US2717855A - Hydrodesulfurization of heavy oils - Google Patents

Description

sept. 13, 195s E. W. S. NICHOLSON HYDRODESULFURIZATION OF HEAVY OILS 2 Sheets-Sheet 1 ou o o 2 o u In LQ. NMYFJW j AI ...01. mu 23u 0T( .E .a anvow. .Nhlr v NwJuUm.. (o 'l Nm zal: m mwo. Mwhuiww mr L3 v n F wm om :ai .Sv Saw 113.12 ON. I lu: Al WN. .WN dmJoOU .UUOOGQ .mE Iwmu. QN. Aymhn* Jfdnv OMNLQDWJDUMO. NuJoOw. .O

Filed July 28 1951 dworc 1575.17 icuolson. 3fm/enter Sept. 13, 1955 E. w. s. NICHOLSON HYDRODESULFURIZATION OF HEAVY OILS Filed July 28 1951 2 Sheets-Sheet 2 Nmmuu N IHL r Q@ vll.. C l am: Ef .m m im? l i e o @www M W rv LA, T t umano, Q N w 4| @wv NN Hw M lv mv wuol+ w mr l d m .uDOOQQ 5. Nm lo# m QF M @uw 20w .UQOONQ 1).... (BH. .fohulxm .w D :211| OuNDkJomuQ d moom 104).? moyvommmulnlw .E 024 .m.\,. il: f n NN u Y .WN Y (0N, ww. dmbh .OT'M Lqwll wQwjOOU M ,.Nwnmww. mT (E. [Il I l- IJ-I @UQ/ s United States Patent O 2,717,855 HYDRGDESULFURIZATION OF HEAVY OILS Edward W. S. Nicholson, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corpora tion of Delaware Application July 28, 1951, Serial No. 239,100 7 Claims. (Cl. 196-24) The present invention relates to the treatment of sulfurcontaining organic materials, in particular, sulfur-bearing hydrocarbon material, to desulfurize the same. More particularly, the present invention relates to the desul* furization of sulfur-containing petroleum fractions, particularly heavy fractions as residua.

The problem of sulfur removal from petroleum fractions and crudes is as old as the petroleum industry. For most purposes it is undesirable to have an appreciable amount of sulfur in any petroleum products. Gasoline should be relatively sulfur-free to make it compatible with lead. Motor fuels containing sulfur as mercaptans are undesirable because of odor and gum formation characteristics. Sulfur is objectionable in fuel oils of any kind because it burns to form SO2 which is obnoxious and corrosive.

Sulfur occurs in petroleum stocks generally in two main forms, as mercaptans and as part of a more or less substituted ring, of which thiophene is the prototype. The former type is generally found in the lower boiling fractions, in the naphtha, kerosene, and light gas oil material, whereas the ring-sulfur compounds form the bulk of the sulfur-bearing material of the high boiling petroleum fractions. Numerous processes for sulfur removal from relatively low molecular weight and lower boiling fractions have been suggested such as doctor sweetening, wherein mercaptans are converted to disulfdes, caustic treating, solvent extraction, copper chloride treating, etc., all of which give a more or less satisfactory decrease in sulfur or inactivation of mercaptans by their conversion into disuldes. The latter remain in the treated product, and must be removed if it is desired to obtain a sulfur-free product.

Sulfur removal from higher boiling fractions however, has been a much more difficult operation. As pointed out, here the sulfur is present for the most part, as a part of a ring. Such sulfur is, of course, not susceptible to chemical operations satisfactory with mercaptan sulfur. Also, extraction processes are unsatisfactory, for solvents specific for sulfur compounds, for instance, boron fluoride complexes or liquid hydrogen fluorideboron fluoride mixture, or liquid SO2, no longer are of much use when possibly every molecule of the oil contains a sulfur ring. Thus, a high boiling product, such as a residuum that contains about 3% of sulfur is estimated to consist extensively of molecules containing sulfur, and so extraction of sulfur-containing material is no longer feasible, inasmuch as the bulk of the extracted material is in the extract and lost, unless a means is present for removing sulfur from this extract.

