Liquefaction of Swedish peats

Peat is a promising raw material for synthetic liquid fuel production. Raw peat with moisture content 85–95 wt% can be liquefied without preliminary drying. It may be treated with CO at an initial pressure of 5.5–8.3 MPa and at a temperature of 300–350 °C in the presence of K₂CO₃. Dewatering and liquefaction take place simultaneously. The peat conversion and the bitumen yield depend strongly on the chosen input material and the operating conditions. The inorganic mineral matter in the peat may also affect the process. Well-humified peat is a suitable raw material for the process with regard to bitumen yield. Some medium-humified peats can also be converted into bitumen in high yield. The process requires no, or low, consumption of CO. The presence of a catalyst is not always needed.     

Preferential CO oxidation over Pt–SnO2/Al2O3 in hydrogen rich streams containing CO2 and H2O (CO removal from H2 with PROX)

The effects of reaction gases including CO₂ and H₂O and temperature on the selective low-temperature oxidation of CO were studied in hydrogen rich streams using a flow micro-reactor packed with a Pt–SnO₂/Al₂O₃ sol–gel catalyst that was initially designed and optimized for operation in the absence of CO₂ and H₂O. 100% CO conversion was achieved over the 1 wt% Pt–3 wt% SnO₂/Al₂O₃ catalyst at 110 °C using a feed composition of 1.0% CO, 1.5% O₂, 25% CO₂, 10% H₂O, 58% H₂ and He as balance at a space velocity of 24,000 cm³/(g h). CO₂ in the feed was found to decrease CO conversion significantly while the presence of H₂O in the feed increased CO conversion, balancing the effect of CO₂.     

Effect of temperature on bitumen conversion in a supercritical water flow

This article deals with a study of bitumen conversion (the gross-formula CH_1.47N_0.01S_0.007) in a supercritical water (SCW) flow continuously supplied at the bottom of the vertically located tubular reactor. At the first stage, bitumen was continuously supplied from the top of the reactor into a counter-current SCW flow (400 °C, 30 MPa) for 60 min. At the second stage (after ceasing the supply of bitumen into the reactor), SCW was pumped through the layer of bitumen residue at uniform (2.5 °C/min) temperature increase from 400 to 700 °C at 30 MPa. The amount and composition of the liquid and volatile conversion products were measured. It is revealed that during bitumen supply into the reactor and subsequent pumping of SCW through the layer of bitumen residue in the temperature increasing mode from 400 to 500 °C, the yields of liquid conversion products are equal to 26.9 and 45.4%, respectively, relative to the weight of bitumen supplied into the reactor. Oils are the major components of these liquid products. Participation of H₂O molecules in redox reactions became evident due to the formation of CO and CO₂ even at 400 °C. A significant increase in the yields of H₂, CH₄, and CO₂ are detected at T > 600 °C. Based on the sulfur balance, it can be stated that the degree of bitumen desulfurization at 400–700 °C due to sulphur removal in form of H₂S accounts for 21.6 wt.% A solid carbonaceous bitumen residue, obtained after SCW conversion, is characterized by high specific surface (224 m²/g).     

Metal oxide-doped Ni/CaO dual-function materials for integrated CO2 capture and conversion: Performance and mechanism

Integrated CO₂ capture and conversion (ICCC) into valuable chemicals such as CH₄ and CO is a promising approach to mitigate anthropogenic CO₂ emissions. In this work, we prepared a series of metal oxide (M_xO_y, M = Mg, Al, Mn, Y, Zr, La, and Ce)-doped Ni/CaO dual-function materials (DFMs) and applied them to the ICCC process. The property–performance relationship of the DFMs was studied, and the conversion mechanism of the captured CO₂ was explored. For any DFM at any ICCC cycle (20 cycles in total), the CO₂ captured at the carbonation stage was completely released as CH₄, CO, and CO₂ at the conversion stage. Among all DFMs, Ni/CaZr(O) showed the best ICCC performance because of its good thermal stability. The conversion of captured CO₂ on the DFMs proceeded via a two-step mechanism, where CO₂ was first released from CaCO₃ and then converted into CH₄ at Ni sites and CO at CaO sites.     

