PT103615A - SEPARATION COLUMN AND ADSORPTION PROCESS WITH PRESSURE MODULATION FOR GAS PURIFICATION - Google Patents

Abstract

This invention relates to a novel type of separation column and ADSORPTION PROCESSES OF THE ADSORPTION TYPE WITH PRESSURE SWING ADSORPTION, AS WELL AS ITS USE FOR THE PURIFICATION OF GASES, SO, THE PRESENT INVENTION CONSISTS OF OBTAINING OF A SEPARATION COLUMN WITH TWO LAYERS OF ADSORVENT MATERIAL BEING CONSTITUTED BY MATERIAL WITH DIFFERENT CHARACTERISTICS WITH REGARD TO ITS FUNCTIONS. IN PARTICULAR THE FIRST LAYER MAKES A KINETIC SEPARATION, WHILE THE SECOND LAYER MAKES A SEPARATION BY BALANCE DIFFERENCE OF BACKGROUND OF THE INVENTION The process of adsorption with pressure modulation consists in performing separation cycles with the use of one or a plurality of said separation columns mentioned above, each being constituted by said one of said cyclic seals OF SEPARATION FOR FIVE STEPS. THIS PROCESS ALLOWS TO REMOVE CARBON DIOXIDE (CO 2) A METHANE (CH4) RICH CHAIN, PREFERENTIALLY FOR PRODUCING METHANE WITH HIGH FUELS WITH VARIOUS INDUSTRIAL APPLICATIONS FROM THE CHEMICAL INDUSTRY OF GASES, AS FOR THE OBTAINMENT OF FUELS, PURIFICATION OF METHANE FOR USE AS A REAGENT IN THE CHEMICAL INDUSTRY AND FOR REMOVAL OF CARBON DIOCIDE IN THE TRANSPORTATION OF NATURAL GAS IN GAS PIPES.

Description

1

DESCRIPTION OF THE SEPARATION COLUMN AND ADSORPTION PROCESS WITH GAS PURIFICATION PRESSURE MODULATION "

Technical field of the invention

This invention relates to a novel type of separation column and adsorption processes of the Pressure Swing Adsorption type, as well as their use for the purification of gases.

This process allows the removal of carbon dioxide (CO2) from a methane-rich (CH4) stream, preferably to produce methane with a fuel grade, and its main application is the purification of biogas and landfill gas streams for the production of methane with fuel grade for be used in cars, preferably on public transport. Other applications of this invention are the purification of methane for use as a reagent in the chemical industry and for the removal of carbon dioxide in the transport of natural gas in pipelines.

SUMMARY OF THE INVENTION The present invention consists in obtaining a separating column with two layers of adsorbent material, with distinct characteristics, the first layer being made up of microporous material, with pores having a size between 4A and 5,5A and having separation functions while the second layer consists of microporous materials, preferably based on inorganic materials of high surface area, with micropores having a size greater than 6A, separating by adsorption equilibrium difference. This layer acts as a " containment barrier " for C02. The pressure modulation adsorption process consists in performing separation cycles using one or more of the above-mentioned separation columns, each of these five-step separation cycles being constituted. This process allows the removal of carbon dioxide (CO2) from a methane-rich (CH4) stream, preferably to produce fuel grade methane with various industrial applications from the chemical gas industry, such as for fuels, methane purification for use as a reagent in the chemical industry and for the removal of carbon dioxide in the transport of natural gas in pipelines.

