Dual-membrane reactor for methane oxidative coupling and dry methane reforming: Reactor integration and process intensification

A novel dual-membrane reactor concept was introduced for integrating the oxidative coupling of methane (OCM) and CO₂ methane reforming (dry reforming) reactors. The OCM reactions occur in a conventional porous packed bed membrane reactor structure and a portion of the undesired produced CO₂ and generated heat are transferred through a molten-carbonate perm-selective membrane and consumed in the adjacent dry methane reforming catalytic bed. This integrated reactor provides a very promising thermal performance by controlling the temperature peak to be below 50 °C in reference to the average operating temperature in the OCM section. This was achieved even for the low methane-to-oxygen ratio 2 by introducing 10% CO₂ as the diluent agent and reactant in this integrated reactor structure. This contributed to the improved selective performance of 32% methane conversion and 25% C₂-yield including 21% C₂H₄-yield in the OCM section which also enhances the performance of the downstream units consequently. Around half of the unconverted methane leaving the OCM section was converted to syngas in the DRM section.The dual-membrane reactor alone can utilize a significant amount of the carbon dioxide generated in the OCM catalytic bed. In combination with adsorption unit in the downstream of the integrated process, 90% of the produced CO₂ can be recovered and further converted to valuable syngas products. The experimental data, obtained from a mini-plant scale experimental facility, were exploited to verify the performance of the OCM reactor and the CO₂ separation section.     

Targeting climate-neutral hydrogen production: Integrating brown and blue pathways with green hydrogen infrastructure via a novel superstructure and simulation-based life cycle optimization

This article addresses the sustainable design of hydrogen (H₂) production systems that integrate brown and blue pathways with green hydrogen infrastructure. We develop a systematic framework to simultaneously optimize the process superstructure and operating conditions of steam methane reforming (SMR)-based hydrogen production systems. A comprehensive superstructure that integrates SMR with multiple carbon dioxide capture technologies, electrolyzers, fuel cells, and working fluids in the organic rankine cycle is proposed under varying operating conditions. A life cycle optimization model is then developed by integrating superstructure optimization, life cycle assessment approach, techno-economic assessment, and process optimization using extensive process simulation models and formulated as a mixed-integer nonlinear program. We find that the optimal unit-levelized cost of hydrogen ranges from $1.49 to $3.18 per kg H₂. Moreover, the most environmentally friendly process attains net-zero life cycle greenhouse gas emissions compared to 10.55 kg CO₂-eq per kg H₂ for the most economically competitive process design.     

Hydrogen production via chemical looping dry reforming of methane: Process modeling and systems analysis

The present study presents and analyses a family of “chemical looping dry reforming” (CLDR) processes that produce inherently separated syngas (H₂ and CO) streams via a combination of methane cracking in a “cracker reactor” and the Boudouard reaction (i.e., conversion of the formed carbon with CO₂ to CO) in a “CO₂ reactor,” and then further maximize the H₂ yield via conversion of the produced CO via water-gas-shift. Remaining CO₂ emissions are minimized via CO₂ capture and sequestration. Four different configurations are evaluated which differ in how the heat required for the highly endothermic dry reforming reaction is supplied: (i) combustion of additional CH₄ feed (CLDR-CH₄); (ii) combustion of some of the CO produced in the CO₂ reactor (CLDR-CO); and combustion of some of the carbon produced in the cracker reactor with (iii) pure oxygen (CLDR-C-oxy); or (iv) with air (CLDR-C-air). Process models are developed to comparatively analyze the mass and energy balances of these configurations, and benchmark them against H₂-production via conventional dry reforming and steam reforming of methane. Our results show that CLDR-C-oxy is the most promising H₂-production pathway among the chemical looping and conventional technologies both in terms of chemical energy efficiency and in terms CO₂ emissions. Thus, the unique flexibility offered by the production of inherently separated syngas streams in CLDR enables overcoming the disadvantage of the strongly endothermic dry reforming reaction by combusting carbon internally in the reactor and thus achieving highly effective heat integration. Overall, the results support the technical viability and demonstrate the promise for strong process intensification of CLDR compared to conventional dry reforming and even steam reforming, the most widely used H₂-production pathway to-date.     