Fischer�CTropsch Synthesis: Influence of CO Conversion on Selectivities, H2/CO Usage Ratios, and Catalyst Stability for a Ru Promoted Co/Al2O3 Catalyst Using a Slurry Phase Reactor

The effect of CO conversion on hydrocarbon selectivities (i.e., CH₄, C₅₊, olefin and paraffin), H₂/CO usage ratios, CO₂ selectivity, and catalyst stability over a wide range of CO conversion (12?C94%) on 0.27%Ru?C25%Co/Al₂O₃ catalyst was studied under the conditions of 220 °C, 1.5 MPa, H₂/CO feed ratio of 2.1 and gas space velocities of 0.3?C15 NL/g-cat/h in a 1-L continuously stirred tank reactor (CSTR). Catalyst samples were withdrawn from the CSTR at different CO conversion levels, and Co phases (Co, CoO) in the slurry samples were characterized by XANES, and in the case of the fresh catalysts, EXAFS as well. Ru was responsible for increasing the extent of Co reduction, thus boosting the active site density. At 1%Ru loading, EXAFS indicates that coordination of Ru at the atomic level was virtually solely with Co. It was found that the selectivities to CH₄, C₅₊, and CO₂ on the Co catalyst are functions of CO conversion. At high CO conversions, i.e. above 80%, CH₄ selectivity experienced a change in the trend, and began to increase, and CO₂ selectivity experienced a rapid increase. H₂/CO usage ratio and olefin content were found to decrease with increasing CO conversion in the range of 12?C94%. The observed results are consistent with water reoxidation of Co during FTS at high conversion. XANES spectroscopy of used catalyst samples displayed spectra consistent with the presence of more CoO at higher CO conversion levels.     

Low Temperature Selective CO Oxidation in Excess of H2 over Pt/Ce—ZrO2 Catalysts

Pt/Ce—ZrO₂ catalysts have been designed and applied to selective CO oxidation at low temperature. Both tetragonal and cubic phase Ce—ZrO₂ supports were prepared by co-precipitation method to get high surface area materials after calcination at 500 °C for 6 h in air. Selective CO oxidation was conducted using stoichiometric amounts of O₂. Cubic Ce—ZrO₂ supported Pt catalyst exhibited 78% CO conversion and 96% CO₂ selectivity even at 60 °C, while Pt/Al₂O₃ catalyst showed less than l% CO conversion at the same condition. The higher CO conversion and CO₂ selectivity (to CO₂ as opposed to H₂O) of Pt/Ce—ZrO₂ catalyst is mainly due to the high oxygen storage capacity of Ce—ZrO₂ and nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂.     

Tri-reforming of surrogate biogas over Ni/Mg/ceria–zirconia/alumina pellet catalysts

The performance of catalytic tri-reforming under industrially relevant situations (e.g., pellet catalysts, pressurized reactor) was investigated using surrogate biogas as the feedstock. Tri-reforming using Ni/Mg/Ce_0.6Zr_0.4O₂/Al₂O₃ pellet catalysts was studied in a bench scale fixed-bed reactor. The feed molar ratio for CH₄:CO₂:air was fixed as 1.0:0.70:0.95. The effects of temperature (800–860°C), pressure (1–6?bar), and H₂O/CH₄ molar feed ratio (0.23–0.65) were examined. Pressure has substantial impact on the reaction and transport rates and equilibrium conversions, making it a key variable. At 860°C, CO₂ conversion increased from 4 to 61% and H₂/CO molar ratio decreased from 2.0 to 1.1 as the pressure changed from 1 to 6?bar. CO₂ conversion and H₂/CO molar ratio were also influenced by the temperature and H₂O/CH₄ molar ratio. At 3?bar, CO₂ conversion varied between 4 and 43% and the H₂/CO molar ratio varied between 1.2 and 1.9 as the temperature changed from 800 to 860°C. At 3?bar and 860°C, CO₂ conversion decreased from 35 to 8% and H₂/CO molar ratio increased from 1.7 to 2.4 when the H₂O/CH₄ molar ratio was increased from 0.23 to 0.65. This work demonstrates that the tri-reforming technology is feasible for converting biogas under scaled-up conditions in a fixed-bed reactor.     

