Process for producing a hydrogen-rich gas stream from the effluent of a catalytic hydrocarbon conversion reaction zone

A process for the production of a hydrogen-rich gas stream from the effluent of a catalytic hydrocarbon conversion reaction zone is disclosed. A hydrogen-containing vapor phase is recovered from the effluent and subjected to cooling in order to produce a hydrogen-rich gas stream. The resulting hydrogen-rich gas stream is expanded to provide the medium used in cooling the hydrogen-containing vapor phase.

BACKGROUND OF THE INVENTION 
The present invention is directed toward an improved method for recovering 
a hydrogen-rich gas stream from a hydrogen and hydrocarbon effluent of a 
catalytic hydrocarbon conversion zone. More particularly the described 
inventive technique is adaptable for utilization in catalytic hydrocarbon 
conversion reactions which result in a net production of hydrogen. 
Various types of catalytic hydrocarbon conversion reaction systems have 
found widespread utilization throughout the petroleum and petrochemical 
industries for effecting the conversion of hydrocarbons to a multitudinous 
number of products. The reactions employed in such systems are either 
exothermic or endothermic, and of more importance to the present 
invention, often result in either the net production of hydrogen or the 
net consumption of hydrogen. Such reaction systems, as applied to 
petroleum refining, have been employed to effect numerous hydrocarbon 
conversion reactions including those which predominate in catalytic 
reforming, ethylbenzene dehydrogenation to styrene, propane and butane 
dehydrogenation, etc. 
Petroleum refineries and petrochemical complexes customarily comprise 
numerous reaction systems. Some systems will be net consumers of hydrogen 
while other systems within the refinery or petrochemical complex may 
result in the net production of hydrogen. Because hydrogen is a relatively 
expensive item, it has become the practice within the art of hydrocarbon 
conversion to supply hydrogen from reaction systems which result in the 
net production of hydrogen to reaction systems which are net consumers of 
hydrogen. Occasionally the net hydrogen being passed to the net 
hydrogen-consuming reaction systems must be of high purity due to the 
reaction conditions and/or the catalyst employed in the systems. Such a 
situation may require treatment of the hydrogen from the net 
hydrogen-producing reaction systems to remove hydrogen sulfide, light 
hydrocarbons, etc., from the net hydrogen stream. 
Alternatively, the hydrogen balance for the petroleum refinery or 
petrochemical complex may result in excess hydrogen, i.e., the net 
hydrogen-producing reaction systems produce more hydrogen than is 
necessary for the net hydrogen-consuming reaction systems. In such an 
event the excess hydrogen may be sent to the petroleum refinery or 
petrochemical complex fuel system. However, because the excess hydrogen 
often has admixed therewith valuable components, such as C.sub.3.sup.+ 
hydrocarbons, it is frequently desirable to treat the excess hydrogen to 
recover these components prior to its passage to fuel. 
Typical of the net hydrogen-producing hydrocarbon reaction systems are 
catalytic reforming, catalytic dehydrogenation of alkyl-aromatics and 
catalytic dehydrogenation of paraffins. Commonly employed net 
hydrogen-consuming reaction systems are hydrotreating, hydrocracking and 
catalytic hydrogenation. Of the above mentioned net hydrogen-producing and 
consuming hydrocarbon reaction systems, catalytic reforming ranks as one 
of the most widely employed. By virtue of its wide application and its 
utilization as a primary source of hydrogen for the net hydrogen-consuming 
reaction systems, catalytic reforming has become well known in the art of 
hydrocarbon conversion reaction systems. Accordingly the following 
discussion of the invention will be in reference to its application to a 
catalytic reforming reaction system. However, the following discussion 
should not be considered as unduly limiting the broad scope of the 
invention which has wide application in many hydrocarbon conversion 
reaction systems. Those having ordinary skill in the art will well 
recognize the broad application of the present invention and the following 
will enable them to apply the invention in all its multitudinous 
embodiments. 
It is well known that high quality petroleum products in the gasoline 
boiling range including, for example, aromatic hydrocarbons such as 
benzene, toluene and the xylenes, are produced by the catalytic reforming 
process wherein a naphtha fraction is passed to a reaction zone wherein it 
is contacted with a platinum-containing catalyst in the presence of 
hydrogen. Generally, the catalytic reforming reaction zone effluent, 
comprising gasoline boiling range hydrocarbons and hydrogen, is passed to 
a vapor-liquid equilibrium separation zone and is therein separated into a 
hydrogen-containing vapor phase and an unstabilized hydrocarbon liquid 
phase. A portion of the hydrogen-containing vapor phase may be recycled to 
the reaction zone. The remaining hydrogen-containing vapor phase is 
available for use either by the net hydrogen-consuming processes or as 
fuel for the petroleum refinery or petrochemical complex fuel system. 
While a considerable portion of the hydrogen-containing vapor phase is 
required for recycle purposes, a substantial net excess is available for 
other uses. 
