Effluent separation method for aromatic hydrocarbon alkylation process

A process for the production of alkylaromatic hydrocarbons uses a light hydrocarbon recycle to reduce the costs of separating an unreacted aromatic feed substrate from aromatic hydrocarbon products. Unreacted aromatic substrate is combined with a light hydrocarbon, such as propane, to form a combined effluent stream. The combined effluent stream enters a flash separator where unreacted aromatic substrate is lifted overhead with the light hydrocarbon while heavier aromatic products are recovered below. The aromatic substrate and light hydrocarbon are easily separated in a simple separation zone. Lifting the aromatic substrate with the light hydrocarbon reduces the volume of aromatic substrate that remains with the aromatic product so that the more energy intensive separation of the aromatic substrate and aromatic product is performed on a reduced volume of material.

FIELD OF THE INVENTION 
The invention relates to a hydrocarbon conversion process. The invention 
more specifically relates to the production of alkylaromatic hydrocarbons 
by the reaction of an acyclic olefinic hydrocarbon with an aromatic feed 
hydrocarbon. 
PRIOR ART 
The alkylation of aromatic hydrocarbons such as benzene using solid 
catalysts is a well-developed art which is practiced commercially in large 
scale industrial units. One commercial application of this process is the 
alkylation of benzene with propylene to form cumene (isopropylbenzene), 
which is subsequently used in the production of phenol and acetone. Those 
skilled in the art are therefore familiar with the general design and 
operation of such alkylation process. 
The prior art is well described in the literature. For instance, a typical 
flow scheme suitable for commercial use is depicted in U.S. Pat. No. 
4,051,191 issued to D. J. Ward. This reference describes in some detail, 
catalyst, reaction conditions, and separatory methods suitable for the 
recovery of cumene. The reactor effluent is passed into a rectification 
zone in which propane, charged to the process in admixture with the feed 
propylene, is separated for recycling and for rejection from the process. 
Liquid phase hydrocarbons recovered in the rectification zone are then 
passed into a two-column fractionation train comprising a recycle column 
and a cumene or product column. The benzene feed aromatic hydrocarbon is 
recycled from the top of the first fractionation column. The product 
cumene is recovered from the top of the second fractionation column, with 
heavy aromatic by-products being withdrawn from the bottom of the second 
column. 
A somewhat different product recovery fractionation train for commercial 
use is described in the article at page 32 of the Mar. 21, 1983 edition of 
Chemical Engineering magazine. This system employs four fractionation 
columns in series. The first fractionation column is a depropanizer 
column. The third column is a product column in which cumene is removed as 
the net overhead product. The net bottoms stream of the product column is 
passed into a recycle column with the overhead stream of this column 
apparently being recycled to the reaction zone. The alkylation process 
described in this article is based upon the use of an aluminum chloride 
catalyst system as compared to the solid phosphoric acid-type catalyst 
which is preferred in the previously cited reference. 
A number of methods are known to enhance the efficiency of separating 
mixtures containing aromatic hydrocarbons. It is known in the art of 
fractional distillation that the latent heat present in the overhead 
vapors of one fractionation column may be employed in the reboiler means 
of another fractionation column for the purpose of supplying heat to the 
other fractionation column. This is shown for instance in U.S. Pat. No. 
3,254,024 issued to H. A. Huckins, Jr. et al. The Huckin's reference is 
directed to the separation of C.sub.8 aromatic hydrocarbons wherein 
overhead vapor from a xylene splitter column is used to reboil an 
ehtylbenzene column. U.S. Pat. No. 4,360,405 issued to U. Tsao is 
pertinent for its showing a fractionation arrangement for use in the 
separation of close boiling mixtures in which the overhead vapor of one 
column is compressed and passed into a bottom portion of an immediately 
upstream fractionation column. The bottoms liquid from this upstream 
column flows into the top of the downstream column. This reference 
indicates this arrangement could be employed for the separation of 
aromatic hydrocarbons exemplified by the xylenes. 
