US3827968A

US3827968A - Aromatization process

Info

Publication number: US3827968A
Application number: US00322812A
Authority: US
Inventors: E Givens; C Plank; E Rosinski
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1973-01-11
Filing date: 1973-01-11
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: NL180833B; NL180833C; BE809523A; NL7400438A; DE2400946C2; IT1006710B; GB1442364A; DE2400946A1; CA1021357A; FR2322917A1; FR2322917B1

Abstract

IN A RECENTLY DISCOVERED PROCESS, A FEED OF OLEFINS, NAPHTHENES OR A MIXTURE OF THESE WITH OR WITHOUT PARAFFINS AND/OR AROMATICS ARE AROMATIZED IN GOOD YIELDS BY CONTACT, IN THE ABSENCE OF ADDED HYDROGEN, WITH A ZSM-5 TYPE OF ZEOLITE CATALYST AT ELEVATED TEMPERATURES, RELATIVELY LOW SPACE VELOCITIES, AND GENERALLY SEVERE CONDITIONS. THERE IS DISCLOSED HERE AN IMPROVEMENT IN THIS PROCESS OBTAINED BY FIRST OLIGOMERIZING THE OLEFIN CONTENT OF THE FEED TO HIGHER MOLECULAR WEIGHT OLEFINS BY COTACTING SUCH WITH A ZSM-5 TYPE OF ZEOLITE CATALYST UNDER MUCH MILDER CONDITIONS THAN THE AFORESAID AROMATIZATION CONDITIONS AND THEN, IF DESIRED, FEEDING THE LIQUID PRODUCT OF THIS OLIGOMERIZATION TO AN AROMATIZATION STAGE. BOTH STAGES ARE OPERATED IN THE ABSENCE OF ADDED HYDROGEN.

D R A W I N G

Description

United States Patent 3,827,968 AROMATIZATION PROCESS Edwin N. Givens, Pitman, Charles J. Plank, Woodbury, and Edward J. Rosinski, Deptford, N.J., assignors to Mobil Oil Corporation Filed Jan. 11, 1973, Ser. No. 322,812 Int. Cl. C07c /30; Cg 39/00 US. Cl. 20849 6 Claims ABSTRACT OF THE DISCLOSURE In a recently discovered process, a feed of olefins, naphthenes or a mixture of these with or without parafiins and/or aromatics are aromatized in good yields by contact, in the absence of added hydrogen, with a ZSM-S type of zeolite catalyst at elevated temperatures, relatively low space velocities, and generally severe conditions. There is disclosed here an improvement in this process obtained by first oligomerizing the olefin content of the feed to higher molecular weight olefins by contacting such with a ZSM-S type of zeolite catalyst under much milder conditions than the aforesaid aromatization conditions and then, if desired, feeding the liquid product of this oligomerization to an aromatization stage. Both stages are op erated in the absence of added hydrogen.

This invention relates to manufacturing gasoline. It more particularly refers to improved techniques for upgrading relatively low octane number feed stocks to products of substantially higher octane number and therefore of substantially greater economic value.

There are several unit processes in a petroleum refinery which produce gas phase products or byproducts which contain, to a greater or lesser extent, olefins in the C to C range. There may be admixed with these olefins more or less paraffinic material. It has recently been proposed to convert these olefinic and paraffiuic materials to aromatics, thereby converting a stream which has essentially fuel value at least in part to a high octane number gasoline blend stock which is highly aromatic in nature.

Application Serial No. 153,855, filed June 16, 1971, now US. Pat. 3,760,024 the substance of which is incorporated herein by reference, discloses such as aromatization process for a feedstock comprising C to C parafiins and olefins by contacting such feedstock with a crystalline aluminosilicate of the ZSM-5 type at a temperature of about 200 to 1400 F., in the absence of added hydrogen, at pressures of about 0 to 1000 p.s.i.g., and space velocities equivalent to about 0.1 to 500 WHSV. The particular combination of these individual operating parameters suited to use with any particular feedstock is to be chosen so that a significant yield of liquid product, which is substantially aromatic in nature, will be produced.

