Conversion of hydrocarbons with "y" faujasite-type catalysts

Abstract

A single riser fluid catalytic cracking operation for converting a gas oil feed material and a gaseous fraction rich in C.sub.3 -C.sub.4 hydrocarbons to form aromatics and isobutane is described. Conversion of the C.sub.3 -C.sub.4 rich fraction is accomplished at a high temperature in an initial annular portion of the riser reactor before charging a gas oil feed to the suspension formed in the annular section. C.sub.3 -C.sub.4 rich hydrocarbon streams may be converted at a lower temperature in a downstream portion of the riser.

Description

BACKGROUND OF THE INVENTION

The field of catalytic cracking and particularly the operations related to dense and dilute fluid phase catalytic operations have been undergoing progressive development since early 1940. As new experience was gained in operating and design parameters, new catalyst compositions were developed which prompted a further refinement in known operating technology. With the development of high activity crystalline zeolite catalyst, the industry found a further need to improve upon its operating parameters to take advantage of the new catalysts activity, selectivity and operating sensitivity. The present invention is thus concerned with an improved method of cracking or catalytic operation which relates the catalyst activity and selectivity to processing parameters in a manner mutually contributing to improving the conversion of available refinery feed materials.

SUMMARY OF THE INVENTION

The present invention is directed to the conversion of hydrocarbons in the presence of a relatively large pore crystalline material of the faujasite type of crystalline zeolite. In a more particular aspect, the present invention is concerned with more completely utilizing the activity and selectivity characteristics of "X" and "Y" faujasite crystalline aluminosilicate conversion catalyst to upgrade gas oil feed materials and normally gaseous hydrocarbon products such as those obtained in a gas oil conversion operation. In yet another aspect the present invention is concerned with using a faujasite cracking catalyst separated from a gas oil hydrocarbon conversion zone to upgrade particularly C.sub.3 and C.sub.4 rich hydrocarbon gaseous material to higher boiling gasoline boiling material. The C.sub.3 -C.sub.4 rich gaseous material may be the product of a high temperature gas oil cracking operation or the gaseous hydrocarbons may be recovered from other available refinery sources. More particularly, the present invention is concerned with the cracking of gas oil boiling range hydrocarbon feed materials with a Y faujasite cracking catalyst under elevated temperature cracking conditions selected from within the range of 900.degree.F. to about 1100.degree.F. at a hydrocarbon residence time in a once through conversion zone restricted to within the range 1 1 to about 12 seconds. Catalyst to oil ratios may be selected from within the range of 4 to about 20. Generally, it is preferred to accomplish cracking of the gas oil in an upflowing riser conversion zone discharging into cyclonic separation means in an upper portion of an enlarged vessel wherein products of gas oil cracking are separated from the catalyst used. The riser suspension may also be discharged adjacent the inlet to cyclonic separating means rather than directly into the cyclonic separating means as shown. The separated catalyst is collected in the lower portion of the vessel which is in open communication with the upper end of a lower extending stripping zone wherein the catalyst is stripped with countercurrent upwardly flowing stripping gas such as steam. The stripped products and products of conversion separated from the catalyst discharge from the riser conversion zone are combined with the cyclonically separated hydrocarbon vapors and passed to one or more downstream separation zones.

In accordance with this invention, C.sub.3 -C.sub.4 rich hydrocarbon mixture or an isobutylene rich stream is contacted with the Y faujasite conversion catalyst before contact with gas oil boiling range feed material in an initial portion of the riser or after initial contact with gas oil feed. The gas oil conversion is accomplished at a catalyst to hydrocarbon feed ratio in the range of 4 to about 10 and an elevated hydrocarbon feed temperature sufficient to form a suspension at a temperature in the range of about 950.degree. to about 1100.degree.F. Conversion of the C.sub.3 -C.sub.4 rich hydrocarbon feed, on the other hand, is accomplished at temperatures above that relied upon for gas oil cracking or under lower temperature gas oil conversion temperatures. Thus the C.sub.3 -C.sub.4 hydrocarbon rich feed which may be charged to the riser to encounter the regenerated catalyst at its highest temperature received from the regeneration zone may be converted at a temperature of about 1250.degree.F. before the suspension thereof is brought in contact with gas oil feed in the riser. Therefore, the residence time of the C.sub.3 -C.sub.4 hydrocarbon rich feed at high temperature conditions before gas oil contact may be up to 1 or 2 seconds or it may be only a fraction of a second, as little as one-tenth of a second, but the contact time under lower temperature conditions may be equal to or greater than that employed for the gas oil conversion operation. In any event, the conversion zone is maintained under conditions which can provide a hydrocarbon residence time within the range of 1 to about 12 seconds before separation of the suspension. This is so since either one of the feeds may be introduced to the riser conversion zone at spaced apart intervals lying in a downstream portion thereof. During this combination conversion operation, the Y faujasite catalyst provides hydrogen transfer activity and cyclization selectivity which converts introduced and formed C.sub.3 -C.sub.4 hydrocarbons to aromatics; alkyl aromatics and some low boiling gaseous material.

