akylation

Advances and Prospects of Isobutane Alkylation on Solid Catalysts
Block 2, Forum 9 paper
Advances and Prospects of Isobutane Alkylation on Solid
Catalysts
Johannes A. Lercher, TU Muenchen
Roberta Olindo, Technische Universität München
Carsten Sievers</author><affiliation>
Abstract:
Alkylation of isobutane with n-butene is one of the important routes to provide high octane
components that can substitute aromatic molecules in gasoline. Traditionally, this route is
catalyzed by sulfuric and hydrofluoric acid. Solid acid catalysts have been explored
frequently, but have not been commercially implemented to date. This is related to the
necessity of frequent regenerations, complex handling of solid catalysts in a liquid-solid
system and inherent differences in the reactivity towards n-butene and isobutane. The main
drawback in the use of solid catalysts for isobutane alkylation is their rapid deactivation, which
so far has prevented their industrial application.
Over the last years, significant progress has been made in this field, leading to the successful
development of alkylation technology on a pilot stage. Insight into surface chemistry, the
advances in catalyst preparation and the integration with novel reactor technology led to
remarkable progress. Catalysts, which surpass the lifetime of sulfuric acid by three orders of
magnitude, show potential for economic feasibility based on frequent mild regenerations. This
progress has been made possible by enhancing the key quality of the solid catalysts, which is
the hydride transfer between the surface bound species and the isobutane.
The lecture will review the potential and limitations of current chemical and engineering
concepts and will give an outlook to new developments in isobutane alkylation.
Introduction
The alkylate produced from isobutane/butene alkylation is an excellent blending component
for gasoline. In 2005 the worldwide alkylation capacity amounted to approximately 2 million
bpd and it is expected to grow further Figure 1. In fact, due to increasingly strict legislation,
the concentration of alkenes and aromatics in the gasoline will be more and more limited in
the next years. Additionally, methyl-tertiary-butyl ether (MTBE), a high-octane-number
oxygenate, is likely to be prohibited as a gasoline compound.
HF
H2SO4
total
0
500
1000
1500
2000
2500
1930 1950 1970 1990 2010
Year
Alkylatecapacity/thousand
bpb
Alkylatecapacity/thousandbpd
Year
Figure 1. World alkylation capacity (Taken from [1]).
Copyright © World Petroleum Congress – all rights reserved

Currently, only liquid acid-catalyzed processes are operated on an industrial scale with
approximately equal market shares for processes using sulfuric and hydrofluoric acid. Both of
these catalysts suffer from serious disadvantages.
Anhydrous HF is a corrosive and highly toxic liquid with a boiling point close to room
temperature. Therefore, refineries with HF alkylation plants are under pressure to install
expensive mitigation systems minimizing the dangers of HF leaks. Moreover, authorities in
many industrialized countries have ceased to license new HF alkylation plants.
Sulfuric acid is also a corrosive liquid, but not volatile, making its handling easier. Its major
disadvantage is the high acid consumption in the alkylation process, which can be as much
as 70–100 kg of acid/ton of alkylate. The spent acid contains water and heavy hydrocarbons
and has to be regenerated, usually by burning. The cost of such a regenerated acid is about
2–3 times the market price for freshly produced sulfuric acid [2].
In the last 30 years considerable efforts have been made to replace the existing liquid
catalysts by solid materials, which are environmentally benign and easier to handle. Among
them the most promising candidates seem to be zeolites. Pioneering work on this field was
done by groups at Mobil Oil [3] and Sun Oil [4] using rare earth exchanged zeolites. In
general, all large-pore zeolites are active alkylation catalysts, giving product distributions
similar to those characteristic of the liquid acids, but, due to their rapid deactivation, an
efficient regeneration procedure is necessary. So far this has been the obstacle to
commercialization. Other solid materials tested in alkylation include sulfated zirconia,
supported Brųnsted and Lewis acids, heteropolyacids and organic resins.
The aim of this paper is to present a general overview on research development for alkylation
processes. A special emphasis will be given only on recent results as a detailed review has
been published recently [5]. Further reviews have been published on both liquid and solid acid
catalysts [6] and on solid acid catalysts alone [7].
Mechanistic aspects
Initiation
Independently of the acid used, the mechanism of isobutane/butene alkylation is essentially
the same [8]. The reaction is initiated by the addition of the acid to the double bond of an
olefin (reaction 1). With sulfuric and hydrofluoric acids alkyl sulfates and fluorides are formed.
In zeolites this reaction leads to the formation of surface alkoxides rather than free carbenium
ions [9]. However, in literature these species are often referred to as carbenium ions.
Branched alkenes do not form esters. It is believed that they easily protonate and polymerized
[10].
Direct activation of isobutane by protonation is only observed at temperatures significantly
higher than those used in typical alkylation reactions [11]. When the olefin is activated it can
abstract a hydride from isobutane to form a tert-butyl carbenium ion (reaction 2).
(1)
(2)
Alkene addition and isomerization
Once tertiary carbenium ions have been formed, they can undergo electrophilic addition to
further alkene molecules forming a larger carbenium ion. When 2-butene is used as alkylation
agent the reaction mainly yields trimethylpentane (TMP) isomers. The primary product of the
addition would be 2,2,3-TMP. However, large amounts of other TMP isomers are usually
observed indicating that isomerization of the primary products plays a significant role. The
+ HX
+
X
+ X-
+
+ + +
Hydride transfer