One satisfactory method for removing sulfur from products wherein it is present as a ring type compound, has been by hydrogenation in the presence of a so-called sulfactive catalyst. Thus, it has been found that certain catalysts, such as cobalt molybdate, tungsten sulfide, nickel sulfide, molybdenum sulfide, etc. are good hydrogenation catalysts and that when these catalyst substances are employed in the hydrogenation of petroleum stocks ICC containing sulfur, these catalysts are not poisoned by sulfur, but on the contrary, tend to reduce the sulfur content of the material being hydrogenated, the sulfur being removed as HzS. However, though this process is quite satisfactory for the hydrogenation, or hydrodesulfurization of low and medium boiling petroleum fractions, the process is completely unsatisfactory for sulfur removal from high boiling stocks, such as cycle stock and residua. The latter, which are the bottoms product after the l050 F. gas oil is taken overhead, are notorious carbonizers. When they are passed over a fixed bed of a sulfactive catalyst of the type described above in order to remove a portion of the sulfur content by catalytic hydrodesulfurization, carbonization of the catalyst proceeds at once, and in an extremely short time, the catalyst is covered by deposition of carbonaceous material and is inactivated. Regeneration is expensive, and since the period of activity is so short, it is economically unfeasible to operate with such a process.

Closely allied to the problem of carbonization and rapid deactivation of the catalyst is the contamination of the latter by ash. Most heavy oils, and particularly crude residua, have high ash contents; the latter may comprise salts and particularly oxides, of iron, magnesium, silica, nickel, vanadium, alumina, etc., and the total ash content of high sulfur residua may be in the range of l0 to 1000 lbs. per 1000 barrels of crude. These ash-forming constituents, upon heat treatment during hydrodesulfurization, precipitate upon and rapidly deactivate the catalyst by agglomerating upon the surface thereof.

It is, therefore, an object of the present invention to provide an improved method of desulfurizing sulfurbearing organic materials, in particular desulfurizing high boiling stocks such as residua which have also high ash content.

A further object of the invention is to provide an improved means of upgrading heavy stocks such as residua without prematurely inactivating the catalyst.

Other objects and advantages of the present invention will become apparent from the following description, read in conjunction with the accompanying drawing describing one embodiment of the present invention.

In accordance with the present invention, the crude residua are de-ashed by rst preheating and then heat soaking the stock to agglomerate the ash-forrning constituents. The total feed plus the agglomerated ash is then added, with or without prior filtration, to a sump phase hydrogenation unit. Any type of hydrogenation catalyst may be employed; preferably an expendable catalyst that may be discarded after hydrodesulfurization is employed. Because of the prior heat-soaking-agglomeration step, the finely-divided ash particles are agglomerated in the soaker rather than in the presence of the catalyst, thus substantially increasing the life of the latter and contributing to a more ecient process. Residua are of little commercial value per se, because of their high coking characteristics and sulfur content, and their high ash and asphaltene content. In accordance with the present invention they may readily and economically be converted into useful products, such as feed stock for catalytic cracking or for bunker and marine fuel, neither of which can tolerate high sulfur content.

The invention will best be understood when read in conjunction with the accompanying drawings, which are diagrammatic representations of preferred embodiments of the present invention. V

Turning now to Figure I, wherein is shown a procedure for hydrosulfurizing and upgrading a heavy residuum, such as Kuwait bottoms, the heavy petroleum stock to be desulfurized is pumped through line 2 and preheater 4, wherein it is preheated to about 700-900 F., and

then is passed into heat soaker 6. The feed is allowed to remain in the soaker for a period of about 0.5 to 5 hours for most effective agglomeration. Pressures within 6 may be substantially the same as those used in carrying out the hydrodesulfurization reaction in reactor 10 as hereinafter described, that is, in the range of 1.00 to 1000 p. s. i. g. Means (not shown) for maintaining the soaking temperature at the desired level may be incorporated in soaker 6.

