US3007849A - Stepwise desulfurization of fluid coke particles with steam and hydrogen - Google Patents

Description

United States Patent Ofiice 3,007,849 Patented Nov. 7, 1961 No Drawing. Continuation of application Ser. No. 472,234, Nov. 30, 1954. This applicationJan. 31, 1958, Ser. No. 712,331

11 Claims. (Cl. 202-31) This invention relates to improvements in desulfurizing and activating coke particles containing high percentages of sulfur. More particularly, it relates to the desulfurization of high sulfur petroleum coke particles from the fluid coking process by subjecting the coke particles to a stepwise treatment at elevated temperatures with steam followed by hydrogen.

This application is a continuation-impart of application, Serial Number 472,234, filed November 30, 1954, by the present inventors and now abandoned.

There has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation the heavy oil to be'processed is injected into the reaction vessel containing a dense turbulent fluidized bed of hot inert solid particles, preferably coke particles. -A transfer line reactor or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partiallyvaporized'and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate. A stream of coke is transferred from the reactor to the heater or burner vessel, such as' a transfer line or fluid bed burner, employing a standpipe and riser system; air being supplied to the. riser for conveying the solids to the burner. Suflicient coke or other carbonaceous matter'is burned in the burning vessel with anoxygen-containing gas to bring the solids therein up to a temperature suflicient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% to' 15% of coke, based on the feed, is normally burned for this purpose. The unburned portion of thecoke represents the netcoke formed in the process and is withdrawn after the required amount for heat. balance in the system has been recycled,

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A.P.I. gravity of about to 20, and a Conradson carbon residue content of about to 40 wt. percent. (As to Conradson carbon residue see A.S.T.M.. Test D-l80-52).

It is preferred to operate with solids having a particle size ranging between 100 and 1000 microns-in diameter sulfur, content coke is desired for the manufacture of with a preferred average particle size range between 150 and 400 microns.

The withdrawn product coke nately, i.e., about 60-90 wt. 150 to 850 microns.

The method of fluid solids circulation described above is well known in the prior art. Solids handling technique is described broadly in Packie Patent 2,589,124, issued March 11, 1952.

Fluid coking has its greatest utility in upgrading the quality of low grade petroleum vacuum residua and pitches from highly asphaltic and sour crudes. Such residua frequently contain high concentrations of sulfur, i.e. 3 wt. percent or more. In general the sulfur content of the coke product from the fluid coking process is about 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residue thus can range from 5% to 8% sulfur or more.

The. high sulfur content of the coke product poses a major. problem in its efficient utilization. For many nonfuel or premium fuel uses a low sulfur content coke, about or below 4 wt. percent sulfur is required. Activated cokes containing a maximum of 4% sulfur are desirable and have many applications. For example, low

has a diameter predomipercent, in the range of about phosphorous, for the production of calcium carbide, for lime burning in the manufacture of soda ash or other alkalis, for various metallurgical applications, for. the production of electrode carbon for various electrochemical applications such as the manufacture of aluminum and the like. Further, coke of high surface area is useful as an absorbent in a number of processes.

The conventional methods of removing sulfurfrom coke from ordinary sources with gaseous reagents have in general not been too satisfactory. The results are even poorer when these procedures are applied to fluid coke as compared to delayed coke or coal. A treating gas has relatively difiicult access to the sulfur in fluid coke compared to other carbons since fluid coke is laminar in structure and may comprise some 30 to 100 superposed layers of coke. Thus, it is diflicult for a reagent, such as a treating gas, to penetrate more than a few outer. layers. These difliculties associated with the treatment of the fluid coke are even further compounded because of the beforementioned possible higher than normal sulfur content of the coke derived from high sulfur petroleum feeds- Thus methods which are efiicient in treating coal or conventional cokes may prove to be ineffective .in treating highly laminarfluid coke.

