Production of C.sub.5 + gasoline from butane and propane

A process is disclosed that provides a high conversion of n-butane to C.sub.5 + gasoline by integrating the medium pore metallosilicate catalyzed process for fresh n-butane conversion to C.sub.5 + gasoline with a medium pore metallosilicate catalyzed process for propane conversion in a manner which allows a portion of the propane by-product of n-butane conversion to be converted to C.sub.4 + alkanes, followed by recycle of the n-butane portion of the C.sub.4 + alkanes. It has been discovered that separation of the products from the separate propane and n-butane conversion steps can be carried out concurrently in a single fractionator to provide the C.sub.5 + gasoline product and the propane and butane recycle streams. Preferably, the fractionator butane cut is treated in a deisobutanizer to recover isobutane and n-butane recycle. A further discovery utilizes the common fractionator not only to separate the products from the conversion processes but to concurrently separate a mixed fresh C.sub.3 -C.sub.4 feedstream to the integrated process.

FIELD OF THE INVENTION 
This invention relates to a process for the production of gasoline from 
lower paraffins comprising butane and propane. The invention particularly 
relates to a continuous integrated process for the independent conversion 
of normal butane and propane to higher hydrocarbons that includes a means 
for utilizing a single fractionator to separate the conversion products as 
well as the mixed C.sub.3 /C.sub.4 paraffinic conversion feedstream. 
BACKGROUND OF THE INVENTION 
Modern petroleum refinery practices regularly result in the production of 
large quantities of lower alkanes, particularly propane and n-butane, as 
by-products of gasoline and distillate production. The supply of 
by-products so produced far exceeds their chemical or energy demand in the 
marketplace so, as a consequence, they are largely consumed as fuel within 
the refinery complex. It now appears that recent changes in clean air 
emission regulations will further compromise the commercial utilization of 
these lower alkanes to the extent that such regulations reduce permissible 
hydrocarbon emissions from gasoline and compel a lowering of gasoline 
butane content. Faced with a new surfeit of propane and n-butane in the 
refinery, the petroleum industry is challenged to develop ways to upgrade 
these hydrocarbons to higher value marketable products. 
Normal butane is a component found in substantial amounts in well-head 
condensates and straight run gasoline, and is formed in a fuels refinery 
employing catalytic reforming and/or cracking processes. Propane is also 
recovered from light petroleum fractions and as a by-product of reforming 
and/or cracking operations. Usually, propane and normal butane occur as a 
mixture produced from refinery operations. Normal butane can be isomerized 
to isobutane and the latter can be alkylated to provide a gasoline 
blending stock, but this is an expensive conversion. Propane can be 
hydrogenated to propene and used as a chemical feedstock. However, neither 
normal butane nor propane are employed in high value applications 
commensurate with their availability. 
In recent years, a major development within the petroleum industry has been 
the discovery of the special catalytic capabilities of a family of zeolite 
catalysts based upon medium pore size shape selective metallosilicates. 
Discoveries have been made leading to a series of analogous processes 
drawn from the catalytic capability of zeolites. Depending upon various 
conditions of space velocity, temperature and pressure lower oxygenates, 
alkenes and alkanes can be converted in the presence of zeolite type 
catalyst to higher hydrocarbons including higher olefins, gasoline or 
distillate, or converted further to produce aromatics. The light aliphatic 
hydrocarbon conversion process to form aromatics may utilize conversion 
conditions described in U.S. Pat. Nos. 3,760,024 (Cattanach); 3,845,150 
(Yan and Zahner); 4,097,367 (Haag et al.); 4,350,835 (Chester et al.); 
4,590,323 (Chu); and 4,629,818 (Burress) incorporated herein by reference. 
The feedstream consists essentially of C.sub.2 -C.sub.4 paraffins and/or 
olefins. 
U.S. Pat. No. 4,686,316 to Morrison, incorporated herein by reference, 
discloses a process for the production of butanes from propane by 
contacting with ZSM-5 zeolite catalyst at moderately high reaction 
operating pressure in the absence of added hydrogen. A mixture of normal 
butane and isobutane is produced with high selectivity. 
