Process for the visbreaking of high-metals crudes and resids

A process for suppressing the coking tendency of heavy crudes and resids in visbreaking operations comprising treating the charge stock with an inorganic sulfide.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the processing of heavy crude and residual 
petroleum charge stocks, and in particular, relates to the visbreaking of 
such charge stocks containing significant quantities of metal values found 
to promote the formation of coke, notably, those of nickel and/or 
vanadium. 
2. Description of the Prior Art 
"Visbreaking", or viscosity breaking, is a well known petroleum refining 
process in which reduced crudes are pyrolyzed, or cracked, under 
comparatively mild conditions without significant coke production to 
provide products having lower viscosities and pour points thus reducing 
the amounts of less-viscous and more valuable blending oils required to 
make the residual stocks useful as fuel oils. In a typical visbreaking 
process, the crude or resid feed is passed through a heater and thereafter 
into a reaction chamber operating at from about 800.degree. to about 
975.degree. F. and at about 50 to about 1000 psig. Light gas oil is 
injected to lower the temperature of the effluent to within about 
830.degree. to about 850.degree. F. Cracked products from the reaction 
chamber are introduced to a flash distillation unit with the vapor 
overhead being separated in a fractionating column into a light distillate 
overhead product (i.e., gasoline) and light gas-oil bottoms, and the 
liquid bottoms being separated in a vacuum fractionating column into heavy 
gas-oil distillate and residual tar. 
Heretofore, high-metals heavy charge stocks have been processed in coking 
or catalytic hydroprocessing operations. Visbreaking has achieved little 
importance with such crudes due to their tendency to produce significant 
quantities of coke which plugs the reactor, shortens production runs and 
results in unacceptably lengthy periods of down time. 
It has now been observed that this tendency of high-metals crudes and 
resids to undergo coking during visbreaking is related to the presence of 
transition metal values therein, notably nickel and/or vanadium. Such 
metals can be removed under hydrodesulfurization conditions with frequent 
catalyst replacement, or in a specially designed cracking unit. However, 
it is desired to effect more direct treatment, advantageously in a 
visbreaking operation. 
SUMMARY OF THE INVENTION 
It has now been discovered that if the visbreaking of crude and resid feeds 
containing relatively high levels of metal values which promote the 
formation of coke is carried out in the presence of an inorganic sulfide 
capable of interacting with the coke promoting metal values, to effect 
their removal from the feed, the coke-forming tendencies of the feeds can 
be reduced with attendant increase in on-stream time. 
Thus, in a particular visbreaking operation utilizing a Melones crude 
treated with 500 ppm Ni, hydrogen/methane ratios increased five-fold, coke 
yield more than doubled and product viscosity deteriorated markedly as 
compared with the treatment of the basic crude. When ammonium sulfide 
(0.5% S) was added to the original crude (90 ppm Ni, 400 ppm V) coke 
yields were almost halved. Investigation has shown that the use of an 
inorganic sulfide in a visbreaking process in accordance with this 
invention does not result in the introduction of any appreciable amounts 
of sulfur in the resulting products. 
Thus, the process of this invention provides an economically attractive and 
technically feasible procedure for treating high-metals crudes and resids, 
particularly Venezuelan crudes, which heretofore have been processed by 
coking or catalytic hydroprocessing. Visbreaking in accordance with this 
invention can be carried out at a site which is removed from the wellhead, 
e.g., at a refinery, but can, if desired, be conveniently employed at or 
near the wellhead. 
