Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/4166—Systems measuring a particular property of an electrolyte
• • 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
  • C10G19/00—Refining hydrocarbon oils in the absence of hydrogen, by alkaline treatment
  • C10G19/02—Refining hydrocarbon oils in the absence of hydrogen, by alkaline treatment with aqueous alkaline solutions
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D21/00—Control of chemical or physico-chemical variables, e.g. pH value
  • G05D21/02—Control of chemical or physico-chemical variables, e.g. pH value characterised by the use of electric means

Definitions

• the present invention relates to a process for monitoring the conversion of mercaptans to disulfides, wherein a mercaptan-containing hydrocarbon feed is contacted with a basic aqueous solvent to produce a mercaptan-depleted hydrocarbon fraction and an enriched aqueous phase.
• a mercaptan-containing hydrocarbon feed is contacted with a basic aqueous solvent to produce a mercaptan-depleted hydrocarbon fraction and an enriched aqueous phase.
• said mercaptan-enriched aqueous phase being separated and contacted with an oxygen-containing gas to produce insoluble disulfides and a regenerated basic aqueous solvent.
• LPG Liquefied petroleum gas
• organosulfur compounds identified in this LPG are mercaptans such as methyl mercaptan and ethyl mercaptan, and hydrogen sulfide (H2S).
• Mercaptans are compounds of formula R-SH where R is a linear, branched or cyclic alkyl group. Hydrogen sulfide (H2S) is therefore not considered a mercaptan in the present application.
• Mercaptans that may be present in LPG generally have a C1-C6 carbon chain, although longer carbon chains may also be present.
• LPG is a useful raw material for the production of ethyl tert-butyl ether (ETBE) or methyl tert-butyl ether (MTBE), which is the formulation of commercial species.
• EBE ethyl tert-butyl ether
• MTBE methyl tert-butyl ether
• LPG used for the production of ETBE / MTBE must have a sulfur content of less than 15ppm. This constraint requires optimizing the operation of the "Extractive Merox" units of LPGs.
• the "Merox Extractive" units extract mercaptans from LPG and convert them into disulfides.
• the process can be summarized as follows: An LPG loaded with sulfur compounds is washed with an alkaline aqueous solution, usually sodium hydroxide, in order to producing on the one hand a LPG depleted of sulfur compounds and on the other hand an alkaline aqueous solution comprising mercaptans in salified form. The latter is separated and placed in the presence of oxygen to transform the mercaptans into disulfides and water.
• the disulfide formation reaction is usually catalyzed by cobalt phthalocyanine, according to a method developed by UOP.
• the disulfides obtained are not soluble in water and are separated by decantation.
• the separated alkaline aqueous solution is recycled.
• the cobalt phthalocyanine used remains in the aqueous alkaline solution.
• the extractive Merox unit is controlled by varying the amount of air injected into the catalytic zone so as to obtain a total conversion to disulfides without excess air. Operation with excess air results in an oxygen supply at the mercaptan extractor. Oxygen reacts with mercaptans to form disulfides that will not be extracted by the aqueous alkaline solution and will remain in LPG.
• the mercaptan content in the form of sodium thiolates, must be between 30 and 100 ppm.
• CH 3 CH 2 SNa, CH 3 SNa and C 6 H 5 SNa are non-limiting examples of sodium thiolates.
• CH3CH2SH, CH3SH and CHHH are non-limiting examples of mercaptans.
• the control of the extractive Merox unit with regard to the oxygen demand, is carried out by means of a visual test called "shake test".
• This test consists in filling half a bottle of transparent glass with the soda solution after regeneration (the sky of the bottle containing air), in the butchering, and shake it until color change. The color changes from blue to green when the cobalt catalyst changes its oxidation state. If the color change occurs in less than 30 seconds, there may be an excess of air. The appreciation of this color may vary according to the operator performing the manipulation.
• the "shake test” shows its limits.
• a rapid change of color does not necessarily imply an excess of air, but may also mean a small proportion of mercaptans or a very active catalyst and / or very concentrated.
