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Methane-to-gasoline process nears commercialization.
Synfuels International, Inc. (Dallas, Tex.;
edlinks.che.com/7370-561) plans to commercialize its patented gas-to-liquids (GTL) process in
Kuwait through a newly
formed partnership with Kuwait's
Aref Energy Holding (edlinks.che.com/7370-562). In contrast with Fischer-
Tropsch technology, the process produces a high-octane gasoline blend, rather
than waxy paraffins for diesel fuel. Within two years, the partners expect to
start up a plant to convert about 50-million scfd of gas to 3,800-4,000 bbl/d
of gasoline-blend feedstock.
Originally conceived at Texas A&M
University
(College Station, Tex.), the process (flowsheet) has been
tested in a 100,000-ft3/d demonstration plant since 2005. Natural
gas is first converted to acetylene (plus some carbon monoxide, carbon dioxide
and hydrogen) by direct-fired pyrolysis, fueled by recycled syngas and oxygen.
Pyrolysis takes about one millisecond at temperatures up to 4,500°F. The
acetylene is then dissolved in a standard commercial solvent and converted to
ethylene by hydrogenation at around 100-300°F and 80-400 psi, over a
proprietary catalyst. Finally, the ethylene is oligomerized, using a zeolite
catalyst, to obtain a gasoline-blend refinery feedstock that is mostly C7-C9
liquids of90-110 octane, says Edward Peterson, chief engineer. The yield is
80-85%.
Performing the hydrogenation step in the
liquid phase is a key part of the process, he explains, since hydrogenation of
acetylene alone is highly exothermic. "Also, we never isolate pure
acetylene, but process it with other components, such as CO, CO2 and
H2, at the appropriate temperature and pressure, to keep it below
the explosive limit." The selectivity for acetylene-to-ethylene conversion
is 98%, he says, and the conversion rate is 96-98%.
Synfuels International expects to produce
gasoline feedstock at a cost "in the mid$20/bbl range," using
stranded gas valued at $1/million ft3, says company chairman Ben
Weber. The process is economical at a smaller scale than that of Fischer-
Tropsch technology, he says, because the reaction times are fast and there is
less recycle.
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