Combination Deasphalting-coking-hydrotreating Process

Abstract

A heavy hydrocarbon residuum is hydrotreated or deasphalted to form a heavy bottoms fraction in which the metals are concentrated. The high-metals fraction is coked to form coke containing the metals and the coke is activated by gasification to form water gas. The activated coke containing the metals, with or without fortification by additional catalytic elements is used as catalyst in a hydrotreating step which may be the hydrotreating step used to concentrate the metals or may be a separate step in which the raffinate with or without the coker gas oil is used as feed. The deasphalting step may be preceded by a vacuum distillation step in which additional gas oil may be formed which can be used as at least part of the feed to the hydrotreating step.

Description

BACKGROUND OF THE INVENTION

This invention relates to a combination of coking and hydroprocessing in which the coke produced serves as catalyst base for the hydroprocessing step.

It is known to produce marketable coke from various petroleum fractions by processes such as fluid coking and delayed coking. In such processes the amount and value of the coke obtained depends on the character of the materials being processed and to some extent upon the coking conditions. In the case of high Conradson carbon stocks, such as heavy vacuum crude residua, the coke yield may be 20 weight percent or higher on the residuum. One of the major uses of coke has been in the manufacture of electrodes. For this purpose petroleum coke is preferable to metallurgical coke made from coal because of the high ash content of the latter. For this reason it has not been profitable to use petroleum residua having high metals content as the source of the petroleum coke, since the resulting coke will have a high content of ash consisting principally of metals.

SUMMARY OF THE INVENTION

It has now been found that the coke prepared from residua having high metals content can be profitably utilized by activating the coke and employing the activated coke with the metals deposited thereon, and with or without the further addition of catalytic materials such as sulfur resistant hydrogenating components, as the catalyst in a subsequent hydroprocessing step.

In one embodiment of the invention an atmospheric residuum is vacuum distilled to separate a gas oil fraction and a bottoms fraction. The bottoms fraction is deasphalted to concentrate the metals in the extract.

The extract is then coked by fluid or delayed coking and the coke is steam or catalytically gasified to produce synthesis gas, CO.sub.2 and activated coke. The activated coke containing the metals, with or without the addition of externally supplied catalytic components is then used as the catalyst in the hydroprocessing of the deasphalted oil with or without the addition of gas oil obtained from the coking step and the gas oil from the vacuum distillation step. If desired the gas oil from the vacuum distillation step may be separately hydrodesulfurized and the resulting desulfurized gas oil may then be mixed with the deasphalted oil with or without the coker gas oil as feed to the hydroprocessing step as described in copending application Ser. No. 813,223 filed Apr. 3, 1969 for Moritz and Welch.

In another embodiment a residuum having a high metals content is first subjected to catalytic hydrotreating. The bottoms product from the fractionation of the hydrotreated product contains most of the metals and is subjected to fluid or delayed coking. The resulting coke is activated by partial gasification with steam and the activated coke containing the metals with or without fortification with additional sulfur resistant hydrogenation catalysts is used as the catalyst in the hydrotreating step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents, in diagrammatic form, one embodiment of the invention in which the residuum is hydrotreated in the presence of activated coke containing metals from the feed and in which the hydrotreater bottoms are coked and the coke activated to form the hydrotreating catalyst.

FIG. 2 represents another embodiment in which the residuum is distilled to separate a gas oil fraction and a bottoms fraction which is deasphalted, the asphalt coked and the coke activated and used as the catalyst in a hydrotreating step in which the deasphalted oil with or without the vacuum gas oil and coker gas oil are used as feed.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, a residuum having a high Conradson carbon and a high metals content is introduced into the bottom of hydrotreating zone 1 by line 2 together with sufficient hydrogen introduced by line 3. Hydrotreating zone 1 contains a mass of fine particles of coke, (e.g., 12-16 mesh), supporting a suitable hydrogenation catalyst such as a Group VB or VIB metal compound, specifically a molybdenum compound, a tungsten compound or vanadium compound, such as the oxide or sulfide and mixtures of these, alone, or together with a Group VIII compound, specifically a nickel or cobalt compound, such as the oxide or sulfide.

The feed is preferably a low value, high-boiling residuum of about -10 to +20 API gravity, about 5 to 50 wt. percent or higher Conradson carbon, containing from 50 to 1000 p.p.m. of metals, such as nickel, vanadium, and the like and boiling above 900.degree. to 1,200.degree. F. However any stock having a Conradson carbon above 5 may be used. The oil entering the bottom of reactor 1 through line 2 flows upwardly through the catalyst bed at a rate of, say, 25 gallons per minute per square foot of horizontal cross section of reactor 1. At this flow rate the catalyst particles are randomly buoyed and moved by the flowing oil. The ebullated catalyst particles give intimate contact to the reactants, provide temperature uniformity throughout the reactor 1, offer extremely little resistance to the flow of the reactants through the reactor 1 and remain active over an extended operating period.

