Catalytic hydrogenation process and apparatus with improved vapor liquid separation

A continuous hydrogenation process and apparatus wherein liquids are contacted with hydrogen in an ebullated catalyst reaction zone with the liquids and gas flowing vertically upwardly through that zone into a second zone substantially free of catalyst particles and wherein the liquid and gases are directed against an upwardly inclining surface through which vertical conduits are placed having inlet ends at different levels in the liquid and having outlet ends at different levels above the inclined surface, such that vapor-rich liquid is collected and discharged through conduits terminating at a higher level above the inclined surface than the vapor-poor liquid which is collected and discharged at a level lower than the inclined surface.

BACKGROUND OF THE INVENTION 
The present invention is directed to an improved method and apparatus for 
chemically reacting liquids or slurries of liquids and solids with 
gasiform materials by the "ebullated bed process." The ebullated bed 
process generally comprises passing concurrently flowing streams of 
liquids or slurries of liquids and solids and gasiform materials through a 
generally cylindrical vessel which contains a mass of particulate contact 
material. The mass of contact particles is placed in random motion in the 
liquid medium, and has a gross volume dispersed through the liquid medium 
greater than the volume of the mass when stationary. This technology has 
found commercial application in the upgrading of heavy liquid hydrocarbons 
or converting coal to synthetic oils. 
The process is generally described in U.S. Pat. No. Re 25,770 to Johanson, 
with particular reference to coal and oil conversion. A mixture of 
hydrocarbon liquid and hydrogen is passed upwardly through a bed of 
catalyst particles at a rate such that the particles are placed into 
random motion as the liquid and gas are passed upwardly through the bed, 
and the catalyst bed motion is controlled by a recycle liquid flow such 
that the majority of the catalyst particles do not rise above a certain 
level in the reactor. The liquid which is being hydrogenated along with 
the vapors present in the reaction pass through that upper level of 
catalyst particles and are removed from the upper portion of the reactor. 
In the normal operation of such a system, there are substantial amounts of 
hydrogen gas and light hydrocarbon vapors which rise through the reaction 
zone into the liquid section from which the liquid is either recycled to 
the bottom of the reactor or forms liquid effluent. The presence of gases 
and vapors in the recycle stream present a separation problem, since a 
liquid portion recycled to the bottom of the reactor passes through a pump 
which must be carefully controlled in order to maintain the expansion and 
random motion catalyst particles at a constant and stable level. Any gases 
or vapors present in the recycled liquid materially decrease the capacity 
and efficiency of the recycle pump as well as the flow pattern and thus 
decrease the stability of the ebullated bed. 
Typically, the reactors employed in catalytic hydrogenation processes using 
ebullated beds of catalyst particles are designed with a central vertical 
conduit which serves as the downcomer for recycling clear liquid from 
above the level of the ebullated catalyst bed to the suction of a recycle 
pump for recirculating the liquid through the catalytic reaction zone. The 
recycling of material from the upper portion of the reactor serves to 
ebullate the catalyst bed, maintain the temperature uniformly throughout 
the reactor, and stabilize the catalyst bed. 
One prior art method for effective gas-liquid recycle is shown in U.S. Pat. 
No. 3,124,518 to Guzman, which discloses a downcomer fitted with a large 
entrance cone or funnel having a maximum cross-sectional area of 
approximately 1/2 that of the entire reaction zone. This permits the 
velocity of the liquid to slow relative to the gas, so the gas which is 
entrained in the liquid can have an opportunity to separate from the 
liquid and rise to the liquid-gas interface above the cup, prior to 
recycling the liquid. 
Another prior art recycle device is disclosed in U.S. Pat. No. 3,227,528 to 
Jaeger which shows a recycle conduit similar to that of Guzman, except 
that it is connected to a pump. 
Another reactor configuration for such gas-liquid separation is disclosed 
in U.S. Pat. No. 3,414,386 to Mattix, which discloses a reactor having a 
conical-shaped recycle device with its outer or upper end in peripheral 
contact with the reactor wall and conduits for the upflow of gas and 
liquid penetrating the device and extending above the reactor liquid 
level; a central conduit returns the liquid to the recycle pump. Also, the 
conduits through which liquids and gases pass are positioned such that the 
lower portion of the conduit for liquids extends into the liquid, whereas 
the conduit for gases is above the liquid interface. The upper ends of 
both conduits terminate in the vapor space of the reactor. 
