WO2008072215A2

WO2008072215A2 - Separation column and pressure swing adsorption process for gas purification

Info

Publication number: WO2008072215A2
Application number: PCT/IB2007/055138
Authority: WO
Inventors: Carlos Adolfo Grande; Simone Cavenati; Alírio EGÍDIO RODRIGUES
Original assignee: Universidade Do Porto
Priority date: 2006-12-14
Filing date: 2007-12-14
Publication date: 2008-06-19
Also published as: PT103615A; PT103615B; WO2008072215A3

Abstract

The invention relates to new separation column and Pressure Swing Adsorption (PSA) processes for utilization in the purification of gas streams. Therefore, the present invention consists of a separation column comprising two layers of adsorbent material with different characteristics concerning their utility. Particularly, the first layer of adsorbent performs a kinetic separation while the second layer of adsorbent performs a separation by difference in adsorption equilibrium. This layer acts as a 'support barrier' to CO2. The PSA process performs separation cycles by using one or more of said separation columns, each cycle comprising five different steps. This process allows removing carbon dioxide (CO2) from a stream rich in methane (CH4), preferably to produce fuel-grade methane with some relevance for the chemical industries, fuel production, methane purification, its use as reagent in chemical industry and in the removal of carbon dioxide in pipeline transport.

Description

SEPARATION COLUMN AND PRESSURE SWING ADSORPTION PROCESS FOR GAS PURIFICATION

Technical field

[1] This invention relates to a new type of separation column and Pressure Swing Adsorption (PSA) processes as well as use thereof in gas purification.

[2] This process allows carbon dioxide (CO₂) removal from a methane-rich stream

(CH₄), preferentially to produce fuel-grade methane being its main application the purification of biogas and landfill gas for the production of fuel grade methane to be employed in vehicles, preferentially in public transportation. Other applications of this invention are the purification of methane for its utilization in the chemical industries and for the removal of carbon dioxide in the transportation of natural gas in pipelines.

Summary of the invention

[3] The present invention consists in obtaining a separation column with two layers of adsorbent materials with different properties. The first adsorbent layer comprises a material where a kinetic separation is performed, while the second adsorbent layer performs a separation based in the differences of adsorption capacities. This second layer acts as a 'support barrier' for CO₂.

The Pressure Swing Adsorption process operates cyclically with the utilization of one or more aforementioned separation columns. Each cycle of the PSA process is composed by five different steps. This process allows removing carbon dioxide (CO₂) from a stream rich in methane (CH₄), preferentially to produce fuel-grade methane. Applications of fuel-grade methane range from chemical industries, such as fuel production, methane purification for its use as chemical and for the removal of carbon dioxide for transport in pipelines.

Background Art

[4] There are many utilization sources of methane currently exploited, or may be exploited for the production of vehicle fuel. The present invention focuses on two methane-rich streams with high concentration in carbon dioxide deriving from landfill gas and biogas. This process can also be employed in natural gas streams contaminated with high amounts of CO₂.

[5] Natural gas exists underground and is frequently contaminated with CO₂. This gas should be purified to be employed as fuel or to be injected in a pipeline. The process described in this invention would be useful in the case of small and medium flowrates, since in high gas flowrates, CO₂ absorption in amines is more economically competitive (Appl et al, 1982).

[6] Biogas and landfill gas are gas mixtures generated by the anaerobic decomposition of organic matter. Normally the composition of biogas and landfill gas ranges from 70-30% of methane, 25-60% of carbon dioxide, hydrogen disulphide, and other contaminants and saturated with water vapor at ambient temperature. Biogas composition (specially the amount and quality of contaminants) strongly depends on the source and production conditions. Due to the high toxicity and fiammability and more recently to stringent control of greenhouse gas emissions, biogas and landfill gas streams cannot be directly emitted to the atmosphere without treatment. Most frequent solution is gas flaring. The first utilization of landfill gas, as well as biogas, was the production of heat for local and specific uses. This was followed by the production of electricity and exploitation of the heat (combined cycles). Presently, there are three different alternatives with proved economical interest: fuel production, chemical production and the most employed, which are the combined cycles of heat and energy. With the recent increase in the price of fuels, the production of methane as fuel is a solution with good economic perspective and also produces a fuel that has the same properties of a fossil fuel, with high performance and low CO₂ emission levels. The PSA process described in this invention is applicable to all the flowrates existent in biogas and landfill sources.

