JOURNAL OF CATALYSIS 158, 76–82 (1996)
ARTICLE NO. 0007
Gas Phase Synthesis of MTBE on Triflic-Acid-Modified Zeolites
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A. A. Nikolopoulos,* A. Kogelbauer,* J. G. Goodwin, Jr.,* and G. Marcelin†
*Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261,
and †Altamira Instruments, Inc., 149 Delta Drive, Suite 200, Pittsburgh, Pennsylvania 15238
Received December 19, 1994; revised August 30, 1995; accepted August 31, 1995
character of the catalyst used. Thus, another outstanding
The gas phase synthesis of MTBE (methyl tert-butyl ether) advantage of zeolites is their alterable acidity, which could
was studied using three series of triflic acid (TFA)-modified be optimized for maximizing the formation of MTBE un-
zeolites, the parent materials being HY, H–mordenite, and
HZSM-5. Impregnation with TFA was found to enhance MTBE
synthesis activity only for the large-pore zeolite Y and only
up to a certain extent of modification. A high level of TFA
modification caused a reduction in activity, apparently due to
blockage of the active sites by TFA molecules and extra-lattice
Al formed during the modification process. The mechanism of
activity enhancement by TFA modification appears to be re-
lated to the formation of extra-lattice Al rather than the direct
der a given set of reaction conditions. Although the synthe-
sis of MTBE on zeolites has been examined (8, 11–16), only
a few studies on the effect of acidity have been reported. In
a study of the effect of acid strength variation on MTBE
formation using a series of partially alkali-exchanged HY
zeolites, no influence in initial MTBE synthesis activity
was observed, apparently due to a strong mediating effect
of adsorbed methanol on the strength of the acid sites (14).
On the other hand, an enhancement in zeolite acidity by
dealumination was found to result in increased activity for
MTBE synthesis (16).
This paper reports on an investigation of the variation of
zeolite acidity by addition of a strong electron-withdrawing
compound, namely triflic acid, and its impact on zeolite
performance for MTBE synthesis. Modification of the acid-
ity of solid acids by incorporation of strong electron-with-
drawing compounds like triflic acid (12) or ammonium
sulfate (17) has been found to result in enhanced activity
for etherification. However, no systematic investigation of
the manner in which such acidity modification methods
influence the zeolite activity has been reported.
presence of TFA.
1996 Academic Press, Inc.
INTRODUCTION
The increasing environmental restrictions concerning
the quality of gasoline (1, 2) have recently resulted in
the extensive use of oxygenates (alcohols and ethers) for
gasoline improvement (3–5). MTBE (methyl tert-butyl
ether) is currently accepted as the most suitable gasoline
additive because of its favorable physicochemical proper-
ties compared to alcohols and its excellent performance in
terms of antiknocking behavior and control of the emis-
sions from the internal combustion engine (4, 6). The
worldwide production of MTBE has increased more than
tenfold in the past decade (7–9).
EXPERIMENTAL
The commercial process currently in application, liquid
phase reaction of methanol (MeOH) and isobutene (2-
methyl propene, IB) at temperatures below 100ЊC and
moderate pressures, uses a sulfonated ion-exchange resin
catalyst whose lack of thermal stability and corrosive prop-
erties are major disadvantages (10). Zeolites have been
considered as promising alternative catalysts for MTBE
synthesis because of their excellent thermal stability and
high selectivity toward MTBE even at less favorable re-
actant ratios (8, 11).
Three series of postsynthesis modified zeolites were
used, the three parent zeolites being HY (LZ210-12, from
UOP), H–mordenite (H-Zeolon, Norton) and HZSM-5
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Mobil), obtained as fine powders (crystalline size of ca.
Ȑm). These zeolites have different structural characteris-
tics, thus allowing a determination of the influence of zeo-
lite morphology on catalytic performance for the formation
of MTBE.
Modification of the parent zeolites was performed by
impregnation with triflic acid (trifluoromethane sulfonic
acid, CF SO H, TFA). TFA in various concentrations was
Being an acid-catalyzed reaction, the formation of
MTBE would be expected to be influenced by the acidic
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dissolved in 5 ml of acetone. Each of these solutions was
used to impregnate ca. 0.5 g of zeolite that had been precal-
cined at 400ЊC in air under shallow bed conditions. The
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To whom correspondence should be addressed.
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Copyright 1996 by Academic Press, Inc.
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