While use of a very high temperature, thermal desulfurization of fluid coke, i.e. temperatures above 2200 F. has been proposed, the expensive refractory materials required forthe treating vessel and the cost of utilizing high temperature levels have offered significant disadvantages. In addition, liberated hydrogen sulfide, becomes highly corrosive at these high temperature levels. While low temperature thermal operations might appear to solve some of the aforementioned difliculties, the excessive treating periods such operations may require for the desired degree of desulfurization make such methods completely impractical for of material. V

The present invention provides an improved process of lowering the sulfur concentration of fluid coke. The

the treatment of large quantities process comprises subjecting high sulfur content, fluid and thus make form treatment. This steam treatment is then followed 7' by a hydrogen treatment at 1200 to 1700 F. whereby the sulfur content of the fluid coke is reduced to 4 wt. percent or less. Good overall yields of a low sulfur content, high surface area fluid coke-product is thus obtained. The increase in surface area due to the high temperature steam activation is generally not diminished by the subsequent hydrogen step.

It is indeed surprising that the present two step process, wherein fluid coke is subjected to individual steam and hydrogen treatments, the steam serving to activate the fluid coke to a surface area above about 300 square meter/ gram, is highly effective in desulfurizing fluid coke. Treatment with hydrogen or steam alone, at temperatures equivalent to that presentlyemployed, fails to give desired sulfur reduction to less than 4 wt. percent. Similarly, treatment with a mixture of steam and hydrogen, rather than the stepwise treatment taught, gives distinctly inferior results. Further, when the product of the steam treatment is not sufficiently activated, i.e. increased in surface area to the present high levels, the required degree of sulfur reduction is not obtained.

With regard to the process conditions employed, the

initial steam treatment is conducted so as to increase the surface area of the fluid coke to above about 300 square meter/ gram. Steam temperatures are greater than 1300", preferably falling in the range of 1400 to 1600" F. While the time interval is dependent upon the temperature employed, it generally ranges from 2 to hours, preferably 3 to 8 hours. The severity of the steam treatment is sufliciently great to give a fluid coke particle of the desired high surface area. Thus the overall quantity of steam used will normally be in excess of about 300 wt. percent (based on fluid coke). Pressures of l to 5 atmospheres are advantageously employed.

' The hydrogen treatment is conducted at a temperature in the range of 1200 to 1700 F. The time interval utilized is in the range of 0.5 to 6 hours, preferably 1 to 4 hours. The amount of hydrogen utilized is in the range of 100 to 4000 v./v. coke/hr. (vol. of gas at S.T.*P./'vo1. of coke/hr.) with the partial pressure of the hydrogen in the treating gas being in the range of 350-750 mm. for atmospheric operation. Inerts, e.-g., nitrogen, 'rnethane, etc., may be used as diluents. The partial pressure of the hydrogen will be correspondingly higher at elevated pressures. Use of moderate elevated pressures, e.g., 1 to 5 atmospheres, is preferred.

The hydrogen-containing gas can be obtained from the gas produced in the coker after removal of most of the hydrocarbons formedin thecokin'g operation. Other sources of hydrogen include the pure gas or the tail gas from a hydroformer. The hydrogen-containing gas is preferably treated in the conventional manner to remove hydrogen sulfide and other sulfur-containing compounds before use.

The stepwise steam and hydrogen treatment of the fluid coke can be conducted while the latter is .in the form of a dense turbulent fluidized bed, a moving bed or'a'fixed bed, usually depending on the equipment avail-. able. 7

Reference to the following examples will further show the advantages 'of the present invention.

EXAMPLE I A sample-of fln'id coke having a surface area of less than 5 mF/g. (square meters per gram) and containing 7.6 wt. percent of sulfur was activated in a fluid bed by treatment with steam at atmospheric pressure and at a temperature of about 1500 to 1 600" F. for an 8 hour period, the steam being utilized at an overall amount of 350 wt. percent based on fluid coke. A 76% yield of a fluid coke product having a surface area of 330 m.'*./ g. was thus obtained. Upon treating this activated coke withhydrogen at a rate of about 3000 v./v./hr., a.9 6% yield of material (based on the activated fluid :coke) having a sulfur content of 3.9% was realized. The hydrogen treatment was carried out at atmospheric pressure for 2 hours at 1300 F. and the surface area of the fluid coke product obtained was about 335 mF/ g. When the hydrogen treating time was doubled, i.e. extended to 4 hours, the fluid coke product obtained contained about 3.5% sulfur.

