Fuel processor based on syngas production via short contact time catalytic partial oxidation reactors

Short contact time catalytic partial oxidation (SCT-CPO) of natural gas is a promising technology for syngas production, representing an appealing alternative to existing processes. The high conversion and selectivity observed since the earlier works in this field can make this process attractive. Moreover, the SCT-CPO reactors can be autothermally operated and the possibility to use air as oxidant appears a feasible route to reduce syngas production costs: these two issues make possible the use of a SCT-CPO reactor as the reformer of a fuel processor for H₂ production for fuel cells.

The present work refers to an experimental study of syngas production from CH₄ and O₂ via a SCT-CPO reactor made of a fixed bed of Rh/-Al₂O₃ spheres. The main obtained results are: (i) an increase in GHSV produces an enhancement of transport rates and this in turn determines an improvement in CH₄ conversion, despite the reduction in residence time; (ii) the catalyst pellets get hotter than the gas phase thus favouring the H₂ and CO production; syngas formation is in fact both thermodynamically and kinetically promoted at high temperatures; (iii) a similar improvement of conversion was obtained with a reduction of the catalyst particle size, thanks once again to an increase in the heat transport and a higher geometrical surface area of the catalyst itself. By a slight increase of the O₂ fed to the reactor, H₂ and CO yields can be maximised and a complete CH₄ conversion achieved.     

Conversion of methane to syngas in a solid oxide fuel cell with Ni-SDC anode and LSGM electrolyte

A solid oxide fuel cell constructed from Ni-SDC anode and LSGM electrolyte was applied to the partial oxidation of methane to syngas (CO+H₂) at 700-800 °C with the merits of co-generation of electricity and controllable O₂ supply. It was found that the co-generated syngas at H₂/CO ratio of 1.4-2.0 varied with applied current densities, CH₄ flow rates and operating temperatures. The cell voltage at 100 mA cm⁻² and 800 °C was 0.90 V, i.e. about 90 mW cm⁻² power density could be obtained. The cell operating at 50 mA cm⁻² for 24 h almost showed no degradation of the cell performance. The observed carbon deposition seemed mainly taking place by CH₄ cracking reaction.     

Investigation on the partial oxidation of methane to syngas in a tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane reactor

A perovskite material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al₂O₃ catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO₂ reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm² min oxygen permeation flux.     

三相床中合成气一步法制二甲醚

在反应温度 2 30～ 2 70℃、压力 2～ 5MPa下 ,以医药用石蜡油为惰性液相介质 ,使用C30 2铜基催化剂和CM - 3- 1改性分子筛组成的复合催化剂 ,在三相搅拌釜中研究了合成气 (CO、CO2 、H2 )一步法合成二甲醚的反应。结果表明随着温度的升高 ,碳的转化率增加 ,二甲醚的选择性提高 ,甲醇的选择性降低 ;随着压力的增加 ,碳的转化率升高 ,二甲醚的选择性提高 ,甲醇的选择性降低     

Effect of reactor internal properties on the performance of a flow reversal catalytic reactor for methane combustion

This paper describes the use of a flow reversal reactor for the destruction of lean emissions of methane with ambient temperature feed. The reactor consisted of two parallel sections, each containing a packed bed reactor and inert sections to act as heat traps. In this paper, the effect on reactor performance of the inert properties is illustrated. Three different inert types are described. These are a ceramic monolith of 100 cells per square inch cell density, a metal monolith and a packed bed of Denstone balls. Use of monolith inserts reduces the reactor pressure drop. Inert sections with lower thermal mass give rise to greater movement in temperature fronts, requiring the use of shorter cycles.     

甲烷部分氧化制合成气反应中床层热点问题研究进展

综述了甲烷部分氧化制合成气反应中催化剂床层热点问题,包括热点产生的原因,热点位置的测定,热点温度的影响因素,以及热点问题的解决方法,对于保护催化剂和反应器,降低反应的危险性起到借鉴作用.     

Performance of a catalytic membrane reactor for the Fischer–Tropsch synthesis

The study of permeable composite monolith (PCM) membranes for the Fischer–Tropsch synthesis is continued. On the scale of membranes with outer diameter of 42 mm, it is proved that PCM can combine high productivity of hydrocarbons (>55 kg_C5+ ( h)⁻¹ at 0.6 MPa, 484 K), high selectivity towards heavy hydrocarbons (_ASF > 0.85, C₅₊ upto 0.9) as well as high heat-conductivity and high mechanical strength.     

