Classifications

• • 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
  • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
  • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
  • C10G9/16—Preventing or removing incrustation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S585/00—Chemistry of hydrocarbon compounds
  • Y10S585/949—Miscellaneous considerations
  • Y10S585/95—Prevention or removal of corrosion or solid deposits

Definitions

• the present invention relates to the field of cracking of hydrocarbons or other organic compounds and more particularly relates to a process for reducing coking on the walls of cracking reactors and heat exchangers used to cool the compounds resulting from the reaction of cracking.
• tubular reactors used are preferably made of steels rich in chromium and nickel while the heat exchangers, subjected to less severe constraints, are made of carbon steels.
• This same type of apparatus also meets to produce other organic compounds such as vinyl chloride by pyrolysis of 1, 2-dichloroethane.
• a first method described in US Pat. No. 4,099,990 and a subsequent publication by D.E. Brown et al. in ACS Symp. Ser. 202 (1982) 23, consists of forming, from alkyloxysilane, a coating of silica by thermal degradation in steam. Some improvement in the quality of the deposit can be obtained by using a silicone oil under specific conditions (Chem. Techn. (Leipzig) 42 (1990) 146). However, the process is quite expensive and the silica layer is not very stable above 750 ° C., the usual temperature for cracking tubes in industrial installations.
• US Pat. No. 4,410,418 describes a method for depositing a film of silica from halogenosilane.
• the silylated compound is deposited liquid, in film, on the metal surface to be treated then, by exposure to humidity, a layer of silica is formed by hydrolysis.
• This technique is difficult to apply to industrial installations because of its delicate implementation; it is also accompanied by the release of acids which can corrode the metal walls.
• EP 540 084, EP 654 544 and EP 671 483 a protective layer of ceramic type is obtained from silylated compounds which do not contain alkoxy groups and which are cracked in the presence of vapor or inert gas.
• US Pat. No. 5,849,176 describes a process in which an additive composed of sulfur and silicon is added to the charge of the cracking unit. Coke formation is reduced more significantly than with a silylated compound alone or a sulfur compound alone.
• This patent claims the use of compounds based on sulfur and silicon to reduce coking in the cracking tubes and also in the heat exchangers placed in line following the cracking reactor. The quantities of silicon thus introduced end up being non-negligible and blockages are to be feared either in the cracking tube or in the section for treating cracked gases.
• Patent application WO 95/22588 claims a process in which the cracking tube is pretreated in an inert gas (nitrogen, methane, hydrogen) with an additive based on sulfur and silicon. A significant reduction in the amount of coke formed during the cracking of the hydrocarbon feed is obtained. A real synergy exists between sulfur and silicon since no additive based on sulfur or silicon alone leads to such results. The use of an inert carrier gas however seems essential to these performances.
• Example 6 and Figure 7 of this patent application show that the use of steam as a carrier gas with an additive consisting of trimethylsilylmethylmercaptan does not lead to any inhibition of the formation of coke.
• an additive consisting of a mixture of sulfur compound and silylated compound can be used to pretreat a hydrocarbon cracking tube in vapor and thus significantly reduce the formation of coke which accompanies the hydrocarbon cracking reaction.
• the first object of the invention is therefore a process for reducing coking on the metal walls of a reactor for cracking hydrocarbons or other organic compounds and on the metal walls of a heat exchanger placed after the cracking reactor, characterized in that the metal surfaces coming into contact with the organic substance to be cracked are pretreated with a stream of water vapor containing at least one silicon compound and at least one sulfur compound, at a temperature between 300 and 1100 ° C, preferably between 400 and 700 ° C for the heat exchanger and preferably between 750 and 1050 ° C for the cracking tube, for a period of between 0.5 and 12 hours, preferably between 1 and 6 hours.
• the silicon compounds which can be used in the process according to the invention may contain one or more silicon atoms and be of inorganic or organic nature.
• inorganic silicon compounds mention may be made more particularly of halides, hydroxides and oxides of silicon, silicon acids, ques, and the alkaline salts of these acids.
• inorganic silicon compounds those which do not contain halogens are preferred.
• organic silicon compounds and, among these, those which contain only silicon, carbon, hydrogen and, optionally, oxygen.
• the hydrocarbon or oxycarbon groups linked to silicon can contain from 1 to 20 carbon atoms and are, for example, alkyl, alkenyl, phenyl, alkoxy, phenoxy, carboxylate, ketocarboxylate or diketone groups.
• tetramethylsiiane tetraethylsilane, phenyltri-methylsilane, tetraphenylsilane, phenyltriethoxysilane, diphenyldimethoxysilane, tetraethoxysilane, tetramethoxysilane, triethyl , poly (dimethylsiloxanes) and especially hexamethyldisiloxane.
• organic silicon compounds containing heteroatoms such as halogen, nitrogen or phosphorus atoms.
• heteroatoms such as halogen, nitrogen or phosphorus atoms.
• chlorotriethylsilane, (3-aminopropyl) triethoxysilane and hexamethyldisilazane examples of such compounds.
• R 1 and R 2 each represent a hydrogen atom or a hydrocarbon group, and x is a number greater than or equal to 1.
• hydrocarbon groups mention may be made of alkyl, alkenyl groups, cycloalkyl, aryl and combinations thereof such as, for example, alkylaryl groups.
• organic sulfur compounds mention may be made more particularly of alkyl mercaptans, dialkyl sulfides, -disulfides and -polysulfides, as well as the sulfur compounds present in certain petroleum fractions (naphtha) such as thiophenic and benzothiophenic compounds. .
• dimethyl sulphide, diethyl sulphide, hydrogen sulphide and especially dimethyldisulphide are used.
• the atomic ratio (Si: S) defining the proportions between the sulfur compound (s) and the silylated compound (s) is preferably between 5: 1 and 1: 5.
