Method for manufacturing an adsorption means for treating a gas and adsorption means obtained by such method

Abstract

The invention relates to a method for manufacturing an adsorption means for treating a gas, in which a first coating layer (7) is formed on a porous open support structure (1) by applying a first coating suspension (2) with a first solvent (4) and an adsorbent (3). The method comprises the steps of: - drying (102) the first coating layer such that the first solvent is partially removed, - diluting (106) the first coating suspension by adding a second solvent (5) to form a second coating suspension (6), - forming a second coating layer (8) on the first coating layer in which the first solvent is still present by applying the second coating suspension.

Description

[0001] Method for manufacturing an adsorption means for treating a gas and adsorption means obtained by such method.

[0002] The present invention relates to a method for manufacturing an adsorption means, more particularly an adsorption means which can be used for treating, for example purifying or separating, gas or compressed gas.

[0003] The gas is typically a gas mixture such as air or a gas mixture containing, among others, the following components: air / H2O, CO2 / H2O, CH4 / H2O, CH4 / N2, CH4 / CO2, N2 / O2, air / CO2, hydrocarbons / air. Examples of treating compressed air with an adsorption means are purifying compressed air by removing moisture with the adsorption means, or in other words, drying compressed air, or separating oxygen and nitrogen from compressed air using the adsorption means.

[0004] Adsorption devices are already known in the form of drying devices for compressed gas, for example, originating from a compressor, which drying devices comprise one or more vessels into which a drying agent is applied. The respective drying agent is usually embodied in the form of a regenerable drying agent, or in other words, a drying agent that can be regenerated after reaching a certain degree of saturation. The respective one or more vessels are provided with an inlet and an outlet. The respective one or more vessels can have a drying or regenerative function, or be used for cyclical drying and regenerating. In case of the drying function, the compressed gas to be dried is supplied through the inlet and the dried gas is discharged through the outlet. In the case of the regenerative function, the (saturated) drying agent is exposed to a regeneration gas stream that extracts the moisture from the drying agent. Such a regeneration gas stream may, for example, consist of a fraction of the dried gas and / or hot gas whose relative humidity is sufficiently low to enable regeneration of the drying agent.

[0005] The drying agent that is used in such vessels comprises, for example, a silica gel, a molecular sieve, an activated alumina, or a combination thereof. Traditionally, the drying agent is in granular or other extruded form. A limitation of the use of a granular drying agent is that gas velocities through the vessels must be limited to prevent wear and fluidization of the granules, and to avoid dust formation and pressure fluctuations.

[0006] To avoid the problems inherent to the use of a granular drying agent, the drying agent can also be applied to an open support structure, such as a corrugated structure of glass fibres or ceramic fibres, for example, in the form of a honeycomb structure, which is fitted into the vessel. A coating of the drying agent is then applied to this support structure. However, known techniques only allow for a relatively thin coating. Consequently, the amount of drying agent present in the vessel is rather limited, requiring larger (or even oversized) vessels to achieve drying at the desired gas velocities. Furthermore, the thickness of the coating is relatively small in relation to the cross-sectional area of the channels, present in the open support structure. This results in an (excessively) high porosity of the coated support structure, which can lead to excessive blow-off.

[0007] The present invention aims to provide a solution to at least one of the aforementioned and / or other disadvantages.

[0008] An object of the invention is to provide a solution that maximizes the amount of adsorbent, applied to an open support structure.

[0009] Another object of the invention is to provide an efficient solution that allows a desired thickness of coating with adsorbent to be applied to an open support structure in as few steps as possible.

[0010] It is also an object of the invention to provide a solution that allows an adsorbent-coated support structure to be realised with a porosity suitable for applications with higher blow-off rates.

[0011] To at least partially solve one or more of the aforementioned or other known problems and / or to meet one or more of the aforementioned objectives, the invention provides a method for manufacturing an adsorption means for treating gas. The method comprises flushing a porous, open support structure with a first coating suspension, comprising a first solvent and an adsorbent, under the influence of a first set pressure difference, to form a first coating layer.

