Published November 2003
The NExOCTANE™ process developed by Fortum's Neste Engineering Oy and licensed exclusively in the Americas through Kellogg Brown & Root selectively converts isobutylene to mainly di-isobutylene (isooctene) that is optionally hydrogenated to paraffinic isooctane. Both di-isobutylene and isooctane are high octane number, high quality gasoline blending stocks. The process is especially attractive for refiners wishing to discontinue methyl tertiary butyl ether (MTBE) production since usually the fixed bed reactors, the fractionator and much of the MTBE unit can be utilized in the conversion into a NExOCTANE plant.
California and some 16 other states banned or limited the use of MTBE due to contamination of underground water by MTBE contained in gasoline leaking from underground storage tanks. The bans in California (31.7% of U.S. MTBE consumption), New York (7.5%) and Connecticut (3.1%) are effective by January 1, 2004. The future use in the rest of the U.S. is in doubt.
In the U.S., 29 refiners have MTBE units. Capacities range from 660 to 20,000 BPCD with the average plant producing 3,000 BPCD. Total North American production at refineries is 114,017 BPCD. Outside North America, 58 refineries produce 95,230 BPCD of MTBE, averaging 1642 BPCD. Worldwide, 91 refiners produce 209,250 BPCD of MTBE with a portion exported to the U.S. market. Already, one Canadian MTBE unit has been converted into a NExOCTANE unit.
Pure isooctane (2,2,4 trimethylpentane) has both a high research octane number (RON) and a high motor octane number (MON): 100 RON and 100 MON. Isooctane's low Reid vapor pressure of 1.8 psi is also attractive for bending into reformulated gasoline. Of course, isooctane is sulfur and aromatic free. The octane number is higher than alkylate or polymerate, two alternate blending stocks that are also made from isobutylene. The low density of isooctane results in more barrels of gasoline per pound of blendstock. In many cases when the olefins can be accommodated in the gasoline pool, blending the di-isobutylene is an attractive option for increasing octane number. The blending octane numbers of isooctene at 10 vol% in CARB base gasoline (from fluid catalytic cracking) are 124 RON and 99 MON.
We review the NExOCTANE process. We develop the economics for a generic grassroots, 1,801 BPSD (69,510 mt/yr or 286.4 m3/SD) NExOCTANE unit producing isooctane at an on stream factor of 0.95. The economics of retrofitting a MTBE unit depend greatly on the specificapplication. These grassroots economics may serve as a starting point and benchmark when considering retrofitting.