Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/10—Working-up natural gas or synthetic natural gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
  • B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/10—Working-up natural gas or synthetic natural gas
  • C10L3/101—Removal of contaminants
  • C10L3/102—Removal of contaminants of acid contaminants
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
  • B01D2253/10—Inorganic adsorbents
  • B01D2253/102—Carbon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
  • B01D2253/10—Inorganic adsorbents
  • B01D2253/106—Silica or silicates
  • B01D2253/108—Zeolites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2256/00—Main component in the product gas stream after treatment
  • B01D2256/24—Hydrocarbons
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/30—Sulfur compounds
  • B01D2257/306—Organic sulfur compounds, e.g. mercaptans
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/06—Polluted air
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2259/00—Type of treatment
  • B01D2259/40—Further details for adsorption processes and devices
  • B01D2259/40083—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption
  • B01D2259/40088—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating
  • B01D2259/4009—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating using hot gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2259/00—Type of treatment
  • B01D2259/40—Further details for adsorption processes and devices
  • B01D2259/40083—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption
  • B01D2259/40088—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating
  • B01D2259/40092—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption by heating using hot liquid

Definitions

• the present invention relates to the purification of a natural gas. More particularly, the present invention provides a method of purification by adsorption of a natural gas to decrease the mercaptan content.
• a raw natural gas containing water, heavy hydrocarbons, acidic compounds such as carbon dioxide (CO2) and hydrogen sulfide (H2S), and sulfur derivatives such as mercaptans, can be processed by processes described by the documents FR 2 605 241 and FR 2 636 857. These processes use a physical solvent such as methanol to carry out the dehydration, degassing and removal of the acidic compounds and mercaptans. At the end of this treatment, the gas is to specifications as to the content of CO2, typically less than 2 mol%, and H2S, typically 4 molar ppm.
• Another gas treatment solution is to perform the deacidification by a method using an amine solvent. Part of the light mercaptans, especially methyl mercaptan, is removed during this step. Heavier mercaptans, such as ethyl, propyl and butyl mercaptan, are not sufficiently acidic to react significantly with amines and, therefore, remain largely in the gas.
• the gas is dehydrated by a process using a solvent such as glycol, for example the process described in document FR 2 740 468. Dehydration enables the water content of the gas to be lowered to a value close to 60 molar ppm.
• a solvent such as glycol
• the aforementioned processes make it possible to obtain a natural gas whose water content, acid compounds and heavy hydrocarbons of the treated natural gas are in accordance with commercial requirements.
• the methyl and ethyl mercaptans are still predominantly in the gas, at levels up to 200 ppm or more, in sulfur equivalent. For some uses these levels of mercaptans are too high.
• the conventional gas phase adsorption processes are the methods commonly known as TSA ("Thermal Swing Adsorption"), in which the adsorption step takes place at ambient or moderate temperature, typically between 20 ° C. and 60 ° C.
• the desorption (or regeneration) stage at a high temperature, typically between 200 ° C. and 350 ° C., under the purge gas (generally a purified gas) whose flow is included between 5% and 20% of the feed gas flow.
• the desorption gas containing a large quantity of mercaptans, must then be treated before being recycled, for example by treatment with a basic solution (sodium hydroxide or potassium hydroxide), or may also be sent to the flare, which is not neither economically nor ecologically very interesting.
• the pressure is either kept substantially constant throughout the cycle, or lowered during the regeneration phase so as to promote regeneration.
• the water content of the gas is less than 1 molar ppm, and the gas is at the total sulfur specifications.
• the adsorption of mercaptans by conventional TSA process has several disadvantages.
• Patent FR 2 861 403 discloses an original process for regenerating an adsorbent loaded with light mercaptans by using a hydrocarbon-type displacement agent consisting of a mixture of compounds of at least five dilute carbon atoms. in a purge gas.
• This displacement phase can last as long as the mercaptan concentration at the outlet of the adsorber is non-zero, the duration being fixed by the desired level of regeneration.
• the adsorbent material contains the displacement agent in place of the mercaptans, at a content of corresponding approximately to the saturation of the adsorbent, ie about 20% by weight.
• the adsorbent material can be:
• the displacement agent is not thermally desorbed, at least partially, the subsequent adsorption of the mercaptans is made more difficult, on the one hand because of the fact that the adsorbent is saturated with the displacing agent, and secondly because the adsorption selectivity is displaced in favor of the displacing agent rather than for the mercaptans if the displacing agent is desorbed, at least partially, thermally, a complementary step is introduced into the complete cycle, thereby lengthening the total time and immobilizing additional adsorbent.
