Method of and apparatus for controlling an alkylation process

Disclosed is a method of alkylating in which a hydrocarbon and acid emulsion is circulated in a reaction loop between a reactor and a cooler. A small sidestream of the reaction emulsion is constantly removed to a liquid-liquid separator where the hydrocarbon and acid phases are separated. The recovered acid is then recycled back to the reaction loop. The amount of recovered acid recycled is controlled by monitoring the density of the reaction emulsion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to alkylation. In another aspect, the present 
invention relates to a method of and apparatus for controlling an 
alkylation process. In even another aspect, the present invention relates 
to a method of and apparatus for controlling an alkylation process by 
monitoring the specific gravity of the reaction emulsion mixture. In still 
another aspect, the present invention relates to a method of and apparatus 
for controlling the amount catalyst to be recycled back to the alkylation 
process by monitoring the specific gravity of the reaction emulsion 
mixture. In yet another aspect, the present invention relates to a method 
of and apparatus for detecting pre-warning signs of an alkylation process 
acid runaway by monitoring the specific gravity of the reaction emulsion 
mixture. 
2. Description of the Related Art 
Alkylation is a well known refinery process for converting light gaseous 
olefins into high-octane gasoline components. Very simply, alkylation 
involves the addition of an alkyl group to an organic molecule. Thus, an 
isoparaffin can be reacted with an olefin to provide an isoparaffin of 
higher molecular weight. Generally, the alkylation of isoparaffins with 
olefins is accomplished by contacting the reactants with an acid acting 
catalyst such as hydrogen fluoride or sulfuric acid, settling the mixture 
to separate the catalyst from hydrocarbons, and further separating the 
hydrocarbons, usually by fractionation to recover alkylate product. The 
resulting alkylate product is typically a mixture of C.sub.5 to C.sub.16 
isomers, with the exact composition depending upon the particular 
isoparaffin and olefin reactants utilized, as well as alkylation process 
conditions. 
Alkylation has recently been increasing in importance as a result of the 
curtailment in the use of tetraethyl lead as an octane-improving additive 
for gasoline, not only has the production of unleaded gasoline increased 
but the octane number specification of all grades of gasoline have 
increased as well. 
Additionally, reformulated gasoline specifications require a reduction in 
both the Reid Vapor Pressure ("RVP") and the olefin content. Alkylate is a 
low vapor pressure, high octane gasoline blending component containing 
substantially no olefins. Thus, alkylate helps refiners meet the new 
reduced RVP and reduced olefin content specifications. Additionally, 
alkylate burns cleanly, resulting in lower levels of undesired emissions 
from gasoline engines. In fact, because of its usefulness eliminating lead 
and in meeting the new reformulated gasoline specifications, alkylate 
typically comprises 10-15% of the gasoline pool. 
Isoparaffin-olefin alkylation processes have become the key route to the 
production of these highly branched paraffin octane enhancers which are 
blended into gasolines. 
As practiced commercially, alkylation most commonly involves reacting 
isobutane, with C.sub.3 to C.sub.5 olefins in the presence of an acid 
catalyst, typically either hydrofluoric acid or sulfuric acid. The 
resulting alkylate product comprises predominately C.sub.7 to C.sub.9 
isoparaffins, along with lesser amounts of lighter and heavier 
isoparaffins in the C.sub.6 to C.sub.12 range, and some isopentane. 
A typical commercial unit will react an isoparaffin with an olefin in the 
presence of the acid catalyst, forming an acid-hydrocarbon mixture which 
is sent to a settler where the hydrocarbon is separated from the acid. A 
portion of the acid is recycled while the remaining acid is discharged 
from the alkylation unit. Fresh acid is added to the recycled acid to 
affect the strength of the acid. 
Two variables which may be used to control an alkylation process includes 
the strength of the acid catalyst and the inventory of acid remaining in 
the system. The inventory of acid is generally utilized to control the 
recycle rate of the acid, while the strength of acid determines the amount 
of fresh acid to be added to the process. 
Historically, it has been customary to obtain a small sample of the 
alkylation emulsion in a sight glass and allow it to stand until the acid 
settles, usually on the order of 30 to 40 minutes. The desired emulsion 
information is obtained by manually timing the settling and visually 
observing the percentage of acid in the emulsion. Based on these physical 
measurements, the alkylation process could then be adjusted to obtain 
optimum results. 
