EP0798363B1 - Reformierungsverfahren mit niedrigem Schwefelgehalt - Google Patents

Reformierungsverfahren mit niedrigem Schwefelgehalt Download PDF

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Publication number
EP0798363B1
EP0798363B1 EP97110024A EP97110024A EP0798363B1 EP 0798363 B1 EP0798363 B1 EP 0798363B1 EP 97110024 A EP97110024 A EP 97110024A EP 97110024 A EP97110024 A EP 97110024A EP 0798363 B1 EP0798363 B1 EP 0798363B1
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EP
European Patent Office
Prior art keywords
tin
reforming
paint
carburization
sulfur
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EP97110024A
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English (en)
French (fr)
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EP0798363A2 (de
EP0798363A3 (de
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John V. Heyse
Bernard F. Mulaskey
Robert L. Hise
Steven E. Trumbull
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Chevron Phillips Chemical Co LP
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Chevron Phillips Chemical Co LLC
Chevron Phillips Chemical Co LP
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Priority to EP98100396A priority Critical patent/EP0845521B1/de
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Publication of EP0798363A3 publication Critical patent/EP0798363A3/de
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G35/00—Reforming naphtha
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G35/00—Reforming naphtha
    • C10G35/04—Catalytic reforming
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G35/00—Reforming naphtha
    • C10G35/04—Catalytic reforming
    • C10G35/06—Catalytic reforming characterised by the catalyst used
    • C10G35/095—Catalytic reforming characterised by the catalyst used containing crystalline alumino-silicates, e.g. molecular sieves

Definitions

  • the present invention relates to a method for increasing the carburization resistance of at least a portion of an apparatus for catalytic reforming, particularly, catalytic reforming under low-sulfur, and low-sulfur and low-water conditions, more specifically, to control problems particularly acute with low-sulfur, and low-sulfur and low-water reforming processes.
  • Catalytic reforming is well known in the petroleum industry and involves the treatment of naphtha fractions to improve octane rating by the production of aromatics.
  • the more important hydrocarbon reactions which occur during the reforming operation include the dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, and dehydrocyclization of acyclic hydrocarbons to aromatics.
  • a number of other reactions also occur, including the dealkylation of alkylbenzenes, isomerization of paraffins, and hydrocracking reactions which produce light gaseous hydrocarbons, e.g., methane, ethane, propane and butane. It is important to minimize hydrocracking reactions during reforming as they decrease the yield of gasoline boiling products and hydrogen.
  • Catalysts for successful reforming processes must possess good selectivity. That is, they should be effective for producing high yields of liquid products in the gasoline boiling range containing large concentrations of high octane number aromatic hydrocarbons. Likewise, there should be a low yield of light gaseous hydrocarbons.
  • the catalysts should possess good activity to minimize excessively high temperatures for producing a certain quality of products. It is also necessary for the catalysts to either possess good stability in order that the activity and selectivity characteristics can be retained during prolonged periods of operation; or be sufficiently regenerable to allow frequent regeneration without loss of performance.
  • Catalytic reforming is also an important process for the chemical industry.
  • aromatic hydrocarbons for use in the manufacture of various chemical products such as synthetic fibers, insecticides, adhesives, detergents, plastics, synthetic rubbers, pharmaceutical products, high octane gasoline, perfumes, drying oils, ionexchange resins, and various other products well known to those skilled in the art.
  • Water sensitivity was found to be a serious drawback which was difficult to effectively address. Water is produced at the beginning of each process cycle when the catalyst is reduced with hydrogen. And, water can be produced during process upsets when water leaks into the reformer feed, or when the feed becomes contaminated with an oxygen-containing compound. Eventually, technologies were also developed to protect the catalysts from water.
  • Figure 1A is a photomicrograph of a portion of the inside (process side) of a mild steel furnace tube from a commercial reformer. The tube had been exposed to conventional reforming conditions for about 19 years. This photograph shows that the surface of the tube has remained essentially unaltered with the texture of the tube remaining normal after long exposure to hydrocarbons at high temperatures (the black portion of the photograph is background).
  • a method for increasing the carburization resistance of at least a portion of an apparatus for catalytic hydrocarbon conversion upon exposure to hydrocarbons at elevated temperatures comprising applying a reducible paint to a steel portion of the apparatus and heating said paint under reducing conditions to form a protective layer that provides said carburization resistance.