This example illustrates that the present two-step process successfully reduces the sulfur content of the fluid coke to less than 4 wt. percent. It further indicates that the ability of hydrogen in removing sulfur from the activated fluid coke is manifested largely in the initial period of hydrogen treatment, since doubling the period of hydrogen treatment only decreased the sulfur content by 0.4%.

EXAMPLE II The same activated fluid coke as described in Example I (surface area of 330 mF/g.) was treated with hydrogen for 1 hour at 1300 F. and at a pressure of 75 psi. The product contained 2.5% sulfur and had a surface area of 370 mP/g.

This example depicts that beneficial results are obtained by utilizing elevated pressures in the hydrogen treatment, e.g. 5 atmospheres.

EXAMPLE III The, same fluid coke as originally employed in Example '1 (surface area of 5 mF/g. and containing 7.6 wt. percent sulfur), was activated in a fluid bed with steam, using a total of 200 wt percent steam, on coke for a period of 5 hours. 'The product, representing an 83% yield, had a surface area of about 200 m. /,-g. When this material was treated under atmospheric conditions with hydrogen introduced at a rate of 1500 v./v./hr. for 2 hours at 1300 F., the sulfur was reduced to only about 5.3% while the surface area was maintained essentially constant at 200 m?/ g.

. The above illustrates that when the steam treatment has not su'fficiently increased the surface area of the fluid coke, the subsequent hydrogen step does not give a coke product of the desired low sulfur content. Further, when the fluid coke product of the steam treatment of Example III (surface area of 200 mfi/g.) was subjected to a 75 p.s.i. hydrogen treatment at 1300 F. for one hour, a hydrogen rate of 3000 v./v./l1r.being employed, the material produced still had a sulfur content greater than 4%. This illustrates that even elevated pressure was ineflective in giving the desired degree of desulfurization of the fluid coke of .insuflicientsteam activation.

EXAMPLE IV Another sample of fluid coke having a sulfur content of 7% and a surface 'area less than 5 m.*/ g. was activated with about 350m. percent steam on coke at 1500 F. for 3% hours to give a 77% yield of coke having a surface area in excess of 320 m.*/ g. When this activated coke was treated with hydrogen for 60 minutes at '1300 F., a product was obtained which had a sulfur content of 3.1% and a surface area in excess of 300 mL /g. The hydrogenation was carried out at atmospheric pressure and at a hydrogen rate of about 1500 v./v./ hr. It'is noteworthy that the previous conditioning of the coke, e.g. burner temperature, initial sulfur content, etc. affects the subsequent desulfurization to some degree.

i This example illustrates that the present two-step process effectively desu'lfurizes fluid coke. "When compared to Example III, the advantage of increasing the surface area of fluid coke to "at least 300 m.- /g. prior to hydrogen treatment so as to make the sulfur accessible to the hydrogen (and thus produce a product of less than 4 wt. percentsulfur) is to be noted.

EXAMPLE v I .In contrast to the above examples, the original fluid coke ofExample IV, when treated with hydrogen for 60 minutes at 1300" to 1500 F. and at atmospheric pressure, gave an 88% yield of product containing 5.1% sulfur. The surface area of the coke was not altered as a result of the hydrogenation. This demonstrates the necessity of preceding the hydrogen treatment with a steam tfeatment in order to increase the surface area of the coke and reduce the sulfur content to acceptable levels,

EXAMPLE VI To show that the present two-stage process has an advantage over a single stage treatment with a mixture of hydrogen and steam, the original coke of Example IV was treated with these .tively. The run was made at atmospheric pressure for gases in a 70/30 volume ratio, respec- EXAMPLE VII .When a mixture of hydrogen and steam (75-25 vol. ratio) was used in a fluid coke treat at 2400 F., the product coke had a low surface area and a sulfur content of 4.8%. The product coke had a density of 1.94. This latter treat was carried out for 120 minutes at atmospheric pressure with a gas rate of about 1300 v./v./hr. This demonstrates that even at temperatures far in excess of that required by the process of this invention a mixture of steam and hydrogen gives inferior results to the stepwise treatment.

