FI87085C - Control of polynuclear aromatic by-products in a hydrocracking process - Google Patents

Description

5,87085

Control of polynuclear aromatic by-products in the hydrocracking process

The technical field covered by this invention is the hydrocracking of a hydrocarbonaceous feedstock, which tends to form polynuclear aromatic (PNA) compounds without unduly contaminating the process unit. More particularly, this invention relates to a catalytic hydrocracking process comprising (a) feeding reduced crude oil to a vacuum distillation zone to produce a vacuum gas oil stream containing materials that tend to form PNAs in the hydrocracking zone and a paraffin wax containing; (b) contacting the vacuum gas oil stream in the hydrocracking zone with added hydrogen and a metal-accelerated hydrocracking catalyst at an elevated temperature and pressure sufficient to achieve substantial conversion to lower boiling products; (c) partially condensing the hydrocarbon effluent from the hydrocracking zone and separating it into a low boiling hydrocarbon product stream and a stream containing unconverted hydrocarbons boiling above about 343 ° C and trace amounts of PNA compounds; and (d) feeding at least a portion of the stream containing unconverted hydrocarbons and PNAs to the vacuum fractionation zone V, wherein a substantial portion of the PNAs are removed with the paraffin wax by-product stream, significantly reducing the supply of harmful PNAs to the hydrocracking zone.

U.S. Pat. No. 4,447,315 (Lamb et al.) Discloses a process for hydrocracking a hydrocarbon feedstock which tends to form polynuclear aromatic compounds, comprising contacting the hydrocarbon feedstock with at least a crystalline zeolite hydrate a portion of the resulting polynuclear aromatic compounds from the 2,87085 unconverted hydrocarbon oil to contact with an adsorbent that selectively retains the polynuclear aromatic compounds;

U.S. Pat. No. 3,619,407 to Hendricks et al. Discloses requirements for a method of preventing fouling of equipment in a hydrocracking process unit by partially cooling the effluent from a hydrocracking zone to cause condensation of a small amount of liquid hydrocarbons normally present therein. a condensate rich in polynuclear aromatics, and removing the by-stream from the condensate. U.S. Patent 3,619,407 recognizes prior art that the aforementioned fouling problem can also be solved by subjecting recycled oil 20 (a heavy portion of the hydrocracking zone effluent) or a substantial portion thereof to atmospheric pressure distillation or vacuum distillation to separate heavy bottoms containing arynuclates.

The present invention is a hydrocracking process that minimizes fouling of the catalyst and equipment used in the hydrocracking process unit with polynuclear aromatic compounds that can precipitate uncontrollably on equipment surfaces, particularly refrigeration equipment, and contaminate the pores of the catalyst. This is accomplished by subjecting the unconverted hydrocarbon recovered from the hydrocracking zone, which contains trace amounts of polynuclear aromatics, to vacuum discharge, whereby a substantial portion of the polynuclear aromatics are removed with a paraffin wax feed. when these recovered hydrocarbons are recycled back into it.

The present invention therefore relates to a catalytic hydrocracking process in which (a) reduced crude oil is fed to a vacuum fractionation distillation zone to produce a vacuum gas oil stream containing compounds which tend to form harmful polynuclear aromatic and hydrocracking aromatic compounds; (b) contacting the vacuum gas oil stream in the hydrocracking zone with added hydrogen and a metal-accelerated hydrocracking catalyst at an elevated temperature and pressure sufficient to achieve substantial conversion to lower boiling products and polynuclear aromatic compounds; (c) partially condensing the hydrocarbon effluent from the hydrocracking zone and separating it into a low boiling hydrocarbon product stream and a stream containing unconverted hydrocarbons boiling above about 343 ° C and polynuclear aromatic compounds; and (d) feeding at least a portion of the stream containing unconverted hydrocarbons 25 and polynuclear aromatics to a vacuum fractionation zone, wherein a substantial portion of the polynuclear aromatics is removed with the paraffin wax by-product stream, significantly reducing harmful polynuclear aromatics.

