was effective for enhancing alcohol formation while suppressing hydrocarbon synthesis. Molybdenum was effective for promoting catalytic activity. Alcohols were mostly composed of straight chain primary alcohols. The carbon number distributions of both hydrocarbon and alcohol followed th Schulz-Flory equation which gave chain growth probabilities of 0.35-0.45 (alcohol) and 0.45-0.55 (hydrocarbon).     

The capture of carbon dioxide by transition metal aluminates,calcium aluminate,calcium zirconate,calcium silicate and lithium zirconate

The capture of CO₂ by transition metal (Mn, Ni, Co and Zn) aluminates, calcium aluminate, calcium zirconate, calcium silicate and lithium zirconate was carried out at pre- and post-combustion temperatures. The prepared metal adsorbents were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), surface area analysis and acidity/alkalinity measurements. The different experimental variables affecting the adsorbents ability to capture CO₂, such as the mol ratio of metal ions, the pressure of CO₂, the exposure time and the temperature of the adsorbent were also investigated. Calcium zirconate captured 13.85 wt-% CO₂ at 650°C and 2.5 atm and calcium silicate captured 14.31 wt-% at 650°C. Molecular sieves (13X) and carbon can only capture a negligible amount of CO₂ at high temperatures (300°C–650°C). However, the mixed metal oxides captured reasonable amount of CO₂ at these higher temperatures. In addition, calcium aluminate, calcium zirconate, calcium silicate and lithium zirconate adsorbents captured CO₂ at both pre and post-combustion temperatures. The trend for the amount of captured carbon dioxide over the adsorbents was calcium aluminate相似文献   

The improvement in oxidation resistance of carbon by a graded SiC/SiO2 coating

A dense functionally gradient SiC/SiO₂ coating has been developed to improve the oxidation resistance of carbon at elevated temperatures. SiC was coated on the surface of a graphite substrate by a reaction between thermally evaporated silicon and carbon at 1400 °C. The SiO₂ layer was deposited by exposing the SiC coated specimens next to a bed of Si powder in a flowing H₂–H₂O gas (P_H2O=2.6×10⁻² atm) at 1400 °C. The formed SiC/SiO₂ layers were dense and had gradient compositions with good adhesion to the carbon substrate. However, as the coating thickness increased, the coating layer became cracked and delaminated from the substrate due to thermal stress. The specimens with the continuous SiC/SiO₂ layer showed a remarkably improved oxidation resistance up to 1200 °C.     

Phase Relations in the System Uranium—Nitrogen

To supplement efforts to develop UN as a nuclear fuel material, a study of the phase relations in the system uranium-nitrogen was conducted. The decomposition behavior and melting point of UN was studied in a controlled nitrogen-pressure apparatus in which cast specimens of UN were heated and observed. UN decomposed at pressures of nitrogen below 2.5 atm at temperatures below 2850° C and melted congruently at 2850° C and pressures of 2.5 atm or greater. The nitrogen content of the liquid uranium phase in equilibrium with UN was determined by heating uranium in a UN crucible and then quenching and analyzing the equilibrated phase. The solubility of nitrogen in atomic percent can be expressed as S = 2.45 × 10⁴ exp (-38,800/RT) for temperatures in OK. Studies in the region U₂N₃-UN₂ of the system which were performed using a Sievert-type apparatus showed that although these compounds are structurally dissimilar, they form a series of continuous solid solutions. Only UN₂ formed at high pressures and low temperatures. A pressure-temperature schematic diagram and a temperature-composition schematic diagram for a nitrogen pressure of 1 atm for the system uranium-nitrogen are presented. At this pressure, UN decomposed at 2800° C and U₂N₃ decomposed at 1345° C.     

