JPH051059B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for catalytic cracking of hydrocarbon feedstocks. More specifically, the present invention includes:
nickel, which is typically present in the hydrocarbon feedstock being processed and deposited on the cracking catalyst;
The present invention relates to a method for reducing the negative effects of metal contaminants such as vanadium and/or iron. BACKGROUND OF THE INVENTION In the catalytic cracking of hydrocarbon feedstocks, particularly heavy feedstocks, nickel, vanadium and/or iron present in the feedstock deposits on the cracking catalyst and promotes excessive hydrogen and coke formation.
These metal contaminants are not removed by conventional catalyst regeneration operations that convert coke deposits on the catalyst to CO and _CO2 . The term "passivation" as used in the present invention is defined as reducing the undesirable catalytic effects of metal contaminants such as nickel, vanadium and/or iron deposited on the cracking catalyst. Ru. Several patents disclose the use of reducing atmospheres to passivate cracking catalysts. U.S. Pat. No. 2,575,258 discloses the method of applying a reducing agent to a regenerated catalyst at multiple locations intermediate the regeneration zone and cracking zone of a transport line for a flow of reducing gas countercurrent to the flow of regenerated catalyst. Disclose to add. This patent also discloses adding steam to the transport line downstream of the point at which reducing gas is added to the transport line to aid in transporting the regenerated catalyst from the regeneration zone to the reaction zone. A flow of reducing gas countercurrent to the catalyst flow is undesirable, especially at relatively high catalyst circulation rates. This is because the catalyst and reducing gas tend to separate into two counter-flowing layers.
This results in reduced catalyst contact. Also,
It may also occur that countercurrently flowing reducing gas bubbles intermittently interfere with catalyst recirculation. International Patent Application (PCT) No. WO82/04063 describes the introduction of a reducing gas into a stripping zone placed between a regeneration zone and a reaction zone to strip the catalyst in the processing of metal-contaminated hydrocarbons. Disclose to add. This patent also discloses adding a reducing gas to a separate vessel and/or riser downstream of the flow control means to reduce at least a portion of the oxidized nickel contaminants present. European Patent Publication No. 52356 also discloses that metal contaminants can be passivated using a reducing atmosphere at elevated temperatures. This publication discloses the use of carbon monoxide, hydrogen, propane, methane, ethane and mixtures thereof as reducing gases to passivate the regenerated catalyst before it is returned to the reaction zone. This publication also discloses that the contact time of the reducing gas with the catalyst is between 3 seconds and 2 hours, preferably between about 5 and 30 minutes. This patent publication further discloses that if antimony is added to the cracking catalyst, the degree of passivation is improved. US Pat. No. 4,377,470 discloses a method for catalytic cracking of hydrocarbon feedstocks with significant vanadium content. A reducing gas can be added to the regenerator and to the transport line between the regenerator and the reactor to maintain the vanadium in a reduced oxidation state. US Patent No. 4280895; 4280896; 4370220;
4372840; and 4372841, the passivation zone is kept at an elevated temperature and has a reducing atmosphere.
It is disclosed that the cracking catalyst can be passivated by passing the catalyst through for a period of seconds to 30 minutes, typically about 2 to 5 minutes. U.S. Pat. Nos. 4,298,459 and 4,280,898 disclose that a spent cracking catalyst is alternately exposed to oxidation and reduction zones maintained at elevated temperatures for up to 30 minutes to reduce hydrogen and coke products.
A method for cracking metal-containing raw materials is described. These patents describe the use of a transport line reaction zone located between a regeneration zone and a stripping zone. US Pat. No. 4,268,416 also describes a method for passivating a cracking catalyst, in which the metal-contaminated cracking catalyst is contacted with a reducing gas at an elevated temperature to passivate the catalyst. US Pat. No. 3,408,286 discloses adding liquid hydrocarbons to the regenerated catalyst under cracking conditions in a transport line before the regenerated catalyst is reintroduced into the cracking zone. Liquid hydrocarbon cracking prior to entering the cracking zone serves to remove entrained regenerator gas from the regenerated catalyst entering the cracking zone. In many existing catalytic cracking systems, space limitations require the use of a separate free-standing structure, especially when the passivation zone has to fit into the existing cracking equipment.
