Conversion of LPG hydrocarbons to distillate fuels or lubes using integration of LPG dehydrogenation and MOGDL

Disclosed is a method and apparatus for producing distillate and/or lubes which employ integrating catalytic (or thermal) dehydrogenation of paraffins with MOGDL. The process feeds the product from a low temperature propane and/or butane dehydrogenation zone into a first catalytic reactor zone, which operates at low pressure and contains zeolite oligomerization catalysts, where the low molecular weight olefins are reacted to primarily gasoline range materials. These gasoline range materials can then be pressurized to the pressure required for reacting to distillate in a second catalytic reactor zone operating at high pressure and containing a zeolite oligomerization catalyst. The distillate is subsequently sent to a hydrotreating unit and product separation zone to form lubes and other finished products.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and apparatus for converting paraffins 
to lubes and other higher hydrocarbons, such as gasoline range or 
distillate range fuels. In particular, it relates to methods and apparatus 
which combine the operation of catalytic (or thermal) dehydrogenation of a 
paraffinic feedstock to produce olefins and the operation of a two-stage 
catalytic reactor system to convert olefins to gasoline and distillate 
boiling range materials, and downstream units to recover lubes from the 
distillate. 
2. Discussion of the Prior Art 
It has been established that the conversion of paraffins, such as propane 
and butane, to mono-olefins, such as propylene and butylene, can be 
accomplished by thermal or catalytic dehydrogenation. A general discussion 
of thermal dehydrogenation (i.e., steam cracking) is presented in 
Encyclopedia of Chemical Technology, Ed. by Kirk and Othmer, Vol. 19, 
1982, Third Ed., pp. 232-235. Various processes for catalytic 
dehydrogenation are available in the prior art. These processes include 
the Houdry Catofin process of Air Products and Chemicals, Inc., Allentown, 
Pa., the Oleflex process of UOP, Inc., Des Moines, Ill. and a process 
disclosed by U.S. Pat. No. 4,191,846 to Farha, Jr. et al. The Houdry 
Catofin process, described in a magazine article, "Dehydrogenation Links 
LPG to More Octanes", Gussow et al, Oil and Gas Journal, Dec. 8, 1980, 
involves a fixed bed, multi-reactor catalytic process for conversion of 
paraffins to olefins. Typically, the process runs at low pressures of 5-30 
inches of mercury absolute, and high temperatures with hot reactor 
effluent at 550.degree.-650.degree. C. Dehydrogenation is an endothermic 
reaction, so it normally requires a furnace to provide heat to a feed 
stream prior to feeding the feed stream into the reactors. The UOP Oleflex 
process, disclosed in an article "C.sub.2 /C.sub.5 Dehydrogenation Updated 
", Verrow et al, Hydrocarbon Processing, April 1982, used stacked 
catalytic reactors. U.S. Pat. No. 4,191,846 to Farha, Jr. et al teaches 
the use of group VIII metal containing catalysts to promote catalytic 
dehydrogenation of paraffins to olefins. 
Recent developments in zeolite catalysts and hydrocarbon conversion methods 
and apparatus have created interest in utilizing olefinic feedstocks for 
producing heavier hydrocarbons, such as C.sub.5.sup.+ gasoline, distillate 
or lubes. These developments have contributed to the development of the 
Mobil olefins to gasoline/distillate (MOGD) method and apparatus, and the 
development of the Mobil olefins to gasoline/distillate/lubes (MOGDL) 
method and apparatus. 
In MOGD and MOGDL, olefins are catalytically converted to heavier 
hydrocarbons by catalytic oligomerization using an acid crystalline 
zeolite, such as a ZSM-5 type catalyst. Process conditions can be varied 
to favor the formation of either gasoline or distillate range products. In 
U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens 
disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in combination 
with paraffinic components, into higher hydrocarbons over a crystalline 
zeolite catalyst. Garwood et al have contributed improved processing 
techniques to the MOGD system, in U.S. Pat. Nos. 4,150,062; 4,211,640; and 
4,227,992. Marsh et al, in U.S. Pat. No. 4,456,781, have also disclosed 
improved processing techniques for the MOGD system. U.S. Pat. No. 