This sight glass method suffers from several disadvantages. 
Sight glasses are normally designed to include ball check valves which 
prevent the contents of the vessel from entering the atmosphere upon the 
sight glass breaking. In the case of the ratio glass used in monitoring 
alkylation processes, the ball check valves are generally removed as they 
restrict flow which interferes with obtaining a representative sample, and 
by-products of the alkylation process tend to plug the restricted ports in 
the ball check valves. While removal of the ball check valve can improve 
the operation of the sight glass, rupture of the sight glass from over 
pressuring, mechanical failure, improper installation or other reasons, 
creates the potential for an emulsion spill. 
Additionally, the accuracy and repeatability of the ratio glass varies from 
operator to operator. It is the experience of the inventors that most 
operations personnel do not understand the calibration range of the sight 
glass and therefore, most readings from the ratio glass are inaccurate. 
And while the inventors believe that sight glass readings should be taken 
at least two times a day, it is their experience that because of the 
difficulty and nuisance of taking sight glass readings, most operators 
take sight glass readings only after they are experiencing alkylation 
problems, rather than taking readings to monitor such problems before they 
happen. 
Even with constant readings, the sight glass requires a settling time of 
about 30 to 40 minutes, which restricts how many readings can be taken, 
and also means there is an informational delay as the data is about 30 to 
40 minutes old by the time the sight glass can be read. Typically, if the 
emulsion requires more than 40 minutes, the system has a "tight" emulsion, 
i.e., high amount of acid. If the emulsion requires less than 10 minutes, 
the emulsion is probably hydrocarbon continuous. 
There has been an attempt in the art to improve over the sight glass method 
of obtaining alkylation emulsion information. U.S. Pat. No. 4,023,096, 
issued May 10, 1977 to Schmidt discloses a method and apparatus for 
determining physical characteristics of emulsions. The U.S. Pat. No. '096 
patent discloses a modified gravity or centrifugal settling cell having 
electrical capacitor plates disposed within the cell such that as the 
emulsion separates relative proportional areas of both of the plates are 
exposed to the components of the emulsion. The strength of the acid, as 
well as the settling time of the emulsion is determined by measuring the 
capacitance of the cell. The capacitance will vary exponentially and reach 
a steady state condition which will remain substantially constant. The 
settling time is related to the time required for the capacitance to reach 
steady state, while the acid strength is related to the magnitude of the 
capacitance in its steady state condition. While the U.S. Pat. No. '096 
patent apparatus eliminates the need for an operator to read a sight 
glass, it still requires a certain settling time between readings. As 
noted above, the settling time limits the frequency at which samples can 
be taken, and causes an informational delay. 
Even with the U.S. Pat. No. '096 apparatus, utilization of a sight glass is 
still the most common method of obtaining alkylation emulsion information. 
In addition to the problem of determining the amount of spent catalyst to 
recycle, an independent and important problem is to maintain watch for an 
acid "run-away". 
When using an acid catalyst in the alkylation of an olefin with an 
isoparaffin, an acid "run-away" can occur without warning as the acid 
starts dropping in acidity very rapidly. If the acidity of the system acid 
drops below a certain minimum, the alkylation reaction ceases and the 
acidity of the acid drops rapidly. If the run-away is not detected almost 
immediately, the acidity may drop so fast, and so far, that it becomes 
necessary to remove the acid from the system. At the same time, the 
alkylate product usually becomes contaminated with sulfur compounds in the 
form of alkyl sulfates. Thus, when such a condition occurs, acid and 
alkylate must be discarded and therefore are lost, or they must be further 
processed to make them suitable for use. 
Generally, in commercial alkylation, if an abnormally fast drop in acidity 
is detected before the acidity drops below the minimum acidity, the 
acidity can usually be brought back to or above the minimum acidity by 
increasing the fresh acid feed and/or by decreasing or shutting off the 
olefin feed. 
An acid run-away can be directly detected by monitoring the acidity of the 
acid. 
