Production of hydrogen and carbon nanotubes from methane decomposition in a two-stage fluidized bed reactor

Methane decomposition over a Ni/Cu/Al₂O₃ catalyst is studied in a two-stage fluidized bed reactor. Low temperature is adopted in the lower stage and high temperature in the upper stage. This allows the fluidized catalysts to decompose methane with high activity in the high temperature condition; then the carbon produced will diffuse effectively to form carbon nanotubes (CNTs) in both low and high temperature regions. Thus the catalytic cycle of carbon production and carbon diffusion in micro scale can be tailored by a macroscopic method, which permits the catalyst to have high activity and high thermal stability even at 1123 K for hydrogen production for long times. Such controlled temperature condition also provides an increased thermal driving force for the nucleation of CNTs and hence favors the graphitization of CNTs, characterized by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and XRD. Multistage operation with different temperatures in a fluidized bed reactor is an effective way to meet the both requirements of hydrogen production and preparation of CNTs with relatively perfect microstructures.     

Conversion of hydrogen chloride to chlorine by catalytic oxidation in a two-zone circulating fluidized bed reactor

A two-zone circulating fluidized bed reactor comprising an oxychlorination zone and a chlorination zone significantly improved the conversion of HCl to Cl₂. A supported catalyst for the process composed of 5% of copper, and promoters K in a molar ratio of K to Cu of one and 2.5% CeCl was highly active and stable. The optimal operation temperatures are 390-400 °C in the oxychlorination zone and 200-240 °C in the chlorination zone. A higher conversion of HCl can be obtained with a lower WHSV of HCl and a lower HCl/O₂ molar ratio, but the height of the reactor must be high enough.     

Oxidative coupling of methane in a bubbling fluidized bed reactor

The oxidative coupling of methane to higher hydrocarbons (C₂₊) was studied in a bubbling fluidized bed reactor between 700°C and 820°C, and with partial pressures of methane from 40 to 70 kPa and of oxygen from 2 to 20 kPa; the total pressure was ca 100 kPa. CaO, Na₂CO₃/CaO and PbO/γ-Al₂O₃ were used as catalytic materials. C₂₊ selectivity depends markedly on temperature and oxygen partial pressure. The optimum temperature for maximizing C₂₊ selectivity varies between 720 and 800°C depending on the catalyst. Maximum C₂₊ selectivities were achieved at low oxygen and high methane partial pressures and amounted to 46% for CaO (T = 780°C; P_CH4 = 70 kPa; P_O2 = 5 kPa), 53% for Na₂CO₃/CaO (T = 760°C; P_CH4 = 60 kPa; P_O2 = 6 kPa) and 70% for PbO/γ-Al₂O₃ (T = 720°C; P_CH4 = 60 kPa; P_O2 = 5 kPa). Maximum yields were obtained at low methane-to-oxygen ratios; they amounted to 4.5% for CaO (T = 800°C; P_CH4 = 70 kPa; P_O2 = 12 kPa), 8.8% for Na₂CO₃/CaO (T = 820°C; P_CH4 = 60 kPa; P_O2 = 20 kPa) and 11.3% for PbO/γ-Al₂O₃ (T 2= 800°C; P_CH4 = 60 kPa; P_O2 = 20 kPa).     

Characterization of nanofibrous carbon produced at pilot-scale in a fluidized bed reactor by methane decomposition

Carbon nanofibers (CNFs) production in the range of hundreds of grams per day has been achieved in a fluidized bed reactor (FBR) by methane decomposition using a nickel based catalyst. The characterization of the carbon produced at different operating conditions (temperature, space velocity and the ratio of gas flow velocity, u_o, to the minimum fluidization velocity, u_mf) has been accomplished by means of X-ray diffraction (XRD), N₂ adsorption, temperature-programmed oxidation (TPO), scanning electron microscope (SEM) and transmission electron microscopy (TEM). It has been concluded that the structural and textural properties of the CNFs obtained in the FBR are analogous to the ones obtained in a fixed bed reactor at a production scale two orders of magnitude lower. Thus, FBR can be envisaged as a promising reaction configuration for the catalytic decomposition of methane (CDM), allowing the production of high quantities of CNFs with desirable structural and textural properties.     

