FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: CATALYST CAGE FOR THREE-PHASE CATALYTIC
HYDROPROCESSING
2. Applicant(s)
NAME NATIONALITY ADDRESS
BHARAT PETROLEUM CORPORATION LTD. Indian Bharat Bhavan, 4 & 6 Currimbhoy Road, Ballard Estate, Mumbai Maharashtra 400001, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICAL FIELD
[0001] The present subject matter relates generally to three-phase fixed bed
reactors and methods for refining hydrocarbons, and in particular, to cross-flow reactors for three-phase hydroprocessing.
BACKGROUND
[0002] Three phase (gas-liquid-solid) fixed bed catalytic reactors or trickle
bed reactors (TBR) are omnipresent in various industries such as petroleum refining, chemical, and petrochemical. In petroleum refining, the reactors are mainly used for hydroprocessing applications where crude oil feedstock is processed to obtain a desired product quality. Crude oil is a hydrocarbon feedstock and predominantly includes various petroleum fractions such as naphtha, diesel, and heavy oils. In a petroleum refinery, the crude oil is distilled to produce light fractions and the heavier hydrocarbons are subjected to secondary processing to maximize the light distillate yields. In hydroprocessing, unsaturated hydrocarbons are saturated, impurities (such as sulfur, nitrogen, metals, etc.) are removed, and long chain hydrocarbons are broken into small chain hydrocarbons.
BRIEF DESCRIPTION OF DRAWINGS
[0003] The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a reference number
identifies the figure in which the reference number first appears. The same numbers
are used throughout the drawings to reference like features and components where
possible.
[0004] Fig. 1 illustrates an example reactor assembly, in accordance with
an embodiment of the present subject matter.
[0005] Fig. 2(a) illustrates an example catalyst cage, in accordance with an
embodiment of the present subject matter.

[0006] Fig. 2(b) illustrates a top view of an example catalyst cage, in
accordance with an embodiment of the present subject matter.
[0007] Fig. 3 illustrates another example reactor assembly, in accordance
with an embodiment of the present subject matter.
[0008] Fig. 4(a) illustrates another example catalyst cage, in accordance
with an embodiment of the present subject matter.
[0009] Fig. 4(b) illustrates a top view of the example catalyst cage, in
accordance with an embodiment of the present subject matter.
[0010] Fig. 5 illustrates an example reactor with multiple catalyst cages, in
accordance with an embodiment of the present subject matter
[0011] Fig. 6 illustrates an example reactor comprising a plurality of
catalyst cages and a liquid distributor, in accordance with an embodiment of the
present subject matter.
[0012] Fig. 7(a) illustrates an example liquid distributor, in accordance with
an embodiment of the present subject matter.
[0013] Fig. 7(b) illustrates a top view of an example liquid distributor, in
accordance with an embodiment of the present subject matter.
[0014] Fig. 8(a) illustrates another example liquid distributor and Fig. 8(b)
illustrates a top view of the liquid distributor, in accordance with an embodiment
of the present subject matter
[0015] Fig. 9 illustrates an example gas distributor, in accordance with an
embodiment of the present subject matter.
[0016] Fig. 10 illustrates another example gas distributor, in accordance
with an embodiment of the present subject matter.
[0017] Fig. 11 illustrates a plot of G/O ratio and superficial liquid velocity,
in accordance with an embodiment of the present subject matter.
[0018] Fig. 12 illustrates a schematic representation of the lengths of
different regions of the gas distributor, in accordance with an embodiment of the
present subject matter.
DETAILED DESCRIPTION

[0019] The present subject matter relates generally to three-phase fixed bed
reactors and methods for refining hydrocarbons, and in particular, to cross-flow reactors for three-phase hydroprocessing.
[0020] Conventionally, hydroprocessing is done in co-current down flow
trickle bed reactors (TBRs) at high temperature and pressure. In the co-current mode, reactants flow in the same direction inside the reactor and in the counter-current mode, the flow of reactants is opposite to each other inside the reactor. Hydroprocessing is highly exothermic in nature where liquid hydrocarbon feedstock reacts with the reacting gas, such as hydrogen, in the presence of a suitable catalyst to achieve several objectives such as desulfurization, denitrogenation, hydrogenation, hydrocracking, and isomerization. These reactions are carried out adiabatically with intermediate quenching to arrest the rise in bed temperature. High gas-to-oil ratios are generally used for hydroprocessing, which results in undesired liquid feed vaporization and increased pressure drop in the catalyst bed. As the hydroprocessing reaction progresses throughout the bed, product gases such as hydrogen sulfide (H2S) and ammonia (NH3) are produced. This causes a decrease in the hydrogen partial pressure and thus results in decreased rate of saturation, desulfurization, and denitrogenation reactions. In addition, production of the product gases causes an increase in gas holdup from the reactor inlet to outlet. Owing to this, catalyst wetting is reduced and product quality is reduced.
[0021] Another issue in TBR is dry spot formation in the middle of the bed.
These dry spots are formed because of the poor distribution of the liquid feedstock in the catalyst bed, vaporization of the liquid feedstock, high gas holdup, etc. which results in underutilization of the catalyst bed.
[0022] An optional reactor proposed in the art is a radial flow reactor, which
is predominantly used for applications such as naphtha reforming, and ammonia synthesis. These reactors overcome the drawbacks of co-current and counter-current reactors and are mainly used for gas phase reactions. Another variant of such reactors for three phase reactions, especially for hydroprocessing, proposed in the art is a cross flow reactor (CFR). In CFR, gas flows in the radial direction and