Effect of CO2 in the feed stream on the deactivation of Co/γ-Al2O3 Fischer–Tropsch catalyst

The influence of CO₂ on the deactivation of Co/γ-Al₂O₃ Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO₂ in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO₂ acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al₂O₃ of 70 h, the CO conversion and C₅₊ selectivity in the presence of CO₂ decreased more significantly than in the absence of CO₂. CO₂ is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water.     

Properties of cold lake bitumen saturated with pure gases and gas mixtures

This paper presents new data for the viscosity, density and gas solubility of Cold Lake bitumen saturated with light gases and gas mixtures over a temperature range of 15 to 103°C at up to 10 MPa pressure. Specifically, the gases whose effects on the bitumen properties were measured are N₂, CH₄, CO₂ and C₂H₆, and two mixtures of CO₂ and CH₄. With CO₂ and C₂H₆, experiments were also performed in the liquid-liquid region, and the results of these experiments generally agree with the previously published predictions. The viscosity of the gas-free Cold Lake bitumen is comparable to that of a Marguerite Lake bitumen that was tested previously. Due to the large solubilities of C0₂ and C₂H₆, the reduction in gas-saturated bitumen viscosity is quite dramatic. The density of the gas-saturated bitumen decreases with increased amounts of the dissolved CH₄ and C₂H₆ gases, but no such trends are evident for the N₂ and CO₂ gases. The results of the experiments with two binary gas mixtures (i.e., CO₂ and CH₄) indicate that the bitumen properties are affected largely by the major gas constituent.     

Oxidation reaction kinetics of Athabasca bitumen

The oxidation reaction kinetics of bitumen from Athabasca oil sands have been investigated in a flow-through fixed bed reactor using gas mixtures of various compositions. The system was modelled as an isothermal integral plug-flow reactor. The oxidation of bitumen was found to be first order with respect to oxygen concentration. Two models were examined to describe the kinetics of bitumen oxidation. In the first, the Athabasca bitumen is considered to be a single reactant and the oxidation reaction a single irreversible reaction. The activation energy for the overall reaction was found to be 80 kJ mol^?1. This model is limited to calculating the overall conversion of oxygen. Because the fraction of oxygen reacting to form carbon monoxide and carbon dioxide increases with temperature, a more sophisticated model was proposed to take this into account. The second model assumes that the bitumen is a single reactant and that the oxidation of bitumen may be described by two simultaneous, parallel reactions, one producing oxygenated hydrocarbons and water, the other producing CO and CO₂. The activation energy for the first reaction was found to be 67 kJ mol^?1, and for the second, 145 kJ mol^?1. This more sophisticated model explains the result that at higher temperatures more oxygen is consumed in the oxidation of carbon, because this reaction has a higher activation energy than the reaction leading to the production of oxygenated hydrocarbons and water. This model can also predict the composition of the product gases at various reaction conditions.     

Hydroformylation of Cyclohexene with Carbon Dioxide and Hydrogen Using Ruthenium Carbonyl Catalyst: Influence of Pressures of Gaseous Components

Hydroformylation of cyclohexene was studied with a catalyst system of Ru₃(CO)₁₂ and LiCl using H₂ and CO₂ instead of CO in NMP. The influence of H₂ and CO₂ pressures on the total conversion and the product distribution was examined. It was shown that increasing total pressure of H₂ and CO₂ promoted the reverse water gas shift reaction and increased the yield of cyclohexanecarboxaldehyde. Its hydrogenation to cyclohexanemethanol was promoted with increasing H₂ pressure but suppressed with increasing CO₂ pressure. Cyclohexane was also formed along with those products and this direct hydrogenation was suppressed with increasing CO₂ pressure. The roles of CO₂ as a promoter as well as a reactant were further examined by phase behavior observations and high pressure FTIR measurements.     

