JPH0260713B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the catalytic reforming of hydrocarbon cuts. In particular, the present invention relates to reforming a feedstock in multiple reaction zones arranged in series to improve its octane number. Reforming of the naphtha fraction is generally carried out by flowing the naphtha through a plurality of reaction zones arranged in series, each containing a catalyst and a hydrogenation-dehydrogenation component supported on a porous solid support. Typical catalysts include platinum supported on alumina with or without promoters such as rhenium, tin, and iridium. The naphtha fraction to be reformed is contacted in a first reaction zone with a platinum-containing catalyst under reaction conditions to convert primarily naphthenes to aromatics. Besides naphthene dehydrogenation,
Side reactions such as isomerization, hydroisomerization and hydrogenolysis may also occur. Typically, the effluent from the first reaction zone is heated before being introduced into the next reaction zone. After a period of reforming use, the catalyst gradually deactivates due to the deposition of coke on its surface and thus a decrease in the octane number of the reformed product is observed. If the octane requirements imposed on a particular reforming system are to be continuously met, the reaction temperature of the catalyst must be increased to compensate for the loss of activity due to coke deposition. Catalyst deactivation occurs fastest in reactors where paraffin dehydrocyclization and hydrogenolysis are the main reactions. Therefore, even if the inlet temperature is constant, the average reaction temperature increases with each successive reactor. This is because the reaction in each successive reactor is not as exothermic as in the previous reactor. Coke deposition on the catalyst not only reduces the activity of the catalyst but also reduces the yield of C ₅₊ gasoline produced. Therefore, the yield of C ₅₊ gasoline product generally decreases throughout the reforming process until it reaches an unacceptable level, at which point regeneration of all or part of the catalyst is typically performed. Typical coke levels on the catalyst at the point of regeneration are 10-12% by weight in the last reactor and 5 or 6% by weight in the first reactor. The coke level on the intermediate reactor catalyst generally falls between these two numbers. Regeneration methods, both continuous and batch, are generally well known in the art. Such methods generally include several steps: contacting the catalyst with an oxygen-containing gas at elevated temperature to burn off the carbon until substantially all of the carbon is removed; contact with an oxygen-containing gas to redistribute platinum group metals, a halogen adjustment step, and an optional step of reducing the regenerated catalyst with a hydrogen-containing gas before returning the catalyst to the reactor. See, eg, US Pat. No. 3,496,096. It is an object of the present invention to provide a reforming method that has a longer operating cycle between regenerations compared to conventional reforming methods. Another object of the invention is to provide a method for extending the useful life of a reforming catalyst near the end of its run. According to one embodiment of the invention, the naphtha feed is contacted with the reforming catalyst of a plurality of reaction zones arranged in series under reforming conditions in the presence of hydrogen, and from the effluent of the last reaction zone. In a reforming process in which the improved octane product is collected and the catalyst is deactivated by coke deposition on the catalyst during the reforming process, ultimately requiring regeneration or replacement of the catalyst, The coke level on the catalyst in the first reaction zone is maintained at less than 1% by weight of the catalyst by adjusting the frequency of regenerating or replacing the catalyst in the reaction zone with fresh or regenerated catalyst. A method is provided for extending the useful life of catalysts in all reaction zones downstream of a first reaction zone. According to another embodiment of the invention, there is provided a multi-stage catalytic reforming process for naphtha feedstock, characterized in that it comprises the following steps: (a) a moving bed reaction in which the catalyst can be moved by gravity flow; (b) reacting the naphtha feed under catalytic reforming conditions in the presence of a catalyst and hydrogen in a zone and collecting the product hydrocarbonaceous effluent from the moving bed reaction zone; or at least periodically introducing regenerated catalyst and at least periodically withdrawing an equivalent amount of coke-contaminated catalyst from the lower end of said moving bed reaction zone; further reacting under catalytic reforming conditions in a fixed bed reactor system containing one fixed bed reaction zone; (d) a catalytic reforming product which is normally liquid from the effluent withdrawn from the last fixed bed reaction zone; The process of collecting. According to another embodiment of the invention, the naphtha fraction is contacted under reforming conditions in the presence of hydrogen with the reforming catalyst of a plurality of reaction zones arranged in series, and the effluent of the last reaction zone is a catalytic reforming process in which an improved octane product is collected from the reforming process, and during the reforming step, coke is deposited on the catalyst, deactivating the catalyst, thereby causing a reduction in the yield of the product. maintaining the coke level on the catalyst in the first reaction zone below 1% by weight by adjusting the frequency with which the catalyst in the first reaction zone is regenerated or replaced with fresh or regenerated catalyst. A method of increasing the characterized yield is provided. The present invention can be applied to a reforming system in which a plurality of reaction zones are arranged in series. Preferably, a preheater is present between the reaction zones so that the temperature of the feedstock to each reaction zone can be controlled. Preferably, each reaction zone is located in a separate reactor.