[7] To produce fuel grade methane from biogas it is necessary to remove contaminants

(mainly sulphurous compounds and water) and afterwards CO₂ (Knaebel e Reinhold, 2003). The process studied in this invention relies in the assumption that all other contaminants were removed and only focus in the binary separation CHVCO₂.

[8] The purification of landfill gas for its injection in pipelines is already employed in

United States of America. Purification of biogas for the production of fuels is already implemented in Sweden and France for fueling cars and buses. The production of fuel from biogas may help to accomplish existing European legislation 2003/30/EG where a low-limit share of 5.75% was established for bio-fuels for year 2010.

[9] There are different industrial processes to remove CO₂ from biogas streams. Many of the technologies applied to this mixture were imported from natural gas industries and adapted to lower pressures. The most employed technologies are absorption of CO 2 in water, absorption of CO₂ in amines, membranes and adsorption processes (Hagen et al., 2001). This invention deals specifically with a new configuration of adsorbents within the column(s) of a PSA unit, as well as a new step arrangement for the selective removal of CO₂.

[10] Previous studies in the separation of biogas streams with absorbents, based on the separation by kinetic differences (carbon molecular sieve 3K) showed that a purity of 98% can be obtained with recoveries of 60% of methane (Cavenati et al., 2005). The four-step cycle comprises pressurization, feed, counter-current blowdown and counter- current purge with product. The results obtained by process simulation were verified experimentally in a lab-scale PSA unit. Recent studies using a carbon molecular sieve (CMS 3A) showed that other research groups obtained similar results in this separation (Bae et al., 2006). Further studies in our research unit (Grande and Rodrigues, 2007) indicated that if we use the same adsorbent (CMS 3K) is possible to increase methane recovery to values higher than 80% (with purity of 98%) by modifying the PSA cycle. A new step was included, with a PSA cycle now comprising five steps: pressurization, feed, co-current depressurization to an intermediate pressure, counter-current blowdown and counter-current purge with product.

[11] It can also be found in literature patents where adsorbents with kinetic selectivity are employed in the selective removal of CO₂ for methane purification. Examples of these adsorbents are clinoptilolites (Seery, 1998), titanosilicates (Dolan and Mitariten, 2003), membranes of DDR zeolites (Fujita et al., 2006) and carbon molecular sieves (Masahiro and Kazuo, 1995).

[12] The main problem of PSA processes that use kinetic adsorbents (comprising the ones using carbon molecular sieves) is the low unit productivity. In the case of the adsorbent CMS 3K the productivity is around 3.5 mol CH₄ /hour .kg adsorbent. The low productivity of these PSA processes is due to the small utilization of the full capacity of the adsorbent (normally smaller than 50%) being the CO₂ concentration profiles very dispersed within each separation column. This means that the feed step should be stopped well before adsorbent saturation, to avoid contamination of the product with more than two or three percent of CO₂, depending on the desired methane specifications. Another problem of kinetic adsorbents in that in the purge step with methane, the adsorbed CO₂ cannot be displaced, reason why this step has low efficiency. Methane is not significantly adsorbed in the micropores of a kinetic adsorbent in the time of a PSA cycle.

[13] The first PSA units employed materials that adsorbed large amounts of CO2 and small amounts of CH₄ so the separation was performed by differences in the adsorption capacities. Examples of these materials are: activated carbon (Sircar et al., 1988; Davis, et al., 1992; Sircar, 1986), zeolite 13X (Sircar, et al., 1988), silica gel (Dolan e Mitariten, 2003) and organometallic frameworks (Mϋller et al., 2005).

[14] For comparison purposes in our research unit we have studied the separation of CH

4/CO₂ separation using an adsorbent with high equilibrium selectivity towards CO₂: zeolite 13X (Grande and Rodrigues, 2007). The process simulations were performed based on pure gas adsorption data and with a mathematical model already tested for the separation of these gases (Cavenati et al., 2006).

[15] For this particular case, the total productivity of the PSA unit was 2 mol CH₄ /hour, kg adsorbent. The low productivity is caused by the small utilization of the total capacity of the adsorbent due to the difficult desorption of CO₂ and also by the large amount of methane retained by the zeolite in the pressurization step.