Because the dehydrogenation of naphthenic hydrocarbons is one of the 
predominant reactions of the reforming process, substantial amounts of 
hydrogen are generated within the catalytic reforming reaction zone. 
Accordingly a net excess of hydrogen is available for use as fuel or for 
use in a net hydrogen-consuming process such as the hydrotreating of 
sulfur-containing petroleum feedstocks. However, catalytic reforming also 
involves a hydrocracking function among the products of which are 
relatively low molecular weight hydrocarbons including methane, ethane, 
propane, butanes and the pentanes, substantial amounts of which appear in 
the hydrogen-containing vapor phase separated from the reforming reaction 
zone effluent. These normally gaseous hydrocarbons have the effect of 
lowering the hydrogen purity of the hydrogen-containing vapor phase to the 
extent that purification is often required before the hydrogen is suitable 
for other uses. Moreover, if the net excess hydrogen is intended for use 
as fuel in the refinery or petrochemical complex fuel system, it is 
frequently desirable to maximize the recovery of C.sub.3.sup.+ 
hydrocarbons which are valuable as feedstock for other processes. It is 
therefore advantageous to devise a method of purifying the 
hydrogen-containing vapor phase to produce a hydrogen-rich gas stream and 
to recover valuable components such as C.sub.3.sup.+ hydrocarbons. 
OBJECTS AND EMBODIMENTS 
A principal object of our invention is an improved process for producing a 
hydrogen-rich gas stream from the effluent of a catalytic hydrocarbon 
conversion reaction zone. A corollary objective is to recover energy from 
the hydrogen-rich gas stream thereby increasing the efficiency of the 
hydrocarbon conversion reaction system. Other objects in applying the 
invention specifically to catalytic reforming involve increased recovery 
of C.sub.3.sup.+ hydrocarbons for further advantageous use. Accordingly a 
broad embodiment of the present invention is directed toward a process for 
producing a hydrogen-rich gas stream by treating a hydrogen and 
hydrocarbon effluent from a catalytic hydrocarbon conversion reaction zone 
comprising the steps of: (a) passing said effluent to a first vapor-liquid 
equilibrium zone, recovering therefrom a hydrogen-containing vapor phase 
and recycling a first portion thereof to said reaction zone; (b) drying at 
least a second portion of the hydrogen-containing vapor phase and 
thereafter cooling the dried portion by indirect heat exchange with a 
hereinafter defined hydrogen-rich gas stream; (c) passing the dried, 
cooled portion of the hydrogen-containing vapor phase to a second 
vapor-liquid equilibrium separation zone to produce a liquid stream 
comprising light hydrocarbons and a hydrogen-rich gas stream; (d) 
expanding at least a portion of the hydrogen-rich gas stream and 
thereafter subjecting it to indirect heat exchange with the dried portion 
of the hydrogen-containing vapor phase pursuant to step (b) above; and, 
(e) recovering the heat exchanged hydrogen-rich gas stream. 
In an alternative and more specific embodiment, the present invention 
provides a process for producing a hydrogen-rich gas stream by treating a 
hydrogen and hydrocarbon effluent from a catalytic reforming reaction zone 
comprising the steps of: (a) passing said effluent to a first vapor-liquid 
equilibrium zone and recovering therefrom a hydrogen-containing vapor 
phase; (b) subjecting a first portion of the hydrogen-containing vapor 
phase to compression and recycling at least part of the compressed first 
portion to the catalytic reforming reaction zone; (c) drying a second 
portion of the hydrogen-containing vapor phase and thereafter cooling the 
dried portion by indirect heat exchange with a hereinafter defined 
hydrogen-rich gas stream; (d) passing the dried, cooled portion of the 
hydrogen-containing vapor phase to a second vapor-liquid equilibrium 
separation zone to produce a liquid stream comprising light hydrocarbons 
and a hydrogen-rich gas stream; (e) subjecting at least a portion of the 
hydrogen-rich gas stream to an expansion and thereafter subjecting it to 
indirect heat exchange with the dried second portion of the 
hydrogen-containing vapor phase pursuant to step (c) above, and effecting 
the compression in step (b) above at least in part with energy resulting 
from said expansion of the portion of hydrogen-rich gas stream; and, (f) 
recovering the heat exchanged hydrogen-rich gas stream. 
These, as well as other objects and embodiments will become evident from 
the following, more detailed description of the present invention. 
INFORMATION DISCLOSURE 
The prior art recognizes myriad process schemes for the obtention and 
purification of a hydrogen-rich gas stream from the effluent of 
hydrocarbon conversion reaction zones. U.S. Pat. No. 3,431,195, issued 
Mar. 4, 1969, discloses such a scheme. The hydrogen and hydrocarbon 
effluent of a catalytic reforming zone is first passed to a low pressure 
vapor-liquid equilibrium zone from which zone is derived a first 
hydrogen-containing vapor phase and a first unstabilized hydrocarbon 
liquid phase. The hydrogen-containing vapor phase is compressed and 
recontacted with at least a portion of the liquid phase and the resulting 
mixture is passed to a second high pressure vapor-liquid equilibrium zone. 
