Thermal treatment of heavy hydrocarbon oil

This invention provides a process for upgrading heavy hydrocarbon oil by thermal treatment which in one preferred embodiment involves heating a petroleum residuum type of heavy oil feedstock at a temperature of 450.degree.-550.degree. C. and a pressure of 10-200 psi for a period of about 0.1-1 hour to convert at least 60 weight percent of the heavy oil to gasoline and gas oil range products, and additionally providing a residual tar fraction which has a fusion temperature below about 160.degree. C. About 1-10 weight percent of solid carbonaceous fines are incorporated in the feedstock to suppress the deposition of coke in the thermal treatment zone.

BACKGROUND OF THE INVENTION 
Various hydrocarbon feedstocks such as crude petroleum oils, topped crudes, 
heavy vacuum gas oils, shale oils, tar sand bitumens, and other heavy 
hydrocarbon fractions such as residual fractions and distillates contain 
varying amounts of non-metallic and metallic impurities. The non-metallic 
impurities include nitrogen, sulfur, and oxygen and these exist in the 
form of various compounds and are often in relatively large quantities. 
The most common metallic impurities include iron, nickel, and vanadium. 
Other metallic impurities including copper, zinc, and sodium are often 
found in various hydrocarbon feedstocks and in widely varying amounts. 
Some of the metal contaminants are present in the form of relatively 
thermally stable organo-metallic complexes such as metal porphyrins. 
Residual petroleum oil fractions produced by atmospheric or vacuum 
distillation of crude petroleum are characterized by relatively high 
metals and sulfur content. This occurs because substantially all of the 
metals present in the original crude remain in the residual fraction, and 
a disproportionate amount of sulfur in the original crude oil also remains 
in that fraction. 
The high metals content of the residual fractions generally preclude their 
effective use as charge stocks for subsequent catalytic processing such as 
catalytic cracking and hydrocracking, because the metal contaminants 
deposit on the special catalysts for these processes and cause the 
formation of inordinate amounts of coke, dry gas and hydrogen. 
It is current practice to upgrade certain residual fractions by a pyrolytic 
operation known as coking. In this operation the residuum is destructively 
distilled to produce distillates of low metals content and leave behind a 
solid coke fraction that contains most of the metals. Coking is typically 
carried out in a reactor or drum operated at about 
800.degree.-1100.degree. F. (426.degree.-593.degree. C.) temperature and a 
pressure of 1-10 atmospheres. The economic value of the coke byproduct is 
determined by its quality, particularly its sulfur and metals content. 
Excessively high levels of these contaminants makes the coke useful only 
as low-valued fuel. In contrast, cokes of low metals content, for example 
up to about 100 ppm (parts per million by weight) of nickel and vanadium, 
and containing less than about 2 weight percent sulfur may be used in 
high-valued metallurgical, electrical, and mechanical applications. 
Certain residual fractions are currently subjected to visbreaking, which is 
a heat treatment of milder conditions than used in coking, in order to 
reduce their viscosity and make them more suitable as fuels. It usually 
involves a short soak time at a temperature of about 
800.degree.-950.degree. F. (443.degree.-510.degree. C.) The mild thermal 
cracking conditions of visbreaking produces about 5-15 percent of gas oil, 
about 5-15 percent of gasoline, and about 70-85 percent of heavy fuel oil. 
Typical visbreaking procedures are described in U.S. Pat. Nos. 2,358,573 
and 2,695,264, and in 1980 Refining Process Handbook, page 158 (Reprinted 
from September 1980 issue of Hydrocarbon Processing, Gulf Publishing Co., 
Houston, Texas). 
Visbreaking does not significantly reduce the metals content of the 
visbroken distillate fractions. For example, the gas oil from the 
visbroken effluent contains at least about 1-25 ppm of nickel and 
vanadium. 
The economic and environmental factors relating to upgrading of petroleum 
residual oils and other heavy hydrocarbon feedstocks have encouraged 
efforts to provide improved processing technology, as exemplified by the 
disclosures of various United States patents such as U.S. Pat. Nos. 
