(337ad) Towards Enhanced Yield of Commodity Chemicals: Acrylonitrile and Ethylene Synthesis

Acrylonitrile (ACN) is the precursor to polyacrylonitrile (PAN), which can in turn be manufactured into acrylic fiber or carbon fiber (CF). CF is used in many applications due to its lightweight and high tensile strength nature. As the demand for CF is growing rapidly, manufacturing capacity of ACN is bound to increase. Traditional steady-state operation (SSO) of ACN production methods are capital intensive. An alternative for ACN prodiction that provides quicker response to market demand is small-scale forced dynamic operation (FDO).

In FDO, the reactor is operated such that the composition is periodically changed to achieve enhanced product selectivity and yield. In this work, we use FDO in ammoxidation of propene over transition metal promoted bismuth molybnate oxide (BMO). FDO schemes with changing composition of reactant gases (C3H6, NH3 and O2) and conditions (cycle period, duty cycle) were tested to identify the best pathway in improving ACN yield. We found a higher than steady state ACN productivity in an FDO scheme that periodically switches between the normal feed and an O2 feed. So-called ACN “spikes” at the transition between FDO phases indicate FDO parameters could be adjusted such that the time-averaged ACN yield can exceed those of SSO. We also found that the dynamic oxygen storage capacity (DOSC) of the BMO-based catalysts correlates with ACN productivity in FDO. By tuning promoter element ratios, the FDO performance can be optimized.

Ethane dehydrogenation to ethylene on Pt-Zn intermetallic nanocatalysts:

Ethylene is an important building block for many value-added chemicals, including polymers (polyethylene), oxygenates (ethylene glycol), and chemical intermediates (ethylbenzene). Steam cracking of crude oil byproducts (Naphtha) is the most common ethylene production method. It involves vaporizing Naphtha at high temperature (750~1100 °C) using superheated steam, and pyrolysis of Naphtha takes place in externally heated furnaces. Naphtha is cracked into smaller molecules without catalysts thus leading to the formation of light alkenes (e.g., ethylene, propylene, butene). Naturally, the low selectivity to ethylene, energy intensity and shrinking oil reserves are limitations on this production method. Catalytic dehydrogenation of ethane (DHE) to ethylene is a production method that yields exclusively the desired alkene of polymer-quality purity rather than a mixture of products.

In this work we synthesized silica supported Pt3Zn1 and Pt1Zn1 intermetallic nanocatalysts by sequential deposition of ZnO via atomic layer deposition (ALD) and Pt via incipient wetness impregnation (IWI) on SiO2. The synthesis method was examined using standard characterization techniques as well as synchrotron X-ray absorption spectroscopy (XAS) under hydrogen reduction conditions. We revealed that ZnO reduction is a key step in the synthesis of Pt1Zn1 phase by providing a detailed picture of Pt and Zn speciation kinetics under H2 reduction via in-situ XAS. Silica supported Pt3Zn1, Pt1Zn1, and Pt monometallic nanocatalysts were tested in DHE, the electronic and geometric effects on the catalytic performance of PtZn intermetallic nanocatalysts are discussed thoroughly. The Pt1Zn1 intermetallic nanocatalysts exhibited improved selectivity and a production rate one order of magnitude greater than those of supported Pt and Pt3Zn1 with similar Pt loading and particle sizes for the dehydrogenation of ethane. Enhanced catalyst stability was also observed.

Research Interests:

My research to date has been focused on nanomaterial synthesis and catalytic conversion of light hydrocarbons. To study the material property-catalytic performance relationship in heterogeneous catalysis is always my goal. I studied Pt-Zn intermetallic nanocatalysts for the dehydrogenation of ethane in my Ph.D years, to deepen the understanding of Pt isolated sites in alkene dehydrogenation in atomic-scale synthesis. And now I am mainly on developing a small-scale/modular process - forced dynamic operation in acrylonitrile production on bismuth molybdate-based catalysts, in my post-doc studies, exploring ways to enhance productivity with unsteady-state, dynamic processes. I also serve a supporting role in a project that uses FDO in the partial oxidation of methane to syngas. New pathways in commodity chemical synthesis via catalytic conversion of light hydrocarbon has been my focus.