[0012] The method according to the invention comprises the further steps of: a) drying the first coating layer such that the first solvent is partially removed, b) diluting the first coating suspension by adding a second solvent to form a second coating suspension, and c) flushing the porous support structure, provided with the first coating layer from which the first solvent has been partially removed, with the second coating suspension under the influence of a second set pressure difference, to form a second coating layer, wherein the second set pressure difference is greater than the first set pressure difference.

[0013] The combination of steps a), b, and c) ensures that the second coating suspension can flow effectively into the open support structure, provided with the first coating layer, and form a second coating layer without blocking the openings and / or passages in the support structure, thereby preventing the second coating suspension from flowing through the support structure without, or virtually without, interaction with the first coating layer, thus hindering the formation of a substantial second coating layer. The inventors have determined that the combination of steps a), b, and c) promotes the adhesion of the second coating layer to the first coating layer by allowing adsorbent particles from the second coating suspension to at least partially penetrate into the first coating layer, in which the first solvent is still partially present, thus forming an interface between the first and second coating layer. The amount of adsorbent, applied to an open support structure, can be increased with this method according to the invention, making the gas treatment more efficient and effective.

[0014] The porous open support structure preferably forms a single unit and is typically constructed from one or more of the following materials: ceramic material, metal foil, a fibre structure, for example based on glass fibre, ceramic fibre or other fibres, or a mixture of different types of fibres, and a polymer. The open support structure preferably comprises channels that allow the gas to flow freely, not only lengthwise but also laterally, to maximize the effectiveness of the adsorbent. The open support structure can be constructed from cells that are in mutual gas communication, by which the channels are formed. The cell density in the open support structure is preferably 200 to 900 CPSI (cells per square inch). The walls of the open support structure, which delimit the channels, preferably have a thickness ranging from 2 to 10 mil (milli-inch).

[0015] In an embodiment according to the invention, the open support structure is a ceramic structure provided with channels whose cross-sections have a geometric shape, such as, for example, a circle, a triangle, a square, a rectangle or other polygon, and the like.

[0016] The first coating suspension preferably comprises a solvent and porous adsorbent particles. The porosity of the adsorbent particles preferably ranges from 10 % to 60 %. The first coating suspension may also comprise one or more of the following components: a binder, non-porous particles, and additives, for example, additives to influence the acidity or prevent foaming. The binder may be an inorganic binder material, such as colloidal silica, aluminium oxide, and / or clay; and / or may comprise an organic material such as methylcellulose, a polymer, and / or a material from the cellulose group.

[0017] The adsorbent comprises one or more of the following materials: a zeolite, silica gel, activated alumina, activated carbon, metal-organic screens, a molecular sieve such as, for example, a carbon molecular sieve ("CMS"), an impregnated adsorbent, and a hybrid adsorbent. The preceding list is not exhaustive; however, other materials are also possible according to the invention. The choice of adsorbent or active substance depends on the intended treatment of the gas to be treated. The particle size distribution of the adsorbent is preferably such that D50 is less than 10 pm and more preferably less than 4 pm.

[0018] In an embodiment of the method according to the invention, the step of drying the first coating layer takes place at a temperature ranging from 50°C to 100°C, preferably from 60°C to 80°C, and more preferably at a temperature of 70°C. Preferably, the step of drying the first coating layer takes place in ambient air with a relative humidity ranging from 1 % to 15 %. Furthermore, the step of drying the first coating layer is preferably such that the solvent content present, relative to the mass of the coated support structure, is reduced by a value ranging from 10 % to 60 %.

[0019] These specifications for drying the first coating layer allow an open support structure with the first coating layer to reach the desired condition, specifically by gentle drying, ensuring that the partially removed first solvent substantially consists of the first solvent present between the adsorbent particles and not, or to a much lesser extent, of the first solvent adsorbed by the adsorbent particles. This promotes adhesion during application of the second coating layer.

[0020] Also, in another embodiment of the method according to the invention, the step of drying the first coating layer is followed by cooling the porous support structure to a temperature between 10°C and 50°C and storing the cooled porous support structure shielded from the environment until the porous support structure is flushed with the second coating suspension. This allows the desired condition to be maintained until the second coating layer is applied.