addition of a carbenium ion to an olefin is exothermic and of all the reaction steps contributes
most to the overall heat of reaction.
(3)
Hydride transfer
Intermolecular hydride transfer (reaction 4), typically from isobutane, to an alkylcarbenium
ion/alkoxi group, transforms the species into the corresponding alkane and forms a new tert-
butyl cation to continue the chain sequence. Hydride transfer is the elementary step that
ensures the perpetuation of the catalytic cycle. A sufficiently high hydride transfer activity is
necessary to prevent oligomerization.
The hydride donor does not necessarily have to be isobutane. In sulfuric acid catalyzed
alkylation hydrides from conjunct polymers are transferred to carbenium ions. Sulfuric acid
containing 4-6 wt% of conjunct polymers produces a much higher quality alkylate than acids
without acid-soluble oil [12]. Similar compounds are also formed in zeolite catalyzed
alkylation. Several groups proposed that these compounds might be responsible for the
deactivation of zeolite catalysts [13,14]. Despite the importance of this elementary step, there
are few studies, in which the kinetics of hydride transfer was investigated directly [11,15,16].
Platon and Thomson proposed a test reaction, in which the hydride transfer occurs between a
cyclohexylcarbenium ion and isobutane using the fact that cyclohexene is moderately stable
against polymerization [17,18].
Oligomerization and cracking
The overall product distribution is governed by the relative rates of alkene addition and
hydride transfer. As depicted in Figure 2, the ratio between rate constant for the addition of an
olefin k3 and the rate constant for the hydride transfer step k2 determines whether the catalyst
will effectively catalyse the alkylation or deactivates quickly through multiple
alkylation/oligomerization reactions [19].
C4
+
O
C8
+ C12
+ C16
+
O O
C8 C12
k1
k2 k4
k3 k5
P P
...C4
+
O
C8
+ C12
+ C16
+
O O
C8 C12
k1
k2 k4
k3 k5
P P
...
Figure 2: Pathway to oligomerization products (adapted from [19]).
Not only alkene addition but also the reverse reaction, i.e., cracking, is observed under
alkylation conditions. This explains the detection of products with carbon numbers, which are
not multiples of four. The fragments are formed following the β-scission rule (reaction 5). In
general, oligomerization and cracking products exhibit octane numbers lower than the TMPs.
Average RON values of 92-93 for C5-C7 and of 80-85 for C9-C16 have been reported [20].
The reactions discussed so far can occur in various combinations and proportions allowing
the formation of a large variety of compounds.
(4)+ + +
+
+
+
+

(5)
Deactivation
Oligomerization is the main cause for catalyst deactivation. Although a certain amount of
conjunct polymers is beneficial during sulfuric acid catalyzed alkylation the catalyst becomes
inactive when their concentration exceeds a certain critical level. During liquid-phase
alkylation compounds with single or conjugated double bonds and five- and six membered
rings are observed [14,21]. Usually, one would not expect aromatic molecules to form under
the conditions of alkylation reactions. However, a series of condensation, hydride abstraction
and cyclization reactions might lead to the formation of alkyl-substituted rings (reactions 6 and
7).
(6
)
(7
)
Developments of new alkylation catalysts
Zeolites
Adsorption of hydrocarbons
One of the major differences between acidic zeolites and liquid acids is their selective and
strong chemisorption of unsaturated compounds. Therefore, considerable concentrations of
alkenes are found in the zeolite pores, even if the alkene concentration in the bulk is kept at a
low level. This favors oligomerization of the alkene and thus deactivation of the catalyst.
Consequently, the control of the alkene concentration is the key for providing zeolite catalysts
with reasonable lifetimes.
An important feature for the adsorption of hydrocarbons in zeolites is the linear increase of the
heat of adsorption with increasing chain length [22] (
Figure 3a and b). The value of this increase depends on the size and shape of zeolite pores.
As a result different apparent activation energies are observed for the transformation of
hydrocarbons with different chain lengths. However, the same intrinsic activation energies
were found [23]. As a consequence of the increase of the heat of adsorption with the chain
length, the rate of desorption decreases by four orders of magnitude with each butene unit
added (
Figure 3c). The tremendous difference illustrates the difficulties encountered for removing
oligomers from the zeolite pores.
Figure 3b demonstrates that, in addition to the heat of adsorption from physisorption, a
relatively small amount of heat is generated by the directed interaction of the Brųnsted acid
sites with the sorbate (chemisorption).
++ +
+ H+
+
+
HT
+
+ H
+
+
HT +