BRIEF SUMMARY OF THE INVENTION 
Briefly stated the invention is the addition of a working stream having a 
high energy content to a product stream comprising aromatic hydrocarbons 
in order to reduce the cost of separating recycled aromatic components 
from the product stream. The working stream comprises hydrocarbons having 
a boiling point which is substantially lower than the aromatic 
hydrocarbons and low enough to vaporize the working stream at the 
temperature of process streams containing unutilized or waste heat. The 
product stream and working stream enter a flash separator where the 
working stream lifts a substantial portion of an aromatic hyrocarbon from 
the product stream. Hydrocarbons of the working stream and the lifted 
aromatic hydrocarbons make up the flash separator overhead stream. This 
overhead stream enters a separation zone where the hydrocarbons of the 
working stream and the aromatic hydrocarbons are split. In this manner, 
the working stream absorbs relatively low level heat from the process and 
concentrates the heat so that it becomes a high enthalpy vapor that is 
used to reduce the external heat requirements of the process. 
In a more specific aspect of this invention, the product stream comprises 
the effluent of a reaction zone and includes unreacted aromatic 
hydrocarbon feed and relatively higher boiling aromatic product 
hydrocarbons and by-products. After passage through the flash separator 
and recovery in the separation zone, the feed aromatic hydrocarbons are 
recycled to the reaction zone while the working stream is recycled to the 
effluent of the reaction zone to facilitate separation of the feed 
hydrocarbons from the product hydrocarbons. This arrangement promotes 
efficiency by lifting a portion of the aromatic hydrocarbon feed in the 
flash separator and allowing a substantial portion of the feed 
hydrocarbons to be carried with the working fluid to the separation zone 
in which the aromatic hydrocarbon feed and working fluid hydrocarbons are 
easily split due to their relative boiling point difference. Therefore, 
the overall amount of feed and product aromatic hydrocarbons that must be 
separated in the fractionation column using external heat input is reduced 
by separating a portion of these hydrocarbons with waste heat from the 
process in the flash separator. This arrangement is particularly 
advantageous when the working fluid is normally present in the feed to the 
reaction zone so that separation facilities for removing the working fluid 
hydrocarbons are usually present. In such cases, the only cost associated 
with the recycling of separation hydrocarbon is the cost of a pump and 
relatively minor increases in flash separator facilities and utilities. 
In a broad embodiment of this invention, a feed aromatic hydrocarbon and an 
acyclic hydrocarbon are alkylated at alkylation conditions in an 
alkylation reaction zone to provide a reaction zone effluent that includes 
unconverted feed aromatic hydrocarbons, product aromatic hydrocarbons and 
hydrocarbon by-products. By the method of this invention, at least a 
portion of the aromatic hydrocarbon feed is recovered by combining the 
reaction zone effluent with a working fluid having a substantially lower 
boiling point than the aromatic hydrocarbon feed. The combined effluent 
stream is maintained at conditions suitable to keep most of the working 
fluid in the vapor phase. The combined effluent passes to a flash 
separator from which an overhead stream containing the working fluid and 
at least a portion of the aromatic hydrocarbon feed is recovered. The 
overhead stream from the flash separator passes to a separation zone from 
which a recycle stream comprising the aromatic hydrocarbon feed and a 
working fluid comprising low boiling hydrocarbons are recovered. At least 
a portion of the recycle stream is returned to the alkylation zone and at 
least a portion of the working fluid is combined with the reactor effluent 
stream.

DETAILED DESCRIPTION OF THE INVENTION 
The principal object of this invention is to decrease the cost of 
recovering alkylatable aromatic hydrocarbons from the effluent of a 
reaction zone for the alkylation of aromatic hydrocarbons by increasing 
the internal heat utilization of the process. Accordingly, this invention 
centers around the separation of the effluent stream and the method of 
operating a recovery section to separate the effluent into products, 
recycle material, and rejected components. Applicable effluent streams are 
those from an aromatic alkylation zone where an aromatic substrate and an 
acyclic alkylation agent are alkylated to yield at least one alkylate 
product having a boiling point that is higher than the boiling point of 
either the aromatic substrate or one of the alkylated aromatic products. 
