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  • 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
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  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
  • C01B3/56—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
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  • B01D2259/414—Further details for adsorption processes and devices using different types of adsorbents
  • B01D2259/4141—Further details for adsorption processes and devices using different types of adsorbents within a single bed
  • B01D2259/4145—Further details for adsorption processes and devices using different types of adsorbents within a single bed arranged in series
  • B01D2259/4146—Contiguous multilayered adsorbents
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  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/042—Purification by adsorption on solids
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  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0465—Composition of the impurity
  • C01B2203/0495—Composition of the impurity the impurity being water
• • 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
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/20—Capture or disposal of greenhouse gases of methane
• • 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
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/40—Capture or disposal of greenhouse gases of CO2
• • 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
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
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• • 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
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  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2
  • Y02P20/156—Methane [CH4]

Definitions

• the invention relates to a process for the purification of hydrogen-based gas mixtures polluted by carbon monoxide and nitrogen and possibly various impurities such as carbon dioxide, water and linear, branched or cyclic, saturated or unsaturated in Ci-Cs-
• the production of high purity hydrogen is of great interest on an industrial level, this being widely used in many synthesis processes such as hydrocracking, methanol production, the production of oxoalcohols and various isomerization processes.
• the process of the invention constitutes an improvement on the conventional processes for the separation of hydrogen of the PSA type, or processes by adsorption by variation of the pressure, using zeoiites as adsorbent.
• the purification of hydrogen by adsorption is an industrial process of great importance: it involves recovering hydrogen from a gaseous mixture originating for example from the catalytic reforming of natural gas, from catalytic or thermal cracking, or hydrocracking of hydrocarbons.
• PSA Pressure Swing Adsorption
• CM pressure-modulated adsorption
• PSA H 2 Pressure-modulated adsorption
• the adsorbents are selected according to their ease of adsorbing and desorbing one or more particular compounds.
• the choice of adsorbents is delicate and depends in particular on the nature of the mixture to be treated.
• the mixture to be purified generally comprises more than one impurity, it is desirable for the adsorbent to be able to adsorb and then desorb, not just one but several of these impurities.
• the profile and the selectivity of adsorption of a given constituent are often influenced by the presence, in the gas mixture, of other impurities, and this, for example, due to a possible competition or poisoning of absorbent.
• These different considerations account for the complexity of the problem of optimizing PSA processes by improving the absorbent.
• the criteria to be taken into account for the choice of padsorbent are its capacity for adsorption of different impurities, its selectivity, its mechanical strength (the packing of padsorbant must be possible over a certain height, without crushing) and the pressure drop caused.
• the gas to be purified contains several impurities, it is often necessary to send the gas to be purified on a bed consisting not only of one but of several adsorbents distributed in the column in the form of layers, so that the impurities adsorb selectively on the different adsorbents according to their affinity.
• PSA processes work with the implementation of pressure cycles;
• the adsorbent bed ensures the separation of at least one constituent of the mixture by adsorption of at least this constituent on the adsorbent bed.
• the absorbent is regenerated by lowering the pressure. With each new cycle, it is therefore essential that the desorption is effective and complete, so as to find a regenerated state identical to each new cycle. It is clear, however, that this facility for adsorbing and then desorbing a particular constituent of a gas mixture is a function of the particular operating conditions of the PSA process envisaged and in particular of the conditions of temperature and pressure.
• the intermediate so-called decompression and compression phases of the various adsorbent beds are synchronized: it is in particular advantageous to introduce pressure equalization steps between two adsorbent beds, one of these two beds being in the decompression phase, the other in the recompression phase, which saves energy.
• These different phases are made possible by a set of suitable pipes and valves.
• the capacity of the adsorbent beds is limited by the maximum size that can be used either because of the mechanical strength of the individual particles of adsorbent, or because of the maximum size that can be used for shipping containers containing adsorbents. This is why the operation of four to twelve beds of adsorbents arranged in parallel is common in existing PSA H 2 installations.