Reactor 1 is maintained at a temperature not to exceed 1000.degree. F., preferably between 725.degree. and 950.degree. F. while the pressure will not exceed 5,000 p.s.i.g. and preferably will be in the range of 800 to 3,000 p.s.i.g. If it is desired to suppress cracking and emphasize only desulfurization then milder conditions should be employed, namely pressures between 600 and 1,500 p.s.i.g. and temperatures between 550.degree. and 800.degree. F., preferably between 600.degree. and 750.degree. F. The hydrogen recycle rate is maintained at about 500 to 10,000, preferably 1,000-5,000 s.c.f./bbl. of feed.

Treated oil is withdrawn through line 4 and after conventional cooling is passed to separator 22 from which recycle hydrogen is removed through line 5. The oil is then passed by line 6 to fractionator 7 from which a gas oil is removed by line 8 for subsequent processing, such as feed for hydrocracking or catalytic cracking. Bottoms from fractionator 7 boiling above about 1,050.degree. F. are removed by line 9 and passed to fluid coker 10 where they are introduced to fluid bed 11 maintained at a temperature of 850.degree.-1,200.degree. F., preferably 900.degree.-1,050.degree. F. and under a pressure ranging from 5 to 150 p.s.i.g. The fluid bed consists of particulate coke particles and are maintained as a fluid bed by the hydrocarbon vapors produced by coking supplemented by the upward passage of fluidizing gas such as steam which enters the lower portion of coking zone 10 through line 12. The contact of the heavy feed and the coke results in the feed being converted to lower boiling vaporous hydrocarbons and more coke which is deposited on the surface of the fluidized coke in the bed along with the metals in the feed. The vaporous hydrocarbons and steam are removed overhead through line 13 while the fluid coke particles descend in bed 11 and are withdrawn from the bottom of coking zone 10 through line 14 and are introduced into the bottom of gasifier 15 where they are introduced into fluidized bed 16. Heat may be supplied to gasifier 15 by means of a conventional coke burner (not shown) or by any other external heat source. The reactions in the gasifier may be effected at a temperature of 1,100.degree.-1,800.degree. F. substantially atmospheric pressure or up to pressures of 150 p.s.i.g., if desired, although it is preferable to operate at substantially atmospheric pressure in order to prevent the saturating effect of hydrogen on any volatile conversion products in the gasifier. Steam for fluidizing bed 16 and for gasifying the coke is introduced through line 17.

It is highly important that no nitrogen be present in the gasifier. Hence care must be maintained to remove it prior to the introduction of the coke-metal contaminated catalyst to the gasifier. The presence of nitrogen will contaminate the synthesis gas product, requiring an extra costly step for its removal.

The gas composition leaves vessel 15 through line 18 and has the following typical composition on a dry basis:

H.sub.2 56.5 CO 16 CO.sub.2 26 CH.sub.4 1.0 H.sub.2 S 0.5

the carbon monoxide may be converted to more H.sub.2 and CO.sub.2 by means of the well-known shift reaction with steam. The CO.sub.2 can be easily removed and the pure hydrogen introduced to the hydrogen recycle line 5 for use in the process.

The residence time of the coke in vessel 15 is sufficient to obtain the desired increase in surface area of the coke, i.e., to activate the coke. After activation, the coke particles are withdrawn through line 19 and recycled to the hydrotreater. If desired a portion or all of the coke may be removed by line 20 and passed to catalyst preparation zone 21 where any desired hydrogenation component may be added to the catalyst. It is however within the spirit of this invention to limit the catalytic metal content of the coke catalyst to the metal compounds, such as those of vanadium and nickel, which are deposited thereon by the residuum feed.

If desired to products from fractionator 7 flowing through line 8 and from the coker 10 flowing through line 13 may be separately or simultaneously hydrodesulfurized in a separate zone (not shown) and the desulfurized product partially recycled as a diluent for the residuum fed to hydrotreater 1 by line 2 as described in application Ser. No. 813,223 filed Apr. 3, 1969, for Moritz and Welch, incorporated herein by reference.

The following represents a typical reaction scheme. ##SPC1##

Referring now to FIG. 2, an atmospheric residuum boiling above 650.degree. F. is fed by line 101 into vacuum distillation tower 103. Steam is fed by line 104 into vacuum tower 103. The feed is preheated to 725.degree. to 875.degree. F. prior to its introduction to tower 103 which is operated to maximize the recovery of a fraction amenable to continuous hydrotreating. Typical vacuum distillation conditions include a temperature in the range of 550.degree. to 850.degree. F. and a pressure in the range of 20 to 100 mm. Hg. Steam is added with the feed and to the bottom of the tower to enhance separation of distillable oil from the bottoms. This steam may amount to 1 to 20 pounds per barrel of oil feed. The velocity of the flow of vapors through the trays or other entrainment barriers above the flash zone is normally in the range of 3 to 10 feet per second and depends upon oil feed rate, temperature and pressure.