On the reaction of oxygen with nitrogen-containing and nitrogen-free carbons

The reaction of three types of carbon with oxygen (1 atm) at different temperatures was investigated. The precursors for the carbons studied were Kapton (polyimide), cellulose and cellulose that was carbonized with ammonium chloride. Two consecutive processes are confirmed to occur during the reaction with oxygen. The build up of oxygenated surface complexes by chemisorption of oxygen and the well-known gasification of these surface groups. The carbons originating from Kapton or cellulose carbonized in the presence of NH₄Cl contain nitrogen. As the nitrogen content in the carbon is higher, the uptake of oxygen at the carbon surface by chemisorption is more pronounced. Hall effect measurements demonstrate that electrons are the major charge carrier in nitrogen containing carbons, while holes are the charge carriers in the nitrogen-free carbons. The determination of the type of charge carrier explains the observation that the nitrogen-containing carbons chemisorb oxygen more readily than the nitrogen-free carbons. Electronic conductivity demonstrates the affect of the sign of the charge carrier on the chemisorption of the carbons during chemisorption of oxygen. While in the case of n-type carbon a decrease in the conductivity was observed, p-type carbons exhibit a slight increase followed by a decrease in the conductivity.     

Herstellung modifizierter Carbonsäuren aus α-Olefinen durch Hydroxycarbonylierung

Preparation of Modified Carboxylic Acids from α-Olefins by Hydroxycarbonylation The hydroxycarbonylation of α-olefins to carboxylic acids was investigated. Yields around 95% were achieved using NiJ₂ as catalyst at temperatures of ca. 200°C and carbon monoxide pressure of 30 atm. and higher for 3–7 hrs. The acids are composed mainly of isomers having 2-methyl branching as well as the normal ones and the 2-ethyl acids. Ca. 95% of the NiJ₂ is recovered from the reaction product by washing with water.     

Hydrogen production via dry reforming of butanol: Thermodynamic analysis

Dry reforming of butanol for hydrogen production has been studied by Gibbs free energy minimization method. The calculation results showed that the formation of hydrogen and carbon monoxide was through a multi-step pathway via the dehydrogenation, dehydration, decomposition and carbon dioxide reforming of butanol. The optimum conditions for hydrogen production are identified: reaction temperatures between 1150 and 1200 K and carbon dioxide-to-butanol molar ratios between 3.5 and 4.0 at 1 atm. Under the above conditions, 100% conversion of butanol, 34.91-37.98% concentration of hydrogen and 57.34−57.87% concentration of carbon monoxide could be achieved in the absence of coke formation. The butanol dry reforming with carbon dioxide is suitable for providing fuels for Solid Oxide Fuel Cell (SOFC). The coke-formed and coke-free regions are found, which are useful in guiding the search for suitable catalysts for the reaction.     

Effect of pressure on three catalytic partial oxidation reactions at millisecond contact times

The effects of pressure on reactant conversion and product selectivities in three catalytic oxidation systems have been examined at pressures between 1 and > 5 atm. Reaction was sustained autothermally near adiabatic operating conditions at temperatures of 1000°C with residence times over the noble metal catalysts between 10^–4 and 10^–2 s. The three systems investigated were (1) HCN synthesis over Pt-10% Rh gauze catalysts, (2) methane oxidation to synthesis gas (CO and H₂) over rhodium-coated monoliths, and (3) ethane conversion to ethylene over platinum-coated monoliths. We find that selectivities in all three reactions do not change dramatically with approximately a five-fold increase in pressure. This strongly suggests that free radical homogeneous chain reactions are not significant in these processes and that they can be operated reliably above atmospheric pressure. For the synthesis of HCN over Pt-10% Rh gauzes, the selectivity to HCN can be maintained above 0.75 at pressures up to 5.5 atm. Selectivities to synthesis gas (CO and H₂) from a methane-air mixture over a Rh-coated foam monolith at pressures up to 5.5 atm were maintained above 0.90. Over a Pt-coated foam monolith, the selectivity to ethylene from ethane-air and ethane-O₂ mixtures was independent of pressure up to 6.5 atm and conversion rose slightly although it was necessary to maintain constant velocity and residence time over the catalyst to avoid carbon formation.This research was supported by DOE under Grant No. DE-FG02-88ER13878.     

ACTIVATION OF STAINLESS STEEL FOR CO HYDROGENATION

An unusual CO hydrogenation catalyst was formed by prolonged contact between 316 stainless steel and a supported tine oxide at temperatures of 623 to 723 K. Neither the stainless steel nor the supported ZnO alone were active for CO hydrogenation. The activation occurred only after migration of Zn from the support to the steel surface. The resulting catalyst converted syngas to C₁-C₄, hydrocarbons at pressures between 3400 and 6200 kN/m² and temperatures between 623-723 K. The catalyst may be suitable for use in tube-wall-type reactors.     

