A dehydrocyclodimerization process employing a catalyst comprising a crystalline aluminosilicate and a metal oxide component is started-up by contacting the catalyst with a start-up gas that contains less than 50 mole percent hydrogen. The catalyst is exposed to the gaseous atmosphere containing less than 50 mole percent hydrogen until a C.sub.2 -C.sub.5 aliphatic hydrocarbon feedstock is contacted with the catalyst at dehydrocyclodimerization reaction conditions at which point hydrogen is generated as a dehydrocyclodimerization reaction product and displaces the non-hydrogen start-up gas from the process.

BACKGROUND OF THE INVENTION 
The present invention relates to a novel process for the 
dehydrocyclodimerization of C.sub.2 to C.sub.5 aliphatic hydrocarbons. 
Specifically, a process for producing aromatics via the 
dehydrocyclodimerization reaction, which utilizes a novel start-up method 
is disclosed. 
Dehydrocyclodimerization is a reaction where reactants comprising paraffins 
and olefins, containing from 2 to 5 carbon atoms per molecule, are reacted 
over a catalyst to produce primarily aromatics with H.sub.2 and light ends 
as by-products. This process is quite different from the more conventional 
reforming or dehydrocyclization process where C.sub.6 and higher carbon 
number reactants, primarily paraffins and naphthenes, are converted to 
aromatics. These aromatics contain the same or less number of carbon atoms 
per molecule as the reactants from which they were formed, indicating the 
absence of reactant dimerization reactions. In contrast, the 
dehydrocyclodimerization reaction results in an aromatic product that 
always contains more carbon atoms per molecule than the C.sub.2 to C.sub.5 
reactants, thus indicating that the dimerization reaction is a primary 
step in the dehydrocyclodimerization process. Typically, the 
dehydrocyclodimerization reaction is carried out at temperatures in excess 
of 500.degree. F. using dual functional catalysts containing acidic and 
dehydrogenation components. These catalysts include acidic amorphous 
aluminas which contain metal promoters. Recently crystalline 
aluminosilicates have been successfully employed as catalyst components 
for the dehydrocyclodimerization reaction. 
An important aspect of any catalytic process is the activity and stability 
of a catalyst composition when exposed to normal process conditions. The 
optimization of hydrocarbon process catalyst activity and stability are 
continuing goals of process and catalyst development efforts. 
It has now been found that a dehydrocyclodimerization process utilizing a 
catalyst comprising a Group IIB-IVB metal component and a crystalline 
aluminosilicate zeolite exhibits improved initial conversion and aromatic 
selectivity in a dehydrocyclodimerization reaction if the process is 
started-up in the relative absence of hydrogen gas. 
OBJECTS AND EMBODIMENTS 
A principal object of this invention is to provide an improved process for 
the dehydrocyclodimerization of aliphatic hydrocarbons. The 
dehydrocyclodimerization process of this invention results in an 
improvement in the amount and rate that an aromatic product is produced by 
the dehydrocyclodimerization process. Accordingly, a broad embodiment of 
the present invention is directed towards a process for the 
dehydrocyclodimerization of dehydrocyclodimerizable hydrocarbons in the 
presence of a catalyst comprising a crystalline aluminosilicate zeolite, 
and a Group IIB-IVB metal component. The process is characterized in that 
the catalyst is exposed to a start-up gas containing 50 mole percent or 
less hydrogen during the start-up of the process and remains exposed to 50 
mole percent or less hydrogen until the dehydrocyclodimerizable 
hydrocarbons are contacted with the catalysts at dehydrocyclodimerization 
reaction conditions, at which point hydrogen is produced as a reaction 
product and displaces any non-hydrogen start-up gas. 
In a narrower embodiment, the instant dehydrocyclodimerization process is 
one in which C.sub.2 -C.sub.5 hydrocarbons are subject to 
dehydrocyclodimerization in the presence of a catalyst comprising a 
phosphorous containing alumina, a gallium component, and a crystalline 
aluminosilicate zeolite having a silica to alumina ratio of at least 12. 