liquid flows in the axial downward direction. The product gases and unreacted gases can travel in an axial direction for exiting the reactor after contact with the catalyst. CFR overcomes the disadvantages of the co-current and counter-current trickle bed reactors and has reduced pressure drop, reduced liquid vaporization, reduced consumption of reactant gas, enhanced reaction rate for desired reaction, reduced product inhibition rate, and reduced bed temperature.
[0023] In a CFR, gas travels in the radial direction and liquid travels in the
axial downward direction because of gravitational force. Liquid hydrocarbon optionally along with H2 may be introduced from the top through a liquid distributor. Any liquid distributor known in the art may be used for spraying the liquid at the top of the bed. The catalyst in the middle region is wetted by the liquid flowing from top to bottom in the downward direction. At the catalyst site, liquid hydrocarbon comes in contact with the reactant gas, such as hydrogen, flowing in the radial direction. This contact of liquid feedstock with reacting gas results in hydroprocessing, which includes reactions like desulfurization, hydrogenation, denitrogenation, and hydrocracking. Product gases like hydrogen sulfide, ammonia, etc. are generated in the catalytic bed section. Product gases along with unreacted reactant gases flow in the radial direction because of pressure difference and are collected in the outer gas conduit. Gases along with any entrained liquid is sent to a separator for recovering unreacted hydrogen and vaporized light liquid hydrocarbons.
[0024] Based on experimental investigations, it was observed that liquid
drift is a significant issue in CFR. Liquid drift or liquid weeping is defined as the volume of the liquid phase coming out of catalyst bed either unreacted or partially reacted and going to the outer gas conduit region. Radial flow of the gas imparts momentum to the liquid phase in the radial direction leading to change in the direction of the liquid flow and hence, some part of the liquid comes out of the catalyst cage. Owing to this, the overall conversion reduces and catalyst in the region close to the gas distributor becomes dry and has no or very less contact with the liquid phase. This results in underutilization of the total catalyst inventory and also leads to poor product quality of the hydroprocessed liquid feed stock. The

volume of liquid drifting out the catalyst bed depends upon the density of the gas phase and liquid phase, bed porosity, viscosity of liquid and gas phase, gas-liquid drag force, gas-solid drag force, liquid-solid drag force, conduit back pressure and process operating conditions. This observation has been confirmed by experiments and momentum calculations. Hence, there is a need for an improved design of the CFR.
[0025] The present subject matter overcomes these and other problems and
relates to a catalyst cage for holding a catalyst and a reactor assembly comprising the catalyst cage. The catalyst cage comprises a hollow mesh structure. The hollow mesh structure comprises an outer wall forming an outer circumference and an inner wall disposed inside the outer wall forming an inner circumference. Catalyst may be disposed in the volume between the outer wall and the inner wall. The hollow mesh structure comprises a top wall disposed on a top portion of the outer wall and a bottom wall disposed on a bottom portion of the outer wall. The top wall and the bottom wall connect the outer wall and the inner wall. A first passage connecting the top wall and the bottom wall allows for a gas distributor to pass through. A plurality of catalyst cages may be disposed in the reactor assembly. A liquid distributor may be removably coupled to the bottom portion of the mesh structure and allow for collecting any weeping liquid from the catalyst cage and distribute it uniformly to the subsequent catalyst cage. In an example, the catalyst cage may comprise a plurality of first passages to allow for multiple gas distributors to pass through.
[0026] The use of the catalyst cages in a reactor assembly allows for
reduced liquid weeping, for example, when the entire CFR is divided into several sections each comprising a catalyst cage. This is analogous to having multiple CFRs in series. This arrangement will reduce liquid weeping, owing to reduced gas-to-oil ratio in individual cages. Smaller the length of cages, the less will be liquid weeping. However, the optimum cage size is decided based on the experimental feasibility curve obtained for CFR and optimum length/diameter ratio. It will also substantially reduce the dry zone in the catalyst bed and ease the operation of catalyst loading and unloading and subsequently reduces the turnaround time.

