are in the process mode, two are in the cold regeneration mode, and one is in the hot
regeneration mode. Automated valves control the flow of streams in and out of each
reactor as each is cycled through the various process steps of reaction, flushing, and
regeneration.
In the UOP Alkylene
TM process (Roeseler et al. 2002), the catalyst is fluidized
and moves through a riser reactor. The catalyst is then disengaged from the product
and flows down through a cold regeneration zone to the bottom of the riser, where
the cycle starts again. A catalyst slipstream goes to another reactivation vessel for
“hot” regeneration. UOP has also introduced a stacked moving bed radial flow
reactor scheme (Sadler 2013), in which catalyst flows in a figure eight pattern first
down through a series of process stages and next down through a hot regeneration
section before completing the cycle. The moving catalyst schemes make more
efficient utilization of the catalyst, since there is no duplication of reactor volumes.
This is critical because of the relatively low space velocities (large catalyst volumes) used and the expense of the platinum on the catalyst. The continuous process
also minimizes isobutane required by swing bed processes for flushing hydrogen
out of the pores of the catalyst after the regeneration before the reactor switches
back into reaction mode, since any residual hydrogen will saturate the olefin feed
and lead to yield losses.
Although the above solid catalyst alkylation processes have been offered to the
commercial market, none has achieved commercial success because of the high
costs of catalyst, platinum and capital equipment required for regeneration.
Ionic Liquid Alkylation
Since about 2000, there has been much interest in using ionic liquids to replace
traditional HF or H 2 SO 4 liquid acid catalysts in alkylation. An ionic liquid is
essentially a salt that is liquid phase at low temperature (<100
C). Typically, the
anion and cation are both large, and the cation has a low degree of symmetry. These
factors reduce the lattice energy of the crystalline form of the salt and significantly
lower its melting point. The field of ionic liquids has been reviewed by several
authors, including Seddon (1997) and Welton (1999). Ionic liquid properties can be
designed to suit the requirements of a particular process. Melting point, viscosity,
density, and hydrophobicity can all be varied by simple changes to the structure of
the ions. Their density can be made sufficiently high to facilitate easy separation by
gravity settling. In addition, ionic liquids have practically no vapor pressure, so they
do not carry the same environmental and safety concerns as HF or H 2 SO 4 , and can
be easily separated by fractionation.
The ionic liquids most commonly used for alkylation have a chloroaluminate
anion. The acidity can be controlled by varying the mole fraction of aluminum
chloride, X(AlCl 3 ). For X(AlCl 3 ) < 0.5, the ionic liquid is basic. For X(AlCl 3 ) =
0.5, the ionic liquid is neutral, and for X(AlCl 3 ) > 0.5, the ionic liquid is acidic. The
most common acidic form, Al 2 Cl 7
À , has 2 mol of AlCl 3 for each mole of the cation,
i.e., X(AlCl 3 ) = 0.67. Higher AlCl 3 mol ratios may be possible depending on the
454
D.A. Nafis et al.
regeneration mode. Automated valves control the flow of streams in and out of each
reactor as each is cycled through the various process steps of reaction, flushing, and
regeneration.
In the UOP Alkylene
TM process (Roeseler et al. 2002), the catalyst is fluidized
and moves through a riser reactor. The catalyst is then disengaged from the product
and flows down through a cold regeneration zone to the bottom of the riser, where
the cycle starts again. A catalyst slipstream goes to another reactivation vessel for
“hot” regeneration. UOP has also introduced a stacked moving bed radial flow
reactor scheme (Sadler 2013), in which catalyst flows in a figure eight pattern first
down through a series of process stages and next down through a hot regeneration
section before completing the cycle. The moving catalyst schemes make more
efficient utilization of the catalyst, since there is no duplication of reactor volumes.
This is critical because of the relatively low space velocities (large catalyst volumes) used and the expense of the platinum on the catalyst. The continuous process
also minimizes isobutane required by swing bed processes for flushing hydrogen
out of the pores of the catalyst after the regeneration before the reactor switches
back into reaction mode, since any residual hydrogen will saturate the olefin feed
and lead to yield losses.
Although the above solid catalyst alkylation processes have been offered to the
commercial market, none has achieved commercial success because of the high
costs of catalyst, platinum and capital equipment required for regeneration.
Ionic Liquid Alkylation
Since about 2000, there has been much interest in using ionic liquids to replace
traditional HF or H 2 SO 4 liquid acid catalysts in alkylation. An ionic liquid is
essentially a salt that is liquid phase at low temperature (<100
C). Typically, the
anion and cation are both large, and the cation has a low degree of symmetry. These
factors reduce the lattice energy of the crystalline form of the salt and significantly
lower its melting point. The field of ionic liquids has been reviewed by several
authors, including Seddon (1997) and Welton (1999). Ionic liquid properties can be
designed to suit the requirements of a particular process. Melting point, viscosity,
density, and hydrophobicity can all be varied by simple changes to the structure of
the ions. Their density can be made sufficiently high to facilitate easy separation by
gravity settling. In addition, ionic liquids have practically no vapor pressure, so they
do not carry the same environmental and safety concerns as HF or H 2 SO 4 , and can
be easily separated by fractionation.
The ionic liquids most commonly used for alkylation have a chloroaluminate
anion. The acidity can be controlled by varying the mole fraction of aluminum
chloride, X(AlCl 3 ). For X(AlCl 3 ) < 0.5, the ionic liquid is basic. For X(AlCl 3 ) =
0.5, the ionic liquid is neutral, and for X(AlCl 3 ) > 0.5, the ionic liquid is acidic. The
most common acidic form, Al 2 Cl 7
À , has 2 mol of AlCl 3 for each mole of the cation,
i.e., X(AlCl 3 ) = 0.67. Higher AlCl 3 mol ratios may be possible depending on the
454
D.A. Nafis et al.