The process is characterized in that the start-up of the process comprises 
the steps of: (a) pressuring up the process with a dry start-up gas 
containing less than 30 mole percent hydrogen; (b) circulating the dry 
start-up gas in a closed loop through the process; (c) heating the 
catalyst to a temperature of about 340.degree. C. by heating the 
circulating dry start-up gas; (d) contacting the C.sub.2 -C.sub.5 
hydrocarbon feed with the heated catalyst; (e) raising the catalyst 
temperature, at a rate of about 15.degree.-30.degree. C. per hour to about 
450.degree. C. to initiate the dehydrocyclodimerization reaction; (f) 
bleeding inert gas contained in the dry start-up gas from the process; (g) 
collecting the reaction products of the dehydrocyclodimerization process. 
These as well as other embodiments of the present invention will become 
evident from the following more detailed description. 
INFORMATION DISCLOSURE 
Hydrocarbon process start-up procedures are often critical in establishing 
the initial performance of a catalyst in a hydrocarbon conversion process. 
Proper start-up procedures can insure that the hydrocarbon catalyst being 
utilized will be in optimum condition for hydrocarbon conversion. The 
ramifications of following improper start-up procedures can be low initial 
catalyst activity due to catalyst coke deactivation, catalyst poisoning, 
or complete catalyst destruction. The prior art however contains 
relatively few references describing detailed start-up procedures for 
hydrocarbon conversion processes. 
U.S. Pat. No. 3,449,237 discloses a method for the start-up of a reforming 
process. The reforming process disclosed utilizes a specific catalyst 
having a platinum and uranium component. The start-up procedure consists 
of pressuring a reaction zone containing the above mentioned catalyst with 
a inert gas to about 20 psig and heating the catalyst to about 650.degree. 
F. before contacting the catalyst with a sulfur free naphtha. In a similar 
disclosure U.S. Pat. No. 3,650,944 describes a process for reforming a 
sulfur free naphtha with a catalyst comprising platinum and rhenium on a 
porous solid carrier. The process consists of at least three reactors in a 
series. The start-up of the process comprises passing an inert gas through 
the catalyst, heating the catalyst to dehydrogenation reaction conditions 
and passing the substantially sulfur free naphtha into contact with the 
catalyst. Both of the disclosures mentioned above describe a start-up 
method for a reforming process. Additionally, both disclosures describe a 
start-up method that is useful in a reforming process where the reforming 
catalyst comprises platinum and rhenium or uranium. The process of this 
invention, however, describes a dehydrocyclodimerization process. The 
process occurs in the presence of a catalyst comprising a crystalline 
aluminosilicate zeolite and a Group IIB-IVB metal component. The instant 
start-up method may occur in the presence of an inert gas, or it may occur 
in the presence of fuel gas, light hydrocarbons, carbon monoxide, carbon 
dioxide, or other similar gaseous components. The essential factor of the 
start-up method of this invention is that the catalyst be exposed to a 
start-up gas comprising 50 mole percent or less hydrogen before the 
catalyst is brought to dehydrocyclodimerization reaction conditions. 
A catalyst that is very useful in the present invention is disclosed in 
U.S. Pat. No. 4,636,483. The particular catalyst comprises a phosphorous 
containing alumina, a gallium component, and a crystalline aluminosilicate 
zeolite having a silica to alumina ratio of at least 12. 
DETAILED DESCRIPTION OF THE INVENTION 
This invention is concerned with a process for the dehydrocyclodimerization 
of hydrocarbons utilizing a catalytic composition comprising a Group 
IIB-IVB metal component and a crystalline aluminosilicate zeolite 
component. The process is characterized by its novel start-up method. The 
start-up method which surprisingly has been found to be most useful in a 
dehydrocyclodimerization process utilizing the above described catalyst, 
comprises the steps of contacting the above catalyst with a start-up gas 
comprising 50 mole percent or less hydrogen, quickly raising the catalyst 
temperature to dehydrocyclodimerization reaction conditions, and 
maintaining contact between catalyst and said start-up gas until the 
appropriate hydrocarbon feed is introduced into the 
dehydrocyclodimerization process. Such a start-up method has been found to 
optimize the catalyst stability and activity so as to produce a high 
amount of aromatic product components upon start-up of the process. 
