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
  • C10G9/007—Visbreaking
• • 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
  • C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
  • C10G75/04—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general by addition of antifouling agents

Definitions

• the present invention relates to a method and to a composition of additive to be used in a thermal conversion operation in petroleum plants, starting from a charge made up of a residue of crude petroleum with a high paraffin component level.
• thermal conversion processes are used to split the largest hydrocarbon molecules, in particular hydrocarbons with a boiling temperature that exceeds 350°C, into smaller hydrocarbon molecules with a lower boiling point.
• the conversion processes transform the heavy residues obtained in the petrol refining industry into intermediate or light products that are more easily commercialised.
• the conversion operation can follow a variety of distinct technologies, which are known by a number of technical names, such as Visbreaking, Coking, Hydrocracking, Thermal Cracking.
• Visbreaking in particular has gained a certain level of importance in Europe and other industrialised countries because of the contraction of the fuel oil market and the expansion of the consumption of medium distillates, in particular gasoline for vehicles.
• the VSB plant is essentially made up of the following parts: a train of exchangers into which the fed charge enters for initial pre-heating, followed by a furnace in which thermal cracking takes place, then a fractionating column, from the base of which flows the residue (TAR), which passes through the exchangers, transferring part of its heat to the charge. It is also possible to foresee a "soaker" between the furnace and the fractionating column.
• the operating conditions of a thermal cracking plant of this kind are basically speaking the following: a charge made up of a primary distillation residue or of a vacuum is introduced into the furnace, which operates at a temperature of 420-500 °C (in the presence or in the absence of "soaker", respectively) at a pressure of between 3 and 20 bar.
• the charge treated in this manner then goes to a fractionating column, from which light distillates (from 3 to approximately 10% by weight), medium distillates (15-20% by weight) and a residue (TAR 65-75% by weight with respect to the weight of the original charge).
• the plant is sized in such a way as to give a permanence at the cracking temperature sufficient to achieve the conversions required by the process.
• conversion yield is used to indicate the percentage of light and medium distillates (gas + petrol + gas oil) with respect to the total charge.
• the VSB process is managed with the aim of obtaining maximum transformation into medium and light distillates, in order to satisfy market requests.
• the factor limiting the production of high conversion yields is the need to obtain a residue (TAR) of a quality capable of conforming with the specifications set down by the markets for the resulting fuel oil.
• the quality of the TAR is evaluated with reference to specifications relating to the following parameters: stability, percentage of asphaltenes, viscosity.
• the stability of the gas oil and the TAR is measured according to the tendency of its polymeric or asphaltene components to separate from the paraffin components over a period of time.
• the composition of these distillation products includes a paraffin, and therefore an aliphatic portion, and an asphaltene, and therefore an essentially aromatic portion.
• asphaltenes are by definition macromolecular aggregates of naphthenic type with a low hydrogen content, which are insoluble in N-hexane, that is to say in paraffin, it will be clearly understood that over a period of time there is a tendency for the two types of component to separate from each other. In this respect it is also found that the ratio between the paraffin portion and the naphthene portion is clearly influenced by the source of the crude oil treated in the plant.
• the percentage of asphaltene compounds is another parameter that is controlled when determining the quality of the fuel oil produced.
• Asphaltenes take on particular importance as the paraffin content of the charge increases. This is due to the fact that cracking of the long paraffin molecules results in a subsequent cyclization of the radicals formed and a consequent generation of asphaltenes. In effect it has been seen in practice that from the cracking of paraffin charges residues are obtained that have a percentage of asphaltenes that is higher than that of the original charge, and not justified by the concentration effect caused by extraction of the light distillates.
• the viscosity is another parameter that has a direct influence on the conversion yield in the plant, as a lower viscosity in the residue requires lower amounts of flux in order to reach commercially required viscosity levels.
• Variation in the viscosity depends not only on extraction of the light products, but also on the ability of the radicals formed during cracking to polymerise. This ability is greater the richer the charge is in paraffin.
• the polymers formed have a direct influence on the viscosity, increasing it and making it necessary to use a larger amount of flux in order to reach standards. This results in a reduction in net yield for an equivalent viscosity.
• the present invention therefore provides a satisfactory completion of the general state of the art as described in the above mentioned patent 1,211,979, extending it to the whole range of raw petroleum products, both those defined as paraffinic crude oil and those defined as naphthenic crude oil.
• Residues of crude petroleum with a high level of paraffin components are intended to mean residue deriving from crude oil that has a low sulphur level, not exceeding 1% by weight, a pour point not lower than -5°C and a TBP distillation product not exceeding 50% by weight at 350°C.
• a low sulphur level not exceeding 1% by weight
• a pour point not lower than -5°C
• a TBP distillation product not exceeding 50% by weight at 350°C.
• the "increase in yield” can be considered both in terms of an increase in conversion of medium and light distillates, and as an improvement in the TAR quality.