  • the apparatus to which the method of the invention is applied can be an apparatus for use in a method for reforming hydrocarbons comprising contacting the hydrocarbons with a reforming catalyst, preferably a large-pore zeolite catalyst including an alkali or alkaline earth metal and charged with one or more Group VIII metals, in a reactor system having a resistance to carburization and metal dusting which is an improvement over conventional mild steel reactor systems under conditions of low sulfur and often low sulfur and low water, and upon reforming the resistance being such that embrittlement from carburization will be less than about 2.5 mm/year, preferably less than 1.5 mm/year, more preferably less than 1 mm/year, and most preferably less than 0.1 mm/year. Preventing embrittlement to such an extent will significantly reduce metal dusting and coking in the reactor system, and permits operation for longer periods of time.
  • a reforming catalyst preferably a large-pore zeolite catalyst including an alkali or alkaline earth metal and charged with one or more Group VIII metals
  • Figure 1B is a photomicrograph of a portion of a mild steel coupon sample which was placed inside a reactor of a low-sulfur/low-water demonstration plant for only 13 weeks.
  • Figure 2 is an illustration of a suitable reforming reactor system for use in the present invention.
  • alloy steels are those steels having no specified minimum quantity for any alloying element (other than the commonly accepted amounts of manganese, silicon and copper) and containing only an incidental amount of any element other than carbon, silicon, manganese, copper, sulfur and phosphorus.
  • Metal steels are those carbon steels with a maximum of about 0.25% carbon. Alloy steels are those steels containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulfur and phosphorus) within the limits recognized for constructional alloy steels, added to effect changes in mechanical or physical properties. Alloy steels will contain less than 10% chromium.
  • Stainless steels are any of several steels containing at least 10, preferably 12 to 30%, chromium as the principal alloying element.
  • reforming reactor systems have been constructed of mild steels, or alloy steels such as typical chromium steels, with insignificant carburization and dusting.
  • mild steels or alloy steels such as typical chromium steels, with insignificant carburization and dusting.
  • 21 ⁇ 4 Cr furnace tubes can last twenty years.
  • these steels are unsuitable under low-sulfur reforming conditions. They rapidly become embrittled by carburization within about one year. For example, it was found that 21 ⁇ 2 Cr 1 Mo steel carburized and embrittled more than 1 mm/year.
  • Alonized Steels aluminized materials such as those sold by Alon Corporation
  • Alonized Steels aluminized materials
  • the application of thin aluminum or alumina films to metal surfaces of the reforming reactor system, or simply the use of Alonized Steels during construction can provide surfaces which are sufficiently resistant to carburization and metal dusting under the low-sulfur reforming conditions.
  • such materials are relatively expensive, and while resistant to carburization and metal dusting, tend to crack, and show substantial reductions in tensile strengths. Cracks expose the underlying base metal rendering it susceptible to carburization and metal dusting under low sulfur reforming conditions.
  • the film When applying an aluminum or alumina film, it is preferable that the film have a thermal expansivity that is similar to that of the metal surface to which it is applied (such as a mild steel) in order to withstand thermal shocks and repeated temperature cycling which occur during reforming. This prevents cracking or spalling of the film which could expose the underlying metal surface to the carburization inducing hydrocarbon environment.
  • the film should have a thermal conductivity similar to that of, or exceeding, those of metals conventionally used in the construction of reforming reactor systems. Furthermore, the aluminum or alumina film should not degrade in the reforming environment, or in the oxidizing environment associated with catalyst regeneration, nor should it result in the degradation of the hydrocarbons in the reactor system.
  • Suitable methods for applying aluminum or alumina films to metal surfaces such as mild steels include well known deposition techniques.
  • Preferred processes include powder and vapor diffusion processes such as the "Alonizing" process, which has been commercialized by Alon Processing, Inc., Terrytown, Pa.
  • Alonizing is a high temperature diffusion process which alloys aluminum into the surface of a treated metal, such as e.g., a commercial grade mild steel.
  • the metal e.g., a mild steel
  • the retort is then hermetically sealed and placed in an atmosphere-controlled furnace.
  • the aluminum deeply diffuses into the treated metal resulting in an alloy.
  • the substrate is taken out of the retort and excess powder is removed. Straightening, trimming, bevelling and other secondary operations can then be performed as required.
  • This process can render the treated ("alonized") metal resistant to carburization and metal dusting under low-sulfur reforming conditions according to the invention.
  • Thin chromium or chromium oxide films can also be applied to metal surfaces of the reactor system to render the surfaces resistant to carburization and metal dusting under low-sulfur reforming conditions. Like the use of alumina and aluminum films, and aluminized materials, chromium or chromium oxide coated metal surfaces have not been used to address carburization problems under low-sulfur reforming conditions.