2,591,525; 2,717,865; 2,761,816; 2,909,476; 2,921,022; 2,950,231; 
2,987,470; 3,094,480, 3,146,188; 3,594,312; 3,663,434; 3,676,369; 
3,696,027; 3,716,479; 3,766,054; 3,772,185; 3,775,303; 3,813,331; 
3,839,187; 3,847,798; 3,876,530; 3,882,049; 3,897,329; 3,901,792; 
4,062,757; and the like, and references cited therein. 
There is continuing research effort to improve the efficiency of processing 
means for upgrading of hydrocarbon feedstocks, with particular reference 
to petroleum residual oils. 
Accordingly, it is an object of this invention to provide an improved 
process for converting heavy hydrocarbon oils into effluent fractions 
having a substantially reduced content of sulfur, metal and nitrogen 
contaminants. 
It is another object of this invention to provide a process for converting 
heavy hydrocarbon feedstocks by thermal treatment into liquid hydrocarbon 
fractions which boil in the gasoline range and in the gas oil range 
between about 400.degree.-900.degree. F. (204.degree.-482.degree. C.), 
substantially without the formation of coke. 
It is a further object of this invention to provide a process for upgrading 
heavy hydrocarbon oils into gasoline and gas oil fractions, and into a 
residual tar fraction which has a fusion temperature below about 
160.degree. C. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and illustrated Example.

DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a process for upgrading heavy hydrocarbon oil by thermal 
treatment which comprises (1) heating heavy hydrocarbon oil at a 
temperature between about 800.degree.-1000.degree. F. 
(425.degree.-550.degree. C.) and a pressure between about 100-2000 psi for 
a soak period between about 0.05-2 hours at the highest Severity 
sufficient to convert at least about 50 weight percent of the heavy 
hydrocarbon oil to gasoline and gas oil range hydrocarbons, substantially 
without the formation of solid coke; and (2) recovering separate fractions 
of gasoline and gas oil, and residual tar which has a fusion temperature 
below about 320.degree. F. (160.degree. C.) and a guinoline-insoluble 
content between about 20-50 weight percent. 
The weight percent yields of conversion products under optimal conditions 
typically are in the ranges between about 1-5 percent of gas, 20-30 
percent of gasoline, 30-40 percent of gas oil (200.degree.-550.degree. 
C.), 20-35 percent of residual tar having a fusion temperature below about 
160.degree. C., and less than about 2 percent of solid coke, based on the 
weight of heavy hydrocarbon oil. 
An important aspect of the present invention process is the achievement of 
an optimal yield of gasoline and gas oil without the formation of solid 
coke, and concomitantly the provision of a residual tar which is pumpable 
at a temperature above about 160.degree. C. 
The term "heavy hydrocarbon oil" is meant to include petroleum oil residua 
and tar sand bitumen feedstocks, in which at least 75 weight percent of 
the constituents have a boiling point above about 700.degree. F. 
(370.degree. C.). 
Typically, a heavy hydrocarbon oil suitable for treatment in accordance 
with the present invention has a metals content of at least 80 ppm, and a 
Conradson Carbon Residue content of at least 10 weight percent. 
The Severity of thermal treatment conditions can be expressed in terms of 
Severity(S), which is equal to Soaking Factor multiplied by reaction time. 
The parameters are reaction temperature and reaction time. 
Severity is conveniently expressed in terms of "equivalent reaction time in 
seconds" (ERT), as measured at 800.degree. F. 
The expressions "Severity"(S) and "Soaking Factor"(SF) as employed herein 
refers to the following algorithmic relationship of thermal treatment 
parameters: 
EQU Severity(S)=Soaking Factor(SF.sub.800).times.Residence Time(.theta.) 
Since the coil temperature is not uniform, the average Soaking Factor(SF) 
for the whole coil reactor is obtained as follows: 
##EQU1## 
In order to express Severity(S) in terms of ERT as measured at 800.degree. 
F., the SF relative to that at 800.degree. F. has to be employed. 
To integrate the above equation, the coil temperature profile relating to 
the reactor volume V (indirectly through distance L) has to be determined 
experimentally or calculated, which can be expressed mathematically as 
follows: 
EQU T=f(L)=F(V) 
By differentiation, we obtain: 
EQU dT=F'(V)dV dV=1/F'(V)dT 
Therefore, SF.sub.800 becomes: 
##EQU2## 
and the equation can be integrated either analytically or graphically to 
obtain SF.sub.800. 
