FR2854819A3 - Solid absorbent material for purifying or separating gases such as air combines open-pore cellular and mechanical reinforcing materials - Google Patents

Abstract

The absorbent material combines a material with an open pore cellular structure with pores being preferably 0.07 - 0.2 mm in size and occupying 30 - 50 per cent of its volume, and a mechanical reinforcing material. The reinforcing material has mechanical and/or thermal properties and is selected from an organic oxide, ceramic, metal, carbon or polymer. The absorbent material combines a material with an open pore cellular structure with pores being preferably 0.07 - 0.2 mm in size and occupying 30 - 50 per cent of its volume, and a mechanical reinforcing material. The reinforcing material has mechanical and/or thermal properties and is selected from an organic oxide, ceramic, metal, carbon or polymer. The absorbent material also contains metal cations in a zeolitic phase selected from alkalis or alkaline earths, transition metals or lanthanides, preferably of lithium, calcium, sodium, potassium or zinc. The solid phase of the absorbent material can also be a zeolite, active carbon, activated aluminum or activated silica gel.

Description

The present invention relates to a purification or separation process

of

  gases or gas mixtures using a monolithic adsorbent having a structure in conduits grouped in bundles with open porosity being in the form of a solid monolith permeable to gas molecules.

  Currently, industrial adsorbents are used in the form of a granular bed. In this configuration, the adsorbent bed appears as a loose stack of particles of any shape: beads, extrusions, more complex shapes.

  This arrangement can be defined as consisting of a locally essentially convex solid phase coexisting with an essentially concave gas phase occupying the space left free by the solid.

  One development path consists in making so-called honeycomb monolithic adsorbents, essentially consisting of a solid structure and of a gas phase arranged essentially in a linear fashion called "in channels" obtained by extrusion.

  A similar approach uses lamellar structures in "millefeuilles", with the two phases arranged in sheets and a two-dimensional gas flow.

  Yet another approach concerns open-cell foam structures allowing the passage of gas.

  Now, the basic problem of solid phase adsorption processes, to which each of the three known arrangements proposes a solution, consists in achieving a good exchange of gas / solid material while maintaining a low pressure drop.

  Thus, a granular bed ensures a good transfer of material in the gas phase but at the cost of a significant pressure drop.

  Furthermore, it is difficult to improve the situation much because the primary cause is the large dimension of the solid phase relative to the gas phase.

  In addition, the solution which consists in reducing the grain size quickly finds its limit by an excessive increase in the pressure drop. In fact, the convex, even spherical, structure of the solid phase imposes a low surface to volume ratio intrinsically unfavorable to diffusion in the solid, and a high surface to volume ratio in the gas phase, when in fact it is the opposite that should be achieved.

  For its part, a honeycomb or mille-feuille structure is essentially linear and the two phases are therefore in equivalent arrangement.

  The gas flow is much more regular than in the case of the granular bed, which leads to a low pressure drop. However, it is found in practice that the transport of material in the gas phase is not satisfactory precisely because of this regular flow, that is to say laminar, unless using channel dimensions of the order 0.05 or 0.3 mm, which poses manufacturing problems.

  From there, the problem then arises of being able to have a gas separation or purification process 5 using an adsorbent having an optimized material exchange between the gas phase and the solid phase, while maintaining the pressure drops. at a low level when using this adsorbent to separate or purify a gas or a gas mixture, in particular a PSA or VSA process to produce, for example, oxygen or hydrogen, or a TSA process used, for example, to remove carbon dioxide, nitrogen oxides and / or hydrocarbons, or water from gases, such as air or H2 / CO mixtures.

  The object of the present invention is then to solve this problem by proposing a method using an improved adsorbent which can be used to purify or separate gases, such as air.

  The solution of the invention is then a process for the purification or separation of a gas or gas mixture using a monolithic adsorbent for the separation or purification of gases or gas mixtures having an open porosity structure in the form of a monolith comprising parallel passages permeable to gas molecules, ie in the form of a network of channels arranged in bundles in a solid matrix permeable to gas molecules.

  Depending on the case, the method of the invention may include one or more of the following technical characteristics: - the size of the parallel passages of the gaseous phase of the adsorbent is between 0.05 and 0.5 mm, preferably between 0.07 and 0.25 mm.

  - The porosity of the adsorbent is between 10 and 60% / o of the volume of the monolith, preferably between 30 and 50%.

  - The adsorbent consists of a solid phase comprising at least 40% by weight of at least one adsorbent material comprising zeolite, silica gel, activated alumina or activated carbon, and the remainder being constituted at least one material of mechanical reinforcement and / or with particular thermal properties.