• the purification process of a natural gas comprises the following phases: a) said gas is purified by adsorption of light mercaptans by contact with an adsorbent material, b) a gaseous effluent is mixed with a hydrocarbon displacement agent, consisting of a hydrocarbon liquid phase comprising more than five carbon atoms, so as to enrich the gaseous effluent with hydrocarbons; c) the mixture obtained in step b is passed through the mercaptan-loaded adsorbent material; ), the amount of displacement agent introduced into the adsorbent material being less than or equal to 50% by mass of the maximum adsorption capacity of the displacement agent on the adsorbent material, d) thermal desorption is carried out using a purge gas for desorbing, the adsorbent material, the hydrocarbon displacement agent introduced in step c), e) cooling the adsorbent material with another effluent gaseous or directly using the gas to be purified.
• this invention has the particular advantage of reducing the amount of hydrocarbon-type displacement agent necessary for the displacement of mercaptans and substantially reduces the cycle time compared to the described mode. in the above patent.
• step a) is carried out under a pressure of between 2 MPa and 10 MPa and a temperature of between -40 ° C. and 100 ° C.
• the flow rate of said gaseous effluent constitutes between 1 and 50% of the flow rate of said natural gas
• said gaseous effluent may consist of purified natural gas or any other gas
• step b) is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 0 ° C. and 150 ° C.
• the displacement phase of step c) is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 0 ° C. and 150 ° C.
• step c) is carried out so that the relative pressure of said displacement agent in said gaseous effluent is less than 0.95 by choosing for example a temperature that is 20 ° C higher than that of step b), or a pressure 2 bars lower than that of step b), or by performing a complementary dilution of the enriched gas in step b) with a purge gas
• step d) the thermal regeneration phase of step d) is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 50 ° C. and 400 ° C.
• step e) the cooling step of step e) is carried out at between 0.5 and 10 MPa.
• the natural gas to be purified may comprise hydrocarbons comprising at least five carbon atoms and, before step a), a fraction of said natural gas may be separated, the fraction comprising hydrocarbons comprising at least five carbon atoms, and said liquid phase of step b) may comprise said fraction.
• the natural gas to be purified may comprise hydrocarbons comprising at least five carbon atoms, and it is possible to separate a fraction of the purified gas obtained in step a), the fraction comprising hydrocarbons comprising at least five hydrocarbons. carbon atoms, and said liquid phase of step b) may comprise said fraction.
• the mercaptan-loaded gas obtained in step c) is washed with a mercaptan absorbent solution and the washed gas is then recycled.
• the adsorbent material may comprise at least one of the following materials: a zeolite, an activated carbon, a mesoporous adsorbent of activated alumina type, and a mesoporous adsorbent of silica gel type.
• the adsorbent material may comprise at least one of the following materials: a type A zeolite, a faujasite type X zeolite, a Y type faujasite zeolite, an activated carbon having a BET specific surface area of between 200 m2 / g and 2000 m2 / g, an activated alumina type mesoporous adsorbent having a BET specific surface area of between 100 m 2 / g and 800 m 2 / g, and a mesoporous adsorbent of silica gel type having a BET specific surface area of between 100 m 2 / g and 800 m 2 / g boy Wut.
• said hydrocarbons containing more than five carbon atoms may comprise at least one of the following compounds: a saturated hydrocarbon, an aromatic hydrocarbon, a paraffin, and a naphthene.
• step a the amounts of CO2, H2S and water contained in the natural gas are reduced.
• FIG. 1 represents a first exemplary embodiment of the method according to the invention.
• FIG. 2 represents a variant of the method according to the invention.
• the process comprises pretreatment, optionally dehydration, adsorption, regeneration, fractionation and optionally washing (to be confirmed).
• gas containing no or little mercaptans is meant for example either part of the purified gas obtained in step a), or a "boil-off gas” mainly composed of methane and nitrogen, or any other gas having the same properties.
• purge gas or gaseous effluents will be used to represent indistinctly these gaseous effluents.
• the natural gas containing in particular water, CO2, I 2 S 2 and mercaptans, arriving via line 1, is deacidified and dehydrated in the treatment unit 30.
• the gas can be a raw natural gas directly from a well. of oil or a gas field.
• the gas is processed by methods known to those skilled in the art.