Application Serial No. 253,942, more recently filed on May 17, 1972 now Pat. No. 3,756,942, whose disclosure is also incorporated herein by reference, discloses a similar process to that of aforesaid Application Ser. No. 3,- 855 now Pat. No. 3,760,024 in that it is directed to contacting a feedstock having a boiling range of C to those fractions wherein at least 50 volume percent boils no higher than 250 F, with acrystalline aluminosilicate zeolite of the ZSM-S type at a space velocity equivalent to about 1 to 15 WHSV, a pressure up to about 35 atmospheres and a temperature of about 650 to 1500 F. The particular combination of these individual operating parameters suited to use with any particular feedstock is to be chosen so that at least 30 grams of aromatics will be produced per 100 grams of aromatizable content of the feedstock.

The catalyst used for this known process has been stated to be a ZSM-S type of catalyst which includes ice ZSM-5, ZSM-8, ZSM-ll and other zeolites having substantially the same crystalline structure.

ZSM-5 is disclosed and claimed in copending application Ser. No. 865,472, filed Oct. 10, 1969 now 'Pat. No. 3,702,886; ZMS-S is disclosed and claimed in copending application Ser. No. 865,418, filed Oct. 10, 1969 now abandoned and ZSM11 is disclosed and claimed in copending application Ser. No. 31,421 filed Apr. 23, 1970 now Pat. No. 3,709,979.

The family of ZSM-5 compositions has the characteristic X-ray diffraction pattern set forth in Table 1 hereinbelow. ZSM-S compositions can also be identified, in terms of mole ratios of oxide, as follows:

wherein M is a cation, n is the valence of said cation, W

is selected from the group consisting of aluminum and gallium, Y is selected from the group consisting of silicon and germanium, z is from 0 to 40 and b is at least 5 and preferably 15-300. In a preferred synthesized form, the zeolite has a formula, in terms of mole ratios of oxides, as follows:

0.9 1 0.2M 2 o A130 15-100810, Z11 0 and M is selected from the group consisting of a mixture of alkali metal cations, especially sodium and alkyl ammonium ions, especially tetraalkylammonium cations, the alkyl groups of which preferably contain 2-5 carbon atoms.

In a preferred embodiment of ZSM-5, W is aluminum,

Y is silicon and the silica/alumina mole ratio is at least 15, preferably at least 30.

Members of the family of ZSM-S zeolites which include ZSM-S, ZSM-8 and ZSM11 possess a definite dis-.

tinguishing crystalline structure whose X-ray diffraction pattern shows the following significant lines:

These values, as well as all other X-ray data were determined by standard techniques. The radiation was the K-alpha doublet of copper, and a scintillation counter spectrometer with a strip chart pen recorder was used. The peak heights, 1, and the positions as a function ,of 2

times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these the relative intensities, N1 where I is the intensity of the strongest line or peak, and d(o bs.), the interplanar spacing in A, corresponding to the recorded lines, were calculated. In Table 1 the relative intensities are given in terms of the symbols S -strong, M=medium, MS=medium strong, MW=medium weak and VS=very strong.

It should be understood that this X-ray diffraction pattern is characteristic of all the species of ZSM-5 compositions. Ion exchange of the sodium ion with other cations reveals substantially the same pattern with some minor shifts in interplanar spacing and variation in relative intensity. Other minor variations can occur, depending on the silicon to aluminum ratio of the particular sample, as well as if it has been subjected to thermal treatment.

Zeolite ZSM-S can be suitably prepared by preparing a solution containing water, tetrapropyl ammonium hydroxide and the elements of sodium oxide, an oxide of aluminum or gallium and an oxide of silica, and having a composition, in terms of mole ratios of oxides, falling within the following ranges:

wherein R is propyl, W is aluminum and Y is silicon. This mixture is maintained at reaction conditions until the crystals of the zeolite are formed. Thereafter the crystals are separated from the liquid and recovered. Typical reaction conditions consist of a temperature of from about 75 C. to 175 C. for a period of about six hours to 60 days. A more preferred temperature range is from about 90 to 150 C., with the amount of time at a temperature in such range being from about 12 hours to 20 days.