[0021] The second coating suspension of the method according to the invention is obtained by diluting the first coating suspension with the first solvent and adding a second solvent. The first and second solvents are chosen to be compatible, for example, both polar or both non-polar. Examples of first and second solvents are alcohols and water. The first and second solvents can also be the same. Preferably, the dilution of the first coating suspension with the second solvent is such that a ratio of the second solvent to the first coating suspension in the second coating suspension ranges from 1:100 to 1:1, and more preferably 1:40.

[0022] The method according to the invention comprises flushing the porous support structure with the first coating suspension and with the second coating suspension under the influence of a first and a second set pressure difference, respectively. Flushing the porous support structure with the first coating suspension and the second coating suspension can occur in the same direction through the open support structure, for example, along the length of the open support structure from bottom to top or from top to bottom. Preferably, flushing the porous support structure with the first coating suspension and with the second coating suspension occurs in opposite directions. This has the advantage that the total thickness of the formed coating layers is more uniform across almost the entire support structure. The second pressure difference is greater than the first pressure difference. Preferably, the second set pressure difference has a value in the range of 10 % to 40 % greater than the first set pressure difference. The dilution and increased pressure difference contribute to the smooth flow of the second coating suspension into the open support structure containing the first coating layer and further allow the coating layers to be applied in such a way that the void ratio in the coated support structure ranges from 5 % to 60 %, compared to the void ratio in the uncoated support structure. This has the advantage that the desired thickness of the adsorbent coating can be achieved on an open support structure in just a few steps, with minimal steps. Furthermore, an adsorbent-coated support structure can be realised with a porosity suitable for applications with higher blow-off rates.

[0023] In an embodiment of the method according to the invention, the second coating suspension is formed such that the adsorbent in the second coating suspension has a particle size that is smaller than the particle size of the adsorbent in the first coating suspension. In practice, the particle size of the adsorbent in the suspension can be reduced, for example, by wet milling. The smaller particle size of the adsorbent particles in the second coating suspension ensures better penetration into the first coating layer, which improves adhesion.

[0024] In an embodiment of the method according to the invention, the method comprises the step of successively applying one or more further coating layers, wherein the application of each further coating layer comprises the sub-steps of:

[0025] - after applying a previous coating layer, drying the coated support structure in such a way that any solvent present is partially removed, - further diluting the first coating suspension relative to the coating suspension applied to form the previous coating layer by adding a further solvent to form a further coating suspension,

[0026] - flushing the porous coated support structure, from which the solvent present has been partially removed, with the further coating suspension under the influence of a further set pressure difference, to form a further coating layer, wherein the further set pressure difference is greater than a set pressure difference when applying the previous coating layer.

[0027] The present invention also concerns an adsorption means obtained by the method as described in the preceding embodiments or a combination thereof.

[0028] In order to better demonstrate the characteristics of the invention, a preferred variant of a method according to the invention for manufacturing an adsorption means for treating gas is described hereinafter, by way of example but not in any way limiting, with reference to the accompanying drawings, in which:

[0029] Figure 1 schematically shows an embodiment of the method according to the invention for manufacturing an adsorption means for treating gas;

[0030] Figure 2 shows an enlarged image of a portion of the adsorption means obtained using the method shown in Fig. 1.

[0031] Figure 1 shows a flowchart schematically illustrating the steps for manufacturing an adsorption means by applying a coating to an open support structure 1. In the example shown, the method comprises constructing the coating on the open support structure 1 in two layers, but more layers can, of course, be provided. The resulting adsorption means is shown in Figure 2.

[0032] The porous open support structure is typically constructed from one or more of the following materials: ceramic, metal foil, a fibre structure and a polymer. The porosity of the wall of the support structure is preferably greater than 5 %, more preferably greater than 10 %, and most preferably greater than 20 %. In the example shown, the support structure 1 to be coated is a monolithic ceramic support structure with a cell density of 400 CPSI and a wall thickness of 6.5 mil. The cell walls define channels with a square cross-section.