As a result of the soaking, a considerable proportion of the dissolved, suspended, and colloidally dispersed ash particles are agglomerated to a particle size readily filterable. Furthermore, a substantial proportion of the unstable asphaltenes and coke-forming constituents are precipitated in the soaker, thus preventing their later precipitation in the hydrogenator, where they would foul and inactivate the catalyst.

After sufficient soaking, when agglomeration is substantially complete, the hot product is passed via line 8 to hydrogeuation reactor 10, together with suspended agglomerated ash particles. lf desired, a hot settler or filtration unit 12 may be incorporated between the soaker and the hydrogenator; this embodiment is employed when it is desired to recover hydrogenation catalyst. However, in a preferred embodiment of the invention an expendable hydrodesulfurization catalyst is employed, and spent catalyst and agglomerated ash particles are removed from the system together and discarded.

Fresh catalyst, such as bauxite, activated alumina, pyrites ash, activated carbon, or cobalt molybdate impregnated on cheap forms of alumina, which may readily be discarded because of its cheapness and availability, is fed to the system from vessel 13. A good method of adding catalyst is to form a slurry with previously desulfurized product. The slurry is pumped via line 14 to hydrogenation reactor 10.

Reaction conditions within hydrogenation reactor 10 are preferably temperatures from about 600 to 1000 F. and pressures ranging from about 100 to 1000 p. s. i. g. Catalyst is added to reactor 10 through line 14 at a rate of about l to 50 pounds of catalyst for each barrel of oil fed through line 2. The reactor is operated so that the catalyst will be held in a concentrated suspension in oil within the reactor in order that maximum utilization of all the catalyst particles added will be obtained before they are carried overhead in the effluent oil stream. The average residence time of the catalyst particles in the reactor may be in the order of l to 500 hours. The residence time of the catalyst particles in the reactor is determined by reactor oil velocity, recycle gas velocity, and catalyst particle size and density. Each of these variables may be changed over wide limits, and many combinations of them may be used to obtain the desired results. In general, however, reactor oil velocities are in the range of 0.001 to 1 ft./sec.; recycle gas rates of 500 to 5000 cubic feet/barrel of oil feed are used; the catalyst is usually of a fairly narrow size range within the broad general range of 10 to 300 mesh; and the catalyst particle density may vary from about 0.7 g./cc. for activated carbons to about g./cc. for pyrites ash. The reactor volume is equivalent to 0.5 to times the volume of oil fed per hour. For the larger reactor volumes (required with less active catalysts) it is necessary to use finer catalysts in order that they will be entrained overhead at the necessarily low velocities in a reactor of reasonable height (although several reactors in series may be used). It is also possible in such cases, however, to increase reactor velocity by recirculating to the reactor inlet hot liquid product taken before the hot filter 24.

The product stream containing in susp'ension considerable amounts of carbonaceous solids, ash, asphaltenes, and catalyst is withdrawn continuously overhead from reactor 10 through line 20, passed through partial cooler 22, wherein the mixture may be cooled to about 200 to 4 500 F., and then is passed to filtration unit 24, of conventional design. Because of the heat soaking step, the ash particles are of size large enough to be retained by the filter. Catalyst and ash, as well as carbonaceous residue, are withdrawn. Because of the problem of separating the spent hydrogenation catalyst from ash particles, it is preferred to operate with an expendable catalyst, and so the residue from filter 24 may be discarded.

The filtrate, comprising the upgraded residua, some lighter product resulting from hydrocracking, and dissolved and admixed gases and vapours, such aS H25, H2, and mercaptans, etc., is passed via line 26 and cooler 28, wherein the product is cooled to about 80 to 150 F., to gas-liquid separator 30. Liquid product is here sep arated from gases, and is withdrawn through line 32 for further processing to make a suitable catalytic cracking feed stock or bunker fuel, as by caustic or water washing, etc., all in a manner known per se.