Where: 
T, T.sub.f =coil temperatures at any position and the outlet, respectively, 
.degree.F. 
SF.sub.800 =soaking factor relative to that at 800.degree. F. base temp. 
(k.sub.T /k.sub.800 =ratio of reaction rate constants at T and 800.degree. 
F. 
dV=differential coil volume, ft.sup.3 /bbl/day. 
.theta.=residence time, seconds. 
L=distance from the inlet, ft. 
Note that S=SF.sub.800 .times..theta. (the first equation above). 
That is, Severity is proportional to residence time (.theta.); that is why 
the Severity is often expressed in terms of .theta., i.e., equivalent 
reaction time at 800.degree. F. 
Typically the highest Severity conditions in the thermal treatment zone 
will be in the range between about 700-2000 seconds, as expressed in 
equivalent reaction time at 800.degree. F. 
As the Severity level in a thermal treatment zone increases, the yield of 
gasoline and gas oil conversion products increases, and the fusion 
temperature (ASTM D 3104-77 or ASTM D 2319-76) and the quinoline-insoluble 
content of the residual tar product increases. For each heavy oil 
feedstock there is a highest Severity level which achieves the desired 
balance of gasoline and gas oil yield relative to the yield of residual 
tar product which has a fusion temperature below about 160.degree. C. and 
a guinoline-insoluble content between about 20-50 weight percent, 
essentially without any formation of coke byproduct. 
In addition to Severity, the yield and quinoline-insoluble content of the 
residual tar product are quantities which are functionally related to the 
asphaltene content of the starting heavy oil feedstock. As demonstrated by 
the data in the Example, nominally the asphaltene content of the heavy 
hydrocarbon oil relates to the residual tar yield and residual tar 
quinoline-insoluble content in accordance with the following equation: 
##EQU3## 
The quinoline-insoluble content of the tar product can be determined by 
means of ASTM D 2318-76. 
The operating range for the invention process is narrow and specific to 
each feedstock (e.g., Khafji and Minas resids). As shown in FIG. 1, for 
each temperature the variation in residence time to obtain bottom residue 
with .+-.10.degree. C. softening point is narrow. Similarly, for each 
residence time, the operable temperature is very narrow. The nature of 
resids is critical in deciding this operable condition due to their 
differences in reactivity. In FIG. 1, the nominal profiles indicate that 
Resid B is much more reactive than Resid A. This is illustrated in the 
Table on page 16 of the specification where the Khafji resid is much more 
reactive than the Minas resid, but the operating window for each resid is 
very narrow within the overall operation range encompassing all kinds of 
residua. 
Further, there is a unique relationship between the softening point (fusion 
temperature) of the residual tar (pitch) and its yield. As shown by the 
data in FIG. 2, this relationship is largely independent of feedstock and 
operating conditions. Thus, by monitoring the yield of residual tar the 
operating conditions can be adjusted to control the quality of the desired 
product. It has been found that a residual tar of about 150.degree. C. 
fusion temperature can be satisfactorily used in conventional furnaces 
with minor modifications. 
In another embodiment, this invention provides a process for upgrading 
heavy hydrocarbon oil by thermal treatment which comprises (1) heating 
heavy hydrocarbon oil at a temperature between about 
425.degree.-550.degree. C. and a pressure between about 100-2000 psi for a 
soak period between about 0.05-2 hours at the highest Severity sufficient 
to convert at least about 50 weight percent of the heavy hydrocarbon oil 
to gasoline and gas oil range hydrocarbons, substantially without the 
formation of solid coke; (2) recovering separate fractions of gasoline and 
gas oil, and residual tar which has a fusion temperature below about 
160.degree. C. and a guinoline-insoluble content between about 20-50 
weight percent; and (3) feeding the residual tar in the form of liquid 
fuel to a furnace. 
In another embodiment, the residual tar which is recovered in step(2) is 
pumped in liquid form (e.g., at a temperature of 200.degree. C.) to a 
gasification system for the production of synthesis gas. 