  • the chromium or chromium oxide can also be applied to carburization and metal dusting susceptible metal surfaces such as the reactor walls, furnace liners, and furnace tubes. However, any surface in the system which would show signs of carburization and metal dusting under low-sulfur reforming conditions would benefit from the application of a thin chromium or chromium oxide film.
  • the chromium or chromium oxide film When applying the chromium or chromium oxide film, it is preferable that the chromium or chromium oxide film have a thermal expansivity similar to that of the metal to which it is applied. Additionally, the chromium or chromium oxide film should be able to withstand thermal shocks and repeated temperature cycling which are common during reforming. This avoids cracking or spalling of the chromium or chromium oxide film which could potentially expose the underlying metal surfaces to carburization inducing environments. Furthermore, the chromium or chromium oxide film should have a thermal conductivity similar to or exceeding those materials conventionally used in reforming reactor systems (in particular mild steels) in order to maintain efficient heat transfer. The chromium or chromium oxide film also should not degrade in the reforming environment or in the oxidizing environment associated with catalyst regeneration, nor should it induce degradation of the hydrocarbons in the reactor system.
  • Suitable methods for applying chromium or chromium oxide films to surfaces include well known deposition techniques.
  • Preferred processes include powder-pack and vapor diffusion processes such as the "chromizing" process, which is commercialized by Alloy Surfaces, Inc., of Wilmington, Delaware.
  • Chromium-rich stainless steels such as 446 and 430 are even more resistant to carburization than 300 series stainless steels. However, these steels are not as desirable for heat resisting properties (they tend to become brittle).
  • Resistant materials which are preferred over the 300 series stainless steels for use in the present invention include copper, tin, arsenic, antimony, bismuth, chromium and brass, and intermetallic compounds and alloys thereof (e.g., Cu-Sn alloys, Cu-Sb alloys, stannides, antimonides, bismuthides, etc.). Steels and even nickel-rich alloys containing these metals can also show reduced carburization. In a preferred embodiment, these materials are provided as a plating, cladding, paint (e.g., oxide paints) or other coating to a base construction material. This is particularly advantageous since conventional construction materials such as mild steels can still be used with only the surface contacting the hydrocarbons being treated.
  • paint e.g., oxide paints
  • tin is especially preferred as it reacts with the surface to provide a coating having excellent carburization resistance at higher temperatures, and which resists peeling and flaking of the coating. Also, it is believed that a tin containing layer can be as thin as 1/10 micron and still prevent carburization.
  • the resistant materials be applied in a paint-like formulation (hereinafter "paint") to a new or existing reactor system.
  • a paint can be sprayed, brushed, pigged, etc. on reactor system surfaces such as mild steels or stainless steels.
  • a paint be a decomposable, reactive, tin-containing paint which reduces to a reactive tin and forms metallic stannides (e.g., iron stannides and nickel/iron stannides) upon heating in a reducing atmosphere.
  • the aforementioned paint contain at least four components (or their functional equivalents); (i) a hydrogen decomposable tin compound, (ii) a solvent system, (iii) a finely divided tin metal and (iv) tin oxide as a reducible sponge/dispersing/binding agent.
  • the paint should contain finely divided solids to minimize settling, and should not contain non-reactive materials which will prevent reaction of reactive tin with surfaces of the reactor system.
  • tin octanoate As the hydrogen decomposable tin compound, tin octanoate is particularly useful. Commercial formulations of this compound itself are available and will partially dry to an almost chewing-gum-like layer on a steel surface; a layer which will not crack and/or split. This property is necessary for any coating composition used in this context because it is conceivable that the coated material will be stored for months prior to treatment with hydrogen. Also, if parts are coated prior to assembly they must be resistant to chipping during construction. As noted above, tin octanoate is available commercially. It is reasonably priced, and will decompose smoothly to a reactive tin layer which forms iron stannide in hydrogen at temperatures as low as 600°F (316°C).
  • Component (iv) is a porous tin-containing compound which can sponge-up an organometallic tin compound, yet still be reduced to active tin in the reducing atmosphere.
  • tin oxide can be processed through a colloid mill to produce very fine particles which resist rapid settling. The addition of tin oxide will provide a paint which becomes dry to the touch, and resists running.
  • Finely divided tin metal, component (iii), is added to insure that metallic tin is available to react with the surface to be coated at as low a temperature as possible, even in a non-reducing atmosphere.