  - The solid phase of the adsorbent comprises at least 60% by weight of at least one adsorbent material.

  the material for mechanical reinforcement and / or with particular thermal properties of the adsorbent is chosen from an inorganic oxide, a ceramic, a metal, carbon 35 or a polymer.

  - the adsorbent contains metal cations in its zeolitic phase.

  The adsorbent contains metal cations chosen from alkali and alkaline earth metals, transition metals, lanthanides, preferably lithium, calcium, sodium, potassium, zinc.

  - the gas is air or an HJ / CO mixture.

  - At least one of the gases chosen from oxygen, hydrogen, CO, CO2 or nitrogen is produced.

  - At least one impurity is removed from the group formed by H20, CO2, NxOy, N2, CO and unsaturated or saturated hydrocarbons.

  - It is chosen from the VSA, PSA or TSA methods.

  - The stream to be purified is air and at least a portion of the air freed from at least a portion of said impurities is subjected to at least one cryogenic distillation step.

  - The gas flow is at a temperature between -40 C and +80 C, preferably between -10 C and +60 C, more preferably between 100 C and +50 C.

  - The adsorption pressure is between 1 bar and 60 bars, preferably between 3 bars and 35 bars, more preferably between 6 bars and 30 bars.

  - the desorption pressure is between 0.2 bar and 60 bar, preferably between 0.25 bar and 6 bar - the gas flow rate is between 0.1 and 106 Nm3 / h, preferably 103 and 5.10 Nm3 / h.

  the regeneration temperature is between -20 ° C. and 400 ° C., preferably between 20 ° C. and 250 ° C., preferably between 20 ° C. and 80 ° C.

  the regeneration gas of the adsorbent is nitrogen or a mixture of nitrogen and oxygen containing a small proportion of oxygen (a few vol%), preferably the nitrogen / oxygen mixture used to regenerate the The adsorbent is a waste gas or a waste gas from a cryogenic air separation unit.

  2 5 - the regeneration gas is oxygen containing a few% of nitrogen, preferably the nitrogen / oxygen mixture used to regenerate the adsorbent is a gas obtained from an adsorber capable of separating oxygen from the air the regeneration gas is hydrogen containing less than 10 ppm of impurities, preferably the gas used to regenerate the adsorbent is a gas obtained from an adsorber capable of separating the hydrogen from a mixture containing it.

  - The process of the invention is implemented in at least one adsorber, preferably in at least two adsorbers operating alternately.

  The invention consists in the preparation and use of a monolith comprising a network of approximately unidirectional channels, prepared from a preform 35 consisting of a set of polymer fibers, deposition of the adsorbent in the concave interstitial volume, then pyrolysis of the polymer and baking of the adsorbent phase.

  The contact between the binder and the polymer preform can be carried out by immersion in a slip containing the adsorbent and optionally a binder and various adjuvants (thickeners, surfactants, dispersants, lubricants etc.) or it can be carried out by injection into the preform.

  The polymer preform consists of a non-heat-fusible material, the decomposition of which leads to the formation of gases with little or no carbon or gum deposition.

  The elimination of the polymer is done so as to leave voids instead, under conditions where the temperature is controlled to avoid hot spots, and also where the gases generated can be eliminated without remaining blocked in the adsorbent structure.

  Among the polymers of interest are oxygen-containing compounds such as polyesthers, polycarbonates, polyacrylates and, in general, polymers containing alcohol, ester, acid, ether groups.

  The polymer fibers can be solid or hollow.

  The invention also results in a monolithic adsorbent which is not subject to movement and which, therefore, can withstand high gas passage rates, i.e. at least 1 m / s real.

  The size and shape of the conduits can be adapted to the constraints of the particular process, in general the channels have a diameter of between 0.05 and 0.3 mm.

  The porosity of the medium can also be adapted and is generally between 10 20 and 60%.

  The solid adsorbent phase consists of a specific adsorbent such as a zeolite, activated carbon, activated alumina or activated silica gel.

  Activation is carried out under conditions where the adsorbent will have the maximum adsorption properties for the application. Typically, the gases and vapors produced during activation are removed so that they do not degrade the structure of the adsorbent. The final activation temperatures depend on the type of adsorbent, for example between 300 C and 450 C for a zeolite, between 150 C and 250 C for silica gel, between 250 C and 400 C for an alumina, between 300 C and 700 C for activated carbon.

  The presence of a binder may be necessary to ensure rigidity, for example a binder of the alumina, clay, silica type. The binder may have been converted at least partly into the adsorbent phase, for example in the case of an agglomerated zeolite whose clay binder has been converted into the same or different zeolite from the main phase.

