US2917452A - Catalytic reforming process and pretreatment of feed stock - Google Patents

Description

Dec- 15, 1959 J. M. BROOKE Erm. 2,917,452

CATALYTIC REFORMlNG PROCESS AND PRETREATMENT OF FEED STOCK Filed May 28, 1956 Y 2,917,452 Patented Dec. l5, 1959 CATALYTIC REFORMING PROCESS AND PRE- TREATMENT OF FEED STOCK Jesse M. Brooke, Sweeny, Tex., and Forest E. Gilmore,

Bartlesville, Okla., asslgnors to Phillips Petroleum Company, a corporation of Delaware This invention relates to an improved catalytic rereforming and sulfur removal process.

The catalytic reforming of gasoline-boiling-range hydrocarbons to improve their antiknock quality is a well developed commercial process.' A great many available feed stocks for catalytic reforming contain deleterious amounts of sulfur and it is common practice to subject the feed stock to a desulfurizing treatment prior to passing the feed to a catalytic reforming zone.- Av common catalyst for use in reforming processes comprises platinum in concentrations of 0.1 to 2 or 3 percent on a suitable porous support or carrier, such as silica-alumina or alumina which may contain a small. concentration of combined fluorine. Various other well known reforming catalysts are commercially available -for reforming processes. A feed to be treated is contacted with the catalyst in admixture with free hydrogen under substantial pressure and at an elevated temperature controlled to provide the desired reformation of the feed stock. It has been discovered that in many commercial reforming processes, even where the feed stock is desulfurized before being passed to the reforming zone, an excessive amount of corrosion has been occurring in the iron equipment which is contacted with the feed at high temperatures. This is particularly true in the charge preheater furnace upstream of the catalytic reactor Where losses of as much as 0.04 inch of metal were experienced in a 6 months period under normal operating conditions. This is found to be common experiencewith catalytic reformers and is so serious that the National Association of Corrosion Engineers has 'delegated a special committee to investigate the problem.

This invention is concerned with la practical solution of the corrosion problem in a catalytic reforming process as applied to gasoline-boiling-range hydrocarbon feed stocks containing minor but deleterious amounts of sulfur.

It is an object 'of the invention to provide a process for reforming gasoline-boiling-range hydrocarbons containing minor but deleterious amounts of sulfur. Another object is to provide a method of reducing corrosion of equipment in a catalytic reforming process due to sulfur present in the feed. A further object is to provide a method of reducing the sulfur content of a hydrocarbon feed stock so as to render the same substantially non-corrosive at high temperatures. -Other objects of the invention will become apparent from consideration of the accompanying disclosure.

In order to provide a clear understanding of the invention, reference is made to the accompanying schematic drawing which shows a flow of a reforming process in accordance with the invention. A suitable charge stock comprising a gasoline-boiling-range hydrocarbon fraction, such as a straight run fraction from a crude distillation unit, is passed via line 10 to a desulfurizing zone as pelleted montmorillonite, an aluminum silicate clay.

Other desulfurizing agents include bauxite, synthetic aluminas, etc. The partially desulfurized efuent is passed via line 14 to fractionator 18 for removal of a heart cut to .be fed by the reformer. In some instances it is desirable to also pass the charge stock thru an additional treating zone such as zone 16 in which the charge stock is contacted with a caustic or amine treating solution which is effective in sulfur removal. In fractionation zone 18 light hydrocarbon material formed in the` desulfurizing step and/or present in the original charge stock, together with HZS and water present in the feed or resulting from the desulfurizing step, are taken overhead thru line 20. Heavy hydrocarbons not suitable for the reforming step are removed via` line 22 and may be charged to a catalytic cracking z'one or to other use as desired. The heart cut from fractionator 18 is pumped via line 24 by pump 25 thru heater 27 to a second desulfurizing zone 26 where the partially desulfurized feed is contacted with a readily suldable or sulfur-accepting metalV under sulliding conditions so as to further deplete the sulfur content of the feed. The sulfur-denuded feed is then passed via line 28 to preheater l30 where `the same is raised to the desired reaction tempressor 46 in line-48 is utilized to boost the hydrogen pressure suicient to permit introduction to line 24. The reformate is recovered from separator'38 in line 40 thru which it is passedk to further processing as desired.