Unfortunately, a major difficulty, especially in commercial operation, is 
that there is usually no continuous monitoring of the acidity, with the 
result that a matter of hours may elapse between the time a sample is 
taken and analytical data on acidity are obtained. Thus, by the time test 
results are obtained, the acidity may already be so low that the acid is 
no longer an alkylation catalyst. The result is that no matter how much 
fresh acid is charged, within the capacity of the reactor and settler, and 
ever if olefin feed is cut out, the acidity cannot be raised to a point at 
which the acid will again act as an alkylation catalyst. 
For example, prior art methods for monitoring alkylation catalyst acidity 
having included spectrophotometry, which suffers from the necessity of 
using relatively expensive spectrophotometers, and suffers from the need 
for the continuous addition of an indicator compound such as alizarin blue 
thus requiring a complicated and expensive indicator control and metering 
system. 
Another acidity monitoring system is disclosed in U.S. Pat. No. 3,653,835, 
issued Apr. 4, 1972 to Brandel in which an acid sample is pumped by a 
first pump from the settler acid recycle line to a stripping chamber where 
volatile hydrocarbons are vaporized through a vent tube, the stripped 
sample then enters a settling chamber where high molecular weight 
hydrocarbons are skimmed off by an overflow tube, with the purified acid 
then pumped by a second pump into a hydrometer pot for analysis. The U.S. 
Pat. No. '835 system is somewhat complex and requires a constant 
temperature bath for maintaining the sample at the stripping temperature, 
vent tube, settler, skimming tube as well as two pumps. In addition to 
controlling the temperature, the pumping rates of the two pumps must be 
controlled. 
The present inventors also suggest that monitoring the change and/or rate 
of change in the acid to hydrocarbon ratio in the reaction emulsion can 
serve as a run-away warning method. However, while the reaction emulsion 
acid/hydrocarbon ratio can be monitored by the prior art sight glass 
methods, such sight glass methods have several disadvantages as described 
above, including accuracy, repeatability, settling time, as well as 
others. 
Thus, there is a need in the art for an improved alkylation process. 
There is also a need in the art for an improved apparatus for and method of 
determining the amount of spent acid catalyst to recycle in the alkylation 
process. 
There is another need in the art for an improved apparatus for and method 
of determining the amount of spent acid catalyst to recycle in the 
alkylation process which does not suffer from the time lag of the prior 
art apparatus and methods. 
There is even another need in the prior art for an improved apparatus for 
and method of monitoring the acid to hydrocarbon ratio for the purpose of 
detecting an acid run-away. 
These and other needs of the art will become evident to those of skill in 
the alkylation art upon reading this specification. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide for an improved 
alkylation process. 
It is also an object of the present invention to provide for an improved 
apparatus for and method of determining the amount of spent acid catalyst 
to recycle in the alkylation process. 
It is another object of the present invention to provide for an improved 
apparatus for and method of determining the amount of spent acid catalyst 
to recycle in the alkylation process which does not suffer from the time 
lag of the prior art apparatus and methods. 
It is even another an object of the present invention to provide for an 
improved apparatus for and method of monitoring the acid to hydrocarbon 
ratio for the purpose of detecting an acid run-away. 
These and other objects of the present invention will become evident to 
those of skill in the alkylation art upon reading this specification. 
According to the present invention there is provided a method of 
controlling the alkylation of an emulsion mixture of hydrocarbons and an 
acid catalyst in a reaction zone, which alkylation produces an emulsion 
product stream of alkylated hydrocarbons and the acid catalyst, which 
product steam is then separated into a hydrocarbon product steam and a 
recycle acid steam, wherein a recycle percentage, of the recycle acid 
steam is recycled to the reaction zone. The method generally includes 
first inputting upper and lower operating setpoint values into a 
controller, wherein the setpoint values are representative of density, 
mole, volume or weight operating limits for the acid or hydrocarbons in 
the emulsion mixture. The method also includes recovering a portion of the 
emulsion mixture as an emulsion sample. The method further includes 
determining the density of the emulsion sample while it is in an emulsion 
state. The method even further includes inputing the density of the 
emulsion sample into the controller. Next, the method includes correlating 
the density of the emulsion sample to the upper and lower setpoint values. 
Finally, the method includes outputting from the controller an indication 
that the recycle percentage should be increased if the density of the 
emulsion sample correlates to a value above the upper setpoint value, and 
an indication that the recycle percentage should be decreased if the 
density of the emulsion sample correlates to a value below the lower 
setpoint value.