One embodiment of the present invention relates to a catalytic hydrocracking process in which (a) reduced crude oil is fed to a fractionation zone to produce a vacuum gas oil stream comprising compounds having: a tendency to form polynuclear aromatic compounds in a hydrocracking zone; 4,87085 (b) removing asphalts from the bottom stream of the vacuum distillation column to produce a deasphalted oil stream suitable for hydrocracking; (c) contacting the vacuum gas oil stream and the deasphalted oil stream in the hydrocracking zone with added hydrogen and a metal-accelerated hydrocracking catalyst at an elevated temperature and pressure sufficient to achieve substantial conversion to lower boiling products; (d) condensing the hydrocarbon effluent from the partially hydrocracking zone and separating it into a low boiling hydrocarbon product stream and a stream containing unconverted hydrocarbons boiling above about 343 ° C and trace amounts of polynuclear aromatic compounds; and (e) feeding at least a portion of the stream containing unconverted hydrocarbons and polynuclear aromatics to a vacuum fractionation zone, wherein a substantial portion of the polynuclear aromatics are removed with the paraffin wax side stream, thereby significantly reducing the risk of harmful polar nucleated aromatic compounds.

Other embodiments of the present invention address additional details, such as types of feedstocks and catalysts, preferred fractional distillation and separation procedures, and preferred operating conditions, including temperature and pressures, all of which are described in the following description of all these aspects of the invention.

The drawing is a simplified process flow diagram of a preferred embodiment of the present invention. The drawing described above is intended to schematically illustrate the present invention and not to limit it.

35 It has now been found that the total recycling of unconverted oil can be maintained indefinitely in the hydrocracking process unit described above without facing the above-mentioned fouling or precipitation problems.

5,87085

In U.S. Patent No. 3,619,407 (Hendrichs et al.), The patent holders state that a small leakage current from the condensate effluent rich in polynuclear aromatic partial condensation reduces or eliminates the problem of fouling or precipitation. However, the leakage stream contains unconverted feedstock, and when this stream is discarded, some of the potential recycle stream is lost and the recovery of low-boiling hydrocarbons tal-10 that could have been derived from the leakage stream deteriorates.

As stated above, it is known that polynuclear aromatic compounds can be efficiently removed from an unconverted hydrocarbon removal stream from a hydrocracking zone by fractional distillation to produce a heavy base fraction containing polynuclear aromatic compounds. However, this method of removing polynuclear aromatic compounds prevents the use of an efficient 20 t heavy base fraction as an additional feedstock to the hydrocracking zone.

U.S. Pat. No. 4,447,315 (Lamb et al.) Discloses ..... the removal of polynuclear aromatic compounds in an unconverted hydrocarbon removal stream before the unconverted hydrocarbon is recycled to the hydrocracking reaction zone, but does not disclose or suggest the process of this invention.

According to the present invention, it has been found that when at least a portion of the unconverted hydrocarbon effluent from the hydrocracking reaction zone is fed to the fractionation zone used to produce the original vacuum gas oil feedstock, a surprising and unexpected amount of polynuclear aromatics In a preferred embodiment of the present invention, the paraffin wax-containing side stream is a side fraction of a vacuum distillation column taken from a point below the heavy vacuum gas oil outlet 5 but above the bottom fraction of the vacuum distillation column. Conventionally, a paraffin wax-containing stream is preferably characterized as a hydrocarbonaceous stream having a 90% boiling point above 565 ° C and an asphaltene content greater than about 0.5 wt%. As a result of this finding, a relatively small stream containing paraffin wax together with polynuclear aromatic compounds, which stream is a low hydrocarbon stream, can then be isolated from the hydrocracking zone and thus any subsequent feed and accumulation of PNAs in the hydrocracking reaction zone can be prevented. Similarly, when a large amount of polynuclear aromatics is removed from the fractionation zone through a stream containing paraffin wax, the bottom stream of the home distillation zone becomes a more suitable stream 20 to be processed into a deasphalted oil stream which can then be suitably charged to the hydrocracking reaction zone.

In some cases where the concentration of contaminants is low, only a portion of the unconverted hydrocarbon effluent may need to be fed to the fractionation zone to remove a substantial portion of the polynuclear aromatics from the paraffin wax stream. thereafter separation on the heat exchange surfaces. The term "trace amounts of polynuclear aromatic compounds" as used herein is preferably described as having a concentration of less than 10,000 parts per million (ppm) and more preferably less than 5,000 ppn.