Design of a two-stage fluidized bed reactor for preparation of diethyl oxalate from carbon monoxide

In this study, a two-stage fluidized bed reactor (TS-FBR) was designed as a new technology to produce diethyl oxalate (DEO) from carbon monoxide (CO) based on the catalytic coupling reaction. Computational fluid dynamics (CFD) approach was adopted to obtain the detailed flow field, the bubble behaviors in the TS-FBR, and further demonstrate the feasibility of the TS-FBR used in producing DEO from CO. Furthermore, the whole preparation process of DEO from CO using the optimum TS-FBR as the central unit is simulated using an advanced software tool, realizing the proper matching of coupling reaction and regeneration reaction. As a result, the realization of the whole preparation process is presented.     

Partial oxidation of methane in a multistage-compression chemical reactor

A theory of noncatalytic partial oxidation of methane in a superadiabatic cyclic compression chemical reactor using the operating principle of internal combustion engine is developed. It is shown that in a two-stroke reactor the conversion of methane to syngas with a H₂/CO ratio equal to 2 reaches 0.95 to 0.99 at low mixture compression ratios of 10 to 15. The energy efficiency (product-yield-to-power ratio) reaches 3 m³ of syngas per 1 kWh of power consumed.     

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     

Reduction of sodium sulphate with hydrogen in a fluidized bed reactor

Reduction of sodium sulphate to sulphide with hydrogen was studied in a batch fluidized bed reactor. The principal difficulty was fusion of the particles, as some melting was found to be present in the practical range of temperatures. Fusion and agglomeration were minimized by pre-heating the gas, increasing particle size, and recycling some reduced material. Reaction rates were studied at 649 to 732°C., and an empirical rate equation was fitted to the data. Possible explanations of the rate equation are discussed: changes in reactive surface area, perhaps by a blocking mechanism, appear to be significant.     

A simplified mathematical modeling for thermo-catalytic decomposition of methane over carbon black catalyst in a fluidized bed reactor

A mathematical model for thermo-catalytic decomposition of methane over carbon black catalysts in a fluidized bed was proposed. The simplified isothermal, uniform flow model was considered and implemented into a computer code to predict the reactor performance. The experiment of methane decomposition into hydrogen and carbon was carried out in a fluidized bed of I.D of 0.055 m and height of 1.0 m. The range of reaction temperature was 850–900 °C, gas velocity was 1.0–3.0 U _mf , and catalyst loading was 50–200 g. The reaction parameters for model equation were determined from the curve fittings and the comparison of experimental data with simulation results showed good agreement for fluidized bed reactor system. From the simulation results, the fluidized bed performance with different operating conditions were obtained, and this simple model can be used to predict the performance of a larger scale fluidized bed reactor and also in determining the optimum operating conditions.     

Hydrogen production by the thermocatalytic decomposition of methane in a fluidized bed reactor

CO₂-free production of hydrogen via thermocatalytic decomposition of methane in a fluidized bed reactor (FBR) was studied. The technical approach is based on a single-step decomposition of methane over carbon catalyst in air/water vapor free environment. The factors affecting Fe catalyst (Iron powder activity in methane decomposition reactions were examined. Carbon species produced in the process were characterized by SEM methods. The fluidization quality in a gas-fluidized bed of Fe (Iron powder) and Fe/Al₂O₃ catalyst was determined by the analysis of pressure fluctuation properties, and the results were confirmed with characteristics of methane decomposition. The effect of parameters on the H₂ yield was examined. Fibrous carbon formed over Fe catalyst surface. The hydrogen yield increased with increasing reactor temperature, and decreased with increasing superficial velocity of methane inlet stream. The conversion rate of methane is maintained by attrition of produced carbon on Fe catalyst surface in a FBR.     