The coke subjected to the treatment of this invention can also be calcined in the conventional manner if it is desired to increase the density and still further lower the volatile content, the resistivity and sulfur. Calcination is conventionally conducted at temperatures above 2000 F. in an atmosphere of air, nitrogen, oxygen, etc.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the coke was prepared. Higher temperatures are utilized in coking for chemicals.

Conditions in fluid coke) reactor Broad Range The advantages of the process of this invention will be apparent to those skilled in the art. The sulfur content is reduced to acceptable levels by an easily controlled economical process and satisfactory yields are maintained.

Various modifications may be made without departing from the inventive spirit of the present invention. For example, several cycles of treatment with steam followed by hydrogen may be employed, if desired.

Having described the invention, what is claimed is set forth as follows:

1. A process for desulfurization of fluid coke particles having a high sulfur content, said fluid coke particles having been produced by contacting a heavy petroleum oil feed with a mass of fluidized inert particles maintained in a coking zone at a coking temperature, said petroleum oil being converted to vaporous products and carbonaceous residue which continuously deposits on said inert particles giving said particles a highly laminar structure, withdrawing vaporous products from said coking zone, removing inert particles from said coking zone and 6 heating at least a portion of said inert particles in a separate heating zone, returning thus heated particles to said coking zone to supply thermal energy thereto, and withdrawing product inert particles, which comprises increasing the surface area of the coke particles above about 300 square meters per gram by contacting the coke particles with steam at a temperature in the range of about 1300 F. to 1600 F., and then contacting the steam treated coke particles with hydrogen at a temperature in the range of about 1200 to 1700 F. whereby the sulfur content of the fluid coke is reduced to below a maximumof about 4 wt. percent. 7

2. The process of claim 1 wherein the hydrogen is utilized in an amount of about 100 to 4000 v./v./hr. with a treating time in the range of 0.5 to 6 hours.

3. The process of claim 1 wherein the'steam is at a temperature in the range of 1400-1600 F., and is utilized in amounts greater than about 300 wt. percent based on the particles being treated.

- 4. The process of claim 2 wherein pressures of about 1 to 5 atmospheres are employed in the hydrogen treatment.

5. The process according to claim 1 wherein the time of contact of the particles with the steam is between about 2 and 10 hours.

6. A method for desulfurizing fluid coke particles having a high percentage of sulfur to give product fluid coke particles of less than about 4 wt. percent sulfur, said fluid coke particles having been formed in a coking system by contacting a heavy oil feed with a mass of inert particles maintained at a coking temperature in a reaction zone, said oil thus being converted to gasiform products and carbonaceous residue which continuously deposits on said contact particles, withdrawing said gasiform products from said reaction zone, passing at least a portion of contact particles removed from said reaction zone to an external heater, returning thus heated solids to the reaction zone to supply thermal energy thereto, and Withdrawing prod uct, contacting particles from said coking system, which comprises increasing the surface area of the coke particles above about 300 square meters per gram by contacting the coke particles with at least about 300 wt. percent of steam on the coke particles at a temperature in the range of about 1300 F. to 1600 F., subsequently subjecting the steam treated particles to treatment with hydrogen at a temperature in the range of about 1200- 1700 F. and at a rate of about to 4000 v./v./hr., the two step treatment thereby reducing the sulfur content of said particles to less than about 4 wt. percent.

7. The method according to claim 6 wherein the time of contact of the particles with the steam is between about 2 and 10 hours and the time of contact of the particles with the hydrogen is between about 0.5 and 6 hours.

