Alkylation process using dual metal ultrastable Y zeolite

A process for the alkylation/transalkylation of benzene is improved by the use of a catalyst prepared by exchanging a sodium Y zeolite with an ammonium salt to replace from about 40 percent to about 90 percent of the sodium ions with ammonium ions; calcining the resulting ammonium-sodium zeolite in steam under conditions sufficient to reduce the unit cell size to about 24.48 to 24.60 angstroms; contacting the calcined catalyst with a rare earth salt and an aluminum salt either simultaneously or sequentially; and calcining the catalyst a second time in the absence of steam.

BACKGROUND OF THE INVENTION 
This invention is related to the liquid-phase alkylation/transalkylation of 
aromatic hydrocarbons, particularly the alkylation/transalkylation of 
benzene and substituted benzenes to form ethylbenzene. 
Various processing schemes comprising alkylation and/or transalkylation 
reactions are known to produce monoalkylaromatic products such as 
ethylbenzene in high yields. However, existing processes are not without 
problems including the production of undesirable by-products. For example, 
the production of unwanted xylenes is a particular problem in the 
production of ethylbenzene in the vapor phase commercial process using 
ZSM-5 zeolites. Another problem with existing processes concerns the use 
of Friedel Crafts catalysts such as solid phosphoric acid or aluminum 
chloride. The phosphoric acid catalysts generally require the use of a 
water co-feed which produces a corrosive sludge by-product. Problems 
concerning the sludge by-product can be avoided by the use of zeolite 
catalysts. 
The use of large pore zeolite catalysts in the alkylation of aromatic 
hydrocarbons is known in the art. Early catalysts were made by simple 
exchange of the zeolite with a metal salt. For example, U.S. Pat. No. 
2,904,607 to Mattox refers to the use of a crystalline metallic 
aluminosilicate having uniform pore openings of about 6 to 15 angstroms in 
the alkylation of aromatic hydrocarbons with an olefin. Zeolite alkylation 
and/or transalkylation catalysts containing a combination of metal and 
hydrogen sites are well known. U.S. Pat. No. 3,251,897 to Wise describes 
liquid phase alkylation in type zeolites containing rare earth and 
hydrogen. Wang 
et al., Journal of Catalysis, 24, 262-271 (1972) describe Y zeolites 
containing a combination of aluminum and hydrogen that have activity for 
toluene disproportionation. 
Despite these teachings, Type Y zeolites have not been generally used in 
commercial alkylation of aromatic hydrocarbons, particularly in the 
production of ethylbenzene. A major problem relating to these catalysts is 
low activity. An additional problem concerns lack of stability, that is, 
the loss of crystallinity when a catalyst containing exchanged (i.e. 
cationic) aluminum and/or hydrogen is exposed to water vapor above 
400.degree. C. This means that the catalyst cannot be effectively 
regenerated. One approach to avoiding this problem is to use a non-metal 
stabilized Y zeolite. Such catalysts are typically prepared by partial 
ammonium ion exchange, steam calcination and further ammonium ion 
exchange. A final heat treatment drives off ammonia gas and leaves an 
activated hydrogen form of the zeolite. Such catalysts are discussed in 
U.S. Pat. Nos. 3,449,070 to McDaniel et al.: 3,493,519 to Kerr et al.: 
3,293,192 to Maher et al.: 3,354,077 to Hansford: 3,929,672 to Ward: and 
3,641,177 to Eberly et al. While these catalysts possess adequate thermal 
and hydrothermal stability, their catalytic properties are not stable as 
selectivities decrease significantly with relatively few regeneration 
cycles, apparently related to the continued shrinkage of the unit cell 
size. 
Thus, Y zeolite catalysts in the hydrogen form are not stable and possess 
low activity. Rare earth exchanged Y zeolites are stable, but again 
possess insufficient activity. Non-metal stabilized Type Y zeolites are 
also stable, but possess selectivities that decline when regenerated. 
There remains a need for an effective process for the preparation of 
alkylated aromatics such as ethylbenzene utilizing a stable catalyst 
having good activity and selectivity. 