Adding passivation or reduction zones may not be desirable. It is also desirable to avoid the costs associated with constructing and installing a separate freestanding structure passivation zone. It would also be desirable to provide a method for adjusting the rate of addition of reducing gas to the passivation zone. It would also be desirable to provide a method that does not significantly impact catalyst circulation rates. The present invention is directed to incorporating a reduction or passivation zone into a transport zone. The passivation zone is preferably located in the transport line between the regeneration zone and the reaction zone, so that at least a portion of the metal-contaminated catalyst circulating between the regeneration zone and the reaction zone is located in the passivation zone. pass through. The passivation zone is preferably located in the transport line through which the regenerated catalyst passes from the regeneration zone to the reaction zone. Depending on the specific operating conditions and desired operating efficiency in the reaction and regeneration zones, a stripping zone is placed before the passivation zone;
It may be desirable to minimize the amount of oxygen introduced into the passivation zone by the regenerated catalyst. DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved method for passivating catalysts used to crack hydrocarbon feedstocks into relatively low molecular weight products in a reaction zone, wherein said feedstocks are contains metal contaminants selected from the group consisting of nickel, vanadium, iron, and mixtures thereof, at least a portion of which metal contaminants settle on the catalyst, and coke deposits on the cracking catalyst. The coke and metal contaminated catalyst is then transported from the reaction zone to a regeneration zone for coke removal. The regenerated catalyst is circulated through a transport zone from the regeneration zone to the reaction zone. The improvements of the present invention include adding a _H2 -containing reducing gas to the transport zone, thereby creating a passivation zone that at least partially passivates the cracking catalyst passing therethrough. The _H2- containing reducing gas (hereinafter sometimes simply referred to as reducing gas) is preferably hydrogen and hydrogen-containing reducing gas.
selected from the group consisting of CO and/or mixtures of hydrocarbons. A stripping gas can be added at the point where the catalyst enters the transport zone, the stripping gas removing at least a portion of the oxygen and/or oxygenated compounds present on the catalyst. In order to maximize the contact time of the reducing gas in the transport zone, the reducing gas is preferably added to the transport zone upstream of the flow control means. Preferably the reducing gas is in a standpipe from the regeneration zone.
added to. The rate of addition of reducing gas to the passivation zone is preferably regulated. This means that
This can be done by monitoring the composition of the cracking product stream from the reaction zone and/or the catalyst circulation rate. If the reducing gas added to the passivation zone includes hydrogen, the rate of reducing gas added to the passivation zone can be adjusted to minimize the hydrogen concentration in the cracking product. The reducing gas addition rate can be adjusted to keep the catalyst circulation rate within a predetermined range. EMBODIMENTS OF THE INVENTION FIG. 1 is a simplified flow sheet of one embodiment for carrying out the invention. FIG. 2 is a flow sheet of another embodiment. FIG. 3 is a graph plotting hydrogen yield and coke yield as a function of residence time of metal contaminated catalyst in the passivation zone. Figure 4 shows the gas generation factor (GPF) as a function of catalyst residence time in the passivation zone, reducing gas used, and temperature of the passivation zone.
This is a graph plotting. First, in FIG. 1, pipes, valves, and equipment that are not important for understanding the invention have been omitted or deleted. Reaction zone or cracking zone 1
0 is a fluidized catalyst bed 1 with 14 levels (heights)
2 into which the hydrocarbon feed is introduced through line 16 for catalytic cracking. Hydrocarbon feedstocks include naphtha, light gas oil, heavy gas oil, residual fractions, extracted crude oil, cycle oils derived from any of these, as well as sier oil kerogen, tar sands, bitumen, process oils,
Suitable fractions derived from synthetic oils, coal hydrogenation, etc. may be included. Such feedstocks can be used alone, separately in parallel reaction zones, or in any desired combination. Typically these raw materials will contain metal contaminants such as nickel, vanadium, and/or iron. Heavy feedstocks typically contain relatively high concentrations of vanadium and/or nickel. Hydrocarbons and steam passing through the fluidized bed 12 maintains the bed in a dense, turbulent fluid state. In the reaction zone 10, the cracking catalyst is deactivated during contact with the hydrocarbon feedstock due to the deposition of coke thereon. That is, as used herein, "deactivated" or "coke contaminated"
The term catalyst shall generally refer to a catalyst which is passed through a reaction zone and has sufficient coke thereon to cause loss of activity and therefore requires regeneration. Generally, the coke content of the deactivated catalyst is
It can be from about 0.5 to about 5% by weight or more. Typically the deactivated catalyst coke content is approximately
0.5 to about 1.5% by weight. Prior to the actual regeneration, the deactivated catalyst is typically passed from the reaction zone 10 to a stripping zone 18.