• the gas is treated by a process using chemical and / or physical solvents, for example based on amines and / or methanol, so as to produce a natural gas with specifications for the content of CO2 and H2S.
• Such processes are described in particular in documents FR 2 605 241, FR 2 636 857 and FR 2 734 083.
• the acidic compounds H2S and CO2 are discharged via line 2.
• Part of the mercaptans, in particular methylmercaptan, is partially removed from the product. gas during this treatment. These mercaptans are also discharged through line 2.
• the content of H2S is of the order of 4 ppm molar, that of CO2 less than 2 mol%.
• the deacidified gas may then be treated by a glycol dehydration process, for example described in document FR 2 740 468.
• the glycol used may be triethylene glycol (TEG).
• TEG triethylene glycol
• a dehydrated gas is obtained, whose residual water content may be of the order of 60 molar ppm. This gas still contains mercaptans and heavy hydrocarbons.
• the water is evacuated via line 4.
• This glycol dehydration step can be replaced by an adsorption dehydration step, for example on molecular sieve 4A, according to a TSA operation, known to those skilled in the art.
• the treated gas leaving unit 30 via line 5 is depleted of water and acidic compounds H2S and CO2, but still contains mercaptans, in a content that may be greater than 200 ppm molar equivalent sulfur.
• the dehydrated and deacidified gas can undergo extensive dehydration by adsorption, for example on molecular sieves.
• the gas flowing in the duct 5 is introduced into the chamber 36 comprising an adsorbent material of dehydration.
• the dehydrated gas is discharged through line 37.
• a water-specific dehydration adsorbent material such as, for example, a type 3A and / or 4A molecular sieve.
• the dehydrating adsorbent material is preferably placed in a specific enclosure different from the enclosure 31 used to remove the mercaptans.
• the regeneration of the dehydrating adsorbent material contained in the chamber 36 is conventionally provided by TSA, the purge gas being, for example, a fraction of the purified gas.
• the dehydrating adsorbent material can also be placed in the same chamber as that containing the adsorbent material used to remove the mercaptans, that is to say in the chamber 31.
• the dehydrated and deacidified gas is then sent to an adsorption adsorption purification unit, for example on molecular sieves, in order to remove the mercaptans still present in this gas.
• This unit comprises at least one chamber 31 containing a suitable adsorbent material allowing especially the adsorption of mercaptans, such as methyl-, ethyl-, propyl-mercaptan, and higher mercaptans.
• the dehydrated and deacidified gas flowing in the duct 5 (with reference to FIG. 1), or possibly flowing in the duct 37 (with reference to FIG. 2), is introduced into the enclosure 31.
• a first step is thus carried out during which the gas is purified by adsorption of the light mercaptans by contacting with a first quantity of adsorbent material.
• the adsorbent material contains in particular light mercaptans of natural gas and hydrocarbon compounds with more than five carbon atoms.
• This adsorption step is stopped when the concentration of mercaptans in the purified gas at the adsorber outlet reaches a non-zero limit threshold.
• the concentration profile in the adsorber can then be represented schematically as follows: the zone located near the inlet of the adsorber is essentially an equilibrium zone, in which the mercaptans and the heavier hydrocarbon compounds of the gas, and in particular the aromatic compounds, are coadsorbed, the respective quantities being a function of the respective temperature and partial pressures of each of the compounds in the gas to be treated,
• the purified gas is evacuated from the chamber 31 via the duct 6.
• the temperature within enclosure 31 is generally between -40 0 C and 100 0 C, preferably between O 0 C and 7O 0 C, preferably between 20 ° C and 60 0 C.
• the pressure of the enclosure 31 may be that of natural gas produced, typically between 2 MPa and 10 MPa.
• the adsorbent materials contained in the chamber 31 are preferably chosen from molecular sieves, also called zeolites, activated carbons, or mesoporous adsorbents of activated alumina or silica gel type.
• zeolites of type A (LTA family), type X or Y (FAU family of faujasites) or of type MFI (ZSM-5 and silicalite), whose pore size is compatible with the size of the mercaptans to adsorb.
• LTA family zeolites of type A
• type X or Y FAU family of faujasites
• type MFI ZSM-5 and silicalite
• zeolites of the family A it is possible to choose a partially exchanged calcium zeolite 4A, preferably having a Na / Ca exchange rate of between 25% and 85% molar.
• zeolites of the X or Y type it is possible to choose a zeolite of the 13X or NaX type, but it is also possible to use other exchange cations, alone or as a mixture, such as for example Ca, Ba, Li , Sr, Mg, Rb, Cs, Cu, Ag ...