  • the particle size of the tin is preferably one to five microns which allows excellent coverage of the surface to be coated with tin metal. Non-reducing conditions can occur during drying of the paint and welding of pipe joints. The presence of metallic tin ensures that even when part of the coating is not completely reduced, tin metal will be present to react and form the desired stannide layer.
  • the solvent should be non-toxic, and effective for rendering the paint sprayable and spreadable when desired. It should also evaporate quickly and have compatible solvent properties for the hydrogen decomposable tin compound. Isopropyl alcohol is most preferred, while hexane and pentane can be useful, if necessary. Acetone, however, tends to precipitate organic tin compounds.
  • tin paint of 20 percent Tin Ten-Cem (stannous octanoate in octanoic acid), stannic oxide, tin metal powder and isopropyl alcohol.
  • furnace tubes of the reactor system can be painted individually or as modules.
  • a reforming reactor system according to the present invention can contain various numbers of furnace tube modules (e.g., about 24 furnace tube modules) of suitable width, length and height (e.g., about 10 feet (3.05m) long, about 4 feet (1.22m) wide, and about 40 feet (12.2m) in height).
  • each module will include two headers of suitable diameter, preferably about 2 feet (0.61m) in diameter, which are connected by about four to ten u-tubes of suitable length (e.g., about 42 feet (12.8m) long). Therefore, the total surface area to be painted in the modules can vary widely; for example, in one embodiment it can be about 16,500 ft 2 (1530 m 2 ).
  • Yet another means for preventing carburization, coking, and metal dusting in the low-sulfur reactor system comprises the application of a metal coating or cladding to chromium rich steels contained in the reactor system.
  • These metal coatings or claddings may be comprised of tin, antimony, bismuth or arsenic. Tin is especially preferred.
  • These coatings or claddings may be applied by methods including electroplating, vapor depositing, and soaking of the chromium rich steel in a molten metal bath. It has been found that in reforming reactor systems where carburization, coking, and metal dusting are particularly problematic that the coating of the chromium-rich, nickel-containing steels with a layer of tin in effect creates a double protective layer.
  • iron, cobalt, and nickel form relatively unstable carbides which will subsequently carburize, coke and dust.
  • Elements such as chromium, niobium, vanadium, tungsten, molybdenum, tantalum and zirconium, will form stable carbides which are more resistant to carburization coking and dusting.
  • Elements such as tin, antimony and bismuth do not form carbides or coke. And, these compounds can form stable compounds with many metals such as iron, nickel and copper under reforming conditions.
  • the selection of appropriate metals which are resistant to carburization and metal dusting, and their use as coating materials for metal surfaces in the reactor system is one means for preventing the carburization and metal dusting problem.
  • carburization and metal dusting can be prevalent in a wide variety of metals; and carburization resistant metals can be more costly or exotic than conventional materials (e.g., mild steels) used in the construction of reforming reactor systems.
  • at least a portion of the furnace tubes, or furnace liners or both may be constructed of ceramic materials.
  • the material selection can be staged, such that those materials providing better carburization resistances are used in those areas of the system experiencing the highest temperatures.
  • oxidized Group VIII metal surfaces such as iron, nickel and cobalt are more active in terms of coking and carburization than their unoxidized counterparts.
  • an air roasted sample of 347 stainless steel was significantly more active than an unoxidized sample of the same steel. This is believed to be due to a re-reduction of oxidized steels which produces very fine-grained iron and/or nickel metals. Such metals are especially active for carburization and coking.
  • an air roasted 300 series stainless steel coated with tin can provide similar resistances to coking and carburization as unroasted samples of the same tin coated 300 series stainless steel.
  • oxidation will be a problem in systems where sulfur sensitivity of the catalyst is not of concern, and sulfur is used to passivate the metal surfaces. If sulfur levels in such systems ever become insufficient, any metal sulfides which have formed on metal surfaces would, after oxidation and reduction, be reduced to fine-grained metal. This metal would be highly reactive for coking and carburization. Potentially, this can cause a catastrophic failure of the metallurgy, or a major coking event.
  • the center pipe screens of reformers have been observed to locally waste away and develop holes; ultimately resulting in catalyst migration.
  • the temperatures within cokeballs during formation and burning are apparently high enough to overcome the ability of process sulfur to poison coking, carburization, and dusting.
  • the metal screens therefore, carburize and are more sensitive to wasting by intergranular oxidation (a type of corrosion) during regeneration.