There it is contacted by a stripping gas introduced into the lower part of zone 18 through line 20. The stripping gas, typically introduced at a pressure of about 10 to 50 psig, serves to remove most of the volatile hydrocarbons from the deactivated catalyst. The preferred stripping gas is water vapor, but nitrogen, other inert gases or flue gases may also be used. Typically, the stripping zone is maintained at approximately the same temperature as the reaction zone, ie, from about 450 to about 600C. The stripped, deactivated catalyst, which has been stripped of most of its volatile hydrocarbons, is then passed from the bottom of the stripping zone 18 through a U-tube 22 and a connecting riser pipe 24 extending to the lower part of the regeneration zone. Ru. Air rising pipe 2
4 through line 28 in an amount sufficient to reduce the density of the catalyst flowing therethrough, i.e. to cause the catalyst to flow upward into the regeneration zone 26 by mere hydrodynamic balance. In the particular configuration illustrated, there are 32 playback zones.
is a separate vessel (located approximately at the same height as the reaction zone 10) containing a rich phase catalyst bed 30 having a level indicated by the amount of coke deposits formed in the reaction zone during the cracking reaction. It is subjected to regeneration to burn off the substances, and on top of this is a lean catalyst phase 34. The oxygen-containing regeneration gas enters the lower portion of the regeneration zone 26 through line 36 and rises through the grid 38 to the rich phase catalyst bed 30 which is subjected to turbulent flow conditions similar to those in the reaction zone 10. Keep it. The oxygen-containing regeneration gas that can be used in the process of the invention is one that contains molecular oxygen mixed with a substantial proportion of an inert diluent gas. Air is a particularly suitable regeneration gas. Another gas that may be used is oxygen-enriched air. Additionally, if desired, water vapor can be added to the dense phase, with or separately from the regeneration gas, to provide additional inert diluent and/or fluidizing gas. Typically, the specific vapor velocity of the regeneration gas is approximately 0.8
~6.0 feet/second. Preferably from about 1.5 to about 4 feet/second. In the regeneration zone 26, flue gases formed during regeneration of the deactivated catalyst enter the lean catalyst phase 34 from the rich phase catalyst bed 30 with entrained catalyst particles. The catalyst particles are separated by suitable gas-solid separation means 54 and returned to the rich phase catalyst bed 30 via a sinking leg 56. The largely catalyst-free flue gas then enters a plenum chamber 58 through line 60 before exiting the regeneration zone 26. When the regeneration zone is operated for near-complete combustion, the flue gas typically contains less than about 0.2% by volume, preferably less than 0.1% by volume, and more preferably less than 0.05% by volume of carbon monoxide. Will. The oxygen content is typically from 0.4 to about 7, preferably from about 0.8 to about 5, more preferably from about 1 to about 3, and most preferably about 1.0.
~2% by volume. The regenerated catalyst exiting the regeneration zone 26 has been stripped of a significant portion of coke. Typically, the carbon content of the regenerated catalyst is from about 0.01 to about 0.6% by weight, preferably from about 0.01 to about 0.1% by weight.
Regenerated catalyst from the rich phase catalyst bed 30 in the regeneration zone 26 enters the reaction zone 10 through a transport zone consisting of a standpipe 42 and a U-tube 44. In FIG. 1, the passivation zone 90 is located in the standpipe 4 in order to obtain substantially the maximum possible residence time.