4,433,185 to Tabak teaches conversion of olefins in a two-stage system 
over a ZSM-5 or ZSM-11 zeolite catalyst to form gasoline or distillate. 
Olefinic feedstocks may be obtained from various sources, including from 
fossil fuel processing streams, such as gas separation units, from the 
cracking of C.sub.2.sup.+ hydrocarbons, such as LPG (liquified petroleum 
gas), from coal by-products and from various synthetic fuel processing 
streams. U.S. Pat. No. 4,100,218 (Chen et al) teaches thermal cracking of 
ethane to ethylene, with subsequent conversion of ethylene to LPG and 
gasoline over a ZSM-5 type zeolite catalyst. 
The conversion of olefins in a MOGDL system may occur in a gasoline mode 
and/or a distillate/lube mode. In the gasoline mode, the olefins are 
catalytically oligomerized at temperature ranging from 
400.degree.-800.degree. F. and pressure ranging from 10-1000 psia. To 
avoid excessive temperatures in th exothermic reactor, the olefinic feed 
may be diluted. In the gasoline mode, the diluent may comprise light 
hydrocarbons, such as C.sub.3 -C.sub.4, from the feedstock and/or recycled 
from debutanized product. In the distillate/lube mode, olefins are 
catalytically oligomerized to distillate at temperature ranging from 
350.degree.-600.degree. F. and pressure ranging from 100-3000 psig. The 
distillate is then upgraded by hydrotreating and separating the 
hydrotreated distillate to recover lubes. 
Although distillate and lubes can be produced from propane and butane by 
the prior art, using dehydrogenation integrated with MOGDL, there are 
several problems with integrating these processes. For example, U.S. Pat. 
No. 4,413,153 (Garwood et al) discloses a system which catalytically (or 
thermally) dehydrogenates the paraffins to olefins, and then reacts the 
olefins by catalytic oligomerization (MOGDL), in a distillate/lube mode, 
to distillate range material which can be upgraded to lubes. Catalytic 
oligomerization in the distillate/lubes mode is a high (100-3000 psig) 
pressure process, whereas dehydrogenation is favored by low (less than 25 
psig) pressure. Also, the dehydrogenation zone effluent is in vapor form. 
As a consequence a compressor is required for pressurizing the effluent to 
feed a catalytic oligomerization reactor zone operating the the distillate 
lube mode, thus resulting in expensive compression costs. Moreover, 
conversion of paraffins to olefins in dehydrogenation is slow, so 
dehydrogenation produces a dilute (20-50%) olefinic stream which requires 
expensive gas plant separation to recycle the paraffins back to a 
dehydrogenation reactor. The olefins should also be separated from 
paraffins prior to compressing and feeding the olefins to a higher 
pressure catalytic oligomerization reactor zone because only olefins 
oligomerize to form heavier hydrocarbons. Sending combined olefins and 
paraffins to the oligomerization reactor zone would increase compression 
costs and require larger reactors. Also, it is preferable to separate 
paraffins from olefins to factilitate recycle of paraffins to the 
dehydrogenation zone where they can be converted to olefins. However, a 
gas plant is required to separate paraffins from olefins because the 
dehydrogenation effluent stream comprises C.sub.4.sup.- olefins and 
C.sub.4.sup.- paraffins which are difficult to separate from one another. 
It would be desirable to provide a method and apparatus for producing lubes 
from paraffins, such as propane and/or butane, which minimizes the 
problems of compression and gas plant costs and these are the problems to 
which the present invention is directed. 