Under the processing of the method of this invention. The hydrocarbon feedstock is a suitably reduced crude oil. Reduced crude oil is generally prepared by fractional distillation of whole crude oil to produce a bottom stream of a fractionation column that boils above about 343 ° C.

According to this method, the reduced crude oil is fed to a fractionation zone to produce a vacuum gas oil stream containing compounds that tend to form polynuclear aromatic compounds in the hydrocracking zone and to produce a paraffin wax-containing stream. This vacuum gas oil stream may consist of a light vacuum gas oil stream and a heavy vacuum gas oil stream, which are produced separately in the fractionation zone and then mixed together to produce a feedstock for the hydrocracking reaction zone. In a preferred embodiment of the present invention, the paraffin wax-containing stream is a by-product of a vacuum fractionation column taken from a point below the vacuum gas oil outlet 30, as described above.

The resulting vacuum gas oil stream produced in the fractionation zone described above is fed to the hydro-cracking zone. The hydrocracking zone contains: preferably a catalyst, generally consisting of any crystalline zeolite cracking catalyst base on which a minor amount of Group VIII metal hydrogenation component is deposited · Additional hydrogenation components may be selected from Group VI B to be attached to the zeolite base. Zeolite cracking bases are sometimes referred to in the art as molecular sieves and usually consist of silica, alumina and one or more exchangeable cations such as sodium, hydrogen, magnesium, calcium, rare earth metals, etc. They are further characterized by relatively uniform diameters. 4-14 A (10 * ° m). It is preferred to use zeolites having a relatively high molar ratio of silica / alumina between about 3-12 and even more preferably between about 4-8. Suitable naturally occurring zeolites include, for example, mordenite, stilbite, heulandite, ferrierite, daciardite, cabazite, erionite and faujasite. Suitable synthetic zeolites include, for example, B, X, Y and L crystal types, e.g. synthetic faujasite and mordenite. Preferred zeolites are those having crystal pore diameters between about 8-12 Å and a silica / alumina molar ratio of about 4-6. The best example of a zeolite that falls into this preferred group is a synthetic Y molecular sieve.

Naturally occurring zeolites are normally found in sodium form, alkaline earth metal form or mixed form. Synthetic zeolites are almost always first prepared in sodium form. In any case, for use as a cracking catalyst base, it is preferred that most or all of the monovalent metals of the original zeolite be replaced with a polyvalent metal and / or ammonium salt, followed by heating to decompose the ammonium ions associated with the zeolite, leaving hydrogen ions and / or exchange sites. 35 huts from which cations have in fact been removed by further removal of water. Hydrogen or "cation-depleted" Y zeolites of this nature are described in more detail in U.S. Pat. No. 3,130,006.

Mixtures of polyvalent metal and hydrogen zeolites can be prepared by first ion exchange with ammonium salt and then partial exchange with polyvalent metal salt and then calcination. In some cases, such as in the case of synthetic mordenite, the hydrogen forms can be prepared by direct acid treatment of the alkali metal zeolites 10. Preferred cracking catalyst bases are those which lack at least about 10% and preferably at least 20% of the metal cation, based on the initial ion exchange capacity.

A particularly desirable and stable class of zeolites 15 are those in which at least about 20% of the ion exchange capacity is saturated with hydrogen ions.

The active metals used as hydrogenation components in the preferred catalysts of this invention include Group VIII VIII metals, i.e., iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum. In addition to these metals, other accelerators can also be used in connection therewith, including Group VI B metals, e.g. molybdenum and tungsten. The amount of hydrogenation metal in the catalyst can vary within wide limits. Broadly speaking, any amount between about 0.05-30% by weight can be used. In the case of precious metals, there is. normally it is preferred to use about 0.05-2% by weight. A preferred method of attaching the hydrogenation metal is to contact the base material of the alloy with an aqueous solution of a suitable compound of the desired metal in which the metal is present in cationic form. After the addition of the selected hydrogenation metal: - or metals, the resulting catalyst powder is then filtered, dried, granulated with added lubricants, binders tsm if desired and calcined in air at e.g. 371-648 ° C to activate the catalyst and decompose ammonium ions. Alternatively, the zeolite component may first be granulated, after which the hydrogenation component is added and activated by calcination. The above catalysts may be used in undiluted form or the ground zeolite catalyst may be mixed and granulated together with other relatively less active catalysts, diluents or binders such as alumina, silica gel, silica-alumina-10 silica co-gels, activated clays and the like. -%. These diluents may be used as such or may contain a minor amount of added hydrogenation metal, such as a Group VI B and / or Group VIII metal.