The foregoing processes individually illustrate that, depending on process 
conditions employing medium pore shape selective metallosilicate catalyst, 
light paraffins can be upgraded to aromatics, propane can be selectively 
upgraded to butanes. 
Accordingly, it is an object of the present invention to improve the 
utilization of propane and butanes in the refinery complex by providing an 
integrated process for the conversion of propane and normal butane to 
C.sub.5 + gasoline. 
A further object of the invention is to provide a high octane aromatics 
and/or C.sub.5 -C.sub.6 paraffins rich gasoline from the integrated 
conversion of propane and normal butane. 
Another object of the invention is to provide the foregoing integrated 
process wherein a single fractionator is used to separate a feedstream 
containing propane and butanes as well as the products from the individual 
conversion steps. 
SUMMARY OF THE INVENTION 
It has been discovered that a high conversion of n-butane to C.sub.5 + 
gasoline can be realized by integrating the medium pore metallosilicate 
catalyzed process for n-butane conversion to C.sub.5 + gasoline with a 
medium pore metallosilicate catalyzed process for propane conversion in a 
manner which allows a portion of the propane by-product of n-butane 
conversion to be converted to C.sub.4 + alkanes, followed by recycle of 
the n-butane and/or isobutane portion of the C.sub.4 + alkanes. 
Advantageously, it has been discovered that separation of the products 
from the separate propane and n-butane conversion steps can be carried out 
concurrently in a single fractionator to provide the C.sub.5 + gasoline 
product and the propane and butane recycle streams. Preferably, the 
fractionator butane cut is treated in a deisobutanizer to recover 
isobutane as a product stream and n-butane as recycle. A further discovery 
utilizes the common fractionator not only to separate the products from 
the conversion processes but to concurrently separate a mixed C.sub.3 
-C.sub.4 feedstream to the integrated process. 
More particularly, the invention comprises a continuous integrated process 
for the conversion of n-butane to C.sub.5 + gasoline, containing the steps 
of: contacting a fresh feedstream comprising normal butane with shape 
selective medium pore zeolite catalyst particles under conditions 
sufficient to convert n-butane to an effluent stream comprising C.sub.3 + 
alkanes; separating the effluent stream in a fractionator to recover an 
overhead stream comprising propane; contacting the propane stream and/or a 
fresh propane feedstream with shape selective, medium pore zeolite 
catalyst particles under conversion conditions sufficient to convert 
propane to a mixture comprising C.sub.2 + alkanes; deethanizing the 
mixture and passing the deethanized product comprising C.sub.3+ alkanes to 
the fractionator for separation concurrent with the effluent stream; 
recovering a bottom stream comprising C.sub.5 + gasoline from the 
fractionator; preferably, distilling an intermediate stream comprising 
C.sub.4 alkanes from the fractionator and recovering a stream comprising 
isobutane and a stream comprising unconverted normal butane; recycling the 
unconverted normal butane to the normal butane feedstream to the 
integrated process. 
In another embodiment of the integrated process the fresh n-butane 
feedsteam can be eliminated and a C.sub.3 -C.sub.4 feedstream passed to 
the fractionator for separation and integration with the aforementioned 
propane and butane cuts from the fractionator which are passed to the 
respective propane and n-butane conversion zones.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention comprises an integrated continuous process for the 
production of C.sub.5 + gasoline from propane and normal butane by 
separating a fresh C.sub.3 -C.sub.4 paraffinic hydrocarbon feedstream in a 
fractionator and recovering a stream comprising propane and another stream 
rich in normal butane. The propane stream is contacted with shape 
selective, medium pore zeolite catalyst particles in a propane conversion 
zone under propane conversion conditions whereby an effluent stream is 
produced rich in C.sub.4 + paraffinic hydrocarbons. The normal butane 
stream is contacted with shape selective, medium pore zeolite catalyst 
particles in a normal butane conversion zone under normal butane 
conversion conditions whereby an effluent stream is produced rich in 
C.sub.3 + paraffinic hydrocarbons. The streams from the two reaction zones 
are separated in a fractionator in conjunction with the C.sub.3 -C.sub.4 
feedstream whereby a bottom stream is recovered from said fractionator 
comprising C.sub.5 + gasoline. 