2 4 6 8 10
0
20
40
60
80
100
120
Carbon number
Heatofadsorption[kJ/mol]
H-MFI MFI H-FAU FAU
a)
b)
100
102
104
106
108
1010
1012
1014
k
C8/k
C12
k
C
8/k
C
16
k
C
8/k
C
20
relativedesorptionrates
c)
2 4 6 8 10
0
20
40
60
80
100
120
Carbon number
Heatofadsorption[kJ/mol]
H-MFI MFI H-FAU FAU
a)
b)
100
102
104
106
108
1010
1012
1014
k
C8/k
C12
k
C
8/k
C
16
k
C
8/k
C
20
c)
100
102
104
106
108
1010
1012
1014
k
C8/k
C12
k
C
8/k
C
16
k
C
8/k
C
20
c)
Figure 3: a) Hydrocarbon in interaction with zeolite framework. b) Heat of adsorption as a function of
carbon number for zeolites MFI and FAU in the acidic and non-acidic form. c) Relative desorption rates
of a C12, C16 and C20 alkane compared to octane.
Acidity
Unlike for liquid acids, zeolite acid sites vary substantially in nature and strength. Different
reaction steps require a different acid strength. Only weak acid sites are needed for double
bond isomerization in alkene, whereas somewhat stronger sites are necessary for
oligomerization. Alkylation needs moderately strong acid sites and very strong acid sites are
required for cracking.
It is beyond discussion that Brųnsted acid sites are the active sites for alkylation. However,
different opinions exist about the ideal strength of these sites [24,25]. It is well known that the
strong Brųnsted acid sites deactivate first. Once this has happened, the selectivity shifts
towards oligomerization and, so, the deactivation process accelerates (Figure 4). This is
explained by the fact that the olefinic oligomers add to existing carbenium ions generating so
large hydrocarbon frameworks that desorption via hydride transfer is not possible.
0
20
40
60
80
100
0 5 10 15 20
Time on stream (h)
Conversion(%)
0
20
40
60
80
100
0 5 10 15 20
Time on stream (h)
Conversion(%)
Figure 4: Typical time-on-stream behavior of a LaX zeolite during isobutane/butene alkylation.
Taken from reference [26].
Lewis acid sites in zeolites result from a partial destruction of the zeolite lattice. During
calcination aluminum is partially hydrolyzed from the zeolite lattice and forms extra-framework
aluminum oxide species (EFAL). This is enhanced in presence of water. Some of the species
formed in this way exhibit strong Lewis acidity. Another source of Lewis acid sites are metal
ions on ion-exchange positions. However, most of these metals exhibit Lewis-acidity weaker
than aluminum species. It has been shown in several studies that Lewis acid sites are
responsible for the formation of unsaturated compounds in zeolite pores [21,24]. The
increased concentration of these compounds leads to premature catalyst deactivation [25].

Silicon/aluminum ratio
The aluminum content of a zeolite influences its acidity. The decrease of the Si/Al ratio leads
to an increase of the concentration of Brųnsted acid sites, while the strength of the individual
acid sites decreases. In contrast to this general trend, several authors have found that the
ratio between strong and weak acid sites increases with decreasing Si/Al ratio [27-29]. This
leads to a beneficial effect on the alkylation performance, because low Si/Al zeolites favor the
hydride transfer [30,31]. However, a low Si/Al ratio reduces the thermal stability of the zeolite
leading to materials, which are more prone to dealumination.
Exchange with rare earth cations could be used to induce increased acidity and stability
[32,33].
Structure types of zeolites
For zeolite catalyzed alkylation large pore zeolites are needed. In materials with small pores
diffusion limitations become a major obstacle and higher operating temperatures are needed.
With large pore materials the product distribution resembles the typical alkylate from liquid
catalyzed processes. Yoo et al. compared various large pore zeolites and found that zeolite
BEA exhibited the best time-on-stream behavior in both lifetime and TMP selectivity [34].
ZSM-12 also showed a long lifetime but obviously catalyzed oligomerization instead of
alkylation. USY, MOR and LTL were found to deactivate quickly. The authors concluded that
zeolites without periodic expansions do not allow extensive coke formation and hence
deactivate at a slower rate. In contrast to these results, other groups found significant coke
deposition in H-BEA zeolite [25]. However, it has to be mentioned that it is difficult to separate
the influences of the pore structure and acidity of the respective samples.
Sulfated zirconia
Besides zeolites, a variety of solid acids has been tested in alkylation reaction. Among those
sulfated zirconia received a considerable interest due to its strong acidity and activity for
isomerization of short linear alkanes at temperatures below 150°C. Corma et al. showed that
sulfated zirconia already catalyzed alkylation at 0°C while only dimerization was observed
over BEA [35]. However, at 50°C a high selectivity to cracking products (65 wt%) was
observed on sulfated zirconia while BEA was selective for TMP.
Like zeolites, sulfated zirconia suffers from rapid deactivation [36]. Additionally, significant
loss of sulfur can affect the catalytic stability. Nevertheless, Xiao et al. reported a lifetime of
sulfated zirconia catalysts of 70 h [37].
Other solid catalysts
Another solid material tested for alkylation, is Nafion-H, a perfluorated sulfonic acid resin with
an H0 value comparable to sulfuric acid. Unsupported Nafion-H suffers from its low surface
area [38]. Botella et al. showed that Nafion-H can be supported on porous carriers or directly
incorporated into silica [39]. Using these methods a material with acidity comparable to zeolite
BEA was obtained, which produces oligomers at low temperatures and saturated products at
higher. Organic resins can also be used to support HF [40], leading to a considerable
reduction of the HF volatility.
Chlorinated alumina was one of the first solids tested in alkylation [41]. The acidity of these
samples can be moderated with Li+
or Na+
cations to prevent excessive cracking and improve
time-on-stream behavior. Other solid materials tested for isobutane alkylation include
fluorinated alumina [42], silica supported 12-tungstophosphoric (H3PW12O40) acid [43] and
silica supported perflouralkanedisulphonic acids [44].