SUMMARY OF THE INVENTION 
The invention minimizes the above-noted problems by adding a first lower 
pressure catalytic oligomerization reactor zone between the 
above-mentioned second higher pressure catalytic oligomerization reactor 
zone and the dehydrogenation zone. The lower pressure catalytic 
oligomerization reactor zone operates at 10-1000 psia. Its pressure should 
be lower than the higher pressure catalytic oligomerization reactor zone, 
but the actual pressure of each catalytic oligomerization reactor zone 
depends on a combination of operating conditions, namely, which of a 
number of commercially available catalysts is in each oligomerization 
reactor zone and the temperature, space velocity and composition of feed 
to each oligomerization reactor zone. 
The lower pressure catalytic oligomerization reactor zone reduces 
compression costs by converting olefins to olefinic gasoline (330.degree. 
F..sup.- bp) which can be pumped to the higher pressure oligermization 
reactor as a liquid. Therefore the compressor normally required to 
pressurize feed to the higher pressure oligomerization reactor zone is 
eliminated and replaced with a lower duty compressor, and a pump to 
pressurize feed to the higher pressure oligomerization reactor zone. 
The invention also reduces gas plant costs associated with producing lubes 
from C.sub.4.sup.- paraffins because the lower pressure catalytic 
oligomerization reactor zone converts 85-95% of the C.sub.4.sup.- olefins 
to olefinic gasoline, which is relatively easy to separate from 
C.sub.4.sup.- paraffins prior to feeding to the higher pressure catalytic 
oligomerization reactor zone. 
Accordingly, it is a primary object of this invention to provide an 
improved method and apparatus for converting paraffins to lubes which 
employs integrating dehydrogenation of propane/butane to produce olefins 
with a two zone oligomerization of olefins to produce heavier 
hydrocarbons. 
It is another object of this invention to provide an improved method and 
apparatus for converting propane/butane to lubes which employs integrating 
dehydrogenation of propane/butane to produce olefins with a low pressure 
oligomerization of olefins and higher pressure oligomerization of olefins 
to produce heavier hydrocarbons which can be upgraded to lubes. 
It is another object of this invention to provide a method and apparatus 
for converting propane/butane to lubes and facilitating recycle of 
paraffins to a dehydrogenation zone. 
It is another object of this invention to provide a method and apparatus 
for converting propane/butane to lubes with reduced gas plant costs. 
It is another object of this invention to provide a method and apparatus 
for integrating dehydrogenation of propane/butane to produce olefins with 
oligomerization of olefins to produce heavier hydrocarbons, which reduces 
the need for compressing olefins from the dehydrogenation plant prior to 
oligomerization. 
In its method aspects, the invention achieves the foregoing objects by a 
method for producing heavier hydrocarbons of gasoline or distillate 
boiling range, which comprises the steps of passing a paraffinic feed 
stream comprising C.sub.3 /C.sub.4, such as LPG, into a dehydrogenation 
zone at conditions of pressure at about 0.1-2 atms. and temperature at 
about 1000.degree.-1700.degree. F., which favor conversion of the 
paraffinic feed stream to an olefin rich effluent stream comprising 
propylene or butylene, depending on whether the feed stream is propane 
rich or butane rich; contacting the olefin rich effluent stream with a 
crystalline zeolite oligomerization catalyst in a first catalytic reactor 
zone at conditions of pressure at about 10-1000 psia and temperature at 
about 400.degree.-800.degree. F., which favor conversion of olefins to a 
first reactor effluent stream rich in olefinic gasoline range 
hydrocarbons; separating the first reactor effluent stream in a first 
separation zone to form a C.sub.4.sup.- rich stream and a C.sub.5.sup.+ 
rich stream; passing the C.sub.5.sup.+ rich stream to a second catalytic 
reactor zone, where it contacts a crystalline zeolite oligomerization 
catalyst at relatively higher pressure than the first catalytic reactor 
zone ranging from 100-3000 psig and temperature ranging from 
350.degree.-600.degree. F. under conditions favorable for production of a 
second reactor effluent stream rich in distillate; passing the second 
reactor effluent stream into a second separation zone, where it is 
separated into an olefinic gasoline stream and a distillate stream; and 
hydrotreating the distillate stream. The hydrotreated distillate stream 
may be separated in a product separation zone into products comprising 
lubes. 
