GB2066287A - Hydrogenation of high boiling hydrocarbons - Google Patents

Abstract

In a process for the hydrogenation of high boiling feeds (such as atmospheric tower bottoms, vacuum tower bottoms, heavy crudes and solvent-refined coal) to produce lower boiling materials the hydrogenation is carried out in at least two catalytic ebullated hydrogenation zones in series, and a recycle, of which at least 25% by volume boils above 510 DEG C (950 DEG F), is recovered from the hydrogenated product, contacted with an adsorbent, such as calcined coke, to remove coke precursors and introduced into at least the last of the hydrogenation zones. Higher conversion levels can be achieved by providing a recycle in this manner. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydrogenation processes This invention relates to hydrogenation processes, and more particularly to the hydrogenation of high boiling hydrocarbon materials to provide valuable lower boiling materials.

In known processes high boiling hydrocarbon materials derived from either petroleum or coal sources, typically petroleum residuum or solvent-refined coal, are hydrogenated in an ebullated (expanded) catalyst bed in order to produce more valuable lower boiling materials. In general, the conversion levels for such an operation are limited by a tendency to form heavy carbonaceous deposits which result in agglomeration of the catalyst. The limit is at a different conversion level for each feedstock.

As a result, there is a need for an improvement in such hydrogenation processes in order to permit operation at higher conversion levels.

According to the present invention, there is provided a process for upgrading high boiling hydrocarbon materials to valuable lower boiling materials, the process comprising the steps of: hydrogenating the high boiling hydrocarbon material in at least two expanded bed catalytic hydrogenation zones in series to produce an upgraded hydrogenated product; recovering from the upgraded hydrogenation product a recycle having a 5-volume percent distillation temperature of at least 232or with at least 25-volume percent thereof boiling above 510 C; contacting the recycle with a solid adsorbent having a surface area of from 1 to 200m2/gram to remove coke precursors therefrom; and providing the recycle to at least the last of the hydrogenation zones.

The applicant has found that by providing recycle in this manner the operability range of the hydrogenation reaction zone can be extended to operate at higher levels of conversion. Representative examples of suitable adsorbents include: activated alumina, bauxite and calcined coke and the like, with calcined coke being preferred. Preferably, the calcined coke has a surface area in the order of from 1 to 5m2/gram.The adsorption of coke precursors is conveniently conducted at a temperature of at least 204'C (400"F), with the adsorption temperature advantageously not exceeding 371 C (700oF) and preferably not exceeding 316 C (6005). The adsorption is suitably conducted at a pressure which exceeds the bubble point pressure of the recycle, the pressure being below the pressure employed in the hydrogenation.

As hereinabove noted, at least 25%, by volume, of the recycle boils above 510,C (950'F). Advantageously, the 5-volume percent distillation temperature of the recycle is at least 288"C (550 F), and most preferably at least 316"C (600"F). The recycle may be conveniently provided by recovering from the product a 288 C+ (550"F+) fraction.

However, the recycle could also be a higher boiling fraction, for example a 316 C+ (600'F+) fraction (wherein the 5-volume percent distillation temperature is at least 316"C (600"F) and at least 25-volume percent boils above 510"C (950"F)), or a 538 C+ (1000oF+) fraction (wherein the 5-volume percent distillation temperature is at least 538"C (1000"F)). The recycle is provided as a high boiling recycle in order to minimize the ratio of the 149-288"C (300"-550"F) distillate to the 538"C+ (1000"F+) residue in the liquid phase in the last hydrogenation zone.

The recycle, after treatment to remove coke precursors as hereinabove described, is provided to at least the last of the hydrogenation zones. The recycle may be provided to the last zone by directly introducing the recycle into the last zone, or all or a portion thereof may be introduced into a preceding zone whereby all or a portion of the recycle to the last zone is provided with the effluent from the preceding zone or zones in the series.

The upgrading of the high boiling hydrocarbon materials by hydrogenation in two or more expanded bed catalytic hydrogenation zones is conducted at such temperatures and pressures, and with such a catalyst, as are generally known in the art; however, by proceeding in accordance with the present invention, it is possible to operate at conversion levels higher than those previously employed in the art, without adversely affecting the overall operation.Preferably, the hydrogenation is conducted at a temperature in the order of from 343-482"C (650 to 900 F), most preferably from 399-454"C (750 to 850 F), and at an operating pressure of from 3447kN/m2g (500 psig) to 27596kN/m2g (4000psig), the hydrogen partial pressure generally being in the order of from 3447 to 20682kN/m2 (500 to 3000psi).