It is in a catalytic reforming plant such as that shown in the drawing, with the exception of desulfurizing zone 26 and the recycle of the hydrogen thru this desulfurizing zone, that we have observed excessive and intolerable corrosion of the equipment particularly in charge preheating zone 30. This is surprising ybecause of the fact that substantial sulfur removal from the charge stock has been effected so that the charge stock is considered substantially sweet It is believed that one probable cause of corrosion is the buildup of sulfur in the hydrogen recycle stream. The minor quantities of sulfur in the charge stock passed to the catalytic reformer substantially all appear in the form of HZS in the hydrogen recycle stream and by continually recycling hydrogen the HZS-content of the recycle stream and consequently ofthe charge stream to the preheater and reformer increases to the point Where the net effect is excessive corrosion, particularly in heating zone 30 where theV hot feed stream has the first opportunity to attack the metal tubing. f

In accordance with the invention, a final sulfur removal step is effected on the charge stock just prior to its introduction to the charge preheater (zone 30). This sulfur removal step comprises contacting the feed with a sulfur-accepting metal under metal sulfiding conditions so as to substantially reduce the residual content of the charge stock to a low level which is not unduly corrosive to metal conduits downstream of the desulfurizer. The hydrogen recycle stream containing substantially all of the sulfur in the eluent from the catalytic reforming zone is recycled to the final desulfurizer along with the charge stock (or separately) so that the HES content of the hydrogen recycle stream does not build up.

Metals which are suitable for the sulfur removal step in zone 26 include iron, copper, and silver. Iron is effective when utilized in particulate form such as shavings and cuttings obtained from machine shops or in the form of iron filings or reduced iron powder. Copper can 1be utilized in similar form. It is also feasible to distend 3. copper and/or silver-on refractory porous support material such as bauxite or' other porous alumina by methods well known in the art.

In operation of the process, two or, more vessels such as --vess'el f26- are manifoldedtogetherY in--known manner so--thabwhile one is on-stream Aeffecting sulfur removal, another fis-being regenerated.-Regeneration of the-particulate iron-is effected by-burning a suitable fuelgas-with excess-oxygen inside vessel 26 so as to convert the-iron -suliide formed during the sulfur removal-step to iron oxide thereby releasing HZS into ue gases. After substantially all of the iron suliidehas been converted to iron oxidehot hydrogen gas is passedthru the hotiron oxide particles so as to reduce the iron oXideto iron. It is also-possible to-utilize the iron oxide -for sulfur removal inasmuch as HZS reacts-With iron oxide to produce iron sullideand Awater but this Ais--not-desirable since water is deleterious in the reforming zonek- When utilizing copper -or silver in the form -of turnings, millings,--shavings,-or `other particulate form, or--deposited ordistended -on porous refractory material, as is preferable -with silver for reasons of economy, the regeneration is preferably effected by merely contacting the sulded metal with hot hydrogen thereby forming HZS which passes off inthe effluent gas. Usually the compressor discharge hydrogen (compressor 46) is hot-enough to eiecty the regenera- `tion and can be-removed via line 50 and -passedto the particular-vessel 26being regenerated atany given-time. In instances where thetemperature of the compressed hydrogen is insucient to be used in the regeneration step additional -heat may be readily added iin-well known manner. A relatively small amount of- H2 is required Vand it -may be-more feasible to heat the treater-material by-means of a re inside the treater before introducing the H2.

It might be well to note that copper-and-silver react rapidly with sulfur compounds in petroleum in 500 to 600 F., which indicates the preferred range of-temperature to be utilized when-desulfurizing with-v these metals. Copper sulfide reacts with hydrogen to vproduce-H25 at about 1600" F. so that a temperature of- -this -order -is suicient to `restore or regenerate the copper-treating agent. Silver sulfide reacts with hydrogen-topproduce H25 at 750 to 850 F. andregeneration-in-thisrange-is -likewse preferred when` utilizing silver-- asthe -treating agent. Since copper and silversuldes reactreadilywith steam to produce the oxides-and copperand -silver oxlides react with hydrogen at-600 F. to -produce-themetals, this regeneration route is-also feasible.

Inorder to illustrate -the invention--therfollowing--data are presented butare-not tobe interpretedY asunnecessarily limiting -the invention. 4A-charge'stockhavinga boiling range of 151 to 402 F. and an API @60 F./ 60 F. of 55.2 and-containing :187' weight percent-sulfur is fed via line to desulfurizing-zone .l2-packedwith -porousA bauxite where it is treated in-known manner to -with copper turnings. IThe low Ysulfur -content'g-cliarge stock is then passedvia line 28 to heating zone 30 where 'the--temperatureis raised Vtoabout v880" vF-.iwhich is--the temperature maintained in reactor -34-along-with--a- -pressure of 560 p.s.i.a. The;l1ydrogentooil-mol` ratio 4in reactor 34 is-maintained atabout 8 tov-1 with anhourly 'space velocity of approximately -3 barrels of oil perhour per barrel of catalyst using commercial platinum reforming catalyst. The hydrogen sulfide concentration in the recycle streamin line-'48-amounts to-0.0lgrain per 100 s.c.f. In conventional operation without sulfur removal in zone 28 the hydrogen sulfide concentration in the hydrogen recycle line runs between 0.5 and 10 grains per 100 s.c.f. depending upon the sulfur content of the feed stock and the percent ofremoval of sulfur in zones 12 and/or `16. In-fthistype of operation in accordance with the inventionV corrosion of ,the apparatus in preheater 30 and reactor 34 is substantially negligible.