The process of the instant invention utilizes a high severity reaction 
section to convert propane to alkanes comprising C.sub.2 and C.sub.4 +, or 
C.sub.2 +, hydrocarbons in contact with zeolite catalyst, and a lower 
severity reaction section to convert normal butane to alkanes comprising 
propane and C.sub.4 + hydrocarbons in contact with zeolite catalyst. A 
single fractionator is used to fractionate a C.sub.3 -C.sub.4 feedstream 
to the process and fractionate the products of the conversion reactions. 
The fractionator bottom stream contains the gasoline product. The top 
fractionator overhead product and a side stripper bottoms stream provide a 
C.sub.3 rich feed stream and a C.sub.4 rich feed stream, respectively. The 
feedstream to the process may also comprise fresh n-butane fed directly to 
the butane upgrader. Optionally, light aromatics such as benzene and/or 
olefins rich streams may be added to either conversion zone containing 
zeolite catalyst to improve product octane and/or yield. 
The propane upgrader operates at least 50.degree. F. and preferably at 
least 150.degree. F. (28.degree. to 84.degree. C.) higher temperature than 
the butane upgrader, assuming the same catalyst activity and weight hourly 
space velocity (WHSV). In addition, if olefins or aromatics are added to 
the propane upgrader the propane upgrading reaction becomes highly 
exothermic. Therefore, the heat content of the propane upgrader effluent 
can be used to supply a portion of the butane upgrading feed preheat. This 
can eliminate the need for a fired furnace which may be environmentally 
undesirable in the process. 
As previously noted, propane upgrading is described in U.S. Pat. No. 
4,686,316. Propane is effectively converted with unexpectedly high 
selectivity to a mixture of normal butane, isobutane and C.sub.5 + 
gasoline by contact with certain intermediate pore size zeolites, as more 
fully described hereinbelow. In particular, the process for the production 
of butanes and C.sub.5 + gasoline from propane, which process comprises 
contacting in the absence of added hydrogen and at a pressure of at least 
about 50 psig a feed consisting essentially of propane with a catalyst 
comprising a crystalline zeolite having a silica-to-alumina ratio of at 
least 12 and a Constraint Index of 1 to 12, said contacting being 
conducted under a combination of conditions of temperature, pressure, and 
WHSV effective to convert said propane to a mixture of hydrocarbons that 
contain butanes in an amount equal to at least 35 wt % of said converted 
propane. The total effluent from the catalytic reactor will also contain 
unreacted propane. Separation can provide a hydrocarbon fraction that may 
contain as much as 80+ wt. % of mixed butanes from which an isobutane 
fraction may be obtained that is useful for conversion to alkylate 
blending stock for gasoline. 
In general, the effective combinations of process conditions for propane 
upgrading will have individual parameters falling within the ranges shown 
below: 
______________________________________ 
Broad Preferred 
______________________________________ 
Temperature, 500-900.degree. F. 
600-800.degree. F. 
Pressure, psig 50-1500 400-1000 
WHSV 0.1 to 10 0.2 to 2.0 
______________________________________ 
The catalysts useful in the process for the conversion of propane as 
described herein comprise shape selective metallosilicate catalyst having 
a Constraint Index (C. I.) between about 1 and 12. It is preferred to use 
a zeolite selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, 
ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-48, ZSM-50, MCM-22 and zeolite Beta as 
the zeolite component of the catalyst used in the process of this 
invention. ZSM-5 is the particularly preferred zeolite. 
ZSM-5 is more particularly described in U.S. Pat. No. Re. 28,341 (of 
original U.S. Pat. No. 3,702,886), the entire contents of which are 
incorporated herein by reference. 
ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, the 
entire contents of which are incorporated herein by reference. 
Zeolite ZSM-12 is described in U.S. Pat. No. 3,832,449, to which reference 
is made for the details of this catalyst. 