Background of the Invention

There are different sources of methane use that are currently being or may be harnessed to obtain fuel for cars. Namely, in this invention two streams rich in methane with high concentrations of carbon dioxide from landfill gas and biogas are contemplated. This process can also be applied in streams of natural gas contaminated with large amounts of CO 2. Natural gas exists underground and is often contaminated with CO 2. This gas must be purified to be used as fuel or to be injected into a pipeline. The process described in this invention would be useful in cases of small or medium flow rates since for high gas flows the absorption processes with 3 amines are more economically competitive (Appl et al., 1982). Biogas and landfill gas are gaseous mixtures that come from the anaerobic decomposition of organic matter. Typically the composition of landfill gas and biogas is 70-30% methane, 25-60% carbon dioxide, hydrogen sulfide and other contaminants and is further saturated with room temperature steam. The composition of biogas (mainly the quantity and quality of contaminants) varies according to the source and the biogas production conditions. Due to the high degree of toxicity and flammability, and more recently the control of greenhouse gas emissions, landfill gas and biogas can not be emitted directly into the atmosphere. The most frequent solution is its flaring. The first use of landfill gas, as well as biogas, was the use of the heat of burning for local and occasional uses. Then followed the production of electric power and use of heat (combined cycles). Currently there are three different alternatives with proven economic interest: fuel production, chemical generation and the most used are still the combined cycles of heat and energy production. With the recent rise in fuel prices, methane as fuel becomes a highly profitable option, and it produces fossil-fuel fuel with high yields and lower CO2 emissions. The PSA process described in this invention is applicable to the flows existing in all sources of biogas and landfill gas. 4

To produce fuel grade methane from biogas it is necessary to remove the contaminants (mainly sulfur compounds and water), and then CO 2 (Knaebel and Reinhold, 2003). The process to be studied in this work is based on the hypothesis that all the contaminants were removed and focused on the CH4 / CO2 binary separation. Landfill gas purification for pipeline injection is already used in the United States of America. Biogas purification for fuel production is already used in Sweden and France for bus and coach fuel. The production of fuel from biogas can help to comply with the European Commission's 2003/30 / EG measure where a value of 5.75% of biofuels was established for the year 2010.

There are different industrial processes to remove CO2 from biogas streams. Many of the technologies applicable to this blend were imported from the natural gas industry and adapted to lower pressures. The most commonly used technologies are the absorption of CO2 in water, absorption of CO2 in amines, membranes and adsorption processes (Hagen et al., 2001). This invention specifically addresses a novel configuration of adsorbents within the PSA unit column (s) as well as a novel step configuration for selective CO2 removal.

A previous study in the separation of biogas using a differential adsorbent by difference in the adsorption kinetics (CK 3K carbon molecular sieve) indicated that with a four-step cycle a purity greater than 98% can be obtained (Cavenati et al. 2005) with recoveries of methane of 60%. The four-step cycle consisted of pressurizing, feeding, counter-current evacuation and back-flow with countercurrent and the results obtained by simulation were confirmed with experimental data in a laboratory unit. Recent studies using a carbon molecular sieve (CMS 3A) show that other research groups have obtained similar results in this separation (Bae et al., 2006). Further studies in our laboratory (results not yet published) indicated that if we use the same adsorbent (CMS 3K) it is possible to increase methane recovery to values of 80% (with 98% purity) by modifying the PSA cycle. A new step in the cycle was included, and a five step cycle consisting of: pressurizing, feeding, co-current depressurising to an intermediate pressure, counter-current evacuation and back-flow product purging.

Patent documents using adsorbents with high kinetic selectivity in the removal of CO2 for methane purification can also be found in the literature. Examples of these adsorbents are clinoptilolites (Seery, 1998), titanosilicates (Dolan and Mitariten, 2003) DDR-type zeolites in membranes (Fujita et al., 2006) and carbon molecular sieves (Masahiro and Kazuo, 1995). The main problem of PSA processes using kinetic adsorbents (among them carbon molecular sieves) is the low productivity. In the case of the adsorbent CMS 3K the productivity is around the 3.5 mol CH4 / hour.kg adsorbent. The low productivity of these PSA processes is due to the low utilization of the total capacity of the adsorbent (usually less than 50%) and the CO2 concentration profiles are very dispersed within each column forcing the feed to be interrupted long before the saturation of the adsorbent to avoid contamination of the product with concentrations greater than two or three percent depending on the intended methane specifications. Another problem of the kinetic adsorbents is that in the purge stage with methane the adsorbed CO2 can not be displaced, reason why this stage is little effective. Methane is not significantly adsorbed on the micropores of the kinetic adsorbents at the time of a PSA cycle.