In regenerating,,the,;copperA turnings in vessel 26,-hydrogen from line50 is heated-.in a conventional indirect heat exchanger to a temperature of about 1600 F. and is passed into.,alternategvessell(ofstream) so as to contact the copper sulfdeand convert the same to metallic copper.

Normally, the initial sulfur removal step removes at leastand up to 90 or more percent of the sulfur from 'the feed-stock, while at--least 65--and,'preferably,70 or more percent of the -remaining-sulfur-in the feed is removed in the sulfurremoval step-just--preceding the 4preheating of: the `feedto -reactortemperature.Y Since 'separation lzone 38 is-maintained at relatively -high pressures,

-suchas about-450 p.s.i.a., only atsmallramount of com 4pression is requiredlin-line-f48 morder-to-reintroduce the recycled hydrogen stream to fthe feed streamv in line 24 where the pressure is only about-600 p.s.i.a., requiring al recycle pressure in line 48 downstream ofcompressor 46in the neighborhood of1613-p.s.i.a. AA significant advantage of the invention resides inftbe fact that-the feed stream isdepleted ofrmost of the sulfur content at Alow pressure in the absence ofhydrogen-which, of course,

is more economical than treatment-athigher.pressure and the high pressuretreatment Awith hot metal is rpositioned in .line-24below pumpor compressorzZS wherefhighpressure is conventionally maintained thereby avoiding a spelcial compression step. Another advantage lies in the fact that bauxite and caustic-treatmentare more ,economical when applied to sulfur removal from-streams inwhich .the sulfur concentration -is relatively high than sulfur removal by contact with hot metalbut thelatteris more eiective'in removing lower concentrations of sulfur.V The `process of the invention is` particularly applicable to ,the

treatment of feed stocks containing at;least,0.05 weight percent sulfur and the sulfurcontent isusually reduced to below 0.003 weight percent by the.process,of the invention.

Certain modifications; of4 theiwirtvention-A will- `become apparent to-.those skilled-in .thegart-and the4 illustrative details disclosed arenot to be construed as imposingun- .necessarylimitations on the invention.

We claim:

Yl. A process for reforming agasoline vboiling range hydrocarbon stockcontaining at least 0.05weight percent sulfur, which comprises contacting said stock in a first-desulfurizing zone with a solid f particulate desulfurizing A agent so as to remove the -major portion -of ,said sulfur;

" of free hydrogen to produce a suitable reformate.

2. The process of claim l including thestep of recovering a hydrogen-containingvstream from said reformate 'including a minor amount of HBS- and recycling same to said second desulfurizing zone.

3.*Thc'process of claim lwherein the metal sulfide formed in said secondl desulfurizing zone is periodically regenerated by oxidation and then reduction with hydrogen.

4. The process of claim 3 wherein said metal comprises particulate iron.

5. The process of claim 1 wherein said metal comprises copper and the resulting copper sul-ide is periodically regenerated by reduction with hot hydrogen at a temperature of at least 600 F.

6. The process of claim 1 wherein said metal comprises silver and the resulting silver sulde is periodically regenerated by reduction with hot hydrogen at a temperature in the range of 750 to 850 F.

7. A process for reforming a gasoline boiling range hydrocarbon stock containing at least 0.05 weight percent sulfur, comprising the steps of contacting said stock in a first desulfurizing zone with a solid, particulate desulfurizing agent and removing light ends including H2S from the eflluent so as to reduce the sulfur content to below 0.010 weight percent; passing the resulting stock to a second desulfurizing zone in contact with a suliidable metal at a temperature of at least 500 F. and in the presence of recycled hydrogen so as to form metal sulde and reduce the sulfur content of said stock to below 0.003 weight percent; thereafter heating the resulting stock to reforming temperature; reforming the heated stock in admixture with desulfurized hydrogen in contact with a platinum reforming catalyst under reforming conditions so as to produce an improved reformate; recovering an H2 fraction from said reformate containing residual sulfur in the form of HZS; and recycling said H2 fraction to said second desulfurizing zone as said recycled hydrogen.

8. The process of claim 7 wherein said metal comprises essentially iron in particulate form.

9. The process of claim 7 wherein said metal comprises essentially copper in particulate form.

10. The process of claim 7 wherein said metal comprises essentially silver distended on a porous refractory support.

11. The process of claim 7 in which said desulfurizing agent comprises bauxite.

12. The process of claim 7 wherein the sulfur content of the feed stock is reduced to the extent of at least 80% in first said desulfurizing zone and wherein at least 70% of the sulfur in the combined feed and recycle streams is removed in said second desulfurizing zone.