Processes for the conversion of light aliphatic hydrocarbons to aromatic or 
nonaromatic C.sub.6 + hydrocarbons have been the subject of significant 
development efforts. The basic utility of the process is the conversion of 
the low cost and highly available C.sub.2 -C.sub.5 hydrocarbons into more 
valuable aromatic hydrocarbons and hydrogen, or to convert the feed 
hydrocarbons to higher molecular weight aliphatic products. Alternatively, 
this may be desired simply to upgrade the value of the hydrocarbons. It 
may also be desired to correct an overabundance of C.sub.2 -C.sub.5 
hydrocarbons or to fulfill a need for the aromatic hydrocarbons. The 
aromatic hydrocarbons are highly useful in the production of a wide range 
of petrochemicals, with benzene being one of the most widely used basic 
feed hydrocarbon chemicals. The product aromatic hydrocarbons are also 
useful as blending components in high octane number motor fuels. 
The feed stream to the dehydrocyclodimerization process is defined herein 
as all streams introduced into the dehydrocyclodimerization reaction zone. 
Included in the feed stream is the C.sub.2 -C.sub.5 aliphatic hydrocarbon. 
By C.sub.2 -C.sub.5 aliphatic hydrocarbons is meant one or more open, 
straight or branched chain isomers having from about two to five carbon 
atoms per molecule. Furthermore, the hydrocarbons in the feedstock may be 
saturated or unsaturated. Preferably, the C.sub.3 and/or C.sub.4 
hydrocarbons are selected from isobutane, normal butane, isobutene, normal 
butene, propane and propylene. Diluents may also be included in the feed 
stream. Examples of such diluents include hydrogen, nitrogen, helium, 
argon, and neon. 
The dehydrocyclodimerization process of the invention must utilize a 
catalyst comprising at least a metal oxide component and an 
aluminosilicate zeolite component. It is believed that the start-up 
method, critical to the process of this invention, is effective in 
maintaining high catalyst initial activity and aromatic selectivity, 
because it reduces the amount of water that may be produced at start-up. 
Water would, if present, be in the form of steam which is known to 
deactivate zeolite catalysts. 
It is believed that one possible method by which water is formed during 
dehydrocyclodimerization process start-up is by the reaction of hydrogen 
with the oxide form of a metal component. As mentioned above, the water 
will be in the form of steam at elevated temperatures during start-up. The 
steam then may attack the crystalline aluminosilicate zeolite structure, 
eventually resulting in a loss of catalyst aromatic selectivity and 
catalyst conversion capability. Alternately, the change in oxidation state 
of the metal component, may also contribute to the loss of catalyst 
aromatic selectivity and catalyst conversion capability. 
Obviously the mechanism mentioned above requires the presence of hydrogen, 
and a catalyst comprising a metal oxide component, and a crystalline 
aluminosilicate zeolite component. Thus, it is the objective of this 
process to minimize the dehydrocyclodimerization catalysts' time and 
temperature weighted exposure to hydrogen during the start-up of a 
dehydrocyclodimerization process. 
The catalyst useful in the present process may be any catalyst known which 
comprises a metal oxide and a crystalline aluminosilicate zeolite. The 
metal oxide component may be any metal component that is in an oxidation 
state greater than zero. It is preferred that the metal oxide is a Group 
IIB-IVB metal oxide. Group IIB-IVB metals that are anticipated as being 
useful in the catalyst of this invention include zinc, cadmium, gallium, 
aluminum, indium, thallium, germanium, tin, and lead. It is preferred that 
the Group IIB-IVB metal component be gallium. 
The metal component of the metal oxide may be present in any amount which 
is catalytically effective in a dehydrocyclodimerization process. Good 
results are obtained when the metal component of the metal oxide is 
present in an amount ranging from about 0.1 to 5.0 percent by weight on an 
elemental basis of the total catalytic composite. Best results are 
ordinarily achieved when about 0.5 to 2.0 wt. % of the metal component on 
all elemental basis is contained in the catalyst. 
The catalyst of this process must also comprise a crystalline 
aluminosilicate zeolite. In particular, a group of crystalline 
aluminosilicate zeolites are preferred, specifically those with silica to 
alumina ratios of at least 12. A particularly preferred group is the one 
identified as the ZSM variety. Included among this ZSM variety are ZSM-5, 
ZSM-8, ZSM-11, ZSM-12, ZSM-35, and other similarly behaving zeolites. It 
is most preferred that ZSM-5 be utilized as the crystalline 
aluminosilicate component of the present invention. These ZSM type 
zeolites are generally prepared by crystallizing a mixture containing a 
source of alumina, a source of silica, a source of alkali metal, water, 
and a tetraalkylammonium compound or its precursors. Of course, other 
crystalline aluminosilicates which meet the silica to alumina ratio 
criteria may be used, such as, faujasites, L-type, mordenites, omega-type, 
and the like. The relative proportions of the crystalline aluminosilicate 
zeolite and the other components of the catalytic composite vary widely, 
with the zeolite content ranging from about 15 percent to about 80 percent 
by weight and more preferably in the range from about 50 to 70 percent by 
weight of composite. 