Ionic liquids
In addition to the development of solid catalysts, ionic liquids have been tested for alkylation.
Yoo et al. used 1-alkyl-3-methylimidazolium halides-aluminum chloride for isobutane/2-butene
alkylation [45]. The best sample of this series showed a higher activity than sulfuric acid, but
TMP selectivity was lower. The authors concluded that an ionic liquid with a higher Brųnsted
acidity is needed to obtain a competitive catalyst.
In a recent publication Olah et al. showed that HF acid can be immobilized as pyridinium
poly(hydrogen fluoride) [40]. Compared to pure HF the volatility was reduced by 95%, while
the activity remained high.
Influence of process condition
The choice of appropriate reaction conditions is crucial for optimized performance in
alkylation. The most important parameters are: reaction temperature, feed paraffin/olefin ratio
(P/O), olefin space velocity (OSV), olefin feed composition and reactor design. Changing
these parameters will induce similar effects independently of the chosen catalyst.
Nevertheless, the sensitivity towards changes is different for the individual catalysts. Table 1
summarizes the most important parameters employed in industrial operations for different
acids. The values given for zeolites refer to operation in a slurry reactor. It is observed that
zeolites can be operated at the same or higher severity (with respect to P/O and OSV) than
liquid acids.
Table 1: Typical values of important process parameters. The numbers for the liquid acids are taken from references
[46-48]. The values given for zeolites refer to operation in a slurry reactor.
HF H2SO4 Zeolites
Reaction temperature (°C) 16-40 4-16 50-100
Feed paraffin/olefin ratio (mol/mol) 11-14 7-10 6-15
Olefin space velocity (kg Olefin/kg Acid h) 0.1-0.6 0.03-0.2 0.2-1.0
Exit acid strength (wt.-%) 83-92 89-93 -
Acid per reaction volume (vol.-%) 25-80 40-60 20-30
Catalyst productivity (kg Alkylate/kg Acid) 1000-2500 6-18 600
The required reaction temperature is determined by the activation energy of the individual
reaction steps on a given catalyst. The viscosity of sulfuric acid and the solubility of
hydrocarbons in HF are further constraints in liquid phase alkylation. Zeolites have to be
operated at a significantly higher temperature due to the higher stability of the surface esters
compared to the esters of sulphuric acid [25]. However, at too high temperatures significant
amounts of unsaturated products will be formed, which lead to rapid catalyst deactivation.
To obtain a high quality alkylate and prevent rapid catalyst deactivation, the ratio between the
hydride transfer and oligomerization rates must be high. This can be achieved at sufficiently
high P/O ratio and a low OSV [28,47]. On the other hand, at high P/O ratios more isobutane
has to be recycled, which leads to increased separation costs. Therefore, a suitable balance
has to be found to optimize the overall economics of the process.
It has been shown that the deposition of coke and, therefore, the catalyst deactivation can be
reduced when the reaction is conducted under supercritical or near-critical conditions instead
than in liquid phase [49,50]. This in turn could beneficially decrease the frequency, and
therefore the cost, of catalyst regeneration. Isobutane, the most abundant species present in
the alkylation reactor, has critical pressure and temperature of 36.5 bar and 135°C. Under
these conditions the occurrence of cracking reaction lowers the octane number and therefore
the alkylate quality. For this reason various groups have investigated the use of inert solvents
which, added to the reactant mixture, allows reaching supercritical conditions or near-critical
condition at lower temperature and pressure [51]. Among the inert solvents, carbon dioxide
received the most attention [50,52]. Ginosar et. al compared various solvents under

supercritical condition and concluded that light hydrocarbons are superior to carbon dioxide
for isobutane/butene alkylation [53].
Industrial processes
Liquid acid-catalyzed processes
Currently all industrial alkylation processes use liquid acid catalysts. Liquid acid-catalyzed
processes require intensive mixing of acid and hydrocarbon phases in order to obtain a
sufficiently large phase boundary. On the other hand an efficient phase separation after the
reaction is required. Even after 50 years of industrial operation the mixing properties of
sulfuric acid and hydrocarbons remains a subject of research [54,55]. In addition, new
methods for adding the olefins still have potential to improve the existing processes.
As alkylation is an exothermic reaction, a complex cooling system is necessary. The HF-
catalyzed processes are operated at temperatures between 16 and 40°C: Therefore the
reactor can be cooled with water. H2SO4-catalyzed processes operate at lower temperature
(4-18°C) and therefore require more complex cooling system, which typically utilize the
processed hydrocarbon steam itself.
Sulfuric acid-catalyzed processes
Two licensors offer sulfuric acid alkylation units, i.e. Stratco and ExxonMobil. Stratco has
developed the Effluent Refrigerated Alkylation Technology [47]. A scheme of the reactor is
shown in Figure 5. It is a horizontal pressure vessel containing an inner circulation tube, a
heat exchanger tube bundle to remove the heat of reaction, and a mixing impeller in one end.
The hydrocarbon feed and recycle acid enter on the suction side of the impeller inside the
circulation tube. This design ensures the formation of a fine acid emulsion and prevents
significant temperature differences within the reactor. A portion of the emulsion is withdrawn
from the reactor and flows to the acid settler. The acid, being the heavier of the two phases,
settles to the lower portion of the vessel and is returned to the suction site of the impeller. The
hydrocarbon effluent from the top of the acid settler is expanded and partially evaporated. The
cold two-phase hydrocarbon is passed through the tube bundle in the Contactor reactor and
removes the heat of reaction.
A - CONTACTOR REACTOR SHELL
B - TUBE BUNDLE ASSEMBLY
C - HYDRAULIC HEAD
D - MOTOR
E - IMPELLER
F - CIRCULATION TUBE
COOLANT
IN
COOLANT
OUT
EMULSION
TO SETTLER ACID
A HCF B
D
CE
A - CONTACTOR REACTOR SHELL
B - TUBE BUNDLE ASSEMBLY
C - HYDRAULIC HEAD
D - MOTOR
E - IMPELLER
F - CIRCULATION TUBE
COOLANT
IN
COOLANT
OUT
EMULSION
TO SETTLER ACID
A HCF B
D
CE
Figure 5: Stratco® Contactor
TM
reactor used in sulfuric acid-catalyzed alkylation [47].
The second process using sulfuric acid is ExxonMobil’s auto-refrigerated process [46]. The
reactor consists of a large horizontal vessel divided into a series of reaction zones, each
equipped with a stirrer (Figure 6). The alkene feed is premixed with recycle isobutane and fed
in parallel to all mixing zones. The acid and additional isobutane enter only the first zone and