Partial oxidation of methane using a microscale non-equilibrium plasma reactor

A flow-type, microscale, non-equilibrium plasma reactor was developed for partial oxidation of methane without a catalyst. A wide range of oxygen and methane mixtures was directly processed without dilution or explosion at ambient temperature because the microscale plasma reactor removes excess heat generated by partial oxidation, thereby maintaining a reaction field at temperatures near room temperature. Consequently, the least reactive methane was excited by high-energy electrons, whereas successive destruction of reactive oxygenates was minimized simultaneously within the extremely confined environment. A highly reactive and quenching environment is thereby obtained within a single reactor: these are paradoxical conditions in conventional thermochemical processes. A major product among liquid oxygenates was methanol, whose selectivity reached 34% at 30% of methane conversion. Selectivity of oxygenates such as methanol and formaldehyde depends strongly on the fragmentation pattern of methane dissociation by electron impact. Maximum selectivity of oxygenates, which is estimated from numerical simulation of a filamentary microdischarge, reaches 60% when the applied electric field corresponds to the breakdown field of methane (80 Td, 1 Td = 10⁻¹⁷ V cm²). The discharge current increases markedly with an applied electric field, but the selectivity of oxygenates decreases as the field strength increases.     

Catalytic oxidation of hydrogen chloride in a fluid bed reactor

The Deacon reaction (HCI + 1/4 O₂ ⇋ 1/2 Cl₂ + 1/2 H₂O) was studied in a catalytic fluid bed reactor. Reaction rates found from measurements in differential and integral reactors were represented by the Langmuir-Hinshelwood type rate equation. Considering the effect of catalysts in the dilute phase, it was found that conversions in a fluid bed reactor can be calculated without any modifying parameters. It is pointed out that the wake fraction, which has been necessary to consider for fast reactions in a fluid bed reactor, is attributed to the dilute phase effect.     

A fluidized bed membrane reactor for the steam reforming of methane

In the present investigation a realistic two-phase model accounting for the change in the total number of moles accompanying the reaction is utilized to explore a novel reactor configuration suggested for the methane steam reforming process. The suggested design is basically a fluidized bed reactor equipped with a bundle of membrane tubes. These tubes remove the main product, hydrogen, from the reacting gas mixture and drive the reaction beyond its thermodynamic equilibrium. The proposed novel design is also equipped with sodium heat pipes which act as a thermal flux transformer to provide the large amount of heat needed by the endothermic reaction through a relatively small heat transfer surface, assuring better reactor compactness. Two options for fluid routing through the membrane tubes are proposed; each is suitable for a certain industrial application. The performance of this novel configuration is compared with that of an industrial fixed bed steam reformer and the comparison shows the potential advantages of the suggested configuration.     

Partial oxidation of methane in a chemical compression reactor with heat regeneration

A method for noncatalytic partial oxidation of methane in a chemical compression reactor with heat regeneration is proposed and the appropriate theory is developed. A reactor is considered that uses the operating principle of an internal combustion engine with a heat regenerator that is located in the channel of a combined exhaust and intake manifold, through which reaction products and reactants alternately pass. Calculations have shown that this method makes it possible to implement noncatalytic conversion of methane in methane-air mixtures with the content of a hydrocarbon of up to 24% at ratios of compression of 14–30 and a maximum process pressure of no more than 10 MPa. The composition of the reaction products in the field of existence of a regenerative cycle as a function of the initial composition of the mixture, the compression ratio, and the crankshaft speed is found. It is shown that the degree of methane conversion can reach above 97% and, in this case, useful power is produced     

Photocatalytic oxidation of ethyl alcohol in an annulus fluidized bed reactor

The photocatalytic oxidation of ethyl alcohol vapor in an annulus fluidized bed reactor of 0.06 m I.D. and 1.0 m long was examined. The TiO₂ catalyst employed was prepared by the sol-gel method and was coated on the silica gel powder. The UV lamp was installed at the center of the bed as the light source. The effects of the initial concentration of ethyl alcohol, the power of UV-lamp, the photocatalysts with different preparation methods, and the superficial gas velocity on the reaction rate of ethyl alcohol decomposition were determined. It was found that, at 1.2 U_mf of flow rate, about 80% of ethyl alcohol was decomposed with initial concentration of 10,000 ppmv and the increase of superficial gas velocity reduced the reaction rate significantly.     