The invention relates to a system of at least two reactors, preferably 3 to 5 reactors arranged in series.
Although some or all of the reactors may be moving bed reactors, the most preferred systems are either all reactors being fixed bed systems or all reactors except the first reactor being fixed bed reactors. system and the first reactor is a moving bed system. In a multi-reaction zone reforming system, the catalyst may be of different composition in different reforming zones, but generally the catalyst is the same in all reactors. However, the capacity of the catalyst typically differs between reaction zones. Typical catalyst loading in a three reactor system is 1/4 of the total catalyst loading in the first reactor, 1/4 loading in the second reactor, and 1/4 loading in the last reactor. 2 is filled. The first reactor generally has a lower amount of catalyst. This is because the highly endothermic reaction that occurs in the first reactor causes the feedstock to cool rapidly. If there is a large amount of catalyst in the first reactor, the temperature of the feed in the lower part of the catalyst bed will be too low and the dehydrogenation reaction will take place significantly, so the lower part of the catalyst bed will not be used effectively. . To achieve the effects of the present invention, the catalyst in the first reaction zone must have a coke level in the catalyst of less than 1% by weight.
It must be replaced or regenerated frequently enough to maintain preferably less than 0.7% by weight, more preferably less than 0.5% by weight. The first reaction zone can contain up to 30% by volume of the total catalyst in the reactor system, but preferably only up to 20% by volume and only up to 15% by volume of the total amount of catalyst in the reactor system. It is more preferable not to do so. The temperature in each reaction zone may be the same or different, but generally between 700 and
1050〓, preferably about 850-1000〓. The final reaction zone generally has the highest average catalyst bed temperature. The pressure in each reactor is usually the same, either atmospheric or superatmospheric. Preferably the pressure is between 25 and 1000 psig, more preferably between 50 and 750 psig. Temperature and pressure favor particularly desirable reforming reactions when correlated to liquid hourly space velocity (LHSV), which is generally between 0.01 and 10, preferably between 1 and 5. It is clear that with different catalyst loadings and different reaction zones, the space velocity of the individual reaction zones can vary considerably. Although hydrogen is generally produced by reforming, it is common to recycle the hydrogen separated from the effluent of any reaction zone, usually the final reaction zone, to the first or subsequent reaction zone. Hydrogen can be mixed with the feedstock prior to contacting the catalyst or at the same time as the feedstock is introduced into the reaction zone. Any presence of hydrogen acts to reduce coke formation, which tends to poison the catalyst. Preferably, hydrogen is introduced into the reforming reaction zone at a rate of 0.5 to 20 moles per mole of feedstock. Hydrogen can be in a mixture with light hydrocarbon gases. The catalyst used in the reaction zone consists of a platinum group component supported on a porous solid support. The platinum group component is preferably platinum, and the preferred porous solid support is a porous refractory inorganic oxide, such as alumina. The platinum group component is present in an amount of 0.01 to 3% by weight, preferably 0.01 to 1% by weight. Other components besides the platinum group components can be present in the porous solid support. Particular preference is given to the presence of rhenium, for example from 0.01 to 5% by weight, especially from 0.01 to 2% by weight. Rhenium considerably improves the yields obtained with platinum-containing catalysts, and platinum-rhenium catalysts are described in U.S. Pat.
It is detailed in the specification of No. 3415737. Generally, the catalyst is activated for reforming action by the addition of halides, in particular fluorides or chlorides.
The halides provide a limited amount of acidity to the catalyst, which is advantageous for most reforming operations. The halide activated catalyst has a total halide content of 0.1 to 3% by weight, with the preferred halide being chloride. The catalyst in the first reaction zone is removed on-site or off-site at a frequency sufficient to maintain less than 1% by weight coke on the catalyst, preferably less than 0.7% by weight, and more preferably less than 0.5% by weight. It can be replaced or regenerated. The amount of coke on the catalyst is
It is calculated as the average amount of coke relative to the total volume of catalyst in the first reaction zone. The catalyst in the first reaction zone is
It can be placed on a fixed or moving bed. If the reaction zone is a fixed bed, it can be of radial flow, upward flow or downward flow type, and if a suspended reactor is provided and the first fixed bed reaction zone is removed for regeneration, It is desirable to use the reactor immediately. Of course, if the first reaction zone is on a mobile catalyst, the reaction zone can be operated while fresh or regenerated catalyst is added to the top of the reaction zone and spent coke-deactivated catalyst is withdrawn from the bottom. It is possible to maintain the condition. The remaining reaction zones of the system can be fixed bed or moving bed reaction zones, however, for the purposes of the present invention, they are advantageously fixed bed reaction zones. The fixed bed reaction zone can be of the upward flow, downward flow or radial flow type, with the radial flow type being preferred. To measure the coke or carbon level on the catalyst in the first reactor, the catalyst can be sampled in the moving bed reaction zone upon removal from the reactor, or the catalyst sample can be conventionally reformed from the reaction zone itself. It can be extracted without destroying the process. Various means are available for removing the catalyst sample from the reactor without shutting down the reactor. For example, U.S. Patent No. 3129590 and
See specification No. 3319469. The level of coke or carbon deposited on the catalyst sample can be determined by any suitable means, such as by burning the carbon and measuring the amount of _CO2 produced, or as described in U.S. Pat. No. 3,414,382. , can be determined by measuring the rate at which the combustion zone passes through the coke-contaminated catalyst bed. The hydrocarbon feedstock used in the reforming operation of the present invention can be any suitable hydrocarbon that can be catalytically reformed under the conditions described above. The feedstock is preferably a naphtha fraction, which is a light hydrocarbonaceous oil, generally having a boiling point of 70-550°, preferably 150-450°. The feedstock can be, for example, straight-run naphtha, pyrolyzed or catalytically cracked naphtha, or mixtures thereof. Generally, the naphtha feedstock is about 25 to 75% by volume, preferably about 35 to 75% by volume.