cascade internally to the other zones. The heat of the reaction is removed by evaporating
isobutane plus added propane from the reaction zones. Thus, cooling coils are not necessary.
Figure 6: ExxonMobil auto-refrigerated alkylation process. Taken from [46].
Hydrofluoric acid-catalyzed processes
ConocoPhillips offers a process where the hydrocarbon mixture is introduced in a non-cooled
riser-type reactor through nozzles at the bottom and along the length of the reactor
[56](Figure 7). The acid is injected at the bottom. Perforated trays provide a high dispersion of
the hydrocarbons in the acid phase. The reaction mixture enters the settler where the acid is
withdrawn at the bottom and cooled in a heat exchanger to remove the heat of reaction. The
hydrocarbons are separated in a fractionation section.
Water
out
Reactor
standpipe
Reactor riser
Additional
hydrocarbon
injection points
located in
various locations
Hydrocarbon
feed bottom
injection nozzles
Water
in
Water
out
Reactor
standpipe
Reactor riser
Additional
hydrocarbon
injection points
located in
various locations
Hydrocarbon
feed bottom
injection nozzles
Water
in
Figure 7: ConocoPhilips HF alkylation reactor [56].

The UOP HF alkylation process uses a vertical reactor-heat exchanger (Figure 8). The
isobutane–alkene mixture enters the shell of the reactor through several nozzles, and HF
enters at the bottom of the reactor. The reaction heat is removed by cooling water, which
flows through cooling coils inside the reactor.
alkene
feed
Recycle i-C4
Regenerated HF
to settlercooling
water
HF from
settler
alkene
feed
Recycle i-C4
Regenerated HF
to settlercooling
water
HF from
settler
Figure 8: UOP HF alkylation reactor [5].
Over recent years, the industry has addressed the issue of the potential environmental impact
of HF leaks and has developed effective mitigation strategies. Two general strategies have
been employed, the first related to the installation of remotely operated isolation valves, water
curtain/cannon systems and rapid acid dump systems. The second strategy relates to the use
of vapor reduction additive. The advantage of this mitigation system, with respect to the
traditional methods of risk mitigation, is that its efficiency does not rely on rapid detection and
localization of HF leaks. Examples of this strategy are the OUP/Texaco Alkad process and
the Philipps/Mobil ReVap technology [1,57]. To face the risks related to HF-catalyzed
alkylation plants, an even more drastic solution consists in converting existing HF alkylation
units to use H2SO4. An example of this technology is the Stratco AlkySafe. Recently, it has
also be claimed the possibility to convert an HF alkylation plant to use solid alkylation
catalysts
Solid acid-catalyzed alkylation.
Regeneration
The overall scheme for solid acid-catalyzed alkylation processes is similar to that for liquid
acid-catalyzed processes, the main difference being the presence of a regeneration unit.
Periodic regeneration is necessary for all solid alkylation catalysts developed, when employed
at commercially feasible conditions. To extend the lifetime of the solid catalysts, several
regeneration methods have been developed, such as combustion or hydrocracking, extraction
with liquid or supercritical fluid, and hydrogenative regeneration.
The main inconvenience of the regeneration by combustion of organic deposits in air is the
reorganization of the hydrocarbons left on the catalyst, changing from an aliphatic to an
aromatic structure, during temperature increase [58]. For this reason to regenerate the
catalyst it is necessary to reach temperature as high as 600°C. This causes dealumination
and degradation of the zeolite and in turn requires catalysts with extremely high temperature

stability. Alternatively Querini suggested a first treatment with ozone (which reduces the
amount of coke and converts it to a structure easier to be burnt, followed by a treatment either
in H2 or in He to complete the operation [58]. However, the use of ozone in large quantities for
oxidative regeneration in ana industrial process is hard to imagine.
Hydrogenative treatment was first patented by Union Carbide as early as 1974 [59,60]. Here
the activity of a fixed bed zeolite containing a metal hydrogenation component (Pt) was fully
recovered by periodic regeneration either with hydrogen dissolved in a liquid hydrocarbon
(typically isobutane) or with gas-phase hydrogen. The efficiency of the method was proved for
12 and 19 cycles alkylation/regeneration. For both treatments a temperature of 65°C was
reported in the application examples, although it was claimed that temperatures between 27
and 300°C could be employed. The treatment pressure was the same used in the alkylation
reaction (33 bar) for liquid-phase regeneration while increasing pressures (from 1 to 33 atm)
were required for gas-phase regeneration.
Since 1974 several patents have claimed the possibility to extend the useful lifetime of solid
acid catalyst by periodic hydrogenative treatments which represents variations of the original
methods from Union Carbide [61-66]. Up to date hydrogenative regeneration is scarcely
documented in the open literature. Recently Weitkamp’s group reported that the alkylation
activity of a 0.4Pt/La-X or 0.4Pt/La-Y can be completely recovered in a cycled regeneration
process where step of alkylation reaction are alternated with hydrogenative gas-phase
regeneration steps performed at 300°C with 15 bar H2 [67,68].
Solid alkylation catalysts can also be regenerated by washing with hydrocarbons. Ginosar et
al. [69-72] in a systematic manner the regeneration of a USY zeolite with light hydrocarbons
(C3-C5). They found supercritical conditions to be more effective than liquid phase and near-
critical conditions. Isobutane was reported to be the most effective reactivation fluid with the
additional advantage that it is an alkylation reactant. Supercritical reactivation could provide
full activity recovery only if performed on catalysts moderately deactivated. The activity
recovery from catalyst completely was not higher than 80%. An alkylation process where the
catalyst is periodically regenerated by extraction with a mixture of C8-C15 saturated
hydrocarbons has been patented [73].
Processes with solid catalysts
The UOP AlkyleneTM
process is schematically shown in Figure 9. It utilizes a vertical riser, in
which the feed, freshly regenerated catalyst and recycled isobutane are injected from the
bottom [74]. At the top of the reactor the catalyst is separated from the products. It sinks down
into the reactivation zone where it is regenerated in a mixture of isobutane and hydrogen. To
provide complete reactivation a small amount of catalyst is withdrawn and regenerated batch-
or semi-batch-wise in a reactivation vessel in vapor phase. The catalyst, which is referred to
as HAL-100TM
, might be alumina-supported AlCl3 modified with alkali metal ions and a
hydrogenation metal such as Ni, Pd or Pt [75].
Isobutane
recycle
Reactivation
wash zone
Feed
treatment
Reactivation
wash zone
Alkylate
Alkylene
reactor
Reactivation
vessel
Light
ends
Fractionation
section
Olefin
feed
LPG
i-C4/H2
i-C4/H2
Isobutane
recycle
Reactivation
wash zone
Feed
treatment
Reactivation
wash zone
Alkylate
Alkylene
reactor
Reactivation
vessel
Light
ends
Fractionation
section
Olefin
feed
LPG
i-C4/H2
i-C4/H2
Figure 9: UOP Alkylene
TM
solid acid-catalyzed alkylation process [74].