In a further embodiment, a portion of the residual tar which is recovered 
in step (2) is recycled in liquid form to step(1) of the process. The 
residual tar contains colloidal solids which function to suppress coke 
deposition on the heater surfaces during the step(1) thermal conversion of 
the heavy hydrocarbon oil feedstock. 
In a typical run, the pressure in the step(1) heating zone reactor is in 
the range between about 200-1000 psi, and the system is operated 
continuously at a liquid hourly space velocity in the range between about 
1-10. 
In still another embodiment, this invention contemplates a process for 
upgrading heavy hydrocarbon oil by thermal treatment which comprises (1) 
heating heavy hydrocarbon oil at a temperature between about 
450.degree.-550.degree. C. and a pressure between about 10-200 psi for a 
soak period between about 0.1-1 hour sufficient to convert at least 50 
weight percent of the heavy hydrocarbon oil to gasoline and gas oil range 
hydrocarbons, substantially without the formation of solid coke; (2) and 
recovering separate fractions of gasoline and gas oil, and residual tar 
which has a fusion temperature below about 160.degree. C. and a 
quinoline-insoluble content between about 20-50 weight percent. 
In one preferred method of practicing the present invention process, an 
inert gas (e.g., steam, nitrogen or gaseous hydrocarbon) is introduced 
into the step(1) heating zone reactor at a partial pressure of about 
10-200 psi and at a temperature of about 535.degree. C. The corresponding 
partial pressure of the hydrocarbon vapor phase is less than about 10 psi, 
and the average temperature in the heating zone reactor is about 
450.degree.-525.degree. C. The system is operated continuously, and the 
average residence time of the hydrocarbon oil in the heating zone is about 
0.2-0.5 hour (e.g., a LHSV of about 2-5). 
To prevent the deposition of coke on the walls of the heating coils and 
reactor, it is advantageous to admix between about 1-10 weight percent of 
finely divided solids in the heavy hydrocarbon oil feedstream. The 
preferred solids are carbonaceous fines derived from coke, coal, sawdust, 
and the like, which have an average particle size in the range between 
about 50-400 mesh. 
Any coke that forms during the soak period deposits on the particles that 
are present and results in coked particles of relatively uniform size and 
shape, which particles do not settle out and which simultaneously serve as 
a scouring agent to cleanse any loose coke deposits from the walls of the 
equipment. As noted previously, the residual tar fraction containing coke 
fines and colloidal solids may also be recycled for the same purpose of 
suppressing coke deposition. 
A unique aspect of the invention process is the recovery of a residual 
bottoms fraction which is in the form of a tar which has a fusion 
temperature below about 160.degree. C. Hence, at a temperature above about 
160.degree. C.,the recovered residual tar fraction is in the form of a 
pumpable liquid stream. 
The said residual tar can be pumped as liquid fuel to the furnace in the 
processing system, or to any other furnace or heat exchanger in a 
proximate operation. The stack gas sulfur oxides from the tar combustion 
can be recovered for the production of elemental sulfur. 
Illustrative of the invention process, the drawing is a schematic 
representation of thermal treatment and steam distillation units in series 
for processing of heavy hydrocarbon oil, with recovery of products and 
residual tar fractions. 
The heavy hydrocarbon oil is an Arabian light vacuum residual fraction 
which has the following analysis: 
API, gravity 8.3 
H, wt% 10.67 
S, wt% 3.93 
N, wt% 0.28 
CCR, wt% 16.13 
V, ppm 68 
Ni, ppm 17 
MW 810 
Referring to FIG. 3, heavy hydrocarbon oil in line 10 is slurried with coke 
fines (50-200 mesh) from line 11 (about 2 weight percent based on the 
weight of hydrocarbon oil) and charged to Furnace 15. The heated slurry 
passes continuously through line 16 into Reactor 20 which functions as a 
soak tank for the thermal conversion of the heavy hydrocarbon oil. 
Reactor 20 is pressurized with superheated steam (about 535.degree. C.) 
through line 21 to a steam partial pressure level of about 150 psi. The 
resultant temperature in Reactor 20 is about 490.degree. C., and the 
partial pressure of the hydrocarbon vapor phase is about 30 psi. The 
average residence time of the hydrocarbon oil in Reactor 20 is about 15 
minutes. 