Simultaneous oxidative conversion and CO2 or steam reforming of methane to syngas over CoO–NiO–MgO catalyst

CO₂ reforming, oxidative conversion and simultaneous oxidative conversion and CO₂ or steam reforming of methane to syngas (CO and H₂) over NiO–CoO–MgO (Co: Ni: Mg=0·5: 0·5:1·0) solid solution at 700–850°C and high space velocity (5·1×10⁵ cm³ g⁻¹ h⁻¹ for oxidative conversion and 4·5×10⁴ cm³ g⁻¹ h⁻¹ for oxy-steam or oxy-CO₂ reforming) for different CH₄/O₂ (1·8–8·0) and CH₄/CO₂ or H₂O (1·5–8·4) ratios have been thoroughly investigated. Because of the replacement of 50 mol% of the NiO by CoO in NiO–MgO (Ni/Mg=1·0), the performance of the catalyst in the methane to syngas conversion process is improved; the carbon formation on the catalyst is drastically reduced. The CoO–NiO–MgO catalyst shows high methane conversion activity (methane conversion >80%) and high selectivity for both CO and H₂ in the oxy-CO₂ reforming and oxy-steam reforming processes at ⩾800°C. The oxy-steam or CO₂ reforming process involves the coupling of the exothermic oxidative conversion and endothermic CO₂ or steam reforming reactions, making these processes highly energy efficient and also safe to operate. These processes can be made thermoneutral or mildly exothermic or mildly endothermic by manipulating the process conditions (viz. temperature and/or CH₄/O₂ ratio in the feed). © 1998 Society of Chemistry Industry     

Hydrogen from steam methane reforming by catalytic nonthermal plasma using a dielectric barrier discharge reactor

A scaled-up dielectric barrier discharge (DBD) reactor has been developed and demonstrated for the production of hydrogen from steam methane reforming (SMR) by catalytic nonthermal plasma (CNTP) technology. Compared to SMR, CNTP offers conversion at ambient pressure (101.325 kPa), low temperature with better efficiency, making it suitable for distributed hydrogen production with small footprint. There have been several lab-scale DBD reactors reported in the literature. Dimension of the scaled-up DBD reactor is about six times the lab-scale version and can produce 0.9 kg H₂/day. The scale-up is, however, nonlinear; several technical innovations were required including spray nozzle for homogeneous introduction of steam, perforated tube central electrodes for generation of homogeneous plasma. Conversion efficiency of the scaled-up DBD reactor is 70–80% at 550°C and 500 W. A continuous run of 8 hr was demonstrated with typical product gas composition of 69% H₂, 6% CO₂, 15% CO, 10% CH₄.     

Effect of catalyst activity in SMR-SERP for hydrogen production: Commercial vs. large-pore catalyst

In this work, we have evaluated the performance of an SMR-SERP unit (steam methane reforming sorption enhanced reaction process), using two different Ni/Al₂O₃ catalysts: commercial “Octolyst 2001” from Degussa and a large-pore catalyst (Catalyst A). The selective CO₂ sorbent was a potassium modified hydrotalcites. Several experiments were performed under different operating conditions to validate a mathematical model.Experimental results show that the Degussa catalyst is more active and more selective to CO₂ producing hydrogen with higher purity and less CO than the large-pore catalyst. Cyclic SMR-SERP experiments were also performed. The cycles comprise four different steps: reaction, depressurization, reactive regeneration and pressurization. In the cyclic experiments, conversion was 43% higher than in an SMR reactor, while H₂ purity was 75%, which is 25% higher than in normal SMR operation. Results indicate that more active catalysts also promote a better reactive regeneration optimizing the use of part of the product (H₂). The proposed mathematical model was validated in a wide range of operating conditions and in a cyclic experiment. The model was able to describe the SMR-SERP experiments without any fitting parameters.     