The first PSA units used materials that adsorbed large quantities of CO2 and little CH4 and so the separation was made by difference in the adsorption equilibria. Examples of these adsorbents are: activated charcoal (Sircar et al., 1988; Davis, et al., 1992; Sircar, 1986), 13X zeolite (Sircar, et al., 1988), silica gel (Dolan and Mitariten, 2003) and organo-metallic compounds (Muller et al., 2005).

For the purpose of comparison, in our laboratory studies of this separation with an adsorbent with high selectivity of adsorption equilibrium of CO2: 13X zeolite were carried out. These studies were carried out with adsorption data of the pure compounds and with a mathematical model already proven for the separation of these gases (Cavenati et al., 2006).

For this particular case, the total productivity of the PSA unit was around 2 mol CH4 / hour.kg adsorbent. The low productivity is caused by the low utilization of the total capacity of the adsorbent due to the great difficulties of desorption of CO 2 and the large amount of methane retained by the zeolite in the pressurizing step. 7

There are also in the literature examples of PSA units composed of different layers of adsorbents, namely for the separation of different gas mixtures. The adsorption of the adsorbents to the adsorbents was carried out in the following manner: (a) the adsorbents of the adsorbents were adsorbed onto the adsorbent, and (b) . In all of the mentioned references, each of the different layers of adsorbent is intended to remove a specific component of a mixed gas mixture. Another type of PSA process with different layers of different adsorbents may be the separation of water from a stream of air or natural gas or N2 / 02 (Lu, et al., 2003). In this example, layers of different adsorbents are used for the sole purpose of removing water from a gaseous stream, and this type of configuration increases the productivity of the process. In the example of water withdrawal, the layers are distributed according to a suitable combination of adsorption properties: first a layer of activated carbon of high capacity at high relative humidities, then a layer of silica gel to remove another large part to lower concentrations to 1% and finally a layer of zeolite to eliminate the water content to a few parts per million (ppm). In this example, all adsorbents strongly adsorb water and the process is controlled by the adsorption equilibrium of this compound in the different materials.

In the foregoing processes the layered adsorbent arrangement had as its objective the selective removal of several components individually (an adsorbent to remove each contaminant). 8

Another application, with the provision of adsorbents in layers for removal of a single contaminant gas, uses a first adsorbent with higher adsorption capacity followed by a lower capacity adsorbent, preferably with no kinetic limitations. The main difference of the present invention with respect to the already known and mentioned processes consists in the existence of two different types of adsorbents together and their innovative arrangement: a first adsorbent, with a lower effective adsorption capacity (either due to lower capacity or diffusion limitations ), followed by another adsorbent, with greater effective capacity and microporous structure, allowing a rapid diffusion of all the components, acting as a containment barrier.

Concurrently, the PSA process when using this type of column, proves to be more effective and productive.

General Description of the Invention The object of the present invention is to improve the performance and productivity of pressure swap adsorption units (PSA) using kinetic adsorbents. Increasing productivity of these units helps reduce installation and operating costs.

This invention can be applied to binary separations where there is a single contaminant gas and a single product gas, carried out by a pressure modulation adsorption process. Specifically, we will discuss the application of this process to CH 4 --CO 2 currents. This mixture is found in natural gas streams and biogas streams, including landfill gas. The product obtained can be used as fuel (high purity methane), but the process can also be used in other applications. This process will be used to remove CO2 contents between 5% to 85% and preferably between 30% and 45%. The process operates between -10 ° C and 100 ° C, but preferably between 25 ° C and 55 ° C. The pressure modulation adsorption process shown here comprises one or more columns arranged to provide continuous or discontinuous operation. Discontinuous operations are characterized by the existence of buffer stabilizer tanks coupled to the PSA system.