Experience has shown that this arrangement with the fluid conduits 
terminating above the liquid level does not provide effective separation 
and actually contributes to gas entrainment in the recycled liquid. Thus, 
there has been a distinct need for an improved means for quickly and 
efficiently separating gas from liquid being recycled in such a catalytic 
reaction step, so that the throughput and efficiency of the entire 
hydrogenation reaction process can be significantly increased. 
SUMMARY OF INVENTION 
Surprisingly, it has now been found that the foregoing disadvantages of the 
prior art can be avoided, and the superficial gas velocity for ebullated 
bed processes substantially increased by an improved reactor design with a 
new recycle device and its method of operation. 
The invention provides a continuous reaction process for treating viscous 
liquids, wherein the feedstock liquid or liquid-solids slurry is contacted 
with a reaction gas at elevated temperature and pressure conditions in an 
ebullated bed vertical reaction zone. In accordance with the invention, 
liquid or a liquid-solids slurry is introduced into a lower portion of the 
reaction zone at an upward flow rate sufficient to produce random motion 
of contact particles in the reaction zone. The entering gas has a 
superficial linear upward velocity greater than about 0.02 ft/sec (0.65 
cm/sec). The ebullated bed of contact material is maintained in random 
motion as described in U.S. Pat. No. Re 25,770, the disclosure of which is 
incorporated by reference, in the reaction zone and is in volumetric 
expansion of between about 10-200% greater than in a settled condition. 
Treated liquid feedstock and gas flow upwardly from the reaction zone 
without substantial contact particle entrainment into an adjacent phase 
separation zone, and through upwardly directed fluid conduit means having 
fluid intake means operatively disposed above the reaction zone to receive 
treated liquid and gas in constricted flow. Fluid from the upwardly 
directed fluid conduit means is discharged at an upper portion of the 
phase separation zone, but below the reactor liquid level so as to 
accomplish substantial disengagement of the gas from the liquid, and a 
major portion of the treated vapor-reduced liquid is collected and 
recycled from the lower level of the phase separation zone through a 
downward directed fluid conduit means having an enlarged upper end. The 
remaining portion of the treated liquid and gas from the phase separation 
zone is withdrawn above the upwardly-directed fluid conduit means. 
The reactor vessel is divided into two parts, a lower reaction zone and an 
upper phase separation zone. The feedstock and gas are introduced into the 
lower end of the reaction zone, which contains an ebullated bed of 
particulate solids or preferably a catalyst material, and rise uniformly 
through the reaction zone to the phase separation zone which contains an 
improved phase separation-collection apparatus. This apparatus provides 
effective separation of the vapor portion from the rising liquid-gas 
mixture, so that a substantially vapor-free liquid can be collected and 
returned through a downcomer conduit to a circulating pump for recycle 
through the ebullated bed reaction zone to maintain the desired ebullated 
bed expansion therein. 
The separation-collection apparatus has an enlarged upper portion and is 
preferably conical or frusto-conical in shape, but may be of any shape, 
such as cylindrical, and has a lower portion comprising a liquid downcomer 
conduit leading to a recycle pump in the bottom of the reactor. The fluid 
intake means, which receive the liquid and gas in constricted flow, 
comprise at least two conduits in fluid communication between the reaction 
section and the upper portion of the separation-collection apparatus. 
The lower inlet and upper outlet ends of a portion of the fluid conduits 
are preferably located above the lower inlet and upper outlet ends of each 
of the remaining fluid conduits, however, the lower and upper ends may be 
at the same level. In addition, the liquid level in the reactor is 
maintained above all of the fluid conduits. 
It is a general object of this invention to provide an improved process and 
apparatus for fluidized catalytic bed reaction of liquid and gaseous 
materials. 
It is another object of this invention to provide a process wherein the 
efficiency of a catalytic hydrogenation process employing an ebullated 
catalyst bed reaction is significantly increased. 
It is still another object of this invention to provide a means for 
efficiently separating hydrogen and other light hydrocarbon gases from 
hydrocarbon liquids being hydrogenated and recycled in an ebullated 
catalyst bed system. 
It is a further object of this invention to provide a means for efficiently 
separating upflowing gases and liquids in a moving particulate mass 
wherein the recycled liquid portion is required to reverse direction from 
generally vertically upward to vertically downward. 
Still other objects will appear from the more detailed description of this 
invention which follows.