• a degraded or diluted soda solution will not be effective enough to extract the mercaptans from LPG and will also distort the results.
• the Applicant has found a method for monitoring the conversion of mercaptans to disulfides, in which a hydrocarbon feedstock containing mercaptans is brought into contact with a basic aqueous solvent for producing a mercaptan-depleted hydrocarbon fraction and a mercaptan-enriched aqueous phase, said mercaptan-enriched aqueous phase being separated and contacted with an oxygen-containing gas to produce insoluble disulfides and a regenerated basic aqueous solvent, characterized in that the evolution of the insoluble disulfide production reaction is controlled by measurement of redox potential.
• the Applicant has surprisingly found that despite the many parameters likely to interfere with the measurement of the redox potential, the latter could be used to control the reaction, for example by controlling the supply of gas containing oxygen (O2). .
• the parameters that may interfere are for example the temperature, the pH, the concentration of the redox couples in solution and their solubilities, a corrosive action of the measured solution and poisoning of the measuring electrode by the sulfur compounds.
• Many redox couples are indeed likely to be present, for example from the catalyst used to catalyze the oxidation reaction of mercaptans to disulfides, for example cobalt complexed by phthalocyanine, but also from different species of mercaptans present in the hydrocarbon load.
• Redox potential measurements performed in a corrosive medium may be distorted due to corrosion of the electrode.
• the basic aqueous solution used can indeed be a very basic solution of 15% sodium hydroxide.
• some electrodes eg Ag / AgCl electrodes
• H2S which leads to their deterioration.
• Such poisoning is also likely to occur in the presence of other sulfur compounds, such as mercaptans.
• the electrodes that can be used are for example silver electrodes (Ag / AgCl), preferably comprising a protection, for example of the polymer type.
• the hydrocarbon feedstock used preferably has an H 2 S content of less than or equal to 50 ppm by weight.
• the hydrocarbon feed may be a liquefied petroleum gas, for example from crude oil fractionation, petroleum cuts or cracking processes.
• the H2S content of the feed may for example be reduced to a content of 50ppm or less by at least one wash with an appropriate alkaline aqueous solution.
• the oxidation-reduction potential measurement is preferably carried out on the regenerated basic aqueous solvent.
• the supply of oxygen-containing gas is regulated according to the measured redox potential.
• the basic aqueous solvent is advantageously sodium hydroxide at 10 to 20% by weight, for example at 15% by weight.
• the supply of oxygen-containing gas is increased or decreased when the redox potential is, respectively, less than -550mV or greater than -500mV relative to a normal hydrogen electrode (NHE).
• NHE normal hydrogen electrode
• the invention relates to a unit for converting mercaptans to disulfides, comprising a first chamber in which a hydrocarbon feedstock containing mercaptans is contacted with a basic aqueous solvent to produce a hydrocarbon fraction depleted in mercaptans and an aqueous phase enriched in mercaptans, said aqueous phase enriched in mercaptans being separated and brought into contact with an oxidant in a second chamber to produce insoluble disulfides and a regenerated basic aqueous solvent, the mercaptans to disulfides conversion unit comprising furthermore, oxidation-reduction potential measuring means.
• the unit for converting mercaptans to disulphides is, for example, of the "extractive Merox" type.
• the first chamber shaped to receive and put in contact a hydrocarbon charge containing mercaptans and a basic aqueous solvent for producing a mercaptan depleted hydrocarbon fraction and an aqueous phase enriched in mercaptans, is for example a mercaptan extractor, in particular intended for an "extractive merox" unit.
• the second chamber shaped to receive and put in contact with said aqueous phase enriched in separated mercaptans and an oxidant to produce insoluble disulfides and a regenerated basic aqueous solvent, is for example an oxidation reactor, in particular intended for an "extractive merox" unit. ".
• the unit preferably comprises a third separation chamber in which the insoluble disulfides and the regenerated basic aqueous solvent are separated.
• the unit includes a first conduit for returning the regenerated basic aqueous solvent from the third enclosure to the first enclosure.