Experimental and modeling analysis of the effect of catalyst aging on the performance of a short contact time adiabatic CH4-CPO reactor

Catalytic partial oxidation of methane at short contact time was studied in a lab-scale packed bed reactor over a 0.5 wt% Rh/A₂O₃ catalyst. Experiments were focused on the investigation of catalyst stability and durability upon repeated start-up/shut-down tests at different inlet temperatures and flow rates. Measurements of the axial temperature profiles evidenced a high sensitivity of the steady state thermal behavior of the reactor on catalyst activity: a decrease of the intrinsic catalytic activity was interpreted as the cause of a progressive over-heating of the bed which, in turn, moderated the loss of methane conversion and syngas productivity. At sufficiently high flow rate the observed temperature rise spread along the whole catalytic bed. Under such conditions both steady state and dynamic reactor performances were affected by the progressive decay of catalyst activity. A rationalization of the observed results was pursued by applying a one dimensional (1D) heterogeneous model of the reactor to the quantitative analysis of experimental results. Model predictions revealed the occurrence of operating surface temperatures up to 1100 °C and allowed to quantify the progressive worsening of reactor performances in terms of a loss of reforming activity localized in correspondence of the catalyst hot spot.     

Preliminary design and simulation of a microstructured reactor for production of synthesis gas by steam methane reforming

The present study considers the potentials of the well-known production of syngas by steam methane reforming (SMR), by operation within microstructured reactors. The model of a microchannel reactor is developed, including very fast kinetic reaction rates on the coated catalytic walls of the reactor module. By varying the characteristic dimensions of the channels, and considering technical constraints on the design and operating conditions, the results demonstrate that the SMR reactor can be drastically miniaturized while maintaining its productivity without any additional pressure drop. Furthermore, by reducing the channel characteristic dimensions, it is possible to suppress heat and mass-transfer limitations enabling SMR reactor operation at thermodynamic equilibrium. A fast method for preliminary design of microstructured heat-exchanger reactors is developed, that enables to identify the optimal channels number and heat power needed to reach process specifications.     

A study of Nusselt and Sherwood numbers in a monolith reactor

A two-dimensional model of a single channel of a monolith reactor is used to evaluate the values of the Nusselt and Sherwood numbers under reaction conditions. The circular channel is assumed to have axisymmetry with a first-order reaction occurring at the wall. The values of the Nusselt and Sherwood numbers do not correlate uniquely with the Graetz number but rather depend on the reaction rate at the wall. Hence they depend on such variables as gas velocity, inlet temperature and reactant concentration.     

Effect of structural, thermal and flow parameters on steam reforming of methane in a catalytic microreactor

Steam reforming of methane in microchannels, embedded in a monolith is numerically modelled. Horizontal heating layers at equal intervals within the monolith are maintained at constant temperature. The channels are coated internally with catalyst to enhance gas–solid heterogeneous reaction. The numerical method combines the analytical solution for heat transfer through a fin, extended to a stack of fins, and the reactive flow of gases through an iterative procedure. The method offers a tool for quick design of a micro-structure, without considering detailed CFD-based model. In addition, the method can be suitably modified to address thermal management in electronic chip.The temperature within a stack between two heating layers drops near the centre of the stack, in case of an endothermic reaction. This drop, signifying the deviation from isothermal behaviour is found more near the heating layer, and tapers off near the centre of the stack. When the feed temperature is significantly less than the temperature of the heating layer, the portion of the reactor, away from the heating layer remains at a substantially lower temperature, particularly when the number of channels between two heating layers is large. Accordingly, the conversions in the individual channels at the outlet are affected. If the channel wall becomes thicker, the drop in fluid temperature away from the heating layer is more. The increase in feed velocity leads to larger drop in temperature and overall conversion. The decrease in thermal conductivity and the increase in number of channels between two heating layers enhance the temperature drop. None of these functionalities appears to be linear.     