Negative Effects of CO<Subscript>2</Subscript> in the Feed Stream on the Catalytic Performance of Precipitated Iron-Based Catalysts for Fischer–Tropsch Synthesis

Abstract  

Fischer–Tropsch synthesis was carried out over precipitated iron-based catalysts with different amounts of CO₂ in the feed stream while maintaining both total reaction pressure (1.5 MPa) and partial pressure of H₂ + CO (0.75 MPa) using an inert balance gas, N₂. The CO₂ in the feed stream decreased the rate of hydrocarbon formation, but it had no significant influence on the carbon number distribution of hydrocarbons. The CO₂ in the feed stream also suppressed CO₂ formation, decreasing both CO conversion and CO₂ selectivity. We attribute the decreased reaction rate to the partial competition in the adsorption behavior between CO and CO₂ as revealed in the temperature-programmed desorption.     

Characteristics of carbon dioxide hydrogenation in a fluidized bed reactor

Characteristics of CO₂ hydrogenation were investigated in a fluidized bed reactor (0.052 m IDxl.5 m in height). Coprecipitated Fe-Cu-K-Al catalyst (d_ρ=75–90 Μm) was used as a fluidized solid phase. It was found that the CO₂ conversion decreases but the CO selectivity increases, whereas the space-time-yield attains maximum values with increasing gas velocity. The CO₂ conversion has increased, but CO selectivity has decreased with increasing hydrogenation temperature, pressure or H₂/CO₂ ratio in the fluidized bed reactor. Also, the CO, conversion and olefin selectivity appeared to be higher in the fluidized bed reactor than those of the fixed bed reactor. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

Phase behaviour of CO2 -bitumen fractions

The phase behaviour of Cold Lake bitumen and its five fractions (or “cuts”) saturated with carbon dioxide is examined. The two lightest fractions (bp < 510°C) were clear liquids, whereas the third and fourth fractions were dark and viscous, i.e. much like the whole bitumen. The fifth fraction was a glass-like solid, with a softening temperature of approximately 100°C. The vapour-liquid equilibrium (VLE) data for the bitumen and bitumen fractions saturated with CO₂ were collected at temperatures from 25 to 150°C and pressures up to 10 MPa. Experiments were also performed at conditions under which pure CO₂ exists as a liquid. The VLE and LLE data were correlated with the Peng-Robinson equation of state by modeling each bitumen fraction as one pseudocomponent whose critical properties and acentric factor were estimated from correlations available in the literature. The CO₂-solubility and density data were used to develop generalized correlations for the critical pressure and the binary interaction parameter (k_ij) in terms of molar mass and critical temperature. The model was subsequently used to predict the solubility of CO₂ in the whole bitumen which was represented as a 5-component mixture. A correlation for Cut i-Cut j binary interaction parameter (k_ij) was developed in terms of temperature and the difference in hydrocarbon molar masses. The average deviation in the predicted and experimental CO₂-solubility in the whole Cold Lake bitumen was less than 7%.     

Slurry-phase CO2 hydrogenation to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst: Investigation of reaction conditions

The hydrogenation of CO₂ to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst was studied in a slurry reactor for the first time. Reducibility of the catalyst and effect of reaction variables (temperature, pressure and H₂/CO₂ ratio of the feed gas) on the catalytic reaction performance were investigated. The reaction results indicated that the Fe-Cu-Al/K catalyst showed a good CO₂ hydrogenation performance at a relatively low temperature (533 K). With the increase of reaction temperature CO₂ conversion and olefin to paraffin (O/P) ratio in C₂-C₄ hydrocarbons as well as the selectivity to C₂-C₄ fraction increased, while CO and CH₄ selectivity showed a reverse trend. With the increase in reaction pressure, CO₂ conversion and the selectivity to hydrocarbons increased, while the CO selectivity and O/P ratio of C₂-C₄ hydrocarbons decreased. The investigation of H2/CO₂ ratio revealed that CO₂ conversion and CH₄ selectivity increased while CO selectivity and O/P ratio of C₂-C₄ decreased with increasing H₂/CO₂ ratio.     