• the oxidation-reduction potential measurement means of the unit are arranged on the third enclosure and / or on the first conduit.
• the oxidation-reduction potential measuring means disposed on the first pipe and / or on the third enclosure comprise a redox potential measurement probe coupled to a reading apparatus.
• the measuring means are advantageously connected to the first pipe by means of a bypass pipe.
• the bypass line may further comprise an isolation valve, a water inlet for cleaning the measuring probe and the housing supporting it, and a purge valve.
• the invention relates to a kit for measuring the redox potential of a corrosive solution comprising (i) a corrosive solution supply line, (ii) a water supply line, (iii) a reservoir, (iv) a redox potential measuring probe, (v) a purge, and optionally a reading apparatus coupled to the probe.
• kit forms a device for sampling and measuring the redox potential of a corrosive solution, which can be used to implement the method according to the invention.
• the kit may include means for isolating the different sections constituted by (i) the corrosive solution supply line and / or (ii) the water supply line and / or (ii) the reservoir, and / or (iii) purging.
• the kit comprises a tank equipped with a potential measuring probe, a pipe intended to supply the tank in corrosive solution, a pipe intended to supply the water tank, a purge of the tank, at least means for isolating the corrosive solution supply line and at least one means for isolating the water supply line.
• isolation means are for example valves.
• the redox potential measurement probe possibly coupled to a reading apparatus, optionally comprises means for coupling to oxygen-containing gas supply regulating means such as those present in a mercaptan conversion unit. according to the second aspect of the invention.
• the invention relates to the use of the kit according to its third aspect, in a refining installation, or a refining installation comprising a kit or sampling and measuring device according to the invention.
• the use of the kit may include the steps of:
• This use may optionally comprise a step of controlling means for regulating the supply of gas to an enclosure from which the corrosive solution to be measured, for example an oxidation reactor, comes from, so that the measured redox potential is in a range of values. predetermined.
• FIGS. 1 -5 describe in a nonlimiting manner the invention in its various aspects.
• FIG. 1 is a graph showing the redox potential variation of mercaptans in 15% sodium hydroxide, when the concentration of mercaptans varies.
• Figure 2 shows a diagram of an extractive merox unit for desulfurizing a LPG.
• Figure 3 shows a redox potential measurement kit, in the form of a diagram.
• Figures 4 and 5 show a variant of the kit shown in Figure 3.
• the curve representing the variation of the mercaptan concentration of the sodium hydroxide solution at 15% by weight as a function of the redox potential has a first inflection towards -500mV and a second inflection towards -550mV.
• This curve is representative of the potential at which the mercaptans (in the form of anions, represented symbolically by RS ⁇ ) are oxidized to disulfides (represented symbolically by RSSR).
• the mercaptan concentration guideline in regenerated soda from an extractive Merox is usually between 30 and 100 ppm (zone A).
• a redox potential of between -500mV and -550mV is maintained.
• the measured redox potential is below -550mV (zone B)
• the measured redox potential is greater than - 500mV (zone C)
• FIG. 2 which represents a conventional extractive Merox type LPG desulphurization plant equipped with a device according to the invention
• LPG 1 is introduced at the bottom of a prewashing flask 2 equipped with a coalescence section 3.
• An aqueous solution of fresh soda is introduced under the coalescing section in order to remove residual L S in the form of sodium sulphide NaSH in solution in spent soda 4, withdrawn by means of a valve 5 2.
• the washed LPG 6 passes through the coalescence section and is introduced at the bottom of a mercaptan extractor 7 forming a first chamber within the meaning of the invention.
• the extractor 7 operates against the current.
• a mercaptan depleted sodium hydroxide solution 8 is introduced at the extractor head 7 and reacts with the mercaptans present in LPG to form sodium thiolates and spent sodium hydroxide.
• the sodium thiolates are entrained in the spent soda at the bottom of the extractor 7, then withdrawn by means of a controlled valve 9. These latter are optionally mixed with a booster in an oxidation catalyst 11 and then reheated in a heat exchanger 10.