• the silicon to aluminum ratio can be between 1 and infinity, by infinity is meant the dealuminated Y zeolites.
• the other adsorbent materials which may be used may be chosen from activated carbons, and preferably those having a BET specific surface area, conventionally determined by nitrogen physisorption at 77K, of between 200 and 2000 m 2 / g, or of activated aluminas or silica gels, and preferably those having a BET specific surface area of between 100 and 800 m 2 / g.
• the adsorbent materials are preferably used in a fixed bed, for example in the form of a ball or an extruded material. They can be used either alone or mixed, for example in multi-bed form.
• a gas is mixed with a hydrocarbon liquid phase comprising more than five carbon atoms, called displacement agent, in order to enrich this gas with hydrocarbon compounds. content in the gas depending in particular on the pressure and temperature conditions in which this mixture is produced. This mixture will be used to displace adsorbed mercaptans.
• displacement agent is meant one or more hydrocarbon compounds, heavy hydrocarbons (C5 +), paraffins, naphthenes or aromatics. These compounds can be chosen from the hydrocarbon compounds of the C5 + fraction of natural gas, which are saturated and / or aromatic.
• These compounds may also be benzene, toluene, isomers of xylenes, or aromatic compounds having a ring substituted with one or more methyl and / or ethyl groups.
• the agent may comprise one of the abovementioned compounds or a mixture of several aforementioned compounds.
• the displacement agent contains at least one compound that can adsorb to the adsorbent material and has an affinity close to that of the mercaptans.
• the displacing agent may preferably contain at least one normal paraffin.
• a 13X zeolite a mixture of saturated and / or aromatic hydrocarbons may be used. Said aromatic compounds may belong to the BTX family.
• the displacement agent can be obtained during the condensation and fractionation stage of the natural gas in the pipe 11 coming from the fractionation unit 34.
• the displacement agent can also be introduced in part or in full by the Annex line 12.
• the displacement agent introduced via the conduit 13 into the contactor 33 is constituted, on the one hand, by the C5 + hydrocarbons, preferably by the C6 + cut, and advantageously by the fraction rich in BTX type aromatic compounds derived from the fractionation unit 34 and, on the other hand, by an addition of heavy hydrocarbon compounds, in particular a C5 + cut, and preferably rich in BTX type aromatic compounds introduced via line 12.
• this regeneration route also has the advantage of using a part of the heavy hydrocarbon compounds. natural gas, and in particular the aromatic compounds, coadsorbed with the mercaptans, as displacement agent, thus limiting the external supply of displacement agent via the purge gas.
• the mixture containing the displacement agent is brought into contact with a quantity of adsorbent material loaded with mercaptans.
• the amount of hydrocarbon displacement agent introduced is less than or equal to 50% by weight of the maximum adsorption capacity of the displacement agent on the adsorbent material. This amount may be between 2 and 40% by weight of this maximum capacity, and preferably between 5 and 20% by weight.
• the duration of contacting therefore depends on the flow rate of the mixture and the concentration of hydrocarbon compounds with more than five carbon atoms in the mixture, and allows the introduction of a desired amount of displacement agent.
• the displacement of the undesirable compounds adsorbed on the adsorbent, in particular mercaptans, is carried out using a gaseous effluent or a purge gas, for example a part of the purified gas obtained during the mercaptan adsorption step, or any other gas enriched with liquid hydrocarbon compounds.
• the amount of hydrocarbon agent to be introduced to completely displace the adsorbed mercaptans is approximately equal, by mass, to the amount of adsorbed mercaptans. on the adsorbent material, to which must be added the amount necessary to saturate the adsorbent in the material transfer zone.
• This additional amount of hydrocarbon displacement agent may be important if the material transfer zone in the adsorber is spread, since a portion of the adsorbent material is only partially used in said area.
• the adsorbent material contains the hydrocarbon displacement agent, and the amount adsorbed on said material corresponds to the thermodynamic equilibrium under partial pressure and temperature conditions, generally close to saturation of the material, about 20% mass.
• the subsequent thermal regeneration step therefore requires a significant amount of energy since the adsorbent material is substantially saturated with displacement agent. Stopping the introduction of the hydrocarbon displacement agent necessary to move the mercaptans corresponds to the moment when the mercaptan concentration at the adsorber outlet is negligible, or deemed sufficiently low to stop this step.