The adsorbent materials within the columns are arranged in two layers: a first adsorbent layer with kinetic selectivity for the contaminating gas preferably where the product gas has a very slow adsorption kinetics and a second layer of adsorbent material with selectivity by equilibrium difference adsorption where the contaminating gas is more adsorbed than the product gas. The first layer of adsorbent must be the first to come into contact with the gas to be purified. The novelty of this invention resides in the arrangement of two layers of adsorbent within the same column in a pressure column adsorption adsorption process of a single column or multiple columns for removal of a CO 2 gas from a product gas (CH 4). The layered arrangement proposed in this invention enables the separation of CO2 with the efficiency of a kinetic separation but increases the productivity of the process due to the existence of a " containment layer " of a material of greater 10 capacity existing only at the end of the column. Within the field of invention, the novelty is the unconventional arrangement of an adsorbent of lower capacity and which acts by kinetic separation followed by a higher capacity adsorbent which acts by separation by difference in the adsorption equilibria. The first layer containing the first adsorbent is to remove large amounts of CO2 from the blend. Examples of kinetic adsorbents that can be applied to this layer are all materials having approximately 4 angstroms micropores: carbon molecular sieves, natural zeolites and zeolite 4A, deca-dodecasil 3R DDR zeolites, ITQ zeolites

Chemistry), clinoptilolites and titanosilicates. Also included in this qualification are other chemically or physically modified zeolites to adjust the micropores to a value close to 4 angstroms. The second layer containing the second adsorbent will be used to remove smaller amounts of CO 2 using much less amount of adsorbent. The inclusion of this adsorbent layer functions as " C02 containment barrier " and is the main modification to the PES process. This allows C02 to take longer to quit and therefore the feed step can purify more mixing, increasing unit productivity. The adsorbent to be used in the second layer should be a material that can adsorb much more C02 than CH4, i.e., materials where the separation is by differences in the adsorption equilibria of the gases. Preferably adsorbents should be used where the diffusivity of both gases is rapid. These materials are usually all high surface area inorganic materials with micropores larger than 6 angstroms. Examples of these materials are: 13X zeolite and zeolite Y, mordenites, activated carbon, aluminas, silica gel and other mesoporous silica matrix materials. Examples of high surface area activated carbons and activated carbons with surface modifications may be used to increase the C02 adsorption capacity.

Each column goes through five steps before completing a cycle. These steps are a) high pressure feed with the gas to be separated; b) depressurising to an intermediate pressure; c) countercurrent evacuation; d) countercurrent product purging and e) pressurizing with countercurrent product. 1) Feeding: The gas mixture is fed from the lower part of the column with C02 retained and methane withdrawn from the top at high pressure. This step ends before C02 exiting the top of the column reaches a concentration higher than that specified to obtain methane grade fuel. 2) Intermediate depressurising: Without feed, the column is depressurised to a pressure lower than that used in the feed, preferably to an intermediate pressure in the range of 20 to 600 kPa. It is intended to decrease the amount of methane retained in the gas phase and thus increase its recovery. This methane may be recompressed or used to pressurize another column (s) or optionally in the bleed stage. The diffusivity of C02 adsorbed on the kinetic adsorbent is slow and therefore only begins to desorb but not in large quantities. This step should be rapid. 3) Countercurrent Evacuation: The outlet of the column is closed and then the column is connected to a line with less pressure. The minimum system pressure is reached in the evacuation, preferably in a range between 100 and 1 kPa of total pressure. This pressure may be lower than atmospheric pressure if the adsorbent is regenerable under these conditions only. At this stage some methane is lost which must be burned before being emitted into the atmosphere. 4) Countercurrent product purge: a part of the product or the outlet of the depressurising step is introduced into the column at the top and the outlet is, along with the exit from the evacuation step, a secondary process stream that can be used to obtain power. In this step the pressure is also the minimum pressure of the system, preferably in a range between 200 and 1 kPa of total pressure in the column, the purpose of this step being to displace the existing CO2 at the end of the column in order to give greater use to the bed in step feed. 5) Pressurizing: With part of the product and the gas coming from the depressurising step, the column pressure is increased from the minimum pressure to the maximum pressure, between 1 and 200 kPa at 250 and 2000 kPa of total pressure, preferably between 200 and 1500 kPa, and more preferably between 400 and 800 kPa. Once this pressure value is reached, you can begin the feeding step and restart a new cycle.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the layered arrangement of a LPSA (Layered Pressure Swing Adsorption) column wherein: (1) represents the purified-CH4 product; (2) represents the separation adsorbent layer by differences in adsorption equilibria; (3) represents the separation adsorbent layer by differences in adsorption kinetics; (4) represents the column feed: CH4 -CO2

