Senior Capstone: MOF Synthesis
Designed and integrated a dual-phase effluent reactor for continuous flow synthesis of metal-organic frameworks (MOFs) using supercritical CO2.
Overview
The Problem
Traditional MOF synthesis uses batch processes with low scalability potential. A continuous flow system was needed to increase production capacity, but required solving complex challenges in fluid dynamics, mixing efficiency, and particle collection.
The Solution
Designed a specialized reactor system that utilizes supercritical CO2 as both a heating and mixing medium, with separate effluent collection capabilities for both gas and liquid states to optimize crystal formation.
Key Outcomes
- •Successfully synthesized HKUST-1 MOF
- •Designed and integrated a larger volume reactor into the existing lab setup
- •Demonstrated different crystallization outcomes between gas and liquid collection methods and variable flow rates
My Role
Lead Mechanical Engineer
(Team of 3)
Project Gallery
Research poster presented at the UW Mechanical Engineering EXPO
Summary presentation delivered to our lab group upon project completion
Full system in operation during MOF synthesis
Gaseous effluent collection
Liquidous (left) vs. gaseous collection (right) showing different macroscale crystallization outcomes
SEM microscopy image of synthesized HKUST-1 MOF crystals from high flow rate gaseous effluent
Design Challenges & Solutions
Nozzle Clogging and Atomization
Small diameters of atomization nozzles frequently clogged with precursor materials due to crystallization prior to injection into the reactor.
Comprehensive Nozzle Testing
We conducted extensive nozzle testing with air, water, and MOF precursors under different pressures and flow rates to determine the usable conditions under which the system could operate while maintaining the reaction in the proper thermodynamic state.
Multi-phase Flow Dynamics
The flow behavior of supercritical CO2 mixed with ethanol solutions containing metal and organic precursors created complex fluid dynamics that affected particle formation.
Precise Flow Rate Calculation
Precise calculations and control of flow rates were crucial to ensure proper mixing while maintaining the supercritical state.
Residence Time Optimization
MOF crystallization requires specific residence times within the reactor for proper crystal growth. Too short and crystals wouldn't form properly; too long and the system could clog or the delicate crystals could be destroyed.
Counterintuitive Flow Rate Discovery
Again, careful reactor volume calculations and flow rate tuning were crucial. Through experimentation, higher flow rates were found to produce better results than lower flow rates. This counterintuitive finding informed our final operational parameters.
Efficient Particle Collection
Many synthesized particles would adhere to reactor walls rather than flow through to collection, particularly traditional liquidous effluents at low flow rates.
Dual-Phase Collection System
We implemented separate collection paths for gaseous and liquidous phases, which revealed that gas-collected particles showed more developed crystal structures. Our reactor geometry facilitated this ability using top & bottom outlets working with and against gravity to further separate phases. This discovery provided valuable insights for future research and optimization.
Impact & Results
Impact
The project successfully demonstrated continuous flow synthesis of HKUST-1 metal-organic frameworks using supercritical CO2 as both a heating and mixing medium. Our findings on the differences between gas and liquid collection methods provided valuable insights for future research in MOF synthesis optimization. The reactor system will continue to be used by the research group for advanced materials development.
Synthesis Success
Successfully synthesized HKUST-1 MOF with characteristic crystalline structure confirmed via SEM
System Integration
Fully integrated reactor into existing laboratory setup with pressure and temperature control
Research Advancement
Generated new knowledge about collection methods and their effects on crystal structure
Key Takeaways
- Practical application of thermodynamic principles and supercritical fluid behavior in reactor design
- Importance of systematic testing and willingness to pivot approach when facing technical challenges
- Relationship between flow dynamics, residence time, and crystallization outcomes in continuous synthesis
- Value of multiple collection methods for optimizing different aspects of product quality
- Cross-disciplinary collaboration between mechanical engineering and chemical synthesis research
Skills Developed
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