Catalytic reactor system

A catalytic reactor system for effecting the contact of a reactant stream with catalyst particles that are movable by gravity flow through the system, which comprises in combination: (a) a vertically elongated confined reaction chamber; (b) a catalyst loading chamber having a fixed volume located outside of and generally overhead of the reaction chamber whereby fresh catalyst particles gravitationally flow downward into the chamber; (c) concentrically spaced apart wall members which provide an annular-form catalyst-retaining section that is spaced inwardly from the wall of the reaction chamber to additionally provide a manifold space around the section and a cylindrical center pipe volume, the wall members having a perforate screen lower end and an imperforate upper end wherein the imperforate upper end defines a portion of the annular-form catalyst-retaining section having a volume of greater than about 100% of the catalyst loading chamber; (d) an imperforate cover means over the annular-form catalyst-retaining section; (e) catalyst transfer means which connects a lower portion of the catalyst loading chamber to the top of the annular-form catalyst-retaining section; (f) catalyst outlet means which connects the annular-form catalyst-retaining section to the lower portion of the reaction chamber; (g) a reactant stream inlet means in communication with the reaction chamber and passageway means to the annular space around the annular-form catalyst-retaining section; (h) a reactant stream outlet means in communication with the reaction chamber and passageway means from the cylindrical center pipe volume within the annular-form catalyst-retaining section to the outlet means; and (i) a plurality of uniformly spaced apart catalyst outlet means provided from the annular-form catalyst-retaining section and from the reaction chamber.

FIELD OF THE INVENTION 
The invention relates to a reactor system and process which is particularly 
useful in the vapor phase conversion of various hydrocarbon feedstocks. In 
particular, the present invention pertains to an apparatus which 
facilitates hydrocarbon conversion wherein the conversion is preferably 
conducted at a high space velocity in a radial flow manner. More 
specifically, the invention relates to a catalytic reactor system for 
effecting the contact of a reactant stream with catalyst particles that 
are movable by gravity flow through the system, which comprises in 
combination: (a) a vertically elongated confined reaction chamber; (b) a 
catalyst loading chamber having a fixed volume located outside of overhead 
of the reaction chamber whereby fresh catalyst and generally particles 
gravitationally flow downward into the chamber; (c) concentrically spaced 
apart wall members which provide an annular-form catalyst-retaining 
section that is spaced inwardly from the wall of the reaction chamber to 
additionally provide a manifold space around the section and a cylindrical 
center pipe volume, the wall members having a perforate screen lower end 
and an imperforate upper end wherein the imperforate upper end defines a 
portion of the annular-form catalyst-retaining section having a volume of 
greater than about 100% of the catalyst loading chamber; (d) an 
imperforate cover means over the annular-form catalyst-retaining section; 
(e) catalyst transfer means which connects a lower portion of the catalyst 
loading chamber to the top of the annular-form catalyst-retaining section; 
(f) catalyst outlet means which connects the annular-form 
catalyst-retaining section to the lower portion of the reaction chamber; 
(g) a reactant stream inlet means in communication with the reaction 
chamber and passageway means to the annular space around the annular-form 
catalyst-retaining section; (h) a reactant stream outlet means in 
communication with the reaction chamber and passageway means from the 
cylindrical center pipe volume within the annular-form catalyst-retaining 
section to the outlet means; and (i) a plurality of uniformly spaced apart 
catalyst outlet means provided from the annular-form catalyst-retaining 
section and from the reaction chamber. 
INFORMATION DISCLOSURE 
Various vapor phase conversion processes have heretofore been effected 
utilizing a reactor system wherein a reactant stream is processed in 
radial flow through a vertically positioned annular-form catalyst bed--an 
arrangement that offers many design and operating advantages, particularly 
with respect to those vapor phase processes for the conversion of 
hydrocarbons. Illustrative of a reactor system wherein a reactant stream 
is caused to flow laterally and radially through an annular-form catalyst 
bed is that described in U.S. Pat. No. 2,683,654. The reactor system 
illustrated is intended for a fixed bed operation. A reactant stream 
charged to a reaction chamber flows from an outer annular-form space 
created between the chamber walls and the annular-form catalyst bed, said 
stream flowing laterally and radially through said catalyst bed and into a 
perforated center pipe to be discharged from the reaction chamber. 