DETAILED DESCRIPTION OF INVENTION 
While the invention is applicable to any process of chemically reacting 
liquid and gasiform materials in the presense of a mass of solid contact 
particles, the invention will be described with particular reference to 
the liquefaction of coal and upgrading of heavy oil, as generally 
disclosed in U.S. Pat. No. Re 25,770. 
The reactor vessel is divided into two parts, a lower reaction zone and an 
upper phase separation zone. The feed liquid and gas are introduced into 
the lower end of the reaction zone, which contains a bed of particulate 
solids, for example, perferably a catalyst material, and rise uniformly 
through the reaction zone, thereby expanding the catalyst mass to form 
what has come to be called an ebullated bed. Liquid and gas pass to the 
phase separation zone which contains an improved phase 
separation-collection apparatus. This apparatus provides effective 
separation of the vaporous and gaseous portion of the rising liquid-gas 
mixture, so that a substantially vapor-free liquid portion can be 
collected and returned through a downcomer conduit to a circulating means 
such as a pump for recycling liquid through the ebullated bed reaction 
zone to maintain the desired ebullated bed expansion therein. 
The separation-collection apparatus has an enlarged upper portion; is 
preferably conical or frusto-conical in shape, but may be of any shape, 
such as cylindrical; and is connected to a liquid downcomer conduit 
leading to the recycle means in the bottom of the reactor. The fluid 
intake means receive the liquid and gas in constricted flow, which 
comprise a plurality of conduits in fluid communication above and below 
the separation-collection apparatus. 
In the most preferred embodiment, the lower inlet end of a portion of the 
fluid intake conduits is located above the lower inlet end of the 
remaining fluid intake conduits, preferably at least two (2) inches above. 
When the inlet ends are so positioned, the higher conduits are herein 
called gas-rich fluid conduits, whereas the lower conduits are called 
liquid-rich fluid conduits. That is, the gas-rich fluid conduits receive a 
fluid that is richer in gas than the liquid-rich fluid conduits. The upper 
outlet end of each gas-rich fluid conduit or passageway is located above 
the upper end of each liquid-rich conduit, preferably at least two (2) 
inches above. In addition, it is critical that the liquid level in the 
reactor is maintained above the uppermost end of the gas-rich fluid 
conduit or passageway, preferably at least two (2) inches above. 
It should be noted that it is within the scope of the invention for the 
intake and outlet ends of the fluid conduits to be at the same level, 
however, the gas concentration passing through each fluid intake conduit 
will be approximately equal. The enlarged surface of the 
separation-collection apparatus is generally inclined upwardly from the 
recycle conduit and may be extended outwardly to peripherally contact the 
inner wall of the reactor. If the separator-collector is not extended to 
the inner wall of the reactor, a generally annular space is formed between 
an outer cylindrical portion of the separator-collector and the reactor 
wall, which acts as a gas-rich fluid intake conduit. 
The total cross-sectional area of both gas-rich and liquid-rich conduits 
should not exceed about 50%, preferably between 10% and 40%, of the 
reactor cross-sectional area. The relative proportion of cross-sectional 
area of liquid-rich and gas-rich conduits is not particularly critical and 
will vary depending on the nature of the liquid. The total cross-sectional 
area of gas-rich risers is preferably between about 5% and 30% of the 
reactor internal cross-sectional area; the total cross-sectional area of 
the liquid-rich riser conduits should preferably be between about 5% and 
30% of the reactor cross-sectional area. Each gas-rich and liquid-rich 
riser conduit should have a minimum transverse dimension sufficient to 
avoid plugging, preferably at least about 0.25 inch (0.64 cm), and most 
preferably between about 0.50 and 12 inches (1.27-30.5 cm) in transverse 
dimension. The conduits should preferably be circular in cross-section, 
but may be made non-circular, such as square, hexagonal, annular or 
oval-shaped, if desired. 
It is a critical feature of this invention that the upflowing liquid-gas 
mixture rising from the reaction zone passes through the fluid intake 
conduits of the separation-collection apparatus and that all conduits are 
below the reactor liquid level. After passage through the 
separation-collection apparatus, the resulting gas portion then rises to 
the vapor space above the phase separation zone, and a portion of liquid 
is collected and returned through a downcomer conduit for recycle to the 
reaction zone, while the remaining liquid portion is withdrawn from the 
reactor as liquid effluent. The recycled liquid passes through the 
downcomer to a circulating pump, then passes through a liquid-gas 
distributor means, together with fresh liquid and gas feed to maintain 
uniform upward fluid flow through the ebullated catalyst bed. The liquid 
and vapor effluent can be withdrawn separately from the upper portion of 
the reactor, in which case the liquid would be drawn from a point in the 
apparatus essentially vapor free. The internal separation of liquids from 
gases by this invention will obviate the need for utilizing an external 
phase separator downstream of the reactor. If desired, liquid and vapor 
portions may be withdrawn together through a single conduit extending into 
the reactor to a point above the top of the separation-collection 
apparatus, but at the liquid-gas interface. 