  • the screen openings enlarge and holes develop.
  • teachings of the present invention are applicable to conventional reforming, as well as other areas of chemical and petrochemical processing.
  • the aforementioned platings, claddings and coatings can be used in the preparation of center pipe screens to avoid excessive hole development and catalyst migration.
  • the teachings can be applied to any furnace tubes which are subjected to carburization, coking and metal dusting, such as furnace tubes in coker furnaces.
  • the techniques described herein can be used to control carburization, coking, and metal dusting at excessively high temperatures, they can be used in cracking furnaces operating at from about 1400° to about 1700°F (760-927°C).
  • the deterioration of steel occurring in cracking furnaces operating at those temperatures can be controlled by application of various metal coatings. These metal coatings can be applied by melting, electroplating, and painting. Painting is particularly preferred.
  • a coating of antimony applied to iron bearing steels protects these steels from carburization, coking and metal dusting under the described cracking conditions.
  • an antimony paint applied to iron bearing steels will provide protection against carburization, coking, and metal dusting at 1600°F (871°C).
  • a coating of bismuth applied to nickel rich steel alloys can protect those steels against carburization, coking, and metal dusting under cracking conditions. This has been demonstrated at temperatures of up to 1600°F (871°C).
  • Bismuth coatings may also be applied to iron bearing steels and provide protection against carburization, metal dusting, and coking under cracking conditions. Also, a metal coating comprising a combination of bismuth, antimony, and/or tin can be used.
  • these agents interact with the surfaces of the reactor system by decomposition and surface attack to form iron and/or nickel intermetallic compounds, such as stannides, antimonides, bismuthides, plumbides, arsenides, etc.
  • intermetallic compounds are resistant to carburization, coking and dusting and can protect the underlying metallurgy.
  • intermetallic compounds are also believed to be more stable than the metal sulfides which were formed in systems where H 2 S was used to passivate the metal. These compounds are not reduced by hydrogen as are metal sulfides. As a result, they are less likely to leave the system than metal sulfides. Therefore, the continuous addition of a carburization inhibitor with the feed can be minimized.
  • organo-metallic compounds include bismuth neodecanoate, chromium octoate, copper naphthenate, manganese carboxylate, palladium neodecanoate, silver neodecanoate, tetrabutylgermanium, tributylantimony, triphenylantimony, triphenylarsine, and zirconium octoate.
  • the agents be provided as a coating prior to construction, prior to start-up, or in-situ (i.e., in an existing system). If added in-situ, it should be done right after catalyst regeneration. Very thin coatings can be applied. For example, it is believed that when using organo-tin compounds, iron stannide coatings as thin as 0.1 micron can be effective.
  • Optimum coating temperatures will depend on the particular organometallic compound, or the mixtures of compounds if alloys are desired.
  • an excess of the organometallic coating agent can be pulsed into the tubes at a high hydrogen flow rate so as to carry the coating agent throughout the system in a mist. The flow rate can then be reduced to permit the coating metal mist to coat and react with the furnace tube or reactor surface.
  • the compound can be introduced as a vapor which decomposes and reacts with the hot walls of the tube or reactor in a reducing atmosphere.
  • Such a process involves preheating the entire reactor system to a temperature of from 750 to 1150°F (399-621°C) preferably 900 to 1100°F (482-593°C), and most preferably about 1050°F (566°C), with a hot stream of hydrogen gas.
  • a colder gas stream at a temperature of 400 to 800°F (204-427°C), preferably 500 to 700, and most preferably about 550°F (288°C)
  • This gas mixture is introduced upstream and can provide a decomposition "wave" which travels throughout the entire reactor system.
  • the feed will preferably contain less than 100 ppb sulfur, and more preferably, less than 50 ppb sulfur. If necessary, a sulfur sorber unit can be employed to remove small excesses of sulfur.
  • Preferred reforming process conditions include a temperature between 700 and 1050°F (371-565°C), more preferably between 850 and 1025°F (454-552°C); and a pressure between 0 and 400 psig (101-2860 kPa abs.), more preferably between 15 and 150 psig (136-1140 kPa abs.); a recycle hydrogen rate sufficient to yield a hydrogen to hydrocarbon mole ratio for the feed to the reforming reaction zone between 0.1 and 20, more preferably between 0.5 and 10; and a liquid hourly space velocity for the hydrocarbon feed over the reforming catalyst of between 0.1 and 10, more preferably between 0.5 and 5.