Other metal-accelerated hydrocracking catalysts may also be used in the process of this invention and include, for example, aluminum phosphate molecular sieves, crystalline chromium silicates, and other crystalline silicates.

Crystalline chromium silicates are more fully described in U.S. Patent No. 4,363,718 (Klotz).

The hydrocracking of the hydrocarbonaceous feedstock in contact with the hydrocracking catalyst is performed in the presence of hydrogen and preferably under hydrocracking conditions including a temperature of about 232-454 ° C with an overpressure of about 3448-20685 kPa, a liquid volume flow rate (LHSV) of about 0.2-20 h. -1 and a hydrogen recycling rate of about 355-1778 std. · M3 / m3.

30

After the hydrocarbonaceous feedstock has been hydrocracked as described above, the product stream, which preferably boils below about 343 ° C, is separated and recovered, and the hydrocarbonaceous stream, which preferably boils above 343 ° C, is separated and recovered as a recycling stream. This separation and recovery is preferably carried out in the partition zone 11b 7 Ο associated with the hydrocracking zone. At least a portion of the recycle stream described above is fed to the fractionation zone described above, which is used to produce a fresh feed 5 of vacuum gas oil. Its amount is typically selected to prevent precipitation of PNA compounds on the heat exchange surfaces of the hydrocracking unit, and in the preferred case, substantially all of the recycle stream is recycled to the vacuum column.

10

As a result of this finding that significant isolation and recovery of polynuclear aromatic compounds is unexpectedly achieved by removing the paraffin wax-containing stream from the vacuum fractionation zone 15, the bottom stream from the fractionation zone then becomes a more desirable stream for the production of deasphalted oil feed. It is preferred that a stream containing paraffin wax containing more than about 50% of the polynuclear aromatic compounds fed to the fractionation zone be produced and separated. In a preferred embodiment of the present invention, at least a portion of the bottom stream from the fractionation zone is fed to a solvent deasphalter 25 to produce deasphalted oil, which is then charged to the hydrocracking reaction zone and to produce a pitch stream.

Those skilled in the art of hydrocarbon processing are well acquainted with solvent deasphalting techniques. Briefly, solvent deasphalting is the countercurrent extraction of an asphaltene-containing oil as a solvent to produce a deasphalted oil and an asphaltene-rich hydrocarbonaceous stream, commonly referred to as pitch.

According to the present invention, the bottoms of the fractionation zone are preferably contacted countercurrently with a hydrocarbon selective solvent in a solvent deasphalting zone under deasphalting conditions selected to produce a low solvent asphalt stream and a solvent rich deasphalted hydrocarbon stream. The resulting solvent-rich deasphalted hydrocarbonaceous stream is fractionally distilled to separate and recover the selective solvent, which can be recovered if desired. A second stream of solvent-free deasphalted hydrocarbon is then charged to the hydrocracking zone.

The solvent deasphalting zone preferably operates at a temperature of about 10-315 ° C, an overpressure of about 689-6895 kPa and a volume ratio of solvent to feedstock of n.

15 2: 1-10: 1. Appropriate temperature and pressure conditions are preferably selected to maintain deasphilization operations in the liquid phase. Recently, solvent deasphalting zones have been run under conditions where the solvent is in a supercritical state.

20

Suitable solvents are light hydrocarbons, such as ethane, propane, butane, isobutane, pentane, pentane, neopentane. hexane, isohexane, heptane, ··. their mono-olefinic counterparts and mixtures.

25

The drawing illustrates the process of the present invention by means of a simplified flow chart, in which details such as pumps, instrumentation, heat exchange and heat recovery circuits, compressors, and the like are omitted because they are not essential to an understanding of the related art. The use of such miscellaneous accessories is well within the knowledge of those skilled in the art. Referring now to the drawing, the crude oil feed stream is passed to process 35 through line 12 and passed to an atmospheric pressure crude oil distillation column 13 to produce a gasoline stream discharged through line 14 137085 to produce a kerosene stream discharged through line 15 to produce which is removed via pipe 1.