[0033] Step 101 of the method comprises flushing the support structure 1 with a first coating suspension 2 under the influence of a first set pressure difference to form a first coating layer 7.

[0034] Preferably, the support structure 1 is flushed from bottom to top, or in other words, in the opposite direction of gravity, by applying a first pressure difference across the support structure 1, causing the first coating suspension 2 to be pumped or sucked upward through the support structure 1. This first pressure difference typically ranges from 200 mbar to 900 mbar.

[0035] The first coating suspension 2 comprises a first solvent 4, a polymer, non-porous particles and an adsorbent 3 comprising porous particles. In this example, the first solvent 4 is water, and the adsorbent 3 is a hydrophilic zeolite.

[0036] A next step of the method comprises drying 102 the first coating layer 7, typically at a temperature in the range of 50°C to 100°C in ambient air with a relative humidity in the range of 1 % to 15 %. The drying 102 is adjusted such that water is still present in the first coating layer 7 after drying 102. The water content present relative to the mass of the coated support structure 1 is reduced by a value in the range of 10 % to 60 % by the drying 102. The resulting dried support structure 1 is actively and / or passively cooled, typically to room temperature, and is sealed off from the environment to maintain the obtained condition until the next step is performed.

[0037] A next step in the method shown is forming a second coating layer 8 on the first coating layer 7 already formed on the support structure 1. To this end, a second coating suspension 6 is first formed by diluting 106 the first coating suspension 2 with a second solvent 5 that is compatible with the first solvent 4. In this example, this second solvent 5 is also water. The diluting 106 of the first coating suspension 2 with the added water is such that the ratio of the added water to the first coating suspension 2 in the second coating suspension 6 has a value in the range of 1:100 to 1:1, for example, 1:40. Depending on the porosity of the first coating layer 7 and the pore size distribution, one can opt to reduce the particle size of the adsorbent 3 in the second coating suspension 6, for example, by wet milling, such that the particle size distribution of the adsorbent particles is better matched to the pore size distribution. Examples of wet milling are attrition milling, roller milling, or immersion milling.

[0038] After preparation of the second coating suspension 6, the next step is flushing 103 the support structure 1, coated with the first coating layer 7, from which the water has been partially removed, with the second coating suspension 6 under the influence of a second set pressure difference, to form a second coating layer 8. Preferably, flushing 103 of the support structure 1 with the second coating suspension 6 takes place in the opposite direction compared to flushing with the first coating suspension 2, in other words in this example from top to bottom.

[0039] The second set pressure difference is set such that it is greater than the first set pressure difference, preferably at least 10 % greater, for example 40 % greater.

[0040] The resulting support structure 1, with the first coating layer 7 and second coating layer 8, is subsequently subjected to a drying step 104, in which any remaining water is completely or almost completely removed. However, if it is desired to apply a further coating layer, this drying step 104 is not yet performed, but instead, the resulting support structure 1, with the first coating layer 7 and second coating layer 8, is first subjected to a drying step, similar to drying 102, in which the remaining water is only partially removed, and subsequently, the resulting support structure 1 is flushed with a further diluted coating suspension.

[0041] In a final step 105 of the method shown, the resulting support structure 1 with coating layers, as obtained after the drying step 104, is subjected to a thermal treatment in order to sinter the coating. During this thermal treatment, the resulting support structure 1 is exposed to a temperature of preferably more than 400°C, and more preferably more than 500°C and in a most preferred embodiment a temperature of 550°C.

[0042] Figure 2 shows an enlarged section of the adsorption means, obtained by performing the method shown in Figure 1. The support structure 1 is a monolithic ceramic support structure with a cell density of 400 CPSI and a wall thickness of 6.5 mil. The cell walls define channels with a square cross-section. The first coating layer 7 and the second coating layer 8 are formed on the support structure 1. The channels, narrowed by the coating, have a circular cross-section. The formation of the coating layers according to the method shown is adjusted such that, after coating, a void space 9 in the coated support structure 1 is approximately 13 % of the void space 9 in the uncoated support structure 1, thus maximizing the amount of adsorbent 3 in the adsorption means. The void space 9 in the resulting coated support structure 1 is reduced to 9 %, which is substantially less than a void space of about 35 % - 45 %, typically obtained with known techniques.