In its apparatus respects, the invention comprises: means for feeding a 
paraffinic feed stream comprising C.sub.3 /C.sub.4, such as LPG, at 
conditions of 0.1-2 atm pressure and 1000.degree.-1700.degree. F. 
temperature to a dehydrogenation zone which favor conversion of the 
paraffinic feed stream to an olefin rich effluent stream; means for 
passing the paraffinic feed stream to a first catalytic reactor zone, 
where it contacts with a crystalline zeolite oligomerization catalyst at 
conditions of 10-1000 psia pressure and 400.degree.-800.degree. F. 
temperature to convert a major portion of olefins to olefinic gasoline 
range hydrocarbons which form a first reactor effluent stream; means for 
separating the first reactor effluent stream in a first separation zone to 
form a C.sub.4.sup.- rich stream and a C.sub.5.sup.+ rich stream; means 
for passing the C.sub.5.sup.+ rich stream to the second catalytic reactor 
zone, where the C.sub.5.sup.+ rich stream contacts with a crystalline 
zeolite oligomerization catalyst at high pressure and high temperature to 
convert a major portion of the C.sub.5.sup.+ rich stream to distillate 
which leaves as a second reactor effluent stream; means for separating the 
second reactor effluent stream into an olefinic gasoline stream, and a 
distillate stream; and a hydrotreating unit for hydrotreating the 
distillate stream. The apparatus may further comprise a product separation 
zone which comprises a means for separating the hydrotreated product into 
products comprising lubes.

DETAILED DESCRIPTION OF THE INVENTION 
The novel method and apparatus of this invention employs feeding the 
product from a low pressure dehydrogenation of low molecular weight 
paraffins, such as propane and/or butane present in LPG, into a low 
pressure catalytic oligomerization reactor, where the olefins produced by 
dehydrogenation are reacted primarily to gasoline range materials, which 
can then be pumped up to the pressure required for reacting to distillate 
in a higher pressure catalytic oligomerization reactor. The distillate is 
then hydrotreated and separated to recover lubes, and lighter products, 
such as diesel fuel or jet fuel. 
In FIG. 1, the overall method and apparatus of the invention are shown in 
diagram form. Means 10 are provided for feeding a first paraffinic feed 
stream 2, comprising C.sub.3 /C.sub.4 hydrocarbons, such as LPG, into a 
low pressure (preferred values are discussed below) dehydrogenation zone 
20. Stream 2 is actually combined with a recycle C.sub.4.sup.- rich stream 
12 to form a second paraffinic feed stream 14 which passes to the 
dehydrogenation zone 20, which operates at low pressure and high 
temperature (preferred values are discussed below) to convert the second 
paraffinic feed stream 13 to an olefin rich effluent stream 24. The 
dehydrogenation zone 20 may be a catalytic dehydrogenation zone. A thermal 
dehydrogenation zone can also be used. Stream 24 passes into a first 
catalytic reactor zone 30, which operates at low pressure and high 
temperature (preferred values are discussed below) to convert the C.sub.3 
/C.sub.4 olefins to olefinic gasoline which exits as a first reactor 
effluent stream 34. Effluent Stream 34 enters a first separation zone 40, 
which forms a C.sub.4.sup.- rich stream 42 and a C.sub.5.sup.+ rich 
stream 50 containing olefinic gasoline. A portion of the C.sub.4.sup.- 
rich stream 42 forms a recycle C.sub.4.sup.- rich stream 12 and is 
recycled to the catalytic dehydrogenation zone 20. An unrecycled portion 
44 of the C.sub.4.sup.- rich stream 42 is sent to a gas plant for 
separation into its components, such as H.sub.2 and fuel gas. The 
C.sub.5.sup.+ rich stream 50 is compressed and pumped to a second 
catalytic reactor zone 60, where typically greater than 90% of the 
olefinic gasoline is converted to distillate. 