When catalyst is to be replaced, the catalyst cages may be easily removed, catalyst replaced, and the catalyst cages replaced. This makes it easier, more efficient, and faster to replace catalysts compared to replacing the catalyst in the entire reactor. Catalyst cages with new or regenerated catalyst may be prepared ahead of time and may be placed into the reactor after removing the catalyst cage with the used catalyst. This makes for much faster turnaround time during catalyst replacement, reducing reactor down time and thus reducing operating costs.
[0027] The use of multiple gas distributors leads to reduced catalyst dry
zone near the gas distributor and causes effective utilization of the catalyst bed. It also reduces the local gas velocity from gas distributors and subsequently, reduced liquid weeping. In addition, the presence of the liquid distributor will not only reduce the liquid weeping but also minimize the liquid drift owing to the cross flow of gas, resulting in good redistribution of liquid across the reactor.
[0028] Aspects of the present subject matter are further described in
conjunction with the appended figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter. It will thus be appreciated that various arrangements that embody the principles of the present subject matter, although not explicitly described or shown herein, can be devised from the description and are included within its scope. Moreover, all statements herein reciting principles, aspects, and implementations of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0029] Fig. 1 illustrates an example cross flow reactor assembly, in
accordance with an embodiment of the present subject matter. The reactor assembly 100 comprises a shell 104. The arrows indicate the direction of flow of liquid and gas. In an example, the reactor assembly 100 may comprise an inner gas distributor zone 108, a central catalyst holding zone 112, and an outer gas conduit zone 116 for collecting product and unreacted gases. In another example, the shell 104 may enclose a catalyst cage 120. The catalyst cage 120 may comprise the inner gas distributor zone 108 and the catalyst holding zone 112. In another example, the reactor assembly 100 may comprise a plurality of catalyst cages 120 (120a, 120b,

120c,…). The catalyst cages 120 may be disposed one on top of the other. Feed
may be introduced from the top of the reactor assembly 100. The feed may be one
of a fresh feed, recycled feed, or a combination thereof. A gas inlet 130 may be
disposed on a top portion of the reactor assembly 100 to allow gas to enter the
reactor assembly 100. In example, the gas introduced may be hydrogen.
[0030] A liquid distributor 140 may be removably coupled to the catalyst
cage 120a. The liquid distributor 140 allows for collecting any weeping liquid and distribute it along with liquid feed to the next catalyst cage 120b. During operation, fresh hydrocarbon feed along with gas enters the reactor assembly 100 from the top. Liquid flows in an axial direction downward and gas flows in a radial direction from the inner gas distributor zone 108 in a substantially cross-flow direction to the flow of liquid. Hydroprocessing reactions occur in the catalyst holding zone 112 comprising catalyst. Reacted liquid may be collected from a liquid outlet 160 disposed on a bottom portion of the reactor assembly 100. The reacted liquid may comprise a mixture of product liquid and unreacted or partially reacted liquid. A portion of the liquid collected from the liquid outlet may be recycled back and allowed to enter the reactor assembly 100 along with fresh feed. Another portion of the liquid collected may be sent for further processing such as purification and separation. Effluent gas 170 comprising product gases and any unreacted gas may be collected from the outer gas conduit zone 116.
[0031] Fig. 2(a) illustrates an example catalyst cage, in accordance with an
embodiment of the present subject matter. In an example, the catalyst cage 120 comprises a hollow mesh structure 210. The mesh structure 210 comprises an outer wall 220 forming an outer circumference of the mesh structure 210. An inner wall 230 may be disposed inside the outer wall 220, the inner wall 230 forming an inner circumference of the mesh structure 210. The outer wall 220 and the inner wall 230 may have a certain thickness. A volume between the outer wall 220 and inner wall 230 may hold catalyst. In an example, the volume may be the catalyst holding zone 112. Any catalyst known in the art may be used. A top wall 240 and a bottom wall 250 are disposed so that they connect the outer wall 220 and inner wall 230 on a top and bottom portion, respectively, of the outer wall 220 and inner wall 230. The