Detailed Description of the Invention 1. Preparation of the separation columns

In order to obtain the separation of carbon dioxide from methane-rich streams it is first necessary to obtain a column with the two layers of adsorbents to be used in the process. The first layer should contain kinetic adsorbents which are the first to come into contact with CO2. Examples of these adsorbents are clinoptilolites, zeolites type deca-dodecasil 3R DDR, titanosilicates, molecular sieves of carbon and LTA-type zeolites modified with Li and K. The second layer should contain an adsorbent with great capacity to retain C02 being that it is desirable that the diffusion of both gases is fast. Examples of these adsorbents are 13X zeolite and zeolite Y, activated charcoal, 14 aluminas, silica gel and other mesoporous silica matrix materials. The amount of material used in each of the layers is directly related to the specifications desired in the product. Usually the second layer of adsorbent occupies between 5 and 50% of the total volume of the column. 2. Development of the separation process The separation process takes place in five-step cycles, each. Each of these steps involves the following steps: a) high pressure feed with the gas to be separated; b) depressurising to an intermediate pressure; c) countercurrent evacuation; d) countercurrent product purging and e) pressurizing with countercurrent product. a) Feeding: the gas mixture is fed from the bottom of the column with the CO2 being retained and the methane withdrawn from the top at high pressure. This step is operated at high pressures between 200 and 1500 kPa, preferably between 400 and 800 kPa. This step ends before the C02 leaving the top of the column reaches a concentration higher than that specified to obtain methane grade fuel; b) Intermediate depressurising: without feed, the column is depressurised to a pressure lower than that used in the feed. It is intended to decrease the amount of methane retained in the gas phase and thus increase its recovery. This methane may be recompressed or used to pressurize another column (s) or optionally in the purge step. This step should be rapid; c) Countercurrent Evacuation: the outlet of the column is closed and then the column is connected to a line with lower pressure. The minimum system pressure is reached in the evacuation. This pressure may be lower than atmospheric pressure if the adsorbent is regenerable and only under such conditions. At this stage some methane is lost which must be burned before being emitted into the atmosphere. d) Purge with countercurrent product: a part of the product or the outlet of the depressurising step is introduced into the column at the top and the outlet is, together with the outlet of the evacuation step, a secondary stream of the process that can be used to obtain power. In this step the pressure is also the minimum pressure of the system. e) Pressurizing: with part of the product and the gas coming from the depressurising step, the column pressure is increased from the minimum pressure to the maximum pressure.

Once this pressure value is reached, you can begin the feeding step and restart a new cycle.

This cycle aims to use the column described in this invention to remove a specific component (CO2) and then regenerate said column for reuse. This process is used to process gas mixtures at temperatures between 20 and 70 ° C and total pressures between 250 and 16000 kPa. When the process is used continuously the behavior of the cyclic steady state is reached, where the desired performance objectives are to be achieved. A PSA process composed of one or more columns can be used with this type of cycles. In a multi-column unit the current from the depressurising step can be used to equalize the pressure from another column to decrease the unit's power consumption.

Application examples EXAMPLE 1: CH4-CO2 separation with CK 3K carbon molecular sieve. The initial study of the CH4-CO2 separation was performed with a 3K CMS adsorbent where CH4 diffusion is very slow. We simulated a PSA process with five steps (feed, intermediate depressurising, countercurrent evacuation, countercurrent product purging and countercurrent pressurizing). The flow to be treated is of the order of 1000 Nm 3 / h (under conditions of 298 K and 101.3 kPa) with a CH 4 content of 55%. To treat this current a PSA with two columns of 4,667m long and 0.4667m radius with a porosity of 0.33 was used. The feed was made at a pressure of 600 and 800 kPa and evacuation and purge at 10 kPa. Simulations with different intermediate pressures were performed. The results obtained can be seen in Table 1.

Table 1. Simulation results of a PSA process using a 3K CMS adsorbent.