The C.sub.3 -C.sub.4 rich hydrocarbon feed material or the isobutylene rich feed may be separately furnace heated or heated by other suitable means to a temperature suitable for introducing to the riser conversion zone. The C.sub.3 -C.sub.4 rich hydrocarbon feed initially contacting the freshly regenerated catalyst may encounter significantly different high temperature residence times depending upon whether the gas oil is introduced to an initial, intermediate or downstream portion of the riser conversion zone.

Catalyst particles separated from the conversion zone are stripped in a stripping zone countercurrent to rising stripping gas such as steam as mentioned above. The stripped catalyst is then transferred to a catalyst regeneration zone, not shown, for the removal of deposited carbonaceous material by burning, thereby heating the catalyst to an elevated temperature in the range of 1150.degree.F. up to 1,500.degree. or 1,600.degree.F.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a diagrammatic sketch in elevation of an arrangement of hydrocarbon conversion zones for catalytically converting selected hydrocarbon feeds with a fluid conversion catalyst.

DISCUSSION OF SPECIFIC EMBODIMENTS

Referring now to the FIGURE, there is shown a riser conversion zone 2 supplied with hot regenerated catalyst by conduit 4 provided with a catalyst flow control valve 6. Steam is introduced to a bottom portion of riser 2 by one or more steam inlet conduits 8 and/or 10 and a gas oil feed is introduced by inlet conduit 12 which projects upwardly into the bottom portion of riser 2. A C.sub.3 -C.sub.4 rich hydrocarbon fraction may be introduced separately or with steam by conduit 8 to the bottom portion of riser 2 for admixture with hot regenerated catalyst. A suspension of catalyst in upflow gasiform hydrocarbon material with or without steam provides a mix temperature of at least 1100.degree.F. initially formed and passed upwardly through an annular section of riser 2 about a gas oil inlet means 12 under velocity conditions selected to provide a hydrocarbon residence time as low as about one-tenth of a second up to about 1 or 2 seconds. The upflowing initially formed suspension in the annulus of riser 2 is thereafter combined with preheated hydrocarbon feed such as a gas oil feed introduced by conduit 12 projecting upwardly into the bottom of riser 2. The thus formed suspension at an elevated cracking temperature of at least 1000.degree.F. is caused to flow upwardly through the remaining portion of the riser under hydrocarbon conversion conditions. On the other hand, the gas oil feed may be introduced at spaced intervals along the riser as by conduits 14 and 16. In yet another embodiment it is contemplated initially lifting the hot regenerated catalyst with steam or other inert gas before contact with the gas oil feed introduced by conduit 12 for upward flow through the riser. Additional gas oil feed may also be added downstream to the thus formed suspension. Thereafter gaseous hydrocarbons rich in C.sub.3 and C.sub.4 hydrocarbons are introduced to the upflowing suspension by conduit 16 or a further downstream inlet conduit not shown permitting a minimum residence time of about 1 second for low temperature upgrading as herein described. In the arrangement of the FIGURE, the suspension in riser 2 is discharged into cyclonic separation zones 18 and 20 housed in the upper portion of vessel 22 wherein separation of catalyst from hydrocarbon vapors is accomplished. Hydrocarbon vapors separated from catalyst then pass into a plenum chamber 24 for removal from the vessel by conduit 26. Catalyst separated from hydrocarbon vapors in cyclonic means 18 and 20 pass by diplegs 28 and 30 to a fluid bed of catalyst 32 maintained in the lower portion of the vessel 22. The fluid bed of catalyst 32 is in open communication with a lower extending stripping zone 34 therebelow to which the fluid bed of catalyst moves generally downward countercurrent to rising stripping gas introduced by conduit 36. The stripping zone is maintained at a temperature within the range of 900.degree.F. to 1150.degree.F. and the higher temperatures may be facilitated by the addition of hot regenerated catalyst to the catalyst in the stripping zone by means not shown. Stripped catalyst is removed from a bottom portion of the stripping zone by conduit 38 for transfer to a catalyst regeneration zone not shown. Stripped catalyst may also be recycled to the riser inlet by conduit means not shown when it is desired to provide catalyst to hydrocarbon ratios greater than 20 and as high as about 80.