hollow mesh structure 210 may comprise grids of a suitable size and shape so the
mesh structure 210 can retain the catalyst. The mesh size is dependent on the type
and size of catalyst to be used for hydroprocessing in the catalyst cage 120. The
fraction of openings of the mesh size is such that it can easily retain the catalyst
within the cage and its value should be more than the bed voidage, which is the
space occupied by gas in the catalyst bed. Any material known in the art, such as
metal and plastic may be used to make the hollow mesh structure 210. In an
example, the hollow mesh structure 210 comprises a plurality of intersecting beams
disposed on a grating structure. The catalyst cage 120 may be of a shape
corresponding to the shape of the shell 104. In an example, when the shell 104 is
cylindrical in shape, the catalyst cage 120 may be cylindrical in shape.
[0032] The hollow mesh structure 210 comprises a first passage 260
connecting the top wall 240 and the bottom wall 250. The inner wall 230 forms an
outer boundary of the first passage 260. In an example, the first passage 260 is to
allow for a gas distributor 270 to pass through. In another example, the first passage
260 may form the gas distributor 270. The inner wall 230 of the hollow mesh
structure 210 may comprise perforations to allow gas to be distributed to the
catalyst. The gas distributor 270 may be removably coupled to the first passage 260.
[0033] In an example, a vertical support 282 may be disposed on the outer
wall 220 for supporting the mesh structure 210 in a vertical direction. The vertical support 282 may comprise metal strips. A horizontal support 286 may be disposed along a radial direction of the hollow mesh structure 210 and connected to the outer wall 220 for supporting the mesh structure 210 along the radial direction. The horizontal support 286 may comprise metal strips. In an example, the vertical support 282 and horizontal support 286 may be welded to each other. In another example, the horizontal support 286 may comprise a plurality of rings disposed along a vertical axis of the hollow mesh structure 210. In another example, the horizontal support 286 may be disposed on a bottom portion of the catalyst cage 120. A gas distributor support may be disposed in a radial direction on a top portion of the mesh structure 210 to support the gas distributor 270. The vertical support 282, the horizontal support 286, and the gas distributor support may be made of any

material strong enough to support the weight of the catalyst and the gas distributor. The liquid feedstock within the catalyst bed may be constrained by a mesh having the same opening size as that of the bottom mesh.
[0034] Fig. 2(b) illustrates a top view of an example catalyst cage, in
accordance with an embodiment of the present subject matter. The catalyst cage
comprises the outer wall 220, the inner wall 230, and the first passage 260. A gas
distributor 270 may be removably coupled to the first passage 260. Horizontal
support 286 may be disposed on a top portion of the catalyst cage 120.
[0035] Fig. 3 illustrates another example reactor assembly, in accordance
with an embodiment of the present subject matter. The reactor assembly 300 comprises a plurality of catalyst cages 320. A liquid distributor 140 may be disposed between two catalyst cages 320. The catalyst cage 320 comprises a plurality of first passage 260 to allow for a plurality of gas distributors 270 to pass through. The volume between the plurality of first passage 260 and the outer wall 220 of the catalyst cages 320 may be filled with catalyst. In an example, a plurality of gas distributors 270 may be removably coupled to the plurality of first passage 260. During operation, liquid feed 150 may be allowed to enter the reactor assembly 300 from the top and allowed to enter the catalyst cage 320. Gas may enter the reactor assembly 300 via the gas inlet 130 disposed on a top portion of the reactor assembly 300. The gas may enter the plurality of gas distributors 270 and enter the catalyst from the gas distributors 270. Liquid product may be collected from a liquid outlet 160 of the reactor assembly 300, and effluent gas 170 comprising product gas may be removed from the outer gas conduit zone 116.
[0036] Fig. 4(a) illustrates another example catalyst cage, in accordance
with an embodiment of the present subject matter. The catalyst cage 320 comprises a hollow mesh structure comprising an outer wall 220 forming an outer circumference of the mesh structure. A top wall 240 and a bottom wall 250 may be disposed on a top portion and a bottom portion of the outer wall 220. A plurality of first passage 260 are disposed in the hollow mesh structure so that the plurality of passages connects the top wall 240 and the bottom wall 250. The plurality of first passage 260 may each comprise an inner wall 230, forming an outer boundary of

the plurality of first passage 260. Catalyst may be disposed in the volume between
the plurality of first passage 260 and the outer wall 220. In an example, the plurality
of first passage 260 allow a plurality of gas distributors to be removably coupled to
the catalyst cage 320. In another example, the inner wall 230 of each first passage
260 may comprise perforations to allow gas to pass through to the catalyst.
[0037] The presence of multiple gas distributors 270 helps reduce weeping
of liquid and allows for introducing fresh gas at high concentration at different radial locations in the catalyst cage 320. Another advantage is that it reduces dry catalyst bed zones that are is due to the decrease in local gas velocity. Dry bed zones also lead to a decrease in conversion and catalyst deactivation. Fresh gas, for example hydrogen, at low temperature is available at different axial locations and radial locations leading to decrease in hot spots and decreased liquid feed vaporization inside the catalyst bed.
[0038] The introduction of the gas through the plurality of gas distributors
270 leads to increased gas partial pressure at all radial locations inside the middle part of the catalyst bed. Reaction rate of hydroprocessing reactions is directly proportional to the hydrogen partial pressure. Increased partial pressure in CFR increases the reaction rate of hydroprocessing, leading to effective removal of unwanted compounds from liquid hydrocarbon feedstock. With the introduction of a plurality of gas distributors 270, the pressure drop is further reduced compared to conventional CFR as the mean flow of the gases is significantly less as compared to counter current, co-current TBR, and conventional CFR. Addition of fresh hydrogen at every axial height in CFR leads to reduced bed temperature and decreases feed vaporization.
[0039] The continuous removal of the product gases in the radial direction
at several axial locations leads to significant reduction in the product inhibition effect. Placement and design of the plurality of gas distributors 270 may be determined based on the operation and reaction kinetics requirement. In one example, five gas distributors 270 may be present, with one in the center of the catalyst cage and the other four gas distributors 270 placed at a distance of 0.5 times the radius of the catalytic cage from the center of the catalyst cage. When a plurality