The digestion of the gel particles is carried out until crystals form. The solid product is separated from the reaction medium, as by cooling the whole to room temperature, filtering and water washing.

ZSM-S is preferably formed as an aluminosilicate. The composition can be prepared utilizing materials which supply the elements of the appropriate oxide. Such compositions include, for an aluminosilicate, sodium aluminate, alumina, sodium silicate, silica hydrosol, silica gel, silicic acid, sodium hydroxide and tetrapropylammonium hydroxide. It will be understood that each oxide component utilized in the reaction mixture for preparing a member of the ZSM-S family can be supplied by one or more initial reactants and they can be mixed together in any order. For example, sodium oxide can be supplied by an aqueous solution of sodium hydroxide, or by an aqueous solution of sodium silicate; tetrapropylammonium cation can be supplied by the bromide salt. The reaction mixture can the prepared either batchwise or continuously. Crystal size and crystallization time of the ZSM-S composition will vary with the nature of the reaction mixture employed.

ZSM-8 can also be identified, in terms of mole ratios of oxides, as follows:

0.9 :l: 0-2M O 2 A1103 2 15-300 Sio: 2 EH20 wherein M is at least one cation, n is the valence thereof and z is from 0 to 40. In a preferred synthesized form, the zeolite has a formula, in terms of mole ratios of oxides, as follows:

0.9 =1: 0.2M 2O A1 0 15-60 SiOg 2 H10 The operable relative proportions of the various ingredients have not been fully determined and it is to be immediately understood that not any and all proportions of reactants will operate to produce the desired zeolite. In fact, completely different zeolites can be prepared utilizing the same starting materials depending upon their relative concentration and reaction conditions as is set forth in United States 3,308,069. In general, however, it has been found that when tetraethylammonium hydroxide is employed, ZSM-S can be prepared from said hydroxide, sodium oxide, aluminum oxide, silica and water by reacting said materials in such proportions that the forming solution has a composition in terms of mole ratios of oxides falling within the following ranges:

SiO /Al O --from about 10 to about 200 Na O/tetraethylammonium hydroxidefrom about 0.05

Tetraethylammonium hydroxide/SiO from about 0.08

l-i O/tetraethylammonium hydroxide-frorn about to about 200 0.9 :1: 0.311 0 A110; zuso s10, z H20 wherein M is at least one cation, n is the valence thereof and z is from 6 to 12. In a preferred synthesized form, the zeolite has a formula, in terms of mole ratios of oxides, as follows:

0.9 :i: 0.3M A1203 20-90 s10, z H20 and M is selected from the group consisting of a mixture of alkali metal cations, especially sodium, and tetrabutylammonium cations.

ZSM-ll can be suitably prepared by preparing a solution containing (R X) O, sodium oxide, an oxide of aluminum or gallium, an oxide of silicon or germanium and water and having a composition, in terms of mole ratios of oxides, falling within the following ranges:

Broad Preferred YOz/WO: 20-90 Na O/Ym. 0. 05-0. 40 4X)20/Y0 0. 02-0. 15 H= INaO loo-e00 wherein R.,)( is a cation of a quaternary compound of an element of Group 5A of the Periodic Table, W is aluminum or gallium and Y is silicon or germanium maintaining the mixture until crystals of the zeolite are formed. Preferably, crystallization is performed under pressure in an autoclave or static bomb reactor. The temperature ranges from 100 C.200 C. generally, but at lower temperatures, e.g. about 100 C. crystallization time is longer. Thereafter the crystals are separated from the liquid and recovered. The new zeolite is preferably formed in an aluminosilicate form.

An embodiment of this catalyst resides in the use of a porous matrix together with the ZSM-S type family of zeolite previously described. The zeolite can be combined, dispersed, or otherwise intimately admixed with.

the porous matrix in such proportions that resulting products contain from 1 to by weight and preferably from 10 to 70% by weight of the zeolite in the final composite.