Purification assay Purification Purity Purification Purification Purification SLPM S S S kPa kPa CH4% ration% CH4 / h. 17 kg A 16666.7 135 0 160 600 200 99.1 53.1 2.63 1 16666.7 135 10 160 600 200 97.2 85.7 4.33 2 16666.7 135 10 160 800 200 97.3 85.6 4.32 3 16666.7 135 10 160 800 250 97.8 81.5 4.09 4 16666.7 130 10 140 800 250 97.9 80.8 4.05 5 16000 130 10 140 800 250 98.1 79.7 3.83

Pressurizing step: 70s; bleed stage: 50s.

This example serves as a basis for comparing the results obtained with a kinetic adsorbent. EXAMPLE 2: CH 4 -CO 2 Separation with LPSA: 3K CMS followed by 13X zeolite.

In this example, a 3K CMS adsorbent followed by a 13X zeolite, known for its large CO 2 adsorption capacity, was used. To compare the results, a PSA unit with two columns of 4,667m long and 0.4667m radius was used. The process also has 5 stages (feeding, intermediate depressurising, countercurrent evacuation, countercurrent product purging and countercurrent pressurizing). The feed pressure was always 800 kPa and the evacuation pressure was 10 kPa. The arrangement of the adsorbents was done so that the first adsorbent to enter and contact with the stream to be purified is the CMS 3K followed by the zeolite 13X. The results of the different simulations can be seen in Table 2. The objective is to place a high capacity adsorbent to adsorb C02 at the end of the bed and can also be purged using methane (purge effectiveness in CMS 3K is low due to the slow diffusivity of CH4 in the adsorbent micropores). In this way the 3K CMS layer is better utilized whereby the last 13X zeolite layer acts as a " containment barrier " for C02. In these simulations we can confirm that at 18 18 the productivity of the LPSA unit is much greater than using only a kinetic adsorbent of the CMS type 3K. 19

Table 2. Simulation results of a LPSA process using vim 3K CMS adsorbent followed by a sorption adsorbent by differences in adsorption equilibria (13X zeolite).

Assay Z13X / CMS3K Qalim SLPM T -1- alim S t despres S t-evac S p -1- inter kPa Purity CH4% Recovery CH4% Productivity molCH4 / h.kg Ia Zeolite 16000 130 10 140 250 97.0 47.8 2.20 3a 9 16000 130 10 140 250 95.3 49.3 2.31 5b 0.111 16000 130 10 140 250 99.2 48.8 2.31 6C 0.111 22000 130 10 140 250 98.3 76.8 5.03 lc 0.25 22000 130 10 140 250 99.8 50.1 3.22 78d 0.25 30000 130 10 140 250 96.7 83.7 7.55 80d 0.429 30000 130 10 140 250 98.7 74.8 6.58

Pressurizing step: 70s; purge stage: 50s a Purge flow rate: 5000 SLPM. b Pressurizing flow rate: 10000 SLPM. c Feed rate: 22000 SLPM. Pressurizing flow: 16000 SLPM. d Pressurizing flow rate: 16000 SLPM.

REFERENCES

Appl, M .; Wagner, U .; Henrici, H. J .; Kuessner, K .; Volkamer, K .; Fuerst, E. Removal of C02 and H2S and / or COS from Gases Containing these Constituents. US 4336233, 1982. Cavenati, S .; Grande, C.A. and Rodrigues, A.E. Upgrade of Methane from Landfill Gas by Pressure Swing Adsorption, Energy & Fuels, 2005, 19, 2545-2555.

Cavenati, S .; Grande, C. A .; Rodrigues, A. E. Separation of CH4 / C02 / N2 Mixtures by Layered Pressure Swing Adsorption for Upgrade of Natural Gas. Chem. Eng. Sci., 2006, 61, 3893-3906. 20

Davis, Μ. M .; Gray, R. L. J .; Patei, K. Process for the Purification of Natural Gas. United States Patent, US 5,177,496, 1992.

Deng, S .; Kumar, R .; Bulow, M .; Fitch, F. R .; Ojo, A. F .; Gittleman, C.S. Air Purification Process. United States Patent, US 6238460, 2001.