• An oxidizing gas 12, for example air, is added to the heated mixture from the heat exchanger 10, and is introduced at the bottom of an oxidation reactor 13 forming a second enclosure within the meaning of the invention .
• the oxidation reactor 13 advantageously comprises an internal lining 14 in order to increase the contact between the oxidizing gas 12 and the spent sodium thiolate-rich soda.
• the sodium thiolates are oxidized by the oxidizing gas 12 to disulfides with the aid of the oxidation catalyst 11 in the oxidation reactor 13 to produce a three-phase mixture of oxygen depleted air (O 2), insoluble disulfides and regenerated sodium hydroxide 15.
• the three-phase mixture 15 is introduced into a separator 16, forming a third enclosure within the meaning of the invention, in which the oxygen-depleted air passes through a separation section 18 which may consist for example of rings
• the disulphides are separated from the regenerated sodium hydroxide by decantation within the separator 16 and pass through a filtration section 19 which can contain coal.
• the extraction of the disulphides from the regenerated sodium hydroxide may possibly be facilitated by the addition of washing gasoline which will cause the residual disulfides in the supernatant 21 comprising the bulk of the disulphides and a lower aqueous phase constituted by the sodium hydroxide depleted in Mercaptans 8.
• the supernatant 21 is collected on the valve 22 to be then transported to a hydrotreating section or to a heavy gas Merox reactor, not shown in this figure.
• the mercaptan depleted sodium hydroxide is returned to the extractor head 7 in a first pipe 39 by means of a pump 23 for a new extraction cycle.
• the LPG freed from mercaptans 24 is collected at the top of the extractor 7 and then sent to a gravity separator 25 in order to eliminate the soda which has been entrained with the LPG.
• the residual soda is collected by a purge valve 26.
• the remaining LPG 27 is washed with water 28 in a first capacity 29 to produce washed LPG 30.
• the washed LPG 30 is returned to a second capacity 31 to be therein. filtered on a bed of sand to rid it of water 32.
• the water 32 is withdrawn at the bottom by a valve 33.
• the LPG disposed of water 34 is collected at the top.
• a redox potential measuring device can be integrated into the conventional LPG desulfurization installation described above. Such a device makes it possible to control the air supply 12 so that the oxidation reaction within the oxidation reactor 13 is complete.
• a redox potential measuring device 35, 36 can be positioned respectively (i) on a first sampling line 37 placed directly on the extractor 7 and / or (ii) on a second sampling line 38, disposed on the first pipe 39, to allow the measurement of the oxidation-reduction potential of the lower aqueous phase, that is to say the regenerated sodium hydroxide.
• the first sampling line 37 is placed before the filtration section 19. However, it can also be placed after the filtration section 19, for example near the tapping of the first pipe 39 on the extractor 7 .
• FIG. 3 shows a redox sampling and measuring device according to the invention.
• a pipe 40 brings the regenerated sodium hydroxide to a reservoir 41.
• the reservoir 41 comprises a redox potential measurement electrode 42 and an evacuation pipe 43.
• the redox potential measurement electrode 42 is connected to a reading device 48, and / or to a signal processing system, not shown, for example a computer.
• a water supply 44 is connected to the pipe 40 at a 3-way valve 45 upstream of the tank 41. The water supply 44 is open when the pipe 40 is closed, in order to rinse the tank 41 and the electrode 42. This step preserves the life of the electrode 42 and limit the risk of chemical burn when it is replaced.
• a purge line 46, provided with a valve 47 is connected at one end to the pipe 40 and at the other end to the discharge pipe 43.
• the reservoir 41 will have the smallest possible volume, in order to improve the response time of the electrode 42 and to limit the losses of regenerated sodium hydroxide.
• FIG. 4 represents a first alternative device for sampling and redox potential measurement according to the invention.
• a pipe 48 brings the regenerated soda to a tank 49.
• a valve
• the reservoir 49 comprises a redox potential measurement electrode 51 and an evacuation conduit 52 provided with a valve 53.