The term porous matrix includes inorganic compositions with which the zeolites can be combined, dispersed or otherwise intimately admixed wherein the matrix may be catalytically active or inactive. It is to be understood that the porosity of the composition employed as a matrix can be either inherent in the particular material or it can be introduced by mechanical or chemical means. Representative of matrices which can be employed include metals and alloys thereof, sintered metals, and sintered glass, asbestos, silicon carbide, aggregates, pumice, firebrick, diatomaceous earths, alumina and inorganic oxides. Inorganic oxide compositions, especially those comprising alumina and those of a siliceous nature are preferred. Of these matrices inorganic oxides such as clay, chemically treated clays, silica, silica alumina, etc. as well as alumina, are particularly preferred because of their superior porosity, attrition resistance and stability.

Techniques for incorporating the ZSM-S type family of zeolites into a matrix are conventional in the art and are set forth in United States 3,140,253.

It is to be noted that when a ZSM5 type zeolite is used in combination with a porous matrix, space velocities which may be set forth as parameters for this process are based on the ZSM-S type zeolite alone and the porous matrix is ignored. Thus, whether a ZSM-S type zeolite is used alone or in a porous matrix, the space velocities in all cases refer to the ZSM-S type component.

It is known that zeolites, particularly synthetic zeolites, can have their composition modified by impregnating certain metals thereonto and/or thereinto. The composition can also be modified by exchanging various anions and/or cations into the crystal structure of the zeolite, replacing more or less of the ions originally present upon production of the zeolite.

The ZSM-S type family of zeolites have been found to be especially active for aromatization if they have at least a portion of the original cations associated therewith replaced by any of a wide variety of other cations according to techniques well known in the art. Typical replacing cations would include hydrogen, ammonium, and metal cations, including mixtures of the same. Of the replacing cations, preference is given to cations of hydrogen, ammonium, rare earth, magnesium, zinc, calcium, nickel, and mixtures thereof. Particularly effective members of the ZSM-5 type family of zeolites are those which have been base exchanged with hydrogen ions, ammonium ions, zinc ions or mixtures thereof. Most especially zinc ZSM-S is the best presently known catalyst for aromatizations as set forth.

Typical ion exchange techniques would be to contact a ZSM-5 type of zeolite with a salt of the desired replacing cation or cations. Although a wide variety of salts can be employed, particular preference is given to chlorides, nitrates and sulfates.

Representative ion exchange techniques are disclosed in a wide variety of patents, including United States 3,140,249; 3,140251; and 3,140,253.

It is also within the scope of the aromatization process to which this application is directed to incorporate a desired metallic component onto the ZSM-5 type family of zeolites by techniques other than ion exchange. Thus, for example, it is possible to impregnate a desired metallic component, such as zinc, platinum or palladium, thereinto by conventional impregnation techniques, as well as merely depositing the elemental metal onto the particular zeolite and in some cases, such as with zinc oxides, to incorporate the metal by physical admixture of the zeolite with an insoluble metal compound.

In any event, following contact with a salt solution of the desired replacing cation, the zeolites are preferably washed with water and dried at a temperature ranging from 150 to about 600 -F. and thereafter heated in air or inert gas at temperatures ranging from about 500 F. to 1500" F. for periods of time ranging from 1 to 48 hours or more. It is noted that this heat treatment can be carried out in situ, i.e. while the particular aromatization reaction is taking place, but it is preferred to carry it out as a separate step prior to carrying out the aromatization reaction.

In furtherance of development of the aromatization processes referred to and generally described above, it has been found that some refinery streams which should be suitable feedstocks for these aromatizations have an accelerated aging effect upon ZSM5 type of catalysts due to components therein other than those defined above, e.g., those containing steam. It has also been found that many of the refinery streams containing the desired feedstock are gaseous in nature and are, singularly or collectively, of insufficient volume to sustain large scale efficient aromatization. This situation raises the difficulty and inconvenience of storing gases until a sufficient quantity of feedstock is accumulated to process through aromatization. Another difficulty which has been found is that many refinery streams which should be suitable for aromatization processing according to the disclosures of the aboveidentified patent applications have an unduly large paraffin content thereby necessitating aromatization under quite severe conditions which leads to rapid catalyst aging and even, in some cases, premature catalyst deactivation at least as to aromatizating certain components of the feedstock.