[16] There are also some examples in literature dealing with PSA units comprising several layers of adsorbents, also employed in the separation of different gas mixtures. Applications of PSA with columns using adsorbents arranged in layers were observed for hydrogen purification from off-gases of steam methane reforming (Golden e Weist, 2004), water and CO2 removal from a gas stream (Deng et al, 2001; Little and Spektor, 2005). In all these references, each layer of adsorbent is placed to remove one or more specific compounds from a multicomponent gas mixture. Another PSA process with different layers of different adsorbents may be the removal of water vapor from air or natural gas streams or the N2/O2 separation (Lu, et al., 2003). In this example, different layers of adsorbents were employed with the objective of removing water from a gas stream, considering that this arrangement may improve the overall productivity of the process. In the example of water removal, the layers are placed according to an adequate combination of adsorption properties: firstly, a layer of activated carbon with large capacity for high relative humidities, followed by a second layer of silica gel to remove other large amount of water until concentrations smaller than 1% and finally a layer of zeolite to remove water to a few parts per million (ppm). In this example, all the materials adsorb water strongly and the process is controlled by adsorption equilibrium of this gas in the different materials.

[17] In some of the processes mentioned above, the arrangement of several adsorbent layers has the objective to selectively remove individual components (one adsorbent per contaminant).

[18] Another application of different layers of adsorbents within a separation column for the removal of a single contaminant gas uses a first adsorbent with higher adsorption capacity followed by an adsorbent with smaller capacity, preferentially without kinetic limitations.

[19] The main difference of this invention to previously known processes is the existence of two different adsorbents and its innovative arrangement: a first adsorbent with smaller effective capacity (either by real smaller capacity or by the existence of kinetic limitations), followed by a second adsorbent with higher effective capacity and with a microporous structure that allows fast diffusion of all components, acting as an additional barrier for CO2.

[20] As a consequence, a PSA process using this layered column is more effective and has higher productivity.

General Description of the Invention

[21] The objective of this invention is to improve the performance and productivity of

Pressure Swing Adsorption (PSA) units employing kinetic adsorbents. The increase of productivity of these units allows reducing installation and operation costs.

[22] This invention may be employed in binary gas separations where there exists a single contaminant gas and a single product gas. The separation should be performed by Pressure Swing Adsorption processes. Specifically, we discuss the application of this process to streams with methane and carbon dioxide (CH₄ - CO₂). This mixture is found in natural gas streams and biogas streams, where landfill gas can be included. The product (CH₄) can be employed as fuel (high-purity methane), but the process may also be employed for other uses. This process is to be applied to remove amounts of carbon dioxide between 5 and 85%, preferentially between 30 and 45%. The process operates between -1O⁰C and 100 ⁰C, preferentially between 25⁰C and 55⁰C. The Pressure Swing Adsorption process presented herein consists of one or several columns arranged to operate continuously or discontinuously. Discontinuous operations are characterized for the existence of buffer tanks coupled to the PSA system.

[23] The adsorbent materials inside the columns are arranged in two separate layers: a first layer of adsorbent with kinetic selectivity to the contaminant gas, preferentially where the product gas has very slow diffusion kinetics. The second layer is composed by an adsorbent material where the separation is performed by differences in equilibrium capacities, where the contaminant gas is more adsorbed than the product gas. The gas employed in the feeding step should be the first to be in contact with the gas meant to be purified.

[24] The novelty of this invention is the arrangement of the two layers of adsorbents within the same column in a Pressure Swing Adsorption process with a single or multiple columns for the removal of a contaminant (CO₂) from a product gas (CH₄). The layer arrangement proposed in this invention allows performing the separation of CO₂ with the efficiency of a kinetic process but enhancing the overall productivity of the process due to an 'support barrier' of a material with higher adsorption capacity only at the end of the column. Within the field of the invention, the major novelty is the arrangement, non-conventional of an adsorbent with smaller capacity and performing a kinetic separation, followed by an adsorbent performing the separation by differences in the adsorption equilibrium of the species.

[25] The first layer that contains the first adsorbent should make the bulk removal of

CO₂ from the gas mixture. Examples of kinetic adsorbents that may be applied in this layer are all the materials having micropores of approximately 4 angstroms: carbon molecular sieves, natural zeolites and zeolite 4A, deca-dodecasil zeolite 3R DDR, zeolites ITQ, clinoptilolites and titanosilicates. In this category are also included other zeolites chemically or physically modified to adjust the micropores to a value close to 4 angstroms.