[0043] The present invention is by no means limited to the embodiments described by way of example and shown in the figures, but a method according to the invention for producing adsorption means can be carried out in many different ways, without departing from the scope of the invention as defined in the claims.

Claims

Claims.1.- A method for manufacturing an adsorption means for treating a gas comprising flushing (101) a porous open support structure (1) with a first coating suspension (2), comprising a first solvent (4) and an adsorbent (3), under the influence of a first set pressure difference, to form a first coating layer (7), characterised in that the method comprises the steps of:- drying (102) the first coating layer such that the first solvent is partially removed,- diluting (106) the first coating suspension by adding a second solvent (5) to form a second coating suspension (6),- flushing (103) the porous support structure, provided with the first coating layer from which the first solvent has been partially removed, with the second coating suspension under the influence of a second set pressure difference, to form a second coating layer (8), wherein the second set pressure difference is greater than the first set pressure difference.2.- The method according to claim 1, characterised in that drying of the first coating layer (7) takes place at a temperature in the range of 50°C to 100°C, preferably at a temperature in the range of 60°C to 80°C, and more preferably at a temperature of 70°C.3.- The method according to any one of the preceding claims, characterised in that drying the first coating layer (7) is such that the solvent content present, in relation to the mass of the coated support structure, is reduced by a value in the range of 10 % to 60 %.4.- The method according to any one of the preceding claims, characterised in that the dilution of the first coating suspension (2) with the second solvent (5) is such that a ratio of the second solvent to the first coating suspension (6) in the second coating suspension has a value in the range of 1:100 to 1:1.5.- The method according to any one of the preceding claims, characterised in that the second coating suspension (6) is formed such that the adsorbent of the second coating suspension has a particle size that is smaller than the particle size of the adsorbent of the first coating suspension (2).6.- The method according to any one of the preceding claims, characterised in that flushing the porous support structure (1) with the first coating suspension (2) and flushing the porous support structure with the second coating suspension (6) takes place in opposite directions.7.- The method according to any one of the preceding claims, characterised in that the step of drying the first coating layer (7) is followed by cooling the porous support structure to a temperature in the range of 10°C to 50°C and keeping the cooled porous support structure shielded from the environment until flushing the porous support structure with the second coating suspension (6).8.- The method according to any one of the preceding claims, characterised in that the step of drying the first coating layer (7) takes place in ambient air with a relative humidity in the range of 1 % to 15 %.9.- The method according to any one of the preceding claims, characterised in that the second set pressure difference has a value in the range of 10 % to 40 % greater than the first set pressure difference.10.- The method according to any one of the preceding claims, characterized in that the first (4) and the second solvent (5) are the same.11.- The method according to any one of the preceding claims, characterised in that the adsorbent (3) comprises porous particles having a porosity value in the range of 10 % to60 %.12.- The method according to any one of the preceding claims, characterised in that themethod comprises the step of successively applying one or more further coating layers, the application of each further coating layer comprising the sub-steps of:- after applying a previous coating layer, drying the coated support structure in such a way that any solvent present is partially removed,- further diluting the first coating suspension (2) relative to the coating suspension applied to form the previous coating layer by adding a further solvent to form a further coating suspension,- flushing the porous coated support structure, from which the solvent present has been partially removed, with the further coating suspension under the influence of a further set pressure difference, to form a further coating layer, wherein the further set pressure difference is greater than a set pressure difference when applying the previous coating layer.13.- The method according to any one of the preceding claims, characterised in that the coating layers are applied such that a void space (9) in the coated support structure has a value in the range of 5 % to 60 %, compared to a void space in the uncoated support structure.14.- The method according to any one of the preceding claims, characterised in that the support structure is a ceramic structure, provided with channels whose cross-sections have a geometric shape.15.- An adsorption means, obtained by the method according to any one of the preceding claims.

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