LURGI and Süd-Chemie AG have developed a solid acid-catalyzed alkylation process called
Lurgi Eurofuel®
. The reactor technology uses a new type of reactive distillation. Isobutane and
suspended catalyst enter at the top of the tower while the alkene with premixed isobutane is
introduced in stages (Figure 10). The evolved heat of reaction is most likely dissipated by
evaporation of the reaction mixture. Thus, the temperature is controlled by the overall
pressure and the composition of the liquid. The catalyst–reactant mixture is agitated by the
boiling mixture of alkylate and isobutane. At the bottom of the column the catalyst is
separated and intermittently regenerated by exposition to hydrogen-rich operating conditions.
The catalyst is faujasite derived, with a high concentration of sufficiently strong Brųnsted acid
sites and a minimized concentration of Lewis acid sites. It also contains a hydrogenation
function.
C4
= +
iC4
iC4
Steam
Cooling
water
Cooling
water
Alkylate
Steam
C4
= +
iC4
iC4
Steam
Cooling
water
Cooling
water
Alkylate
Steam
Figure 10: Lurgi Eurofuel
®
solid acid-catalyzed alkylation process [76].
Akzo Nobel and ABB Lummus recently stated a solid acid-catalyzed alkylation process,
referred to as AlkyCleanTM
in a pilot plant in Finland [77]. The demonstrative unit incorporates
three reactors where one is used for alkylation alternating with another in mild regeneration
and a third reactor undergoing high temperature regeneration. Hydrogen is used to
regenerate the catalyst. The catalyst is reported to be a “true solid acid” without halogen ion
addition. In the patent describing the process [61], a Pt/USY zeolite with alumina binder is
employed.
Fixed-bed alkylation (FBATM
) process of Haldor Topsųe uses liquid triflic acid, which is
supported on a porous material [78-80]. This allows the use of a simple fixed-bed reactor as if
the catalyst was truly solid. The acid in the bed is concentrated in a distinct band, the
“reactive band”. The liquid hydrocarbon phase passes through the reactor in plug flow. In the
top of the reactive band the olefin comes into contact with a supported acid molecule and
forms an ester. The ester is less strongly adsorbed on the solid support than the acid and
tends to move down with the flow direction into the acid-rich zone Figure 11. The acid in the
acid-rich zone catalyses the reaction of the ester with isobutane to form alkylate and an acid
molecule. The acid readsorbs on the support and the alkylate molecule flows downward with
the hydrocarbon phase. The reaction mechanism results in a downward but slow movement
of the reactive band, in the direction of the hydrocarbon flow. The spent acid can be
withdrawn from the reactor without interrupting the production. The acid is regenerated in a
proprietary acid recovery unit, which produces some oil as a by-product.

