Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
1998-05-29
2001-08-07
Preisch, Nadine (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S058000, C208S059000, C208S108000, C208S143000, C208S153000, C208S157000
Reexamination Certificate
active
06270654
ABSTRACT:
BACKGROUND OF INVENTION
This invention pertains to improved catalytic hydrogenation of heavy hydrocarbonaceous feedstocks utilizing catalytic multi-stage ebullated bed reactors for producing desired lower boiling hydrocarbon liquid products. It pertains particularly to such catalytic multi-stage hydrogenation processes having increased catalyst loading and liquid volume together with reduced gas hold-up in each reactor, and thereby provides improved performance efficiency for the processes.
In conventional catalytic hydrogenation processes for heavy hydrocarbon feedstocks utilizing multi-stage ebullated bed reactors, the hydrogen gas recycle rate in each reactor is usually kept relatively high to assure that excess hydrogen gas exists in the catalyst bed to provide the necessary chemical hydrogenation reactions with the feedstock. However, such excess hydrogen flow requires relatively high superficial gas velocities in the reactor(s), which results in less available volume for the reacting liquid and increased gas hold-up in the reactor. Because the feedstock hydrogenation and hydrocracking reactions occur predominantly in the liquid phase, this conventional practice has the result of undesirably reducing the percentage of feedstock liquid being exposed to and reacted with the catalyst in the reactor, and undesirably reduces process performance. Also, for known catalytic ebullated bed type reactors which utilize internal gas/liquid separation devices, the volume of catalyst in a particular size reactor is undesirably limited.
Many prior art patents have been directed to various improvements in catalytic hydrogenation processes for heavy hydrocarbon feedstocks utilizing catalytic ebullated bed reactors, and have disclosed various operational parameters for such reactors. For example, U.S. Pat. No. 3,183,180 to Schuman et al, U.S. Pat. Nos. 4,217,206 and 4,427,535 to Nongbri et al disclose hydrogenation of petroleum residua using catalytic single stage ebullated bed reactors having internal gas/liquid separation, and U.S. Pat. No. 4,576,710 to Nongbri et al and U.S. Pat. No. 4,853,111 to MacArthur et al disclose use of such catalytic two-stage reactors. Other prior art patents have disclosed hydrogenation process improvements utilizing catalysts having various compositions and pore structures, and specific reaction conditions based on characteristics of the feedstocks. However, a need still remains for providing a comprehensive improved catalytic multi-stage ebullated bed reactor system which is capable of producing improved hydrogenation process performance efficiencies.
SUMMARY OF INVENTION
This invention provides an improved catalytic multi-stage hydrogenation process for treating heavy hydrocarbonaceous feedstocks and producing desired lower boiling hydrocarbon liquid products with enhanced process performance. For this improved hydrogenation process, we have discovered that a more efficient catalytic multi-stage ebullated bed reactor system having improved performance results can be achieved by maximizing the catalyst loading and also providing increased reactor liquid residence time in each reactor, by utilizing reduced catalyst space velocity and reduced superficial gas velocity which are maintained within desired critical ranges in each reactor. These process improvements result in desirably increasing the liquid hold-up volume percent and reducing excessive gas hold-up volume percent in each of the reactors. These desirable reaction results are accomplished by providing such increased volume percent of particulate catalyst and lower catalyst space velocities in each reactor by utilizing an external gas/liquid separator, in combination with utilizing lower superficial upward gas velocities and reduced gas hold-up in each reactor, while providing a desired outlet hydrogen partial pressure and desired level of hydrogenation or hydroconversion as selected for any particular feedstock.