SUMMARY OF THE INVENTION 
The present invention is a process for the preparation of a dual metal 
ultrastable Y zeolite comprising the following steps: 
(a) contacting a Y zeolite with an ammonium salt to replace from about 40 
percent to about 90 percent of the alkali metal ions with ammonium ions: 
(b) calcining the zeolite resulting from step (a) in steam under conditions 
sufficient to reduce the unit cell size to about 24.48 to about 24.60 
angstroms: 
(c) contacting the calcined zeolite of step (b) with a rare earth salt 
under conditions sufficient to result in the zeolite containing from about 
2 to about 5 weight percent of the rare earth: 
(d) calcining the zeolite a second time in the absence of steam following 
step (c): and 
(e) contacting the zeolite a second time with an aluminum salt to further 
reduce the alkali metal content to below about 0.3 weight percent. 
In the practice of the present invention, steps (c) and (e) may be 
conducted simultaneously or step (e) may follow step (d). 
The present invention also comprises the use of the zeolite prepared as 
described above in the alkylation of aromatic compounds such as the 
alkylation of benzene with ethylene to produce ethyl benzene. 
The zeolite of the present invention demonstrates good catalytic activity 
and selectivity levels in the alkylation and transalkylation of aromatic 
compounds and retains its stability and high selectivity after 
regenerations. Without wishing to be bound by theory, it is believed that 
the specified unit cell size contributes to the good selectivity and is 
stabilized by the rare earth exchange and that the activity level is 
achieved by the aluminum exchange.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
The zeolite material used as a starting material herein is faujasite or 
Type Y zeolite. Such zeolites are well known and have been described, for 
example in U.S. Pat. 3,130,007. The zeolite has a Si to Al ratio ranging 
from about 3:1 to about 6:1. Such zeolites may be synthesized by reacting 
silica, sodium aluminate and caustic in water according to the mole ratio: 
EQU 3.4 Na.sub.2 O : 1.0 Al.sub.2 O.sub.3 : 9.5 SiO.sub.2 : 136 H.sub.2 O. 
Water and caustic are mixed and then a mixture of sodium aluminate, caustic 
and water is added. The temperature of this material is maintained below 
about 40.degree. C. and silica is added. This mixture is stirred slowly 
for 24 hours and the temperature is then increased to about 100.degree. C. 
and maintained. The Type Y zeolite forms in about 24 to 36 hours. 
Alternatively, Type Y zeolite may be obtained commercially. The sodium 
form of Type Y zeolite is typically used although Type Y zeolite with 
other metal cations may be used. It will be recognized when sodium 
zeolites are referred to herein, that other metal cations may be 
substituted for the sodium. 
The zeolite is exchanged with an ammonium salt in aqueous solution such 
that from about 40 to about 90 percent of the sodium ions (or other 
cations) are replaced with ammonium ions. Examples of ammonium salts that 
are useful include, for example, nitrate, chloride, sulfate and acetate 
salts. Since the anion is passive in the ion exchange, its identity is not 
critical. It is preferred that from about 50 to about 80 percent of the 
sodium ions are exchanged and more preferred that about 60 to about 70 
percent are exchanged. The sodium content is preferably reduced to a range 
of from about 2.5 to about 6.5 weight percent as Na.sub.2 O. This exchange 
may be accomplished using known techniques such as simply heating the 
zeolite in an aqueous solution of the ammonium salt for one to two hours 
at 100.degree. C. 
The exchanged zeolite is then calcined in the presence of steam. A 
combination of degree of ammonium exchange, calcination temperature, steam 
partial pressure and calcination time is selected to result in a reduction 
of the unit cell size (u.c.s.) of the zeolite to the range of from about 
24.48 to about 24.60 angstroms, preferably from about 24.50 to 24.57 
angstroms. The specified u.c.s. is critical to the zeolite of the present 
invention in order to obtain good selectivity. 
In a preferred embodiment wherein about 60 to about 70 percent of the 
sodium ions have been replaced with ammonium ions, calcination temperature 
is from about 450.degree. to about 600.degree. C., steam partial pressure 
is from about 10 to 15 psi and the time for calcination is in the range of 
from about 2 to about 8 hours. 