8. A method for desulfurizing fluid coke particles having a high percentage of sulfur to give product fluid coke particles of less than about 4 wt. percent sulfur, said fluid coke particles having been formed in a coking system by contacting a heavy oil feed with a mass of inert particles maintained at a coking temperature in a reaction zone, said oil thus being converted to gasiform products and carbonaceous residue which continuously deposits on said contact particles, withdrawing said gasiform products from said reaction zone, passing at least a portion of coke particles removed from said reaction zone to an external heater, returning thus heated solids to the reaction zone to supply thermal energy thereto, and withdrawing product, coke particles from said coking system, which comprises increasing the surface area of the coke particles above about 300 square meters per gram by contacting the coke particles with about 350 wt. percent of steam on the coke particles at a. temperature of about 1500 F. for about 8 hours, then subjecting the steam treated coke particles to treatment With hydrogen at a temperature of about 1300" F. for about 2 hours at the rate of about 3000 v./v./hr. to reduce the sulfur content of said coke particles below about 4 wt. percent. 1

9. A process for desulfurization of fluid coke particles having a high sulfur content, said fluid coke particles having been produced by contacting a heavy petroleum oil feed with a mass of fluidized inert particles maintained in a coking zone at a coking temperature, said petroleum oil being converted to vaporous productsaud. carbonaceous residue which continuously deposits on said inert particles giving said particles a highly laminar structure, withdrawing vaporous products from said coking zone, removing inert'particles from said coking zone and heating at least a portion of said inert particles ,in a separate heating zone, returning thus heated particles to said coking zone to supply thermal energy thereto, and withdrawing product inert particles, which comprises the steps of contacting the coke particles with a gas consisting essentially of steam at a temperature above about 1300 F. for at least about 2 hours and utilizing at least about 300 wt. percent of steam to increase the surface area of said coke particles above about 3 00 mF/g, and

then su je ting the steam trea e ok Pa ticles o t ea ment with hydrogen at a temperature aboveabout 1200?" F, for at least 0.5 hour at he rate of at least about 100 v.'/v coke/hr. to reduce the sulfur content of said colge particles below about 4 wt. percent.

10. A process according to clai particles are treated with steam at a temperature of about 1500 F. for about 8 hours and the steam treated Coke particles are then treated with hydrogen at a temperature of about 1300 F. for about 2 hours at a rate of about 3000 v./v. coke/hr.

.11- .A process a ording to laim 9 he in h tr atment with hydrogen is carried .out for 1 hour at a Ir sure of about 75 psi. and the sulfur content of the coke particles is reduced to 2.5%,.

References Cited in the file of this patent UNITED STATES PATENTS 9 h re n the oke

Claims (1)

1. A PROCESS FOR DESULFURIZATION OF FLUID COKE PARTICLES HAVING A HIGH SULFUR CONTENT, SAID FLUID COKE PARTICLES HAVING BEEN PRODUCED BY CONTACTING A HEAVY PETROLEUM OIL FEED WITH A MASS OF FLUIDIZED INERT PARTICLES MAINTAINED IN A COKING ZONE AT A COKING TEMPERATURE, SAID PETROLEUM OIL BEING CONVERTED TO VAPOROUS PRODUCTS CARBONACEOUS RESIDUE WHICH CONTINUOUSLY DEPOSITS ON SAID INERT PARTICLES GIVING SAID PARTICLES A HIGHLY LAMINAR STRUCTURE, WITHDRAWING VAPOROUS PRODUCTS FROM SAID COKING ZONE, REMOVING INERT PARTICLES FROM SAID COKING ZONE AND HEATING AT LEAST A PORTION OF SAID INERT PARTICLES IN A SEPARATE HEATING ZONE, RETURNING THUS HEATED PARTICLES TO SAID COKING ZONE TO SUPPLY THERMAL ENERGY THERETO, AND WITHDRAWING PRODUCT INERT PARTICLES, WHICH COMPRISES INCREASING THE SURFACE AREA OF THE COKE PARTICLES ABOVE ABOUT 300 SQUARE METERS PER GRAM BY CONTACTING THE COKE PARTICLES WITH STEAM AT A TEMPERATURE IN THE RANGE OF ABOUT 1300*F. TO 1600*F., AND THEN CONTACTING THE STEAM TREATED COKE PARTICLES WITH HYDROGEN AT A TEMPERATURE IN THE RANGE OF ABOUT 1200 TO 1700*F. WHEREBY THE SULFUR CONTENT OF THE FLUID COKE IS REDUCED TO BELOW A MAXIMUM OF ABOUT 4 WT. PERCENT.