Among the inorganic sulfides which are advantageously employed herein are 
included one or more of the alkali metal sulfides, the alkaline earth 
metal sulfides, hydrogen sulfide, ammonium sulfide and other sulfides of 
similar reactivity with nickel and/or vanadium values present in crude and 
resid feeds. Of the foregoing, hydrogen sulfide, sodium sulfide and 
ammonium sulfide have been found to provide excellent results. As will be 
appreciated by those skilled in the art, the amount of inorganic sulfide 
employed will depend upon such factors as the amount of coke promoting 
metal values in the feed, the reactivity of the selected sulfide for such 
metal values, and the desired extent of demetalation. These factors can be 
readily determined for a particular set of conditions employing known and 
conventional techniques. In general, the amount of sulfide should be 
selected so as to minimize the formation of coke during the visbreaking 
operation. 
In most cases, predicated upon the usage of a representative charge stock 
comprising about 100 ppm of nickel and about 400 ppm of vanadium (among 
other metal values in the usual proportions) the amount of sulfide 
employed to significantly suppress coking will range from about 0.05%, 
preferably at least 0.25-0.5%, up to 5% S. Charge stocks, however, may 
vary from 50 to 2000 ppm nickel, and while the desired sulfide level may 
be correlated with the transition metal content, it appears that the 
effect may not necessarily be stoichiometric. Accordingly, any sulfide 
levels effective in suppressing coking, whether by demetallizing or 
passivating the charge stock or by other unknown mechanisms are 
contemplated as within the scope of the invention. 
Any charge stock having significant transition metal levels may be 
processed with advantage in the manner described. Thus, a charge stock 
containing 90 ppm Ni and 400 ppm V additionally treated with an aqueous 
feed containing 1000 ppm Ni has been successfully processed, extending 
on-stream time from 8 to 27+ hours. Concomitant results may be secured at 
intermediate or extended transition metal levels, having regard for the 
balance of metal values present, and their relative coking tendency. 
The present invention is illustrated in an operation employing steam at 
(e.g., 100-2000 psig) to increase vapor velocities, thereby further 
suppressing coking. Water may similarly be injected, or hydrogen employed, 
although none of these expedients is essential to the process described. 
Other conditions of the visbreaking process herein, i.e., flow rates of 
crude or resid feed, steam, hydrogen gas, working pressures and 
temperatures, and the like are well known parameters and can be optimized 
for the process herein in the usual manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, vycor-packed reactor chamber 10 with 10 cc free volume and 
having a preheater section 11 internally heated to 300.degree. C. is fed 
with aqueous treating solution through line 12, hydrogen gas through line 
13 and crude petroleum (Melones, containing 90 ppm Ni, 400 ppm V, and 
3.94% S) at 120.degree. C. through line 14 converging through line 15 into 
the base of the preheater. The temperature profile of the reactor chamber 
throughout its length is as shown in the temperature profile curve 
adjacent the chamber. Pressure is 1000 psig. Reaction effluent at 
200.degree. C. leaving reactor chamber 10 through line 16 is introduced to 
high pressure separator 17 operated at an internal temperature of 
250.degree. C. (1000 psig) which separates the reaction products into 
crude and a gaseous product which is discharged from the separator through 
line 18 and collected in recovery unit 19, and an aqueous product which is 
discharged from the separator through line 20 and collected in recovery 
unit 21. Na Cl brine is introduced into line 16 through line 22. 
In the runs whose results are given in the data below, flow rates averaged 
60 cc/hr. for the aqueous treating solution, 80 cc/hr. for the crude and 
50 cc brine (20% Na Cl). The temperature profile shown in the attached 
schematic diagram was held constant to the extent possible (300.degree. C. 
preheater, 447.degree. C. center of bed, 449.degree. C. outlet) in order 
to avoid any thermal reactions in the preheater section or in the initial 
section of the reactor chamber. When the reactor chamber plugged, the 
solid coke was generally found in the upper half thereof. 
Liquids were analyzed for Ni, V, S and N after centrifuging to remove any 
residual water. Asphaltenes were removed by treatment of 35 g liquid with 
250 cc pentane. Both asphaltenes and resins were then analyzed for Ni, V, 
S and N. Viscosities were measured at 130.degree. F. and at 160.degree. F. 
with a Brookfield Micro-viscometer. 
