Kinetic parameter estimation of the Fischer-Tropsch synthesis reaction on K/Fe-Cu-Al catalysts

This paper addresses the development of a mathematical model for a fixed-bed reactor where the Fischer-Tropsch synthesis reaction takes place. The model includes the consumption rate of carbon monoxide and the production rates for paraffin and olefin chains (up to the length of 47). The kinetic parameters are estimated using the experimental data under various experimental conditions with the effect of temperature, space velocity, the composition of feed mixture and pressure included. The simulation results with the estimated parameters predict the CO conversion, methane selectivity, paraffin selectivity and the entire distribution of hydrocarbon products satisfactorily. A further investigation on the effect of operating conditions shows that the ratio of hydrogen to carbon monoxide and the pressure are the effective variables for the determination of the entire distribution.     

一氧化碳等温变换技术进展

对现代合成氨CO变换技术中发展起来的不同种类的固定床等温反应器进行了比较 ,从转化率、操作稳定性、结构复杂程度及发展前景等方面进行了论述。特别分析了另一类等温反应器———流化床反应器的特点 ,并结合其在传热、传质、处理量及操作等方面的优势和流态化技术的发展。流化床反应器在CO变换过程中的工业化应用很有前景     

生物质合成气甲烷化与变换反应串联偶合新工艺

以模拟生物质合成气为原料,在固定床反应器中,对合成气甲烷化反应工艺条件进行优化,并在此反应中串联偶合水煤气变换反应,以此提高生物质合成气中碳氢的比例,从而弥补生物质合成气碳氢比较低的不足,使生物质合成气甲烷化反应更彻底,进而提高甲烷的收率。实验结果表明,在水煤气变换空速为15 000 h~(-1)、进水量0.02 m L·min~(-1)和还原温度为450℃条件下,甲烷化催化剂的性能最优,CO转化率100%,甲烷选择性对于整个偶合反应为50%,但就单一甲烷化反应高达99%。     

浆态床中二氧化碳加氢合成甲醇

研究了浆态床中自行开发的LP201甲醇合成催化剂上二氧化碳加氢合成甲醇的过程。探讨了不同操作条件,如温度、压力、气体空速、原料气配比等对反应的影响;考察了该催化剂在浆态床二氧化碳加氢合成甲醇过程中的稳定性。实验结果表明,浆态床二氧化碳加氢合成甲醇过程中主要产物为甲醇、CO和水;随温度的增加,CO2的转化率和甲醇产率呈现上升的趋势,但甲醇的选择性明显下降;压力的升高有利于CO2的转化率、甲醇产率以及甲醇的选择性提高;原料气空速的提高会增大甲醇产率,但同时降低CO2的转化率以及甲醇的选择性;CO2的转化率、甲醇收率以及甲醇的选择性在氢碳摩尔比4～5获得极大值。LP201催化剂的寿命考察结果表明,该催化剂具有较好的催化活性和稳定性。     

费托合成鼓泡浆态床反应器气体添加模拟研究

采用建立数学模型的方法在鼓泡浆态床反应器体系中讨论了气体添加对费托合成反应行为的影响。先采用惰性气体添加的方法找到最适合鼓泡塔反应器体系的气体添加模拟方法,在最优方法中,随气体添加相应改变总压和扩散高度以保持合成气分压和空速不变。采用该方法讨论了二氧化碳和烯烃对反应行为的影响。结果表明,随二氧化碳添加量的增加,合成气转化率降低,二氧化碳的添加使得总烯烷摩尔比增加,二氧化碳添加主要通过水煤气变换反应影响费托合成行为;烯烃添加将抑制小于其碳数的烃类的生成,促进大于其碳数的烃类的生成。     

Steam reforming of biogas over a Rh/Al2O3 catalyst in an annular microreactor

The article deals with the catalytic steam reforming of biogas of model composition into hydrogen and carbon monoxide over a Rh/γ-Al₂O₃ catalyst in an annular microchannel reactor. The reforming of biogas consisting of 60% methane and 40% carbon dioxide in a steam medium has been experimentally investigated under isothermal conditions while activating the reactions on the inner convex wall of the annular microchannel with a thin catalyst layer. The experiments have been performed at a residence time of 0.12 s, reactor temperatures of 750 and 860°C, and a water: biogas molar ratio of 0.8 to 3.1 in the feed. The range of water: biogas molar ratios maximizing the hydrogen yield has been determined for the model biogas. By changing the reactor temperature and water: biogas molar ratio, it is possible to widely vary the hydrogen: carbon monoxide molar ratio in the resulting synthesis gas.     