The catalyst of this process may also comprise other components known to 
impart a dehydrocyclodimerization catalyst with desirable catalytic 
properties. One example of such a component is a phosphorous-containing 
alumina component. It is preferred that the catalyst useful in this 
invention comprises a phosphorous-containing alumina component. 
A phosphorous-containing alumina component may be prepared by a method 
which comprises admixing the alumina hydrosol with a phosphorus-containing 
compound, the phosphorus to alumina molar ratio in the resulting 
phosphorus-containing admixture being from 1:1 to 1:100 on an elemental 
basis and subsequently mixing in a crystalline aluminosilicate and then 
gelling said admixture to obtain said phosphorus-containing alumina. The 
amount of phosphorus in the preferred catalyst can vary over a wide range. 
A phosphorous to aluminum molar ratio ranging from about 1:1 to about 
1:100 is preferred. The 1:1 molar ratio corresponds to a 
phosphorus-containing alumina containing 24.7 wt. % aluminum and 20.5 wt. 
% phosphorus, while the 1:100 corresponds to 0.6 wt. % phosphorus and 52.0 
wt. % aluminum. 
The preferred catalyst of this process comprises the crystalline 
aluminosilicate, ZSM-5, which is present in an amount ranging from 40 to 
80 wt. %. In addition, the most preferred catalyst comprises from 0.1 to 
5.0 wt. % gallium and from 20 to 60 wt. % of a phosphorus-containing 
alumina component. Such a catalyst is described in U.S. Pat. No. 4,636,483 
which is incorporated herein by reference. 
The configuration of the dehydrocyclodimerization process of this invention 
is not a basic element or limiting characteristics of the invention. 
Nevertheless, in order to provide a background to the subject process, it 
is felt useful to describe the preferred reactor system for use in the 
invention. This system comprises a moving bed radial flow multi-stage 
reactor such as is described in U.S. Pat. Nos. 3,652,231; 3,692,496; 
3,706,536; 3,785,963; 3,825,116; 3,839,196; 3,839,197; 3,854,887; 
3,856,662; 3,918,930; 3,981,824; 4,094,814; 4,110,081; and 4,403,090. 
These patents also describe catalyst regeneration systems and various 
aspects of moving catalyst bed operations and equipment. This reactor 
system has been widely employed commercially for the reforming of naphtha 
fractions. Its use has also been disclosed as being useful for the 
dehydrogenation of light paraffins. 
The preferred moving bed reactor system employs a spherical catalyst having 
a diameter between about 1/64-inch (0.04 cm) and 1/8-inch (0.32 cm). The 
catalysts useful in this process are described above. 
The dehydrocyclodimerization conditions which will be employed for use with 
the process of the present invention will, of course, vary depending on 
such factors as feedstock composition and desired conversion. A desired 
range of conditions for the dehydrocyclodimerization of a feedstock 
comprising essentially C.sub.2 -C.sub.5 hydrocarbons include a temperature 
from about 350.degree. to about 700.degree. C., a pressure from about 0.25 
to about 20 atmospheres, and a liquid hourly space velocity from about 0.5 
to about 20 hr.sup.-1. The preferred process conditions are a temperature 
in the range from about 400.degree. to 650.degree. C., a pressure in the 
range of from 0.25 to 10 atmospheres, and a liquid hourly space velocity 
of between 0.5 and 10.0 hr.sup.-1. It is understood that, as the average 
carbon number of the feed increases, a temperature in the lower end of 
temperature range is required for optimum performance and, conversely, as 
the average carbon number of the feed decreases, a higher temperature is 
required in the reaction zone. 