Natural gas conversion to liquid fuels in a zone reactor

A process for conversion of natural gas to liquid fuels is described. The process can be conducted in a “zone reactor” in which oxygen or air is first contacted with solid metal bromide, producing bromine and metal oxide. The bromine passes into a second zone, in which it reacts with natural gas, producing alkyl bromides and hydrogen bromide. The products of the second zone pass into a third zone, in which they react with metal oxide, producing metal bromide and liquid product. At the end of the cycle the oxygen feed and product streams are switched and the flow reversed. The advantages of the process including safety and capital cost reduction are presented and results discussed.     

Conversion of CH<Subscript>4</Subscript> and CO<Subscript>2</Subscript> to syngas and higher hydrocarbons using dielectric barrier discharge

The conversion of methane to syngas and other hydrocarbons in dielectric barrier discharge plasma under the presence of CO₂ was investigated. Effects of the input voltage on the conversion of methane and CO₂ and the ratio of syngas were analyzed experimentally. The results of numerical simulations showed good quantitative agreement with those of experiments.     

Combustion of toluene-hexane binary mixtures in a reverse flow catalytic reactor

This work is focused on the application of reverse flow reactors to the combustion of lean mixtures of aliphatic and aromatic hydrocarbons in air. For this purpose, hexane and toluene were chosen as model compounds. The combustion of binary mixtures of these compounds (up to 500 ppmV total hydrocarbon concentration) over a commercial Pt/Al₂O₃ catalyst in reverse flow reactors has been studied both experimentally, in a bench-scale unit, and by simulations, using a heterogeneous mono-dimensional dynamic model, good correspondence being observed between both approaches.As general trend, it was observed that the behaviour of the reactor is determined mainly by the combustion enthalpies and reactivities of toluene and hexane. Hence, increasing total concentration and increasing fraction of toluene (the most reactive compound) lead to more stable operation. Regarding the kinetic inhibition effects, in the conditions studied no influence on the reactor performance was observed, probably because the hydrocarbons combust in different reactor zones. This behaviour can be extended to the combustion of aromatic and C₅-C₈ alkanes, characterised by their relatively low concentrations (determined by their vapour pressure) and high reaction rates.     

Mixed reforming of heptane to syngas in the Ba0.5Sr0.5Co0.8Fe0.2O3 membrane reactor

Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al₂O₃ catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃ which has an oxygen permeation flux around 11.5 ml/cm² min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al₂O₃ in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H₂ selectivity of 95–97% have been achieved.     

A compact and high throughput reactor of monolithic‐structured catalyst bed for conversion of syngas to liquid fuels

Syngas conversion is needed for the production of liquid fuels and/or chemicals from renewable or remote feedstock at capacities much smaller than the conventional Fischer–Tropsch (F–T) plant. Here, we present a multiscale‐engineered, modular‐type design approach toward the development of a compact reactor unit to make syngas‐to‐liquids economically feasible at small scales. The fundamental design idea is tested by using a Re‐Co/alumina catalyst coated on a monolith support of channel size about 0.9 mm. One‐pass CO conversion (92–98%) with <10% of CH₄ selectivity is obtained with the structured bed under typical F–T reaction conditions. The gas superficial linear velocity was found as one critical parameter that may allow scale‐up of the hydrodynamics from the small‐scale laboratory tests directly to practical sizes of the reactor with the proposed design strategy. A pore wetness and surface perspiration model is proposed to explain the experimental data and rationalize the new design concepts. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Simulation of biomass char gasification in a downdraft reactor for syngas production

A steady state, one‐dimensional computational fluid dynamics model of wood char gasification in a downdraft reactor is presented. The model is not only based on reaction kinetics and fluid flow in the porous char bed but also on equations of heat and mass conservation. An original OpenFOAM solver is used to simulate the model and the results are found to be in good agreement with published experimental data. Next, a sensitivity analysis is performed to study the influence of reactor inlet temperature and gas composition on char conversion, bed temperature profile and syngas composition. In addition, the evolution of the complex reaction mechanisms involved in mixed atmosphere gasification is investigated, and the most suitable operating parameters for controlling syngas composition are evaluated. Our simulation results provide essential knowledge for optimizing the design and operation of downdraft gasifiers to produce syngas that meets the requirements of various biofuel applications. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1079–1091, 2016     

Off-line optimization and control for real time integration of a three-phase hydrogenation catalytic reactor

In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO₂.