The invention is further illustrated by reference to FIG. 1. Reaction 
vessel 10 is disposed with its long axis in a vertical position and is 
generally of a circular cross-section, although the exact shape of the 
cross-section is not critical. Although this FIG. 1 drawing is schematic 
in order to show its various features, it will be understood that the 
reactor is constructed in such a fashion and from such materials that it 
is suitable for reacting liquids, liquid-solid slurries, solids and gases 
at elevated temperatures and pressures and in a preferred embodiment for 
treating hydrocarbon liquids and coal-oil slurries with hydrogen at high 
pressures and high temperatures, e.g. 100-5000 psi and 
300.degree.-1500.degree. F. The reactor 10 is fitted with a suitable inlet 
conduit 12 for feeding heavy oil, or a mixture of oil with small particles 
of coal, and a hydrogen-containing gas. Outlet conduits are located in the 
upper portion of reactor 10, outlet 14 being designed to withdraw vapor 
and liquid, and outlet 16 to withdraw mainly liquid product, if desired. 
The reactor also may contain means for introducing and withdrawing 
catalyst particles, which are shown schematically as inlet 15 and outlet 
17. 
Feedstock, such as oil or oil slurried with coal particles, is introduced 
through line 11, while hydrogen-containing gas is introduced through line 
13, and may be combined with the feedstock and fed into reactor 10 through 
inlet 12 in the bottom of the reactor. The incoming fluid passes through 
grid tray 18 containing suitable fluid distribution means. In this 
drawing, bubble caps 19 are shown as the fluid distribution means, but it 
is to be understood that any suitable device known in the prior art which 
will serve to uniformly distribute the fluid coming from inlet 12 over the 
entire cross-sectional area of reactor 10 may be utilized. 
The mixture of liquid and gas flows upwardly, and the catalyst particles 
are thereby provided with an ebullated movement by the gas flow and the 
liquid flow delivered by recycle pump 20. If desired, recirculated oil may 
also be fed into reactor 10 by an external recycle pump. The upward liquid 
flow delivered by this recycle pump is sufficient to cause the mass of 
catalyst particles in bed 22 to expand by at least 10% and usually by 
20-200%, thus permitting gas and liquid flow as generally shown by 
direction arrow 21 through reactor 10 at a steady rate. Due to the 
upwardly directed flow provided by the pump and the downward forces 
provided by gravity, the catalyst bed particles will reach an upward level 
of travel or ebullation while the lighter liquid and gas will continue to 
move upward beyond that level. In this drawing, the upper level of 
catalyst or catalyst interface is generally shown at 23, and the reaction 
zone extends from approximately grid tray 18 to level 23. Catalyst 
particles in bed 22 in this reaction zone move in random motion and are 
generally uniformly distributed through this entire zone in reactor 10. 
Substantially no catalyst particles rise above catalyst interface 23. The 
volume above the catalyst interface is filled with liquid and entrained 
gas or vapor up to the liquid-gas interface which is shown as level 24. 
The upper portion of the reactor is the phase-separation zone in which the 
liquid and gas are separated in the separation-collection apparatus 30 to 
collect and recycle through downcomer 25 a liquid with a substantially 
reduced gas and vapor content. A substantially liquid product may be 
withdrawn separately from gas and vapor through outlet 16, in which event 
conduit 14 terminates in the vapor space and is used to withdraw vapor 
only, or gases, vapors, and liquids may be withdrawn together. 
The upper portion of downcomer 25 is enlarged and is preferably inverted 
frusto-conical in shape, the inclined portion of which is surface 26. 