Because the second catalytic reactor zone 60 receives a liquid 
C.sub.5.sup.+ rich stream 50, which may be easily compressed to a required 
pressure of the second reactor (preferably 800-2000 psig), compression 
costs are reduced in comparison with prior MOGD techniques, such as 
disclosed in U.S. Pat. No. 4,413,153 (Garwood et al), wherein a C.sub.3 
/C.sub.4 feed is employed. The distillate and unconverted olefins pass 
from the second catalytic reactor zone 60 as a second reactor effluent 
stream 62 into a second separation zone 70. The second separation zone 70 
separates the second reactor effluent stream 62 into a distillate stream 
64 and an olefinic gasoline stream 72. Portions of streams 50,72 may be 
recycled (not shown) to dilute the feed to the first and second catalytic 
reactor zones 30,60, respectively to aid in reactor temperatures control 
due to the exothermic nature of the oligomerization reactions in both 
catalytic reactor zones. The distillate stream 64 is fed to a 
hydrotreating unit 80 and contacted with H.sub.2 from H.sub.2 stream 82 
and the hydrotreated distillate stream 85 feeds a product separation zone 
90 to recover a lube stream 95, and other products, such as jet fuel and 
diesel fuel. The lube stream 95 contains 650.degree. F.+ boiling range 
material. 
As noted, this process reduces gas plant and compression costs for an 
integrated dehydrogenation/oligomerization method and apparatus by 
converting a major portion of the C.sub.3 /C.sub.4 type olefins produced 
in the catalytic dehydrogenation zone 20 to olefinic gasoline in the first 
catalytic reactor zone 30 at low pressure. This facilitates the separation 
of olefinic materials from the paraffinic materials in the first 
separation zone 40, because it is much easier to separate the olefinic 
gasoline from C.sub.4.sup.- paraffins than to separate C.sub.4.sup.- 
olefins from C.sub.4.sup.- paraffins. Therefore, the paraffinic materials 
are mainly removed in the C.sub.4.sup.- rich stream 42, whereas the 
olefinic materials are mainly removed as olefinic gasoline. 
The oligomerization catalysts preferred for use herein include crystalline 
alumina silicate zeolites having a silica-to-alumina ratio of at least 12, 
a Constraint Index of about 1 to 12 and acid cracking activity of about 
160-200. Representative of suitable ZSM-5 type zeolites are ZSM-5, ZSM-11, 
ZSM-12, ZSM-23, ZSM-35 and ZSM-38. ZSM-5 is disclosed and claimed in U.S. 
Pat. No. 3,702,886 and U.S. Pat. No. Re. 29,948; ZSM-11 is disclosed and 
claimed in U.S. Pat. No. 3,709,979. Also see U.S. Pat. No. 3,832,449 for 
ZSM-12; U.S. Pat. No. 4,076,842 for ZSM-23; U.S. Pat. No. 4,016,245 for 
ZSM-35 and U.S. Pat. No. 4,046,849 for ZSM-38. The disclosures of the 
above patents are incorporated herein by reference. A suitable shape 
selective catalyst for a fixed bed reactor is a HZSM-5 zeolite with 
alumina binder in the form of cylindrical extrudates of about 1-5 
millimeters. Other catalysts which may be used in one or more reactor 
stages include a variety of medium pore (5 to 9 Angstroms) siliceous 
materials, such as borosilicates, ferrosilicates and/or aluminosilicates, 
disclosed in U.S. Pat. Nos. 4,414,143 and 4,417,088, incorporated herein 
by reference. 
The catalytic dehydrogenation zone 20 operating conditions will depend upon 
which of a number of commerically available methods is used. Typical 
catalytic dehydrogenation pressure and temperature conditions range from 
about 0.1-2 atmospheres, and 1000.degree.-1700.degree. F. C.sub.3 /C.sub.4 
paraffins can also be dehydrogenated to olefins by thermal cracking. 