U.S. Pat. No. 3,692,496 describes a somewhat related reactor system in that 
a reactant stream charged to a reaction chamber is caused to flow 
laterally and radially from an outer annular-form space through an 
annular-form catalyst section and into an inner or center manifold to be 
discharged from said chamber. In the latter case, the reactor system 
comprises stacked reaction chambers (and consequently stacked annular-form 
catalyst sections) designed to process catalyst particles downwardly via 
gravity flow from one annular-form catalyst section through the next lower 
annular-form catalyst section, the catalyst particles being recovered from 
the lowermost reaction chamber for regeneration. A variation of the last 
described reactor system appears in U.S. Pat. No. 3,725,248 wherein the 
annular-form catalyst sections are individually contained in side-by-side 
reaction chambers, and in U.S. Pat. No. 3,882,015 wherein the reactant 
stream is reversed to flow laterally and radially from a center reactant 
conduit through an annular-form catalyst section and into an outer 
annular-form space formed by the annular-form catalyst section and the 
reaction chamber walls. 
U.S. Pat. No. 3,706,536 discloses a reactor wherein the reactants flow 
laterally and radially across an annular-form moving catalyst bed. This 
patent is pertinent for its teaching that cylinder form baffle plates 
placed adjacent to each concentric catalyst-retaining screen to 
accommodate varying height catalyst beds in the annular-form catalyst 
section. 
The foregoing reactor systems have heretofore been described with respect 
to vapor phase conversion processes wherein they are employed to effect a 
number of catalyst-promoted conversions. Prominent among such conversion 
processes are the hydrocarbon conversion processes and include catalytic 
reforming, hydrogenation, hydrocracking, hydrorefining, isomerization, and 
dehydrogenation, as well as alkylation, transalkylation, steam reforming, 
and the like. The reactor system of the present invention can be similarly 
employed but is of particular advantage with respect to high space 
velocity operation, such as hydrocarbon dehydrogenation at 
near-atmospheric pressures. 
The present invention provides a novel apparatus adapted to be employed in 
the conversion of hydrocarbons while utilizing reaction conditions which 
include high linear mass velocity perpendicular (radial) to the catalyst. 
Utilization of this apparatus results in the ability to operate a 
hydrocarbon conversion process at conditions which restrict the movement 
or flow of catalyst (pinning) and hold the catalyst against the 
catalyst-retaining screen and yet still change the catalyst inventory in 
the reactor without totall discontinuing the hydrocarbon conversion 
operation. 
BRIEF SUMMARY OF THE INVENTION 
The reactor system of the present invention provides for the containment of 
catalyst particles within an annular-form catalyst-retaining section 
contained in a reaction chamber whereby a reactant stream is contacted 
with said annular-form catalyst section which contacting is conducted at a 
high space velocity--a feature which is of particular advantage with 
respect to certain catalytic hydrocarbon conversion processes. Briefly, 
the reactor system of this invention comprises an annular-form 
catalyst-retaining section being defined by an inner tubular-form 
catalyst-retaining screen coaxially disposed within a vertically 
positioned outer tubular-form catalyst-retaining screen. The lower end of 
said annular form catalyst-retaining section is constructed of perforate 
screen which permits the flow of reactants therethrough and a top end 
which is constructed of an imperforate screen which prevents the flow of 
reactants through the upper portion of said catalyst-retaining section. 
The imperforate upper end defines a portion of said annular-form 
catalyst-retaining section which is sized to have a volume of greater than 
about 100% of the volume of the vessel which is used to introduce catalyst 
into said catalyst-retaining section. Catalyst particles are preferably 
movable through the resulting annular-form catalyst section in a dense 
phase via gravity flow. The reactant stream is introduced into the 
reaction chamber and distributed through the reaction chamber void space 
and distributed into said annular-form catalyst-retaining section across 
the outer catalyst-retaining screen, the reactant stream being directed 
inwardly from said outer catalyst screen, through the annular-form 
catalyst-retaining section in a substantially radialy flow, and into the 
fluid flow conduit defined by the inner catalyst-retaining screen to be 
recovered by means of an outlet port. The reaction chamber of the present 
invention has associated therewith an inlet port and said outlet port each 
located at opposite ends of the reaction chamber. The inlet port serves as 
a means for introducing reactants to the reaction chamber and, as 
mentioned above, the outlet port is used to recover the reactants. 