According to the present invention, the dehydrocyclodimerization reaction 
zone hydrocarbon feed stream is contacted with a catalytic composite in a 
dehydrocyclodimerization reaction zone maintained at 
dehydrocyclodimerization conditions. This contacting may be accomplished 
by using the catalytic composite in a fixed bed system, a moving bed 
system, a fluidized bed system, or in a batch-type operation; however, in 
view of the danger of attrition losses of the valuable catalyst and of the 
well-known operation advantages, it is preferred to use either a fixed bed 
system or a dense-phase moving bed system such as shown in U.S. Pat. No. 
3,725,249. It is contemplated that the contacting step can be performed in 
the presence of a physical mixture of particles of any 
dehydrocyclodimerization or similarly behaving catalyst of the prior art. 
In a fixed bed system or a dense phase moving bed, the feed stream is 
preheated by any suitable heating means to the desired reaction 
temperature and then passed into a dehydrocyclodimerization zone 
containing a bed of desired catalytic composite. It is, of course, 
understood that the dehydrocyclodimerization zone may be one or more 
separate reactors with suitable means therebetween to assure that the 
desired conversion temperature is maintained at the entrance to each 
reactor. It is also important to note that the reactants may be contacted 
with the catalyst bed in either upward, downward, or radial flow fashion, 
with the latter being preferred. In addition, the reactants may be in the 
liquid phase, admixed liquid-vapor phase, or a vapor phase when they 
contact the catalyst, with the best results obtained in the vapor phase. 
The dehydrocyclodimerization system then preferably comprises a 
dehydrocyclodimerization zone containing one or more fixed or dense phase 
moving beds of a catalytic composite described above. In a multiple bed 
system, it is, of course, within the scope of the present invention to use 
one dehydrocyclodimerization catalyst composite in less than all of the 
beds with another dehydrocyclodimerization or similarly behaving catalyst 
being used in the remainder of the beds. In a multiple reactor 
dehydrocyclodimerization zone, there may be one or more separate reactors 
with suitable heating means therebetween to compensate for any heat loss 
encountered in each catalyst bed. Specific to the dense phase moving bed 
system, it is common practice to remove catalyst from the bottom of the 
reaction zone, regenerate it by conventional means known to the art, and 
then return it to the top of the reaction zone. 
The instant process is characterized in that it utilizes a unique start-up 
method that has been tailored to be effective when used in conjunction 
with a metal oxide/crystalline aluminosilicate zeolite 
dehydrocyclodimerization catalyst. The start-up method is able to maximize 
the initial aromatic conversion and selectivity of the above described 
catalyst in a dehydrocyclodimerization process. 
It should be noted that by start-up we mean that this method can be used in 
any instance where a dehydrocyclodimerization catalyst that is not being 
contacted with a hydrocarbon feedstock is prepared for contact with a 
hydrocarbon feedstock. This can occur when the catalyst is fresh and newly 
loaded into the process. It can occur during a process upset when the 
hydrocarbon feed has been temporarily removed from the unit. It can also 
occur after the catalyst has been regenerated in the absence of a 
hydrocarbon feedstock. Such catalyst regeneration may occur in a batch or 
continuous catalyst regeneration system. 
The method for starting-up the dehydrocyclodimerization process of this 
invention comprises exposing the catalyst of this invention to a start-up 
gas containing 50 mole percent or less hydrogen under strictly limited 
conditions of time and temperature. The catalyst is contacted with this 
start-up gas during all aspects of process start-up including process 
pressurization, start-up gas circulation, catalyst heat-up, and continuing 
up until the point that the hydrocarbon feed is introduced into the 
process and the dehydrocyclodimerization reaction occurs. The catalyst 
heat up should be accomplished as rapidly as the mechanical limitations of 
the catalyst and equipment will allow. It is preferred that the start-up 
gas contains 30 mole percent or less hydrogen and it is most preferred 
that the start-up gas contain essentially no hydrogen. By essentially no 
hydrogen, it is meant 2.0 mole % or less hydrogen in the start-up gas. 
Minimizing the hydrogen in the start-up gas, minimizes the loss in catalyst 
activity resulting from zeolite deactivation. The process described in 
this invention is cognizant of the fact that it may be impossible for a 
refiner to completely eliminate hydrogen from the process start-up gas. 
For this reason, the maximum level of hydrogen in the start-up gas that is 
likely to be tolerated by the catalyst during start-up is about 50 mole 
percent. 