DETAILED DESCRIPTION OF THE INVENTION 
Alkylation processes in general are well known to those of skill in the 
art. For example, see "Catalytic Alkylation", Petri/Chem Engineer, 
December 1961 and January 1962, "Alkylation will be key process in 
reformulated gasoline era", Oil & Gas Journal, Nov. 12, 1990, pp. 79-92, 
"H.sub.2 SO.sub.4, HF processes compared, and new technologies revealed", 
Oil & Gas Journal, Nov. 26, 1990, pp. 70-77, and "Which alkylation--HF or 
H.sub.2 SO.sub.4 ?", Hydrocarbon Processing, September 1985, all herein 
incorporated by reference. Additionally, alkylation is generally disclosed 
in U.S. Pat. Nos. 4,018,846; 4,225,740; 4,276,731; 4,371,731; 4,383,977; 
4,404,418; 4,467,131; 4,513,165; 4,777,323, and 5,157,196; all herein also 
incorporated by reference. 
In the alkylation process of the present invention, a large stream of 
hydrocarbons undergoes alkylation in the presence of an acid catalyst. An 
emulsion of the hydrocarbons and the catalyst is continuously circulated 
between a reaction zone and a cooling zone, with a small portion of the 
reaction emulsion continuously removed to a liquid-liquid separator where 
the hydrocarbons and catalyst are separated. The hydrocarbons recovered 
from the liquid-liquid separator include alkylate, propane and n-butane, 
which are later separated, generally by fractionation. The catalyst 
recovered from the liquid-liquid separator is either discarded, or all or 
a portion of the catalyst is recycled to the reaction zone. The amount of 
catalyst to be recycled is dependent upon the density of the reaction 
emulsion, which is monitored. 
According to the present invention, the density of the reaction emulsion is 
first determined. Control of the alkylation reaction acid recycle is 
accomplished by correlating the emulsion density to the ratio of 
hydrocarbons to catalyst in the reaction emulsion. Of course, as specific 
gravity is a ratio of the emulsion density to water density, specific 
gravity may also be utilized in the practice of the present invention. 
The emulsion density may be determined by any suitable method and by any 
suitable apparatus. As an improvement over prior art methods of 
controlling alkylation reactions, the emulsion density is preferably 
determined while the hydrocarbon/catalyst mixture is in an emulsion state, 
that is prior to any settling or separation. The emulsion density can be 
determined on an emulsion sample batch wise, that is from a now flowing 
emulsion mixture. An alternate and preferred method is to determine the 
emulsion density from a flowing emulsion stream, in which case, an in-line 
density measurement device is utilized. By its very nature, "in-line" 
would of course mean that the device is suitable for measuring the density 
of the emulsion, without a need for first settling the emulsion. Such a 
device must provide accurate measurement of the density while not 
generating too substantial of a pressure drop. Preferably, the density 
measuring device will provide readings with a minimal amount of time 
between readings. A non-limiting example of suitable in-line density 
measurement device includes the Model CMF050 Mass Flow and Density Sensor 
available from Micro Motion of Boulder Colo. 
Once the density of the emulsion is determined, the density measurement 
must be correlated to the liquid volume ratio of acid to hydrocarbon in 
the emulsion reaction. The density of various volume ratios of acid to 
mixtures of hydrocarbons is easily determined through experimental 
procedures. This relationship of density to volume ratios can then be 
utilized in table or graph form, or even stored in a computer look-up 
file. Once the density of the emulsion is obtained, the corresponding 
volume ratio is determined either from a table or graph, or from a 
computer look-up file. This volume ratio is then compared to the desired 
volume ratio operating range, with adjustments made accordingly. 