of gas distributors 270 are present, the main gas comes through a single or multiple manifold and is divided into the number of individual gas distributors 270. Design and number of gas distributors 270 may be changed according to the need and may be estimated by a person skilled in the art.
[0040] Fig. 4(b) illustrates a top view of the example catalyst cage, in
accordance with an embodiment of the present subject matter. The catalyst cage 320 comprises the outer wall 220 and a plurality of first passage 260.
[0041] Fig. 5 illustrates an example reactor with multiple catalyst cages, in
accordance with an embodiment of the present subject matter. In an example, first catalyst cage 320a is disposed on top of second catalyst cage 320b and may be enclosed in the shell 104. In an example, the catalyst cage 320 may be the same as the catalyst cage 120. The catalyst cages 320a and 320b comprise a plurality of first passage 260 and the catalyst cages 320a and 320b are aligned so that the plurality of first passage 260 of the first catalyst cage 320a correspond to the plurality of first passage 260 of the second catalyst cage 320b. The catalyst cages 320a and 320b are connected in series so that liquid feed and gas flow down from the first catalyst cage 320a to the second catalyst cage 320b. In an example, when catalyst is to be replaced, one or both catalyst cages 320a and 320b may be removed and replaced with catalyst cages 320 comprising fresh or regenerated catalyst. This allows for reduced reactor downtime time, increased efficiency, and lower operating costs. In another example, any number of catalyst cages 320 or 120 may be disposed in the reactor assembly 100 and 300, respectively.
[0042] The catalyst in the catalyst cages 120 and 320 may vary depending
on the reaction taking place. For hydroprocessing applications, the exothermicity of the reactor decreases with increase in the bed height and the maximum bed temperature is observed in the first few meters of the catalyst bed. Therefore, the probability of catalyst coking is maximum in the catalyst cages 120 and 320 at the top of the catalyst bed. In an example, catalyst diluent material may be added along with the catalyst in the catalyst cages 120 and 320 at the top of the bed. The ratio of catalyst to diluent can vary depending upon the reaction and operating condition.

A person skilled in the art can estimate the ratio of catalyst to diluent based on the above considerations.
[0043] Fig. 6 illustrates an example reactor comprising a plurality of
catalyst cages and a liquid distributor, in accordance with an embodiment of the present subject matter. In an example, the first catalyst cage 320a is disposed on top of the second catalyst cage 320b. The liquid distributor 140 is disposed between the first catalyst cage 320a and the second catalyst cage 320b. The liquid distributor 140 allows for collecting any weeping liquid from the first catalyst cage 320a and distribute it along with liquid feed to the second catalyst cage 320b. Depending on whether the catalyst cages 120 and 320 have a single first passage 260 or plurality of first passage 260, the liquid distributor 140 may have the corresponding number of second passages. The liquid distributor 140 and the catalyst cage 120 and 320 may be aligned so that the first passage 260 and the second passage form a continuous passage.
[0044] Fig. 7(a) illustrates an example liquid distributor, in accordance with
an embodiment of the present subject matter. The liquid distributor 140 may be removably coupled to a bottom portion of a first hollow mesh structure 210a of the catalyst cage 120 and 320. The first hollow mesh structure 210a may be of the catalyst cage 120 and 320 placed on top of the liquid distributor 140. The liquid distributor 140 receives fluid flowing from the catalyst present in the first hollow mesh structure 210a and any weeping liquid.
[0045] The liquid distributor 140 comprises a bottom lid 710 comprising a
plurality of outlets 720. The bottom lid 710 comes in contact with the top wall 240 of a second hollow mesh structure 210b. The second hollow mesh structure 210b may be of the catalyst cage 120 and 320 disposed below the liquid distributor 140. The plurality of outlets 720 allows fluid collected in the liquid distributor 140 to exit the liquid distributor 140 and flow into the catalyst disposed in the second hollow mesh structure 210b.
[0046] The liquid distributor 140 comprises a first circumferential wall 730
extending from the bottom lid 710 and the first circumferential wall 730 forms an outer circumference of the liquid distributor 140. In an example, a diameter of a top