The start-up gas obviously must contain other gaseous components besides 
hydrogen. Any gaseous component used in the start-up gas must be capable 
of remaining gaseous at process start-up conditions. Such start-up 
conditions include temperatures of from -40.degree. to 450.degree. C. and 
pressures of from 0.25 to 20 atmospheres. Gaseous components which fall 
into this definition include the noble gases, including helium, neon, and 
argon. Gaseous hydrocarbons may also be used in the start-up gas. Such 
gaseous hydrocarbons include, but are not limited to, methane, ethane, 
propane, fuel gas, and the like hydrocarbons. Additionally, the following 
gaseous components may be useful in the start-up gas; nitrogen. Obviously, 
mixtures of any and all of the above named gaseous components may be 
utilized as the start-up gas. It is, however, preferred that the start-up 
gas comprise nitrogen or fuel gas or mixtures thereof. 
The specific start-up procedure is not critical to the invention. It is 
critical, however, that the start-up gas employed in the start-up 
procedure contains 50 mole percent or less hydrogen, and that the time the 
catalyst is exposed to high temperature start-up gas be limited. 
The start-up method detailed below is not intended to limit the scope of 
the process of this invention. It is merely intended to present one of 
many possible methods of starting-up a dehydrocyclodimerization process 
such as that disclosed in this invention. 
The start-up of the process of this invention will be preceeded by 
prestart-up activities. Such prestart-up activities may include equipment 
leak testing, reactor dry-out, reactor catalyst loading and the initial 
purging of the unit with the desired start-up gas. The unit purge is 
undertaken to eliminate any oxygen that may be contained in the unit. Once 
these initial start-up tasks have been completed the process is ready for 
operation. 
To begin the start-up of the process, the reactor system of the process is 
pressurized with dry start-up gas. The pressure of the system may range 
from 0.25 to 20 atmospheres, consistent with the design or operating 
pressure of the unit. The start-up gas utilized may be chosen from the 
list of start-up gases detailed herein above. It is an important aspect 
that the start-up gas used in this process is dry. By dry it is meant that 
the start-up gas should contain less than 20 ppm water and preferably less 
than 5 ppm water. If the start-up gas contains large amounts of water then 
the effectiveness of the start-up of the process in the relative absence 
of hydrogen will be negated. 
Once the reactor system has been pressured with the start-up gas, the gas 
is circulated throughout the process with the process recycle compressors. 
At this point, the start-up gas will be heated utilizing the hydrocarbon 
feed preheat furnaces. The heated gases will be passed across the 
dehydrocyclodimerization catalyst and the catalyst heated to a temperature 
of about 340.degree. C. The time during which hot start-up gas is in 
contact with the catalyst should be minimized. 
Once the catalyst has reached a temperature of about 340.degree. C., the 
hydrocarbon feed may be introduced into the catalyst bed. At a temperature 
of about 340.degree. C., there will be little, if any, 
dehydrocyclodimerization occurring in the reaction zone. Therefore, at 
this point, the catalyst bed temperature should be raised to a temperature 
of about 450.degree. C., at a rate of about 15.degree. to 30.degree. C. 
per hour in order to initiate and sustain the dehydrocyclodimerization 
reaction. Once the dehydrocyclodimerization reaction is initiated, 
hydrogen will be produced as a reaction product. At this point, the 
pressure of the process will be controlled by bleeding the gaseous 
products of the reaction from the unit. Any inert gases, such as nitrogen, 
helium, argon, and the like, contained in the start-up gas may be bled 
from the process, typically from the high pressure separator at this time. 
Finally, once the dehydrocyclodimerization reaction is occurring, the 
liquid reaction products of the dehydrocyclodimerization process can be 
collected. 
As mentioned, this start-up procedure or permeations thereof, may be 
utilized when the process is being initially started-up; started-up 
following maintenance or emergency shut-down; or started-up following 
catalyst replacement or the like. It is also anticipated in a process 
utilizing continuous catalyst regeneration, that the start-up method 
outlined above may be engineered into the continuous process such that the 
regenerated catalyst from the continuous regeneration step of a continuous 
regeneration process will not be exposed to any hydrogen after 
regeneration and until it is contacted with the hydrocarbon feedstock.

The following example serves to illustrate the process of this invention. 
