Based on these studies and for these particular base stocks, it was determined
that propylene-derived polymer gasoline had blending octanes of 94 RON and
83 MON; these values are almost identical to its clear values with no synergism
with the base stock. The situation with the propylene–butenes polymer gasoline is
quite different. Here, the blend stock had RON and MON of 96 and 83, respectively,
but it blended with the base stock at the 10 % level as though the octane numbers of
the blend stock were 103 RON and 97 MON, a clear display of synergism with the
base stock. Slightly smaller, but still very high blending values are obtained when
blended at the 20 vol.% level. Naturally, the blending values decline progressively
when the blend stock is added in higher and higher proportions, until they reach the
clear measured values on the blend stock at a 100 % blend stock proportion.
The impact of synergism was even higher for the butene-derived polymer
gasoline. Here, instead of the measured octanes of 98 RON and 83 MON, blending
octanes of 126 and 99 were calculated, displaying a synergism of 28 numbers for
RON and 16 numbers for MON.
The above observations are for the olefinic catalytic condensation products.
Similar observations can be made with the hydrogenated products. In general,
however, the paraffinic product does not exhibit significant synergism with this
type of base stock.
A corollary from these observations is that propylene polymer gasoline is fairly
poor for most motor fuel applications. Propylene–butene feeds can make reasonably good gasolines, and the gasoline products from the catalytic condensation
process based on butenes are excellent.
Selective and Nonselective Gasoline Production
with the Catalytic Condensation Process
Most catalytic condensation operations with SPA catalysts on propylene and
propylene–butene feeds are conducted in a nonselective mode to maximize light
olefin conversion to gasoline. To drive gasoline yield, nonselective units tend to be
operated at higher temperatures between 160
C inlet and 200
C reactor outlet
temperatures. This typically produces a broad olefin distribution with minor
amounts of C 6 ’s and primarily C 7 –C 11 ’s with significant amounts of C 12 ’s. While
this maximizes LPG conversion and gasoline yield, it does not maximize octane,
due to partial skeletal rearrangement to less branched, lower octane isomers.
For butenes, however, there are significant octane advantages for selective operations that were first utilized in World War II to maximize aviation fuel octane.
Selective operations are generally carried out at lower temperatures, lower space
velocity, and with C 4 recycle. Under these conditions, butenes react selectively with
each other to form almost exclusively dimers, C 8 , and trimers, C 12 . Most of the dimers
are codimers produced by the reaction of one molecule of isobutene with one molecule
of n-butene. The resulting codimers are high-octane trimethylpentenes or isooctenes.
The typical properties of the codimers and their hydrogenated counterparts called
“hydrocodimers” are shown in Table 5. The total codimer product comprises the C 8
466
R.L. Mehlberg et al.
that propylene-derived polymer gasoline had blending octanes of 94 RON and
83 MON; these values are almost identical to its clear values with no synergism
with the base stock. The situation with the propylene–butenes polymer gasoline is
quite different. Here, the blend stock had RON and MON of 96 and 83, respectively,
but it blended with the base stock at the 10 % level as though the octane numbers of
the blend stock were 103 RON and 97 MON, a clear display of synergism with the
base stock. Slightly smaller, but still very high blending values are obtained when
blended at the 20 vol.% level. Naturally, the blending values decline progressively
when the blend stock is added in higher and higher proportions, until they reach the
clear measured values on the blend stock at a 100 % blend stock proportion.
The impact of synergism was even higher for the butene-derived polymer
gasoline. Here, instead of the measured octanes of 98 RON and 83 MON, blending
octanes of 126 and 99 were calculated, displaying a synergism of 28 numbers for
RON and 16 numbers for MON.
The above observations are for the olefinic catalytic condensation products.
Similar observations can be made with the hydrogenated products. In general,
however, the paraffinic product does not exhibit significant synergism with this
type of base stock.
A corollary from these observations is that propylene polymer gasoline is fairly
poor for most motor fuel applications. Propylene–butene feeds can make reasonably good gasolines, and the gasoline products from the catalytic condensation
process based on butenes are excellent.
Selective and Nonselective Gasoline Production
with the Catalytic Condensation Process
Most catalytic condensation operations with SPA catalysts on propylene and
propylene–butene feeds are conducted in a nonselective mode to maximize light
olefin conversion to gasoline. To drive gasoline yield, nonselective units tend to be
operated at higher temperatures between 160
C inlet and 200
C reactor outlet
temperatures. This typically produces a broad olefin distribution with minor
amounts of C 6 ’s and primarily C 7 –C 11 ’s with significant amounts of C 12 ’s. While
this maximizes LPG conversion and gasoline yield, it does not maximize octane,
due to partial skeletal rearrangement to less branched, lower octane isomers.
For butenes, however, there are significant octane advantages for selective operations that were first utilized in World War II to maximize aviation fuel octane.
Selective operations are generally carried out at lower temperatures, lower space
velocity, and with C 4 recycle. Under these conditions, butenes react selectively with
each other to form almost exclusively dimers, C 8 , and trimers, C 12 . Most of the dimers
are codimers produced by the reaction of one molecule of isobutene with one molecule
of n-butene. The resulting codimers are high-octane trimethylpentenes or isooctenes.
The typical properties of the codimers and their hydrogenated counterparts called
“hydrocodimers” are shown in Table 5. The total codimer product comprises the C 8
466
R.L. Mehlberg et al.