The steam calcined zeolite is then contacted with an aqueous solution of a 
rare earth salt. By rare earth is meant the elements Y, La, Ce, Pr, Nd, 
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. After this exchange, the 
zeolite contains from about 2 to about 5 weight percent of the rare earth. 
This exchange step is conducted at a temperature of from about 25 to about 
250.degree. C., more preferably from about 70.degree. to about 100.degree. 
C. Without wishing to be bound by any theory, it is assumed that the 
presence of the rare earth ion which is relatively larger than aluminum or 
hydrogen provides the needed stability to prevent shrinkage of unit cell 
size when the catalyst is subjected to regeneration. 
Following the rare earth exchange, the zeolite is calcined. The temperature 
of this calcination is preferably from about 400.degree. to about 
700.degree. C. for 1 to 10 hours, more preferably at a temperature of from 
about 500.degree. to 600.degree. C. for about 2 to 5 hours. It is also 
preferred that this calcination step is conducted in a purge of dry air or 
nitrogen. Without wishing to be bound by theory, it is believed that this 
calcination drives the rare earth into zeolitic sites which are optimum 
for unit cell size stabilization. 
After this calcination, the zeolite is contacted with an aqueous solution 
of an aluminum salt, so that the final sodium content of the zeolite is 
reduced below about 0.3, more preferably about 0.15 weight percent. In an 
alternative embodiment, the aluminum and rare earth exchange is performed 
simultaneously followed by the calcination. Due to the acidic nature of 
the aluminum salt, some cationic hydrogen is exchanged simultaneously with 
the aluminum. The combination of aluminum and hydrogen is believed to 
contribute significantly to the activity and selectivity exhibited by the 
catalyst of the present invention. 
The zeolite catalyst may be used in combination with a support or binder 
material such as, for example, a porous inorganic oxide support or a clay 
binder. Non-limiting examples of such materials include alumina, zirconia, 
silica, magnesia, thoria, titaria, boria, beryllia, chromia and 
combinations thereof. Suitable clay materials include bentonite and 
kieselguhr. The relative proporation of zeolite can be between about 1 and 
99 weight percent, more preferably between 10 and 95 weight percent. The 
binder or support may be added at any stage of the catalyst preparation. 
In a preferred embodiment, the initial NaY zeolite is mixed with the 
binder or support to produce tablets or extrudates through conventional 
procedures. The ion exchanges can then be carried out by pumping the 
exchange salts through a bed of the tablets or extrudates to effect the 
exchange. 
The preparation of the zeolite catalyst of the present invention may 
comprise, consist essentially of or consist of the steps described above. 
It will also be recognized that the dual metal ultrastabilized zeolite of 
the present invention may be prepared in the absence of any additional 
elements not specifically mentioned above. 
Hydrocarbons which are alkylated or transalkylated by the process of the 
present invention include aromatic compounds such as benzene, napthalene 
and anthracene and substituted versions thereof. Examples of substituents 
include lower alkyl, tertiarybutyl, cycloalkyl, phenyl and napthyl. In a 
preferred embodiment, benzene is alkylated, and substituted benzenes are 
transalkylated, to produce ethylbenzene. 
Alkylating agents include C.sub.2-24 alkenes, C.sub.1-24 alkyl halides, 
C.sub.1-24 alcohols and formaldehyde. Preferred alkylating agents include 
ethylene, propylene and dodecylene with ethylene being more preferred. 
As will be recognized by one skilled in the art, operating conditions 
employed in the process of the present invention are critical and will 
depend, to a great extent, on the particular alkylation reaction being 
effected. 
In a preferred embodiment wherein benzene or substituted benzene is the 
aromatic hydrocarbon to be alkylated, the ratio of the benzene or 
substituted benzene to catalyst may be any weight ratio which produces the 
desired alkylated benzene with a relatively high selectivity and a low 
level of impurities. Preferred ratios will also be dependent on the 
reactor configuration. For example, in batch reactors, the weight ratio of 
benzene or substituted benzene to catalyst is preferably in the range from 
about 0.1:1 to about 2000:1. More preferably, the weight ratio is in the 
range from about 10:1 to about 500:1. Most preferably, the ratio is in the 
range from about 50:1 to about 100:1. Below the preferred lower limit of 
0.1:1, the productivity will be very low. Above the preferred upper limit 
of 2000:1, the conversion of the aromatic compound may be low. 