It is therefore an object of this invention to provide a novel process for upgrading C to C olefin-containing pertoleum refinery streams.

It is another object of this invention to provide an improved process for aromatizing gaseous feedstocks.

It is a further object of this invention to provide an improved process for upgrading the octane number of certain gaseous petroleum fractions.

Other and additional objects of this invention will be apparent from a consideration of this entire specification including the claims and the drawing hereof.

Understanding of this invention will be facilitated by reference to the accompanying drawing in which:

FIG. 1 is a schematic flow diagram of an embodiment of this invention;

FIG. 2 is similar to FIG. 1 showing an alternate flow sequence; and

FIG. 3 is similar to FIGS. 1 and 2 showing another alternative flow sequence.

In accord with and fulfilling the above objects, one aspect of this invention resides in a process comprising feeding a gaseous C to C olefin-containing stream into contact with a ZSM-5 type of zeolite in the absence of added hydrogen, at about 550 to 850 R, up to about 800 p.s.i.g. and about 0.5 to 50 WHSV under such combination of conditions, dependent upon the exact feed composition, to produce a product having a liquid portion consisting principally of C to C olefins which may have minor amounts of parafiins and/ or aromatics and/or naphthenes admixed therewith. This liquid product has a substantially improved octane value as compared to the feed and can be used directly as gasoline blend stock.

Of greater importance, howeber, is the fact that this liquid product is exceptionally well suited to use as the feed to an aromatization unit process ofthe type referred to above as having been described in U.S. Patent Applacation 253,942. Under there conditions, that is that this particular C -C olefins stream is the feed, this aromatization will utilize a ZSM-S type of catalyst, preferably Zn ZSM- 5, a temperature higher than that used in the first, or oliigomerization, stage of about 800 to 1200 F., a pressure of about 1 to 10 atmospheres and a lower space velocity equivalent to about 0.1 to 10 WHSV. The aromatization takes place in the absence of added hydrogen. The particular combination of conditions chosen for this second, or aromatization stage is of course dependent upon the exact composition of the liquid feed thereto as well as upon the composition of the product desired therefrom. The product of the aromatization stage is partly liquid and partly gas with the liquid being substantially all, at least about 90%, aromatic in nature and the gas being principally paraffinic C; and hydrogen.

If desired, the gas product streams of either the first or the second stages or both can be recycled for feeding to the first and/or second stages to extinction. These streams or one of them can be taken oif and used as fuel. One or both of these streams can be fed to a pyrolysis unit in order to make more low molecular weight olefins for charging to the first stage oligomerizer.

The first and second stage catalysts have been noted to be zeolites of the ZSM5 type. These catalysts can be in particulate form of a size sufiicient to be in a fixed or fluidized bed. The catalyst bed, and in fact the reactor itself, may be designed for downfiow or upfiow of raw material feed therethrough. The catalysts may be the same or diiferent in each stage. For example, it is preferred to use HZSM-S in the first stage and Zn ZSM-S in the second stage. The zeolite in the first stage may be exchanged and/or impregnated with nickel, zinc, copper, platinum, palladium, calmium, silver or mixtures thereof. It is within the scope of this invention to utilize a zeolite of the erionite, mordenite or ferrierite type in the first stage oligomerization but not in the second stage aromatization. The first stage catalyst is subject to substantially less severe operating conditions than is the second stage catalyst and therefore there can be used in this first stage a zeolite catalyst which has been partially deactivated through use either in the second stage of this process or in another process, such as cracking or hydrocracking. The feed to the first stage of the process described herein may be all or part of the gas product stream from a fluid or thermofor catalytic cracker (FCC or TCC) or it may be the gaseous byproduct from a riser cracking unit. This type feed will generally contain hydrogen, hydrogen sulfide and C5 olefins and parafiins.

This first stage feed may be a C cut from the gaseous overhead leaving a cracking unit. Such feed will also contain significant amounts of hydrogen and perhaps some hydrogen sulfide. Similarly the gas stream from a coking unit, a pyrolysis unit or an unsaturates plant can be used as feed. The C cut from cracked gasoline also serves as an adequate oligomerization feed stream.