  • furnace tubes can often range from 600 to 1800°F (320-980°C), usually from 850 and 1250°F (450-680°C), and more often from 900 and 1200°F (480-650°C).
  • heat transfer areas can be used with resistant (and usually more costly) tubing in the final stage where temperatures are usually the highest.
  • superheated hydrogen can be added between reactors of the reforming system.
  • a larger catalyst charge can be used.
  • the catalyst can be regenerated more frequently. In the case of catalyst regeneration, it is best accomplished using a moving bed process where the catalyst is withdrawn from the final bed, regenerated, and charged to the first bed.
  • the reactor system can also be operated using at least two temperature zones; at least one of higher and one of lower temperature.
  • This approach is based on the observation that metal dusting has a temperature maximum and minimum, above and below which dusting is minimized. Therefore, by “higher” temperatures, it is meant that the temperatures are higher than those conventionally used in reforming reactor systems and higher than the temperature maximum for dusting. By “lower” temperatures it is meant that the temperature is at or about the temperatures which reforming processes are conventionally conducted, and falls below that in which dusting becomes a problem.
  • Operation of portions of the reactor system in different temperature zones should reduce metal dusting as less of the reactor system is at a temperature conducive for metal dusting.
  • other advantages of such a design include improved heat transfer efficiencies and the ability to reduce equipment size because of the operation of portions of the system at higher temperatures.
  • operating portions of the reactor system at levels below and above that conducive for metal dusting would only minimize, not completely avoid, the temperature range at which metal dusting occurs. This is unavoidable because of temperature fluctuations which will occur during day to day operation of the reforming reactor system; particularly fluctuations during shut-down and start-up of the system, temperature fluctuations during cycling, and temperature fluctuations which will occur as the process fluids are heated in the reactor system.
  • Another approach to minimizing metal dusting relates to providing heat to the system using superheated raw materials (such as e.g., hydrogen), thereby minimizing the need to heat the hydrocarbons through furnace walls.
  • superheated raw materials such as e.g., hydrogen
  • catalytic reforming is well known in the petroleum industry and involves the treatment of naphtha fractions to improve octane rating by the production of aromatics.
  • the more important hydrocarbon reactions which occur during the reforming operation include the dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkycyclopentanes to aromatics, and dehydrocyclization of acyclic hydrocarbons to aromatics.
  • reaction refers to the treatment of a hydrocarbon feed through the use of one or more aromatics producing reactions in order to provide an aromatics enriched product (i.e., a product whose aromatics content is greater than in the feed).
  • While the present invention is directed primarily to catalytic reforming, it will be useful generally in the production of aromatic hydrocarbons from various hydrocarbon feedstocks under conditions of low sulfur. That is, while catalytic reforming typically refers to the conversion of naphthas, other feedstocks can be treated as well to provide an aromatics enriched product. Therefore, while the conversion of naphthas is a preferred embodiment, the present invention can be useful for the conversion or aromatization of a variety of feedstocks such as paraffin hydrocarbons, olefin hydrocarbons, acetylene hydrocarbons, cyclic paraffin hydrocarbons, cyclic olefin hydrocarbons, and mixtures thereof, and particularly saturated hydrocarbons.
  • feedstocks such as paraffin hydrocarbons, olefin hydrocarbons, acetylene hydrocarbons, cyclic paraffin hydrocarbons, cyclic olefin hydrocarbons, and mixtures thereof, and particularly saturated hydrocarbons.
  • paraffin hydrocarbons examples include those having 6 to 10 carbons such as n-hexane, methylpentane, n-haptane, methylhexane, dimethylpentane and n-octane.
  • acetylene hydrocarbons examples include those having 6 to 10 carbon atoms such as hexyne, heptyne and octyne.
  • acyclic paraffin hydrocarbons are those having 6 to 10 carbon atoms such as methylcyclopentane, cyclohexane, methylcyclohexane and dimethylcyclohexane.
  • Typical examples of cyclic olefin hydrocarbons are those having 6 to 10 carbon atoms such as methylcyclopentene, cyclohexene, methylcyclohexene, and dimethylcyclohexene.
  • the present invention will also be useful for reforming under low-sulfur conditions using a variety of different reforming catalysts.
  • Such catalyst include, but are not limited to Noble Group VIII metals on refractory inorganic oxides such as platinum on alumina, Pt/SN on alumina and Pt/Re on alumina; Noble Group VIII metals on a zeolite such as Pt, Pt/SN and Pt/Re on zeolites such as L-zeolites, ZSM-5, silicalite and beta; and Nobel Group VIII metals on alkali- and alkaline-earth exchanged L-zeolites.