Annular space 29, between the interior wall of reactor 10 and phase 
separator 30, permits fluid flow therebetween. A plurality of vertically 
directed conduits 27 and 28 intersect surface 26, providing fluid 
communication between the reaction zone and phase separator-collector 
apparatus. Gas-entrained fluid moves upwardly through the phase-separation 
zone, and upon leaving the upper ends of these conduits, the liquid 
portion reverses direction and flows downward to and through downcomer 25 
in the direction of arrow 31 to the inlet of pump 20 and thereby is 
recycled through the lower portion of reactor 10. Gases and vapors which 
are separated from the liquid rise to the liquid-gas interface 24 and are 
collected in the upper portion of reactor 10 and removed through outlet 
conduit 14. The gases and vapors removed at this point are treated using 
conventional means to recover as much hydrogen as possible for recycle 
into the gas feed inlet 13. 
FIG. 2 shows a cross-sectional plan view of the FIG. 1 configuration, with 
both liquid-rich conduits 27 and gas-rich conduits 28 being located at the 
same diameter and surrounded by annular-shaped gas-rich passageway 29. 
While this configuration shows five (5) conduits, it will be understood 
that as few as two (2), and as many as will accommodate the above-noted 
relationships between cross-sectional area of the conduits and reactor, 
may be utilized. 
The liquid-gas separation accomplished in accordance with this invention 
will be better understood by reference to FIGS. 3 and 4, which show 
enlarged views of separation-collection apparatus 30 and fluid intake 
conduits 27 and 28, and 29. In FIG. 3, it may be seen that the fluid rises 
above catalyst level 23 to the lower side of separation-collection 
apparatus 30, which meets lower inclined surface 26 of the 
separation-collection apparatus and has an increasing diameter with 
increasing height. Gas bubbles entrained in the liquid will tend to rise 
within the liquid because of their buoyancy, and thus will travel upwardly 
along the inclined under surface of apparatus 30 until the inlet to one of 
the conduits is reached, which will permit the gas bubble and the liquid 
surrounding it to selectively continue their upward movement. In 
accordance with this invention, conduits 27 and 28 preferably have both 
inlet and outlet ends located at different vertical levels within reactor 
10. It has been determined that if the inlet end of a conduit (gas-rich 
conduit) is above the inlet of other conduits (liquid-rich conduits), and 
preferably at inclined surface 26, the fluid which flows through that 
conduit tends to be richer in gas than the fluid which flows through 
conduits having inlet ends below conical portion 26. Thus, it has been 
found that by positioning the inlet ends of the fluid conduits at 
different levels, one can effect an increased concentration of liquid in 
those conduits having inlets at lower levels and an increased 
concentration of gas in those conduits or passageways having their inlets 
at higher levels, which significantly increases the separation of liquid 
from vapor and permits increased gas velocities through the reactor. 
Similarly, it has also been found that if a gas-rich conduit has its 
outlet at a higher level in reactor 10 than the outlet of a conduit which 
is rich in liquid, the gas bubbles will tend to continue in their upward 
movement as shown at arrows 33 and not be diverted in the direction of 
liquid flow as shown at arrows 35 into a downward direction and into 
downcomer 25. 
In FIG. 3, the conduits which serve as passageways for gas-rich fluid are 
noted as 28, having inlet ends 28a at inclined surface 26 of apparatus 30 
and outlet ends 28b at a higher elevation. While it is preferred that the 
conduit for gas-rich fluids not extend below the inclined surface of the 
apparatus, such is within the scope of this invention; however, the most 
preferred embodiment has the inlet end higher relative to the conduit for 
receiving liquid-rich fluids. Similarly, conduits which serve to transport 
liquid-rich fluid and have a low concentration of gas are noted as 27, 
with inlet ends 27a at a level below conical surface 26 of apparatus 30 
and outlet ends 27b also at a low elevation. Accordingly, annular-shaped 
conduit 29 surrounding apparatus 30 will also selectively pass gas-rich 
fluid and will function as a gas-rich fluid conduit 28. 
FIG. 4 shows a cross-sectional plan view of the phase separation-collection 
apparatus of FIG. 3, having an increased number of liquid-rich fluid 
conduits 27 and gas-rich conduits 28 located outwardly therefrom, and 
surrounded by annular-shaped gas-rich passageway 29. In FIG. 4, there may 
be seen a preferred distribution of different conduits in the plan view of 
reactor 10. Each conduit labeled "G" is one which has its inlet end at the 
lower surface of apparatus 26 and its outlet end at a higher elevation, 
and thus is similar to conduit 28. Each conduit labelled "L" is one which 
has its inlet end at an elevation below the surface of conical portion 26 
and its outlet end at a low elevation, similar to conduit 27. It is 
usually preferable to have a larger proportion of "G" conduits located 
nearer the outer wall of reactor 10 and a larger proportion of "L" 
conduits located nearer the center of reactor 10 near liquid downcomer 25. 