2 and U-tube 44 to the point where the hydrocarbon feed enters line 16 . If a shorter residence time is desired, the passivation zone 90 may be removed from the standpipe 42 and/or U-tube 44.
It can consist of only a portion of the length. Conversely, if a longer residence time is desired, the cross-sectional area of standpipe 42 and/or U-tube 44 can be increased. The stripping gas flow is optionally
To minimize mixing of regeneration zone gas and passivation zone reducing gas, it can be fed to the inlet of passivation zone 90. The stripping gas can be any gas that does not adversely affect the passivated catalyst and does not interfere with processing of the feedstock in the reaction zone. The preferred stripping gas is water vapor, although reducing gases and other gases may also be satisfactory. In this embodiment, line 92 is connected to the passivation zone 90 to minimize mixing of the reducing gas in the passivation zone 90 with the gas stream from the regeneration zone 26 by stripping entrained oxygen from the regeneration catalyst. Placed upstream. Since the catalyst residence time in standpipe 42 and U-tube 44 is only about 0.1 to about 2 minutes, the amount of reducing gas increases until additional amounts of reducing gas are no longer beneficial in the cracking process. It may often be advantageous to maximize the effectiveness of catalyst residence time in the passivation zone 90 by injecting the catalyst into the passivation zone. This means that
This can occur if the addition of reducing gas adversely affects the catalyst flow rate through the passivation zone. This is also
It may also occur that increasing the rate of reducing gas addition to the passivation zone does not result in a reduction in hydrogen and/or coke production in the reaction zone 10. In FIG. 1, the reducing gas flow rate through line 70 is regulated by control means, such as control valve 72. In FIG. Reducing gas passing through control valve 72 and into line 70 essentially passes through lines 74 , 76 , 78 , 80 and 96 to distribute the reducing gas into passivation zone 90 .
Pass through a large number of lines like . control valve 72
is shown as being regulated by cracking product monitoring means such as analyzer 82. Analyzer 82 can be adapted to monitor the content of one or more products in stream 52. Since the hydrogen content of the cracked product is a function of the degree of catalytic metal passivation in a preferred embodiment, analyzer 82 can be a hydrogen analyzer. Alternatively, since the rate of coke formation is also a function of the degree of catalytic metal passivation, the rate of reducing gas addition can be adjusted by monitoring the rate of coke formation. This is reaction zone 10
and/or by monitoring the heat balance of the regeneration zone 26. The rate of addition of reducing gas to passivation zone 90 must also be kept below the rate at which it causes significant fluctuations in catalyst circulation rate. 1st
In the illustrated embodiment, the rate of catalyst circulation through the passivation zone 90 is as follows: the regeneration zone 26, the standpipe 4
2 and control valve 72 can be monitored by a sensing means such as sensor 84 shown connected thereto. In industrial operation of this embodiment, the hydrogen concentration in the product stream 52 may be monitored by an analyzer 82, which controls the rate of addition of reducing gas by the control valve 72 to minimize the hydrogen concentration in the stream 52. Adjust. Sensor 84 acts as a limit to control valve 72 by reducing the rate of addition of reducing gas to passivation zone 90 when the rate of addition of reducing gas begins to adversely affect the catalyst circulation rate. Referring now to FIG. 2, another embodiment for carrying out the invention is shown. The operation of this aspect is generally the same as previously described in FIG. In this embodiment, the riser reaction zone 110 consists of a tubular vertical vessel having a relatively large height compared to its diameter. Reaction zone 110 communicates with release zone 120, which is illustrated as being located significantly higher than regeneration zone 150. Catalyst circulation rate is controlled by valve means such as slide valve 180, which separates the release zone 120 and regeneration zone 150.
A deactivated catalyst transport line 140 extending between In this embodiment, the hydrocarbon feedstock is injected through line 112 into a riser reaction zone 110 having a catalyst bed for catalytic cracking of the feedstock. The steam is used in the regeneration zone 150 to act as a diluent and provide the power to move the hydrocarbon feed upward and keep the catalyst fluid.
and a return line 15 extending between the reaction zone 110 and the reaction zone 110.