The most benefit is obtained from the invention when the hydrocarbons of 
the effluent are primarily in a liquid phase. 
According to this invention, the effluent stream is admixed with a working 
fluid comprising hydrocarbons that aid in the separation of the aromatic 
substrate from the aromatic reaction products. The hydrocarbons of the 
working fluid are acyclic hydrocarbons having a substantially lower 
boiling point than that of the aromatic substrate. Preferably, the boiling 
point difference will be at least 60.degree. C. The working fluid 
hydrocarbon is preferably a light hydrocarbon composed of C.sub.4 or lower 
carbon number paraffins and more preferably, a C.sub.3 paraffin. Normally, 
the addition rate of the working fluid hydrocarbon is equal to 2%-20% of 
the net effluent mass flow rate. Essentially all of the working fluid will 
be in a vapor phase before it is combined with the effluent stream. The 
working fluid is vaporized by heat exchange with one or more process 
streams. Therefore, a suitable working fluid must be able to extract heat 
from one or more process streams at temperature levels that will vaporize 
the working fluid or preferably super heat the working fluid. In addition, 
the working fluid must be easily separated from the aromatic substrate. It 
is also desired to recycle the working fluid as a pumpable liquid; 
therefore, the working fluid is preferable condensable at ordinary process 
pressure levels without refrigeration. 
The combined effluent and working fluid enter a flash separator at a 
temperature sufficient to maintain a majority of the working fluid and a 
portion of the effluent in the vapor phase. This temperature is less than 
the boiling point of the aromatic substrate. The combined effluent and 
working fluid may be brought to a suitable temperature by external heating 
of the separation hydrocarbon, heating of the combined effluent stream, 
heat addition to the flash separator or a combination of the foregoing 
methods. The flash separator is maintained at temperature equal to or near 
the temperature of the aromatic substrate, such that the separation 
hydrocarbon will be primarily in the vapor phase and travel upward in the 
flash separator zone while essentially all the heavier aromatic reaction 
products will fall to the bottom of the flash separator. Since the working 
fluid is above its boiling point at the conditions of the flash separator, 
a portion of the lighter aromatic hydrocarbons will be vaporized so that 
the rising working fluid hydrocarbons will lift the aromatic substrate to 
the top of the flash separator. In this manner, the flash separator 
performs a rough split of the aromatic substrate between an overhead 
fraction which is relatively free of aromatic alkylation product and a 
bottom fraction which is relatively free of working fluid hydrocarbons. 
The working fluid hydrocarbon serves dual purposes of supplying internal 
heat from the process to lift a proportionately greater amount of aromatic 
substrate while at the same time acting as a diluent or stripping medium 
to lower the flash temperature of the effluent mixture in the flash 
separator. 
The flash separator is simple in design and may consist of a single vessel 
having an open interior. If desired, the flash separator may contain 
internals such as sieve trays, valve trays or packing. When boiling points 
are close, a small amount of reflux may be included to enhance the 
separation between the aromatic substrate and the aromatic alkylate 
product. The only major control variable for the flash separator is its 
temperature. By adjusting this temperature and the working fluid flow 
rate, it is possible to vary the quantity of aromatic substrate entering 
either the upper or lower effluents within a range of about 10%-70% of the 
total aromatic substrate entering the flash separator. In the case of a 
C.sub.3 hydrocarbon, working fluid and a benzene substrate, the flash 
separator is operated such that the effluent from the flash separator has 
a temperature of less than 205.degree. C. (400.degree. F.) and more 
preferably less than 190.degree. C. (370.degree. F.). The simple 
construction of the separator and the relatively easy means of operation 
makes the flash separator a relatively inexpensive adjunct to the recovery 
process. 