• the minimum number of adsorbers in industrial PSA H 2 installations being four, there is: a column in the adsorption phase, a column in the decompression phase, the latter being able to operate at co- or counter-current with respect to to the column in the adsorption phase; in practice, most often co-current, a column in the purge phase (recycling of part of the purified hydrogen), the latter being able to operate in co-or counter-current with respect to the column in phase adsorption; in practice, most often against the current, - a column in the phase of recompression with purified hydrogen, the latter being able to operate in co- or counter-current with respect to the column in the adsorption phase; in practice, most often against the tide.
• the pressure for the adsorption phase is most often between 2 to 5 MPa and the purge pressure (the lowest) is typically around 0.1 to 0.5 MPa.
• adsorbent beds are often encountered, first comprising a first layer of alumina and / or silica gel intended to trap water and heavy hydrocarbons, then a layer of activated carbon intended to trap CO 2 , methane and some light hydrocarbons, finally a layer of molecular sieve or zeolite in order to trap carbon monoxide and nitrogen.
• the proportion of each layer depends on the composition of the gas to be purified and on the operating conditions of the process; see for example the publication of C.-H. Lee et al., AlChE Journal, March 1999, Vol.45, N ° 3, p 535.
• WO 97/45363 describes the association of an adsorbent of the silica gel type, activated carbon which allows the elimination of impurities such as carbon dioxide, linear, branched or cyclic hydrocarbons, saturated or unsaturated in C Cs and a faujasite-type zeolite with an Si / Ai ratio of less than 1.5 exchanged at least 80% with lithium intended to adsorb carbon monoxide and nitrogen in place of a zeolite 5A; this association allows a significant increase in hydrogen yield and productivity.
• impurities such as carbon dioxide, linear, branched or cyclic hydrocarbons, saturated or unsaturated in C Cs and a faujasite-type zeolite with an Si / Ai ratio of less than 1.5 exchanged at least 80% with lithium intended to adsorb carbon monoxide and nitrogen in place of a zeolite 5A; this association allows a significant increase in hydrogen yield and productivity.
• EP 855.209 describes the use, instead of the molecular sieve 5A intended to adsorb CO and N 2 , of a faujasite type zeolite with an Si / Ai ratio between 1 and 1.5 exchanged with at least 85% lithium or lithium + calcium with a Li / Li + Ca molar ratio> 0.7.
• each adsorbent bed is subjected to a succession of treatment cycles comprising the steps consisting in: a) passing a gaseous mixture based on hydrogen polluted by monoxide of carbon and nitrogen and optionally containing at least one other impurity such as carbon dioxide, water, hydrocarbons in CrCs in an adsorption zone comprising:
• first adsorbent bed consisting of one or more adsorbents selective for impurities such as carbon dioxide, CrCs hydrocarbons, saturated or not, linear, branched or cyclic, saturated or unsaturated, of the methane type , ethane, butane, propane, benzene, toluene or xylene, Skin,
• a second adsorbent capable of selectively adsorbing carbon monoxide, which is preferably a type A zeolite of which at least 35% and advantageously at least 60% of the exchangeable sites are occupied by calcium ions,
• a third adsorbent capable of selectively adsorbing nitrogen which is a zeolite X of the faujasite type with an Si / Ai ratio is less than 2, preferably close to 1 commonly called LSX zeolite (for Low Silica X translated by low zeolite X silica content), of which at least 60% and preferably at least 80% of the exchangeable sites are occupied by calcium and possibly lithium ions; b) desorbing the carbon monoxide, nitrogen and any other impurity (s) adsorbed on the adsorbents by setting up a pressure gradient and gradually lowering the pressure in said adsorption zone so as to recover carbon monoxide, nitrogen and any other impurity (s) by entering said adsorption zone, this step being able to be completed by a purging phase consisting in recycling part of the purified hydrogen; and c) raising the pressure of said adsorption zone by introducing a stream of pure hydrogen through the outlet of the adsorption zone.
• the gaseous mixture contains, in addition to hydrogen, carbon monoxide and nitrogen, at least carbon dioxide and methane.
• gas mixtures originating from catalytic cracking units, thermal cracking units, catalytic reforming units or hydrotreating units.
• the process of the present invention relates very particularly to the purification of hydrogen resulting from the reforming of natural gas, the molar composition of impurities of which is as follows approximately 20% in CO 2 , 5% in CO, 5% in CH 4 , and approximately 5% in N, as well as traces of water and some hydrocarbons.