Lines 160 and 1 to the second transport zone such as 8
62. The product from the vaporized, cracked feedstock ascends into the release zone 120 where most of the entrained catalyst is separated. The gas stream is then passed through a gas-solid separation means, such as a two-stage cyclone 122, which further separates the entrained catalyst and returns it to the release zone through submerged legs 124 and 126. The gaseous stream enters the plenum chamber 132 and exits through line 130 to the next process (not shown). The catalyst moving upward through the reaction zone 110 is gradually covered with carbonaceous material, which reduces its catalytic activity. When the catalyst reaches the top of the reaction zone 110, it is removed by the stripping zone 1 in the deactivated catalyst transport line 142 by the grid 128.
40, where it is contacted with a stripping gas, such as steam, entering through line 144 to partially remove remaining volatile hydrocarbons from the deactivated catalyst. The deactivated catalyst is then passed through the deactivated catalyst transport line 142 to the regeneration zone 15.
0 rich phase catalyst bed 152 . Oxygen-containing regeneration gas enters the rich phase catalyst bed 152 through line 164 and maintains the bed in a turbulent fluid state similar to that in the riser reaction zone 110. The regenerated catalyst gradually rises through the rich phase catalyst bed 152 and eventually flows into an overflow well 156 that connects with a return line 158. Return line 158 is shown passing through the center of rich phase catalyst bed 152 and connecting to riser reaction zone 110 . The flue gas formed during the regeneration of the deactivated catalyst is
From the rich phase catalyst bed 152, a lean catalyst phase 154 is entered. The flue gases then pass through cyclone 170 to plenum chamber 17 before being discharged through line 174.
Enter 2. Catalyst entrained in the flue gas is removed in cyclone 170 and returned to catalyst bed 152 through submerged legs 176, 178. The regenerated catalyst is transferred from the regeneration zone 150 to the overflow well 1
56 and return line 158 to reaction zone 110. As previously discussed in the embodiment of FIG. 1, a passivation zone, such as passivation zone 190, can be located in or consist essentially entirely of overflow well 156 and/or return line 158. The added reducing gas is passed through passivation zone 1.
90 through lines 160 and 162 and back into line 158. If the amount of reducing gas added through lines 160 and 162 to passivate the catalyst is insufficient to sufficiently aerate the regenerated particles, the reducing gas added through lines 160 and 162 may be replaced by water vapor or other It may be desirable to dilute with a diluent of As shown in the embodiment of FIG. 1, it may be desirable to add a stripping gas, such as steam, through line 192 to overflow well 156 to remove entrained oxygen from the regenerated catalyst. The reducing gas is preferably supplied through reducing gas supply line 2.
Lines 202, 204, 206 extending from 00,
It is added to passivation zone 190 at multiple locations through branch pipes such as 208, 210, and 212. As previously discussed in FIG. 1, control valve 220
A control means, such as a control means, is placed in the reducing gas supply line 200 to adjust the rate of addition of reducing gas to the passivation zone 190. A cracking product monitoring means, such as analyzer 230, includes:
It is shown connected to cracking product line 130 and control valve 220 to maintain the harvested cracking product component within desired limits by adjusting the rate of addition of reducing gas to passivation zone 190. Since hydrogen is one of the products created by the unfavorable catalytic properties of metal contaminants, hydrogen may be a preferred component to be regulated. Since metal contaminants also catalyze the formation of coke, the rate of reducing gas addition may also be adjusted by monitoring the rate of coke formation, such as monitoring the heat balance around the regeneration zone 150 as described above. . Similar to the embodiment of FIG. 1, the catalyst circulation rate is monitored by sensing means such as sensor 240 connected to valve 220 to control the maximum rate of addition of reducing gas to passivation zone 190. can. The industrial operation of this embodiment is essentially the same as described above for the embodiment of FIG. Components such as hydrogen in the product stream are monitored by analyzer 230, which
Passivation zone 1 to minimize hydrogen content in
Control valve 220 is controlled to adjust the rate of addition of reducing gas to 90. A sensor 240 connected to the regeneration zone 150 and line 158 monitors the catalyst circulation rate and controls the control valve 220 to reduce the rate of reducing gas addition if the reducing gas is or is likely to adversely affect the catalyst circulation rate. Works as a “weight”. The metal concentration deposited on the catalyst is not believed to be significantly related to whether the embodiment of FIG. 1 or the embodiment of FIG. 2 is used. That is, Fig. 1, Fig. 2