of the first circumferential wall 730 may be larger than a diameter of the first hollow mesh structure 210a. In another example, the diameter of the top of the first circumferential wall 730 is larger than a diameter at a bottom of the first circumferential wall 730. A second circumferential wall 740 may be disposed inside the first circumferential wall 730 extending from the bottom lid 710. The second circumferential wall 740 may form an outer boundary of a second passage 760. The second passage 760 corresponds to the first passage 260, and the second passage 760 and the first passage 260 form a single passage when the liquid distributor 140 is coupled to the hollow mesh structure 210. The second passage 760 allows gas flowing from the first passage 260 of the first hollow mesh structure 210a to flow to the first passage 260 of the second hollow mesh structure 210b. The size of the second passage is substantially the same or slightly larger than the size of the gas distributor 270.
[0047] In an example, the plurality of outlets 720 comprise circular holes.
The plurality of outlets 720 may be of the same size or of varying size. The shape of the plurality of outlets 720 may be any shape such as elliptical, circular, or others. Sufficient liquid head may be maintained in the liquid distributor 140 to avoid short circuiting of gas through liquid distributor 140 and for ensuring proper liquid distribution to the next catalyst cage 120 or 320. The liquid distributor 140 is properly sealed with the catalyst cages 120 and 320 to avoid any leakage of gas or liquid. The gas distributor 270 may be properly sealed in the second passage 760 to prevent leakage of gas and liquid. In an example the gas distributor 270 may be removably coupled to the liquid distributor 140. In another example, the gas distributor 270 may be welded to the liquid distributor 140.
[0048] Fig. 7(b) illustrates a top view of an example liquid distributor, in
accordance with an embodiment of the present subject matter. The liquid distributor 140 comprises the bottom lid 710 comprising the plurality of outlets 720. The first circumferential wall 730 extends from the bottom lid 710. The second circumferential wall 740 may be disposed inside the first circumferential wall 730 and extend from the bottom lid 710 and form the second passage 760. A gas distributor 270 may be disposed in the second passage 760.

[0049] Fig. 8(a) illustrates another example liquid distributor and Fig. 8(b)
illustrates a top view of the liquid distributor, in accordance with an embodiment of the present subject matter. In an example, when the catalyst cage 320 comprises a plurality of first passage 260, the liquid distributor 140 may comprise a plurality of second passages 760, corresponding to the plurality of first passage 260. The size of the plurality of second passages 760 may be substantially the same or slightly larger than the size of the gas distributor 270 to allow the gas distributor 270 to pass through the plurality of second passages 760. The plurality of gas distributors 270 may be sealed properly with the liquid distributor 140 to prevent any leakage of liquid.
[0050] Fig. 9 illustrates an example gas distributor, in accordance with an
embodiment of the present subject matter. In an example, the gas distributor 270 may comprise a single pipe passing through the first passage 260 and second passage 760 along the axis of the reactor assembly 100 or 300 and comprises perforations 910. The perforations 910 are present on a portion of the gas distributor 270 in contact with the catalyst cages 120 and 320. A portion of the gas distributor 270 in contact with the liquid distributor 140 does not have any perforations. The number and size of perforations for a catalyst cage 120 or 320 depends upon the axial height of the reactor and reaction occurring in the bed. For example, in hydroprocessing applications, requirement of H2 is maximum at the top of the catalyst bed and the requirement decreases with the increase in axial length. This requirement of H2 is dictated by conversion and heat generation due to reaction, which decreases with increase in distance through the catalyst bed. In an example, the number of perforations 910 in the gas distributor 270 decreases along the vertical axis of the reactor assembly. Hence, more hydrogen will be available for hydroprocessing in the top catalyst cage 120 and 320. In another example, the perforations 910 in the gas distributor 270 may be evenly spaced along the vertical axis of the reactor assembly 100 or 300.
[0051] Fig. 10 illustrates another example gas distributor, in accordance
with an embodiment of the present subject matter. In an example, the gas distributor 270 may comprise a primary gas distributor 1010 and a set of secondary gas