The bottoms stream from the flash separator will enter additional 
separation facilities to perform the more complete separation of the 
aromatic substrate and light hydrocarbon by-products from the aromatic 
alkylation product. Thus, energy usage in the subsequent separation stage 
is reduced proportionally by the amount of the aromatic substrate 
recovered in the rectification zone. Small amounts of light hydrocarbon 
by-products or working fluid hydrocarbons that are carried over with the 
bottoms stream are also received with the aromatic substrate. 
The upper stream from the flash separator, containing the aromatic 
substrate, the working fluid and in some cases a small amount of 
alkylation product is partially condensed for heat recovery purposes and 
then transferred to another separation zone. The desired degree of 
separation between the aromatic substrate and the working fluid 
hydrocarbons is readily accomplished in the next separation zone due to 
the difference in boiling points between the two compounds. The working 
fluid is principally recovered as an upper or overhead stream and at least 
a portion of it is recycled again to the reaction zone effluent to perform 
the lift function as previously described. Most of the aromatic substrate 
leaves the separation zone in a bottoms stream. At least a portion of the 
bottoms stream is recycled to the reaction zone. The separator may be 
operated to obtain a desired exclusion of working fluid hydrocarbons from 
the bottoms stream containing the aromatic substrate. 
As stated, this invention comprises passing an alkylating agent and an 
aromatic substrate to an alkylation reaction zone to obtain an alkylated 
aromatic product. Thus, this invention can be applied to a wide variety of 
aromatic alkylation operations. The aromatic substrate for this invention 
may be benzene or an alkyl substituted benzene. Examples of such 
substrates include benzene, toluene, xylene, and ethyl benzene. A wide 
range of alkylating agents may be used in the alkylation reaction zone and 
include monoolefins, diolefins, polyolefins, acetylenic hydrocarbons, 
alkyl halides, alcohols, ethers, and esters. The preferred alkylation 
agent comprises monoolefinic hydrocarbons. 
More specifically, it is preferred that the monoolefin is propylene. A 
highly advantageous embodiment of this invention uses a propane/propylene 
stream to supply a propylene alkylating agent and recovers propane as the 
working fluid. Since propane is normally present in the feed components, 
its use as the working fluid requires no additional facilities for 
recovery, recycle or make-up considerations. 
The alkylation reactor of this invention will include at least one zone for 
alkylation of the substrate by the alkylation agent. Greatest advantage is 
obtained by the method of this invention when the alkylation reaction zone 
operates at relatively low temperature and at liquid phase conditions. 
These conditions include a temperature of from 150.degree. C. to about 
210.degree. C. The alkylation zone should be operated to obtain an 
essentially complete conversion of the alkylating agent. To achieve this 
effect, additional aromatic substrate will usually be charged to the 
reaction zone. In a preferred form of this invention, the reaction zone 
contains an amorphous silica aluminum catalyst that is used for the 
alkylation of propylene and benzene. The preferred catalyst will be a 
cogelled silica aluminum composite which comprises from about 40 to 99 wt. 
% silica and from about 1 to about 60 wt. % alumina. The feed admixtures 
are introduced into reaction zone at a constant rate and in a molar ratio 
of about 1:1 to 20:1 aromatic substrate to olefinic alkylating agent with 
a ratio of about 2:1 to 6:1 being preferred. These include solid 
phosphoric acid catalyst, aluminum chloride catalyst, and amorphous silica 
alumina catalyst. 
A wide range of operating conditions are used in the alkylation of aromatic 
hydrocarbons. Temperatures range from 100.degree. C. to about 390.degree. 
C. the range of 150.degree. C. to about 275.degree. C. being preferred 
when used in conjunction with the preferred amorphous silica alumina 
catalyst. Pressures can also vary within a range of about 1 atmosphere to 
130 atmospheres. Generally, the pressure should be sufficient to maintain 
the reactants in a liquid phase and will fall in a range from about 10 to 
40 atmospheres. Reactants are generally passed through the alkylation zone 
at a mass flow rate sufficient to yield a liquid hourly space velocity 
(LHSV) of from about 0.5 to 50 hrs..sup.-1 and especially from about 2 to 
10 hrs..sup.-1. 