For this invention, the catalytic ebullated bed reactor construction arrangement for the first stage reactor does not include an internal gas/liquid separation device, but instead utilizes an efficient external gas/liquid separator. Utilizing such external gas/liquid separation results in an increased volume of particulate catalyst being provided in a particular size reactor and reduces the catalyst space velocity, which is defined as the volumetric rate of feedstock processed per unit weight of fresh catalyst in the reactor. For such commercial size reactors having outside diameter of 12-14 ft. and a height of 50-60 ft., a vertical distance of 5-10 ft. should be maintained between the ebullated bed maximum expansion level and the reactor outlet conduit, so as to avoid any carryover of catalyst from the reactor. Also, operating conditions for each of the two-staged catalytic ebullated bed reactors are selected so that the upward superficial gas velocity is maintained within a desired critical range, and the gas hold-up volume percentage in each reactor is beneficially reduced, which consequently permits more reactor liquid to be in contact with the catalyst bed, so that the reactor performance as well as the overall process performance results are enhanced. This invention is useful for processing heavy hydrocarbonaceous feedstocks and providing overall hydroconversions in the range of 50-100 vol. % to produce desired lower boiling hydrocarbon liquid products.
The broad and preferred characteristics for the hydrocarbonaceous feedstocks and the reactor broad and preferred operating condition ranges for which this invention is useful are provided in Table 1 below:
TABLE 1
FEEDSTOCK AND REACTOR OPERATING CONDITIONS
Condition
Broad
Preferred
Feedstock Residua Content, vol. % 975° F.
+
30-100
50-90
Feedstock CCR*, wt. %
1-50
10-40
Feedstock Nickel plus Vanadium, Wppm
Up to 1,000
100-800
Reactor LHSV**, hr
−1
(per Reactor Stage)
0.2-2.0
0.4-1.2
Reactor Temperature, ° F.
700-850
750-840
Reactor Total Pressure, Psig
1,000-4,000
1,500-3,000
Reactor Outlet Hydrogen Partial Pressure,
800-3,000
1,000-2,500
Psi
Reactor Superficial Gas Velocity, fps
0.02-0.30
0.025-0.20
Catalyst Space Velocity, BPD/Lb (per Stage)
0.03-0.33
0.04-0.20
Catalyst Replacement Rate, Lb/Bbl
0.05-0.5
0.1-0.4
(per Stage)
Catalyst Bed Expansion, %
25-75
35-50
Vacuum Bottoms Recycle Rate, V
r
/V
feed
0-1
0.2-0.7
Cutpoint of Vacuum Bottoms Recycle, ° F.
650
+
900
+
*CCR = Conradson carbon residue.
**LHSV = Liquid hourly space velocity in each reactor, as defined as volumetric fresh feed rate divided by reactor total volume.
In the process, the fresh feedstock together with hydrogen are introduced into a first stage catalytic ebullated bed reactor, which does not contain an internal gas/liquid phase separator device. The catalyst bed is expanded by 25-75 percent above its settled level by the upflowing liquid and gas streams, and is maintained within the broad operating conditions of 700-850° F. temperature, 800-3,000 psig hydrogen partial pressure at the reactor outlet, liquid hourly space velocity of 0.20-2.0 volume fresh feed per hour per volume of reactor (V
f
/hr/V
r
) and at catalyst space velocity of 0.03-0.33 barrel feed per day per pound fresh catalyst in the reactor. Because of the lower catalyst space velocity and superficial gas velocity being utilized in the reactor, the reacting liquid volume percentage is increased and gas hold-up volume is desirably reduced. The first stage reactor usually hydroconverts 30-95 vol. % of the fresh heavy feedstock and any recycled residua material to a lower boiling hydrocarbon effluent material.
The first stage reactor effluent material is phase separated in an external gas/liquid separator, a gas fraction is removed, and a sufficient portion of the remaining liquid is recycled to the reactor to maintain the desired 25-75% catalyst bed expansion therein. The remaining liquid fraction is passed together with additional hydrogen to a second stage catalytic ebullated bed type reactor. The second stage ebullated bed reactor is operated similarly to the firs
Colyar James J.
MacArthur James B.
Peer Eric D.
IFP North America, Inc.
Preisch Nadine
Ritter John F.
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