Because the second zone is maintained at a higher pressure, a new 
vapor-liquid equilibrium is established resulting in a hydrogen-rich gas 
phase and a second unstabilized hydrocarbon liquid phase. A portion of the 
hydrogen-rich vapor phase is recycled back to the catalytic reforming 
reaction zone with the balance of the hydrogen-rich vapor phase being 
recovered as a hydrogen-rich gas stream relatively free of C.sub.3 
-C.sub.6 hydrocarbons. 
U.S. Pat. No. 3,516,924, issued June 23, 1970, discloses a more complex 
system. In this reference the reaction zone effluent from a catalytic 
reforming process is first separated in a vapor-liquid equilibrium zone to 
produce a hydrogen-containing vapor phase and an unstabilized liquid 
hydrocarbon phase. The two phases are again recontacted and again 
separated in a higher pressure vapor-liquid equilibrium zone. A first 
portion of the resulting hydrogen-rich vapor phase is recycled back to the 
catalytic reforming zone while the remaining portion of the hydrogen-rich 
vapor phase is passed to an absorber column in which stabilized reformate 
is utilized as the sponge oil. A high purity hydrogen gas stream is 
recovered from the absorption zone and the sponge oil, containing light 
hydrocarbons is recontacted with the hydrocarbon liquid phase from the 
first vapor-liquid equilibrium zone prior to the passage thereof to the 
second high pressure vapor-liquid equilibrium zone. 
U.S. Pat. No. 3,520,800, issued July 14, 1980, discloses an alternative 
method of obtaining a hydrogen-rich gas stream from a catalytic reforming 
reaction zone effluent. As in the previously discussed methods, the 
reforming reaction zone effluent is passed to a first vapor-liquid 
equilibrium zone from which is obtained a first hydrogen-containing vapor 
phase and a first unstabilized hydrocarbon liquid phase. The 
hydrogen-containing vapor phase is compressed and recontacted with the 
hydrocarbon liquid phase. Thereafter the mixture is passed to a second 
vapor-liquid equilibrium zone maintained at a higher pressure than the 
first vapor-liquid equilibrium zone. A second hydrogen-containing vapor 
phase of higher hydrogen purity is recovered from the second vapor-liquid 
equilibrium zone with a portion thereof being recycled back to the 
catalytic reforming reaction zone. The remaining amount of the resulting 
hydrogen-containing vapor phase is passed to a cooler wherein the 
temperature of the phase is reduced at least 20.degree. F. lower than the 
temperature maintained in the second vapor-liquid equilibrium zone. After 
cooling, the hydrogen phase is passed to a third vapor-liquid equilibrium 
zone from which a high purity hydrogen gas stream is recovered. 
U.S. Pat. No. 3,520,799, issued July 14, 1970, discloses yet another method 
for obtaining a high purity hydrogen gas stream from a catalytic reforming 
reaction zone effluent. As in all the previous schemes, the reaction zone 
effluent is passed to a low pressure vapor-liquid equilibrium zone from 
which is produced a hydrogen-containing vapor phase and an unstabilized 
liquid hydrocarbon phase. After compression the hydrogen-containing vapor 
phase is recontacted with the unstabilized liquid hydrocarbon phase and 
the resulting mixture is passed to a high pressure vapor-liquid 
equilibrium zone. A second hydrogen-containing vapor phase is produced of 
higher purity than the hydrogen-containing vapor phase from the low 
pressure vapor-liquid equilibrium zone. A first portion of this higher 
purity hydrogen-containing vapor phase is recycled back to the catalytic 
reforming zone. The balance of the higher purity hydrogen-containing vapor 
phase is passed to an absorption zone where it is contacted with a lean 
sponge oil preferably comprising C.sub.6.sup.+ hydrocarbons. A 
hydrogen-containing gas stream is removed from the absorber and after 
cooling passed to a third vapor-liquid equilibrium zone. The sponge oil, 
containing constituents absorbed from the higher purity 
hydrogen-containing vapor phase is removed from the absorption zone and is 
admixed with the unstabilized liquid hydrocarbon stream from the low 
pressure vapor-liquid equilibrium zone prior to the recontacting thereof 
with the compressed hydrogen-containing vapor phase. A stream of high 
purity hydrogen gas is removed from the third vapor-liquid equilibrium 
zone. 