Typically, 30-40% of the C.sub.3 /C.sub.4 paraffins dehydrogenate to 
C.sub.3 /C.sub.4 olefins, respectively, with about 10% C.sub.2.sup.- gas 
made per pass through the dehydrogenation zone. Thermal cracking is 
carried out at a temperature of about 1400.degree.-1700.degree. F., at a 
pressure of 0-30 psig and a residence time not exceeding 1 second. 
Catalytic dehydrogenation is more selective to the formation of 
C.sub.3.sup.+ olefins than thermal dehydrogenation, which yields large 
amounts of ethylene. U.S. Pat. No. 4,413,153 (Garwood et al) provides more 
detailed information on catalytic and thermal dehydrogenation systems 
which can be used for zone 20. 
The effect of olefin pressure on oligomerization product is significant 
because increased pressure results in a heavier, higher boiling range 
product. The first reactor zone 30 would typically operate at lower 
pressure and therefore make lighter products (olefinic gasoline) than the 
second reactor zone 60, which primarily converts light olefins and 
olefinic gasoline to distillate. 
A suitable first catalytic reactor zone 30 would comprise a down flow 
reactor operating at pressures ranging from 10-1000 psia, preferably 10-40 
psia, and from 400.degree.-800.degree. F., preferably 
450.degree.-600.degree. F. Typical single pass conversions would be from 
70-95%, and preferably 80-95%. Streams 24 and 34 would be representative 
of feed and product, respectively. Space velocities would range from 0.2-4 
WHSV, weight hourly space velocity, and preferably 0.5-1.5 WHSV. A typical 
unit which can be used for the first catalytic reactor zone, is described 
in more detail in U.S. Pat. No. 3,960,978 and in Example 2 of U.S. Pat. 
No. 4,211,640 (both Givens et al). 
The general operating parameters for production of lube boiling range 
materials (650.degree. F..sup.+ bp) in the second catalytic reactor zone 
60 are pressures from 100-3000 psig (preferably 800-2000 psig) at room 
temperatures ranging from 350.degree.-600.degree. F., and space velocities 
of 0.1 to 5 WHSV. Conversion of olefinic gasoline to distillate is 
typically greater than 90%. A suitable system for conversion of olefins to 
distillate and upgrading of the distillate to recover lube oil is 
described in more detail in U.S. Pat. No. 4,413,153 (Garwood et al). 
Distillate upgrading comprises hydrotreating and separating to form lube 
oil and other products. The distillate stream 64, obtained from the second 
separation zone 70, is subjected to hydrotreating to stabilize the 
distillate stream 64 by saturation of olefins and diolefins and to 
increase the cetane value of the distillate. Hydrogen gas may be obtained 
by sources such as steam reforming or hydrogen recovered from the 
dehydrogenation zone 20. The hydrotreating is by hydrogenation, which is a 
catalytic process which preferably uses a Pt or Pd supported catalyst, 
which does not require the addition of sulfur to maintain activity. Such a 
catalyst produces sulfur-free products, unlike Co/Mo/Al or Ni/W/Al 
catalysts. A typical catalyst is 0.4% Pt on gamma-alumina. Saturation of 
the olefin double bond is essentially complete under hydrogenation 
conditions of 550.degree.-700.degree. F., a pressure of 100-500 psig, and 
a space velocity of 0.5-5 LHSV (liquid hourly space velocity) and a 
hydrogen volume rate of 1000-5000 SCF/bbl. U.S. Pat. No. 4,413,153 
(Garwood et al) discloses a system, for hydrotreating of distillate and 
separation of hydrotreated distillate by distillation to recover lubes, 
which can be used for unit 80. U.S. Pat. No. 4,456,781 (Marsh et al) also 
discloses a system, for separation of MOGD products by distillation, which 
can be used for zone 70. 
While specific embodiments of the method and apparatus aspects of the 
invention have been shown and described, it should be apparent that many 
modifications can be made thereto without departing from the spirit and 
scope of the invention. Accordingly, the invention is not limited by the 
foregoing description, but is only limited by the scope of the claims 
appended hereto.