• the additive according to the present invention has proved that: a) at the same furnace temperature it is possible to increase the yield due to the reduction of TAR viscosity, accompanied by an improvement in TAR quality in terms of stability and asphaltene content, whereas b) following an increase in the furnace temperature it is possible to produce an increase in yield due to reduction in the viscosity, accompanied by a further increase in the conversion yield of the medium distillates.
• the continuous addition of additive can take place in the charge feed upstream of the furnace, on the quench, at the bottom of the fractionating column, or at the outlet from the bottom of the column itself, preferably on the charge upstream of the furnace.
• reference parameters are determined for the quality of the TAR at the outlet from the thermal conversion plant fractionating column, in order to determine the amount of additive to be used.
• a fresh check is carried out on the new reference parameters for the quality of the TAR at the moment in which the system reaches normal operation after introduction of the amount of additive and, optionally, after increasing the temperature of the furnace in the thermal conversion plant, until the TAR quality reference parameters return to the initial value, if the aim is to obtain an increase in the level of medium distillate.
• the object of the present invention is therefore a method to increase the yield in a thermal conversion operation in petroleum plants, starting from a charge formed by a residue deriving from crude oil with a high level of paraffin components, having a low sulphur content, not exceeding 1% by weight and/or a pour point not lower than -5°C and/or a TBP distillation product not exceeding 50% by weight at 350°C, in which
• a further object of the present invention is an additive for use in the method described above, in which said additive has the composition indicated above.
• the additive to be used in the present invention in combination with per se known solvents, is essentially made up of one or more active ingredients.
• active ingredients catechol derivatives are preferred. Among the latter particular mention is made to 4-tert.butyl-catechol and pyrocatechin.
• phenolic type ingredients those in which at least one tert.butyl substituent group is in an ortho position with respect to the hydroxyl in the phenol group.
• bisphenols to be used as active ingredient in the additive according to the present invention particular mention can be made of 4,4'-methylene-bis(2,6-di-tert.butylphenol), 4,4'-thio-bis(6-tert.butyl-m-cresol), 2,2'-methylene-bis(4-methyl-6-nonylphenol), 2,2'-methylene-bis(4-methyl-6-tert.butylphenol).
• alkylsuccinimides As a further active ingredient in the additive it is also possible to add alkylsuccinimides of the type used in the method described in the patent No. 2,211,979 mentioned above. However, addition of the succinimides is not essential to the effects of the present invention.
• the above alkylsuccinimides are the ones with a nitrogen content of from 1 to 8% and a total basic number of 20-200 mg/KOH/g, and optionally containing atoms of an element chosen from the class made up of boron and phosphor.
• the alkylsuccinimides can be added up to a proportion of 30% by weight with respect to the total weight of the additive.
• this proportion can be limited to less than 5% by weight.
• the proportion of active principles with respect to the total weight of the additive amounts to a percentage of from 5 to 95% by weight, so that the proportion of solvents is between 95 and 5%.
• the additive may also optionally include metal deactivators in a proportion by weight not exceeding 5% of the total weight of active ingredients in the additive.
• the additive of a known kind is an additive as described in the patent No. 1,211 979, comprising as active ingredients succinimides and phenolic antioxidants in a ratio of 3:1.
• the additive according to the invention does not comprise succinimides and includes as active ingredients sterically impeded phenols with tert.butyl groups in an orthic position, catechol derivatives and bisphenols.
• the viscosity was measured at zero hour (T0) and again after a period of 24 hours, for a sample without additive (S.A.), using an additive according to the patent No. 1,221, 979 (A.V.) and using an additive according to the invention (A.N.), respectively.
• the results are indicated in table 1, with the viscosity indicated in centipoise.
• the viscosity was determined according to Brookfield (TL 6-vel.60) at 100°C. T0 T 24 hours No additive S.A. 126 cPs ⁇ 310 cPs Known additive A.V. 129 cPs ⁇ 298 cPs New additive A.N. 128 cPs ⁇ 235 cPs
• a high paraffin residue was treated in a Visbreaking plant with Soaker.
• the charge included 85% of paraffin residues and 15% of asphaltene residues from a vacuum fractionating tower.
• a comparison test was carried out in the absence of additives (B1) and with the addition of a known additive (A.V.) according to the patent 1.211.979.
• the percentage isoviscous yield i.e. at an equivalent viscosity of TAR produced, does not show a significant difference when the known additive is used with a paraffin residue.
• a mixed charge of AMNA-SARIR 60 : 40, with a very high paraffin content was treated in a Visbreaking plant with Soaker.
• a comparison test was carried out without additive (B3) and with an additive according to the present invention (A.N.). The additive was dosed upstream of the cracking furnace. The two tests were carried out at the same furnace temperature.

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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)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Liquid Carbonaceous Fuels (AREA)
• Tires In General (AREA)
• Compounds Of Unknown Constitution (AREA)
• Fertilizers (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Working-Up Tar And Pitch (AREA)

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Cited By (2)

Citations (8)

• 1996
  • 1996-07-08 IT IT96RM000487A patent/IT1284204B1/it active IP Right Grant
• 1997
  • 1997-07-02 AT AT97830333T patent/ATE264381T1/de not_active IP Right Cessation
  • 1997-07-02 DK DK97830333T patent/DK0818524T3/da active
  • 1997-07-02 ES ES97830333T patent/ES2219744T3/es not_active Expired - Lifetime
  • 1997-07-02 DE DE69728609T patent/DE69728609T2/de not_active Expired - Fee Related
  • 1997-07-02 EP EP97830333A patent/EP0818524B1/fr not_active Expired - Lifetime
  • 1997-07-02 PT PT97830333T patent/PT818524E/pt unknown

Patent Citations (8)

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