60% by volume paraffins, about 15-65% by volume naphthenes, preferably about 25-55% by volume and about 5-65% by volume naphthenes.
Contains 20% aromatics by volume. Catalyst regeneration methods are well known in the art and generally include:
It involves contacting the catalyst with an oxygen-containing gas at an elevated temperature of about 700 to 1100 °C to burn off carbon from the catalyst. Preferably, the oxygen concentration and temperature are increased stepwise as regeneration progresses. After burning off the carbon, halogen gas can be introduced and brought into contact with the catalyst. The catalyst can then be dried and reduced and returned to the reforming zone. An example of a suitable reclamation method is U.S. Pat.
3134732 and 3496096. EXAMPLES The invention will be further elucidated by considering the following examples, which are purely illustrative and do not limit the invention. Example 1 shows that the presence of a small amount of fresh catalyst on top of a catalyst bed containing 10.9% carbon substantially increases C ₅₊ yield and hydrogen production and is necessary to produce a given octane product. This indicates that the average catalyst temperature decreases. These results indicate that the presence of a small amount of fresh catalyst upstream of a larger amount of coke-contaminated catalyst significantly extends the amount of time that the entire amount of catalyst can be used in the reforming process before regeneration. Example 2 shows that the yield deteriorates as the amount of coke increases on a small amount of catalyst placed on top of a larger amount of coke deactivated catalyst. These results indicate that the lower the amount of carbon present in the catalyst in the first reaction zone, the higher the overall yield. Example 3 is
At the top of the test catalyst bed with various coke levels
There is a side-by-side comparison of reforming with a catalyst bed containing 10% fresh catalyst, which demonstrates the activity and yield benefits of having a small layer of fresh catalyst on top of the catalyst bed. explain. EXAMPLE 1 Mid-continent naphtha having the properties shown in the table was transferred to a series of four reactors containing a platinum-rhenium reforming catalyst at a pressure of 200 psig, a liquid hourly space velocity of 2, and a hydrogen to hydrocarbon molar ratio. 3 and temperature adjusted to obtain a reformed product with a research octane rating of 98 net. Table Midcontinent naphtha Specific gravity ÅPI 55.0 D-86 distillation IBP−〓 174 10%−〓 214 30%−〓 239 50%−〓 263 70%−〓 294 90%−〓 342 EP−〓 390% Paraffins 43.1% Naphthenes 46.8% Aromatics 10.0 After 55 days of operation, a portion of the catalyst was removed from the last reactor in the series. The catalyst containing an average of 10.9% by weight of coke was extracted from the top 10% and 20% of the spent catalyst in a micro-sized pilot plant reformer.
and 30% replaced with an equivalent amount of new catalyst3
Subjected to two separate tests. The results shown in Figure 1 and the table show that replacing a larger amount of coke-contaminated catalyst with fresh catalyst at the top results in (1)
The activity of the total amount of catalyst is 19〓, 20〓 for 10% fresh catalyst.
22〓 for % fresh catalyst and 32〓 for 30% fresh catalyst
(2)C ₅₊ yield is approximately 78.6% liquid volume (LV
(3) Hydrogen production increased by approximately 11% from 1217 standard ft ³ to 1356−1347 standard ft ³ per barrel of feedstock, (4)
_CH4 production shows a 23-26% reduction from 108 standard ^ft3 to 80-83 standard ^ft3 per barrel of feedstock.
Therefore, the presence of a small amount of fresh catalyst on top of a larger amount of coke-fouled catalyst will result in a much smaller amount of fresh catalyst than would be expected from the addition of a small amount of fresh catalyst.
