Hydrocracking and hydrotreating shale oil in multiple catalytic reactors

Raw shale oil containing precipitable inorganic compounds such as iron and arsenic are preheated to below the precipitation temperature and then catalytically hydrocracked in an ebullated bed catalytic reactor. The metal compounds are deposited on the catalyst in the reactor, from which they are withdrawing along with used catalyst which is replaced with fresh catalyst. The reactor effluent is further hydrotreated in a fixed bed catalyst reactor, usually at more severe conditions of 800.degree.-840.degree. F. and 2000-2800 psig, hydrogen partial pressure. The resulting material is phase-separated and distilled to provide jet fuel and diesel oil product meeting commercial and military specifications.

BACKGROUND OF INVENTION 
This invention pertains to processing hydrocarbon feedstocks containing 
precipitable impurities which deposit out during preheating, and 
particularly to processing raw shale oil containing such precipitable 
materials to produce catalytically refined liquid fuels. 
Attempts to hydrotreat and/or hydrocrack raw shale oil in conventional 
fixed-bed catalytic reactor operators, usually using multiple beds with 
quench steps between the beds, have been plagued by operating problems of 
fouling preheaters, plugging the beds, or both. Such fouling of flow 
passages and/or catalyst beds is evidently caused by precipitation of 
inorganic constituents of inorganic/organic complexes contained in the 
oil, and which decompose at temperatures below the desired hydrogenation 
reaction temperature. These precipitable inorganic materials contain 
arsenic and iron compounds and ash which cannot be readily filtered out of 
the feed stream at near ambient conditions. Shale oil contains small 
quantities of metals, such as about 60 ppm iron and 10 ppm arsenic, as 
weakly bonded chemical complexes. These compounds evidently decompose at 
about 500.degree.-600.degree. F. and precipitate the metal, which deposits 
on solid surfaces, thereby plugging heater tubes and fixed catalyst beds. 
It has been proposed to provide a low temperature guard bed containing 
particulate solids to remove the metals, and then heat the effluent to the 
hydrogenation reaction conditions of 700.degree. F. or more required in a 
second catalytic reactor. However, the deposits occurring in such guard 
traps cause high pressure drops and even plugging, so that they are 
inconvenient and expensive to use. Thus, a better solution has been sought 
for avoiding or preventing such metal compound deposits and fouling 
problems in processing raw shale oil, so as to permit continous catalytic 
treating such oils to produce upgraded fuel products. 
The multi-stage catalytic processing of heavy petroleum crude oils and 
residuum is known. For example, U.S. Pat. No. 3,705,849 to Alpert 
discloses a process for desulfurization of petroleum residuum feedstocks 
using ebullated catalytic bed hydrogenation reactors in series to reduce 
hydrogen consumption and increase catalyst life. U.S. Pat. No. 3,773,653 
to Nongbri and U.S. Pat. No. 3,788,973 to Wolk dislose similar multistage 
catalytic conversion processes for petroleum residuum. Also, U.S. Pat. No. 
3,887,455 to Hamner discloses a process for hydrotreatment of heavy crudes 
and residua using ebullated catalytic beds or fixed-bed reactors in 
series, using catalyst having smaller pore size in the second reactor. 
U.S. Pat. No. 4,046,670 to Seguchi discloses a process for thermal cracking 
heavy petroleum oil in a tubular type heating furnace, and wherein an 
inorganic substance containing iron oxide is added to the feed as an 
anti-clogging agent. U.S. Pat. No. 4,181,596 to Jensen discloses treating 
shale oil retort effluent to lower pour point and reduce contaiminants, 
such as soluble arsenic and iron, by cooling the effluent and maintaining 
the liquid phase in a critical temperature range of 
600.degree.-800.degree. F. for 1-120 minutes. Also, U.S. Pat. No. 
4,158,622 to Schwarzenbek discloses a two-stage hydrogenation process for 
hydrocarbons such as shale oil containing particulate fines, utilizing an 
ebullating bed catalytic reactor from which a vapor portion is passed to a 
stationary bed reactor for further hydrotreatment. 
Despite the prior activity, a need still exists for improvements in 
processing raw shale oil which contains precipitatable inorganic materials 
and compounds so as to avoid fouling of equipment passages and catalytic 
beds and provide improved operations. The present invention uses the 
hydrogenation exotherm in an ebullated bed reactor to eliminate the feed 
heater and any guard bed, and then finish hydrotreats the light material 
in a fixed bed catalytic reactor. Inorganic materials are deposited in the 
ebullated bed reactor on the catalyst, and the deposits are removed from 
the bed along with the used catalyst. 
SUMMARY OF INVENTION 
The present invention discloses a process for hydrocracking and 
hydrotreating hydrocarbon feedstocks which contain precipitable components 
or contaminants, such as raw shale oil feed, to produce upgraded fuel 
oils. The hydrocarbon feed is first heated to below the precipitation 
temperature of the inorganic compound, such as to about 400.degree. 