U.S. Pat. No. 3,882,014, issued May 6, 1975, discloses another method of 
obtaining a high purity hydrogen stream from the reaction zone effluent of 
a catalytic reforming process. The catalytic reforming reaction zone 
effluent is first passed to a vapor-liquid equilibrium zone from which is 
recovered an unstabilized liquid hydrocarbon stream and a 
hydrogen-containing vapor phase. After compression the hydrogen-containing 
vapor phase is passed to an absorption zone wherein it is contacted with a 
sponge oil comprising stabilized reformate. A high purity hydrogen gas 
stream is recovered from the absorption zone with one portion thereof 
being recycled back to the catalytic reforming reaction zone while the 
remainder is recovered for further use. A liquid stream is recovered from 
the absorption zone and admixed with the unstabilized liquid hydrocarbon 
stream from the vapor-liquid equilibrium zone. The admixture is then 
fractionated in a stabilizing column to produce the stabilized reformate, 
a first portion of which is utilized as the sponge oil in the absorption 
zone. 
More recent, U.S. Pat. No. 4,212,726, issued July 15, 1980, discloses yet 
another variation of the previously described methods for recovering high 
purity hydrogen stream from catalytic reforming reaction zone effluents. 
In this reference the reaction zone effluent from the catalytic reforming 
process is passed to a first vapor-liquid equilibrium zone from which is 
recovered a first unstabilized hydrocarbon stream and a first 
hydrogen-containing vapor stream. After compression the 
hydrogen-containing vapor stream is passed to an absorption column wherein 
it is contacted with the first liquid hydrocarbon phase from the 
vapor-liquid equilibrium zone and stabilized reformate. A high purity 
hydrogen gas stream is recovered from the absorption zone with one portion 
being recycled back to the reaction zone and the balance being recovered 
for further use. 
U.S. Pat. No. 4,364,820, issued Dec. 21, 1982, discloses a more complex 
method of recovering high purity hydrogen gas from a catalytic reforming 
reaction zone effluent. In this reference the reaction zone effluent is 
first separated in a vapor-liquid equilibrium zone into a first 
hydrogen-containing vapor phase and a first liquid hydrocarbon phase. One 
portion of the first hydrogen-containing vapor phase is compressed and 
recycled back to the catalytic reaction zone. The balance of the 
hydrogen-containing vapor phase is compressed and contacted with a second 
liquid hydrocarbon phase recovered from a hereinafter described third 
vapor-liquid equilibrium zone. The admixture is then passed to a second 
vapor-liquid equilibrium zone from which is derived a third liquid 
hydrocarbon phase comprising unstabilized reformate and a second 
hydrogen-containing vapor phase of higher purity than the first 
hydrogen-containing vapor phase derived from the first vapor-liquid 
equilibrium zone. The second hydrogen-containing vapor phase is subjected 
to compression and then contacted with the first liquid hydrocarbon phase 
from the first vapor-liquid equilibrium zone. The resulting admixture is 
then passed to a third vapor-liquid equilibrium zone from which is derived 
a hydrogen gas stream of high purity and the aforementioned second liquid 
hydrocarbon phase. 
Recent U.S. Pat. No. 4,374,726, issued Feb. 22, 1983, discloses a further 
method of obtaining a high purity hydrogen gas stream from the reaction 
zone effluent of a catalytic reforming process. In this reference, the 
reaction zone effluent is passed to a vapor-liquid equilibrium zone to 
produce a first hydrocarbon liquid phase and a hydrogen-containing vapor 
phase. A first portion of the hydrogen-containing vapor phase is 
compressed and recycled to the catalytic reforming reaction zone. A second 
portion of the hydrogen-containing vapor phase is compressed and 
thereafter recontacted with the first liquid hydrocarbon phase from the 
vapor-liquid equilibrium zone. The resulting admixture is then passed to a 
second vapor-liquid equilibrium zone to produce a hydrogen gas stream of 
high purity and a second liquid hydrocarbon phase comprising unstabilized 
reformate. 
In addition to the above-mentioned patent literature, the technical 
literature within the art has also disclosed methods for separating 
reaction zone effluents to obtain hydrogen-containing gas streams. For 
example, the Nov. 10, 1980 issue of the Oil and Gas Journal discloses an 
LPG dehydrogenation process in which the entire reaction zone effluent is 
first dried, then subjected to indirect heat exchange with a cool 
hydrogen-containing gas stream. The cool hydrogen-containing gas stream is 
derived by passing the entire cooled reaction zone effluent to a 
vapor-liquid equilibrium separation zone. The hydrogen-containing gas 
stream is removed from the separation zone and is then expanded. 
Thereafter it is subjected to indirect heat exchange with the entire 
reaction zone effluent. After the indirect heat exchange step, a portion 
of the hydrogen-containing vapor phase is recycled to the reaction zone. 
In brief summation, the prior art which employs various vapor-liquid 
equilibrium separations, expansions, recontacting steps and/or absorption 
to produce high purity hydrogen streams or hydrogen-containing streams 
from reaction zone effluents of catalytic hydrocarbon conversion processes 
is not cognizant of the technique herein described which employs the 
vapor-liquid equilibrium separation, indirect heat exchange, and the 
expansion of vapor techniques herein described in order to produce a high 
purity hydrogen gas stream. 