The catalyst which is employed may be any one of a wide variety of catalysts for hydrogenation of heavy materials. Representative examples of such catalysts include cobaltmolybdate, nickel-molybdate, cobalt-nickelmolybdate, tungsten-nickel sulphide and tungsten-sulphide. The catalyst is preferably supported on a suitable support such as alumina or silica-alumina and is maintained in the hydrogenation reactor as an expanded or ebullated bed, as known in the art.

The recycle provided in accordance with the invention is employed in an amount whereby the ratio of recycle to total fresh feed to the hydrogenation is from 0.2 1 to 10: 1, preferably from 0.4 1 to 1.0 1.

Each of the hydrogenation zones may or may not include an internal recycle depending on the total flow to the zone. The amount of internal recycle, if any, is adjusted in accor dance with the amount of external recycle provided in accordance with the present invention.

The feed to the process is one which has high boiling components, which are to be converted to more valuable low boiling components. In general. such a hydrocarbon feed has at least 25% by volume of material boiling above 510"C (9503F) and it may be derived from petroleum and/or coal surfaces, the feed generally being a petroleum residuum, such as atmospheric tower bottoms, vacuum tower bottoms, heavy crudes or tars containing small amounts of material boiling below 343to (650 F), or a solvent-refined coal, and the like.

So that the invention may be more readily understood and so that further features may be appreciated, a process in accordance with the present invention will now be described by way of example with reference to the accompanying drawing which is simplified schematic flow diagram of the process.

A hydrocarbon feed to be upgraded, in a line 10, is combined with a recycle stream in a line 11 (if a recycle stream employed, as hereinafter described) and the combined stream in a line 1 2 is passed through a heater wherein the combined stream is heated to an appropriate hydrogenation inlet temperature, for example, a temperature in the order of from 316"C-426"C (600'F to 800'F). The heated hydrocarbon feed is withdrawn through a line 14 and is combined with a gaseous hydrogen-containing stream in a line 1 5. The combined stream, in a line 16, is introduced into the bottom of a first one of two ebullated bed hydrogenation reactors 1 7 and 18.

The reactors 1 7 and 1 8 are of a type known in the art, and each may include respective means 21, in the form of an internal tube provided with a pump at the bottom thereof (not shown), for providing an internal recycle within the reactor sufficient to maintain the flow for providing an ebullated or expanded catalyst in the reactors. If the flow of fresh feed and recycle is sufficient to maintain an expanded catalyst bed, then an internal recycle tube and pump can be eliminated.

the first reactor 1 7 is operated at temperatures and pressures as known in the art and as hereinabove described. Thus, the feed is passed upwardly through the first reactor 1 7 in contact with the hydrogenation catalyst therein, and an effluent is withdrawn through a line 22 for introduction into the second hydrogenation reactor 18.

The effluent in the line 22 may be combined with a recycle stream, as hereinafter described in more detail, from a line 23, in which case the recycle functions to cool the reaction effluent prior to the introduction into the second reactor 1 8. Alternatively, as hereinafter described, the recycle may be provided through another line 24. The effluent, which thus may or may not contain recycle, is then quenched with a hydrogen-containing gas in a line 25, and the combined stream in a line 26 is then introduced into the bottom of the second ebullated bed hydrogenation reactor 18.

The second hydrogenation reactor 1 8 is operated at conditions as hereinabove described to hydrogenate the feed and to upgrade it to lower boiling components. As particularly shown, the second reactor 1 8 is provided with an internal recycle; however as hereinabove described, the internal recycle could be eliminated if the total flow were sufficient to maintain an expanded catalyst bed.

A reaction effluent is withdrawn from the second reactor 1 8 through a line 28 and 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 29 may include one or more gas-liquid separators and coolers, as appropriate, in order to provide for separation and recovery of the hydrogen gas.

The hydrogen recycle gas is recovered through a line 31 and after purging (as appropriate), compression (not shown), and addition of make-up hydrogen through a line 32, a portion of the hydrogen is provided to the second reactor 1 8 through a line 25, and a further portion, after heating in heater 33, is provided to the first reactor 1 7 through line 15.