The general size relationships for the cross-sectional areas of liquid-rich 
conduits 27 and gas-rich conduits 28 in FIGS. 1-4 will vary depending upon 
the nature of the liquid, which can be readiy determined by one skilled in 
the art. The cross-sectional area of downcomer 25 need only be sufficient 
to return the recycled liquid at low pressure drop to the pump suction, 
and may be between 1 to 10 percent of the cross-sectional area of reactor 
10. The number of fluid conduits 27 and 28 which may be employed in a 
single reactor is not critical. If the transverse dimension or diameter of 
the conduits is too small, there is a possibility of plugging by particles 
of coal solids within the conduit. It is believed preferable to employ as 
many conduits as necessary to have good mechanical strength and good flow 
districution with a minimum of fluid cross flow within the apparatus. The 
proportion of conduits G to L as shown in FIG. 2 (i.e. the proportion of 
those carrying gas-rich fluid to those carrying liquid-rich fluid) will 
depend upon the amount of total gas in the reactor. 
The liquid-rich and vapor-rich fluid conduits may both be located on the 
same radius or diameter, as shown in FIGS. 1-2, or they may each be 
located at different diameters as shown in FIGS. 3-4. 
FIG. 5 shows in an alternative embodiment that the enlarged conical portion 
of the separation-collection apparatus may be extended to be in peripheral 
contact with the reactor inner wall, thereby eliminating the annular space 
used for upflow of vapor-rich fluid. The numbers shown correspond to the 
description in FIG. 3. 
The different levels of elevation for the inlet and outlet ends of conduits 
27 and 28 in FIGS. 1, 3, and 5 are not particularly critical. However, it 
is preferred that the inlet ends of gas-rich conduits 28 intersect the 
surface of inclined, enlarged portion 26 and not extend below that 
surface. The inlet ends of liquid-rich conduits 27 must be below the 
inclined surface, in order to avoid collecting any more gas than happens 
to flow directly into the conduit open end. 
The upper ends of conduits 27 and 28 are intended to be placed at 
convenient locations to provide the maximum opportunity for gas to 
separate from upflowing liquid-gas mixture and for the liquid to be 
collected and returned through downcomer 25 to recycle pump 20. With 
respect to liquid-rich conduits 27, it is necessary that their upper 
outlet end be located below the upper outlet end of gas-rich conduit 28 or 
passageway 29. Both conduits must be below liquid interface 24. The upper 
end of gas-rich conduits 28 should be at least about 2 inches (5.1 cm) 
below liquid-gas interface 24 and may preferably be about 6 inches to 6 
feet below that interface. If conduit 28 extends above interface 24, gas 
will be entrained in the turbulent liquid and carried downwardly into 
downcomer 25 to recycle pump 20. The elevation of the outlet ends of 
gas-rich conduits 28 should be sufficiently above corresponding outlet 
ends of liquid-rich conduits 27 so as to be relatively unaffected by the 
liquid flow from conduits 27, which is reversing direction to flow 
downwardly into downcomer 25. 
One of the parameters for operation of a hydrogenation reaction process is 
the superficial gas velocity, calculated as a linear velocity of gas 
flowing vertically upward through the empty reaction zone. Before this 
invention, the superficial gas velocity was maintained at an undesirably 
low level in order to achieve a satisfactory degree of liquid-gas 
separation and minimum amount of gas entrainment in the liquid being 
recycled through the reactor. Specifically, a superficial gas velocity of 
about 0.08-0.10 feet/second (2.4-3.1 cm/sec) was found to be the 
approximate upper limit in coal hydrogenation processes without causing 
excessive gas entrainment in the recycle liquid and instability of the 
ebullated bed. It has now been found that with the improved gas-liquid 
separation achieved by this invention, such superficial gas velocity can 
be increased to about 0.15-0.20 feet/second (4.6-6.1 cm/sec) without 
causing excessive gas entrainment in the recycle liquid and instability of 
the ebullated bed. This permits a significant increase in reactor catalyst 
bed stability. In terms of gas concentration, the present process is able 
to produce liquid which can be recycled through downcomer 25 containing 
less than 8% gas by volume. The procedures encountered in the past, 
wherein the superficial gas velocity was as low as 0.08 feet/sec., 
produced liquid for recycle to the pump containing as much as 20% gas by 
volume. 