SUMMARY OF THE INVENTION 
To reiterate briefly, the process encompassed by our inventive concept is 
suitable for use in hydrocarbon conversion reaction systems which may be 
characterized as single or multiple reaction zones in which catalyst 
particles are disposed as fixed beds or movable via gravity flow. 
Moreover, the present invention may be advantageously utilized in 
hydrocarbon conversion reaction systems which result in the net production 
or the net consumption of hydrogen. Although the following discussion is 
specifically directed toward catalytic reforming of naphtha boiling range 
fractions, there is no intent to so limit the present invention. 
The art of catalytic reforming is well known to the petroleum refining and 
petrochemical processing industry. Accordingly, a detailed description 
thereof is not required herein. In brief, the catalytic reforming art is 
largely concerned with the treatment of a petroleum gasoline fraction to 
improve its anti-knock characteristics. The petroleum fraction may be a 
full boiling range gasoline fraction having an initial boiling point of 
from about 50.degree. to about 100.degree. F. and an end boiling point 
from about 325.degree. to about 425.degree. F. More frequently the 
gasoline fraction will have an initial boiling point of about 150.degree. 
to about 250.degree. F. and an end boiling point of from about 350.degree. 
to 425.degree. F., this higher boiling fraction being commonly referred to 
as naphtha. The reforming process is particularly applicable to the 
treatment of those straight run gasolines comprising relatively large 
concentrations of naphthenic and substantially straight chain paraffinic 
hydrocarbons which are amenable to aromatization through dehydrogenation 
and/or cyclization. Various other concomitant reactions also occur, such 
as isomerization and hydrogen transfer, which are beneficial in upgrading 
the anti-knock properties of the selected gasoline fraction. In addition 
to improving the anti-knock characteristics of the gasoline fraction, the 
tendency of the process to produce aromatics from naphthenic and 
paraffinic hydrocarbons makes catalytic reforming an invaluable source for 
the production of benzene, toluene, and xylenes all of great utility in 
the petrochemical industry. 
Widely accepted catalysts for use in the reforming process typically 
comprise platinum on an alumina support. These catalysts will generally 
contain from about 0.05 to about 5 wt. % platinum. More recently, certain 
promoters or modifiers, such as cobalt, nickel, rhenium, germanium and 
tin, have been incorporated into the reforming catalyst to enhance its 
performance. 
The catalytic reforming of naphtha boiling range hydrocarbons, a vapor 
phase operation, is effected at conversion conditions which include 
catalyst bed temperatures in the range of from about 700.degree. to about 
1020.degree. F.; judicious and cautious techniques generally dictate that 
the catalyst temperatures not substantially exceed a level of about 
1020.degree. F. Other conditions generally include a pressure of from 
about 50 to about 1000 psig, a liquid hourly space velocity (defined as 
volumes of fresh charge stock per hour per volume of catalyst particles in 
the reaction zone) of from about 0.2 to about 10.0 hr..sup.-1 and a 
hydrogen to hydrocarbon mole ratio generally in the range of from about 
0.5:1.0 to about 10.0:1.0. As those possessing the requisite skill in the 
petroleum refining art are aware, continuous regenerative reforming 
systems offer numerous advantages when compared to the fixed bed systems. 
Among these is the capability of efficient operation at comparatively 
lower pressures--e.g. 50 to about 200 psig--and higher liquid hourly space 
velocities--e.g. about 3.0 to about 10 hr..sup.-1. As a result of 
continuous catalyst regeneration, higher consistent inlet catalyst bed 
temperatures can be maintained--e.g. 950.degree. to about 1010.degree. F. 
Furthermore, there is afforded a corresponding increase in hydrogen 
production and hydrogen purity in the hydrogen-containing vaporous phase 
from the product separation facility. 
The catalytic reforming reaction is carried out at the aforementioned 
reforming conditions in a reaction zone comprising either a fixed or a 
moving catalyst bed. Usually, the reaction zone will comprise a plurality 
of catalyst beds, commonly referred to as stages, and the catalyst beds 
may be stacked and enclosed within a single reactor vessel, or the 
catalyst beds may each be enclosed in a separate reactor vessel in a 
side-by-side reactor arrangement. Generally a reaction zone will comprise 
two to four catalyst beds in either the stacked and/or side-by-side 
configuration. The amount of catalyst used in each of the catalyst beds 
may be varied to compensate for the endothermic heat of reaction in each 
case. For example, in a three catalyst bed system, the first bed will 
generally contain from about 10 to about 30 vol. %; the second, from about 
25 to about 45 vol. %; and the third, from about 40 to about 60 vol. %, 
all percentages being based on the amount of catalyst within the reaction 
zone. With respect to a four catalyst bed system, suitable catalyst 
loadings would be from about 5 to about 15 vol. % in the first bed, from 
about 15 to about 25 vol. % in the second, from about 25 to about 35 vol. 