The fluid bed of catalyst 32 separated from the riser conversion zone 2 is at an elevated temperature and may be in the range of from about 900.degree.F. to about 1100.degree.F. As suggested above, gaseous hydrocarbon feed such as a mixture of C.sub.3 -C.sub.4 hydrocarbons may be used to form a high temperature suspension in a bottom portion of riser 2 by use of either conduit 12 or 8 alone or in combination with one another before gas oil is introduced to a downstream portion of riser 2 as by one or both of conduits 14 and 16. Also, as a means for controlling catalyst to hydrocarbon ratios in the riser an inert gas may be initially employed to form a suspension in a bottom portion of the riser into which C.sub.4 and lighter hydrocarbons and gas oil are dispersed as herein provided. The suspension formed will vary considerably in temperature as herein provided and in catalyst/hydrocarbon ratio but generally will be in the range of 10 to about 40.

The method and system of the FIGURE above described may be modified considerably in operating combinations without departing from the concepts of the present invention. In addition to the embodiments above identified, riser 2 may be substantially external to vessel 22 and stripping zone 34 rather than pass upwardly through substantially the center thereof. In this arrangement, the riser relied upon to upgrade C.sub.4 and lower boiling hydrocarbons and gas oil may be provided with additional hot freshly regenerated catalyst in a downstream portion of the gas oil riser conversion section. In one or more of the above defined embodiments, the C.sub.4 and lower boiling gaseous feed components contact active conversion catalyst of the faujasite type at a temperature within the range of 700.degree.F. up to about 1100.degree.F. and the gas oil feed contacts the faujasite catalyst preferably at temperatures in excess of 900.degree.F. and as high as 1100.degree.F. In yet a further embodiment it is contemplated employing a riser system in which the gas oil feed initially forms a high temperature catalyst/oil suspension in the bottom annular portion of the riser about inlet conduit 12 through which dispersion steam is introduced, additional gas oil feed may be added to the suspension as by conduit 14 and a C.sub.4 rich stream may then be added to the upflowing suspension as by conduit 16. In other words, lower boiling gaseous hydrocarbons such as a C.sub.3 -C.sub.4 rich stream is brought in contact with the gas oil-catalyst suspension in a downstream or upper portion of the riser conversion zone.

DISCUSSION OF SPECIFIC EXAMPLE

A series of conversion runs with an isobutylene rich feed were made under selected temperature and hydrocarbon residence time conditions which support the improved operations contemplated by the present invention and variations thereon. A catalyst comprising 15 percent REY was contacted under the conditions identified in the table below which produced the results identified. It was observed upon examination of the product that a considerable amount of hydrogen transfer occurred along with the production of a significant amount of liquid product. The liquid product was identified as consisting chiefly of toluene, xylenes, trimethylbenzenes and naphthalenes. Runs were made at a temperature of 1050.degree.F. and 850.degree.F. using a wide spread in hydrocarbon residence time.

TABLE __________________________________________________________________________ Unit Hopper (dense bed) Riser (dilute phase, steady state) Run No. 180C- 193 194 195 196 197 Temp., .degree.F 1050.degree. 1050.degree. 1050.degree. 850.degree. 850.degree. .tau. gas, sec. 46 22 7 8 17 Cat/gas (wt/wt) 29 41 40 40 80 __________________________________________________________________________ Conversion (NLB): Unconv. butylene 5.4 8.7 17.4 29.3 27.4 31.7 9.1 14.6 Propylene 3.3 4.1 11.9 4.3 5.5 Isobutane 19.9 23.7 34.1 42.0 47.4 C.sub.5 + gaso. 3.3* 4.3* 19.8 13.8 17.3 Other C.sub.4 - gases 39.1 32.4 8.0 16.8 2.5 12.5 6.5 20.6 Coke 29.0 26.8 8.8 10.0 14.1 __________________________________________________________________________ *No liquid trap used

It will be observed from these data, that at the shorter residence time used for the riser conversion runs, cracking of isobutylene to lower molecular weight gases and to coke is much reduced. However, at total conversion levels of 82.6, 67.8 and 90.9 percent of the isobutylene, losses to undesirable products are 12.21 percent and the ratios of isobutane to butylene plus propylene range from 1.15 to 3.25.