气煤联供实现资源高效利用和碳减排技术进展

为解决煤化工过程资源利用率低和碳排放高的问题,有研究者提出以天然气、焦炉气、页岩气等富氢资源和煤炭资源联供方案,旨在实现源头碳减排。文章指出依据联供过程技术的差异,较有代表性的方案可分为集成甲烷部分氧化和集成甲烷干/水蒸气重整的气煤联供过程。文章以生产甲醇为例,从资源利用和经济效益等方面对集成甲烷部分氧化和集成甲烷干/水蒸气重整的气煤联供过程进行分析和比较。集成甲烷部分氧化的工艺碳元素利用率达到57.9%,每吨甲醇排放CO₂为1.50t,较传统煤制甲醇工艺排放减少37.5%。甲醇产品成本稍低于传统工艺。集成甲烷干/水蒸气重整工艺的碳元素利用率最高,达到83.7%。减排效果最明显,每吨甲醇排放CO₂为0.90t,较传统工艺排放减少62.5%,但是由于CO₂转化增加能耗,甲醇产品成本有所提升。由于气煤联供过程有利于CO₂减排,当碳税高于65CNY/tCO₂时,两个气煤联供工艺的生产成本低于传统的煤制甲醇工艺。     

Hydrogen production by sorption-enhanced steam methane reforming process using CaO-Zr/Ni bifunctional sorbent–catalyst

A bifunctional CaO-Zr/Ni (13, 18, and 20.5 wt% NiO) sorbent–catalyst was developed using the wet-mixing/sonication technique and applied for hydrogen production by sorption-enhanced steam methane reforming (SESMR), an intensified process that integrates hydrogen production with CO₂ capture. The material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N₂ physisorption (BET). CO₂ sorption efficiency of the developed materials was evaluated during 25 CO₂ sorption/regeneration cycles. The prepared sorbent–catalysts were then applied in the SESMR during 10 reaction cycles. The results showed that the bifunctional sorbent–catalyst with 20.5 wt% NiO loading presented the most suitable activity. The H₂ yield of ∼91% at the end of the 10th SESMR cycle is considerably higher than equilibrium H₂ yield that could be obtained by traditional steam methane reforming.     

Doped Ni Catalysts for Methane Reforming with CO<Subscript>2</Subscript>

Pb, Sb, Bi and Te doped Ni catalysts were prepared and used for methane reforming with CO₂ in order to diminish coke deposition. It was found that small amounts of Pb doped Ni catalysts exhibited excellent coke resistance ability with minor loss of the reforming activity. As the added amount of Pb increased from 0 to 0.015 (mole ratio between Pb/Ni), coke formation rate decreased from 166.7 mg-coke/g-cat h (on Ni/SiO₂) to 0, while the reforming activity decreased slightly from 73.2% to 63.3% (conversion of CO₂) at 800 °C, 60,000 ml(STP)/g-cat·h (CH₄ CO₂=1:1, no dilution gas in feed). Higher amounts of Pb and Sb, Bi, Te made Ni catalyst deactivated for methane reforming with CO₂.     

An efficient technique for improving methanol yield using dual CO2 feeds and dry methane reforming

Steam methane reforming (SMR)-based methanol synthesis plants utilizing a single CO₂ feed represent one of the predominant technologies for improving methanol yield and CO₂ utilization. However, SMR alone cannot achieve full CO₂ utilization, and a high water content accumulates if CO₂ is only fed into the methanol reactor. In this study, a process integrating SMR with dry methane reforming to improve the conversion of both methane and CO₂ is proposed. We also propose an innovative methanol production approach in which captured CO₂ is introduced into both the SMR process and the recycle gas of the methanol synthesis loop. This dual CO₂ feed approach aims to optimize the stoichiometric ratio of the reactants. Comparative evaluations are carried out from a techno-economic point of view, and the proposed process is demonstrated to be more efficient in terms of both methanol productivity and CO₂ utilization than the existing stand-alone natural gas-based methanol process.     

Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts

A partial oxidation of methane was carried out using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H₂O and CO₂, followed by the reforming of methane from CO₂ and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity for the reforming of methane from CO₂ was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO₂ with iridium catalysts was as follows: TiO₂≧ZrO₂≧Y₂O₃>La₂O₃>MgO≧Al₂O₃>SiO₂. The same order was observed in the synthesis gas production from the partial oxidation of methane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Innovative steam methane reforming for coproducing CO-free hydrogen and syngas in proton conducting membrane reactor

Steam methane reforming (SMR) is a commercial process to produce syngas. Normally, the as-produced syngas is characterized by a H₂/CO ratio of 3. However, such H₂/CO ratio is unsuitable for Fischer–Tropsch synthesis. The hydrogen obtained by subsequent upgrading of syngas usually contains residual CO, which readily deactivates Pt electrocatalysts in fuel cells. Here we report an innovative route by coupling SMR with H₂ removal in a proton conducting membrane reactor to coproduce syngas with a preferable H₂/CO ratio of 2 and CO-free H₂ on opposite sides of the membrane, which can be directly used for Fischer–Tropsch synthesis and fuel cells, respectively. Notably, H₂ is in-situ extracted by the membrane that only allows the permeation of H₂ as protons through the oxide lattice with infinite selectivity, and thus the obtained H₂ is CO-free. This work could provide an alternative option in one-step conversion of methane into two inherently separated valuable chemicals.     

Evaluation of the economic and environmental impact of combining dry reforming with steam reforming of methane

Lately, there has been considerable interest in the development of more efficient processes to generate syngas, an intermediate in the production of fuels and chemicals, including methanol, dimethyl ether, ethylene, propylene and Fischer–Tropsch fuels. Steam methane reforming (SMR) is the most widely applied method of producing syngas from natural gas. Dry reforming of methane (DRM) is a process that uses waste carbon dioxide to produce syngas from natural gas. Dry reforming alone has not yet been implemented commercially; however, a combination of steam methane reforming and dry reforming of methane (SMR + DRM) has been used in industry for several years.     

Pure hydrogen generation in a fluidized-bed membrane reactor: Experimental findings

A pilot-scale fluidized-bed membrane reactor was tested for the production of hydrogen. The prototype reactor operated under steam methane reforming (SMR) and autothermal reforming (ATR) conditions, without membranes and with membranes of different total areas. Heat was added either externally or via direct air addition. Hydrogen permeate purity of up to 99.995+% as well as a pure-H₂-to-natural-gas yield of 2.07 were achieved with only half of the full complement of membrane panels active under SMR conditions. A permeate-H₂-to reactor natural gas feed molar ratio >3 was achieved when all of the membrane panels were installed under SMR conditions. Experimental tests investigated the influence of such parameters as reactor pressure, hydrogen permeate pressure (vacuum vs atmospheric pressure), air top/bottom split, feed flowrate and membrane area. Reactor performance was strongly dependent on the active membrane surface area.     

Enhanced stability of a direct-methane and carbon dioxide protonic ceramic fuel cell with a PrCrO3 based reforming layer

Dry reforming of methane (CH₄ + CO₂ = 2CO + 2H₂) is a very interesting approach both to reduce the overall carbon footprint of the increasing worldwide fossil-based methane consumption as well as to cut emission greenhouse gas of CO₂. Utilizing the produced syngas as fuel directly in protonic ceramic fuel cell can further kill two birds with one stone: obtain power output and high purity CO. However, the drawback of the coking deposition limits the process of the above strategy. Here, we synthesis a Ni-based catalyst with high conversion rates (∼88% for CO₂ and ∼89% for CH₄) and excellent stability (>160 h at 700 °C) proceeded by Ce doping, and further employ it as reforming layer on solid oxide fuel cell. The results demonstrate that the Ce substitution plays an important role for homogenous Ni nanoparticles exsolution, benefiting for the coking resistance of the catalyst then the stability of the cell using CH₄ and CO₂ as fuel directly.     

Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield

A new process to integrate coal pyrolysis with CO₂ reforming of methane over Ni/MgO catalyst was put forward for improving tar yield. And several Chinese coals were used to confirm the validity of the process. The experiments were performed in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer to investigate the effect of pyrolysis temperature, coal properties, Ni loading and reduction temperature of Ni/MgO catalysts on tar, water and char yields and CH₄ conversion at fixed conditions of 400 ml/min CH₄ flow rate, 1:1 CH₄/CO₂ ratio, 30 min holding time. The results indicated that higher tar yield can be obtained in the pyrolysis of all four coals investigated when coal pyrolysis was integrated with CO₂ reforming of methane. For PS coal, the tar, water and char yield is 33.5, 25.8 and 69.5 wt.%, respectively and the CH₄ conversion is 16.8%, at the pyrolysis temperature of 750 °C over 10 wt.% Ni/MgO catalyst reduced at 850 °C. The tar yield is 1.6 and 1.8 times as that in coal pyrolysis under H₂ and N₂, respectively.     

Process intensification aspects for steam methane reforming: An overview

Steam methane reforming (SMR) is the most widely used process in industry for the production of hydrogen, which is considered as the future generation energy carrier. Having been perceived as an important source of H₂, there are abundant incentives for design and development of SMR processes mainly through the consideration of process intensification and multiscale modeling; two areas which are considered as the main focus of the future generation chemical engineering to meet the global energy challenges. This article presents a comprehensive overview of the process integration aspects for SMR, especially the potential for multiscale modeling in this area. The intensification for SMR is achieved by coupling with adsorption and membrane separation technologies, etc., and using the concept of multifunctional reactors and catalysts to overcome the mass transfer, heat transfer, and thermodynamic limitations. In this article, the focus of existing and future research on these emerging areas has been drawn. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Response Surface Optimization of Hydrogen-Rich Syngas Production by Greenhouse Gases Reforming

The effect of process interaction and response surface optimization of hydrogen-rich syngas production by catalytic carbon dioxide (CO₂) reforming of methane (CH₄) was evaluated. The Box-Behnken design was applied to investigate the influence of CH₄ partial pressure, CO₂ partial pressure, and temperature on the hydrogen yield. The analysis of variance indicated that temperature and CH₄ partial pressure had the most significant impact on the hydrogen yield. Under optimum conditions a maximum hydrogen yield of 71.38 % was achieved. Model validation with the ideal conditions confirmed close agreement of the predicted hydrogen yields with experimental values.     

Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane

Supported nickel catalysts with core/shell structures of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al₂O₃ and MgO-Al₂O₃, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al₂O₃ and Ni/MgO-Al₂O₃ yielded methane conversions of 92% and 92.5%, respectively and CO₂ conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH₄/CO₂ = 1. Those were near thermodynamic equilibrium values.     

Acid-base properties and the directions of oxidative transformation of methane over nickel-based catalysts

The reactions of dry (CO₂) reforming and partial oxidation of methane have been investigated in a membrane reactor. The membrane is composed of a dense thin silica (SiO₂) film supported on porous Vycor tubes and was synthesized by chemical vapor deposition. The hydrogen permeance of the membrane was 0.2–0.3 cm³/(cm² min atm) at 600°C combined with a H₂/N₂ selectivity of 200–300. Significant increases in methane conversion were attained in both reactions at 500–750°C, albeit at very low space velocities. The membrane permeance declined by 50% after exposure to feeds containing H₂O, but otherwise exhibited excellent stability under reaction conditions.