An Innovative Process for the Production of Polymer Grade Propylene From Propane

The availability of natural gas from shale basins has had a profound impact on the U.S. Petrochemical Industry by decreasing
the costs of both raw materials and energy. The price of US natural gas has declined from $12.50/MBTU in 2008 to approximately $3.00/MBTU in 2012, with prices expected to decline even further.^[1]  Shale gas has also resulted in the availability of tremendous quantities of low cost natural gas liquids (ethane, propane and butane) recovered as byproducts of natural gas processing which have the potential to transform the chemical industry.  It has already made a significant impact on the ethylene industry, as a number of producers have switched the feedstock for their steam crackers from naphtha to ethane for higher yield and lower production costs.

Propylene is one of the largest commodity chemicals in the world with an annual worldwide demand of ~ 70 million metric tons, and projected growth at over 6% per year.  Propylene is primarily produced (~94%) as a co-product of naphtha cracking (ethylene is the primary product) and FCC units in refineries (gasoline is the primary product).  As ethylene manufactures switch feedstock from naphtha to ethane, combined with a reduced gasoline demand, co-production will not be able to satisfy the growing demand for propylene.  It is estimated that by 2020, ~ 20% of propylene demand will be satisfied by on-purpose technologies.  This shortfall in supply, coupled with the availability of inexpensive propane from shale gas, has resulted in significant interest in the manufacture of on-purpose propylene from propane.  The only commercially available technology for achieving this is propane dehydrogenation (PDH) from UOP (Oleflex) and Lummus Technology (CATOFIN).

As a result of a multi-year research and development effort, GRT Inc., has developed a proprietary technology for the sustainable production of high purity (polymer grade) propylene using propane as the feedstock.  In the GRT process, propane is first reacted with bromine under relatively mild conditions to produce propyl bromide and HBr.  Propyl bromide is subsequently dehydrobrominated in the presence of a catalyst to produce propylene and HBr.  All of the HBr produced in the process is recovered and reacted with oxygen from air over a catalyst to form bromine and water.  The water produced is discharged from the process, while the bromine is recycled to the bromination step.

Based on capital and operating cost estimation performed by a top-tier Engineering Company, compared to current state of the art propane dehydrogenation (PDH) processes, the GRT process has a number of important advantages:

•         Highly selective production of propylene; no significant byproducts

•         Simple energy efficient separations; no propane/propylene splitter or cold box

•         Minimal coke formation – infrequent de-coking and simple reactor design

•         No refrigeration

•         ~ 9% improvement in feedstock conversion efficiency (98% vs. 90%)

•         21% reduction in energy requirements

•         82% reduction in CO₂ emission

•         30% reduction in capital cost (450 kta plant)

These advantages result in a total cost of production advantage of ~ $200 per metric ton of propylene. 

This paper describes the GRT propane-to-propylene process in detail, including the underlining chemistry, catalyst development, engineering design/analysis, and economic analysis.  The paper also discusses next steps for technology commercialization.

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[1] Scamuffa, Anthony, et. al. PriceWaterhouseCoopers LLP (2012) Shale gas: Reshaping the US chemicals industry.