In alkylating the aromatic substrate with the alkylating agent, a 
substantial quantity of polyalkylated aromatic compounds may also be 
formed, particularly when using the preferred catalyst, lower operating 
temperatures and lower aromatic substrate to olefinic alkylating agent 
ratios. Therefore, it is common practice for the reactor to include an 
additional transalkylation zone for monoalkylated hydrocarbons are the 
desired product. A highly desirable form of reactor has an upper catalyst 
bed which provides an alkylation zone for incoming aromatic substrate and 
alkylation agent and a lower transalkylation zone that receives polyalkyl 
aromatic compounds and additional aromatic substrate. In a preferred form 
reactants and products pass downwardly through the alkylation zone and 
upwardly through the transalkylation zone and are combined at a common 
central point in the reactor to provide an effluent stream containing 
aromatic substrate, monoalkylated product, and polyalkylated compounds 
that are subsequently separated to provide aromatic substrate for return 
to the alkylation and transalkylation zone, a monoalkylated product stream 
and a stream of polyalkylated hydrocarbons for feed to the transalkylation 
zone. A wide variety of transalkylation catalysts can be used in the 
transalkylation zone. These catalysts include Friedel-Crafts catalysts 
such as sulfuric acid, phosporic acid and aluminum chloride. A preferred 
catalyst is an acid-washed crystalline alumina silicate material and a 
refractory inorganic oxide material with the composite having an average 
pore diameter of 6 angstroms or greater and a surface area of 590 m.sup.2 
/g or greater. A particularly useful form of crystalline alumina silicate 
material for the transalkylation catalyst is a hydrogen form silica 
alumina having either a three-dimensional or channel pore structure 
crystal lattice framework. A particularly preferred channel pore 
crystalline alumina silicate is mordenite. The preferred inorganic oxide 
for use in the transalkylation catalyst is alumina with gamma-alumina, 
eta-alumina, and mixtures thereof being particularly preferred. The 
hydrogen form alumina silicate may be present in a range of from 5 to 99.5 
wt. % and the refractory. inorganic oxide may be present in a range of 
from 0.5 to 95 wt. %. A transalkylation reaction can be carried out in a 
broad range of operating conditions including temperatures from 
100.degree. C. (210.degree. F.) to about 390.degree. C. (735.degree. F.) 
and pressures ranging from 1 atmosphere to about 130 atmospheres. The 
pressure will generally be selected such that the reactants will remain in 
the liquid phase and will, therefore, be from about 10 to about 40 
atmospheres. A liquid hourly space velocity based on the combined aromatic 
substrate and poly or alkyl aromatic feed rate from about 0.1 to 50 
hrs..sup.-1 is desirable. A more desirable range of LHSV is from 0.5 to 5 
hrs..sup.-1. 
This invention will be further described in the context of a preferred 
embodiment which is the alkylation of propylene with benzene to obtain 
cumene. The description of this invention, in terms of a preferred 
embodiment, is not meant to limit the claims of this invention to the 
particular details disclosed herein. The flow scheme for this example is 
that shown in FIG. 1. This example is based on engineering calculations 
and actual operating experience with similar processes. In describing this 
example, valves, pumps, heaters, instruments, and heat exchangers other 
than those necessary for an understanding and appreciation of the 
invention have been omitted. The feed to the process consists of benzene 
and a mixture of propane and propylene. The C.sub.3 portion of the feed 
admixture will consist primarily of propylene in an amount from 60-80 wt. 