• the originality of the process according to the invention stems from the fact that it is possible to use a quantity of hydrocarbon agent that is significantly lower than this theoretical amount, by introducing this hydrocarbon agent for a limited time shorter than the theoretical duration which would lead to to the thermodynamic equilibrium, and thus saturation of the adsorbent, described above, and then imposing a higher temperature and a zero partial pressure of displacement agent in the purge gas, before-even the concentration of mercaptans in the output gas is negligible.
• This amount can be estimated for example by knowing the microporous volume of adsorbent, determined by conventional solid characterization techniques.
• the maximum adsorbable amount of displacement agent can be estimated from the density of said displacement agent.
• a faujasite zeolite adsorbent solid for example X or Y faujasite, such as NaX (13X) or NaY zeolites, this maximum capacity is of the order of 20% by weight of the adsorbent solid.
• Thermal desorption is then performed using a purge gas to desorb the hydrocarbon displacement agent introduced in the preceding contacting step.
• the purge gas used contains no or very few mercaptans.
• phase of displacement and regeneration can be divided into two sequences:
• the hydrocarbon displacement agent is introduced into the gaseous effluent or the purge gas at the inlet of the adsorber, and the mercaptans adsorbed in this zone will be progressively displaced from the inlet. from the adsorber to a more central zone located downstream in the adsorber. The zone located at the inlet of the adsorber will therefore contain the displacement agent.
• a hot purge gas for example a part of the purified gas or a gas which does not contain mercaptans and is not enriched with displacement agent, is introduced as input; of the adsorber.
• the action of this hot gas is to thermally desorb the displacement agent adsorbed in the adsorber inlet zone, and thus to regenerate the adsorbent material in said zone.
• the displacement agent thus desorbed migrates into the adsorber and in turn displaces the mercaptans adsorbed in the central zone of the adsorber at room or moderate temperature, the temperature of the adsorbent material in this central zone being between a temperature ambient neighbor and the temperature of the hot gas.
• the high temperature thermal front thus progressively advances in the adsorber, preceded by a material transfer front, at a moderate temperature, corresponding to the adsorption of the displacement agent and the displacement of the mercaptans.
• the adsorbent is cooled using a gas containing no mercaptans or directly using the gas to be purified.
• the step of cooling the adsorbent prior to a new adsorption cycle, to purify the gas loaded with mercaptans, even before the concentration of displacement agent at the outlet of the adsorbent.
• adsorber is zero or considered negligible, using either a purge gas containing no mercaptans, or directly the gas to be purified.
• the adsorber inlet cold gas will heat up by exchange with the hot adsorbent solid located in the adsorber inlet, and the calories thus transported will be used to complete the thermal desorption of the displacement agent in a zone of the adsorber located near the exit.
• the adsorbent is the gas to be purified, the mercaptans present in this gas will then be adsorbed directly on the solid located at the inlet of the adsorber.
• the pressure and temperature conditions of the mixing step between the gaseous effluent or the purge gas and the liquid displacement agent will be such that the relative pressure of the displacement agent in the purge gas is less than 0.95 in the displacement conditions so as to avoid any liquid condensation of said displacement agent, especially in the mesopores of the adsorbent, and preferably less than 0.80.
• the displacement agent is a mixture of liquid hydrocarbon compounds with more than five carbon atoms
• the pressure and temperature conditions of the contacting step will be chosen so as to be located outside the condensation zone. of liquid of the phase envelope of the mixture constituted by the purge gas enriched with displacement agent, at the temperature and at the displacement pressure, so as to avoid any phenomenon of condensation of liquid, in particular in the pores of the adsorbent.
• One way to avoid any risk of condensation of liquid may consist, for example:
• the flow of gas purge dilution of the enriched gas leaving the contactor will be in particular between 2 and 100% of the total flow, and preferably between 5 and 50%, and preferably between 10 and 30% by volume.
• the operating conditions of the process according to the invention can be as follows:
• the adsorption step is carried out under a pressure of between 2 MPa and 10 MPa and a temperature of between -40 ° C. and 100 ° C.
• the flow rate of said purge gas constitutes between 1 and 50% of the flow rate of said natural gas
• said purge gas may consist of purified natural gas or any other gas such as, for example, a "boil-off gas" rich in nitrogen
• the mixing step is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 0 ° C. and 150 ° C.
• the displacement phase is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 0 ° C. and 150 ° C.