ZSM-22 is more particularly described in U.S. Pat. No. 4,046,859, the 
entire contents of which is incorporated herein by reference. 
ZSM-23 is more particularly described in U.S. Pat. No. 4,076,842, the 
entire contents of which are incorporated herein by reference. 
ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, the 
entire contents of which are incorporated herein by reference. 
ZSM-48 is more particularly described in U.S. Pat. No. 4,397,827, the 
entire contents of which are incorporated herein by reference. 
Zeolite ZSM-50 is described in U.S. Pat. No. 4,640,829, to which reference 
is made for details of this catalyst. 
MCM-22 is more particularly described in U.S. Pat. No. 4,954,325, the 
entire contents of which are incorporated herein by reference. 
Zeolite Beta is described in U.S. Pat. No. Re. 28,341 (of original U.S. 
Pat. No. 3,308,069), to which reference is made for details of this 
catalyst. 
It is particularly effective to include a hydrogenation-dehydrogenation 
metal in the zeolite catalyst composition employed in the propane 
upgrading process. Phosphorous-containing zeolites such as ZSM-5 
containing phosphorous can also be effective. Although the process can be 
practiced in the absence of an hydrogenation-dehydrogenation component, in 
some instances the presence of such component induces an increase in 
activity and/or selectivity. Platinum or palladium metal acts in such 
fashion. Other metals which can facilitate hydrogenation-dehydrogenation 
or olefin disproportionation, such as the Fe or Pt metals of Group VIII of 
the Periodic Table, metals of Group IIb, titanium, vanadium, chromium, 
molybdenum, tungsten, rhenium and gallium, may be useful. (Chem. Rubber 
Handbook, 45th Ed., back cover). 
Normal butane is converted directly to propane and high octane gasoline 
with no substantial formation of hydrocarbons having less than three 
carbon atoms by contact with intermediate pore size zeolites such as 
HZSM-5 under specified conversion conditions including a relatively low 
temperature of not more than 800.degree. F. (426.degree. C.) and a 
pressure of at least 400 psig (2800 kPa). The butane upgrading process 
provides a simple catalytic process for the production of propane and high 
octane gasoline, which process comprises contacting in the absence of 
added hydrogen at a temperature of 475.degree. F. (246.degree. C.) to 
about 800.degree. F. (426.degree. C.) and at a pressure of 600 to about 
2000 psig (4200-14,000 kPa) a feed consisting essentially of n-butane with 
a catalyst comprising a crystalline zeolite having a silica-to-alumina 
ratio of at least 12 and a Constraint Index of 1 to 12, said contacting 
being conducted under a combination of conditions of temperature, 
pressure, and WHSV effective to convert about 45 wt % to about 90 wt % of 
said n-butane to a mixture of propane and heavier hydrocarbons, with no 
substantial conversion to hydrocarbon by-products having less than three 
carbon atoms. Propane and high octane gasoline are readily recovered from 
the reaction mixture. The total effluent from the catalytic reactor will 
contain unreacted normal butane and a small amount of isobutane. The 
isobutane preferably is separated and diverted to an alkylation unit. 
The n-butane catalytic conversion is effected under a combination of 
conditions of temperature, pressure, and weight hourly space velocity 
(WHSV) effective to convert in a single pass up to about 90 wt % of the 
butane feed to a C.sub.3 plus mixture of hydrocarbons without substantial 
formation of hydrocarbon by-product having less than three carbon atoms. 
In general, increase of temperature, or of pressure, or decrease of space 
velocity all serve to increase conversion, so that many combinations of 
these parameters will produce conversion and selectivity within the 
desired range. In general, the effective process conditions will have 
individual parameters falling within the ranges shown below: 
______________________________________ 
Broad Preferred 
______________________________________ 
Temperature, 475-800.degree. F. 
550-750.degree. F. 
Pressure, psig 400-2000 600-1500 
WHSV 0.1-50 0.1-10 
______________________________________ 
Within the described constraints, high single pass conversions with useful 
yields of propane and C.sub.5 plus gasoline are achieved without 
encountering rapid aging. 