One embodiment of the invention may be characterized as a catalytic reactor 
system for effecting the contact of a reactant stream with catalyst 
particles that are movable by gravity flow through the system, which 
comprises in combination: (a) a vertically elongated confined reaction 
chamber; (b) a catalyst loading chamber having a fixed volume located 
outside of and generally overhead of the reaction chamber whereby fresh 
catalyst particles gravitationally flow downward into the chamber; (c) 
concentrically spaced apart wall members which provide an annular-form 
catalyst-retaining section that is spaced inwardly from the wall of the 
reaction chamber to additionally provide a manifold space around the 
section and a cylindrical center pipe volume, the wall members having a 
perforate screen lower end and an imperforate upper end wherein the 
imperforate upper end defines a portion of the annular-form 
catalyst-retaining section having a volume of greater than about 100% of 
the catalyst loading chamber; (d) an imperforate cover means over the 
annular-form catalyst-retaining section; (e) catalyst transfer means which 
connects a lower portion of the catalyst loading chamber to the top of the 
annular-form catalyst-retaining section; (f) catalyst outlet means which 
connects the annular-form catalyst-retaining section to the lower portion 
of the reaction chamber; (g) a reactant stream inlet means in 
communication with the reaction chamber and passageway means to the 
annular space around the annular-form catalyst-retaining section; (h) a 
reactant stream outlet means in communication with the reaction chamber 
and passageway means from the cylindrical center pipe volume within the 
annular-form catalyst-retaining section to the outlet means; and (i) a 
plurality of uniformly spaced apart catalyst outlet means provided from 
the annular-form catalyst-retaining section and from the reaction chamber. 
Another embodiment of the invention may be characterized as a catalytic 
reactor system for effecting the contact of a reactant stream with 
catalyst particles that are movable by gravity flow through the system, 
which comprises in combination: (a) a vertically elongated confined 
reaction chamber; (b) a catalyst loading chamber having a fixed volume 
located outside of and generally overhead of the reaction chamber whereby 
fresh catalyst particles gravitationally flow downward into the chamber; 
(c) concentrically spaced apart wall members which provide an annular-form 
catalyst-retaining section that is spaced inwardl from the wall of the 
reaction chamber to additionally provide a manifold space around the 
section and a cylindrical center pipe volume, the wall members having a 
perforate screen lower end and an imperforate upper end wherein the 
imperforate upper end defines a portion of the annular-form 
catalyst-retaining section having a volume of greater than about 100% of 
the catalyst loading chamber; (d) an imperforate cover means over the 
annular-form catalyst-retaining section; (e) catalyst transfer means which 
connects a lower portion of the catalyst loading chamber to the top of the 
annular-form catalyst-retaining section; (f) catalyst outlet means which 
connects the annular-form catalyst-retaining section to the lower portion 
of the reaction chamber; (g) a reactant stream inlet means in 
communication with the reaction chamber and passageway means to the 
cylindrical center pipe volume within the interior of the annular-form 
catalyst-retaining section; (h) a reactant stream outlet means in 
communication with the reaction chamber and passageway means from the 
annular space around the annular-form catalyst-retaining section to the 
outlet means; and (i) a plurality of uniformly spaced apart catalyst 
outlet means provided from the annular-form catalyst-retaining section and 
from the reaction chamber. 
Yet another embodiment of the invention may be characterized as a 
continuous process for hydrocarbon conversion in a high space velocity 
moving bed radial flow reactor containing catalyst which process 
comprises: (a) reducing the inlet temperature of the reactor thereby 
lowering the rate of the hydrocarbon conversion; (b) reducing the mass 
flow rate of the hydrocarbon charge stock sufficiently to unpin the 
catalyst from the reactor thereby ensuring uniform gravitational catalyst 
flow through the reactor; (c) introducing a quantity of fresh catalyst 
into an upper portion of the reactor while simultaneously removing a 
similar quantity of spent catalyst from a lower portion of the reactor; 
(d) increasing the mass flow rate of the hydrocarbon charge stock; and (e) 
increasing the inlet temperature of the reactor to restore the hydrocarbon 
conversion. 
Other embodiments of the present invention encompass further details such 
as preferred mechanical components and design details, all of which are 
hereinafter disclosed in the following discussion of each of these facets 
of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
As illustrated in the drawing, a hydrocarbon charge stock is provided via 
conduit 1 and admixed with a hydrogen-rich stream which is introduced via 
conduit 2 and introduced into charge heater 3 where the reactants are 
heated to a suitable hydrocarbon conversion temperature. The heated 
reactants are removed from charge heater 3 via conduit 4 and introduced 
into reaction chamber 6 via reactant inlet port 5. A product stream is 
removed from reaction chamber 6 via product outlet port 32 and conduit 33. 