% propylene. The feed admixture flows through a line 12 where it is 
admixed with the contents of line 14 which comprise a benzene recycle 
stream obtained in a manner hereinafter described. Benzene is added to the 
feed admixture in order to increase the total concentration of benzene 
rings relative to propylene such that the benzene to propylene ratio is 
between 1:1 to 8:1 with a ratio between 2:1 and 6:1 being preferred. The 
feed components are exchanged in exchanger 17 against a hereinafter 
described flash separator overhead stream, carried by line 16, to raise 
its temperature to 150.degree.-190.degree. C. Line 18 carries a 
hereinafter described effluent recycle stream which is combined with the 
contents of line 12. The effluent recycle stream further increases the 
concentration of benzene rings to propylene alkylating agent to a ratio of 
from 3:1 to 15:1. Line 12 discharges the feed components into an 
alkylation reaction zone 19. 
The alkylation reaction zone contains an amorphous silica alumina catalyst 
of the preferred type hereinbefore described. Contact of the feed 
components with the catalyst will result in an essentially complete 
conversion of propylene into cumene (isopropyl benzene), up to 30 wt. % of 
di-isopropyl benzene, trace amounts of tri-isopropyl benzene, lesser 
amounts of propylene condensation products such as hexene, nonene, etc., 
condensed benzene ring derivatives such as biphenyls and other heavy 
alkylate products that include hexyl and nonyl benzenes. Since the 
alkylation reaction is highly exothermic, a temperature rise of 
approximately 30.degree. C. is held through the alkylation zone by 
adjusting the flow and heat removal rates of the effluent recycle. 
Reactants and products from the alkylation zone flow downwardly where they 
are combined in a collection zone 22 with upflowing reaction products and 
reactants from a transalkylation zone 24. The products and reactants from 
zone 24 include benzene, isopropyl benzene, and di- and tri-propyl 
benzenes plus minor amounts of other heavy alkylate components. 
Line 26 collects the reaction products of the alkylation and 
transalkylation zones in an effluent at a temperature of about 
180.degree.-220.degree. C. Between 35-75% of the effluent stream is taken 
by line 18 n exchanger 28. Passage through exchanger 28 lowers the 
temperature of the effluent recycle material in line 18 to about 
165.degree.-205.degree. C. as it imparts some of the heat of reaction from 
the alkylation zone to the contents of line 27. 
Line 27 contains C.sub.3 's, predominantly propane from a hereinafter 
described separator 30, which is combined with the net effluent from the 
reaction zone in line 26 to provide the working fluid. Passage through 
heat exchanger 28 will provide a majority of the heat necessary for 
vaporization and possible superheating of the C.sub.3 's before they are 
added to the contents of line 26. The combined recycle stream and effluent 
stream should be kept at a temperature sufficient to maintain a 
substantial quantity of the benzene in a vaporized state. Any additional 
heat required for this purpose is added by exchanger 29. The combined 
stream enters flash separator 20 at a temperature of from 
155.degree.-200.degree. C. and a pressure of 13-17 atmospheres. Flash 
separator 20 is a simple disengaging vessel with a substantially open 
interior. The mixed phase components enter in the center of the vessel. 
The thermal equilibrium in the vessel is such that substantially all of 
the C.sub.3 's and a significant portion of the benzene are in the vapor 
phase while substantially all of the alkyl aromatic products and the rest 
of the benzene are in the liquid phase, thereby effecting a relatively 
inexpensive separation of at least a portion of the benzene from the alkyl 
aromatic products contained in the effluent. Flash separator 20 can be 
operated to recover between 10-70% of the benzene from the net reactor 
effluent. The benzene and substantially all the C.sub.3 's are collected 
overhead in line 16. The flash separator overhead of line 16 is cooled in 
exchanger 17 to a temperature of about 145.degree.-170.degree. C. This 
cooling condenses benzene and a portion of the propane prior to entering 
separator 30. 