[26] The second layer where the second adsorbent is placed will be employed to remove smaller amounts of CO₂ using less amount of adsorbent. The use of this second layer acts as a 'support barrier for CO₂' and constitutes the main modification in the PSA process. With the use of this additional second layer, the CO₂ takes more time to breakthrough and thus the feed step may purify a larger amount of mixture per cycle, increasing the productivity of the unit.

[27] The adsorbent to be employed in the second layer should be a material that may adsorb more CO₂ than CH₄, that is, a material where the separation is by the difference in the adsorption equilibrium of the two gases. Preferentially, the adsorbents to be employed should allow a fast diffusion of both gases. These materials are the inorganic materials with high surface area with micropores larger than 6 angstroms. Examples of these materials are: zeolite 13X, zeolite Y, mordenites, activated carbon, aluminas, silica gel and other silica-matrix mesoporous materials. It should also be included in this group high-surface are activated carbons and chemically-modified activated carbons to enhance CO₂ selectivity or capacity.

[28] Each adsorption column operates cyclically and goes through five different steps before finishing a cycle. These steps are: a) feeding at high pressure with the gas mixture to be separated; b) depressurization to an intermediate pressure; c) counter- current blowdown; d) counter-current purge with product and e) counter-current pres- surization with product.

1. Feed: the mixture is introduced to the bottom of the column. The CO₂ is selectively adsorbed in the column and methane is being collected in the top of the column at high pressure. This step ends before the CO₂ exits the column with a concentration higher than specifications to obtain fuel grade methane;

Intermediate depressurization: without feeding, the column is depressurized until a pressure lower than used in the feeding step. The objective of the step is to reduce the amount of methane in the gas phase, enhancing its recovery. This methane may be recompressed or employed to pressurize another/other column(s) or eventually in the purge step. The diffusion of CO₂ retained in the kinetic adsorbent is slow reason why in this step CO₂ only starts to desorb but not in massive amounts. This step should be fast;

Counter-current blowdown: the top of the column is closed and then the column is depressurized. The lowest pressure of the system is achieved in this step. This pressure may be lower than atmospheric pressure if the adsorbent should be regenerated under these conditions. Some methane is lost in this step that should be burned before being emitted into the atmosphere;

4. Counter-current purge with product: a portion of the product or of the outlet from the depressurization step is introduced by the top of the column. This step and the blowdown steps produce a secondary stream that may be employed in energy production. In this step the pressure is also the lowest pressure of the process and the objective of the step is to help in the regeneration of the adsorbent by displacing the CO₂ from the top of the column; 5. Pressurization: With part of the product and the gas coming from the depres- surization, the pressure of the column is increased from the lowest pressure of the system to the maximum pressure. Once this value is achieved, the feeding step may be again performed, starting a new cycle.

Breef Description of the Drawings

[29] Figure 1 shows the layered arrangement of adsorbents within a separation column in a LPSA (Layered Pressure Swing Adsorption) process wherein:

(1) Represents the product - purified CH₄;

(2) Represents the layer of adsorbent acting by differences in the adsorption equilibrium of the species;

(3) Represents the layer of adsorbent acting by differences in the adsorption kinetics of the species;

(4) Represents the column feed: mixture CH₄ - CO2

Detailed Description of the Invention

[30] 1. Preparation of the separation columns

To separate carbon dioxide from methane-rich streams it is firstly necessary to obtain the separation column with two different layers of adsorbents to be used in the process.

The first layer should contain kinetic adsorbents, which are the first to be in contact with the CO₂. Examples of these adsorbents are clinoptilolites, deca-dodecasil 3R DDR zeolites, titanosilicates, carbon molecular sieves and zeolites LTA modified with Li and K.

The second layer of adsorbent should contain an adsorbent with a high capacity to adsorb CO₂, being preferably that diffusion of both methane and carbon dioxide is fast. Examples of these adsorbents are zeolite 13X, zeolite Y, activated carbon, alumina, silica gel and other mesoporous materials with silica matrix.