  It is also possible to use a mixed structure consisting of a rigid structure 35 covered by a particular active phase, different from the underlying phase, for the purpose for example of separating the mechanical support and adsorption functions. The rigid structure may consist of an oxide of the silica, alumina, ceramic or metal type.

  More complex structures can also be used, for example a monolith on which an adsorbent phase is deposited. In this case, the metal structure performs a dual function of mechanical reinforcement and heat conduction. The metal of the structure can be copper, aluminum, iron, steel, an alloy chosen as a function of thermal conductivity, mechanical strength, density, porosity and compatibility with the adsorbent phase chosen.

  The metallic phase can be covered with an adherent ceramic or oxide phase, in order to facilitate and / or reinforce the deposition of adsorbent phase.

  The adsorbent can also be made using the gel or aerogel technique.

  The basic principle consists in carrying out the gelling of a liquid phase, then, optionally after rinsing, in removing the solvent.

  The structural parameters, such as size and spacing of the conduits, density, porosity or shape of the monolith, can be adjusted in terms of the formation of the preform and / or the deposition of support phase or active phase.

  In practice, all the adsorption systems using a granular bed or a honeycomb or mille-feuille structure can advantageously be replaced by a particular implementation of the invention which has the advantage of being easy to implement. compared to honeycomb or millefeuille structures, which require the production of very regular three-dimensional structures and very small dimensions.

  The monolithic adsorbent can be formed from a single block or from the stack of several blocks. In the latter case, it is possible to use blocks having different properties between them. For example, monoliths characterized by porosities, channel sizes, pore densities or chemical compositions (binder content, nature of the zeolite, nature and proportions of the cations, mechanical support) can be stacked in different ways. to optimize each stack or layer of adsorber as a function of the flow which passes through it.

  It is also possible to produce a gradient of properties in a single block, such as for example a gradient of exchange rate or porosity.

  The monolithic nature of these forms of adsorbent must be taken into account for their handling. Indeed, such shaped adsorbents are rigid and a scratch, a fracture or the loss of part of the mass cannot be spontaneously compensated by a geometric rearrangement. This can have important consequences since preferential passages or dead volumes are formed for the gas, which greatly degrade the performance of the adsorption unit.

  Furthermore, the monolithic adsorbents must be placed in the adsorbers and fixed therein so as to suppress any overall movement and any passage of gas outside the monolith, which increases the risks of deterioration mentioned above.

  Another problem concerns the implementation of the ion exchange operation to which the monoliths can be subjected. The ion exchange consists in bringing the zeolitic adsorbent into contact with a solution of a salt to be exchanged, for example a lithium salt for the manufacture of a lithium faujasite. The ion exchange is in this case difficult and must be carried out with the adsorbent placed in a column. With a granular adsorbent, there is no major problem in filling the column and then emptying it after exchange. On the other hand, in the case of a monolith, one understands the difficulty of introducing and removing the product from the column without damaging it, or the problem of preferential passages between the monolith and the wall of the column. Activation of the monolith is also a problem with the handling and passage of gas through the monolith.

  It can therefore be seen that the processing, transport, storage and installation of these monoliths are difficult, and all the more so since these monoliths are large and of complex structure. One possibility of overcoming this difficulty consists in increasing the rate of binder but then one loses capacity.

  The invention also proposes a solution to the problem of the fragility of the monoliths, by allowing easy handling and transport, storage and installation, whatever the intrinsic resistance of the material of which they are made. It also makes it possible to increase the intrinsic capacity of the adsorbent material.

  The invention proposes to surround the monolith with a rigid hull capable of withstanding shocks and mechanical stresses and also capable of being introduced as it is into the adsorption columns. The monolith can then be handled and transported without problem, the adjustment in the adsorption column can be carried out by means of seals 25 and shims. Optionally, the hull can serve as an adsorption column.

  In fact, the fairing of the monolith makes it possible to use combinations of binder and active material that are too weak to support their own weight alone, and therefore it leads to materials having a higher proportion of active material. For example, adsorbents having less than 10% by weight of binder can be produced. This also makes it possible to produce monoliths of very fine structure, for example channels of the order of 0.05 or 0.2 mm with walls of 0.05 to 0.5 mm, which do not have the mechanical strength allowing them to form structures of large dimension.

  To separate the gases or purify them using the so-called PSA or TSA technique, the hull must be able to withstand temperature variations without contact with the monolith being degraded.

  One can proceed for example by introducing the "green" mixture of binder and adsorbent shaped in a metallic or ceramic shell, then bake the whole to harden the binder and activate the adsorbent. During this operation, a sweeping gas can be passed through the adsorbent passages, which makes it possible to remove the water and the gases evolved effectively. It is also possible to add a blowing agent which will adjust the monolith against the internal wall of the shell, with the consequence of a solid adhesion, further improved if necessary by surface treatment of the metal.