13. The process of claim 7 wherein the pressure in said rst desulfurizing zone is low and the pressure in the second desulfurizing zone is of the order of 600 p.s.i.a.

14. A process for reducing the sulfur content of a hydrocarbon feed containing at least 0.05 weight percent sulfur which comprises contacting said feed and reducing the same to below 0.003 weight percent, thereby reducing the corrosion effect of said feed in a rst desulfurizing zone with a solid, particulate desulfurizing agent so as to remove at least percent of said sulfur and thereafter contacting the partially desulfurized feed in a second desulfurizing zone with a sulfur accepting metal under metal sulfide-forming conditions including a temperature in the range of 500 to 600 F. so as to remove at least 70 percent of the remaining sulfur therein and reducing the same to below 0.003 weight percent, thereby reducing the corrosion effect of said feed.

15. 'I'he process of claim 14 wherein said metal comprises essentially particulate iron.

16. The process of claim 14 wherein said metal comprises essentially copper.

17. The process of claim 14 wherein said metal comprises essentially silver dispersed on a porous refractory support.

18. In a process for reforming a gasoline boiling range hydrocarbon stock containing a minor but substantial amount of sulfur comprising the steps of contacting said stock in a desulfurizing zone with a solid particulate desulfurizing agent so as to reduce the sulfur content to not more than 0.010 weight percent; removing light ends including resulting H2S from said stock; reforming the remaining stock in admixture with free hydrogen in a catalytic reforming zone so as to produce an improved reformate; recovering an H2 fraction containing HzS formed in said reforming zone from said reformate; and recycling said H2 fraction to said reforming zone without sulfur removal whereby the residual sulfur from the desulfurizing step and recycling of same in said H2 fraction results in excessive corrosion of metal in said reforming zone: the improvement comprising passing said remaining stock, together with said H2 fraction, to a second desulfurizing zone in contact with a readily suliidable metal and forming metal suliide therein so as to reduce the sulfur content of the feed stock to said reforming zone not more than 0.003 weight percent of said feed stock before passing same to the reforming step.

References Cited in the file of this patent UNITED STATES PATENTS 2,151,721 Schulze Mar. 28, 1939 2,315,144 Watson Mar. 30, 1943 2,376,086 Reid May 15, 1945 2,417,308 Lee Mar. 11, 1947 2,671,754 De Rosset et al Mar. 9, 1954 2,746,907 Hanson May 22, 1956 2,758,059 Berg Aug. 7, 1956 2,769,758 Porter et al. Nov. 6, 1956 2,769,763 Annable et al Nov. 6, 1956 2,773,008 Hengstebeck Dec. 4, 1956 2,891,540 Kimbcrlin et al May 7, 1957 R UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION December 151 1959 Patent No., 2,917,452

Jesse Mo Brooke et al.,

52 and 53, strike out a:x1d reducin thereby reducing the ight percentv eeoV; column 6v line 36L after "zonen Column 5, lines 5ls the same to below 0.003 we corrosion effect of said f insert to Signed and sealed this 9th day of August 1960a (SEAL) Attest:

KARL H., AXLINE ROBERT C. WATSON Commissione;` `of Patents Attesting Ofcer

Claims (1)

1. A PROCESS FOR REFORMING A GASOLINE BOILING RANGE HYDROCARBON STOCK CONTAINING AT LEAST 0.05 WEIGHT PERCENT SULFUR, WHICH COMPRISES CONTACTING SAID STOCK IN A FIRST DESULFURIZING ZONE WITH A SOLID PARTICULATE DESULFURIZING AGENT SO AS TO REMOVE THE MAJOR PORTION OF SAID SULFUR; FRACTIONATING THE PARTIALLY DESULFURIZED STOCK SO AS TO REMOVE AT LEAST THE LIGHTER COMPONENTS, INCLUDING H2S; CONTACTING THE REMAINING STOCK WITH A SULFUR-ACCEPTING METAL IN A SECOND DESULFURIZING ZONE UNDER METAL SULFIDE-FORMING CONDITIONS INCLUDING A TEMPERATURE OF AT LEAST 500*F. SO AS TO REMOVE THE MAJOR PORTION OF THE REMAINING SULFUR AND REDUCE THE SULFUR CONTENT BELOW 0.003 WEIGHT PERCENT; AND PASSING THE RESULTING STOCK TO A CATALYTIC REFORMING ZONE IN CONTACT WITH A REFORMING CATALYTIC MAINTAINED UNDER REFORMING CONDITIONS INCLUDING A SUBSTANTIAL AMOUNT OF FREE HYDROGEN TO PRODUCE A SUITABLE REFORMATE.

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