Oxidative methane conversion to carbon monoxide and hydrogen at low reactor wall temperatures over ruthenium supported on silica

Oxidative methane conversion to carbon monoxide and hydrogen is catalyzed over ruthenium supported on silica at reactor wall temperatures as low as 400° C when the flow rate of reactants (methane and oxygen) is significantly high. The conversion of methane and the yields of carbon monoxide and hydrogen increase with increase in the flow rate of the reactants while oxygen is always completely consumed. Addition of carbon dioxide to the reactant flow can increase the yield of carbon monoxide in the reaction, suggesting that carbon dioxide functions as an oxidant and the actual surface temperature of the catalyst is sufficiently high that thermal conversion of methane via carbon dioxide and water can take place.     

基于Ba-Ce-Co-Fe-O膜反应器的甲烷部分氧化反应研究

为开发稳定性和透氧量俱佳并适用于甲烷部分氧化反应(POM)的透氧膜材料,采用溶胶凝胶工艺合成了具有纯相钙钛矿结构的BaCe0.1Co0.4Fe0.5O3-δ混合导体陶瓷材料。POM操作结果表明:BaCe0.1Co0.4Fe0.5O3-δ膜反应器透氧量高于同类材料,875℃时透氧量达到了8.9 mL/(cm2.m in)。在1 000 h寿命实验中,膜反应器各项反应指标没有出现任何衰减,反应性能稳定,甲烷转化率和CO的选择性都在97%以上。SEM表征表明,反应后膜片表面微观结构的变化虽然不可避免,但是其仍然保持比较完整的结构。因此,该材料良好的透氧量和稳定性说明其具有较好的应用前景。     

Propenoxide isomerization in a fluidized bed reactor

Propenoxide isomerization, over lithium orthophosphate as a catalyst, was investigated in a fluidized bed reactor. A mathematical model of the process was developed and its kinetic parameters identified. There is a high degree of selectivity for allyl alcohol.     

Pure hydrogen generation in a fluidized bed membrane reactor: Application of the generalized comprehensive reactor model

A generalized comprehensive model was developed to simulate a wide variety of fluidized-bed catalytic reactors. The model characterizes multiple phases and regions (low-density phase, high-density phase, staged membranes, freeboard region) and allows for a seamless introduction of features and/or simplifications depending on the system of interest. The model is implemented here for a fluidized-bed membrane reactor generating hydrogen. A concomitant experimental program was performed to collect detailed experimental data in a pilot scale prototype reactor operated under steam methane reforming (SMR) and auto-thermal reforming (ATR) conditions, without and with membranes of different areas under diverse operating conditions. The results of this program were published in Mahecha-Botero et al. [2008a. Pure hydrogen generation in a fluidized bed membrane reactor: experimental findings. Chem. Eng. Sci. 63(10), pp. 2752-2762]. The reactor model is tested in this second paper of the series by comparing its simulation predictions against axially distributed concentration in the pilot reactor. This leads to a better understanding of phenomena along the reactor including: mass transfer, distributed selective removal of species, interphase cross-flow, flow regime variations, changes in volumetric flow, feed distribution, and fluidization hydrodynamics. The model does not use any adjustable parameters giving reasonably good predictions for the system of study.     

Elemental mercury vapor capture by powdered activated carbon in a fluidized bed reactor

A bubbling fluidized bed of inert material was used to increase the activated carbon residence time in the reaction zone and to improve its performance for mercury vapor capture. Elemental mercury capture experiments were conducted at 100 °C in a purposely designed 65 mm ID lab-scale pyrex reactor, that could be operated both in the fluidized bed and in the entrained bed configurations. Commercial powdered activated carbon was pneumatically injected in the reactor and mercury concentration at the outlet was monitored continuously. Experiments were carried out at different inert particle sizes, bed masses, fluidization velocities and carbon feed rates. Experimental results showed that the presence of a bubbling fluidized bed led to an increase of the mercury capture efficiency and, in turn, of the activated carbon utilization. This was explained by the enhanced activated carbon loading and gas-solid contact time that establishes in the reaction zone, because of the large surface area available for activated carbon adhesion/deposition in the fluidized bed. Transient mercury concentration profiles at the bed outlet during the runs were used to discriminate between the controlling phenomena in the process. Experimental data have been analyzed in the light of a phenomenological framework that takes into account the presence of both free and adhered carbon in the reactor as well as mercury saturation of the adsorbent.