Table I summarizes the hydrogen and coke yield data for the runs of 
Examples 1-22 as follows: 
TABLE I 
__________________________________________________________________________ 
HYDROGEN AND COKE YIELDS 
Yield, percent 
H.sub.2 /CH.sub.4 
Hours 
Example 
Treating Solution 
Coke 
H.sub.2 
(moles) 
Asphaltenes.sup.a 
On Stream 
__________________________________________________________________________ 
1 to 3 
H.sub.2 O 
0.5 0.07 
1.1 15.7% 18.8 
4 to 6 
7.5MNH.sub.4 OH 
7 H.sub.2 O 0.5 0.10 
1.1 16.9% 
8 and 9 
0.13% S.sup.= 
0.5 0.06 
1.0 15.6% 12.8 
10 500ppm Ni (II).sup.b 
1.2 0.15 
4.0 18.0% 
11 to 13 
500ppm Ni (II).sup.b 
1.2 0.21 
5.6 18.2% 8.2 
14 to 22 
0.5% S.sup.= 
0.3 0.08 
1.3 17.2 &gt;35.sup.c 
__________________________________________________________________________ 
.sup.a Charge = 15.8% 
.sup.b = Nickel added in aqueous treating solution to simulate highmetals 
crude. 
.sup.c = Arbitrarily terminated; had not plugged. 
The data in Table I show the major, deleterious effect of nickel-containing 
crude. In Examples 10 to 13 where 500 ppm nickel (as the acetate) was 
present in the aqueous treating solution, hydrogen yield, the amount of 
coke and the asphaltene content of the reaction effluent increased 
markedly. When 0.1-0.5% sulfur present as either Na.sub.2 S or 
(NH.sub.4).sub.2 S was present instead of the aqueous feed, the amount of 
coke produced was at a minimum (Examples 14 to 22). 
The data set forth in Table II below show that the added sulfide was not 
incorporated into the crude product (compare Examples 8 to 10 and 14 to 22 
with 1 to 7): 
TABLE II 
______________________________________ 
PRODUCT QUALITY 
Average 
Treating Percent Removal Viscosity, cps 
Example 
Solution Ni V S N 130.degree. F. 
160.degree. F. 
______________________________________ 
Charge -- -- -- -- -- 2990 -- 
1 to 3 H.sub.2 O 
23 15 5 10 680 -- 
4 to 6 7.5MN 34 24 8 0 740 240 
H.sub.4 OH 
7 H.sub.2 O 
16 4 2 10 210 70 
8 and 9 
0.13% 21 18 10 17 390 130 
S.sup.= 
10 500ppm 56 49 33 31 1320 480 
Ni(II) 
11 500ppm 0 3 0 10 570 240 
Ni(II) 
12 500ppm 2 6 0 46 970 370 
Ni(II) 
13 500ppm 28 16 1 34 2000+ 1160 
Ni(II) 
14 to 22 
0.5% S.sup.= 
26 27 16 12 700 250 
______________________________________ 
It is also evident from Examples 11 to 13 that the greater amount of coke 
and hydrogen observed with added nickel were not merely a function of 
higher conversion levels, as viscosities deteriorated significantly with 
time on stream as nickel built up on the reactor coke. 
EXAMPLE 23 
Additional runs of the type reported in Examples 1-22 were carried out 
utilizing the same charge stock with similar results. When the treating 
phase contained only water or ammonium hydroxide, coke blocked the reactor 
after 19 hours on stream. When 1000 ppm Ni was present in the treating 
phase, blocking occurred after only 8 hours. When the treating phase 
contained 0.5% sulfur (as Na.sub.2 S) blockage had not occurred after 27 
hours on stream. In another run treatment with 0.4% sulfur as Na.sub.2 S 
yielded a product which contained 3.57% S, compared with 3.94% S in the 
feed, while about 20% of the Ni and V were removed from the crude.