F.-600.degree. F., and is then reacted with hydrogen in an ebullating 
catalytic bed first-stage reaction zone at conditions sufficient to cause 
some hydrocracking and hydroconversion of the feed and precipitation of 
the precipitable components in the ebullated catalyst bed. Useful reaction 
conditions are 700.degree.-860.degree. F. temperature, 1500-3000 psig 
hydrogen partial pressure, and liquid hourly space velocity of 0.5-3 
V.sub.f /hr/V.sub.r. 
The first reaction zone effluent is passed to a phase separation step, from 
which the light fraction is preferably further reacted in one or more 
fixed catalytic bed second-stage reaction zones. Reaction conditions can 
be similar to the first stage, but are usually at somewhat more severe 
conditions such as within the range of 750.degree.-850.degree. F. 
temperature, 2000-2800 psig hydrogen partial pressure and lower space 
velocity of about 0.5-2.0 V.sub.f /hr/V.sub.r. The effluent from the fixed 
bed reaction zone is then cooled, preferably against the feed stream, and 
phase-separated. The vapor fraction is treated to remove contaminants 
prior to recycle, and the heavy fraction is passed to a distillation step, 
from which is withdrawn a gas stream and product liquid streams suitable 
for jet and diesel engine fuels. 
It should be noted that by employing an ebullated catalyst bed cracking 
reactor for the initial reaction step, followed by further reaction in one 
or more fixed bed catalytic reactors, several process advantages are 
provided. One advantage is that the backmixing ebullated bed cracking 
reactor utilizes the exothermic heat of reaction to further preheat the 
feed. This lowers heat transfer temperatures and reduces or eliminates 
fouling of heater passages in the initial preheater. Also because the 
ebullated bed catalytic reactor can handle a solids-containing feed, 
deliberately depositing the feedstock precipitable solids in the 
ebullating bed from which they can be withdrawn along with used catalyst, 
eliminates reactor plugging problems. 
Another advantage of the present invention is that after such solids 
removal from the feed, the second stage reaction zone can comprise one or 
more plug flow fixed bed type catalytic reactors which takes advantage of 
the better hydrogenation kinetics provided by fixed catalyst beds. If it 
is desired to operate the second stage reactor at a lower temperature than 
the ebullated bed cracking reactor, heat can be removed from the effluent 
streams by useful heat exchange steps between the reactors, which is more 
desirable than the use of a quenching step in the fixed bed reactor, which 
is thermally inefficient. A further advantage is that the heavy liquid 
from the hot separator is substantially free of such precipitated solids, 
and can be recycled to the ebullated bed reactor if desired.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As shown in FIG. 1, raw shale oil feedstock at 10 containing iron and 
arsenic compounds is heated in heat exchanger 12 to a temperature 
sufficiently low to avoid precipitation of contained inorganic material 
such as iron and arsenic compounds. Such heating is usually to at least 
about 400.degree. F. and usually not above about 600.degree. F., and 
preferably is against a product oil stream. The warmed feedstream 14 is 
then introduced with hydrogen from 15 into an ebullated bed catalytic 
reactor unit 16 containing catalyst bed 16a. The reactor has provision for 
fresh catalyst addition either with the feed at 14a, or by addition 
directly into the reactor at 17, and withdrawal of used catalyst at 18 as 
shown. Reaction conditions are usually 700.degree.-850.degree. F. 
temperature, 1500-3000 psig hydrogen partial pressure and liquid hourly 
space velocity within the range of 0.5-3.0 V.sub.f /Hr/V.sub.r. Suitable 
catalyst is commercially available cobalt-molybdenum or nickel-molybdenum 
on alumina support and having 0.005 to 0.200 inch particle size range. 
Used catalyst and deposited solids are withdrawn either from the reactor 
at connection 18 or with non-vaporized effluent stream 20 from the hot 
separator 22. 
Hot effluent liquid at 20 is phase separated in hot separator 22, and the 
vapor portion 24 is withdrawn and passed directly to an on-line 
hydrotreater 30. The liquid portion 26 can be further flashed at reduced 
pressure for light material recovery and such material combined with 
stream 24. The residual liquid 28 is either partially recycled to the 
reactor 16 for further cracking, is further fractionated for recovery of 
light materials, or burned as fuel. 
The vapor and light fractions at 24 introduced directly to downflow fixed 
bed catalytic hydrotreater 30, usually have additional hydrogen added at 
25. In the hydrotreater 30, which may be operated at substantially the 
same temperature and pressure conditions existing for the reactor unit 16, 
or usually at somewhat more severe conditions, preferably at 
780.degree.-850.degree. F. temperature, 2000-2800 psig hydrogen partial 
pressure, and space velocity of 0.8-1.3 V/Hr/V, the light fractions are 
cracked further and virtually completely desulfurized and denitrogenated. 