• the redox potential measurement electrode 51 is connected to a reading device 54, and / or to a signal processing system, not shown, for example a computer.
• a water supply 55 is connected to the reservoir 49 at a valve 56 placed near the reservoir 49. The water supply 55 is open when the pipe 48 is closed, in order to rinse the reservoir 49 and the electrode 51. This step preserves the life of the electrode 51 and limit the risk of chemical burn when it is replaced. For design reasons, it is preferable to position the exhaust pipe 52 on the top of the tank 49.
• valves 50 and 56 it is preferable to position the valves 50 and 56 as close as possible to the tank 49 in order to limit the dead volumes. and the passage times between the regenerated sodium hydroxide solution and the water. Finally, it is necessary to prevent air from entering the reservoir 49, at the risk of distorting the redox potential measurement. Moreover, the reservoir 49 will have the smallest possible volume, in order to improve the response time of the electrode 51 and to limit the losses of regenerated sodium hydroxide.
• FIG. 5 represents a second alternative device for sampling and measurement of redox potential according to the invention.
• a line 57 brings the regenerated sodium hydroxide to a reservoir 58 via a 3-way valve 59.
• the reservoir 58 comprises a redox potential measurement electrode 60 and an evacuation conduit 61.
• the electrode redox potential measurement 60 is connected to a reading apparatus 62, and / or to a signal processing system, not shown, for example a computer.
• a water supply 63 is connected to the reservoir 58 at the 3-way valve 59. The water supply 63 is open when the pipe 57 is closed, in order to flush the reservoir
• the electrode 60 This step preserves the life of the electrode 60 and limit the risk of chemical burn when it is replaced.
• the reservoir 58 will have the smallest possible volume, in order to improve the response time of the electrode 60 and to limit the losses of regenerated sodium hydroxide.
• a device is installed on an extractive Merox unit of design close to that described in FIG. 2, on the first outlet pipe 39 of the regenerated soda 8 coming from the separator 16.
• the tank 41 has a capacity 500mL. Part of the regenerated sodium hydroxide circulating in the first pipe 39 is diverted into the pipe 40 and fills the tank 41. The excess of regenerated sodium hydroxide 8 flows through the purge pipe 43.
• the redox potential is measured (at 20 ° C.). ° C, at atmospheric pressure) using a redox polymer (polysulfone) gel electrolyte probe model EMC 233. The value of the redox potential is obtained after stabilization of the measurement.
• the 3-way valve 45 is operated and water from line 44 rinses the reservoir 44, while the supply of regenerated soda 8 is stopped.
• the measured redox potential is less than -550mV (ENH)
• the air flow admitted to the inlet of the oxidation reactor 13 is increased.
• the redox potential is greater than -500mV (ENH)
• the air flow admitted to the inlet of the oxidation reactor 13 is decreased.
• a device according to Figure 3 is installed in the laboratory.
• a capacity C containing 2800 ml of 15% sodium hydroxide containing a few drops of Europtal 8090 oxidation catalyst (cobalt phthalocyanine) is deaerated under argon for 30 minutes.
• This capacity is connected to the device according to FIG. 3 at the level of the pipe 40.
• the gas head of the tank 41 as well as the pipes connected to it are deaerated with argon.
• Known masses of octanethiol are injected into the C capacity to obtain mercaptan concentrations ranging from 0 to 160 ppm (by weight).
• the redox potential is raised after stabilization of the measurement (at 20 ° C., under atmospheric pressure), using the same probe as in Example 1.

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• 2010
  • 2010-11-24 FR FR1059662A patent/FR2967778A1/fr not_active Withdrawn
• 2011
  • 2011-11-22 WO PCT/FR2011/052719 patent/WO2012069751A1/fr active Application Filing
  • 2011-11-22 EP EP11802492.6A patent/EP2643684A1/de not_active Withdrawn
  • 2011-11-22 CN CN2011800567134A patent/CN103229050A/zh active Pending
  • 2011-11-22 US US13/884,168 patent/US20130277236A1/en not_active Abandoned

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