A stream comprising light ends and steam is recovered by line 105. Steam can be recovered and recycled by means not shown. A residuum fraction having an initial boiling point of 1,050.degree. F. is recovered by line 107. A vacuum gas oil boiling 650.degree.-1,050.degree. F. is removed by line 108.

The residuum flowing in line 107 is passed through cooler 109 to deasphalting zone 110. The deasphalting step may be a batch operation using one or more treating vessels or a continuous liquid-liquid countercurrent operation using a treating tower having baffles or rotating disc contactors. The residuum is introduced into the top of the particular vessel used and contacted with a suitable deasphalting solvent. This solvent may be any of the conventional solvents but is preferably such solvents as aliphatic hydrocarbons having between two and eight carbon atoms per molecule or a mixture thereof. Certain additives such as heavy coker gas oil, aromatic wash oil, inorganic acids and halogens may be added to the solvent to improve the deasphalting operation by increasing the yield and quality of the deasphalted fraction which is free of metallic contaminants and asphaltic materials. A commercial deasphalting solvent comprises propane or a mixture of 65 percent propane and 35 percent butanes.

The asphalt phase from deasphalter 110 is removed by line 111 and passed to coker 112 which is identical in all respects with coker 10 of FIG. 1. Coke containing deposited metals is removed from the bottom of coker 112 by line 113 and passed to gasifier 114 where the coke is activated by steam introduced through line 115 in the same manner as described in connection with gasifier 15 of FIG. 1. The activated coke from coker 114 passes by line 116 to hydrotreater 117 as catalyst therein which operates with a slurry or ebullating bed as described in connection with hydrotreater 1 of FIG. 1. A portion or all of the activated coke flowing in line 116 may be withdrawn through line 118 and passed to catalyst preparation unit 119 where it is impregnated with desired hydrogenation catalysts as described in connection with unit 21 of FIG. 1. It is then returned to line 116 and introduced to hydrotreater 117.

The raffinate from deasphalting zone 110 is withdrawn through line 120 and mixed with the coker gas oil withdrawn from coker 112 by line 121 and also with virgin gas oil from line 108. The mixture is then fed to the bottom of hydrotreater 117 by line 122 as described in connection with hydrotreater 1 of FIG. 1, hydrogen being introduced through line 123. Treated product is removed from hydrotreater by line 124 and after cooling is passed to separator 125 from which hydrogen is removed and recycled by line 126. ##SPC2##

The deasphalting operation shown in FIG. 2 may be employed in FIG. 1 as replacement for the vacuum tower operation downstream from the hydrotreater. If required, the raffinate from deasphalting may be partially recycled to the hydrotreater in FIG. 1. The extract from deasphalting is fed to coking in place of the 1,050.degree. F.+ vacuum bottoms.

Example i

to demonstrate the utility of the high surface area coke catalyst, a high metals coke from coking Tia Juana medium residuum was gasified with 50 percent steam in the presence of K.sub.2 CO.sub.3 promoter at 1,400.degree. F. to obtain a surface area of approximately 400 square meters/gram and pore volume of approximately 0.25. The activated metal coke was impregnated with a solution of CoCl.sub.2, NiCl.sub.2, ammonium molybdate and vanadate to give a catalyst having the following composition of metal components and physical properties.

Ni, Wt.% 1.8 V, Wt.% 2.4 Co, Wt.% 2.4 Mo, Wt.% 5.2 K, Wt.% 0.18 C, Wt.% 88.0*

Surface Area 265 Pore Volume 0.21 --------------------------------------------------------------------------- *Reduced metal basis prior to sulfiding.

A Safaniya heavy gas oil (650.degree.-1,050.degree. F.) containing 3.1 wt. percent sulfur was hydrotreated over the above catalyst at the following conditions, showing sulfur removal data on the stabilized liquid product. ---------------------------------------------------------------------------

700.degree. F. 1 V/V/Hr. 800 p.s.i.g. 4,000 SCF H.sub.2 /bbl. Without Steam With Steam (10 Wt.% on Feed) Stabilized Feed Liquid Product __________________________________________________________________________ Gravity, .degree.API 19.0 21.4 22.1 Sulfur, Wt.% 3.1 2.27 1.80 __________________________________________________________________________

The stabilized liquid products showed 27 percent and 42 percent sulfur reduction without and with steam respectively. These data show good desulfurization at mild-treating conditions when using a metals-high surface coke catalyst. Also the data show that steam promotes the hydrodesulfurization reaction with the high metals high surface area coke.

Example ii

to demonstrate the use of high surface area coke containing lower metals content the following catalyst was prepared with the base coke used in example I. The catalyst had the following composition.