Thus run 195 effected at a high temperature and short residence time supports a concept of the present invention where the hot freshly regenerated catalysts initially contact the C.sub.3 -C.sub.4 rich feed in the lower portion of the riser reactor before coming in contact with gas oil feed material. On the other hand, run 196 supports a concept of this invention wherein previously used catalyst reduced to a lower temperature is contacted in a down-stream portion of the riser reactor with a C.sub.3 -C.sub.4 rich gaseous hydrocarbon feed material. Thus in any of the operating embodiments herein contemplated and defined, a Y faujasite conversion catalyst has activity and selectivity for hydrogen transfer reaction and olefin cyclization reaction leading to the production of significant quantities of isobutane and aromatics.

In the method and system of this invention it is contemplated processing hydrocarbon feed materials other than gas oil as specifically discussed above. That is, it is contemplated processing higher boiling residual oils, resids and hydrogenated charge materials such as hydrogenated gas oils, and hydrogenated resid.

Having thus generally described the method and means of the present invention and discussed specific embodiments related thereto, it is to be understood that no undue restrictions are to be imposed by reason thereof except as defined by the following claims.

Claims

I claim:

1. A method for converting hydrocarbons with faujasite conversion catalyst which comprises,

passing an upflowing suspension of hot regenerated faujasite conversion catalyst in a C.sub.3 -C.sub.4 gaseous hydrocarbon fraction at a temperature of about 1250.degree.F. through a lower annular portion of a riser conversion zone for a residence time in the range of 0.1 to 2 seconds,

introducing a higher boiling hydrocarbon fraction of at least gas oil boiling range into said upflowing suspension downstream of said annular zone at one or more spaced apart downstream intervals and converting the introduced higher boiling fraction at a temperature in the range of 900.degree.F. to 1000.degree.F. at a hydrocarbon residence time up to about 10 seconds to a product rich in aromatics,

separating the suspension following traverse of said riser conversion zone into a hydrocarbon phase and a catalyst phase, and sequentially stripping and regenerating said separated catalyst phase.

2. The method of claim 1 wherein the suspension after traversing the riser conversion zone is cyclonically separated into a hydrocarbon phase and a catalyst phase, the catalyst phase is stripped with stripping gas and a portion of the stripped catalyst is recycled to the inlet of the riser conversion zone.

3. A method for converting gas oils and low boiling C.sub.3 -C.sub.4 hydrocarbons with a faujasite conversion catalyst which comprises,

passing a suspension of faujasite cracking catalyst suspended in a hydrocarbon feed material of at least gas oil boiling range at an initial temperature of at least 1000.degree.F. upwardly through a riser conversion zone under conditions to provide a hydrocarbon residence time up to about 10 seconds, introducing hydrocarbons rich in C.sub.3 and C.sub.4 hydrocarbons into said suspension to obtain conversion thereof to aromatics and isobutane,

separating the suspension into a hydrocarbon phase and a catalyst phase, recovering the hydrocarbon phase, and stripping the separated catalyst before regeneration thereof.

4. In a riser hydrocarbon conversion operation the improvement which comprises,

passing a suspension comprising a gas oil high boiling hydrocarbon fraction admixed with faujasite catalyst at a temperature of at least 950.degree.F. upwardly through a conversion zone,

adding the high boiling fraction incrementally to the upflowing suspension,

introducing a hydrocarbon fraction rich in C.sub.3 and C.sub.4 hydrocarbons into a downstream portion of said suspension in said riser conversion zone maintained under conditions to produce a product rich in isobutane,

separating the suspension upon discharge from the conversion zone into a hydrocarbon phase and a catalyst phase, recovering the hydrocarbon phase, recovering and stripping the catalyst phase.