Hydrogenation of high boiling hydrocarbons

Abstract

.[.In a hydrogenation operation employing an ebullated catalytic bed, recycle is recovered from the hydrogenated product with at least 25%, by volume, of the recycle boiling above 950.degree. F. The recycle is cooled to a temperature of from 350.degree. to 600.degree. F. to separate coke precursors, prior to recycle to the hydrogenation. Higher conversion levels can be achieved by effecting recycle in such manner..]..Iadd.Disclosed is a hydrogenation process using at least one fluidized catalytic stage and a recycle material of heavy hydrogenated effluent. The heavy effluent material is cooled to a temperature within 350.degree.-600.degree. F. to separate toluene and heptane insoluble coke precursors prior to recycle. This separation may be enhanced by the use of centrifugation, filtration or a bed of particulate material (e.g. calcined coke). .Iaddend.

Description

The present invention will be further described with respect to a preferred embodiment thereof illustrated in the accompanying drawing, wherein:

The drawing is a simplified schematic flow diagram of an embodiment of the present invention.

It is to be understood, however, that the scope of the invention is not limited to such preferred embodiment. Thus, for example, although the embodiment is described with respect to the use of two hydrogenation zones, the invention is equally applicable to the use of a single hydrogenation zone, or to the use of more than two hydrogenation zones.

Referring now to the drawing, a hydrocarbon feed to be upgraded, in line 10, is combined with recycle in line 11, if employed as hereinafter described, and the combined stream in line 12 passed through a heater wherein the combined stream is heated to an appropriate hydrogenation inlet temperature, e.g., a temperature in the order of from 600.degree. F. to 800.degree. F. The heated hydrocarbon feed, in line 14, is combined with a gaseous hydrogen containing stream, in line 15, and the combined stream in line 16 introduced into the bottom of the first of two ebullated bed hydrogenation reactors 17 and 18.

The reactors 17 and 18 are of a type known in the art, and may include means 21, in the form of an internal tube, provided with a pump at the bottom thereof, (not shown), for providing internal recycle within the reactor sufficient to maintain the flow for providing an ebullated or expanded catalyst in reactors 17 and 18. If the flow of fresh feed and recycle is sufficient to maintain an expanded catalyst bed, then the internal recycle tube and pump can be eliminated. The reactor 17 is operated at temperatures and pressures as known in the art, and as hereinabove described. Thus, the feed is passed upwardly through reactor 17 in contact with the hydrogenation catalyst therein, and the effluent is withdrawn from reactor 17 through line 22 for introduction into the second hydrogenation reactor 18.

The effluent in line 22 may be combined with recycle, as hereinafter described in more detail, from line 23, in which case the recycle functions to cool the reaction effluent prior to the hydrogen quench. Alternatively, as hereinafter described, the recycle may be provided through line 24, subsequent to hydrogen quenching. The effluent, which may or may not contain recycle, is then quenched with hydrogen containing gas in line 25, and the combined stream in line 26 is then introduced into the bottom of the second ebullated bed hydrogenation reactor 18.

The hydrogenation reactor 18 is operated at conditions as hereinabove described to effect hydrogenation of the feed and upgrading thereof to lower boiling components. As particularly shown, reactor 18 is provided with internal recycle; however as hereinabove described, the internal recycle could be eliminated if the total flow is sufficient to maintain an expanded catalyst bed.

A reaction effluent withdrawn from reactor 18 through line 28 is introduced into a gas separation zone, schematically generally indicated as 29 in order to recover a hydrogen recycle gas from the effluent. The gas separation zone may include one or more gas-liquid separators, and coolers, as appropriate, in order to provide for separation and recovery of the hydrogen recycle gas. Hydrogen recycle gas is recovered through line 31 and after purging, as appropriate, and compression (not shown), and addition of make-up hydrogen through line 32, a portion of the hydrogen is provided to reactor 18 through line 25, and after heating in heater 33 to reactor 17 through line 15.

Liquid product from the gas separation zone 29, in line 35 is introduced into a product separation and recovery zone, schematically generally indicated as 36.

The separation and recovery zone 36 may include one or more fractionating towers, and/or separators, designed and operated to recover various products, and recycle streams, from the hydrogenation effluent. In particular, in accordance with the present invention, there is recovered a liquid recycle stream in line 37, having the characteristics hereinabove described; i.e., a 5-volume percent distillation temperature of at least 450.degree. F. with at least 25 volume percent thereof boiling above 950.degree. F. The recycle is preferably a 550.degree. F..sup.+ or 1000.degree. F..sup.+ fraction recovered from the product.