In any and all of these cases, the feed contains parafiins as well as unsaturates of the Cf, C nC iC (if and mixed C types. These various gas streams can be mixed together and jointly fed into and through the oligomerizer to produce a mixed gas-liquid product.

The liquid product can be stored, accumulated, blended into gasoline or some mixture of these three. It can preferably, however, be used as feed to a second stage aromatizer. In this regard it should be noted that the liquid product can be used partially as feed to the aromatizer and partially as gasoline blend stock.

The gas product evolved from the oligomerizer is a highly paralfinic stream which is principally C although it may save some C paraffinic material therein. This gas may be recycled to extinction in the oligomerizer, however, it is quite difficult to work with parafiins and to oligomerize and dehydrogenate them under the mild conditions of the instant first stage. It is therefore preferred to utilize at least part of this gas product stream as feed to a pyrolysis unit, perhaps the same one feeding the fresh feed to the first stage, or perhaps to a methanization process for making synthetic natural gas. If needed, this gas product, which may comprise up to about 50% of the product evolved from the first stage, can be used as fuel in this process or in other parts of the refinery.

Where the feed to the oligomerizer is rich in higher molecular Weight compounds, e.g., Q; with some C and higher, the gas product will usually contain significant quantities of isoC parafiins which are good blend stock for combining with cracked gasoline.

The second or aromatization process is made considerably more efiicient by having its feed limited to the liquid phase product of the first stage oligomerization. This is mainly olefinic and possibly slightly naphthenic-With perhaps some small quantity of aromatics which were formed in the first stage. The paraifins in the original feed have mostly gone overhead and out of the picture at least as far as the direct production of aromatics is concerned. This aromatization stage, however, produces a gas/liquid mixed product of its own of which the liquid is the'more valuable, highly aromatic, high octane portion. Thegas byproduct will amount up to about 50% of the total product from the aromatizer and will be principally composed of hydrogen and C; parafiins.

It will be noted that on a once through basis, the original C gaseous feed may be converted to aromatics to an extent of only about 25% (about 50% converted to liquid oligomers in the first stage and about 50% of that converted to aromatics in the second stage). Therefore, it is most important to the economic viability of this process to utilize the gas product streams to their greatest advantage. The least advantageous use of these gas streams is as fuel. However, it should be recognized that a petroleum refinery is delicately heat balanced. Since certain refinery operations are endothermic (e.g., reforming), it may be necessary to use part of the gas byproduct hereof as fuel to make up this heat requirement.

On the other hand, the gas byproduct contains sufficient quantities of crackable parafiins to make it an excellent feed to a pyrolysis unit. In the case of the initial C feed being from a pyrolysis unit, the gas byproduct should be used at least in part as a recycle stream to the pyrolysis unit. In this regard, hydrogen should be stripped from the gas byproduct before recycle. Accumulated hydrogen sulfide should be separated from the gas byproduct.

It is also within the scope of this invention to resolve the gas byproduct, without recycle or fuel use, in order to recover the propane and butanes for LPG use. Methane can be recovered and used.

Referring now to the drawing and particularly to FIG. 1 thereof, a gas stream 1 of C is admixed with a recycle C gas stream 2 and fed as a mixed stream 3 into intimate contact with a ZSM-S type of oligomerization catalyst 4 in a first stage reactor 5. A product 6 is produced in this first stage which is passed through a gas-liquid separator 7 from which a gas C product 8 is evolved which becomes part of the recycle stream 2 and from which a liquid product 9 is evolved.

The intermediate liquid product 9 is fed into intimate contact with a ZSM-S type of aromatization catalyst 10 in a second stage reactor 11. A mixed gas-liquid product 12 is generated out of this second stage reactor 11 which is passed to a second gas-liquid separator 13. A gas prod uct 14 is taken from the second gas-liquid separator 13 which is wholly or partially recycled 15 for combination with the gas 8 evolved from the first stage separator 7 from the recycle stream 2. If desired, a part of this gas 14 can be taken as product 17 for other uses (not shown). A liquid product 16 from the second separator 13 is rich in aromatics and is the most valuable product produced in this process.