The amount of material used in each layer is directly related to the desired specifications of the product and the feed inlet conditions. Normally, the second layer of adsorbent occupies between 5 and 50% of the total volume of the column. [31] 2. Description of the separation process

The separation process includes five steps per cycle. These steps are: a) feeding at high pressure with the gas mixture to be separated; b) depressurizing to an intermediate pressure; c) counter-current blowdown; d) counter-current purge with product and e) counter-current pressurization with product.

a) Feeding: the gas mixture is introduced in the lower part of the column. The CO₂ is selectively adsorbed in the column and methane is withdrawn from the upper part of the column at high pressure. This step is operated at pressures between 200 and 1500 kPa, preferentially between 400 and 800 kPa. This step ends before the CO₂ exits the column with a concentration higher than specifications to obtain fuel-grade methane;

b) Intermediate depressurization: without feeding, the column is depressurized until a pressure lower than used in the feed step. The objective of the step is to reduce the amount of methane in the gas phase, enhancing its recovery. This methane may be re- compressed or employed to pressurize another/other column(s) or eventually in the purge step. This step should be fast.

c) Counter-current blowdown: the outlet of the column is closed and then the column is connected to a line comprising lower pressure. The lowest pressure of the system is achieved in this step. This pressure may be lower than the atmospheric pressure if the adsorbent should be regenerated under these conditions. Some methane is lost in this step that should be burned before being emitted to atmosphere.

d) Counter-current purge with product: a portion of the product or outlet from the depressurization step is introduced in the upper end of the column. This step and the blowdown steps produce a secondary stream that may be employed in energy production. In this step the pressure is also the lowest pressure of the process.

e) Pressurization: With part of the product or part of the gas coming from the depressurization, the pressure of the column is increased from the lowest pressure to the maximum pressure.

Once this value is achieved, the feed step may be again performed, starting a new cycle.

The cycle described should employ the column described in this invention to remove one specific compound (CO₂) and then regenerate the column to be employed in a cyclic fashion. This process is employed to process gas mixtures in temperatures between 2O⁰C and 7O⁰C and total pressures between 250 and 2000 kPa. When the process is continuously operated, a cyclic steady state is reached where the desired performance objectives should be reached. A PSA process comprising one or more than one column may employ these cycles. In a multi-column array, the depressurization step may be employed to equalize the pressure of another column to reduce the energy consumption of the unit.

Examples

[32] EXAMPLE 1: Separation Of CH₄-CO₂ mixtures with carbon molecular sieve CMS 3K.

The initial study Of CH₄-CO₂ separation was performed with a kinetic adsorbent CMS 3K where the diffusion of CH₄ is very slow. We have simulated a PSA process with five steps (feeding, intermediate depressurization, counter-current blowdown, counter- current purge with product and counter-current pressurization). The flowrate to be treated is in the order of 1000 NmVh (at 298K and 101.3 kPa) with a CH₄ content of 55% balanced by CO₂. To treat this stream, a two-column PSA unit was employed, with columns of 4.667m length and 0.4667m radius and a porosity of 0.33. The feeding step was performed at total pressures between 600 and 800 kPa and blowdown and purge at 10 kPa. Several simulations were performed with different intermediate pressures. The results obtained can be observed in Table 1.

[33] Table 1. Simulation results of a PSA process using a kinetic adsorbent CMS 3K. ^*

Pressurization step: 70s; purge step: 50s.

The objective of this example is to be the base reference case obtained with a kinetic adsorbent.

[34] EXAMPLE 2: Separation of CH₄-CO₂ mixtures with LPSA: CMS 3K followed by zeolite 13X.

In this example a kinetic adsorbent CMS 3K was used followed by zeolite 13X, known by its high capacity to adsorb CO₂. For a straight comparison of the results we have employed the same PSA unit with two columns of 4.667m length and 0.4667m radius. The process also includes five different steps (feeding, intermediate depressurization, counter-current blowdown, counter-current purge with product and counter-current pressurization). The feeding pressure was always 800 kPa and blowdown pressure was 10 kPa. The adsorbents were placed in the column to ensure that the first adsorbent to be in contact with the gas mixture is CMS 3K followed by the layer of zeolite 13X. The results of the different simulations are reported in Table 2. The objective is to place an adsorbent with a high capacity to remove CO₂ at the end of the column that can also be purged using methane (effectiveness of purge in the CMS 3K adsorbent is low because of the slow diffusion of methane in the micropores of the adsorbent). With this arrangement a better utilization of the CMS 3K was obtained considering that the layer of zeolite 13X acts as an 'additional barrier' to CO₂. In these simulations we can confirm that the productivity of the LPSA process is much higher than the process employing only the kinetic adsorbent.