Unreacted hydrogen and hydrogen sulfide are removed overhead from 30 through line 38. To prevent too high a sulfide content in the system, a portion of this gas stream may be purged from the system through line 34, and any known means of hydrogen sulfide recovery may be employed. The balance of the gas stream withdrawn overhead may be recycled through pump 36 and line 38 to the hydrogenation reactor.

Under some conditions the reactor velocity within 10 is of necessity quite low in order to avoid the employment of a reactor of an undesirable heighth-to-diameter ratio. This could be overcome to some extent by using two or more normal size reactors in series. Nevertheless, considerably more fiexibility is obtained by incorporating in the system, provision for recycle of hot reactor effluent liquid back to the reactor inlet. This permits operation of the reactor at such velocities that a moderately coarse catalyst can be used and a slurry consisting of catalyst and precipitated ash may thus be recycled to insure cornplete utilization of the catalyst. The average catalyst residence time in the reactor system is determined by the rate of drawoff of catalyst from the separator-settler.

Such a liquid recycle system is shown in Fig. 2 and may be described as follows.

The total reactor efliuent passes overhead through line to separator-settler 11 operated at essentially the same temperature as that in the reactor. Here hydrogen, hydrogen sulfide, and small amounts of low molecular weight hydrocarbons formed by cracking of the feed in the vreactor and hot soaker pass overhead through line 27, through cooler 29, to cold separator which is hereinafter described. Vessel 11 is designed to provide concentration by settling of the catalyst and precipitated ash materials in the reactor liquid products. This concentrated slurry is withdrawn from the bottom of the vessel 11 through line 17 and pump 19, and reintroduced into the bottom of reactor 10 through line 21 and line 8. The rate of circulation of this liquid through lines 17 and 21 may be at any desired rate to provide a desired velocity in reactor 10, and to insure complete utilization of the catalyst before discard.

Liquid product is Withdrawn from the separator-settler 11 through line 40. This point of drawoff is located near the top of the liquid level in vessel 11 so as to provide a minimum concentration of solids in the liquid stream, and this separation of solids from the withdrawn liquid is enhanced by providing a vertical bafe 1S within vessel 11. The liquid product withdrawn through line 40 passes through partial cooler 22, where the temperature is reduced to about 200-500 F., then to a hot filtration unit 24 where catalyst and precipitated solids from the feed are removed. The filtered liquid is vthen cooled in cooler 28 to about 80 -l50 F. and the liquid is combined with the gas stream separated from vessel 11 in cold separator 30. The desulfurized liquid product is withdrawn through line A32. Recycle gas rich in hydrogen is r returned to reactor 10 through line 38 and booster compressor 36. Gas may be purged through line 34 for trol of hydrogen sulfide concentration, and fresh hydrogen may be introduced through line 16.

The average residence time of the catalyst in the reactor in series with the soaking zone. By operating in accordance with the process of the invention, it is thus possible to achieve high eciencies and extended periods of operation without necessity of shutdowns.

Example I The effectiveness of the heat soaking step as a means for agglomerating the ash and reducing thereby the catalyst contaminating quality of the feed to the hydrodesulfurization stage may be shown in the following specific example in whimh Kuwait reduced crude containing 19.2 lb./ 1000 bbl. of soluble ash was treated.

Temperature, F. 775

Pressure, p. s. i. g. 500

Holding time, hr. 3.0

Soluble ash in product, lb./ 1000 bbl. 2.7 Example II The greatly improved activity and life obtained from the catalyst when using a heat-soaked, low soluble-ash feed as compared to the results obtained with the untreated feed are shown from the following data taken during experiments with a Kuwait reduced crude using a cobalt molybdate on alumina catalyst.