Visbroken effluent is passed from Reactor 20 via line 23 into Steam 
Distillation unit 25. Superheated steam as required is supplied through 
line 22 to Steam Distillation unit 25. The steam distillation procedure 
strips the visbroken constituents which have a boiling point below about 
1000.degree. F. (537.degree. C.), and the stripped constituents are 
recovered overhead through line 26 for transfer to Gas Separator 30. A 
residual tar fraction is withdrawn from Steam Distillation 25 by means of 
line 27. A portion of the residual tar fraction optionally is recycled 
through line 28 to Furnace 15, in place of or in addition to the coke 
fines being supplied through line 11. The incorporation of carbonaceous 
fines into the heavy hydrocarbon oil feedstock suppresses the deposition 
of coke in Furnace 15 and Reactor 20 and the connecting lines. 
In Gas Separator 30, a gasiform stream is recovered through line 31, and 
the main liquid product stream is withdrawn through line 32 and charged to 
Vacuum Distillation unit 35. 
The vacuum distillation of the product mixture yields fractions which 
include gasoline, light gas oil, heavy gas oil and a residual tar bottoms 
which are isolated via lines 36 through 39, respectively. 
The residual tar fractions recovered through lines 27 and 39 are pumpable 
liquids at a temperature of 180.degree. C. A portion of the residual tar 
is fed as liquid fuel to furnace 40. The overhead stack gas is transferred 
via line 41 to Sulfur Dioxide Scrubber 45 which contains a scrubbing 
medium of activated charcoal. A clean gas stream is vented through line 
46. 
A concentrated stream of SO.sub.2 /SO.sub.3 is recovered from Scrubber 45 
through line 47 and transferred as feed to a Claus plant. The SO.sub.2 
/SO.sub.3 feed is reacted with hydrogen sulfide to produce elemental 
sulfur. 
The following Example is further illustrative of the present invention. The 
specific ingredients and processing parameters are presented as being 
typical, and various modifications can be derived in view of the foregoing 
disclosure within the scope of the invention. 
EXAMPLE 
This Example illustrates the thermal conversion of heavy hydrocarbon oils 
in accordance with the present invention. 
The reactor is a stainless steel tube (3/8" ID.times.16"). The reactor 
temperature is controlled with a four zone furnace to obtain a uniform 
temperature. The reactor pressure is controlled by use of a back pressure 
controller. 
The reactor is first pressurized to the reaction pressure with nitrogen. 
The residuum feed is then pumped through the reactor at the desired rate 
using a positive pump to assure accurate flow rate and residence time. The 
product is separated into gas and liquid with a high pressure separator, 
and the gaseous product is measured and analyzed. 
The liquid product is vacuum distilled to obtain a residual tar. The end 
point of the distillation is adjusted so that the melting point of the tar 
is lower than 160.degree. C. Typically the distillation end point is about 
540.degree. C. (at atmospheric pressure). 
The residual properties, reaction conditions, product yield and residual 
tar properties are listed in the Table. 
Substantially all of the sulfur, metal and nitrogen contaminants of the 
original heavy hydrocarbon oil are concentrated in the residual tar 
fraction. The gas oil distillate which is recovered is suitable as 
feedstock for a conventional fluidized catalytic cracker unit. 
TABLE 
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MINAS KHAFJI 
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Residua Properties 
Specific gravity, 15/4.degree. C. 
0.937 1.032 
CCR, wt % 10.4 20.9 
Asphaltenes, wt % 5.1 16.8 
Pour point, .degree.C. 
47.5 62.5 
Sulfur, wt % 0.2 5.43 
Ni, ppm 37.2 52.0 
V, ppm 0.9 154 
Reaction Conditions 
Reaction Temp., .degree.C. 
465 465 
Reaction Press., psi 
200 200 
Reaction Time, min. 
110 60 
Product Yield, wt % 
Gas 4.0 6.0 
Oil 66.0 51.0 
Residual Tar 30.0 43.0 
Tar Properties 
Volatile Matter, wt % 
42 44 
Quinoline-insoluble, wt % 
50 23 
Fusion Temp., .degree.C. 
150 150 
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