% in the third and from about 35 to about 50 vol. % in the fourth. The 
reactant stream, comprising hydrogen and the hydrocarbon feed, should 
desirably flow serially through the reaction zones in order of increasing 
catalyst volume with interstage heating. The unequal catalyst 
distribution, increasing in the serial direction of reactant stream flow, 
facilitates and enhances the distribution of the reactions. 
Upon removal of the hydrocarbon and hydrogen effluent from the catalytic 
reaction zone, it is customarily subjected to indirect heat exchange 
typically with the hydrogen and hydrocarbon feed to the catalytic reaction 
zone. Such an indirect heat exchange aids in the further processing of the 
reaction zone effluent by cooling it and recovers heat which would 
otherwise be lost for further use in the catalytic reforming process. 
Following any such cooling step which may be employed, the reaction zone 
effluent is passed to a vapor-liquid equilibrium zone to recover a 
hydrogen-containing vapor phase from the effluent, at least a portion of 
which is to be recycled back to the reforming zone. The vapor-liquid 
equilibrium zone is usually maintained at substantially the same pressure 
as employed in the reforming reaction zone, allowing for the pressure drop 
in the system. The temperature within the vapor-liquid equilibrium zone is 
typically maintained at about 60.degree. to about 120.degree. F. The 
temperature and pressure are selected in order to produce a 
hydrogen-containing vapor phase and a principally liquid phase comprising 
unstabilized reformate. The unstabilized reformate is then further treated 
in a fractionation column for the recovery of reformate product. In 
addition a fractionation column overhead product is recovered comprising 
light hydrocarbons which are generally gaseous at standard temperature and 
pressure and include C.sub.3 and C.sub.4 hydrocarbons. 
One portion of the hydrogen-containing vapor phase is recycled to the 
catalytic reforming reaction zone while in accordance with the invention a 
second portion which may comprise the balance of the hydrogen-containing 
vapor phase is dried before cooling. Drying of the hydrogen-containing 
vapor phase is necessary because water, which may be intentionally 
injected into the reaction zone or which may comprise a reaction zone feed 
contaminant, must be substantially removed to avoid formation of ice upon 
cooling. By drying the hydrogen-containing vapor phase, formation of ice 
and the concomitant reduction of heat transfer coefficients in the heat 
exchanger apparatus utilized to effect the cooling are avoided. The drying 
may be effected by any means known in the art. Absorption using liquid 
desiccants such as ethylene glycol, diethylene glycol and triethylene 
glycol may be advantageously employed. In such an absorption system a 
glycol desiccant is contacted with the hydrogen-containing vapor phase in 
an absorber column. Water-rich glycol is then removed from the absorber 
and passed to a regenerator wherein the water is removed from the glycol 
desiccant by application of heat. The resulting lean glycol desiccant is 
then recycled to the absorber column for further use. As an alternative to 
absorption using liquid desiccants, drying may also be effected by 
adsorption utilizing a solid desiccant. Alumina, silica-gel, 
silica-alumina beads, and molecular sieves are typical of the solid 
desiccants which may be employed. Generally the solid desiccant will be 
emplaced in at least two beds in parallel flow configuration. While the 
hydrogen-containing vapor phase is passed through one bed of desiccant, 
the remaining bed or beds are regenerated. Regeneration is generally 
effected by heating to remove desorbed water and purging the desorbed 
water vapor from the desiccant bed. The beds of desiccant may, therefore, 
be cyclically alternated between drying and regeneration to provide 
continuous removal of water from the hydrogen-containing vapor phase. 
Regardless of the exact method employed to effect the removal of water, 
after drying the hydrogen-containing vapor phase is subjected to an 
indirect heat exchange in order to remove heat from the 
hydrogen-containing vapor phase to effect condensation therefrom of light 
hydrocarbons, principally C.sub.3.sup.+ hydrocarbons. As will be 
explained hereinafter more fully, because the noncondensed portion of the 
hydrogen-containing vapor phase, comprising principally hydrogen, is 
subjected to an expansion and then utilized as the cooling medium in the 
indirect heat exchange step, substantial amounts of heat may be removed 
from the hydrogen-containing vapor phase and the temperature thereof may 
be greatly reduced provided sufficient heat transfer surface is available 
within the heat transfer apparatus used to effect the indirect heat 
exchange. 
Following cooling the hydrogen-containing vapor phase is separated in a 
second vapor-liquid equilibrium separation zone to provide a hydrogen-rich 
gas stream and a liquid stream, comprising C.sub.3.sup.+ hydrocarbons. 
The pressure maintained in the second vapor-liquid equilibrium separation 
zone is substantially the same as that maintained in the first 
vapor-liquid equilibrium separation zone allowing for pressure drop 
through the drying apparatus, the heat exchange apparatus and associated 
piping. The temperature within the second vapor-liquid separation zone is 
substantially that of the hydrogen-containing vapor phase upon exit from 
the heat exchange apparatus which is dependent on the heat transfer 
surface area for a given pressure reduction ratio across the means 
utilized to effect the expansion of the hydrogen-rich gas stream. 