The ratio of benzene or substituted benzene to alkylating agent may vary 
depending on the identity of the alkylating agent, type of reaction such 
as batch or continuous and reaction conditions such as temperature, 
pressure and weight hourly space velocity (WHSV). When the alkylating 
agent is ethylene, the ratio of benzene to ethylene is preferably from 
about 10:1 to about 3:1 in a continuous reactor. As is recognized by one 
skilled in the art, when different reactor configurations are used, 
different ratios of reactants may be preferred. 
The alkylating agent may be introduced to the reaction all at once, as in 
the case of a liquid alkylating reagent. Alternatively, the alkylating 
agent may be introduced to the reaction on demand until the desired degree 
of conversion is achieved, as in the case of a gaseous alkylating agent 
which is continuously fed into the reactor. 
The contacting of the benzene or substituted benzene with the alkylating 
agent in the presence of the catalyst may occur in a reactor of any 
configuration. Batch-type and continuous reactors, such as fixed bed, 
slurry bed, fluidized bed, catalytic distillation, or countercurrent 
reactors, are suitable configurations for the contact. Preferably, the 
reactor is fit with a means for observing and controlling the temperature 
of the reaction, a means for observing and measuring the pressure of the 
reaction, and optionally a means for agitating the reactants. The benzene 
or substituted benzene may be in the liquid form or in solution. The 
alkylating agent may be introduced in the liquid or gaseous state, and may 
be added all at once at the start of the reaction, or fed continuously on 
demand from the reaction. The catalyst may be used in various forms, such 
as a fixed bed, moving bed, fluidized bed, in suspension in the liquid 
reaction mixture, or in a reactive distillation column. 
The contacting of the reactants in the presence of the catalyst may occur 
at any temperature or pressure which will produce the desired alkylated 
products. In the production of ethylbenzene, the temperature is preferably 
in the range from about 100.degree. C. to about 300.degree. C., more 
preferably about 180.degree. C. to 250.degree. C. Below the preferred 
lower limit of 100.degree. C. the reaction proceeds slowly. Above the 
preferred upper limit of 300.degree. C., the impurity level increases. 
The pressure in the reactor is preferably in the range where the aromatic 
compound to be alkylated is maintained in the liquid phase. When benzene 
is the aromatic compound, the pressure is generally in the range of from 
about 500 psig to about 1000 psig to keep benzene in the liquid phase at 
reactor conditions. Below the preferred lower limit of about 500 psig, the 
benzene is in the vapor phase and time between regenerations cycles is 
substantially decreased. 
The benzene, alkylating agent and/or transalkylating agent and catalyst are 
contacted for a time sufficient to convert the benzene to alkylated 
products, and sufficient to produce the desired yield of product. 
Generally, the contact time will depend on other reaction conditions, such 
as temperature, pressure and reagent/catalyst ratios. 
Following the alkylation/transalkylation of the benzene or substituted 
benzene, the product mixture may be separated by standard techniques. 
In a preferred embodiment of this invention, benzene is alkylated with 
ethylene in the liquid phase by contact in a reaction zone with the rare 
earth/aluminum containing ultrastable Y zeolite catalyst described above 
under alkylation and/or transalkylation conditions sufficient to produce 
ethylbenzene. 
The following examples are given to illustrate the catalyst and the process 
of this invention and should not be construed as limiting its scope. All 
percentages in the examples are mole percent unless otherwise indicated. 
EXAMPLE 1 
Catalyst Preparation 
A commercially available 1/8 inch extrudate of a sodium form of Type Y 
zeolite bonded with 20 weight percent acid-washed inorganic oxide is used 
as the starting material. The extrudates are exchanged with aqueous 
ammonium chloride to replace 67 percent of the sodium with ammonium ions. 