distributors 1020. The secondary gas distributor 1020 may be of a size larger than the primary gas distributor 1010 and may be disposed concentric to the primary gas distributor 1010. The secondary gas distributor 1020 may comprise openings, for example, vertical slits 1030. In an example, the vertical slits 1030 may be present throughout the secondary gas distributor 1020. In another example, the vertical slits 1030 may be present on portions of the secondary gas distributor 1020. Gas coming out of the primary gas distributor 1010 hits these vertical slits 1030 and its velocity is reduced when it enters the catalyst cage 120 or 320. This allows for reduced catalyst attrition in the region close to the gas distributor 270. In an example, the primary gas distributor 1010 may be a single pipe running from the top to the bottom of the reactor assembly 100. In another example, the primary gas distributor may be a plurality of pipes disposed at specific radial locations when the catalyst cage 320 comprises a plurality of first passage 260. In yet another example, both the primary and secondary gas distributor may pass through all the catalyst cages 120 and 320 in one piece. In another example, the secondary gas distributor may be welded to the catalyst cage 120 or 320. Here, every catalyst cage 120 and 320 may have its own secondary gas distributor 1020 and the primary gas distributor 1010 runs through all catalyst cages 120 and 320 in one piece.
[0052] During operation of the reactor assembly 100 or 300, plurality of
catalyst cages 120 or 320 may be disposed one of top of the other, separated by the liquid distributor 140. Partially reacted feed exiting from one catalyst cage 120 or 320 enters the next catalyst cage 120 or 320. In an example, the activity of the catalyst disposed in the catalyst cages 120 and 320 may increase from the top to the bottom of the reactor assembly 100 and 300. The dimension of the catalyst cages 120 and 320 may be determined based on the requirement of gas-to-oil (G/O) ratio, superficial liquid velocity or throughput. The cumulative length of the catalyst cages 120 and 320 may be equivalent to the reactor height. Fig. 11 illustrates a plot of G/O ratio and superficial liquid velocity, in accordance with an embodiment of the present subject matter. The plot is based on the experiments performed on different lab scale CFR setups. This plot gives the weeping free operating regime, which is the region below the curve shown by region 1110. To operate in the

weeping free regime for a particular superficial liquid velocity, the G/O ratio may be determined from the graph, or vice versa. The region above the curve is the weeping region 1120. The dimensions of the cage, i.e., the diameter and length may be determined by fixing the G/O ratio and superficial liquid velocity and utilizing the weeping plot as shown in Fig. 11.
EXAMPLES
[0053] The disclosure will now be illustrated with working examples,
which are intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply. EXAMPLE 1
[0054] For the case where the number of perforations in the gas distributor
decreases along the vertical axis of the reactor assembly depending on the requirement of gas to oil ratios, a calculation was performed to estimate the length of the different regions of the gas distributor and the corresponding gas to oil ratios requirement.
[0055] The reactor and catalyst included a reactor of 3.5 m diameter and a
bed length of 16.9 m with 140 tonnes of catalyst and gas to oil (G/O) ratio was taken in the range of 400-800 Nm3/m3. For the calculation, the reactor pressure was taken as 40 bar and the inlet gas and liquid temperature as 326 ⁰C. During calculation, a CFR with one gas distributor placed at the center was taken into consideration. The dimensions were selected based in the existing reactor in operation. Table 1 shows the fluid properties used for calculation.

Table 1: Fluid properties

Liquid Gas
Mass flow rate 4200 TPD 188 TPD
Density 859.6 (kg/m3) 0.08375 (kg/m3)
[0056] Calculations were then performed to determine the length of
different regions and corresponding gas to oil ratios. Fig. 12 illustrates a schematic representation of the lengths of different regions of the gas distributor, in accordance with an embodiment of the present subject matter. Region I is a dimensionless length taken as L1/L where L1 is a length denoted by 1210 and L is the total length of the gas distributor, region II is L2/L where L2 is denoted by 1220, region III is L3/L where L3 is denoted by 1230, and region IV is L4/L where L4 is denoted by 1240. In this case L is the total bed length and L1, L2, L3 and L4 are the length of the first, second, third, and fourth region, denoted by 1210, 1220, 1230, and 1240, respectively. Table 2 shows the dimensionless values of the different regions.
Table 2: Values of the different regions of a gas distributor

(-)
L1/L 0.03
L2/L 0.04
L3/L 0.28
L4/L 0.65
Table 3 shows the range of gas-to-oil ratios required in the different regions.
Table 3: Gas-to-oil (G/O) ratios in different regions of a gas distributor

Region Minimum G/O (Nm3/m3) Maximum G/O (Nm3/m3)
I 16 32
II 11 22

III 4.8 9.6
IV 0.05 0.1
[0057] Based on the G/O ratio shown in Table 3, total gas flow in the
different regions can be calculated and correspondingly a person skilled in the art
can calculate the number of holes in each region of the gas distributor.
[0058] Although embodiments for the present subject matter is described in
language specific to structural features, it is to be understood that the specific features and methods are disclosed as example embodiments for implementing the claimed subject matter.