Upon withdrawal from the second vapor-liquid equilibrium separation zone, 
the liquid stream, comprising C.sub.3.sup.+ hydrocarbons, may be sent to 
the reformate stabilizer column if desired or subjected to any other 
processing step for the advantageous use thereof. 
The hydrogen-rich gas stream is recovered from the second vapor-liquid 
equilibrium zone and is then subjected to an expansion in order to 
decrease the temperature thereof. Pursuant to one of the aforesaid objects 
of the invention, it is essential that the expansion be effected in such a 
manner as to produce work by recovery of energy from the hydrogen-rich 
vapor gas stream. Accordingly the expansion is preferabaly effected by use 
of a turboexpander means. The turboexpander means may in turn be connected 
to a shaft which may be employed to drive one or more pieces of equipment. 
For example the shaft may be connected to an electrical power generation 
means for the production of electrical power. The electricity so generated 
may be used to drive pumps, compressors, etc. If desired the electricity 
may be passed into a power grid system for use elsewhere in the refinery 
or petrochemical complex or for sale to electrical utilities. 
Alternatively the shaft may be utilized to directly provide shaft power 
for driving compressors, pumps or other pieces of process equipment. 
As indicated previously, extremely cold temperatures may be achieved in 
subjecting the hydrogen-containing vapor phase to indirect heat exchange 
with the hydrogen-rich gas stream providing there is sufficient heat 
transfer surface in the heat transfer apparatus and a sufficient expansion 
pressure ratio across the turboexpander means. The greater the heat 
transfer surface area in the heat transfer apparatus, the more heat may be 
transferred from the hydrogen-containing vapor phase to the cooled 
hydrogen-rich gas stream. Moreover, as heat is transferred from the 
hydrogen-containing vapor phase and its temperature is reduced, the cooler 
the resulting hydrogen-rich gas stream will be prior to expansion and in 
turn, the cooler the expanded hydrogen-rich gas stream will become. 
Accordingly by increasing the heat transfer surface in the heat transfer 
apparatus, a hydrogen-rich gas stream of greater purity may be obtained. 
However, it should be remembered that heat energy transferred from the 
hydrogen-containing vapor phase to the hydrogen-rich gas stream in the 
heat exchange apparatus will be unavailable for recovery by the 
turboexpander means and hence the amount of available shaft power will be 
reduced. 
To more fully demonstrate the attendent advantages of the present 
invention, the following example, based on engineering calculations, is 
set forth.

DETAILED DESCRIPTION OF THE DRAWING 
Specifically referring now to the drawing, a naphtha boiling range 
hydrocarbon charge stock is introduced via line 1 and mixed with a 
hydrogen-containing vapor phase recycled via line 2. The admixture is then 
passed through line 3 into fired heater 4 wherein it is brought up to a 
reaction zone inlet temperature of about 950.degree. F. 
After heating, the naphtha-hydrogen admixture is passed through line 5 to a 
reaction zone 6 which has emplaced therein a reforming catalyst comprising 
platinum on alumina. Reaction zone 6 has been depicted here as a single 
zone for convenience; however, as previously noted generally the reaction 
will comprise two or more catalyst beds in series with inter-catalyst bed 
heating either in heater 4 or in separate heaters. 
Regardless of the exact configuration of the reaction zone, the effluent 
therefrom is cooled (via heat exchange with the feed and via externally 
cooled heat exchangers which are not depicted) and passed via line 7 into 
first vapor-liquid equilibrium separation zone 8 which is maintained at a 
temperature of 100.degree. F. and a pressure of 250 psig. A liquid 
hydrocarbon stream comprising an unstabilized naphtha containing dissolved 
hydrogen, C.sub.1 and C.sub.4 light hydrocarbons is withdrawn via line 9 
for passage to a stabilizing column. A hydrogen-containing vapor phase 
comprising in mol. % on a water-free basis 82.1% H.sub.2, 6.1% C.sub.1, 
5.2% C.sub.2 and 6.6% C.sub.3.sup.+ is withdrawn from the first 
vapor-liquid equilibrium separation zone 8 through line 10. 
A first portion of the hydrogen-containing vapor phase sufficient to 
provide a hydrogen to hydrocarbon mole ratio of about 7.0 is passed to 
compressor 12 via line 11 wherein it is compressed and recycled through 
line 2 for admixture with the naphtha boiling range charge stock. The 
remaining portion of hydrogen-containing vapor phase is sent for drying 
via line 13. 
In this instance the hydrogen-containing vapor phase is dried in mole sieve 
dryers 16 and 17; however, as noted previously, a glycol absorption system 
or other suitable dryer system could be employed in place of the mole 
sieve dryers. Here the flow of hydrogen-containing vapor phase is directed 
through dryer 16 and block valves 14a and 14b are opened. Dryer 17 is 
undergoing regeneration (the regeneration equipment and lines are not 
depicted for simplicity) and block valves 15a and 15b remain closed. 