  • a preferred embodiment of the invention involves the use of a large-pore zeolite catalyst including an alkali or alkaline earth metal and charged with one or more Group VIII metals. Most preferred is the embodiment where such a catalyst is used in reforming a naphtha feed.
  • large-pore zeolite is indicative generally of a zeolite having an effective pore diameter of 6 to 15 Angstroms.
  • Preferable large pore crystalline zeolites which are useful in the present invention include the type L zeolite, zeolite X, zeolite Y and faujasite. These have apparent pore sizes on the order to 7 to 9 Angstroms. Most preferably the zeolite is a type L zeolite.
  • the composition of type L zeolite expressed in terms of mole ratios of oxides may be represented by the following formula: (0.9-1.3)M 2 / n O:AL 2 O 3 (5.2-6.9)SiO 2 :yH 2 O
  • M represents a cation
  • n represents the valence of M
  • y may be any value from 0 to about 9.
  • zeolite L, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in, for example, U.S. Patent No. 3,216,789, the contents of which is hereby incorporated by reference.
  • the actual formula may vary without changing the crystalline structure.
  • the mole ratio of silicon to aluminum (Si/Al) may vary from 1.0 to 3.5.
  • the chemical formula for zeolite Y expressed in terms of mole ratios of oxides may be written as: (0.7-1.1)Na 2 O:Al 2 O 3 :xSiO 2 :yH 2 O
  • x is a value greater than 3 and up to about 6.
  • y may be a value up to about 9.
  • Zeolite Y has a characteristic X-ray powder diffraction pattern which may be employed with the above formula for identification. Zeolite Y is described in more detail in U.S.Patent No. 3,130,007 the contents of which is hereby incorporated by reference.
  • Zeolite X is a synthetic crystalline zeolitic molecular sieve which may be represented by the formula: (0.7-1.1)M 2/n O:Al 2 O 3 :(2.0-3.0)SiO 2 :yH 2 O
  • M represents a metal, particularly alkali and alkaline earth metals
  • n is the valence of M
  • y may have any value up to about 8 depending on the identity of M and the degree of hydration of the crystalline zeolite.
  • Zeolite X, its X-ray diffraction pattern, its properties, and method for its preparation are described in detail in U.S. Patent No. 2,882,244 the contents of which is hereby incorporated by reference.
  • alkali or alkaline earth metal is preferably present in the large-pore zeolite.
  • That alkaline earth metal may be either barium, strontium or calcium, preferably barium.
  • the alkaline earth metal can be incorporated into the zeolite by synthesis, impregnation or ion exchange. Barium is preferred to the other alkaline earths because it results in a somewhat less acidic catalyst. Strong acidity is undesirable in the catalyst because it promotes cracking, resulting in lower selectivity.
  • At least part of the alkali metal can be exchanged with barium using known techniques for ion exchange of zeolites. This involves contacting the zeolite with a solution containing excess Ba ++ ions.
  • the barium should preferably constitute from 0.1% to 35% by weight of the zeolite.
  • Group VIII metals are introduced into large-pore zeolites by synthesis, impregnation or exchange in an aqueous solution of appropriate salt. When it is desired to introduce two Group VIII metals into the zeolite, the operation may be carried out simultaneously or sequentially.
  • Tests were conducted to determine suitable materials for use in low-sulfur reforming reactor systems; materials which would exhibit better resistance to carburization than the mild steels conventionally used in low-sulfur reforming techniques.
  • Samples of mild steels (C steel and 21 ⁇ 4 Cr) and samples of 300 series stainless steels were tested at 1100°F (593°C), 11.50°F (621°C) and 1200°F (650°C) for twenty-four hours, and 1100°F (593°C) for ninety hours, under conditions which simulate the exposure of the materials under conditions of low-sulfur reforming.
  • the samples of various materials were placed in an open quartz boat within the hot zone of the furnace tube.
  • the boats were one inch (25.4mm) long and 1 ⁇ 2 inch (12.7mm) wide and fit well within the two-inch (50.8mm) hot zone of the tube.
  • the boats were attached to silica glass rods for each placement and removal. No internal thermocouple was used when the boats were placed inside the tube.
  • each material was carefully noted. Typically the boat was photographed. Then, each material was weighed to determine changes while taking care to keep any coke deposits with the appropriate substrate material. The samples were then mounted in an epoxy resin, ground and polished in preparation for petrographic and scanning electron microscopy analysis to determine the coking, metal dusting and carburization responses of each material.