• the purity of the hydrogen obtained according to the process of the invention can reach 99.999%, when the gas mixture to be purified comprises more than 45 mol% of hydrogen gas.
• the purification of a gaseous mixture containing less than 45 mol% of gaseous hydrogen is not desirable, insofar as this requires an excessive amount of adsorbent and an inordinate size of industrial plants so as to be able to achieve purity acceptable. It is clear that the greater the proportion of hydrogen in the starting gas mixture, the purer the hydrogen recovered at the outlet of the adsorption zone. Preferably, the purification of a gas mixture containing more than 70 mol% of hydrogen will be chosen.
• the adsorption zone is maintained at a pressure of between 0.5 and 7 MPa, when the gaseous mixture to be purified is brought into contact with said first (optional) and second adsorbents.
• higher pressure does not harm the conduct of the purification.
• pressures generally above 7 MPa are generally avoided. Pressures below 0.5 MPa are not usually used for the production of hydrogen by adsorption of impurities on an adsorbent bed, for reasons of efficiency.
• the pressure prevailing in the adsorption zone will be maintained at a value less than 5 MPa, better still less than 3 MPa.
• the adsorption zone is maintained, preferably, above 0.5 MPa, preferably, above 1.5 MPa.
• the temperature of the incoming gas mixture and of the adsorption zone is not critical and is generally kept constant during the adsorption phase of the impurities. Usually this temperature is between 0 and 80 ° C, preferably between 20 and 50 ° C during adsorption.
• the present invention applies to any type of PSA process for the purification of hydrogen and thus any modification of parameter such as pressure level, purge rate, etc., aimed at improving the performance of the process which can be combined with the characteristics essentials of the process according to the invention described above.
• the present invention can be applied either during the design of a new PSA installation for the purification of hydrogen, which allows, compared to an industrial installation of the prior art operating with the same hydrogen productivity, a reduction in the size of the columns (therefore a reduction in investment), ie in the case of the replacement of the adsorbents of the columns of an existing industrial installation by the adsorbents of the present invention, a significant improvement in productivity.
• the 1 st , 2 nd and 3 rd adsorbents are arranged so that the gas mixture first passes through the possible 1 st adsorbent, selective at least for impurities such as carbon dioxide, the C Cs hydrocarbons, then the 2 nd adsorbent, selective at least for CO, finally the 3 rd adsorbent, selective at least for nitrogen, during the adsorption stages.
• selective adsorbent at least carbon dioxide and CrCs hydrocarbons (1 st optional adsorbent)
• activated carbon, alumina, silica gel or a mixture of these different adsorbents in any proportion.
• the various constituents of the mixture can be arranged either in the form of a dry or dry-blend or preferably in the form of separate layers so that the gaseous mixture successively comes into contact with each of the layers.
• silica gels which can be used according to the invention are the most commonly used in industrial PSA H 2 installations for adsorbing water and hydrocarbons. These gels are commercially available, in particular from SOLVAY (sorbead gels).
• Activated carbon is for example marketed by the companies CECA, NORIT, CARBOTECH, PICA or CHEMVIRON.
• the zeolites A and X can be in the form of crystalline powders or agglomerates, the latter form being preferred since it makes it possible to avoid pressure drops during handling of said said adsorbents during the loading and unloading stages of columns in industrial installations.
• the zeolite agglomerates are obtained in a conventional manner by implementing conventional agglomeration processes.
• the agglomerated zeolite can, for example, be prepared by mixing a crystalline zeolite powder with water and a binder (generally also in the form of a powder), then spraying this mixture onto agglomerates of zeolites acting as agglomeration germ.
• a binder generally also in the form of a powder
• spraying the zeolite agglomerates are subjected to a continuous rotation on themselves. This can be achieved by placing the agglomerates in a reactor rotating on itself around an axis of rotation, said axis of rotation being preferably inclined relative to the vertical direction.
• the agglomerates thus obtained are then subjected to baking at a temperature between about 400 and 700 ° C.
• binder mention may be made of clays such as kaolin, silica and / or alumina.