The catalysts useful in the process for the conversion of normal butane as 
described herein comprise shape selective metallosilicate catalyst having 
a Constraint Index (C. I.) between about 1 and 12. It is preferred to use 
a zeolite selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, 
ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-48, ZSM-50, MCM-22 and zeolite Beta as 
the zeolite component of the catalyst used in the process of this 
invention. ZSM-5 is the particularly preferred zeolite. 
The zeolite catalyst is converted to the hydrogen form prior to use in the 
process of this invention. The catalyst, after extended use in the process 
of this invention, will require regeneration to restore activity. This may 
be effected with hydrogen gas at elevated temperature, or by burning in 
air, or by combinations thereof. 
A convenient measure of the extent to which a zeolite provides controlled 
access to molecules of varying sizes to its internal structure is the 
aforementioned Constraint Index of the zeolite. A zeolite which provides 
relatively restricted access to, and egress from, its internal structure 
is characterized by a relatively high value for the Constrain Index, i.e., 
above about 2. On the other hand, zeolites which provide relatively free 
access to the internal zeolitic structure have a relatively low value for 
the Constraint Index, i.e., about 2 or less. The method by which 
Constraint Index is determined is described fully in U.S. Pat. No. 
4,016,218, to which reference is made for details of the method. 
Constraint Index (CI) values for some zeolites which can be used in the 
process of this invention are: 
______________________________________ 
Constraint Index 
Zeolite (At Test Temperature, .degree.C.) 
______________________________________ 
ZSM-5 6-8.3 (371-316) 
ZSM-11 5-8.7 (371-316) 
ZSM-12 2.3 (316) 
ZSM-35 4.5 (454) 
ZSM-48 3.5 (538) 
ZSM-50 2.1 (427) 
Zeolite Beta 
0.6-2.0 (316-399) 
______________________________________ 
The above-described Constraint Index is an important and even critical 
definition of those zeolites which are useful in the instant invention. 
The very nature of this parameter and the recited technique by which it is 
determined, however, admit of the possibility that a given zeolite can be 
tested under somewhat different conditions and thereby exhibit different 
Constraint Indices. Constraint Index seems to vary somewhat with severity 
of operation (conversion) and the presence or absence of binders. 
Likewise, other variables, such as crystal size of the zeolite, the 
presence of occluded contaminants, etc., can affect the Constraint Index. 
Therefore, it will be appreciated that it may be possible to so select 
test conditions, e.g., temperatures, as to establish more than one value 
for the Constraint Index of a particular zeolite. This explains the range 
of Constraint Indices for zeolite Beta. 
Referring to FIG. 1, one embodiment of the instant invention is illustrated 
in a process schematic. A C.sub.4 feedstream 101 is passed to a reactor 
zone 110 containing medium pore shape selective metallosilicate catalyst. 
Optionally, if the feedstream 101 contains isobutane a separation step to 
recover isobutane can be carried out in deisobutanizer 150. Under 
relatively low severity reaction conditions as previously described herein 
normal butane is converted 110 to alkanes consisting of propane and higher 
hydrocarbons. The effluent 102 from the conversion zone 110 also contains 
unconverted normal butane and a small amount of C.sub.2 - hydrocarbons in 
addition to propane and C.sub.5 + alkanes. The effluent 102 is passed to 
fractionator 120 for separation into an overhead stream 104 comprising 
propane, a bottom stream 106 comprising C.sub.5 + gasoline and an 
intermediate fractionator cut 108 comprising C.sub.4 hydrocarbons 
including isobutane. The propane 104 stream is introduced into reactor 
zone 130 containing medium pore shape selective metallosilicate catalyst 
particles under high severity reaction conditions previously described 
herein. In the conversion zone 130 propane is converted to C.sub.2 + 
alkanes. The effluent 112 from conversion zone 130 contains unconverted 
propane as well as ethane rich light gases and C.sub.4 + paraffinic 
hydrocarbons. The effluent 112 is passed to a separator comprising 
deethanizer 140 wherein a stream 114 comprising C.sub.2 - hydrocarbons is 
removed overhead. From the deethanizer unconverted propane and C.sub.4 + 
hydrocarbons are passed 116 and 118 to fractionator 120 for separation of 
the components into propane C.sub.5 + gasoline and C.sub.4 hydrocarbons. 