At a minimum, the liquid volume of acid in the reaction emulsion must be 
suitable to avoid a hydrocarbon continuous emulsion. At the upper limit, 
the liquid volume of the acid in the reaction emulsion is generally 
selected to provide proper hydraulics and mixing performance in the 
reaction zone. Generally, some reactors may be operated at a liquid volume 
of acid in the emulsion reaction as low as about 40 volume percent, and 
some reactors may be operated at a liquid volume of acid in the emulsion 
reaction as high as about 65 volume percent. However, it must be 
understood that each unit will have its own optimum based on the feed 
stoichiometry, and it is hard to place a particular range on this 
variable. However, with the reactors operated by the inventors, they have 
generally found that the liquid volume of acid in the reaction emulsion is 
maintained in the range of about 45 volume percent to about 60 volume 
percent. Preferably for their reactors, the liquid volume of acid in the 
reaction emulsion is maintained in the range of about 50 volume percent to 
about 60 volume percent, and most preferably maintained in the range of 
about 50 volume percent to about 55 volume percent. 
The density or specific gravity of the reaction emulsion is a function of 
the acid strength, temperature, hydrocarbon composition and acid diluents. 
The inventors have determined that acid strength has the most affect on 
specific gravity, with temperature being quite minimal (0.00086 per 
.degree.F.), with acid diluents and hydrocarbon composition even less 
significant so as to be considered negligible. 
Thus, for a given operating temperature or range, the density or specific 
gravity of the acid at a given strength and of the reactor effluent are 
weighted based on volume percentage, to obtain a weighted density. A lower 
density number corresponding to a lower operating acid volume, and a 
higher density number corresponding to an upper operating acid volume are 
both calculated to establish the operating ranges. An acid density reading 
above the upper limit indicates that too much acid is being recycled, and 
that some acid should be removed from the alkylation unit. An acid density 
reading below the lower limit indicates that too little acid is being 
recycled, and that less acid should be removed from the alkylation unit. 
The acid reading can also be used to make adjustments in the acid recycle 
rate as the acid reading approaches each of these upper and lower limits. 
The above embodiment generally includes determining the emulsion density, 
determining the volume ratio from the density, and then comparing the 
determined volume to the desired volume operating range, with adjustments 
made accordingly. As an alternative method, it is also possible to convert 
the desired volume operating range into a desired density operating range. 
Thus, another embodiment of the method of the present invention would 
include determining the emulsion density, and then comparing the 
determined density to the desired density operating range, with 
adjustments made accordingly. 
The present invention will now be explained by reference to FIG. 1, which 
is a schematic drawing showing reactor 12, circulation pump 15, cooler 18 
and liquid-liquid separator 34. In operation, hydrocarbon reactants are 
introduced to line 2 through line 31 controlled by valve 30, with acid 
catalyst introduced to line 2 through line 38 controlled by valve 37. 
Circulation pump 15 circulates a reaction emulsion between cooler 18 and 
alkylation reactor 12 through lines 2, 3, and 5 as shown in FIG. 1. During 
operation, a small side stream 21 of the emulsion reaction mixture is 
routed to liquid-liquid separator 34 where the acid and hydrocarbon 
components of the emulsion are separated. Hydrocarbon components are 
removed via line 33. The acid component is recycled back to the alkylation 
line 2 via lines 36 and 43 as shown in FIG. 1. The amount of acid recycled 
is controlled by valve 47. Excess acid recycle is removed from the system 
by opening valve 47 with excess acid exiting the system through line 49. 
According to the present invention, a density measuring device 40 is 
installed in line 23, a sidestream off of line 21. As explained above, 
density measuring device 40 is preferably an in-line measuring device. 
Opening valve 24 will allow the emulsion mixture from line 21 to be 
sampled by density measuring device 40. 
It is understood that the density data from density measuring device 40 may 
be obtained by the operator, compiled in a recording device, or even input 
directly into a computer or process controller. As shown in FIG. 1, 
density measuring device is connected via wire 51 to computer 45. 
Into computer 45 will be input set points of either the upper and lower 
operating densities for the reaction emulsion in reactor 12, or the upper 
and lower operating percent volumes or volume ratios for the reaction 
emulsion in reactor 12. 
When the operating percent volumes or volume ratios are utilized as set 
points, computer 45 will utilize some scheme to relate the emulsion 
density to liquid volumes of the hydrocarbon mixture and acid catalyst. 
For example, computer 45 may utilize a look-up table relating emulsion 
density to the liquid volume ratio of hydrocarbons to acid catalyst. 
Alternatively, the computer my utilize some mathematical relationship to 
relate emulsion density to the liquid volumes of hydrocarbons and acid 
catalyst. Of course, the relationship between emulsion density and the 
percent volume of the components will vary slightly with the type of 
catalyst and hydrocarbons utilized in the emulsion. 
