Presidential Green Chemistry Challenge: 2010 Greener Synthetic Pathways Award
The Dow Chemical Company
Innovative, Environmentally Benign Production of Propylene Oxide via Hydrogen Peroxide
Summary of Technology: Propylene oxide (PO) is among the top 30 largest-volume chemical intermediates produced in the world; its annual worldwide demand is estimated to be over 14 billion pounds. It is a key raw material for manufacturing a wide range of industrial and commercial products, including polyurethanes, propylene glycols, and glycol ethers, which are used in a diverse array of applications including automobiles, furniture, and personal care. Historically, manufacturing propylene oxide either produced significant volumes of coproducts or required recycling of organic intermediates. Traditional PO production uses chlorohydrin or one of a variety of organic peroxides, which lead to coproducts such as t-butyl alcohol, styrene monomer, or cumene. In each case, there is a substantial amount of coproduct and waste. Although most of the coproducts are recovered and sold, demand for these coproducts does not necessarily parallel the demand for PO, leading to imbalances in supply and demand.
Dow and BASF have developed the Hydrogen Peroxide to Propylene Oxide (HPPO) process, a new, innovative route to PO based on the reaction of hydrogen peroxide and propylene. It has high yields and produces only water as a coproduct. The Dow-BASF catalyst is a ZSM-5-type zeolite with channels of about 0.5 nm in diameter. In this catalyst, titanium replaces several percent of the silicon of the zeolite in a tetrahedral coordination environment. With this novel catalyst, the HPPO process is relatively straightforward. Propylene is epoxidized by hydrogen peroxide in a fixed-bed reactor at moderate temperature and pressure. The reaction occurs in the liquid phase in the presence of methanol as a solvent. The process is characterized by both high conversions of propylene and high selectivity for propylene oxide. Hydrogen peroxide is completely converted to product. In contrast with processes using organic peroxides, the HPPO process uses substantially less peroxide and eliminates the need to recycle peroxide. Production facilities are up to 25 percent cheaper to build because there is no need for equipment to collect and purify the coproduct.
The HPPO process also provides substantial environmental benefits. It reduces the production of wastewater by as much as 70–80 percent and the use of energy by 35 percent over traditional technologies. BASF performed an Eco-Efficiency Analysis of the various PO processes and found the HPPO process is cheaper and has substantially lower negative impacts than alternative processes. The first commercial process based on this technology was successfully commissioned in 2008 at the BASF production facility in Antwerp, Belgium. A second PO plant based on this technology is scheduled to begin production in Map Ta Phut, Thailand in 2011.
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