Steam reforming of methanol over a CuO/ZnO/Al2O3 catalyst part II: A carbon membrane reactor

The reaction of methanol steam reforming was studied in a carbon membrane reactor over a commercial CuO/ZnO/Al₂O₃ catalyst (Süd-Chemie, G66 MR). Carbon molecular sieve membranes supplied by Carbon Membranes Ltd. were tested at 150 °C and 200 °C. The carbon membrane reactor was operated at atmospheric pressure and with vacuum at the permeate side, at 200 °C. High methanol conversion and hydrogen recovery were obtained with low carbon monoxide permeate concentrations. A sweep gas configuration was simulated with a one-dimensional model. The experimental mixed-gas permeance values at 200 °C were used in a mathematical model that showed a good agreement with the experimental data. The advantages of using water as sweep gas were investigated in what concerns methanol conversion and hydrogen recovery. The concentration of carbon monoxide at the permeate side was under 20 ppm in all simulation runs. These results indicate that the permeate stream can be used to feed a polymer electrolyte membrane fuel cell.     

CFD analysis of water gas shift membrane reactor

Fuel cell based modular power generation can be achieved by miniaturization and process intensification of equipments in the process. Fuel cells require hydrogen rich gas which can be generated through reforming and water gas shift reaction. The water gas shift reactor being kinetically limited occupies more volume to achieve the required CO conversion. A membrane reactor integrates the reaction and hydrogen separation stages and hence reduces the volume requirement. Computational Fluid Dynamics offers virtual prototyping of the reactor and thus helps in design, optimization and scale up of reactors. In this study customized User Defined Functions (UDFs) were developed to analyze the performance of low temperature water gas shift membrane reactor. The models were validated using literature data for the parameters – synthesis gas compositions, time factor, sweep flow rate and steam to CO ratio. The effect of all these parameters on the reactor was analyzed for CO conversion, H₂ recovery, DaPe, concentration polarization, concentration profiles and conversion index. The simulations have showed that the UDFs developed were capable of simulating the membrane reactor and this can be used for the design and optimization of the membrane reactor for any process conditions.     

Enhancement of gasoline selectivity in combined reactor system consisting of steam reforming of methane and Fischer-Tropsch synthesis

A two-stage, one-dimensional configuration model including the steam reforming of methane (SRM) and Fischer-Tropsch (FT) synthesis has been developed for the production of hydrocarbons. This configuration is used to investigate hydrocarbon product distribution, such as gasoline. The first SRM reactor is fed by methane and steam, and the products are converted to hydrocarbons by the second FT reactor. The model was solved numerically by applying the finite difference approximation, and the set of first-order ODEs was solved in the axial direction. The results show that complete conversion of hydrogen in the second reactor can be achieved although a small amount of carbon monoxide remains. Furthermore, at higher H₂O/CH₄ ratio (and low CO in feed), lower C₂-C₅ yield and selectivity is obtained.     

Water Gas Shift in Microreactors at Elevated Pressure: Platinum-Based Catalyst Systems and Pressure Effects

A new lab-scale microstructured reactor was used for investigations on enhancing the H₂/CO ratio in synthesis gas from biomass feedstocks via the water gas shift reaction. A model mixture of carbon monoxide, carbon dioxide, water, and hydrogen was used to reproduce the typical synthesis gas composition from dry biomass gasification. Catalyst layers were prepared and characterized; a combined incipient wetness impregnation and sol–gel technology was applied. The catalytic activities of Pt/CeO₂ and Pt/CeO₂/Al₂O₃ films were determined at temperatures of 400–600 °C and pressures of up to 45 bars. Increased pressure leads to higher values of CO conversion and to increased formation of hydrocarbons (CH₄, C₂H₆, etc.) and coke. Methane is the main by-product, and coke formation was attributed to the catalytic activity of peripheral reactor components.     