  • Samples of 446 stainless steel and 347 stainless steel were placed in a sample boat and tested simultaneously in the carburization apparatus at 1100°F (593°C) for a total of two weeks.
  • the 446 stainless steel had a thin coating.of coke, but no other alteration was detected.
  • the 347 stainless steel on the other hand, had massive localized coke deposits, and pits more than 4 mils (0.102mm) deep from which coke and metal dust had erupted.
  • Samples were tested of a 304 stainless steel screen; each sample being electroplated with one of tin and chromium. These samples were tested along with a sample of 446 stainless steel in a carburization test at 1100°F. The samples were exposed or five weeks. Each week the samples were cooled to room temperature for observation and photographic documentation. They were then re-heated to 1100°F (593°C). The tin plated screen was free of coke; the chromium-plated screen was also free of coke, except locally where the chrome plate had peeled; and the piece of 446 stainless steel was uniformly coated with coke.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
  • Catalysts (AREA)
  • Hydrogen, Water And Hydrids (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
  • Paints Or Removers (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)

Claims (15)

  1. Verfahren zur Erhöhung der Carbonisierungsfestigkeit mindestens eines Abschnitts einer Vorrichtung zur katalytischen Umwandlung von Kohlenwasserstoffen bei einem Freiliegen gegenüber Kohlenstoffen von höherer Temperatur, umfassend das Aufbringen eines reduzierbaren Anstrichs auf einen Stahlabschnitt der Vorrichtung und Erwärmen des Anstrichs unter reduzierenden Bedingungen, so dass eine Schutzschicht entsteht, welche die Carbonisierungsfestigkeit gibt.
  2. Verfahren nach Anspruch 1, wobei der Anstrich ein zinnhaltiger Anstrich ist.
  3. Verfahren nach Anspruch 1 oder 2, wobei der Anstrich ein zersetzbarer zinnhaltiger Anstrich ist, der zu reaktivem Zinn reduziert wird, welches ein Eisenstanid mit dem Stahl bildet, auf dem es unter reduzierten Bedingungen aufgebracht ist.
  4. Verfahren nach Anspruch 2 oder 3, wobei der zinnhaltige Anstrich umfasst (i) eine von Wasserstoff zersetzbare Zinnverbindung; (ii) ein Lösungsmittelsystem; (iii) ein fein verteiltes Zinnmetall; und (iv) ein Zinnoxid.
  5. Verfahren nach Anspruch 4, wobei das fein verteilte Zinnmetall eine Teilchengröße von etwa 1 bis 5 Mikrometer besitzt.
  6. Verfahren nach Anspruch 2 oder 3, wobei der Anstrich ein oder mehrere zinnhaltige Verbindungen enthält und ein oder mehrere Eisenverbindungen, wobei das Gewichtsverhältnis von Fe zu Sn bis 1:3 ist.
  7. Verfahren nach Anspruch 6, wobei die Eisenverbindung Fe2O3 ist.
  8. Verfahren nach irgendeinem oder mehreren der Ansprüche 1 bis 7, wobei der Anstrich auf einem Ofenteil der Vorrichtung aufgebracht wird.
  9. Verfahren nach Anspruch 8, wobei der Anstrich auf einem Heizrohr aufgebracht ist.
  10. Verfahren nach irgendeinem oder mehreren der Ansprüche 1 bis 9, wobei die Vorrichtung eine Reaktoranlage zum katalytischen Reformieren und zur Umwandlung von Kohlenwasserstoffen in Aromaten ist.
  11. Verfahren nach Anspruch 1 oder 2, wobei der Anstrich Metalloxid enthält.
  12. Verfahren nach Anspruch 1 oder 2, wobei der Anstrich eine von Wasserstoff zersetzbare Verbindung enthält.
  13. Verfahren nach irgendeinem oder mehreren der Ansprüche 1 bis 12, wobei der aufgebrachte Anstrich in Gegenwart von Wasserstoff erhitzt wird.
  14. Verfahren nach Anspruch 13, wobei der aufgebrachte Anstrich mit einem heißen Wasserstoffstrom zusammengebracht wird.
  15. Verfahren nach Anspruch 2, wobei die Schutzschicht Metallstannide enthält.
EP97110024A 1991-03-08 1992-03-06 Reformierungsverfahren mit niedrigem Schwefelgehalt Expired - Lifetime EP0798363B1 (de)

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