Solid supported material
(particulate porous solid)
Direction of movement
of reactive band
Acid-rich zone
Ester formation zone
Flow of Hydrocarbon phase
(olefin feed and isoparaffins)
SLP
Catalyst
zone
Solid supported material
(particulate porous solid)
Direction of movement
of reactive band
Acid-rich zone
Ester formation zone
Flow of Hydrocarbon phase
(olefin feed and isoparaffins)
SLP
Catalyst
zone
Figure 11: Reaction zone in Haldor Topsųe’s alkylation process [78].
Conclusions
The alkylation mechanism, the influence of the catalyst type and reaction conditions show
that, in essence, the chemistry is identical with all the examined liquid and solid acid catalysts.
Differences in the importance of individual reaction steps originate from the variety of possible
structures and distributions of acid sites of solid catalysts. Changing process parameters
induces similar effects with each of the catalysts. However, the sensitivity to a particular
parameter depends strongly on the catalyst. All the acids deactivate by the formation of
unsaturated polymers, which are strongly bound to the acid.
Liquid acid-catalyzed processes are mature technologies, which are not expected to undergo
dramatic changes in the near future. Solid acid-catalyzed alkylation now has been developed
to a point where the technology can compete with the existing processes. Catalyst
regeneration by hydrogen treatment is the method of choice in all the process developments.
Some of the process developments eliminate most, if not all, the drawbacks of the liquid acid
processes. The verdict about whether solid acid-catalyzed processes will be applied in the
near future will be determined primarily by economic issues.
Bibliographic references
(1) Pryor, P. S., PTQ Winter 2004, 69.
(2) Furimsky, E. Catal. Today 1996, 30, 223.
(3) Garwood, W. E.; Venuto, P. B. J. Catal. 1968, 11, 175.
(4) Kirsch, F. W.; Potts, J. D.; Barmby, D. S. J. Catal. 1972, 27, 142.
(5) Feller, A.; Lercher, J. A. Adv. Catal. 2004, 48, 229.
(6) Corma, A.; Martķnez, A. Catal. Rev. 1993, 35, 483.
(7) Weitkamp, J.; Traa, Y. In Handbook of Heterogeneous Catalysis; Ertl, G., Knözinger, H.,
Weitkamp, J., Eds.; VCH: Weinheim, 1997; Vol. 4; pp 2039.
(8) Feller, A.; Zuazo, I.; Guzman, A.; Barth, J. O.; Lercher, J. A. J. Catal. 2003, 216, 313.
(9) Kazansky, V. B. Catal. Today 1999, 51, 419.
(10) Albright, L. F.; Spalding, M. A.; Nowinski, J. A.; Ybarra, R. M.; Eckert, R. E. Ind. Eng. Chem. Res.
1988, 27, 381
(11) Sanchez-Castillo, M. A.; Agarwal, N.; Miller, C.; Cortright, R. D.; Madon, R. J.; Dumesic, J. A. J.
Catal. 2002, 205, 67.
(12) Li, K. W.; Eckert, R. E.; Albright, L. F. Industrial & Engineering Chemistry Process Design and
Development 1970, 9, 441.
(13) Feller, A.; Barth, J.-O.; Guzman, A.; Zuazo, I.; Lercher, J. A. J. Catal. 2003, 220, 192.
(14) Pater, J.; Cardona, F.; Canaff, C.; Gnep, N. S.; Szabo, G.; Guisnet, M. Ind. Eng. Chem. Res.
1999, 38, 3822.
(15) Yaluris, G.; Rekoske, J. E.; Aparicio, L. M.; Madon, R. J.; Dumesic, J. A. J. Catal. 1995, 153, 54.
(16) Beirnaert, H. C.; Alleman, J. R.; Marin, G. B. Ind. Eng. Chem. Res. 2001, 40, 1337.
(17) Platon, A.; Thomson, W. J. Appl. Catal. A-Gen. 2005, 282, 93.
(18) Platon, A.; Thomson, W. J. Catal. Lett. 2005, 101, 15.
(19) Simpson, M. F.; Wei, J.; Sundaresan, S. Ind. Eng. Chem. Res. 1996, 35, 3861.
(20) Albright, L. F. Chemtech 1998, 40.