These data clearly show the sustained life of the hydrogenation catalyst resulting from the agglomeraton and removal of the colloidal ash particles as compared with the inactivation of the catalyst when hydrogenation is attempted on the unheat-soaked crude.

While the foregoing description and exemplary opera- Other modications may appear to those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The process of desulfurizing and upgrading a sulfurand ash-containing heavy petroleum fraction boiling above about 1050 F. which consists of preheating said fraction to about 700 to 900 F., passing said fraction to a heat soaking zone, maintaining a residence time within gen, dissolved metallo-organic compounds and finelydivided ash solids and thermally unstable high molecular weight constituents, maintaining said fraction substanzone, maintaining a temperature of about 600 to 1000 F. within said zone, maintaining a pressure of about and slurry catalyst is recycled to said hydrogenation zone.

3. The process of claim 1 wherein said hot filtration is carried out at a temperature of 200 to 500 F.

4. The process of claim 1 wherein said hydrogenation catalyst is bauxite.

5. The process of claim l wherein said hydrogenation catalyst is pyrites as 6. The process of claim 1 wherein said hydrogenation catalyst is cobalt molybdate supported on alumina.

7. The process of claim 2 wherein said reactor effluent and catalyst is passed to a separation zone and a concentrated stream of slurry catalyst and desulfurized petroleum product recycled to said hydrogenation zone.

References Cited in the le of this patent UNITED STATES PATENTS 1,955,862 Peck Apr. 24, 1934 2,121,046 Pew June 21, 1938 2,353,923 Nelson July 18, 1944 2,367,348 Harrington Ian. 16, 1945 2,371,298 Hudson et al. Mar. 13, 1945 2,417,308 Lee Mar. 11, 1947 FOREIGN PATENTS 345,738 Great Britain Apr. 2, 1931 493,470 Great Britain Dec. 31, 1937

Claims (1)

1. THE PROCESS OF DESULFURIZING AND UPGRADING A SULFURAND ASH-CONTAINING HEAVY PETROLEUM FRACTION BOILING ABOVE ABOUT 1050* F. WHICH CONSISTS OF PREHEATING SAID FRACTION TO ABOUT 700* TO 900* F., PASSING SAID FRACTION TO A HEAT SOAKING ZONE, MAINTAINING A RESIDENCE TIME WITHIN SAID ZONE OF ABOUT 0.5 TO 5 HOURS SUFFICIENT TO COAGULATE AND PRECIPITATE THERMALLY IN THE ABSCENCE OF ADDED HYROGEN, DISSOLVED METALLO-ORGANIC COMPOUNDS AND FINELYDIVIDED ASH SOLIDS AND THERMALLY UNSTABLE HIGH MOLECULAR WEIGHT CONSTITUENTS, MAINTAINING SAID FRACTION SUBSTANTIALLY IN THE LIQUID PHASE WITHIN SAID SOAKING ZONE UNDER A PRESSURE OF ABOUT 100 TO 100 P.S.I.G., PASSING SAID THERMALLY TREATED LIQUID MATERIAL CONTAINING IN SUSPENSION COAGULATED AND PRECIPITATED SOLIDS TO A HYDROGENATION ZONE, MAINTAINING A TEMPERATURE OF ABOUT 600* TO 1000* F. WITHIN SAID ZONE, MAINTAINING A PRESSURE OF ABOUT 100 TO 1000 P.S.I.G. WITHIN SAID ZONE, PASSING TO SAID ZONE A HYDROGEN-CONTAINING GAS AND 1 TO 50 POUNDS OF A HYDROGENATION CATALYST PER BARREL OF SAID THERMALLY TREATED LIQUID MATERIAL, COOLING LIQUID EFFLUENT FROM SAID HYDROGENATION ZONE, PASSING PRODUCT TO A HOT FILTRATION ZONE AND RECOVERING AN UPGRADED LIQUID PETROLEUM FRACTION OF SUBSTANTIALLY DECREASED SULFUR AND ASH CONTENT.

Images