A liquid product from the gas separation zone 29 is introduced via a line 35 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 liquid product of the gas separation zone 29. In particular, in accordance with the present invention, a liquid recycle stream is recovered in line 37 having the characteristics, hereinabove described, namely a 5-volume percent distillation temperature of at least 232"C (450"F) with at least 25-volume percent thereof boiling above 510"C (950"F).

The recycle is preferably a 288 C+ (550"F+) or 538 C+ (1000 F+) fraction recovered from the product. The recycle in the line 37 is introduced into an adsorption zone, schematically generally indicated as 38, wherein the recycle is contacted with an adsorbent, preferably calcined coke, to adsorb coke precursors as hereinabove described. The recycle from the adsorption zone 38 is then employed in lines 11 and/or 23 and/or 24 in order to provide a recycle to the second reactor 1 8.

Thus, all or a portion of the recycle to the second reactor 1 8 may be provided directly or indirectly through the first reactor 1 7.

Although the embodiment has been particu larly described with reference to the use of two hydrogenation reactors, it is to be understood that there may be more than two reactors. In such a case, the last reactor is provided with recycle as hereinabove described, the recycle being provided directly to the last reactor or indirectly by providing recycle to one or more of the preceding reactors.

In one embodiment of the present invention external recycle is provided to the last reactor of the series and the recycle is pretreated to remove coke precursors and has boiling char- acteristics to minimize, in the liquid phase of the last reactor, the ratio of the 149"C-260"C (300"-500"F) distillate to the 538 C+ (1000'F+) residue.

The present invention will be further described with respect to the following Example: EXAMPLE The following is illustrative of conditions for hydrogenation of a reduced crude, employing three expanded bed reactors in series. The catalyst was nickel molybdate supported on aluminal Operating Conditions of Reactors Temperature, "C 433 ( F 811) Pressure, kN/m2 15512 (psig 2250) Liquid Feed, kg/hr 1.81 (Ib/hr 3.98) Hydrogen Rate, m3/hr 1.67 (SCFH 59) Conversion of 524 C+ (975 F+), Vol% 71.6 The recycle, a 288 C+ (550 F+) fraction recovered from the hydrogenation product, was contacted with calcined coke (6-20 mesh, bulk density 690 kg/m3 (431 Ib/ft3)) at a temperature of 288"C (550"F). The recycle was then heated to 343"C (650"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.

Processes in accordance with the present invention have been found to be particularly advantageous in that it is possible to extend the range of operable conversion rates for a given feedstock. Also it has been found that 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 preferred methods in accordance with the present invention, hydrogenation of heavy hydrocarbon feedstocks can be effected at higher conversion rates, without an increase in pressure drop or difficulty in controlling reaction temperatures.

Claims (11)

1. A process for upgrading high boiling hydrocarbon materials to valuable lower boiling materials, the process comprising the steps of: hydrogenating the high boiling hydrocarbon material in at least two expanded bed catalytic hydrogenation zones in series to produce an upgraded hydrogenated product; recovering from the upgraded hydrogenation product a recycle having a 5-volume percent distillation temperature of at least 232"C with at least 25-volume percent thereof boiling above 510"C; contacting the recycle with a solid adsorbent havng a surface area of from 1 to 200 m2/gram to remove coke precursors therefrom; and providing the recycle to at least the last of the hydrogenation zones.

2. A process according to claim 1 wherein the adsorbent is calcined coke.

3. A process according to claim 1 or 2 wherein the recycle is a 316"C+ fraction.

4. A process of claim 1 or 2 wherein the recycle is a 538"C+ fraction.

5. A process according to any one of the preceding claims wherein the adsorbent has a surface area of from 1 to 5 m2/gram.

6. A process accoding to any one of the preceding claims wherein the said 5-volume percent distillation temperature is at least 288"C.

7. A process according to claim 6 wherein said 5-volume percent distillation temperature is at least 316"C.

8. A process according to any one of the preceding claims wherein the adsorption is effected at a temperature between 204"C and 317"C.

9. A process according to any one of the preceding claims wherein the hydrogenation is conducted at a temperature between 343'C and 482"C.

10. A process according to claim 9 wherein the hydrogenation is conducted at a temperature between 399"C and 454"C.

11. A process substantially as herein described with reference to the accompanying drawings.

1 2. An upgraded hydrogenated product whenever made by a process according to any one of the preceding claims.

1 3. Any novel feature or combination of features described herein.