(368w) Liquid Metal Catalysts As a Robust Medium for Hydrocarbon Processing

Hydrocarbons are an integral part of our daily lives and a key driver of the global economy. They are used in the synthesis of fertilizers, pharmaceuticals, specialty chemicals, and a wide range of consumer goods. However, processing of hydrocarbons, typically catalyzed by heterogeneous (solid) catalysts is challenged by catalyst deactivation due to coke formation resulting from deep dehydrogenation at the elevated process temperatures. Various strategies, including the integration of catalyst regeneration steps into the process, have been developed to counter catalyst deactivation during continuous production. In severe cases, catalytic processes are entirely abandoned. An illustrative example is the steam cracking of ethane to ethylene, which to this day continues to be a non-catalytic process due to the rapid deactivation of catalysts. The inability to use a catalyst for this process and hence the necessity to operate at high-temperature conditions, renders steam cracking the second largest greenhouse gas emitter in the entire chemical industry. It is for these reasons that we are exploring liquid metals as an alternative, robust catalytic reaction medium.

Liquid metals, i.e. metals with melting points typically below ~300^oC, have recently emerged as a novel reaction medium. Among many interesting properties, such as very high thermal and electronic conductivity, they are characterized by an exceptional resistance to coking due to their ability to effectively separate coke from the bulk of the liquid metal based on their density differences. This ability positions liquid metals as a promising solution to combat catalyst deactivation during hydrocarbon processing, enabling continuous operation and removal of coke without disrupting the production process.

My research project explores the use of liquid metals as an innovative catalytic reaction medium for hydrocarbon processing, focusing specifically on two processes with large existing and emerging industrial relevance: ethane dehydrogenation (EDH) and plastic waste pyrolysis.

In a first step, we investigated the use of liquid bismuth as a non-catalytic "carbon filter" for ethane dehydrogenation, with the aim of eliminating the need for steam addition and for periodic reactor shutdowns to remove coke deposits. Our experimental investigations, coupled with detailed homogeneous gas phase simulations, demonstrated that liquid bismuth can indeed serve as an effective coke filter, eliminating the need for steam in this process while achieving competitive conversion and selectivity benchmarks.

Next, we alloyed bismuth with catalytically active metals in order to demonstrate that liquid bismuth can be activated for EDH via addition of small amounts of transition metals. Notably, we found that using a molten NiBi catalyst resulted in a remarkable reduction in deactivation rate by six orders of magnitude compared to solid Ni catalysts. In parallel to screening different liquid alloys for their activity and selectivity in EDH, we are now exploring fundamental questions regarding liquid metal catalysis, including catalytic effects associated with the phase transition from solid to liquid.

In the long run, we aim to decarbonize the liquid-metal catalyzed EDH process via electrification using inductive heating. Concurrently, we are conducting a life cycle assessment (LCA) to evaluate the environmental impact associated with liquid metal catalysts. Our preliminary results for an electrified, non-catalytic liquid bismuth system show a reduction in the global warming potential impact associated with ethylene production by more than 50% compared to conventional steam cracking processes.

Building on the insights gained from EDH, we have now started to apply liquid metal catalysis to more complex feedstocks, in particular polyurethane and polycarbonate plastics. Here, we conduct catalytic pyrolysis of these polymers in liquid metals to leverage the uniformity and robustness of the catalytic reaction medium they offer. Initial results confirm the catalytic activity of liquid metals in these pyrolysis reactions and indicate the possibility to reduce the pyrolysis temperature by >100°C compared to non-catalytic pyrolysis, as well as the potential to narrow the product distribution.

Overall, my research project aims to advance our understanding of liquid metal catalysis and its potential applications in hydrocarbon processing, paving the way for novel, more sustainable, robust and efficient catalytic processes.

Research Interests

1. Catalysts and reactor design and optimization

My primary focus has been on designing liquid metal catalyst reactors for catalytic studies and using conventional solid catalyst synthesis methods, such as colloidal synthesis and galvanic replacement, to create monodisperse nanoalloys with uniform composition, aimed at understanding the catalytic effects associated with the liquid phase transition from the solid phase. Additionally, I have utilized detailed homogeneous gas phase simulations to better understand gas phase reactions in liquid metal reactors. During my internship at H-Quest Vanguard, I applied these gas phase simulation techniques to optimize commercial-scale reactors. I am interested in applying these techniques to various chemical processes with the goal of promoting sustainable catalytic processes.

2. Sustainable process development

My interest extends beyond fundamental studies of catalyst design and performance to overall process performance, particularly in terms of sustainability. I have used lifecycle assessment to guide catalyst selection during my PhD project and am eager to further explore sustainable process development by focusing on process intensification and life cycle assessments.

3. Decarbonization of chemical processes

Decarbonization through electrification is a part of my PhD thesis, and I am interested to pursue its application in the chemical industry as we move towards a more sustainable future.