In the hydroconversion of oil, the maximum superficial gas velocity that 
has been heretofore attained in the reactor is 0.20 ft/sec, whereas by the 
use of the instant invention, the maximum superficial gas velocity that 
will result in an operable process can be increased to greater than 0.26 
ft/sec. 
It will be understood by one skilled in the art that the maximum amount of 
gas entrained in the recycle fluid which will produce a stable ebullated 
bed will vary with the density and viscosity of the reactor fluid, as well 
as the density of the contact material. 
The invention will be further illustrated and described by the following 
examples comparing the operating results of various apparatus 
configurations and embodiments. In order to compare the performance of 
separation-collection apparatuses of differing design, it is necessary to 
determine at various superficial gas velocities how much gas is entrained 
in the recycle fluid. Relative amounts of gas entrained in the recycle 
liquid can be measured by monitoring the recycle pump discharge pressure 
at a constant recycle flow measured in gallons per minute per square foot 
of reactor cross-sectional area (gpm/ft.sup.2). As the gas velocity is 
increased, the volume percent of gas in the recycle liquid flow increases 
up to a maximum. Beyond the maximum, an unstable recycle flow results, 
which leads to ebullated bed instability and process inoperability. As the 
amount of gas in recycle stream increases, pump and pressure discharge 
decreases. Likewise, the recycle flow rate also decreases. Therefore, FIG. 
7 is a graph plotting flow rate against gas velocity. FIG. 8 plots 
discharge pressure against gas velocity. 
Examples 1 through 3 were conducted in a glass tube (simulated reactor) 6 
inches in diameter and 10 feet in length, at near ambient pressure and 
temperature conditions, using kerosene and air to simulate the reaction 
fluids, and using typical particulate cobalt molybdenum catalyst of 1/16" 
diameter extrudates. 
EXAMPLE 1 
A conical-shaped separation-collection device similar to Guzman--U.S. Pat. 
No. 3,124,518 and having cross-sectional area about 45% that of the glass 
tube was first tested at superficial upward gas velocities ranging from 0 
to 0.18 ft/sec. Results shown in FIG. 7, Curve 1, indicate that excessive 
gas was entrained in the recycle pump suction liquid at gas velocities 
above about 0.08 ft/sec, so that the ebullated catalyst bed operation 
became unstable in operation. 
EXAMPLE 2 
A separation-collection apparatus having two 2-inch diameter tubular-shaped 
risers for fluid upflow so that the recycle apparatus is effectively 
extended to the wall of the reactor, as shown by FIG. 6, was constructed 
and tested. The liquid level was maintained first 5 inches above the upper 
end of the fluid intake conduits (Curve 2(a)). Another run was made with 
the liquid level 4 inches below the upper end of the fluid intake conduits 
(Curve 2(b)). Results of these tests in the glass-tube simulated reactor 
are also shown in FIG. 7, comparing the recycle pump flow pressure versus 
superficial upward gas velocity. It is evident that operation of the 
tubular-type recycle apparatus having the reactor liquid level and fluid 
take-off point located above the tubular risers (Curve 2a), is superior to 
the prior art conical-shaped apparatus design of Example 1, as it provides 
generally increased pump recycle-liquid flow and discharge pressure, 
thereby providing more stable catalyst bed ebullation. However, the 
tubular-type collection apparatus, having the reactor-liquid level 
maintained below the upper end of the tubular risers (Curve 2b), was 
clearly inferior in performance to the other two apparatus configurations. 
EXAMPLE 3 
A separation-collection apparatus configuration, as generally shown in FIG. 
1, was constructed and tested in the 6-inch diameter glass-tube simulated 
reactor, with the liquid level and fluid withdrawal point being maintained 
at least about 2 inches above the lip of the apparatus. Specifically, the 
FIG. 1-type recycle cup had a 0.22 inch wide annular conduit between the 
separation-collection apparatus and glass-tube wall and a 2-inch diameter 
gas-rich tubular riser located above a 2-inch diameter liquid-rich riser. 
Comparison results for this recycle apparatus are also shown in FIG. 7 and 
indicate that the improved tubular design apparatus (Curve 3) provides 
performance superior to both other apparatus configurations tested, as it 
provided both higher recycle liquid flow rate and pump discharge pressures 
at all superficial gas velocities up to about 0.18 ft/sec than for either 
(a) the conventional conical-shaped recycle apparatus or (b) the 
tubular-type recycle apparatus with tubular risers extending above the 
liquid level per FIG. 6. 