Once density data is obtained, recycle control valve 47 may be controlled 
by an operator or by a computer or process controller. As shown in FIG. 1, 
recycle control valve is connected via wire 53 to computer 45. 
Based on the emulsion density reading from density measuring device 40, 
recycle valve 47 may be controlled utilizing any type of control scheme, 
including proportional, integral , differential control schemes or any 
combination of the foregoing. 
While density measuring device 40 is shown in FIG. 1 as being located in 
sidestream 23 off of stream 21, it is to be understood that density device 
40 may be located in any position suitable to obtain density readings of 
the reaction emulsion. For example, density measuring device 40 could be 
located in-line in lines 2, 3, 5 or 21, or in sidestreams connected to 
lines 2, 3, 5 or 21. Furthermore, density measuring device 40 could be 
connected directly to reactor 12. 
In the practice of the alkylation process of the present invention, the 
precise process steps and process conditions will vary somewhat depending 
upon the catalyst system utilized, the alkylate product desired, available 
equipment, process economics and other factors. It is anticipated that any 
suitable catalyst may be utilized. The preferred types of catalysts are 
liquid or gaseous catalysts. 
In the practice of the present invention, the reacting hydrocarbons may 
include C.sub.3 to C.sub.5 olefins as well as C.sub.4 to C.sub.5 
paraffins. 
The alkylation process of the present invention is generally operated with 
ratios of isoparaffin to olefin in the feed streams to the reactor of 
greater than 1 to minimize undesired polymerization reactions. The 
isoparaffin to olefin ratio is generally in the range of about 2:1 to 
about 50:1, and preferably in the range of about 4:1 to about 20:1. Most 
preferably for hydrogen fluoride catalyzed alkylation, the isoparaffin to 
olefin ratio is in the range of about 10:1 to about 15:1. Most preferably 
for sulfuric acid catalyzed alkylation, the isoparaffin to olefin ratio is 
in the range of about 5:1 to about 10:1. 
For the present invention the alkylation is generally carried out by 
contacting the catalyst and the reacting hydrocarbons in a reactor under 
closely controlled conditions. Alkylation reactions are very exothermic 
and require cooling to remove the heat of reaction from the reactor. 
Reactor systems useful in the practice of the present invention include 
time-tank or pipe reactors, the Stratco.RTM. Contactor reactor, cascade 
reactors, gravity reactors, solid catalyst reactors, and the like, and 
other types of alkylation reactors known to those of skill in the 
alkylation art. 
The catalyst and the reacting hydrocarbons are generally contacted together 
in the reactor utilizing a sufficient level of agitation to provide 
intimate contact between the two liquid phases. High levels of agitation 
are generally more important for sulfuric acid alkylation than for HF 
alkylation. The agitation is generally provided utilizing baffling, 
positioning of the impeller and by recycle streams. 
Additionally, with some reactor systems, the hydrocarbons may be contacted 
with a liquid catalyst in the form of a fine dispersion in the liquid 
catalyst. The hydrocarbon droplet size utilized will be in the range of 
about 10 to about 1000 microns, preferably about 10 to about 100 microns 
to give good contact with the catalyst. The fine dispersion of 
hydrocarbons may be obtained by any suitable method, including introducing 
the hydrocarbons into the reactor at high velocity through nozzles, by 
utilizing a high shear mechanical device such as a centrifugal pump, by 
utilizing a static mixer, or by any other suitable method. 
The alkylation catalyst utilized in the present alkylation invention may be 
any catalyst that will catalytically effect the reaction of the paraffins 
and olefins. Non-limiting examples of suitable catalysts include strong 
acid catalysts such as hydrofluoric acid, sulfuric acid, phosphoric acid, 
mixtures of sulfuric and phosphoric acids, metal halides such as aluminum 
chloride or aluminum bromide, certain complexes of aluminum chloride and 
sulfuric acid, and the like. 
Acid strength of the catalyst utilized in the present invention is 
generally maintained high enough to avoid dilution of the acid catalyst 
but low enough to avoid excessive side reactions. For example, the range 
of useful strengths of sulfuric acid is generally in the range of about 86 
to about 99 weight percent. 