The amount of reducing gas consumed in each passivation zone 90, 190 of the illustrated embodiment should not differ significantly. Each passivation zone 90, 1 in FIGS. 1 and 2
Although the rate of reducing gas consumption in 90 is partially a function of the amount of metal contaminants on the catalyst, the degree of passivation desired, and the amount of reducing gas leakage into the regeneration zone, the overall rate of reducing gas consumption is , if hydrogen is used as reducing gas, the passivation zone 90,190
It is believed that the range is from about 0.5 to about 260 SCF, preferably from about 1 to about 110 SCF per ton of catalyst passing through. In the embodiment of FIG. 1, it is believed that the combustion of coke in each regeneration zone 26 or 150 is sufficient to heat the cracking catalyst which then passes through each passivation zone 90, 190. A temperature of at least 500°C, preferably about 600°C or higher is required for sufficient passivation of the catalyst. If the temperature of the catalyst entering the passivation zone 90 or 190 is not high enough, direct heating, such as by preheating the reducing gas or addition of steam, or the addition of a heat exchanger before or within the passivation zone. indirect heating can be applied to the passivation zone by Each reaction zone 10, 110 and regeneration zone 26, 150 of FIGS. 1 and 2 can be of conventional design and can be operated under conditions well known to those skilled in the art. The regeneration zone 26,150 can be operated in either a net oxidation mode or a net reduction mode. In net oxidation mode, coke is
Oxidizing gas is added to the regeneration zone in excess of the amount required for complete combustion to _CO2 . In net reduction mode, insufficient oxygen gas is added to completely burn the coke to _CO2 . Play zone 26
and 150 are preferably operated in a net reduction mode. Because carbon monoxide is a reducing gas, this means that the catalyst
This is because it reduces the unfavorable catalytic properties of metal contaminants on the catalyst before entering 0.190. The required residence time of the catalyst in the passivation zone 90, 190 depends on the metal contaminant content of the catalyst, the degree of passivation required, the concentration of reducing gas in the passivation zone,
and passivation zone temperature. If the required residence time is greater than possible, modifications can be made to increase the passivation zone volume and/or increase the rate at which the catalyst is passivated. This can be accomplished by adding to the catalyst effective amounts of passivation rate enhancers such as cadmium, germanium, indium, tellurium, zinc and tin or by adding passivation promoters such as antimony, tin, bismuth and manganese. . Laboratory tests presented in the Examples below illustrate that effective metal passivation can be achieved in continuous operation using a transport zone for metal passivation. Example 1 This test shows that effective metal passivation could be achieved in a passivation zone with relatively low hydrogen partial pressure. This test was performed using the Super DX manufactured by Davison Chemical's WRGrace and Co. division.
1300〓 (704℃) using equilibrium cracking catalyst
The study was carried out in a continuous circulation pilot plant with a complete passivation zone operated at 190wppm
of nickel, 220wppm vanadium, 50wppm
of copper and 5500 wppm iron is further
Impregnated with 500wppm nickel and 1500wppm vanadium. The impregnated catalyst was used in the reaction zone for several hours and then in the regeneration zone prior to this test. The test results are shown in Table 1 below. In this test, the effectiveness of different hydrogen-nitrogen gas mixtures for metal passivation was determined. The sample was first exposed to a simulated net oxidizing regeneration zone atmosphere with about 2.5 to about 3.5 volume percent excess oxygen.
The sample was then exposed to the indicated passivating atmosphere maintained at 1300°C (704°C) for approximately 3 minutes.

Table 1 shows that even the use of a reducing gas with a hydrogen partial pressure of only 0.20 atmospheres was able to significantly passivate the undesirable catalytic effects of metal contaminants present on the catalyst. This shows that significant passivation can be achieved even with relatively low reducing gas concentrations in the passivation zone. Example 2 This test demonstrates that passing a metal-contaminated catalyst through a passivation zone maintained at an elevated temperature with a relatively short residence time is effective in passivating the catalyst. show. This test was performed using Super impregnated to the same metal contaminant content as described above.