Referring now to FIG. 2 there is shown a slightly modified process for maximizing aromatics production from this process. A gas stream 21, of C is combined with an olefin rich recycle stream 22 and the mixed feed stream 23 is fed into intimate contact with a ZSM-S type of oligomerization catalyst 24 in a first stage reactor 25. The product 26 from this first stage reactor is mixed gas 27 and liquid 28 which are resolved in a first separator 29. The liquid product 28 is suitably split into a gasoline blend stock and a feed 30 to a second stage aromatization reactor 31. The feed 30 is intimately contacted in the second stage reactor 31 with a ZSM-S type of aromatization catalyst 32 whereupon a mixed gas-liquid product 33 is evolved which is resolved in a second separator 34 into an aromatics rich liquid product 35 and a C gas product 36. The two

gas products

27 and 36 are combined 37 and fed to a pyrolysis unit 38 to convert paraffins therein to olefins. The product 39 of this pyrolysis is separated 40 into an olefin rich stream 22 which is recycled as aforesaid and a paraffin rich-hydrogen rich stream 41 is recovered. If desired, the olefin-paraifin splitter 40 can be omitted and the pyrolysis product 39 recycled in its entirety.

Referring now to FIG. 3, a C feed stream 51 is intimately contacted with a ZSM-S type of oligomerization catalyst 52 in a first stage oligomerization reactor 53 to produce a mixed gas-liquid product 54 which is resolved in a gas-liquid separator 55 into a C gas stream 56 and a C to C liquid product 57.

The gas stream 56 is passed through a pyrolysis unit 57 to produce a product 58 comprising substantial quantities of olefins. The olefins 59 are separated 60 from the rest of the product 58 and combined with at least part 61 of the liquid product 57 from oligomerizer. A portion 62 of this liquid product is shown being taken oil? as direct gasoline blend stock.

The C -C liquid product 61 from the first stage 53 and olefin product 59 from the pyrolysis 57 are mixed 63 and fed into intimate contact with a ZSM-S type of aromatization catalyst 64 in a second stage, aromatization reactor 65 whereupon a mixed gas-liquid product 66 is produced. This mixed product 66 is resolved in a second separator 67 into an aromatic rich liquid product 68 and a C4 mostly paraffinic and hydrogen gas 69 which is taken as a gas byproduct for such uses as have been outlined above or others.

The pyrolysis product 58, after having the olefins content thereof 59 removed in the olefin-paraffin splitter 60, also yields a C +hydrogen gas 70 byproduct which is mostly paraffinic. The two

gas products

69 and 70 can be combined or used separately as noted above as feed to pyrolysis, for methanization, as fuel or a source of LPG and hydrogen, or a combination of any or all of these.

This invention is illustrated by the following Examples which are not to be considered to be restrictive of the scope thereof. All parts and percentages expressed in the Examples are by weight unless specifically indicated to be to the contrary.

Example 1 Propylene was intimately contacted with a nickel exchanged HZSM-S catalyst at 13.65 WHSV and 600 F. for 28 hours. The following Table 1 shows the product composition as a function of on stream time. No recycle was used.

TABLE 1 Time (hours) Percent:

Gas product 17. 3 22. 1 26. 6 30. C1 0. 1 0. 1 1. 2 1. 0 0. 7 1. 0

Total product- 100. 1 100. 1 100. 2 100. 0

The octane number of the liquid product at the end of the run was 96 clear RON.

Example 2 The liquid product of Example 1 was subjected to aromatization by contacting it with Zn ZSM-S catalyst at 1.0 WHSV and 950 F. The following Table 2 gives product distribution as a function of time on stream.

TABLE 2 Time on stream (hrs.)