Direct synthesis of dimethyl ether from carbon-monoxide-rich synthesis gas: Influence of dehydration catalysts and operating conditions

Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO/ZnO system) with catalysts for methanol dehydration based on γ-Al₂O₃ or zeolites and γ-Al₂O₃ was identified as the most favorable dehydration catalyst. Various reaction parameters such as temperature, H₂/CO ratio and space velocity were studied. The impact of water on Cu/ZnO/Al₂O₃-γ-Al₂O₃ catalysts was investigated and no deactivation could be observed at water contents below 10% during running times of several hours. A running time of several days and a water content of 10% led to a significant increase of CO conversion but the water gas shift reaction became dominating and CO₂ was the main product. After termination of water feeding significant deactivation of the catalyst system was observed but the system returned to high DME selectivity. Catalyst stability and the influence of CO₂ in the gas feed were studied in experiments lasting for about three weeks. The presence of 8% of CO₂ caused an approximately 10% lower CO conversion and an about 5% lower DME selectivity compared to the reaction system without CO₂.     

Selective methanation of CO over supported Ru catalysts

The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO₂ has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al₂O₃, TiO₂, YSZ, CeO₂ and SiO₂). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H₂ 15% CO₂ and 0–30% H₂O (balance He). It has been found that, for all catalysts investigated, conversion of CO₂ is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO₂ methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO₂ hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO₂ catalysts, TOFs of both CO (at 215 °C) and CO₂ (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al₂O₃. Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO₂, compared to YSZ or SiO₂, whereas CeO₂- and Al₂O₃-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO₂ catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO₂ conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO₂ catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.     

Tuning product selectivity of CO2 hydrogenation by OH groups on Pt/γ-AlOOH and Pt/γ-Al2O3 catalysts

Herein, we explore how OH groups on Pt/γ-AlOOH and Pt/γ-Al₂O₃ catalysts affect CO₂ hydrogenation with H₂ at temperatures from 250°C to 400°C. OH groups are abundant on γ-AlOOH, but rare at Pt-(γ-AlOOH) interface which is the most favorable site for CO₂ conversion on Pt/γ-AlOOH. This makes CO₂ hydrogenation on Pt/γ-AlOOH form CO weakly bonding to γ-AlOOH, which prefers to desorption from Pt/γ-AlOOH rather than further conversion, thus enhancing CO production on Pt/γ-AlOOH. Different from Pt/γ-AlOOH, OH groups are abundant at Pt-(γ-Al₂O₃) interface which is the most favorable site for CO₂ conversion on Pt/γ-Al₂O₃. This promotes CO₂ hydrogenation on Pt/γ-Al₂O₃ to form CO strongly bonding to Pt, which prefers to further hydrogenation to CH₄, and thereby increases CH₄ selectivity on Pt/γ-Al₂O₃. Therefore, the OH groups at metal-support interface are crucial factor influencing product distribution, and must be considered seriously when fabricating catalysts.     

Role of CO/CO2 co-feeding in the dehydrogenation of cyclohexanol to cyclohexanone over Cu–ZnO based catalysts

The present work highlights the role of CO/CO₂ co-feeding in the dehydrogenation of cyclohexanol to cyclohexanone over Cu–ZnO–Cr₂O₃ and Cu–ZnO–Cr₂O₃–La₂O₃ catalysts in the temperature range of 448–523 K at atmospheric pressure under vapor phase conditions. Both the catalysts are prepared by coprecipitation technique and are characterized by BET surface area, XRD, TPR and N₂O pulse chemisorption under dynamic conditions. The co-feeding of CO/CO₂ along with cyclohexanol results in enhanced conversion of cyclohexanol and additional formation of methanol. The hydrogen generated in the dehydrogenation of cyclohexanol to cyclohexanone promotes the methanol formation from CO/CO₂. This is the first report where in methanol formation is observed at atmospheric pressure from CO/CO₂ co-feeding in cyclohexanol dehydrogenation.