Activity, C ₅₊ liquid yield and hydrogen production rate are increased.

Table Example 2 A study was conducted to determine the effect on yield of the amount of coke on the top 10% catalyst in the catalyst bed. FIG. 2 shows the effect on C ₅₊ and H ₂ yields with increasing carbon content of the catalyst in the top 10% of the catalyst bed. Using a catalyst bed containing 10% fresh catalyst on top of 90% catalyst containing 13.3 wt% carbon, a catalyst containing 2 wt% carbon on top
Catalyst beds containing approximately 6 wt. % carbon in the top 10% bed have a 1 vol. % reduction in C ₅₊ yield.
A catalyst bed containing 10% of the catalyst containing about 12% carbon by weight has a 2% reduction in C ₅₊ yield by volume, and a catalyst bed containing 10% of the catalyst containing about 12% carbon by weight has a reduction in C ₅₊ yield of about 3% by volume. . Hydrogen yield loss also occurs at the top 10 of the catalyst bed.
% carbon content increases. Therefore, in order to obtain maximum yield benefits from the process of the invention, it is necessary to have as low a carbon content on top of the catalyst as possible. Example 3 The performance of a coke-deactivated platinum-rhenium catalyst bed is
A test was conducted comparing an equivalent capacity catalyst with 10% by volume fresh catalyst on top of 90% deactivated catalyst. Catalyst samples from a commercial reformer were collected at approximately 0.28,
Collected after 61, 89 and 122 days of operation. A portion of each catalyst sample was prepared for the feedstocks shown in the table.
Reforming conditions were tested including a pressure of 200 psig, a liquid hourly space velocity of 2, a hydrogen to hydrocarbon molar ratio of 3, and a temperature adjusted to obtain a reformed product with a research octane number of 98 net. A layer of 10% fresh catalyst was placed on top of a 90% layer of catalyst from each of the 61, 89 and 122 day samples and tested under identical reforming conditions. As shown in the figure, the results show that the catalyst containing 10% fresh catalyst is much more active (20〓 after 120 hours) and more selective than the bed containing only coke-contaminated catalyst. (4% C ₅₊ yield after 120 hours). The fouling rate of the catalyst bed containing 10% fresh catalyst is less than the coke contaminated catalyst bed...0.15〓/day vs. 0.33〓/day, indicating that the effectiveness of fresh catalyst is not proportional to its capacity. . From the foregoing, the present invention operates in a novel and effective manner in the reforming reaction zone to increase the activity, selectivity (C ₅₊ yield), or both of the total amount of catalyst, thus reducing regeneration. Alternatively, the useful life of the entire catalyst before it needs to be replaced can be extended. Although only specific devices and modes of operation of the invention have been described, various modifications may be made without departing from the spirit of the invention, and changes that fall within the scope of the claims are intended to be included within the scope of the invention. Ru.

[Brief explanation of drawings]

Figure 1 shows 0 and 0 at the top of the coke-contaminated catalyst layer.
Graph showing the effect of catalyst beds containing 10, 20 and 30% fresh catalyst on reaction temperature, C ₅₊ yield and hydrogen production. Figure 3, a graph showing yield loss based on coke level, is a graph showing comparative reforming results between a coke contaminated catalyst and a catalyst with 10% fresh catalyst on top of the coke contaminated catalyst.

Claims (1)

[Claims] 1. A method for catalytic reforming of a naphtha feedstock in a plurality of reaction zones arranged in series, comprising: (a) a moving bed reaction in which a catalyst is moved by gravity flow; reacting the catalyst under catalyst reforming conditions in the presence of catalyst and hydrogen in a zone and collecting the product hydrocarbonaceous effluent from said moving bed reaction zone; (b) placing fresh or regenerated catalyst at the top of said moving bed reaction zone; The amount of coke deposited on the catalyst in the moving bed reaction zone is maintained below 1% by weight by at least periodically introducing and at least periodically withdrawing an equivalent amount of coke-contaminated catalyst from the lower end of the moving bed reaction zone. (c) further reacting said effluent of said moving bed reaction zone under catalytic reforming conditions in a fixed bed reactor system having at least one fixed bed reaction zone, and (d) a final fixed bed reaction zone. collecting a normally liquid catalytic reforming product from the effluent withdrawn from the reaction zone. 2. The method of paragraph 1, wherein the coke-contaminated catalyst withdrawn from the moving bed reaction zone is regenerated and returned to the top of the moving bed reaction zone as the regenerated catalyst. 3. The method of paragraph 1, wherein the first reaction zone contains less than 30% by volume of the total catalyst in the reaction zone. 4. The method of claim 1, wherein the catalyst comprises an intimate mixture of 0.01-3% by weight platinum and 0.01-5% rhenium supported on an alumina support.