Suitable catalyst are cobalt-molybdenum on alumina support having slightly 
higher metal content than for catalyst bed 16a, and having particle size 
of 0.060-0.250 inch. The fluid temperature will increase through the 
catalyst bed due to exothermic reaction. If hydrotreater 30 comprises two 
or more catalyst beds arranged in series, the bed temperatures can be 
controlled by injecting cooler hydrogen gas between the beds such as at 
30a. 
The resulting product stream 31 from reactor 30 is cooled at 32 against a 
suitable stream or streams such as water to produce steam, and phase 
separated at separator 34. The resulting liquid portion is 
pressure-reduced at 35 and fractionated at 36 into naphtha 37, jet fuel 
38, and diesel fuel product streams. The 650.degree. F. .sup.+ liquid 
fraction 39 from fractionator 36 can be used to preheat the raw shale oil 
fed in heater 12 prior to being recycled, or can be sold as heavy fuel oil 
product. 
The effluent vapor fraction at 33 from phase separator 34 can be treated at 
40 to remove contaminants such as H.sub.2 S, CO.sub.2, NH.sub.3, and 
H.sub.2 O at 42. A portiion of the treated hydrogen-containing gas at 41 
is recompressed at 44, heated to 900.degree.-950.degree. F., at fired 
heater 45, and recycled as stream 15 directly to the reactor 16. The 
balance of the treated gas 43 from treating step 40 can be stream-reformed 
at 50, along with natural gas or methane make up at 49, to make additional 
hydrogen as needed in the process. The additional hydrogen 46 from 
reformer 50 is recompressed at 48 and joins recycle stream 15. 
It is pointed out that the important features of this process for upgrading 
hydrocarbon feeds such as shale oil are preheating of the feedstock to 
only about 350.degree. F. to 600.degree. F. temperature range to minimize 
or prevent precipitation of inorganic material in the preheater passages, 
then further heating the feed to reaction temperature of 
700.degree.-900.degree. F. in an ebullated bed reaction step for initial 
hydrocracking reaction. Further reaction preferably occurs in an on-line 
hydrotreating step or steps, which are usually operated at somewhat more 
severe conditions than for the ebullated catalyst bed reactor, to produce 
finished liquid fuel products. These process steps as well as other 
features of the process are applicable to processing coal, heavy oil and 
tar sand bitumen, as well as for preferably processing of raw shale oil to 
produce fuel oil products. 
This invention is further illustrated by the following examples, which 
should not be construed as limiting the scope of the invention. 
EXAMPLE 1 
Upgrading operations are conducted with raw shale oil containing 1.6 W % 
nitrogen, 20 ppm arsenic, 60 ppm iron and about 0.06 W % ash impurities. 
The oil is preheated in fired tubular heat exchanger to about 400.degree. 
F., then passed into an upflow type reactor containing an ebullated bed of 
commercially available cobalt-molybdenum catalyst extrudate particles. 
Hydrogen is heated to 900.degree.-910.degree. F. and also introduced into 
the bottom of the reactor. The reaction zone conditions are maintained 
within the range of 780.degree.-825.degree. F. temperature, 2000-2500 
psig, partial pressure of hydrogen, and space velocity of 1.0 V.sub.f 
/hr/V.sub.r. An effluent stream is removed from the upper end of the 
reactor and passed to further processing steps. The arsenic and iron 
compounds or impurities are deposited on the catalyst and are removed from 
the reactor along with the used catalyst, thus avoiding difficulties with 
precipitation of such contaminants from the shale oil feed causing 
increased pressure drop and operating problems in the process, and 
permitting continuous extended operations. 
EXAMPLE 2 
The pretreated effluent stream from the ebullated bed catalyst reactor, 
containing nitrogen content of about 1.27 W %, 0.1 W % arsenic, and sulfur 
of 0.75 W %, is passed on to a second-stage fixed-bed catalytic reactor 
for further processing. The oil is hydrotreated at conditions of 
800.degree.-840.degree. F. temperature and 2000-2800 psig, partial 
pressure of hydrogen by passing it over a suitable hydrotreating catalyst, 
usually nickel-molybdenum on alumina support at space velocity of 1.0 
V.sub.f /Hr/V.sub.r. The resulting hydrotreated oil product has increased 
API gravity, nitrogen content of less than about 4 ppm and sulfur content 
less than about 0.01 W %, thus making it suitable fuel oil for jet and 
diesel engine use. 
Although I have disclosed certain preferred embodiments of my invention, it 
is recognized that modifications may be made thereto within the spirit and 
scope of the disclosure and as defined solely by the following claims.