Gas product, percent 25. 3 22. 5 23.4 20 22.0 Composition:

0. 1 Qs- 0.1 0.1 0.2 0.1 Liquid product, percent 74. 6 77. 6 75. 6 79. 9 78. 0 Composition, percent:

Parafiins 2.8 3. 0 3. 2 3. 1 0. 4 11.1 12. 0 10. 9 11. 6 11. 5 30. 1 32. 6 30.9 33. 4. 32. 8 20. 8 21. 2 21. 4 22. 6 21. 7 4. 8 4. 2 5. 1 5. 0 4. 1 0.4 0. 4 0. 5 0. 4 3. 8 3. 5 3.1 2. 6 2. 6 2. 5 1. 0 0. 9 0. 8 0. 8 0. 8 0. 1 0. 2 0. 3 0. 2 0. 3 Other (by subtraction). 0. 7 0. 7 0. 8 0. 6 0. 2 Total product 97. 9 100. 1 99. 0 90. 9 100. 0 Average aromatic molecular weight 96. 9 96. 2 96. 7 96. 4 97. 3

What is claimed is:

1. A process which comprises contacting a C olefincontaining gas stream with a first ZSM-S type of synthetic aluminosilicate zeolite catalyset at about 550 to 850 F., at about 0.1 to 800' p.s.i.g., at a space velocity equivalent to about 0.5 to 50 WHSV and in the absence of added hydrogen under such combination of conditions to produce a product consisting of up to about 50% of a first gas and a first liquid comprising C -C olefins; contacting at least a portion of said first liquid product with a second ZSM-S type of synthetic aluminosilicate zeolite catalyst at about 800 to 1200 F., about 1 to 10 atmospheres, a space velocity equivalent to about 0.1 to 10 WHSV andin the absence of added hydrogen under such combination of conditions, more severe than those specified with respect to said first catalyst, to produce a product consisting of up to about 50% of a second gas and a second liquid comprising at least about 75% aromatics.

2. A process as claimed in claim 1 wherein said first liquid product is at least about 70% of said first product and wherein said aromatics are at least about of said second liquid product.

3. A process as claimed in claim 1 wherein said first catalyst is HZSM-S and said second catalyst is Zn ZSM- 5.

4. A process as claimed in claim 1 wherein said second temperature is higher than said first temperature.

5. A process as claimed in claim 1 including subjecting at least some of said gas product to pyrolysis under conditions sufficient to convert paraffins therein to olefins and feeding at least the olefins portion of the pyrolysis product in to contact with said first catalyst.

6. A process as claimed in claim 1 including subjecting at least some of said gas product to pyrolysis under conditions suflicient to convert paraflins therein to olefins and feeding at least the olefins portion of the pyrolysis product in to contact with said second catalyst.

References Cited UNITED STATES PATENTS 3,202,725 8/ 1965 =Lorz et a1. 260-6735 3,374,282 3/1968 Soderquist et al. 260-6735 3,516,923 6/1970 Kirk 260-673.5 3,702,886 11/ 1972 Argauer et a1. 208-411 HERBERT LEVIN-E, Primary Examiner US. Cl. X.R. 260673.5

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,327,968 Dated August 6, 1974 Edwin N. Givens et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columnv 7, line 70, after "with" insert possibly Column 8, line 56, "Product 17" should read product 15 Signed and sealed this 28th day of January 1975.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 U.i GOVERNMENT PRINTING OFFICE: 9 930 FORM PO-1050 (10-69) 1333; sums PATENT omen CERTIFICATE OF CDRRECTION.

Patent No. 3, 7,9 baud Aug 197A Inventor) EDWIN N. .GIVENS, CHARLES J. PLANK, EDWARD J. ROSINSKI It is certified the: ma: appeal in the IbOVl-identified patent and that aid Letters Potent are hereby corrected as shown below:

' Column 6, line 59 "howeber" should be "however".

Column 6, line 63 "there" should be --chese--. Column 6, line 67 "oliigomerization" should be e -oligomeriza tion--.

Column 7, line 21: 'Y I z "calmium" should bee -cadmium"..

Column '7, line 5 7 1 "save'? should be "have".

Column 10, line 19 "subtraction" should read -substraction--.

Column 10, line 20: d Fourth column figure should be I -99.9- not "90.9"

Column 10, line 28 "catalyset" should be --.cata.lyst--.

Signed and sealed this 19th day of Noirember 1 974.

(SEAL) Attest:

McCOY IfI. GIBSON JR. C. MARSHALL DANN Atizesting' Officer Commissioner of Patents