Generation of Hydrogen Peroxide in CO2 from H2 and O2 and Subsequent Green OxidationsEPA Grant Number: R831533
Title: Generation of Hydrogen Peroxide in CO2 from H2 and O2 and Subsequent Green Oxidations
Investigators: Beckman, Eric J.
Institution: University of Pittsburgh
EPA Project Officer: Bauer, Diana
Project Period: February 18, 2004 through February 17, 2007
Project Amount: $375,000
RFA: Technology for a Sustainable Environment (2003) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Current industrial processes for the manufacture of propylene oxide (PO), phenol, and adipic acid (AA) generate billions of pounds of product each year, yet they each suffer from inefficiencies that directly lead to production of large volumes of waste and/or require substantial energy input. Previous work has shown that each of these compounds can be synthesized cleanly and efficiently from conventional starting materials using aqueous hydrogen peroxide as a green oxidant. However, H2O2 is too expensive to be routinely employed in commodity chemical processing, a somewhat counterintuitive condition given that H2O2 appears to be a commodity itself. However, 95% of the worlds H2O2 is synthesized using sequential hydrogenation and oxidation of 2-ethyl anthraquinone (AQ), a process that itself generates substantial waste streams and consumes considerable amounts of energy. We propose to circumvent these problems through the in-situ generation of H2O2 from H2 and O2 in carbon dioxide. CO2 provides a unique combination of advantages to this process: CO2 can solubilize large quantities of gases, is immune to oxidative degradation, provides a non-flammable environment in which to mix H2 and O2, and is miscible with all of the substrates involved. We propose to examine the synthesis of PO using this system in depth and also to evaluate whether this platform can be extended to the one-step synthesis of phenol from benzene and a clean route to adipic acid from cyclohexene.
We have previously found that H2O2 can be generated directly from H2 and O2 using CO2 as the sole solvent, and when generated in the presence of propylene and a suitable oxidation catalyst (TS-1), promotes the formation of PO with selectivity greater than 90%. Using a batch reactor coupled to 2 gas chromatographs, we propose to examine the effect of several variables, namely temperature, pressure, O2/H2 ratio, and catalyst (type and loading) on the conversion of substrate and the selectiveness for the desired products. Because the conversion of H2 and O2 to H2O2 is a key intermediate step in the generation of the various products, we also will independently measure the conversion of H2 and selectivity to H2O2 using in-situ dye bleaching and high pressure UV spectroscopy. For the generation of PO and phenol, the catalyst will be a Pd/Pt mixture supported on the titanium silicalite oxidation catalyst TS-1; the effect of Pd/Pt ratio on conversion and selectivity will be evaluated. For the case of adipic acid, Pd-containing polyoxometallates will be employed.
Resulting data on the effect of pressure, temperature, O2/H2 ratio, and catalyst (type and loading) on conversion and selectivity in the generation of propylene oxide, phenol, and adipic acid will provide the basis for evaluating the feasibility of large scale processes to generate these valuable commodity chemicals using an intensified scheme that generates substantially less waste than conventional routes. This study will provide a framework for clean oxidation using hydrogen peroxide enabling the use of H2O2 in processes where it was previously too expensive.
How Pollution will be Prevented or Avoided: The research proposed above, if successful, would result in the creation of highly intensified processes for the synthesis of propylene oxide, phenol, and adipic acid. Current processes to synthesize these products operate at 108 – 109 pounds per year throughputs, and hence the volume of waste generated (even at relatively low E-factors) is large. For example, the chlorohydrin process for PO creates approximately 500 million gallons of salt-contaminated wastewater from U.S. production alone. Well over half of the energy used in the peroxidation process for PO goes to creation and purification of the co-product and the generation and oxidation of ethyl benzene produces substantial waste steams. The waste streams generated by adipic acid production are infamous, as AA production is by itself responsible for 10% of global N2O emissions to the atmosphere (typically 0.3 kg N2O/kg AA). The Office of Industrial Technologies at the U.S. Department of Education has estimated that a single-step route to phenol would save 65 trillion BTU/year by 2020, eliminate 50 billion pounds of waste, and significantly reduce capital costs of the plants involved. In each of these cases, recent research has shown that environmentally benign H2O2 can be used to greatly reduce the waste generated by these processes, yet production of H2O2 using the conventional anthraquinone