The separation and fractionation of polystyrene at a lower critical solution point

Solutions of polystyrene in methyl acetate separate into two liquid phases at lower critical solution temperatures which lie above 120°C. Phase boundaries were determined for one broad, one moderately sharp and five very sharp fractions of polystyrene. Pressures up to 45 atm displace the curves uniformly to higher temperatures.

The phase boundaries of the sharp fractions form a regular family of curves which is cut by the curves of the broader fractions. It is suggested that the determination of such a curve is a rapid way of characterizing a polymer.

The broadest sample was separated into seven fractions by successive precipitation in an apparatus that could be used up to 50 atm. The efficiency of the fractionation was good at high molecular weights but poor at low molecular weights.     

Structure and properties of hard carbon films depending on heat treatment temperatures via polymer precursor

Phenylcarbyne polymer films were coated on silicon substrates and heat treated in 1 atm pressure of argon at various temperatures. The structural changes occurring during the heat treatment process of the polymer were investigated by Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The Raman and FTIR spectra features of the polymer showed a dependence on the heat treatment temperatures. At low temperatures (below 400°C), the Raman and IR spectra of the polymer were similar to those of the original polymer. The hardness and Young's modulus of the polymer films were below 1 and 50 GPa, respectively. With increasing temperature (above 400°C), thermal decomposition of the polymer occurred, resulting in structural changes of the polymer from soft amorphous hydrocarbon (400–600°C) phases to hard carbon phases (above 600°C). The hardness and Young's modulus increased from 1.5 and 65 GPa at 600°C to 9 and 120 GPa at 1000°C, respectively. It is assumed that the hard carbon film converted from the polymer might contain sp² and sp³ carbon phases; high temperature of heat treatment resulted in increasing sp² (glassy) carbon phase in the films.     

Polystyrene-supported aluminium silver chloride as selective ethylene adsorbent

Polystyrene-supported aluminium silver chloride was prepared as a solid and selective adsorbent for ethylene by refluxing silver chloride, aluminium chloride, and macroreticular-type polystyrene resin in carbon disulfide, followed by removal of the solvent in vacuo. The adsorbent rapidly adsorbed ethylene about equimolar to aluminium silver chloride under 1 atm at 20°C. Almost all the ethylene adsorbed was released by subjecting the adsorbent to a reduced pressure 8 mm Hg at 20°C for 10 min. The adsorbent, however, showed no adsorption of carbon monoxide under 1 atm at 20°C.     

Graphite intercalation compound of magnesium fluoride and fluorine

A graphite intercalation compound of C_xF(MgF₂)_y was prepared under a fluorine atmosphere of 1 atm at temperatures of 20–350°C. The 1st stage compound has the identity period of 9.3–9.4Å. ESCA and ¹⁹F NMR spectra indicate that the chemical interaction of intercalated fluorine with carbon is similar to that for graphite fluoride, however, with C_xF(MgF₂)_y having slightly mobile fluorine atoms chemically adsorbed on carbon atoms of graphite layers.     

Selective carbon monoxide adsorbent composed of polystyrene resin having amino groups and copper(I) chloride

A carbon monoxide adsorbent composed of 10 g of a polystyrene resin having amino groups and 70 mmol of copper(I) chloride was prepared by refluxing the resin and copper(I) chloride in acetonitrile, followed by evaporation of the liquid phase at 5 mmHg, 80°C. The adsorbent rapidly adsorbs 15.9 mmol of carbon monoxide under 1 atm at 20°C. 11.4 mmol of adsorbed carbon monoxide are desorbed when the adsorbent is subjected to a reduced pressure (5 mmHg) at 80°C for 10 min. In the second and the later adsorptions, the amount of adsorbed carbon monoxide is virtually constant at 11.4 mmol. The amount of carbon dioxide adsorbed by the adsorbent under 1 atm at 20°C is 2.8 mmol, and the value for methane is 0.0 mmol. The prepared adsorbent is applicable to selective separation of carbon monoxide from gas mixtures containing both carbon dioxide and methane.