EXAMPLE 4 
Comparison runs were performed in a 6-inch diameter, 22 ft. long ebullated 
catalytic bed reactor processing about 250 lb/hr Illinois No. 6 coal 
slurried with recycle oil at elevated pressure and temperature conditions. 
The first run utilized in the reactor a conventional prior art phase 
separation-collection device similar to that in Example 1, and having 
cross-sectional area about 44% that of the reactor. Stable operation of 
the ebullated catalyst bed could not be achieved at superficial upward gas 
velocities exceeding about 0.07 ft/sec due to excessive entrained gas in 
the liquid to the recycle pump. Next, a phase separation-collection device 
similar to that illustrated in FIG. 1 and having an annular gas-rich 
conduit, one additional gas-rich fluid conduit, and one liquid-rich fluid 
conduit was installed in the reactor and operated with the liquid level 
about 4 inches above the upper end of the gas-rich conduit. As a 
percentage of reactor cross-sectional area, the cross-sectional area of 
the annular conduit around the apparatus was about 14%, that of the 
gas-rich conduit about 7%, and that of the liquid-rich conduit about 10%, 
thus making the total cross-sectional area of all fluid carrying conduits 
and passageways about 31% of the reactor cross-sectional area. Using this 
apparatus, it was possible to increase the superficial gas velocity in the 
reactor to 0.18 ft/sec before instability of the ebullated bed was 
encountered due to entrained gas in the recycled liquid. Compararative 
results are given in Table 1. 
TABLE 1 
______________________________________ 
Prior Art Invention 
______________________________________ 
Reactor Feed Illinois No. 6 Coal 
in Oil Slurry 
Catalyst Used 1/16" Diameter Cobalt- 
Molybdenum Extrudates 
Dry Coal Feed Rate, Lb/Hr/Ft.sup.3 
65 60 
Reactor Conditions 
Temperature, degrees F. 
848-850 825-850 
Pressure, psig 2700 2500 
Coal/Slurry Oil Weight Ratio 
0.25 0.25 
H.sub.2 Gas Recirculation Rate, 
SCF/Lb Dry Coal 15.7 15 
Maximum Superficial Gas 
Velocity Achieved, Ft/Sec 
0.07 0.18 
Continuous Operation 
Duration, Hours 534 475 
______________________________________ 
EXAMPLE 5 
A larger phase separation-collection apparatus, having multiple riser tubes 
as generally illustrated by FIGS. 3 and 4, was subsequently constructed 
and tested in a 5-foot diameter model reactor, using nitrogen and kerosene 
at near ambient conditions to simulate operation with hydrogen and 
hydrocarbon liquids at elevated temperature and pressure conditions. The 
separation-collection apparatus utilized an annular conduit 0.81 inches 
wide and had six 8.75-inch diameter gas-rich riser conduits and six 
7.25-inch diameter liquid-rich riser conduits located inward from and 
below the gas-rich risers. The total cross-sectional area for the gas-rich 
conduits and liquid-rich conduits was about 20% and 10%, respectively, of 
the reactor cross-sectional area. A large prior art conical-shaped recycle 
device, similar to that of Example 1 and having a cross-sectional area 
about 75% that of the reactor, was also constructed and tested in this 
same facilility for comparison. Results of these comparison tests at 
liquid recycle flow rates of 35 and 50 gpm/ft.sup.2 are presented in FIG. 
8. 
It is evident that the tubular design separation-collection apparatus 
having the reactor-liquid level maintained above the uppermost fluid 
passageway or riser conduit is superior to the conventional conical-shaped 
recycle apparatus configuration at each liquid-recycle flow rate tested, 
in that higher pump recycle-flow rates and discharge pressures were 
sustained at each superficial upward gas velocity. This indicates that for 
the present invention less gas was being entrained in the liquid being 
recirculated through the simulated reactor. Accordingly, the less gas 
being entrained in the recycle pump suction liquid, the more stable will 
be the catalyst bed ebullation. 
Although the invention has been described in considerable detail with 
reference to certain preferred embodiments thereof, it will be understood 
that variations and modifications in the configurations can be made within 
the spirit and scope of the invention, as described hereinabove and as 
defined in the appended claims.