Hydrodenitrogenation reaction of quinoline with nascent hydrogen generated from water gas shift reaction

The HDN of quinoline was investigated for the purpose of utilizing the hydrogen which could be generated from the water gas shift reaction (WGSR). The optimum concentration of hydrogen were produced under 1.5 of water to carbon monoxide mole ratio and 6 hr^-1 of space velocity at 390°C of temperature during WGSR over Co-Mo/γ-Al₂O₃ catalyst. The HDN reactions were compared by using the pure hydrogen and the nascent hydrogen which was produced by a WGSR. The pure hydrogen gave much higher activity in the overall HDN reaction than the nascent hydrogen. However, kinetic study on the hydrogenation, hydrogenolysis and cracking reaction steps showed that only at the cracking reaction step the nascent hydrogen gave the superiority to the pure hydrogen. This inferiority of the nascent hydrogen in overall HDN reaction could be resulted from the negative effect of water which should be accompanied during WGSR. The conversion of the HDN reaction was maximized at the water pressure of 150 kpa.     

Co‐current and Countercurrent Configurations for a Membrane Dual Type Methanol Reactor

A dynamic model for a membrane dual‐type methanol reactor was developed in the presence of catalyst deactivation. This reactor is a shell and tube type where the first reactor is cooled with cooling water and the second one with feed synthesis gas. In this reactor system, the wall of the tubes in the gas‐cooled reactor is covered with a palladium‐silver membrane which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. Moreover, the performance of the reactor was investigated when the reaction gas side and feed gas side streams are continuously either co‐current or countercurrent. Comparison between co‐current and countercurrent mode in terms of temperature, activity, methanol production rate as well as permeation rate of hydrogen through the membrane shows that the reactor in co‐current configuration operates with lower conversion and also lower permeation rate of hydrogen but with longer catalyst life than does the reactor in countercurrent configuration.     

A new process for synthesis gas by co-gasifying coal and natural gas

Production of synthesis gas with coal and natural gas co-gasification is a new process based on coupling of methane steam-reforming and coal gasification. The process concept is discussed in this paper. Experiments are carried out in a laboratory fixed-bed gasifying reactor to investigate the effect of feedstock on composition, ratio of hydrogen to carbon monoxide, concentrations of hydrogen and carbon monoxide in the produced raw synthesis gas. Preliminary experimental results indicate that the effect of steam flow rate on component, ratio of hydrogen to carbon monoxide and concentrations of hydrogen and carbon monoxide of the raw synthesis gas is slight, while the effect of oxygen flow rate is pronounced. When the ratio of oxygen to methane in feedstock is below 1, the ratio of hydrogen to carbon monoxide is greater than 1 and the total concentration of hydrogen and carbon monoxide is above 90%. Comparison of experimental results with calculated results shows that the composition of raw synthesis gas is near equilibrium.     

Carbon monoxide hydrogenation over cobalt catalyst in a tube-wall reactor: Part II. Modelling studies

A mathematical model was developed to predict the performance of Fischer-Tropsch Synthesis over cobalt catalyst in a tube-wall reactor. Comparison was made between model predictions and previous experimental results (part 1 of this paper) for pressures 0.35-1.03 MPa, temperatures 250?275°C, and exposure velocities 139-722 μ/s. The agreement was good. The model predicts an increase in methanation activity with temperature. Carbon monoxide and hydrogen conversions, and water and carbon dioxide concentrations increase along the reactor axis. With an increase in exposure velocity, hydrocarbons and carbon dioxide production increase, but water production decreases. However, the water-gas shift activity increases continuously along the reactor axis. The model is based on two-dimensional transport equations, and employs the orthogonal collocation method in its numerical predictions.     

PEM – Fuel Cell System for Residential Applications

Viessmann is developing a PEM fuel cell system for residential applications. The uncharged PEM fuel cell system has a 2 kW electrical and 3 kW thermal power output. The Viessmann Fuel Processor is characterized by a steam‐reformer/burner combination in which the burner supplies the required heat to the steam reformer unit and the burner exhaust gas is used to heat water. Natural gas is used as fuel, which is fed into the reforming reactor after passing an integrated desulphurisation unit. The low temperature (600 °C) fuel processor is designed on the basis of steam reforming technology. For carbon monoxide removal, a single shift reactor and selective methanisation is used with noble metal catalysts on monoliths. In the shift reactor, carbon monoxide is converted into hydrogen by the water gas shift reaction. The low level of carbon monoxide at the outlet of the shift reactor is further reduced, to approximately 20 ppm, downstream in the methanisation reactor, to meet PEM fuel cell requirements. Since both catalysts work at the same temperature (240 °C), there is no requirement for an additional heat exchanger in the fuel processor. Start up time is less than 30 min. In addition, Viessmann has developed a 2 kW class PEFC stack, without humidification. Reformate and dry air are fed straight to the stack. Due to the dry operation, water produced by the cell reaction rapidly diffuses through the electrolyte membrane. This was achieved by optimising the MEA, the gas flow pattern and the operating conditions. The cathode is operated by an air blower.     

A comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane dual-type FTS reactor in GTL technology

In this work, a comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane reactor for Fischer-Tropsch Synthesis (FTS) has been carried out. In both modes of operations, a system with two-catalyst bed instead of one single catalyst bed is developed for FTS reactions. In the first catalytic reactor, the synthesis gas is partly converted to products in a conventional water-cooled fixed-bed reactor, while in the second reactor which is a membrane fixed-bed reactor, the FTS reactions are completed and heat of reaction is used to preheat the feed synthesis gas to the first reactor. In the co-current mode, feed gas is entered into the tubes of the second reactor in the same direction with the reacting gas stream in shell side while in the counter-current mode the gas streams are in the opposite direction. Simulation results for both co-current and counter-current modes have been compared in terms of temperature, gasoline and CO₂ yields, H₂ and CO conversion, selectivity of components as well as permeation rate of hydrogen through the membrane. The results showed that the reactor in the co-current configuration operates with lower conversion and lower permeation rate of hydrogen, but it has more favorable profile of temperature. The counter-current mode of operation decreases undesired products such as CO₂ and CH₄ and also produces more gasoline.     

Mechanism of the partial oxidation of methane to synthesis gas on a silica-supported nickel catalyst

In the present study we investigated the mechanism involved in the partial oxidation of methane with oxygen to synthesis gas on a reduced silica-supported nickel catalyst in an isothermal fixed-bed reactor at temperatures up to 920 K. Firstly, the deep oxidation of methane with oxygen to carbon dioxide and water proceeds. Subsequently, the remaining part of the methane reacts with the initially formed water and carbon dioxide to synthesis gas. The final hydrogen-to-carbon monoxide ratio is determined by the water-gas shift conversion.     

Decomposition of polyethylene in radio-frequency nitrogen and water steam plasmas under reduced pressures

The possibility of radio-frequency (RF) nitrogen and water steam plasmas under reduced pressures for gasification of plastic waste as a thermal recycling method has been investigated in order to develop an innovative method for directly recycling plastic waste to hydrogen, synthesis gases or fuels. The products of pyrolysis were analyzed and classified into gaseous fraction and solid soot; and analytical interest was focused on the gaseous product composition. It was found that the electrode geometry, input power, reactor pressure and plasma working gas were the key parameters affecting the plasma characteristics and pyrolysis product. Experiments with different plasma media indicated that when polyethylene (PE) powder was injected into nitrogen plasma, the PE was decomposed and hydrogen formed as a main product by reaction with the plasma; when water steam plasma was used for conversion of PE, the carbon conversion to gas was dramatically enhanced in the presence of water steam, and the main gas products were carbon monoxide and hydrogen. Preliminary solid products analysis and pyrolysis mechanisms for the different plasmas processes were also discussed.     

Water Gas Shift Reaction in a Membrane Reactor Using a High Hydrogen Permselective Silica Membrane

A membrane reactor (MR) for the water gas shift (WGS) reaction was developed by integrating a highly hydrogen permselective silica membrane. The membrane was prepared using an extended counter-diffusion chemical vapor deposition (CVD) method. A tetramethylorthosilicate (TMOS) silica source was fed from one side of the membrane support and oxygen gas fed from the other. The dense silica film was deposited on a porous support by pressurizing the side that TMOS is supplied. A high hydrogen permselective silica membrane was obtained by this method. A commercial Pt catalyst was used in the WGS reaction. Efficacy of the silica membrane toward the WGS reaction was investigated as a function of temperature (523-623 K), steam/carbon monoxide (S/C) ratio (1-3), differential pressure (0-100 kPa), and gas hourly space velocity (GHSV; 1800-5400 h^?1). The CO conversion in the MR was higher than that for a fixed bed reactor (FBR) under all experimental conditions, and was also higher than the thermodynamic equilibrium conversion under almost all experimental conditions. This was due to the selective abstraction of hydrogen from the product stream by the silica membrane. At an S/C of 1.0, the CO conversion in the MR was superior to that in a FBR by 16.8%.