The resulting dried hydrogen-containing vapor phase is passed through line 
18 to heat exchanger 19 wherein it is subjected to indirect heat exchange 
with a cool hydrogen-rich gas stream from line 33. As indicated 
previously, the amount of heat transferred in exchanger 19 is dependent on 
the heat transfer surface area. In this instance, exchanger 19 has a heat 
transfer surface area of about 1114 ft..sup.2 and as a result, the 
hydrogen-containing vapor phase is cooled to a temperature of about 
0.degree. F. 
After cooling, the hydrogen-containing vapor phase leaves heat exchanger 19 
via line 20 and is separated in second vapor-liquid equilibrium separation 
zone 21 into a liquid phase comprising C.sub.1.sup.+ hydrocarbons and a 
hydrogen-rich gas stream comprising on a mol. % basis about 85% H.sub.2, 
6.1% C.sub.1, 5.1% C.sub.2 and 3.8% C.sub.3.sup.+. The second vapor-liquid 
equilibrium separation zone is maintained at a pressure of about 245 psig 
and a temperature of about 0.degree. F. Although the hydrogen purity is 
improved from about 82% in the hydrogen-containing vapor phase to about 
85% in the hydrogen-rich gas stream, the amount of liquid recovered from 
the second vapor-liquid equilibrium separation zone may be significant. 
For example, in the present instance, a flow rate of 61,590.6 lbs/hr of 
hydrogen-containing vapor phase results in a recovery of about 15,089.3 
lbs/hr of liquid comprising C.sub.1.sup.+ hydrocarbons and trace amounts 
of dissolved hydrogen. Thus substantial amounts of valuable hydrocarbon 
products are recovered in addition to obtaining a gas stream of increased 
hydrogen purity. 
The liquid hydrocarbon stream is withdrawn from second vapor-liquid 
equilibrium separation zone 21 via line 22 and may be sent to the reformer 
stabilizer column or other suitable unit operation for further processing. 
The hydrogen-rich gas stream is removed from second vapor-liquid 
equilibrium separation zone 21 via line 23 through which it is passed to 
the inlet of turboexpander means 24. In this example the hydrogen-rich gas 
stream is to be passed to the refinery fuel system. The pressure of such a 
system is typically 50 psig. Accordingly the turboexpander 24 inlet 
temperature is about 0.degree. F. and the inlet pressure is about 245 
psig. The expander 24 outlet pressure is 55 psig and expander 24 is 
assumed to have an 85% isentropic efficiency. Accordingly then, the 
temperature of the hydrogen-rich gas stream at the expander outlet is 
-102.degree. F. The now cool hydrogen-rich gas stream is passed via line 
33 to heat exchanger 19 wherein it is subjected to the aforementioned 
indirect heat exchange with the hydrogen-containing vapor phase from line 
18. Upon. leaving heat exchanger 19, the hydrogen-rich gas stream is 
passed to the fuel system via line 34. 
As a result of expanding the hydrogen-rich gas stream in the turboexpander 
24, about 2600 Hp of shaft power is available via shaft 25 to electric 
generator 26. Electric power from generator 26 may in turn be passed via 
electrical lines 27 and 28 to compressor motor 29 where it is utilized to 
drive shaft 30 and compressor 12. Alternatively or if excess electric 
power is available, it may be passed via lines 27 and 31 to the refinery 
power grid 32 depicted herein as a box for use elsewhere or for sale to a 
local electric utility. 
As noted previously by increasing the heat transfer surface area in 
exchanger 19, more heat exchange may take place and, correspondingly, more 
hydrocarbon liquid may be recovered from vapor-liquid equilibrium 
separation zone 21. Thus if heat exchanger 19 has 3486 ft..sup.2 of heat 
transfer area, a 61,590.6 lbs/hr hydrogen-containing vapor phase may be 
cooled to a temperature of -50.degree. F. and 24,588.7 lbs/hr of liquid 
hydrocarbon may be recovered from vapor-liquid equilibrium separation zone 
21. The hydrogen-rich gas stream will have a hydrogen purity of about 87 
mol. % and a temperature at the expander 24 outlet of about -147.degree. 
F.; however, only about 1900 Hp of shaft power will be available from 
expander 24. The limiting case of course would be an infinite heat 
exchange surface in exchanger 19. As the heat transfer area approaches 
infinity, the temperature of the hydrogen-containing vapor phase from 
exchanger 19 approaches -100.degree. F. For a hydrogen-containing vapor 
phase rate of 61,590.6 lbs/hr, the amount of hydrocarbon liquid recovered 
from separator 21 approaches 33,349.1 lbs/hr and the hydrogen purity of 
the hydrogen-rich gas stream approaches 90 mol. %. However the shaft power 
extracted by expander 24 approaches 1100 Hp. 
Accordingly it can be seen from the above that extremely low temperatures 
may be achieved and in turn that hydrogen-rich gas streams of improved 
purity may be obtained along with the concomitant recovery of energy by 
means of the present invention.