Ethylene and propylene are produced by several different processes in the chemicals and refining industries. The first process, used in chemical plants, is steam cracking of feeds comprising ethane, propane, mixtures of the two or butane (all derived from natural gas) as well as naphtha and gas oil. The preferred feedstocks are the natural gas liquids (NGLs) because the yield of desired products is greater. The second process involves the recovery of light ends from fluid catalytic cracking.
In both cases, the products of the conversion reactors are mixtures of chemicals that require further separation and purification. Traditionally, this has been done by distillation; and the separation of ethylene from ethane or propylene from propane must be carried out under cryogenic conditions at elevated pressures, because of the low boiling points of these liquids. Cryogenic distillation, however, is extremely energy intensive, resulting in substantial costs to separate olefins from paraffins. Over a decade ago Humphrey and coworkers [1], in a report prepared for DOE, estimated that these two separations "accounted for 6.3 % (about 0.15 quadrillion BTUs) of the energy used by the chemical and petrochemical industries" leading the National Research Council to suggest in their 1999 report [2] that "less energy-intensive separations would be useful for the petroleum refining industry."
Trans Ionics is developing an olefin/paraffin separation process called MMEO (for Membrane Mediated Extraction of Olefins) that has shown promise in Phase I tests supported by the U. S. Department of Energy as a potential replacement for cryogenic distillation. MMEO incorporates several unique process components to recover olefins under non-cryogenic conditions; and Trans Ionics was awarded a Phase II SBIR grant totaling $750,000 (over two years) to carry out laboratory and pilot plant studies to scale up MMEO for commercial application in early 2009.