• the agglomerated zeolite thus obtained which comprises a binder, can be used for the preparation of agglomerated zeolite with a low level of binder also usable in the process of the invention.
• Such zeolitic agglomerates with a low level of binder are obtained according to techniques known to those skilled in the art, such as zeolitization of the binder.
• An example of the preparation of a zeolite with a zeolitized binder is described in EP 893.157, the teaching of which is incorporated by reference.
• Zeolites A and X are generally synthesized in sodium form, ie the majority of their exchangeable sites are occupied by sodium ions; for these sodium zeolites to be usable as 2 nd and 3 rd adsorbents, it is necessary to subject them to an additional treatment, in the case of zeolite in the form of agglomerates before or after the agglomeration step, aimed at introduce calcium or (calcium and lithium) cations into the crystal lattice.
• activation of a zeolite is understood to mean its dehydration, that is to say the elimination of the water of hydration contained in the zeolite.
• the partial pressure of the water in the gas in contact with the zeolite is made to be less than about 40 kPa, preferably 10 kPa after activation.
• the methods of activating zeolites are known per se.
• One of these methods consists in subjecting the zeolite to a pressure of between approximately 10 kPa to 1 MPa while passing a current of an inert gas through the adsorbent in the form of a bed made up of said zeolite and while heating said zeolite up to a temperature between 300 and 650 ° C at a rate of temperature increase of about 0.1 to 40 ° C per minute.
• the zeolite can be activated by maintaining it under a vacuum of about 10 kPa or less while heating the zeolite to a temperature of about 300 to 650 ° C without the need for sweeping by an inert gas.
• Another alternative consists in activating the zeolite by a process using microwaves, as described for example in US 4,322,394.
• the productivity of the PSA process is defined as the ratio of the volume of hydrogen produced, measured under normal conditions of temperature and pressure, per unit of time and per volume. adsorbent.
• the yield is defined as the ratio of the volume of pure hydrogen produced, measured under normal pressure and temperature conditions, by the volume of hydrogen contained in the gas to be purified, also measured under normal pressure and temperature conditions. .
• Each column passes from one phase to another in the order indicated above, each phase lasting 3 min.
• the high pressure is 2.5 MPa
• the low pressure is 0.3 MPa.
• the gas to be purified has the following molar composition: 5% CO, 5% N 2 , 90% H 2 .
• a base a gas which would therefore have already been purified by passing over the preliminary layers of alumina, silica gel and / or activated carbon (possible 1st adsorbent).
• V is filled with adsorbent, or with 2 adsorbents which are agglomerated zeolites with 20% by weight of clay binder, CaA, CaLSX and LiLSX of exchange rate of calcium respectively at 84% and 97 % of lithium whose filling densities are: zeolite 5A 0.72 - zeolite CaLSX 0.66 zeolite LiLSX 0.63
• the 4 columns are filled with a single adsorbent which is the agglomerated zeolite 5A defined above.
• the installation is operated for several cycles until a steady state is reached, that is to say a constant purity and yield of hydrogen. We deduce the productivity obtained for this adsorbent, calculated according to the previous definition.
• the 4 columns are filled with a single adsorbent which is the agglomerated CaLSX zeolite defined above. As in Example 1, the installation is operated for several cycles until a steady state is reached.
• the four columns are filled with a mixed bed of two adsorbents: the 1 st layer consists of zeolite 5A of Example 1 and occupies 65% of the total volume of each of the columns, the 2 nd layer is made of zeolite CaLSX of example 2 and occupies 35% of the total volume of each of the columns.
• Example 1 the installation is operated for several cycles until a stationary speed is reached, it being specified that during the phases adsorption, the gases pass first over the layer of zeolite 5A, then over that of CaLSX.
• the four columns are filled with a mixed bed of adsorbent 2: 1 ⁇ re the layer consists of zeolite 5A of Example 1 and occupies 65% of the total volume V of each column, the 2 nd layer is constituted of the zeolite LiLSX defined above and occupies 35% of the total volume V of each of the columns.
• Example 1 the installation is operated for several cycles until a stationary regime is reached, it being specified that during the adsorption phases, the gases pass first over the layer of zeolite 5A, then over that of LiLSX.

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