• the displacement phase is carried out so that the relative pressure of said displacement agent in said purge gas is less than 0.95 and preferably less than 0.80, for example by choosing a temperature which is 2 ° C. higher than that of the mixing step, or a lower pressure of 2 bar than that of the mixing step, or by performing a complementary dilution of the purge gas enriched in the mixing step with a purge gas
• the thermal regeneration phase of the thermal desorption step is carried out under a pressure of between 0.5 and 10 MPa and at a temperature of between 50 ° C. and 400 ° C., preferably between 100 ° C. and 300 ° C.
• the cooling step is carried out under a pressure of between 0.5 and 10 MPa.
• part of the methane, or the light fraction C1-C2, constituting the purified gas from the enclosure 31 is used as a purge gas.
• the flow rate of purge gas can be between 1% and 50% of the flow rate of the feed gas arriving via line 1, for example between 1% and 20%, advantageously between 1 and 10%, and preferably between 1% and % and 5%.
• part of the gas directly from the enclosure 31 and / or part of the light fraction of the gas (section C1 and / or C2) coming from the fractionation unit 34 are respectively sent through the ducts 15 and 14 into the contactor 33 gas / liquid to be charged with the moving agent.
• the choice of the pressure and temperature conditions in the gas / liquid contactor 33 for charging the purge gas with displacement agent are preferably chosen in such a way that the relative pressure of the displacement agent in the contactor 33 is less than 0.95, preferably less than 0.8 so as to limit the phenomenon of capillary condensation in the mesopores of the adsorbent.
• the pressure in the contactor 33 may be between 0.5 MPa and 10 MPa, preferably between 2 MPa and 8 MPa, preferably between 3 MPa and 7 MPa.
• the temperature in the contactor 33 may be between 0 ° C. and 150 ° C., and preferably between 20 ° C. and 100 ° C., and advantageously between 30 ° C. and 80 ° C.
• the gas from the contactor 33 charged with the heavy hydrocarbon fraction, under the pressure, temperature and flow conditions of the contactor 33, thus constitutes the purge gas or gaseous effluent, and is sent via line 18 into the chamber 31. .
• the adsorption step will preferably be carried out at the same time as the following steps, so as to use the hydrocarbon compounds from natural gas coadsorbed with the mercaptans at the inlet of the adsorbent bed as displacement agent.
• the adsorber contains both an adsorbent used to dehydrate the natural gas, such as for example an activated alumina or a molecular sieve, in particular of type 3A or 4A, and an adsorbent used to remove the mercaptans, such as a type X zeolite (13X) or Y
• the adsorbent solid used to carry out the dehydration of the gas will be placed upstream of the adsorbent solid used to remove the mercaptans.
• the adsorption step will preferably be carried out counter-current of the following steps so as to avoid the desorption of water from the adsorbent solid used to dehydrate the gas, towards the adsorbent solid used to remove the downstream mercaptans.
• This mode of operation makes it possible in particular to protect the solid adsorbent used to remove the mercaptans from the water which would be produced, during the thermal regeneration phase, from the adsorbent solid used to carry out the dehydration, and which could damage said adsorbent solid used to remove the mercaptans.
• the purified gas is then sent to the fractionation unit 34 to separate the different sections, for example by distillation.
• methane line 7
• ethane line 8
• propane line 9
• butane line 10
• a heavy hydrocarbon fraction containing more of five carbon atoms line 11
• the gas from the enclosure 31 through the conduit 19 is loaded with mercaptans.
• This gas is treated in the washing unit 35 in order to eliminate the mercaptans as much as possible, for example by washing with an alkaline solution of sodium hydroxide or potassium hydroxide.
• the mercaptans are evacuated via line 21.
• the washed gas is returned via line 20 with the raw natural gas to be processed.
• the washed gas may not undergo the deacidification treatment and, optionally, the dehydration treatment operated in the treatment unit 30.
• the washed gas is mixed with either the raw gas flowing in the pipe 1, or with the gas deacidified crude obtained in unit 30, either with the deacidified and dehydrated raw gas circulating in line 5.

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• Engineering & Computer Science (AREA)
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• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Analytical Chemistry (AREA)
• Separation Of Gases By Adsorption (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)

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• 2007
  • 2007-11-21 FR FR0708174A patent/FR2923838B1/fr not_active Expired - Fee Related
• 2008
  • 2008-11-21 WO PCT/FR2008/001635 patent/WO2009098389A2/fr active Application Filing
  • 2008-11-21 EP EP08872225A patent/EP2212407A2/de not_active Withdrawn

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