Preferably, C.sub.4 hydrocarbons in stream 108 from the fractionator 120 
are further separated by fractionation in a deisobutanizer 150 to recover 
isobutane stream 122 which may be utilized for alkylation or 
dehydrogenated to produce isobutene. Stream 124 consists primarily of 
normal butane which is recycled 126 to the normal butane feedstream 101. 
Optionally, stream 126 is recycled through heat exchanger 135 to recover 
some of the heat from stream 116 from the high severity zone 130. This 
recovered heat is effective in preheating fresh normal butane feedstream 
101; thereby reducing furnace requirements to preheat the total feed to 
reaction zone 110. Also, a fresh propane, olefinic, and/or aromatics 
stream can be introduced in the process through feedstream 128 to enhance 
the process yield and/or the octane value of the C.sub.5 gasoline 
recovered in stream 106. 
The fractionator 120 may also be designed as two towers: one for 
debutanizing and one for depropanizing the debutanizer overhead; or a 
depropanizer followed by a debutanizer. 
Referring now to FIG. 2, another embodiment of the instant invention is 
illustrated in a process schematic. This embodiment differs fundamentally 
from the embodiment described in FIG. 1 in that it illustrates a means for 
utilizing the main fractionator 220 of the process for separation of a 
fresh paraffinic feedstream 201 comprising C.sub.3 -C.sub.4 hydrocarbons 
as well as or concurrent with the separation of products from the 
individual propane 230 and normal butane 210 conversion zones. FIG. 2 also 
illustrates the use of stripper 260 wherein the C.sub.4 rich intermediate 
stream from fractionator 220 is separated to recycle 232 C.sub.3 alkanes 
to the fractionator 220 while passing 234 C.sub.4 's to deisobutanizer 
250. With these distinctions presented, the process illustrated in FIG. 2 
is analogous to that described in FIG. 1. Propane from fractionator 220 is 
passed 204 as an overhead stream to the high severity conversion zone 230 
containing the previously described zeolite catalyst. The C.sub.2 + 
effluent 212 from 230 is separated in deethanizer 240 to produce a C.sub.2 
- overhead stream 214 and a stream 216 comprising C.sub.4 + hydrocarbons 
and unconverted propane which is passed to fractionator 220 for 
separation. Normal butanes are recovered from the fractionator by 
separation of intermediate fractionator cut 208 in stripper 260 from which 
propane overhead is recycled to the fractionator as described above. The 
C.sub.4 stream 234 is preferably deisobutanized 250 to provide the 
isobutane stream 222 and the normal butane stream 224. Isobutane may be 
utilized in alkylation or dehydrogenated to provide isobutene. Heat 
exchanger 235 can optionally be employed to recover heat from the 
deethanizer effluent 216 and preheat the normal butane feedstream to the 
normal butane conversion zone 210. In the 210 conversion zone normal 
butane is converted to C.sub.3 + paraffinic hydrocarbons. The effluent 202 
from 210 is separated in the main process fractionator 220 concurrently 
with separation of the fresh C.sub.3 -C.sub.4 feedstream 201. C.sub.5 + 
gasoline is recovered as a bottom stream 206 from the fractionator 220. As 
with the embodiment described in FIG. 1, a fresh propane, olefinic, and/or 
aromatics stream can be introduced in the process through feedstream 228 
to enhance the process yield and/or the octane value of the C.sub.5 
gasoline recovered 206. 
The fractionator 220 may also be designed as two towers: one for 
debutanizing and one for depropanizing the debutanizer overhead; or a 
depropanizer followed by a debutanizer. 
Although the present invention has been described with preferred 
embodiments, it is to be understood that modifications and variations may 
be resorted to, without departing from the spirit and scope of this 
invention, as those skilled in the art will readily understand. Such 
modifications and variations are considered to be within the purview and 
scope of the appended claims.