The volume ratio of catalyst to total hydrocarbons is generally in the 
range of about 10:1 to about 1:10, and preferably in the range of about 
10:1 to about 1:2. 
The alkylation temperature and pressure utilized in the present invention 
is generally selected to yield the desired alkylation products without 
undue detrimental effects upon the catalyst or alkylation reactants. 
Generally, the alkylation temperature utilized in the present invention is 
in the range of about -60.degree. F. to about 1000.degree. F. Preferably, 
the alkylation temperature utilized in the present invention is in the 
range of about -40.degree. F. to about 200.degree. F., more preferably in 
the range of about 35.degree. F. to about 200.degree. F., and most 
preferably in the range of about 35.degree. F. to about 125.degree. F. It 
is observed that at lower temperatures the rate of reaction is generally 
slower, and at higher temperatures, some cracking, polymerization and 
carbon formation occurs. The alkylation temperature utilized will 
generally also be influenced by economy of equipment and operating costs. 
Additionally, it is also noted that the most preferred alkylation 
temperatures will also vary depending upon the type of catalyst utilized. 
The upper limit on the alkylation temperature is generally selected to 
avoid undue temperature degradation of the catalyst and to keep the 
catalyst in the desired state. For example, with sulfuric acid catalysts, 
the alkylation temperature is most preferably in the range of about 
40.degree. F. to about 50.degree. F. and generally requires some type of 
refrigeration, while the most preferable alkylation temperature when 
utilizing hydrogen fluoride catalysts is in the range of about 85.degree. 
F. to about 115.degree. F., which can generally be maintained utilizing 
cooling water. 
The alkylation pressure utilized in the present invention is generally 
selected to maintain at least a portion of, and preferably a majority of, 
the hydrocarbon reactants in a liquid phase. Generally, the reaction 
pressure is in the range of about atmospheric to about 5000 psi or more, 
preferably in the range of about 45 psi to about 1000 psi, and most 
preferably in the range of about 45 psi to about 250 psi. 
Although the residence time of the reactants in the reactor or reaction 
zone can vary widely depending upon the process variables, the residence 
time is generally in the range of about 0.01 minutes to about 100 minutes. 
Preferably, the residence time is in the range of about 0.1 minutes to 
about 30 minutes, and more preferably in the range of about 1 minutes to 
about 20 minutes, and most preferably in the range of about 5 minutes to 
about 20 minutes. 
EXAMPLES 
Calculated Example 1 
For this example, it is assumed that at the lower limit that 90 wt % 
H.sub.2 SO.sub.4 is utilized, that at the upper limit 97 wt % H.sub.2 
SO.sub.4 is utilized, that the acid volume percent operating ranges are 
from 45 to 60 volume percent. 
The specific gravities of the acid and hydrocarbon components are shown in 
TABLE 1 as follows: 
TABLE 1 
______________________________________ 
Component SG's 
Component Specific Gravity (SG) 
______________________________________ 
90 wt % H.sub.2 SO.sub.4 
1.7250 
97 wt % H.sub.2 SO.sub.4 
1.8300 
reaction effluent 
0.6300 
______________________________________ 
The high and low specific gravities are calculated in the following TABLE 2 
as follows: 
TABLE 2 
______________________________________ 
Calculations 
LV % Acid 
Acid Strength Specific 
in Effluent 
(wt %) Calculation Gravity 
______________________________________ 
45 90 (0.45*1.7250) + (0.55*0.6300) 
1.1228 
45 97 (0.45*1.8300) + (0.55*0.6300) 
1.1700 
60 90 (0.60*1.7250) + (0.55*0.6300) 
1.2870 
60 97 (0.60*1.8300) + (0.55*0.6300) 
1.3500 
______________________________________ 
While the illustrative embodiments of the invention have been described 
with particularity, it will be understood that various other modifications 
will be apparent to and can be readily made by those skilled in the art 
without departing from the spirit and scope of the invention. Accordingly, 
it is not intended that the scope of the claims appended hereto be limited 
to the examples and descriptions set forth herein but rather that the 
claims be construed as encompassing all the features of patentable novelty 
which reside in the present invention, including all features which would 
be treated as equivalents thereof by those skilled the art to which this 
invention pertains.