5 The reduced crude oil stream is fed through line 1 to a vacuum distillation column 2. The hydrocarbonaceous recycle stream, which is passed as described below, is fed to the vacuum distillation column 2 via line 10. The vacuum gas oil stream is removed from the vacuum distillation column 2 via line 3 and fed to hydrocracking zone 8 via line 3 and line 7. The hydrocarbonaceous stream containing paraffin wax with polynuclear aromatic compounds is removed from the vacuum distillation column 2 via line 11 15. The bottom stream of the vacuum distillation column is removed from the vacuum distillation column 2 via line 4 and fed to the solvent deasphalting device 5. The deasphalted oil stream is removed from the solvent deasphalting device 5 through line 7 and fed to hydrocracking zone 20 8. Heavy leachate is removed from the solvent deasphalting device The hydrocarbonaceous product stream is removed from the hydrocracking zone 8 via a pipe 9. The unconverted hydrocarbonaceous recycle stream is removed from the hydrocracking zone 8 via line 10 25 and fed to a vacuum distillation column 2 as described above.

The following example is provided to further illustrate the hydrocracking catalyst of this invention. Example 30 is not to be construed as unduly limiting the general broad scope set forth in the appended claims of this invention and is therefore intended to be illustrative and not restrictive.

. 35 14

8 7 O 8 S

Example

Reduced crude oil at 100 kg / h having the properties shown in Table 1 and a recycle stream of 24.5 kg / h described below were fed to a vacuum distillation column to produce 77.0 kg / h of vacuum gas oil, 5.5 kg / h stream containing paraffin wax and 42.0 kg / h bottom fraction of a vacuum distillation column.

10

Table 1 - Properties of reduced crude oil

Specific gravity 0.9633

Distillation,% by volume Boiling point, ° C

15 336 (start) 10 411 20 443 30 465 40 494 20 50 521 60 568 End point, recovery 66% 597

Sulfur,% by weight 2.5

Nitrogen,% by weight 0.15 25

The resulting vacuum gas oil stream with a specific gravity of 0.991 and a boiling range of 270-565 ° C was fed to the hydrocracking zone mixed with the deasphalted oil described below at a rate of 17.5 • :: 30 kg / h and hydrogen at a rate of 1300 std m3 / h. m3 of feedstock, The bottom flow of the vacuum distillation column is · ;;; was subjected to solvent deasphalting to produce the deactivated oil stream of 17.5 kg / h mentioned below. Feedstock containing gas oil and; 35 deasphalted oil, and the hydrogen was then contacted with two solid catalyst layers in the hydrocracking zone. The first catalyst layer consisted of a silica-alumina support containing nickel and tungsten and was used at a liquid volume flow rate of about 0.4 and an average catalyst temperature of about 390 ° C. The second catalyst layer consisted of an alumina-silica-zeolite Y support containing nickel and tungsten and used at a liquid volume flow rate of about 1 and an average catalyst temperature of about 349 ° C. Each of the 10 catalyst layers was operated at an overpressure of about 16548 kPa. The stream leaving the catalyst layers was cooled to about 49 ° C and then passed to a high pressure separator maintained at an overpressure of about 13790 kPa. The hydrogen-rich gas stream 15 was removed from the high pressure separator and returned together with fresh make-up hydrogen to the hydrocracking catalyst zone. The liquid hydrocarbons from the high pressure separator were charged to a fractionation column where normally liquid hydrocarbons boiling below about 343 ° C were separated and removed as a product at 68.8 kg / h. Hydrocarbons boiling above about 343 ° C at 24.5 kg / h and containing about 115 parts per million by weight (wppm) of polynuclear aromatic compounds were removed from the fractionation column and returned to the vacuum distillation column. .

: · .. A study of the selected hydrocarbon streams and the stream ID and the corresponding concentration of polynuclear aromatic compounds were performed as shown in Table 2.

35 16 8 7 or. ;;

Table 2. - Polynuclear aromatic compound content

Hydrocarbon stream PNA content (ppm) 5 Reduced crude oil feedstock 0

Vacuum gas oil 12

Bottom fraction of the vacuum distillation column 3

Recycling to a vacuum distillation column 115

Paraffin wax from a vacuum distillation column 190 10 This study shows that the reduced crude oil feed does not contain a detectable amount of polynuclear aromatics, while the recycle stream to the vacuum distillation column from the hydrocracking zone contains 115 15 ppm. In this case, it appears that the hydrocracking zone generates polynuclear aromatic compounds which are known to be detrimental to the successful operation of the hydrocracking zone if they were to be fed to the hydrocracking zone through the recycling of unconverted vacuum gas oil.