The example should not, however, be construed as limiting the scope of the 
invention as set forth in the claims as there are many variations which 
may be made thereon without departing from the spirit of the invention as 
those skilled in the art will recognize. 
EXAMPLE I 
The following tests were performed to demonstrate the benefit of utilizing 
a dehydrocyclodimerization start-up procedure that does not utilize 
hydrogen. 
A dehydrocyclodimerization catalyst was prepared as follows: A first 
solution was prepared by adding phosphoric acid to an aqueous solution of 
hexamethylenetetramine (HMT). A second solution was prepared by adding a 
ZSM-5 type zeolite to enough alumina sol, prepared by digesting metallic 
aluminum in hydrochloric acid, to yield a zeolite content in the finished 
catalyst equal to about 50-75 wt. %. These two solutions were commingled 
to achieve a homogeneous admixture of HMT, phosphorus, alumina sol, and 
zeolite. This admixture was dispersed as droplets into an oil bath 
maintained at about 200.degree. F. The droplets remained in the oil bath 
until they set and formed hydrogel spheres. These spheres were removed 
from the oil bath, water washed, air dried, and calcined at a temperature 
of about 900.degree. F. A solution of gallium nitrate was utilized to 
impregnate the spheres to achieve a gallium content on the finished 
catalyst equal to about 1 wt. %. After impregnation the spheres were 
calcined a second time, in the presence of steam, at a temperature of 
about 1200.degree. F. 
Further information of the catalyst preparation method can be obtained from 
U.S. Pat. No. 4,636,483. 
Two quantities of the catalyst above were subjected to a pilot plant 
start-up procedure, utilizing hydrogen as the start-up gas in the first 
test, and nitrogen as the start-up gas in the second test. 
The start-up method consisted of purging the pilot plant with the start-up 
gas followed by heating of the reaction zone to 550.degree. C. for leak 
testing of the pilot plant in the presence of the same start-up gas. After 
leak testing, propane was introduced into the pilot plant reactor at 
dehydrocyclodimerization reaction conditions. The dehydrocyclodimerization 
reaction conditions included a temperature of 540.degree. C., a pressure 
of 1.0 atmosphere gauge and a liquid hourly space velocity of 0.8 
hr.sup.-1. The products of the reaction of each test were analyzed and the 
C.sub.3 -C.sub.4 conversion and aromatic selectivity values for each test 
were determined after the catalyst of each test had been exposed to the 
propane feed for 34 hours. The above results are detailed in Table I 
below. 
TABLE 1 
______________________________________ 
Test # 1 2 
______________________________________ 
Start-up Gas H.sub.2 
N.sub.2 
C.sub.3 -C.sub.4 Conversion, Wt % 
62.2 68.3 
Aromatic Selectivity, Wt % 
56.1 58.8 
______________________________________ 
The results in Table I above clearly indicate that a 
dehydrocyclodimerization process that utilizes a gas besides hydrogen as a 
start-up gas exhibits a dehydrocyclodimerization performance superior to 
that of a process utilizing a hydrogen start-up gas. 
EXAMPLE II 
A dehydrocyclodimerization catalyst as prepared in Example I was subjected 
to a soaking step for 100 hours in the presence of a start-up gas 
consisting of 40 mole % nitrogen and 60 mole percent methane at 
580.degree. C. The soaked catalyst was then subjected to a synthetic 
regeneration step in which the catalyst was exposed to a gas comprising 99 
mole % nitrogen, 1 mole % oxygen and 600 mole ppm of water at 530.degree. 
C., for 6 hours at a gas hourly space velocity of 2400 hr.sup.-1. 
The soaked and regenerated catalyst was then placed in a 
dehydrocyclodimerization pilot plant subjected to a nitrogen gas start-up 
after which the plant, subjected to a nitrogen gas start-up after which 
the C.sub.3 /C.sub.4 conversion ability of the catalyst was evaluated 
utilizing the pilot plant conditions detailed in Example I. The results of 
the pilot plant testing are found in Table III below. 
TABLE II 
______________________________________ 
Test Catalyst Fresh Catalyst 
Start Up Gas (Mole %) 
40%N.sub.2 /60% CH.sub.4 
-- 
Time C.sub.3 C.sub.4 Conversion 
C.sub.3 /C.sub.4 Conversion 
Hours Wt % Wt % 
______________________________________ 
30 75.0 75.4 
______________________________________