As further illustrated in the drawing, the apparatus of the present 
invention comprises reaction chamber 6 which is an elongated vertically 
oriented chamber. At the upper end of reaction chamber 6 is catalyst 
storage vessel 23 which is capable of being emptied in order to transfer 
fresh, either new or regenerated, catalyst particles via conduit 21 and 
valve 22 into catalyst loading chamber 20. In the appropriate sequence, 
the fresh catalyst particles which have been previously loaded are 
permitted to gravitationally flow from catalyst loading chamber 20 via 
conduit 18, valve 19 and conduits 16 and 17 and through catalyst inlet 
ports 15 into reaction chamber 6 via catalyst conduits 14. 
In accordance with the present invention, reaction chamber 6 is provided 
with upper spaced concentric imperforate screen members 10 and 11, 
respectively, and lower spaced concentric perforate screen members 12 and 
13, respectively, to thereby define an annular-form catalyst-retaining 
section 34 and cylinder center pipe volume 8. It will also be noted that 
there is an outer annular-form void space 7 around the full height of the 
outer concentric screen members 10 and 12 whereby there is a resulting 
flow of the reactant stream passing from reactant inlet port 5 and into 
void space 7 and a radial inward flow through perforate screen member 12. 
Imperforate screen member 10 serves to prevent the flow of the reactant 
stream into the upper end portion of catalyst-retaining section 34 and 
thereby precluding the contact of the reactant stream with the catalyst 
until it has gravitationally flowed to the lower end portion of 
catalyst-retaining section 34 which is defined by perforate screen members 
12 and 13. In order to preclude the by-passing of the reactant stream from 
void space 7, there is transverse partition 9 over the upper end portion 
of catalyst-retaining section 34 and cylindrical center pipe volume 8. In 
addition to transverse partition 9, cylindrical center pipe volume 8 is 
defined by inner concentric screen members 11 and 13. Cylindrical center 
pipe volume 8 serves to collect the converted reactants after passage 
through the lower end of catalyst-retaining section 34 and then conducts 
the converted reactants to product outlet port 32 from which a product 
stream is removed from reaction chamber 6 via conduit 33. 
At the desired intervals, the fresh catalyst particles gravitate downwardly 
through catalyst conduits 14 and into the upper end portion of 
catalyst-retaining section 34 and simultaneously, spent catalyst particles 
gravitate downwardly from the lower end portion of catalyst-retaining 
section 34 via catalyst outlet ports 24, conduits 25, 26 and 27, and valve 
28 into catalyst collector hopper 29. After valve 28 has been closed to 
isolate reaction chamber 6 and at the convenience of the operator, the 
spent catalyst particles are then removed from catalyst collector hopper 
29 via conduit 30 and valve 31. 
In accordance with a preferred embodiment of the present invention, a 
hydrogen-rich gas is introduced into the upper portion of annular-form 
catalyst-retaining section 34 via conduits 35 and 36 in conjunction with 
catalyst conduits 14. The introduction of a hydrogen-rich gas via conduits 
35 and 36 is employed when it is desired to reduce the fresh catalyst 
before contact with the hydrocarbonaceous charge stock. This flow of the 
hydrogen-rich gas may be a continuous or intermittent addition and the 
flow volume is relatively small and is preferably less than about 10% of 
the total hydrogen-rich gas introduced into reaction chamber 6. 
While the drawing depicts a sequential flow of hydrocarbon reactants into 
an inlet port at an upper portion of the reaction chamber, through an 
outer annular-form void space, through (in a radially inward fashion) 
perforate screen members containing catalyst, into cylindrical center pipe 
volume and finally through a product outlet port located in a lower 
portion of the reaction chamber, it is understood that the flow of the 
hydrocarbon stream may be reversed so that the hydrocarbon reactant inlet 
is at the lower portion of the reaction chamber and that the product 
outlet port is at the upper portion of the reaction chamber. 