1300〓(704
The experiments were carried out in a continuous circulation pilot plant with a complete passivation zone operated at 30°F (°C). The results are shown in Figure 3. From FIG. 3, it can be seen that hydrogen production and coke production can be reduced by passing the catalyst through the passivation zone for a relatively short period of time, such as the residence time typically available in a regenerated catalyst transport zone. Example 3 To determine whether the majority of the amount of passivation achieved in a single pass through the passivation zone is retained or whether circulation through the reaction and/or regeneration zone reactivates the catalyst Further tests were conducted in a microcatalytic cracking (MCC) device. Table 2 below shows that the degree of passivation of metal contaminated catalysts is cumulative to some extent. This further indicates that a relatively short residence time in the passivation zone is effective for catalyst passivation. This test was performed using 1000wppm nickel and
Super DX impregnated with 4000wppm vanadium
It was carried out in a batch gas processing vessel operated at 1300 °C (704 °C) using an equilibrium catalyst. Changes in the catalytic activity of metal contaminants are caused by microactivity test gas generation factor (MAT GPF).
production factor). In Table 2, test data is shown in which the catalyst was exposed only to a pure hydrogen atmosphere for the indicated periods of time. Also shown are test data in which the catalyst was exposed alternately to a pure hydrogen atmosphere for 30 seconds and to a gas mixture consisting of 8% CO, 12% CO ₂ and 80% N ₂ for 9 minutes. This latter atmosphere is designed to approximate conditions in a regeneration zone operated in net reduction mode. When compared for the same hydrogen treatment time, it can be seen that the pure hydrogen atmosphere produced a catalyst with a lower gas production factor than the catalyst exposed alternately to the passivation zone atmosphere and the regeneration zone atmosphere. However, it must be noted that the gas production factor decreases with time as the cumulative hydrogen treatment time increases. This further shows that short residence times in passivation zones, such as those located in transport zones, are advantageous especially over long operating periods.

Table: In a typical industrial cracking system, such as that shown in FIG. It is 2 minutes. Similarly, in a typical industrial cracking system, such as that shown in FIG. 2, the average residence time of the catalyst in the second transport zone 190 is about 0.1 to about 1.0 minutes. The temperature of the regenerated catalyst in the regenerated catalyst transport zone of FIGS. 1 and 2 is typically about 600°C to 790°C. That is, the regenerated catalyst transport zone of FIGS. 1 and 2 typically has catalyst at a sufficiently high temperature and with sufficient residence time to passivate the catalyst through the introduction of reducing gas. A process gas containing industrial grade CO and H ₂ and/or CO can be used as the reducing gas in the passivation zone 90. Hydrogen or a reducing gas stream containing hydrogen is preferred. This is because it provides the highest rate of passivation and achieves the lowest level of metal contaminant capability. This can be seen from the MCC device data shown in FIG.
Preferred reducing gas streams containing hydrogen include cracker tail gas stream, reformer tail gas stream, spent hydrogen stream from catalytic hydrogenation, synthesis gas, steam cracker gas, flue gas,
and mixtures thereof. The reducing gas concentration in the passivation zone is approximately 2% of the total gas composition, depending on the hydrogen concentration of the reducing gas and the rate at which the reducing gas can be added without adversely affecting the catalyst circulation rate.
% to about 100%, preferably between about 10% to about 75%. If the stripping gas is
and added through line 192 in FIG. 2, this will be partially a function of catalyst flow rate. Typically, the stripping gas flow rate through each of these lines is approximately
0.1SCF to about 80SCF, preferably about 8 to about 25SCF
It can be. Passivation zones 90, 190 can be constructed from chemically resistant materials that can withstand the relatively high temperatures and corrosive conditions typically associated with recycling cracking catalysts. The materials of construction used here in the transport pipeline of the catalytic cracking system were satisfactory. Respective passivation zones 90 and 19 in Figures 1 and 2
The pressure in zero will be about the same or only slightly higher than the pressure in the regenerated catalyst transport zone of existing catalyst cracking systems. When using the embodiment of FIG. 1, the pressure in the passive zone 90 ranges from about 5 to about
It can be 100 psig, preferably about 15 to about 50 psig.