The recycle in line 37 is introduced into zone 38, wherein the recycle is cooled to a temperature of from 350.degree. F. to 600.degree. F. to separate coke precursors from the liquid recycle. In accordance with a preferred embodiment, the cooled recycle is passed through a bed of particulate material, such as, for example, calcined coke, to deposit the precipitated coke precursors on such solids.

The recycle from zone 38 is then employed in lines 11 and/or 23 and/or 24 in order to provide recycle to the last reactor 18. Thus, all or a portion of the recycle to reactor 18 may be provided directly to reactor 18 or indirectly through reactor 17.

It is to be understood that the hereinabove described embodiment may be modified within the spirit and scope of the present invention. Thus, for example, separation of the coke precursors may be enhanced by providing filtration and/or centrifugation, and/or a low boiling solvent in zone 38.

Thus, in accordance with the present invention external recycle is provided to the last reactor of the series and such recycle is pretreated to remove coke precursors and has boiling characteristics to minimize in the liquid phase of the last reactor the ratio of the 300.degree.-500.degree. F. distillate to the 10,000.degree. F..sup.+ residue.

The present invention will be further described with respect to the following example; however, the scope of the invention is not to be limited thereby:

EXAMPLE

The following is illustrative of conditions for hydrogenation of a reduced crude, employing three expanded bed reactors in series. The catalyst is nickel molybdate supported on alumina.

Operating Conditions of Reactors:

Temperature, .degree.F.--811

Pressure, psig--2250

Liquid Feed, lb./hr.--3.98

Hydrogen Rate, SCFH--59

Conversion of 975.degree. F..sup.+, Vol %--71.6

The recycle is a 550.degree. F..sup.+ fraction recovered from the hydrogenation product, which is contacted with calcined coke (6-20 mesh, bulk density 43 lb/ft3) at a temperature of 550.degree. F. The recycle is then heated to 650.degree. F. and introduced into the second and third reactors, with the ratio of combined recycle to total fresh feed ranging from 2:1 to 10:1.

The present invention is particularly advantageous in that it is possible to extend the range of operable conversion rates for a given feedstock. Thus, by operating in accordance with the invention, a higher rate of conversion may be employed without the difficulties heretofore encountered in the art. Thus, in accordance with the present invention, hydrogenation of heavy hydrocarbon feedstock is effected at higher conversion rates, without an increase in pressure drop, or difficulty in controlling reaction temperatures.

Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, within the scope of the appended claims, the invention may be practised otherwise than as particularly described.

Claims

1. In a process for upgrading high boiling hydrocarbon materials to valuable lower boiling materials.[.is.]..Iadd.in.Iaddend.a hydrogenation operation including at least one expanded bed catalytic hydrogenation zone to produce an upgraded hydrogenated product, the improvement comprising:

recovering from the upgraded hydrogenation product a recycle liquid having a 5-volume percent distillation temperature of at least 450.degree. F. with at least 25 -volume percent thereof boiling above 950.degree.F.; cooling the liquid recycle to a temperature of at least 350.degree. F. and no greater than 700.degree. F. to.[.separate.]..Iadd.precipitate coke precursors;.Iaddend..Iadd.removing essentially only.Iaddend.coke precursors from the.Iadd.cooled.Iaddend.liquid recycle; and subsequent to.[.separation.]..Iadd.removal.Iaddend.of said coke precursors providing the liquid recycle to an expanded bed catalytic hydrogenation zone.

2. The process of claim 1 wherein the cooled liquid recycle is passed through a bed of particulate solids to deposit separated coke precursors on the solids.

3. The process of claim 2 wherein the recycle liquid is a 600.degree. F..sup.+ fraction.

4. The process of claim 1 wherein the recycle liquid is a 1000.degree. F..sup.+ fraction.

5. The process of claim 1 wherein the recycle is cooled to a temperature of at least 400.degree. F.

6. The process of claim 1 wherein the recycle is cooled to a temperature of no greater than 600.degree. F..Iadd.7. The process of claim 1 wherein the cooled liquid recycle is centrifuged to enhance separation and removal of coke precursors..Iaddend..Iadd.8. The process of claim 7 wherein the

recycle liquid is a 600.degree. F..sup.+ fraction..Iaddend..Iadd.9. The process of claim 7 wherein the recycle is a 1000.degree. F..sup.+ fraction..Iaddend. 10. The process of claim 7 wherein the recycle is cooled to a temperature of no greater than 600.degree. F.