  The heating can be carried out by the purge gas of the solid, or by external heating by conduction or microwave, or else by a combination.

  Another method consists of cooking the monolith separately, then introducing it into the shell, the adjustment being made by the use of glue (taken cold or hot) at the inter wall.

  A variant consists in using a ferrule made of a shape memory material which will shrink by adjusting the monolith.

  Yet another yet further method is to wrap a sheet of flexible material around the monolith, baking and activation being done before or after.

  In all cases, it may be useful to use an adhesive which will make the adsorbent and the hull secure, the adhesive may be organic or mineral (silicate).

  Yet another method is to use the ferrule in place at the time of fiber extrusion.

  It is possible to use the hull directly as an adsorption column or to place it inside a shell with reinforced mechanical properties. In the latter case, several monoliths can be arranged in series. The adjustment of the ferrule to the column can be done by any means known to those skilled in the art: O-rings or flat plates, wedges, guides, rails, etc.

  In general, the shrouded adsorbent has surfaces which must be impermeable to gases and liquids, responsible for channeling the flow, and surfaces permeable to gases and liquids by o entering and leaving the gas or the liquid. The gas and liquid impermeable part can be made of any rigid impermeable material such as metal, ceramic, plastic. The part permeable to gases and liquids can be made of any metallic, mineral or organic permeable material produced so as to ensure the passage of gas, such as perforations, weaving, stamping, etc. The part permeable to gases and liquids can also not contain fairing.

  Another advantage of a streamlined adsorbent is that it allows easy treatment of the adsorbent, for example to achieve ion exchange, or activation. The fairing allows the exchange solution or the activation gas to be percolated directly through the monolith, limiting the problem of sealing the inlet and the outlet.

  In the case of an exchange in columns, the hull can be used to channel the exchange solution, or even to serve as a complete support. It is then sufficient in this case to ensure the circulation of the exchange solution by a system of valves and pipes. In the preferred procedure, the column is placed as it is in the solution circuit, then is removed after ion exchange.

  In the same way, the adsorbent can be activated after ion exchange by passage of hot gas, possibly dried and decarbonated through the foam, the hull serving at least to channel the activation gas, or even to ensure the function full structure support. Of course, all the ways of conducting activation or ion exchange or any contacting of the adsorbent material with a columnar fluid can be imported from the methods of treatment of granular beds.

  The adsorbent material according to the invention can be used in on-board oxygen production systems in aircraft or the like, that is to say systems called OBOGS (on-board oxygen generating system), or in concentrations 10 oxygen intended for the medical field.

Claims (10)

claims   1. Adsorbent material for purifying or separating a gas or gas mixture using a monolithic adsorbent for separating or purifying gases or gas mixtures having an alveolar structure with open porosity in the form of a network of channels arranged in bundles in a solid matrix permeable to gas molecules.   2. adsorbent material according to claim 1, characterized in that the gas phase of the adsorbent has a structure in bundles arranged in a substantially parallel manner.   3. adsorbent material according to one of claims 1 or 2, characterized in that the pore size of the gas phase of the adsorbent is between 0.05 and 0.5 mm, preferably between 0.07 and 0.2 mm.   4. adsorbent material according to one of claims 1 to 3, characterized in that the porosity of the adsorbent is between 10 and 60% of the volume of the monolith, preferably between 30 and 50%.   5. adsorbent material according to one of claims 1 to 4, characterized in that the adsorbent consists of a solid phase comprising at least 40% by weight of at least one adsorbent material comprising zeolite, gel silica, activated alumina or activated carbon, and the remainder consisting of at least one material of mechanical reinforcement and / or with particular thermal properties.   6. Adsorbent material according to claim 5, characterized in that the solid phase of the adsorbent comprises at least 60% by weight of at least one adsorbent material.   7. adsorbent material according to claim 5, characterized in that the material for mechanical reinforcement and / or with particular thermal properties of the adsorbent is chosen from an inorganic oxide, a ceramic, a metal, carbon or a polymer.   8. adsorbent material according to claim 5, characterized in that the adsorbent contains metal cations in its zeolitic phase. O10   9. adsorbent material according to claim 5, characterized in that the adsorbent contains metal cations chosen from alkali and alkaline earth metals, transition metals, lanthanides, preferably lithium, calcium, sodium, potassium , zinc.   10. A method of separation and / or purification of gas using the adsorbent material according to one of claims i to 9, the gas being air or an H2 / CO mixture.