The reactor system of the present invention is of particular advantage with 
respect to the conversion of hydrocarbons and, in particular, the 
dehydrogenation of hydrocarbons in the presence of a dehydrogenation 
catalyst--an established and well-known hydrocarbon conversion process in 
the petroleum refining industry. The invention offers special advantage 
when the hydrocarbon charge stock to be dehydrogenated comprises 
C.sub.2.sup.+ normally gaseous hydrocarbons with the desired product 
comprising the corresponding monoolefins. The monoolefinic products are 
generally useful as intermediates in the production of other more valuable 
products, and the catalytic dehydrogenation process is typically utilized 
in conjunction with various other hydrocarbon conversion processes to 
yield a desired final product. For example, utilizing liquid petroleum gas 
(LPG)--a compressed or liquefied gas consisting of propane and butane or 
mixed butane--as a starting material, catalytic dehydrogenation can be 
utilized to produce propylene and/or butylene in conjunction with an HF 
alkylation unit wherein said olefins are alkylated with isobutane to 
produce a high octane motor fuel; or in conjunction with a catalytic 
condensation unit wherein said olefins are condensed to form tetramers or 
polymer gasoline; or in conjunction with an etherification unit wherein 
isobutylene is reacted with methanol to produce methyl t-butyl ether, a 
highly desirable gasoline additive. Also, for example, the dehydrogenation 
of C.sub.10 -C.sub.14 linear paraffins to C.sub.10 -C.sub.14 linear 
olefins which upon subsequent alkylation with benzene produces linear 
alkylbenzenes which are a valuable biodegradable detergent raw material. 
In addition, any other desired hydrocarbon which may be vaporized can be 
utilized as a charge stock to a dehydrogenation process. 
The catalytic dehydrogenation process will preferably utilize a catalytic 
composite comprising a platinum group metal component, a tin component, 
and an alkali metal component composited with a porous, high surface area, 
adsorbent support or carrier material. Of the platinum group metals, i.e., 
platinum, palladium, ruthenium, rhodium, osmium and iridium, platinum is a 
preferred catalyst component. The platinum component will generally 
comprise from about 0.01 to about 2.0 wt. % of the catalytic composite, 
and the tin component will generally comprise from about 0.1 to about 5 
wt. % thereof. Of the alkali metals, i.e., cesium, rubidium, potassium, 
sodium, and lithium, lithium and/or potassium are preferred. The alkali 
metal will generally constitute from about 0.1 to about 3.5 wt. % of the 
catalytic composite. One preferred catalytic composite comprises from 
about 0.1 to about 1 wt. % platinum, and from about 0.1 to about 1 wt. % 
tin and from about 0.2 to about 3 wt. % lithium or potassium composited 
with a porous adsorbent support or carrier material having a surface area 
of from about 25 to about 500 m.sup.2 /g. The preferred carrier materials 
are the refractory inorganic oxides with best results being obtained with 
an alumina support or carrier material. 
The catalytic dehydrogenation process herein contemplated is a relatively 
high temperature operation effected at a temperature of from about 
700.degree. F. (371.degree. C.) to about 1400.degree. F. (760.degree. C.), 
and preferably from about 850.degree. F. (454.degree. C.) to about 
1300.degree. F. (704.degree. C.). The process is also a relatively low 
pressure operation effected at a pressure of from subatmospheric to about 
50 psig (345 kPa gauge), preferably from about 5 psig (34.5 kPa gauge) to 
about 30 psig (207 kPa gauge). Notwithstanding that the catalytic 
dehydrogenation process involves hydrogen-producing reactions, it has been 
the practice to charge hydrogen to the reaction zone, typically recycle 
hydrogen, in admixture with the hydrocarbon feedstock--a practice which 
has been found to promote catalyst activity as well as stability. 
