Dry Reforming of Methane (DRM) is a relatively new process technology that provides economic and environmental incentives for several industries that rely heavily on Hydrogen (H₂) and syngas (H₂ and Carbon Monoxide (CO)) utilization. The process utilizes Carbon Dioxide (CO₂) and Natural Gas, containing mainly Methane (CH₄), as a feedstock to produce H₂ and CO. Hydrogen intensive applications and syngas processing facilities benefit mostly by generating new revenue streams as well as achieving a reduced overall carbon footprint of their operations, since CH₄ and CO₂ are both powerful greenhouse gases. This process can be considered on a reactive basis to treat flue gases and emitted streams rich in CO₂, and it also can be a proactive approach to eliminating CO₂ emissions before they occur. The focus in this work is on the latter approach, where DRM, deposited on a low-pressure monolith, is being studied as a relatively new process to produce a pure H₂ gas stream (+99.9% purity) while maintaining carbon neutrality and prove its superiority to the dominating technology today; Steam Methane Reforming (SMR) which utilizes steam (H₂O) as a reactant instead of CO₂, and reacts with Natural Gas to produce H₂ and CO, however, they are accompanied by a large generation of CO₂ emissions.
A comprehensive life cycle assessment (LCA) analysis was conducted to compare both technologies, DRM and SMR, and has demonstrated the feasibility of DRM in almost all environmental impact categories with a significant reduction in CO₂ equivalent emissions. This study assessed the performance of SMR and DRM in various indicators, including energy consumption, air emissions, global warming potential, water consumption, wastewater production, solid catalyst utilization and solid waste production. Although DRM requires higher energy in the reformer, its overall energy consumption is lower than SMR since steam generation needed is only roughly one third that of SMR. Harmful components released by DRM in air emissions are lower in all categories which reduces global warming potential to a large extent and in particular, CO₂ is reduced by approximately 61% when compared with SMR. Since SMR relies heavily on steam input and cooling purposes, water consumption and wastewater generation indicators are more adverse compared to DRM. This outcome acts as a strong driver to invest more in this research field and accelerate commercialization of this process technology.
The research focus around DRM has been studied for over 20 years focusing on landfill gas (CO₂:CH₄ with a ratio of 0.8) and only few commercial testing facilities exist as of today due to major catalyst stability drawback, due to excess CH₄ causing coking issues. While most of the research body is considering DRM to process landfill gas, this research work has found out that by moving to a coke-free regime, the catalyst retains excellent initial stability properties. Thermodynamic analysis demonstrated that ratios of CO₂:CH₄ equal to and greater than 1.5, solid carbon no longer thermodynamically forms, and indeed, the experimental studies have confirmed the same conclusion evident by stable catalyst performance. Both Nickle (Ni) and Rhodium (Rh) in powder forms exhibited excellent activity and stability levels under a CO₂:CH₄ ratio of 1.5. This was the first and most important stepping stone in constructing a solid argument supporting DRM as a stable process with great potential for commercialization. This ratio is possible when separate sources of CO₂ and CH₄ are available and thus ratios can be adjusted unlike in landfills where CH₄ is always in excess. The work continued in performing several parametric experiments and screening multiple catalysts with different metal loadings. Three active metals were tested, Ni, Rh, and Ruthenium (Ru), and the results concluded that the most promising formulations are 10% Ni on Alumina (Al2O3) and 1% Rh on Al₂O₃. Those were further investigated in details for artificially aging by intentionally forming coke and successfully regenerated by steam gasification. The catalysts were coked and regenerated to essentially fresh activity.
Commercial SMR is operated with a packed-bed reactor design and utilizing catalysts (most commonly Ni on alpha Al₂O₃.) in the form of pellets and rings, which lead to large pressure drops and ultimately large reactor design and increased energy requirements. To help overcome the design challenges, this research work has considered monolithic catalysts for testing and scale-up purposes. Monoliths, with their high open frontal areas and large geometric surface areas, overcome the challenges of high pressure drop, experienced in pellets, exhibit solid mechanical strength and provide large geometric surface areas of catalysts (washcoat) contact for reactions to take place, and hence, significantly reduce reactor sizes and eventually, overall capital and operating costs. The monolithic catalysts were prepared by washcoating 10% Ni and separately 1% Rh, both on gamma Al₂O₃. on their walls. The same parametric studies conducted for powders were tested for monolithic catalysts, and the results were positively surprising. Monolithic catalysts possessed extremely high activities, far better than all powders tested even at higher loadings. Moreover, their excellent stability results provide a possible road to a more compact reactor design. One conclusion; monolithic catalysts, or washcoated structured reactors as known in industry, are strong competitors that have the potential to deliver superior results when compared to packed-bed reactors. Therefore, this research is proposing the use of monolithic catalysts working under the favorable thermodynamic environment, as a potential solution to accelerate DRM advanced testing for H₂ production.
To further support the thesis argument, a basic process design of the DRM was carried out to understand the various compositions of streams and the material and energy requirements for a feasible commercial plant. The design resembled very closely that of an SMR plant with the major difference in the main reactor, known as the “Reformer”. With this data on hand, a financial modelling was constructed to preliminarily prove the feasibility of this technology when compared to competitors in the market. Consequently, when compared to SMR with and without carbon capture (CC), DRM achieved relatively low H₂ prices in the range of 1.07-1.32 $/kg in the case of a Methanator design case and up to 1.91 $/kg for the CC design case, while SMR exceeded 2.1 $/kg for sustainable H₂ production; indicating that DRM, on preliminary basis, is a very profitable process technology. In conclusion, the laboratory research work combined with process design and financial feasibility, strongly supports the grounds of recommending DRM as a viable H2 production technology for a future pilot plant testing and advancement for commercialization. A more detailed engineering design and financial assessment would provide more accurate results after the successful pilot plant testing.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/n5cv-rc82 |
| Date | January 2022 |
| Creators | Alkhani, Anas Farkad |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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