A 380 gram portion of the extrudates are loaded into a tubular reactor and 
calcined at 550.degree. C. for six hours. Steam at one atmosphere pressure 
is maintained by pumping water into the top of the reactor at about 0.5 
ml/minutes. Excess water is allowed to drain out the bottom of the reactor 
through a water trap. 
The zeolite is cooled and then 8 liters of 0.25 M cerium nitrate are pumped 
over the zeolite at about 33 ml/minute. This exchange is carried out at 
90.degree. C. in a liquid-full vessel. Excess salt is flushed out with 
water. The cerium exchanged ultrastable Y zeolite is for about fifteen 
hours at 220.degree. C. in dry nitrogen. The bed temperature is then 
increased to 510.degree. C. and held for three hours under nitrogen flow. 
The bed is cooled and the zeolite is re-hydrated by passing water 
saturated nitrogen over the bed for about six hours. 
Eight liters of 0.25 M aluminum chloride is then pumped over the zeolite 
bed at about 33 ml/minute. This exchange is carried out at 90.degree. C. 
in a liquid-full vessel. Excess salt is flushed out with water and the 
catalyst is oven dried at 100.degree. C. 
EXAMPLE 2 
Catalyst Preparation 
The procedure outlined in Example 1 is followed with the exception that 8 
liters of a mixture of cerium nitrate (0.125 molar) and aluminum chloride 
(0.125 molar) are pumped over the zeolite at a rate of about 33 ml/minute 
rather than having the cerium and aluminum exchanges being conducted 
sequentially. The remainder of the catalyst preparation is not changed. 
EXAMPLE 3 
Alkylation of Benzene with Ethylene 
Sixty milliliters of the catalyst prepared in Example 1 are loaded into a 
one inch diameter stainless steel reactor and dried overnight at 
200.degree. C. in a flow of dry nitrogen. The bed temperature is then 
increased to 500.degree. C. and held for three hours while maintaining 
nitrogen flow. The bed is then cooled and benzene is pumped over the 
catalyst at 360 ml/hour. A backpressure of about 500 psig is maintained 
while the reactor temperature is increased to about 200.degree. C. 
Ethylene is then added at a rate so as to produce an epsilon of 0.21 
(epsilon is defined as the total moles of ethyl groups divided by the 
total moles of benzene rings). The temperature is adjusted to keep the 
ethylbenzene concentration at about 19 weight percent. The reactor is 
operated continuously for six days and the benzene feed rate is then 
reduced to 180 ml/minute and the ethylene feed rate is decreased to 
maintain an epsilon of 0.21. A maximum reactor temperature of 254.degree. 
C. was required to obtain a 19 weight percent ethylbenzene concentration. 
The reactor is operated continuously an additional six days during which 
the ethylbenzene concentration remained at 19 weight percent with a 
temperature increase of 2.degree. C. to 256.degree. C. 
EXAMPLE 4 
Two-stage Alkylation of Benzene with Ethylene 
Using the general procedure outlined in Example 3, benzene is alkylated 
with ethylene at an epsilon of 0.15. The product so obtained is then 
passed at 180 ml/hour over a 60 ml bed of the catalyst which had been 
regenerated eleven times by standard burn off in air. The backpressure is 
maintained at about 500 psig. The temperature is slowly increased to keep 
the ethylbenzene concentration about 26 percent. The reactor is operated 
continuously for 27 days during which the reactor temperature is increased 
from 217.degree. C. to 279.degree. C. 
EXAMPLE 5 
Two-stage Alkylation of Benzene with Ethylene 
Using the general procedure outlined in Example 4, benzene is alkylated 
with ethylene at an epsilon of 0.21. The product so obtained is then 
passed at 180 ml/hour over a 60 ml bed of the catalyst which had been 
regenerated ten times by standard burn off in air. The backpressure is 
maintained at about 500 psig. The temperature is slowly increased to keep 
the ethylbenzene concentration about 30 percent. The reactor is operated 
continuously for 24 days during which the reactor temperature is increased 
from 223.degree. C. to 301.degree. C.