In the embodiment of FIG. 2, the pressure is about 15 to about 100 psig;
Preferably it may be about 20 to about 50 psig. In general, any industrial catalytic cracking catalyst designed for high temperature stability could be suitably used in the present invention. Such catalysts include those containing silica and/or alumina. Catalysts containing combustion promoters such as platinum may also be used. Other refractory metal oxides such as magnesia or zirconium oxide may be used, limited only by their ability to be effectively regenerated under the selected conditions. For catalytic cracking, preferred catalysts include combinations of silica and alumina containing 10 to 50% by weight alumina, and especially their mixtures with molecular sieves or crystalline alumina silicates. Suitable molecular aluminosilicates are, for example, faujasite, chabasite, X- and Y-type aluminosilicate materials and ultrastable, large-pore crystalline aluminosilicate materials. When mixed with e.g. silica alumina to provide a petroleum cracking catalyst, the molecular sieve content of the freshly prepared catalyst particles is suitably from 5 to 35% by weight, preferably from 8 to 20% by weight. Equilibrium molecular sieve cracking catalysts may contain as little as about 1% by weight of crystalline material. Alumina mixed with white clay can also be used. Such catalysts can be made by any suitable method, such as impregnation, grinding, cogelation, etc., provided that the resulting catalyst is in a fluidizable physical form.

[Brief explanation of drawings]

1 and 2 are flow sheets of an apparatus for carrying out the present invention. FIG. 3 is a graph showing the relationship between catalyst residence time in the passivation zone, hydrogen yield, and coke yield. FIG. 4 is a graph showing the relationship between catalyst residence time in the passivation zone and gas production factors.

Claims (1)

[Scope of Claims] 1. A method for passivating a fluidized bed cracking catalyst used to crack metal-contaminated hydrocarbon feedstocks into lower molecular weight products, comprising: nickel, vanadium, iron and A hydrocarbon feedstock containing metal contaminants selected from the group consisting of mixtures thereof is added to a fluidized bed cracking catalyst to obtain a cracking product, and a fluidized bed cracking catalyst contaminated with deposited coke and the metals mentioned above is incorporated therein. the coke is removed from the fluidized bed cracking catalyst in a regeneration zone, and at least a portion of the coke-free and metal-contaminated fluidized bed cracking catalyst is transferred from the regeneration zone to the regeneration zone. and a hydrogen-containing reducing gas to at least partially passivate metal contaminants deposited on the fluidized bed cracking catalyst. into the transport zone from a plurality of locations in substantially cocurrent with the catalyst stream, and adjusting the rate of addition of the hydrogen-containing reducing gas to maintain the cracking catalyst circulation rate above a predetermined minimum. A method characterized by: 2. The method of claim 1, wherein the transport zone includes catalyst flow control means and at least a portion of the hydrogen-containing gas is added upstream of the control means. 3. A method according to claim 1 or 2, wherein the catalyst exiting the regeneration zone is catalyzed with a stripping gas before entering the passivation zone. 4. The method of claim 1, 2 or 3, wherein the hydrogen content of the cracking product stream is monitored and the rate of addition of the hydrogen-containing gas is adjusted in response. 5. The method of claim 4, wherein the rate of addition of the hydrogen-containing gas is adjusted to substantially minimize the hydrogen content in the cracking product stream. 6. A method according to any one of claims 1 to 5, wherein the passivation zone is maintained at a temperature of at least 500<0>C. 7 The rate of addition of hydrogen-containing gas to the transport zone is
Approximately per ton of catalyst circulated through the transport zone
7. A method according to any one of claims 1 to 6, between 0.5 and about 260 SCF. 8. The method according to any one of claims 1 to 7, wherein the hydrogen-containing gas is selected from the group consisting of hydrogen, a mixture of hydrogen and carbon monoxide and/or hydrocarbons.