[35] Table 2. Simulation results of a LPSA process using kinetic adsorbent CMS 3K followed by an adsorbent with separation by adsorption equilibrium (zeolite 13X). ^*

^* Pressurization step: 70s; purge step: 50s. ^a Purge flowrate: 5000 SLPM.

b Pressurization flowrate: 10000 SLPM.

c Feed flowrate: 22000 SLPM. Pressurization flowrate: 16000 SLPM.

d Pressurization flowrate: 16000 SLPM. [36] REFERENCES

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Claims

[1] Separation column for gas purification characterized in that its constitution includes two different layers of adsorbent materials, with different selectivities to the contaminant gas and the product gas, the first layer being constituted by an adsorbent material with kinetic selectivity to the contaminant gas and with slow diffusion kinetics of the product gas, the second layer of adsorbent being constituted by a material with selectivity by differences in the adsorption equilibrium, adsorbing more contaminant gas than product, this second layer acting as a support barrier to the breakthrough of contaminant gas at the end of the column.

[2] Separation column for gas purification, according to claim 1 , characterized in that the first layer consists of microporous adsorbent materials with micropores around 4#, such as, althought in a non-limitative example, molecular sieves, natural zeolites and zeolite 4A, zeolites LTA modified with Li and K, DDR zeolites, ITQ zeolites, clinoptilolites and ti- tanosilicates.

[3] Separation column for gas purification, according to claim 1 , characterized in that the second layer is made of microporous adsorbent material, preferentially with large surface area based on inorganic materials with micropores larger than 6 #, such as, although in a non-limitative example, zeolite 13X, zeolite Y, mordenites, activated carbon, aluminas, silica gel and other porous materials of silica matrix and surface-modified activated carbons.

[4] Pressure Swing Adsorption process for gas purification comprising continuous and individual cycles, each including five steps from claims 1 to 3, consisting of two layers of absorbent material with different selectivities for the contaminant gas and product gas, the second layer forming a support barrier for the contaminant gas, in one end of the column.

[5] Pressure Swing Adsorption process for gas purification according to the preceding claim, characterized in that each cycle occurs in five steps comprising: a) Feeding at least one column including two layers of adsorbent at high pressure and using the mixture to be separated; b) Depressurization of the mixture up to an intermediate pressure in a value ranging between 20 and 600 kPa; c) Counter-current blowdown; d) Counter-current purge with product, and e) Counter-current pressurization with product ranging between 200 to 15000 kPa, preferentially between 400 and 800 kPa.

[6] Pressure swing adsorption process for gas purification according to the preceding claim, characterized in that the feeding pressure ranges between 200 and 1500 kPa, preferentially between 400 and 800 kPa.

[7] Pressure swing adsorption process for gas purification according to claim 5 characterized in that the intermediate depressurization step occurs rapidly, up to a pressure level lower than the feeding pressure.

[8] Pressure swing adsorption process for gas purification according to claim

5, characterized in that a counter-current blowdown is obtained by closing the outlet of the column and connecting the bottom of the column to a line with lower pressure.

[9] Pressure swing adsorption process for gas purification according to the preceding claim characterized in that the column is connected to a low pressure line with lower pressure, this pressure being lower than the atmospheric pressure, should the adsorbent be regenerated.

[10] Pressure swing adsorption process for gas purification according to claim 5 characterized in that the counter-current purge is performed by total or partial introduction of the product, being performed at the lower pressure of the system, i.e. in a pressure range between 1 and 200 kPa of total pressure.

[11] Pressure swing adsorption process for gas purification according to claim 5 characterized in that the pressurization step is performed with the entire or a partial portion of the product stream and gas from the intermediate depressurization step, the pressure of the column being raised from the minimum pressure to the maximum pressure, i.e. from (between 1 and 200 kPa) to (between 250 to 2000 kPa of total pressure).

[12] Pressure swing adsorption process for gas purification according to claims

4 to 11 comprising a continuous operation with an array of multiple separation columns starting a new cycle when the maximum pressure is achieved according to the previous claim.

[13] Utilization of the separation column according to claims 1 to 3, characterized in that it is applicable to gas purification, by means of removing to CO₂ from a CH₄-rich gas stream.

[14] Utilization of the Pressure Swing Adsorption process for gas purification according to claims 4 to 12 characterized in that it is applicable in the removal of CO₂ from CH₄-CO₂ mixtures in natural gas, biogas and landfill gas streams.

[15] Utilization of the pressure swing adsorption process for gas purification according to the preceding claim characterized in that it is applicable in the removal of CO₂ from CH₄-CO₂ streams whose CO₂ molar fraction may vary from 0.15 to 0.85, preferentially between 0.45 and 0.55.