Dehydrogenation conditions thus further include a hydrogen to hydrocarbon 
mole ratio from about 0.5 to about 10, and more preferably from about 1 to 
6. Additionally, the catalytic dehydrogenation process is preferably 
conducted at relatively high liquid hourly space velocity so that the 
reactants have minimal exposure to thermal conversion conditions prior to 
contact with the dehydrogenation catalyst to substantially obviate 
conversion to other than the desired dehydrogenation products, that the 
reactants are not overly-converted when they are contacted with the modern 
high activity dehydrogenation catalysts which are available and that the 
resulting dehydrogenation products are not subjected to an inordinate 
heat-soak before exiting from the dehydrogenation zone. Catalytic 
dehydrogenation is preferably conducted at liquid hourly space velocities 
from about 5 to about 40 hr.sup.-1 and more preferably from about 10 to 
about 20 hr.sup.-1. Especially preferred conditions for the 
dehydrogenation of C.sub.10 -C.sub.14 linear paraffins include a 
temperature from about 800.degree. F. (426.degree. C.) to about 
1000.degree. F. (538.degree. C.), a pressure from about 5 psig (34.4 kPa 
gauge) to about 30 psig (207 kPa gauge), a hydrogen to hydrocarbon mole 
ratio from about 2 to about 6, and a liquid hourly space velocity from 
about 10 to about 40 hr.sup.-1. Such relatively high space velocities 
conducted in a radial flow catalyst system tends to cause moderate to 
severe catalyst pinning which prevents or hinders the uniform flow of 
catalyst into and out of the catalyst bed by gravity flow. The result of 
pinning is that the high velocity horizontally flowing gases hold the 
catalyst next to the catalyst-retaining screen which prevents smooth, 
unimpeded gravity flow of the catalyst particles through the reaction 
zone. Previously, those practicing hydrocarbon conversion at high space 
velocities had to deal with the problem of removing catalysts from a 
catalyst bed by shutting down and reloading the catalyst bed with fresh 
catalyst or switching to another catalyst bed which has been prepared with 
fresh catalyst. In modern day hydrocarbon conversion processes, the 
ability to operate on a continuous basis is a great advantage. Previously, 
in a high space velocity hydrocarbon conversion process, a swing reactor 
system was utilized to maintain processing continuity. Since the reactant 
stream in a hydrocarbon dehydrogenation process is a high temperature 
vaporous stream moving at a high velocity, the swing reactor system 
requires additional extensive large diameter piping and valving in order 
to be able to switch from one catalyst bed to another. The valves utilized 
in this service are required to be large in diameter, to be able to 
operate in the open position without unduly restricting flow, to possess 
the ability to operate at high temperatures and to reliably stop the flow 
of hot hydrocarbonaceous reactants. These valves are by their very nature 
expensive and have a tendency to leak and therefore constantly require 
continuous maintenance for the sake of overall safety and operability. 
Therefore, in accordance with the present invention the capital cost of a 
hydrocarbonaceous dehydrogenation process is reduced since there is no 
longer a need for the piping manifold, block valves, parallel reaction 
vessel, and an auxiliary pre-heat furnace needed to preheat the standby 
reactor before switching it to the processing mode. 
In addition to the catalytic dehydrogenation of hydrocarbons, the present 
invention is particularly useful for catalytic reforming which is also an 
established and well-known hydrocarbon conversion process in the petroleum 
refining industry. 
In accordance with one embodiment of the present invention, the mass flow 
rate is preferably reduced by about 10% to about 80% after the inlet 
temperature of the reactor has preferably been reduced by about 18.degree. 
F. (10.degree. C.) to about 108.degree. F. (60.degree. C.) in order to 
ensure that the catalyst is no longer pinned to the catalyst-retaining 
screen which promotes gravity flow of the catalyst particles. It is 
preferred that the mass flow rate is reduced by lowering both the 
hydrocarbon feed and the recycle hydrogen while maintaining a constant 
recycle hydrogen to hydrocarbon feed ratio to avoid catalyst damage. The 
reduction in inlet temperature is accomplished by reducing the heat 
supplied to the combined feed by heat exchangers and/or charge heaters. 
During the period of reduced mass flow rate, product recovery facilities 
including fractionation may be conveniently "turned down" without the 
discontinuation of operation which avoids the inconvenience of a complete 
shutdown. 
In a commercial size processing unit, we contemplate that the reduced mass 
flow rate will last for about 2 to 8 hours. Under certain circumstances, 
the duration of the reduced mass flow rate could be even less. In 
addition, we contemplate that the removal of a portion of catalyst from 
the reaction zone would occur, for example, once every week. 
As hereinabove described, the annular form catalyst-retaining section is 
constructed of a top end which is an imperforate screen which prevents the 
flow of reactants through the upper portion of the catalyst-retaining 
section. This imperforate upper end defines a portion of the annular-form 
catalyst-retaining section which is sized to have a volume of greater than 
about 100% of the volume of the vessel (catalyst loading chamber) which is 
used to introduce catalyst into the catalyst-retaining section. The 
purpose of having such an imperforate upper end is to permit the gradual 
heating of the newly introduced fresh catalyst before this catalyst is 
contacted with hot hydrocarbonaceous reactant feedstock. This heatup of 
fresh catalyst in the absence of hydrocarbon reactants is desirable to 
avoid condensation of the vapor hydrocarbons on cold catalyst. Contact of 
liquid hydrocarbons with the catalyst during increasing temperature 
promotes accelerated undesirable coke formation on the catalyst which is 
manifested by catalyst deactivation. 
The foregoing description clearly illustrates the advantages encompassed by 
the apparatus and process of the present invention and the benefits to be 
afforded with the use thereof.