In separator 30, a relatively simple split between C.sub.3 's and benzene 
is performed at a low energy cost. C.sub.3 's, primarily propane, are 
recovered overhead from separator 30 to an overhead line 31. The working 
fluid is withdrawn from line 31 by line 27 as hereinbefore described. Net 
C.sub.3 's and any lighter hydrocarbons that enter with the feed are 
recovered from line 31 and removed from the process. By adjusting the net 
recovery through line 31 the working fluid volume is maintained at desired 
levels. A benzene bottom stream containing a relatively small amount of 
propane leaves separator 30 through line 32 and provides a portion of the 
recycled benzene that is added to the feed components by line 14. The 
separator is operated to minimize benzene in the overhead and allows a 
small quantity of C.sub.3 's, less than about 15% in the bottom stream of 
line 14. Limiting the amount of C.sub.3 's and lighter hydrocarbons to the 
reaction zone prevents vaporization of the combined reactor feed at the 
reactor operating conditions. 
Benzene and higher boiling hydrocarbons are taken by a bottoms line 34 from 
the lower section of flash separator 20 and transferred to a recycle 
fractionation column 40. The flash separator bottoms stream has a 
temperature of from 155.degree.-200.degree. C. Column 40 is a trayed 
column designed to perform a good split between the desired product cumene 
and the other lower boiling effluent components. As hereinabove mentioned, 
the net products from the reactor section will contain small quantities of 
propylene condensation products such as hexene and nonene. These 
components must be separated from the alkyl aromatic product at this point 
in the flow scheme, otherwise they will detrimentally contaminate the 
final cumene product. Thus, the overhead of column 40 typically has a 
small quantity of cumene in it. This amount may equal approximately 2.5 
wt. % of the overhead based on benzene. Taking cumene overhead ensures 
that nonene, which has a boiling point of about 5.degree. C. lower that 
cumene is carried overhead with the benzene. The contaminants make up a 
relatively small percentage of the overhead which consists primarily of 
benzene. Thus, this invention confers substantial heat savings on the 
operation of column 40 by reducing the amount of benzene that must be 
vaporized therein in direct proportion to the amount of benzene removed by 
flash separator 20. A portion of the overhead from line 35 is withdrawn by 
line 36 to supply benzene to transalkylation zone 24. The amount of 
overhead withdrawn by line 36 is on the order of one-half. The remainder 
of the overhead taken by line 35 is mixed with benzene from line 32 to 
make up the remainder of the benzene recycle of line 14. 
Line 42 transfers the heavier effluent components from column 40 to a 
product fractionation column 50. Column 50 separates the product cumene 
from yet higher boiling effluent components. Column 50 is a trayed column, 
designed to provide cumene at a desired degree of purity The cumene 
products are taken overhead by a product line 44 while the heavier 
components are transferred to a heavy alkylate column by line 46. 
Heavy alkylate column 60 is designed to recover di- and tri-isopropyl 
benzenes and reject heavier undesirable by-products of the alkylation and 
transalkylation reactions. Such by-products include condensed benzene ring 
compounds and aromatics substituted with propylene condensation products. 
These heavy products are taken from the bottom of column 60 through a line 
48 and removed from the process. Di-isopropyl benzene and tri-isopropyl 
benzene are taken overhead by line 57 and combined with benzene from line 
36 in a transfer line 52. The benzene and poly-substituted benzenes make 
up the feed inputs to the transalkylation zone 24. 
After any appropriate heat exchange, the contents of line 52 enter the 
transalkylation zone 24 at a temperature of 220.degree. C. and a pressure 
of 35 atmospheres. The reactants flow upwardly and contact a crystalline 
alumina silicate catalyst of the preferred composition as hereinbefore 
described. Reactants flow upward in a quantity sufficient to provide an 
LHSV in a range of 0.5 hr.sup.-1 to 5.0 hr.sup.-1. Reaction products and 
reactants comprising benzene, isopropyl benzene, di- and tri-propyl 
benzenes plus minor amounts of other heavy alkylate components enter 
collection zone 22 where they are combined with the reaction zone effluent 
in the manner hereinbefore described.