• an Si: S ratio of between 2: 1 and 1: 2 is used.
• the concentration of the additive constituted by the mixture of the sulfur compound (s) and the silylated compound (s) can range from 50 to 5000 ppm by mass in the carrier fluid consisting of steam alone or mixed with an inert gas (nitrogen, hydrogen, methane or ethane). Preferably, this concentration is between 100 and 3000 ppm.
• the pressure of the carrier fluid is generally equal to that usually used in cracking furnaces (between 1 and 20 bars absolute, advantageously between 1 and 5 bars absolute).
• the pretreatment according to the invention can be implemented in any new cracking unit or in any existing unit after each decoking operation.
• the invention also relates to a cracking process in which a sulfur compound and, optionally, a silylated compound is added during cracking to the charge of organic compounds.
• the temperature at which this addition takes place depends directly on the cracking conditions; it generally varies between 400 and 1000 ° C. and is preferably between 700 and 950 ° C.
• the sulfur compounds and, optionally, those of silicon to be used in the context of this embodiment are the same as those mentioned above.
• the sulfur-containing compound can be used alone or as a mixture with a silylated compound in an Si: S atomic ratio less than or equal to 2: 1, preferably less than or equal to 1: 2.
• the organic compound to be cracked already contains sulfur in organic form, only the silylated compound can optionally be added.
• an Si: S atomic proportion of less than or equal to 2: 1, preferably less than or equal to 1: 2 must be respected, the concentration of silicon in the compound to be cracked should not exceed 500 ppm.
• the concentration of sulfur additive, with or without silylated compound, is chosen so that the sulfur concentration in the organic compound to be cracked is between 10 to 1000 ppm by mass, preferably between 20 and 300 ppm by mass.
• the cracking tube with an internal diameter of 9 mm and a length of 4.6 m was made of Incoloy 800 HT steel and included an additional length of 1.45 m from the same tube for preheating fluids.
• the additive concentration in the water vapor was 2970 ppm by mass.
• the cracking conditions were as follows:
• the decoking of the reactor was carried out by means of a mixture of air (1.2 kg / h) and water vapor (4.5 kg / h) brought to 800 and then 900 ° C. in order to completely oxidize coke to carbon oxides. Carbon oxide concentrations were continuously measured by an infrared detector. Part of the coke that came off was entrained by the gas flow and then trapped by a cyclone. The mass of coke initially formed in the cracking tube is given by the sum of the coke which has been entrained and the coke which has been oxidized.
• This example shows the effectiveness of a pretreatment based on sulfur and silicon diluted in steam to inhibit the formation of coke during cracking of propane.
• the cracking tube was made of Incoloy 800 HT steel with an inside diameter of 7.7 mm and a length of 9 meters.
• the gases were preheated to 200 ° C before their introduction into the cracking tube.
• the pretreatment used a mixed flow of steam (0.7 kg / h) and nitrogen (3.5 kg / h) for 4 hours.
• the temperature of the gases leaving the cracking tube was 1010 ° C.
• the cracking conditions were as follows:
• the decoking was carried out using air (240 g / h) diluted in nitrogen (1, 2 kg / h) at a temperature between 900 and 1000 ° C. Carbon oxide concentrations were continuously measured by an infrared detector.
• This example shows the coke-inhibiting properties of a pretreatment based on sulfur and silicon diluted in steam, to which is added a continuous addition of dimethyldisulfide to the feed.
• a reference test was carried out under identical conditions but without adding the pretreatment additive based on dimethyldisulfide and hexamethyldisiloxane.
• This example shows the coke-inhibiting properties of a pretreatment based on sulfur and silicon diluted in steam, to which is added a continuous addition to the feed of a dimethyldisulfide-hexamethyldisiloxane mixture.
• Example 2 The general experimental conditions as well as those of pretreatment were identical to those of Example 2.
• An additive composed of dimethyldisulfide and hexamethyldisiloxane having an atomic ratio Si: S equal to 1:20 was injected at the inlet of the tube. cracking at a rate of 1.88 g / h during the 20 hours that the cracking of propane lasted.
• Example 2 The general experimental conditions were identical to those of Example 2 but using as an additive the hexamethyldisiloxane injected at the inlet of the cracking tube at the rate of 2.3 g / h during the 4 hours of pretreatment.
• This example shows the effectiveness of a pretreatment using an additive based on sulfur and silicon diluted in water vapor to inhibit the formation of coke in a heat exchanger.
• the micropilot was divided into two parts, a cracking reactor followed by a heat exchanger.
• a small metal coupon (P-22 type carbon steel containing 2.25% chromium and 1.0% molybdenum) was placed in the gas flow passing through this heat exchanger. The coking reactions took place on the surface of this coupon, causing an increase in its mass which could be translated into coking speed per unit of area.
• the pretreatment conditions were as follows:
• the cracking conditions were as follows: temperature of the cracking reactor 850 ° C. contact time of the cracking reactor 0.5 second hydrocarbon to be cracked isobutane isobutane flow rate 10 l / h nitrogen flow rate 10 l / h cracking severity (propylene / ethylene) 0.6 heat exchanger temperature 500 ° C duration 1 hour
• the coke formed in the cracking reactor and the heat exchanger was removed (decoking) by a high temperature air treatment to transform the carbon into carbon oxides gas.
• the following table 2 indicates the coking speeds observed on the metal coupon placed in the heat exchanger, under standard cracking conditions, during each coking phase.
• the coking speeds of the coupon pretreated with the sulfur and silicon-based additive are compared to the coking speeds obtained on a coupon of the same kind, under the same conditions, but having not undergone any pretreatment.
• the anti-coke properties of the sulfur-silicon pretreatment are expressed by the term "inhibition of coke” defined as follows:

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• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Silicon Compounds (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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• 1999
  • 1999-09-24 FR FR9911965A patent/FR2798939B1/fr not_active Expired - Fee Related
• 2000
  • 2000-09-12 AR ARP000104787A patent/AR025643A1/es active IP Right Grant
  • 2000-09-18 KR KR1020027003848A patent/KR100729188B1/ko not_active IP Right Cessation
  • 2000-09-18 JP JP2001525294A patent/JP2003510404A/ja active Pending
  • 2000-09-18 CN CNB008161712A patent/CN1263828C/zh not_active Expired - Fee Related
  • 2000-09-18 WO PCT/FR2000/002583 patent/WO2001021731A1/fr active IP Right Grant
  • 2000-09-18 US US10/088,738 patent/US7604730B1/en not_active Expired - Fee Related
  • 2000-09-18 RU RU2002110818/15A patent/RU2002110818A/ru not_active Application Discontinuation
  • 2000-09-18 EP EP00964312A patent/EP1226223A1/de not_active Withdrawn
  • 2000-09-18 MX MXPA02003075A patent/MXPA02003075A/es active IP Right Grant
  • 2000-09-18 AU AU75276/00A patent/AU7527600A/en not_active Abandoned
  • 2000-09-18 BR BR0014221-2A patent/BR0014221A/pt not_active Application Discontinuation
  • 2000-09-18 CZ CZ20021039A patent/CZ294442B6/cs not_active IP Right Cessation
  • 2000-09-18 PL PL354579A patent/PL192646B1/pl not_active IP Right Cessation
  • 2000-09-18 CA CA2385372A patent/CA2385372C/fr not_active Expired - Fee Related
  • 2000-09-22 TW TW089119613A patent/TWI286569B/zh not_active IP Right Cessation
• 2002
  • 2002-03-21 NO NO20021425A patent/NO20021425D0/no not_active Application Discontinuation
  • 2002-04-15 ZA ZA200202939A patent/ZA200202939B/xx unknown

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