Ni, Wt.% 0.24 V, Wt.% 0.37 Co, Wt.% 1.9 Mo, Wt.% 2.4 Fe, Wt.% 0.37 K, Wt.% 0.36 C, Wt.% 94.0

Surface Area 380 Pore Volume 0.26

The gas oil feed used in example II was processed over this catalyst at the following conditions. Sulfur removal data on the stabilized liquid product are shown. ---------------------------------------------------------------------------

800.degree. F. 1 V/V/Hr. 1,000 p.s.i.g. 4,000 SCF H.sub.2 /bbl. Inspections Feed Stabilized Liquid Product __________________________________________________________________________ Gravity, .degree.API 19.0 25.0 Sulfur, Wt.% 3.1 1.42 __________________________________________________________________________

A desulfurization level of 54 percent is realized when processing at higher temperature over a low metals loaded activated coke catalyst.

Claims

We claim: The nature of the present invention having thus been fully described and illustrated and specific examples of the same given, what is claimed as new, useful and unobvious and desired to be secured by Letters Patent is:

1. A self-sustaining integrated process for the hydrotreating of residual hydrocarbon fractions having a metals content of at least 50 p.p.m. which comprises selecting a feed suitable for coking from the group consisting of the bottoms from the hydrofining of said high-metals residuum and the extract from the deasphalting of said residuum, coking said feed to form coke containing said metals and cracked hydrocarbons, subjecting said coke to treatment with steam and/or oxygen-containing gas to increase the surface area of said coke and produce water gas, using said activated coke as a catalyst and hydrogen from said water gas in the hydroprocessing of a feed chosen from the group consisting of said high-metals residuum and the raffinate from the deasphalting of said residuum.

2. A self-sustaining integrated process for the hydroprocessing of residual hydrocarbon fractions having a metals content of at least 50 p.p.m. which comprises hydrotreating said high-metals residuum in the presence of coke having a surface area of at least 50 square meters per gram and containing at least 0.5 percent by weight of metals derived from said residua, coking the effluent from said hydroprocessing step to form coke containing said metals and cracked hydrocarbons, subjecting said coke to treatment with steam and/or oxygen-containing gas to increase the surface area of said coke and produce water gas, recycling said activated coke and hydrogen from said water gas to said hydroprocessing step as the catalyst and hydrogen source respectively.

3. A self-sustaining integrated process for the hydroprocessing of residual hydrocarbon fractions having a metals content of at least 50 p.p.m. which comprises deasphalting a heavy residuum to form a raffinate and an extract containing the metal from said residuum, coking the extract from the deasphalting step to form coke containing said metals and cracked hydrocarbons, including a gas oil fraction, subjecting said coke to treatment with steam and/or oxygen-containing gas to increase the surface of said coke and produce water gas, and hydrotreating either or both the raffinate from the deasphalting step and the gas oil from the coking step in presence of the metals-containing coke from the coking step as a catalyst.

4. The process of claim 3 in which a residuum boiling 650.degree. F.+ is subjected to vacuum distillation prior to the deasphalting step to separate at least a gas oil fraction and a bottom fraction boiling 1,050.degree. F.+, using the bottoms fraction as feed to the deasphalting step and hydrotreating a mixture of the gas oil fraction from the vacuum distillation, the gas oil from the coking step and the raffinate from the deasphalting step with the said metals-containing coke.

5. The process of claim 1 wherein said activated coke employed in said hydroprocessing additionally contains a Group VB or VIB metal compound alone or in combination with a Group VIII metal compound.

6. The process of claim 5 wherein said Group VB or VIB metal compound is an oxide or sulfide of molybdenum, tungsten or vanadium.

7. The process of claim 6 wherein said Group VIII metal compound is an oxide or sulfide of nickel or cobalt.

8. The process of claim 1 wherein the treatment of said coke with steam and/or oxygen-containing gas is continued in the further presence of an alkali metal salt.

9. The process of claim 8 wherein said alkali metal salt is potassium carbonate.

10. The process of claim 1 wherein said hydroprocessing is conducted in the presence of steam.

11. The process of claim 2 wherein said activated coke employed in said hydrotreating additionally contains a Group VB or VIB metal compound alone or in combination with a Group VIII metal compound.

12. The process of claim 11 wherein said Group VB or VIB metal compound is an oxide or sulfide of molybdenum, tungsten or vanadium.

13. The process of claim 12 wherein said Group VIII metal compound is an oxide or sulfide of nickel or cobalt.

14. The process of claim 2 wherein the treatment of said coke with steam and/or oxygen-containing gas is continued in the further presence of an alkali metal salt.

15. The process of claim 14 wherein said alkali metal salt is potassium carbonate.

16. The process of claim 2 wherein said hydrotreating is conducted in the presence of steam.