(21) Flego, C.; Kiricsi, I.; Parker, J., W. O.; Clerici, M. G. Appl. Catal. A-Gen. 1995, 124, 107.
(22) Eder, F.; Lercher, J. A. Zeolites 1997, 18, 75.
(23) Haag, W. O. Stud. Surf. Sci. Catal. 1995, 84, 1375.
(24) Diaz-Mendoza, F. A.; Pernett-Bolano, L.; Cardona-Martinez, N. Thermochim. Acta 1998, 312, 47.
(25) Nivarthy, G.; Seshan, K.; Lercher, J. A. Micropor. Mesopor. Mater. 1998, 2, 379.
(26) Feller, A.; Guzman, A.; Zuazo, I.; Lercher, J. A. J. Catal. 2004, 224, 80.
(27) Corma, A.; Martinez, A.; Martinez, C. J. Catal. 1994, 146, 185.
(28) de Jong, K. P.; Mesters, C. M. A. M.; Peferoen, D. G. R.; van Brugge, P. T. M.; de Groot, C.
Chem. Eng. Sci. 1996, 51, 2053.
(29) Weitkamp, J.; Traa, Y. Catal. Today 1999, 49, 193.
(30) Cumming, K. A.; Wojciechowski, B. W. Catal. Rev.-Sci. Eng. 1996, 38, 101.
(31) Wielers, A. F. H.; Vaarkamp, M.; Post, M. F. M. J. Catal. 1991, 127, 51.
(32) Ward, J. W. J. Catal. 1969, 14, 365.
(33) Ward, J. W. J. Catal. 1969, 13, 321.
(34) Yoo, K.; Burckle, E.; Smirniotis, P. Catal. Lett. 2001, 74, 85.
(35) Corma, A.; Juan-Rajadell, M. I.; Lopez-Nieto, J. M.; Martinez, A.; Martinez, C. Appl. Catal. A-Gen.
1994, 111, 175.
(36) Corma, A.; Martinez, A.; Martinez, C. Appl. Catal. A-Gen. 1996, 144, 249.
(37) Xiao, X.; Tierney, J. W.; Wender, I. Appl. Catal. A-Gen. 1999, 183, 209.
(38) Rorvik, T.; Dahl, I. M.; Mostad, H. B.; Ellestad, O. H. Catal. Lett. 1995, 33, 127.(39) Botella, P.;
Corma, A.; Lopez-Nieto, J. M. J. Catal. 1999, 185, 371.
(40) Olah, G. A.; Mathew, T.; Goeppert, A.; Torok, B.; Bucsi, I.; Li, X. Y.; Wang, Q.; Marinez, E. R.;
Batamack, P.; Aniszfeld, R.; Prakash, G. K. S. J. Am. Chem. Soc. 2005, 127, 5964.
(41) Clet, G.; Goupil, J. M.; Szabo, G.; Cornet, D. Appl. Catal. A-Gen. 2000, 202, 37.
(42) Moreno, M.; Rosas, A.; Alcaraz, J.; Hernandez, M.; Toppi, S.; Da Costa, P. Appl. Catal. A-Gen.
2003, 251, 369.
(43) He, Y.; He, Y. Appl. Catal. A-Gen. 2004, 268, 115.
(44) Ingallina, P.; de Angelis, A.; Parker, W. O.; Clerici, M. G. Catal. Lett. 2002, 78, 297.
(45) Yoo, K.; Namboodiri, V. V.; Varma, R. S.; Smirniotis, P. G. J. Catal. 2004, 222, 511.
(46) Ackerman, S.; Chitnis, G. K.; McCaffrey, D. S. J. Prepr. Div. Petrol. Chem., Am. Chem. Soc.
2001, 46, 241.
(47) Kinnear, S. "STRATCO Alkylation Seminar", 1998, Phoenix, AZ.
(48) Gary, J. H.; Handwerk, G. E. In Petrolium Refining-Technology and Economics; Albright, L. F.,
Maddox, R. N., McKetta, J. J., Eds.; Marcel Dekker: New York, 1979; pp 142.
(49) Husain, A., 1994, US patent 5,304,698.
(50) Lyon, C. J.; Sarsani, V. S. R.; Subramaniam, B. Ind. Eng. Chem. Res. 2004, 43, 4809.
(51) Ginosar, D. M.; Fox, R. V.; Kong, P. C., 2000, US Patent 6,103,948.
(52) Santana, G. M.; Akgerman, A. Ind. Eng. Chem. Res. 2001, 40, 3879.
(53) Ginosar, D. M.; Thompson, D. N.; Coates, K.; Zalewski, D. J. Ind. Eng. Chem. Res. 2002, 41,
2864.
(54) Chen, W.-S. Appl. Catal. A-Gen. 2003, 255, 231.
(55) Albright, L. F. Ind. Eng. Chem. Res. 2003, 42, 4283.
(56) http://fuelstechnology.com/soft_processoverview.htm, 2000.
(57) Tyas, A. R.; Parker, T., PTQ spring 2002, 65.
(58) Querini, C. A. Catal. Today 2000, 62, 135.
(59) Yang, C.-l., 1974, US patent 3,851,004.
(60) Yang, C.-l., 1975, US Patent 3,893,942.
(61) Van Broekhoven, E. H.; Cabre, F. R. M.; Bogaard, P.; Klaver, G.; Vonhof, M., 1999, US Patent
5,986,158.
(62) Zhang, S. Y.-F.; Gosling, C. D.; Sechrist, P. A.; Funk, G. A., 1997, US Patent 5,675,048.
(63) Zhang, S. Y.-F.; Gosling, C. D.; Sechrist, P. A.; Funk, G. A., 1997, US Patent 5,675,048.
(64) Kojima, M.; Kocal, J. A., 1994, US patent 5,310,713.
(65) Gosling, C. D.; Weiler, D. L.; De Villiers, R. A., 1998, US Patent 5,849,976.
(66) Shields, D. J. S., P.A., 2002, US Patent 6,392,114.
(67) Klingmann, R.; Josl, R.; Traa, Y.; Glaser, R.; Weitkamp, J. Appl. Catal. A-Gen. 2005, 281, 215.
(68) Josl, R.; Klingmann, R.; Traa, Y.; Glaser, R.; Weitkamp, J. Catalysis Communications 2004, 5,
239.
(69) Ginosar, D. M.; Thompson, D. N.; Burch, K. C. Appl. Catal. A-Gen. 2004, 262, 223.
(70) Ginosar, D. M.; Thompson, D. N.; Coates, K.; Zalewski, D. J.; Fox, R. V., 2003, US Patent
6,579,821.
(71) Petkovic, L. M.; Ginosar, D. M. Appl. Catal. A-Gen. 2004, 275, 235.
(72) Thompson, D. N.; Ginosar, D. M.; Burch, K. C. Appl. Catal. A-Gen. 2005, 279, 109.
(73) He, Y. H., Y.; Xie, W.; Fu, Q., 2002, US Patent 6,492,571.
(74) Black, S. M.; Gosling, C. D.; Steigleder, K. Z.; Shields, D. J. NPRA Annual Meeting, 2000, San
Antonio, TX, USA.
(75) McBride, T. K.; Bricker, M. L.; Steigleder, K. Z., 1999, 5,883,039.
(76) Buchold, H.; Dropsch, H.; Eberhardt, J. 17th World Petroleum Congress, 2002, Brazil.

(77) D'Amico, V. J. v. B., E.H.; Nat, P.J.; Nousiainen, H.; Jakkula, J. NPRA Annual Meeting, 2002,
San Antonio, Tx, USA.
(78) Hommeltoft, S. I. Appl. Catal. A-Gen. 2001, 221, 421.
(79) Hommeltoft, S. I. Ind. Eng. Chem. Res. 2003, 42, 5526.
(80) Jonsdottir, J. H. S.-A. P., PTQ summer 1998.

akylation

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (19)

Ähnlich wie akylation

Ähnlich wie akylation (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

akylation