According to the instructions of U.S. Pat. No. 3,619,407 (Hendrichs et al.) ____; The compounds can be at least partially isolated and removed by partially condensing a portion of the normally liquid hydrocarbons leaving the hydrocracking catalyst zone. are not available to produce a valuable distillate product stream and therefore the loss of a potentially valuable product represents a disadvantage of the prior art process in this field.

_- ··. Another prior art in the art teaches that the fouling problem can be solved by subjecting at least 35 parts of the recycled oil to distillation to separate the heavy bottom fraction containing polynuclear aromatic compounds.

li 17 87085

As discussed above, it has now been found that only a very small percentage of polynuclear aromatics are actually recovered from the heavy bottom fraction of the fractional distillation column 5 and that, surprisingly and unexpectedly, the majority of polynuclear aromatic compounds are recovered from the fractional distillation column by-pass flow. The paraffin-wax-containing stream 10 is a heavy, asphaltene-containing hydrocarbon-containing stream, and therefore the removal of polynuclear aromatic compounds with the paraffin-waxy stream reduces, if not completely eliminates, the loss of gas oil and thus allows gas oil conversion In addition, in accordance with the present invention, a greater proportion of polynuclear aromatic compounds are removed from the system by discarding the paraffin-20-level stream than by discarding the bottom stream of the fractionation column. According to one embodiment of the present invention, since the bottom stream of the fractionation column has been found to contain only trace polynuclear aromatics, this bottom stream can then be deasphalted to obtain a deasphalted oil stream which can then be charged to a hydrocracking zone to maximize the valuable hydrocarbon product.

The foregoing description, drawing, and example clearly illustrate the advantages and benefits of the process of the present invention.

35

Claims (8)

1. Catalytic hydrocracking process, characterized in that (a) inputs reduced crude oil into a suppression fractionation zone to produce an underpressure gas oil stream containing compounds which are prone to form harmful polynuclear aromatic compounds in a hydrocracking zone zone, vacuum bottom stream; (b) contacting the pressurized gas oil stream in a hydrocracking zone with added hydrogen and a metal-promoted hydrocracking catalyst at elevated temperature and pressure sufficient to effect a significant conversion to lower boiling products and to ί S form barriers of polynuclear aromatic compounds; (c) partially condensing the hydrocracking zone recovered from the hydrocracking zone stream and separating it into a low boiling hydrocarbon product stream and a stream containing at above about 343 ° C boiling unconverted hydrocarbons and the polynuclear aromatic compounds; and (d) feeding at least a portion of the stream containing unconverted hydrocarbons and polynuclear aromatic hydrocarbons into the vacuum fractionation zone, whereby a significant portion of the polynuclear aromatic compounds is removed with the paraffin wax side-aromatic degradable polynucleic acid stream, which labeling the compounds in the hydrocracking zone. 15 Process according to claim 1, characterized in that the hydrocracking zone is poured at an overpressure of about 3448-20685 kPa and at a temperature of about 232-454 ° C. Process according to claim 1, characterized in that the metal-promoted hydrocracking catalyst is synthetic faujasite, nickel and tungsten. A process according to claim 1, characterized in that the paraffin wax side stream contains more than about 50% of the polynuclear aromatic hydrocarbons fed into the fractionation zone. Process according to claim 1, characterized in that the underpressure bottom stream is subjected to solvent decay to produce a deasphalted oil stream which is subsequently fed into the hydrocracking zone (b). Process according to Claim 5, characterized in that the solvent desalting is carried out under conditions comprising a temperature of about 10-315 ° C, an overpressure of about 689-6895 kPa and a volume ratio of solvent to feed raw material of about 2: 1- 10: 1. 21 87085 Process according to Claim 5, characterized in that the solvent desalting is carried out with a solvent selected from the group consisting of ethane, propane, butane, isobutane, pentane, isopentane, neopentane, hexane, isohexane, heptane, mono-olefin equivalents thereof and mixtures thereof.