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Heterogeneous Catalysis for Organic Reactions

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This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel

This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication of which I am a co-author, as cited below.

Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.

Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.

This work is the subject of a publication of which I am a co-author, as cited below.

D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430

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2019-05

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Heat Transfer in a Rotary Drum Using Infrared Camera Temperature Measurement

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Rotary drums are commonly used for their high heat and mass transfer rates in the manufacture of cement, pharmaceuticals, food, and other particulate products. These processes are difficult to model because the particulate behavior is governed by the process conditions

Rotary drums are commonly used for their high heat and mass transfer rates in the manufacture of cement, pharmaceuticals, food, and other particulate products. These processes are difficult to model because the particulate behavior is governed by the process conditions such as particle size, particle size distribution, shape, composition, and operating parameters, such as fill level and rotation rate. More research on heat transfer in rotary drums will increase operating efficiency, leading to significant energy savings on a global scale.

This research utilizes infrared imaging to investigate the effects of fill level and rotation rate on the particle bed hydrodynamics and the average wall-particle heat transfer coefficient. 3 mm silica beads and a stainless steel rotary drum with a diameter of 6 in and a length of 3 in were used at fill levels of 10 %, 17.5 %, and 25 %, and rotation rates of 2 rpm, 6 rpm, and 10 rpm. Two full factorial designs of experiments were completed to understand the effects of these factors in the presence of conduction only (Case 1) and conduction with forced convection (Case 2). Particle-particle friction caused the particle bed to stagnate at elevated temperatures in Case 1, while the inlet air velocity in Case 2 dominated the particle friction effects to maintain the flow profile. The maximum heat transfer coefficient was achieved at a high rotation rate and low fill level in Case 1, and at a high rotation rate and high fill level in Case 2. Heat losses from the system were dominated by natural convection between the hot air in the drum and the external surroundings.

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2019

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Numerical Modeling and Experimental Studies on the Hydrodynamics and Heat Transfer of Silica Glass Particles

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Granular material can be found in many industries and undergo process steps like drying, transportation, coating, chemical, and physical conversions. Understanding and optimizing such processes can save energy as well as material costs, leading to improved products. Silica beads are

Granular material can be found in many industries and undergo process steps like drying, transportation, coating, chemical, and physical conversions. Understanding and optimizing such processes can save energy as well as material costs, leading to improved products. Silica beads are one such granular material encountered in many industries as a catalyst support material. The present research aims to obtain a fundamental understanding of the hydrodynamics and heat transfer mechanisms in silica beads. Studies are carried out using a hopper discharge bin and a rotary drum, which are some of the most common process equipment found in various industries. Two types of micro-glass beads with distinct size distributions are used to fill the hopper in two possible packing arrangements with varying mass ratios. For the well-mixed configuration, the fine particles clustered at the hopper bottom towards the end of the discharge. For the layered configuration, the coarse particles packed at the hopper bottom discharge first, opening a channel for the fine particles on the top. Also, parameters such as wall roughness (WR) and particle roughness (PR) are studied by etching the particles. The discharge rate is found to increase with WR, and found to be proportional to (Root mean square of PR)^(-0.58). Furthermore, the drum is used to study the conduction and convection heat transfer behavior of the particle bed with varying process conditions. A new non-invasive temperature measurement technique is developed using infrared thermography, which replaced the traditional thermocouples, to record the temperatures of the particles and the drum wall. This setup is used to understand the flow regimes of the particle bed inside the drum and the heat transfer mechanisms with varying process conditions. The conduction heat transfer rate is found to increase with decreasing particle size, decreasing fill level, and increasing rotation speed. The convection heat transfer rate increased with increasing fill level and decreasing particle size, and rotation speed had no significant effect. Due to the complexities in these systems, it is not always possible to conduct experiments, therefore, heat transfer models in Discrete Element Method codes (MFIX-DEM: open-source code, and EDEM: commercial code) are adopted, validated, and the effects of model parameters are studied using these codes.

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2020