I/We Claim:
1. A catalyst cage (120, 320) for holding a catalyst comprising:
a hollow mesh structure (210) comprising:
an outer wall (220) forming an outer circumference of the
hollow mesh structure (210);
an inner wall (230) disposed inside the outer wall (220)
forming an inner circumference of the hollow mesh structure (210),
wherein a volume between the outer wall (220) and the inner wall
(230) is for holding a catalyst;
a top wall (240) and a bottom wall (250) connecting the
outer wall (220) and the inner wall (230) on a top portion and a
bottom portion, respectively, of the outer wall (220); and
a first passage (260) connecting the top wall (240) and the
bottom wall (250) of the hollow mesh structure (210) to allow for a
gas distributor (270), wherein the inner wall (230) forms an outer
boundary of the first passage (260);
a vertical support (282) disposed on the outer wall (220) for supporting the hollow mesh structure (210) in a vertical direction;
a horizontal support (286) disposed along a radial direction of the hollow mesh structure (210) and connected to the outer wall (220) for supporting the hollow mesh structure (210) along the radial direction;
a gas distributor support disposed in a radial direction on a top portion of the hollow mesh structure (210) to support the gas distributor (270); and
a liquid distributor (140) removably coupled to a bottom portion of a first hollow mesh structure (210a) to collect liquid from the first hollow mesh structure, the liquid distributor (140) comprising:
a bottom lid (710) comprising a plurality of outlets (720),
wherein the bottom lid (710) is to come in contact with the top wall
(240) of a second hollow mesh structure (210b) and the plurality of
outlets (720) is to allow fluid to exit the liquid distributor (140) and

flow into the catalyst disposed in the second hollow mesh structure (210b);
a first circumferential wall (730) extending from the bottom lid (710), the first circumferential wall (730) forming an outer circumference of the liquid distributor (140) and wherein a diameter of a top of the first circumferential wall (730) is larger than a diameter of the first hollow mesh structure (210a); and
a second circumferential wall (740) disposed inside the first circumferential wall (730) and extending from the bottom lid (710), wherein the second circumferential wall (740) forms an outer boundary of a second passage (760), wherein the second passage (760) corresponds to the first passage (260) to allow for forming a single passage when the hollow mesh structure (210) and the liquid distributor (140) are coupled.
2. The catalyst cage (120, 320) as claimed in claim 1 comprising a plurality of first passage (260) and a plurality of second passages (760) to allow for a plurality of gas distributors (270).
3. The catalyst cage (120, 320) as claimed in claim 2, wherein the plurality of gas distributors (270) comprises a primary gas distributor (1010) and a set of secondary gas distributors (1020), wherein the set of secondary gas distributors (1020) comprise vertical slits (1030).
4. The catalyst cage (120, 320) as claimed in claim 1, wherein the vertical support (282) comprises metal strips.
5. The catalyst cage (120, 320) as claimed in claim 1, wherein the horizontal support (286) comprises metal strips.
6. The catalyst cage (120, 320) as claimed in claim 1, wherein the horizontal support (286) and the vertical support (282) are welded to each other.
7. The catalyst cage (120, 320) as claimed in claim 1, wherein the hollow mesh structure (210) comprises a plurality of intersecting beams disposed on a grating structure.

8. The catalyst cage (120, 320) as claimed in claim 1, wherein gas distributors (270) are removably coupled to the first passage (260) and second passage (760).
9. The catalyst cage (120, 320) as claimed in claim 1, wherein the gas distributors (270) are welded to the hollow mesh structure (210) and the liquid distributor (140).
10. The catalyst cage (120, 320) as claimed in claim 1, wherein the first passage (260) forms the gas distributor (270) and wherein the inner wall (230) of the hollow mesh structure (210) comprises perforations (910) to allow gas to be distributed to the catalyst.
11. The catalyst cage (120, 320) as claimed in claim 1, wherein the plurality of outlets (720) on the liquid distributor (140) comprises circular holes.
12. The catalyst cage (120, 320) as claimed in claim 1, wherein the plurality of outlets (720) is of same size.
13. The catalyst cage (120, 320) as claimed in claim 1, wherein the plurality of outlets (720) is of varying size.
14. The catalyst cage (120, 320) as claimed in claim 1, wherein the diameter of the top of the first circumferential wall (730) is larger than a diameter at a bottom of the first circumferential wall (730).
15. The catalyst cage (120, 320) as claimed in claim 1, wherein the horizontal support (286) comprises a plurality of rings disposed along a vertical axis of the hollow mesh structure (210).
16. A reactor assembly (100, 300) comprising the catalyst cage as claimed in claim 1.
17. The reactor assembly (100, 300) as claimed in claim 16, wherein a
plurality of catalyst cages (120, 320) is disposed one on top of the other,
wherein partially reacted feed exiting from one catalyst cage (320a) enters
the next catalyst cage (320b).
18. The reactor assembly (100, 300) as claimed in claim 17, wherein activity
of the catalyst disposed in the catalyst cages (120, 320) increases from the
top to the bottom of the reactor assembly (100, 300).

19. The reactor assembly (100, 300) as claimed in claimed in claim 16, wherein the number of perforations (910) in the gas distributor (270) decreases along a vertical axis of the reactor assembly (100, 300).
20. The reactor assembly (100, 300) as claimed in claimed in claim 16, wherein perforations (910) in the gas distributor (270) are evenly spaced along a vertical axis of the reactor assembly (100, 300).