Dolan, W. B .; Mitariten, M. J. C02 Rejection from Natural Gas. United States Patent US 2003/0047071, 2003.

Dolan, W. B .; Mitariten, M. J. Heavy Hydrocarbon Recovery from Pressure Swing Adsorption Unit Tail Gas. United States Patent, U.S. 6,610,124.

Fujita, S .; Himeno, S .; Suzuki, K .; Method for Concentration Methane from Sewage Sludge and Methane Storage Equipment. European Patent, EP 1,647,531, AI.

Golden, T. C .; Weist, E. L. J. Layered Adsorption Zone for Hydrogen Production Swing Adsorption. United States Patent, US 6814787, 2004.

Hagen, M .; Polman, E .; Jensen, J. K .; Myken, A .; Jõnsson, O .; Dahl, A. Adding gas from biomass to the gas grid, Swedish Gas Center, Report SGC 118, 2001.

Kim, M-B .; Bae, Y-S .; Choi, D.K .; Lee, C-H. Kinetic Separation of Landfill Gas by a Two Bed Pressure Swing Adsorption Process Packed with Carbon Molecular Sieve: Nonisothermal Operation. Ind. Eng. Chem. Res. 2006, 45, 5050-5058.

Little, W.A .; Spektor, S. Device and Method for Removing Water and Carbon Dioxide from a Gas Mixture Using Pressure Swing Adsorption. World Patent, WO 2005/089237 A2, 2005.

Lu, Y .; Doong, S-J .; Bulow, M. Pressure-Swing Adsorption Using Layered Adsorbent Beds with Different Adsorption Properties I- Results of Process Simulations. Adsorption, 2003, 9, 337-347. 21

Knaebel, K. S .; Reinhold, Η. E. Landfill Gas: From Rubbish to Resource. Adsorption 2003, 9, 87-94.

Masahiro, I .; Kazuo, H. Method for Removing Carbon Dioxide from Mixed Gas and Alternative Natural Gas Generating Device Using the Method. World Patent, WO95526804.

Miiller, U .; Hesse, M .; Piitter, H .; Schubert, M .; Mirsch, D. Adsorptive Anreicherung von Methan in Methan-haltigen Gasmischen. European Patent EP 1674555, 2005.

Seery, M. W .; Bulk Separation of Carbon Dioxide from Methane Using Natural Clinoptilolite. World Patent, WO 98/58726, 1998.

Sircar, S .; Kock, W. R. Adsorptive Separation of Methane and Carbon Dioxide Gas Mixtures. European Patent EP 0193716, 1986.

Sircar, S .; Kumar, R .; Koch, W.R .; Vansloun, J. Recovery of Methane from Landfill Gas. United States Patent 4,770,676, 1988.

Sircar, S .; Kock, W. R. Adsorptive Separation of Gas Mixtures. European Patent EP 0 257 493, 1988

Lisbon, August 12, 2010

Claims (14)

Separation column for gas purification characterized in that it consists of two layers of adsorbent material, being: a. the first layer is between 50 and 95% of the total volume of the column, consisting of a microporous material with pores between 4Â ° and 5.5Â ° and adsorbent with kinetic selectivity for the contaminating gas and with slow adsorption kinetics; and b. the second layer is between 5 and 50% of the total volume of the column, consisting of microporous materials, preferably based on high surface inorganic materials, with micropores larger than 6Â ° and adsorbent with a higher adsorption capacity for the contaminating gas which for the product gas, this second layer forming a containment barrier for the contaminating gas at the end of the column. Separation column for gas purification according to the preceding claim, characterized in that the first layer consists of carbon molecular sieves, natural zeolites and zeolites 4A, Li and K-modified LTA zeolites, DDR zeolites, ITQ zeolites , clinoptyltites or titanium silicates. Separation column for gas purification according to any one of the preceding claims, characterized in that the second layer consists of 13X zeolite, zeolite Y, mordenites, activated carbon, 2 aluminas, silica gel, and other porous materials of silica matrix or activated carbons with surface modifications. A pressure modulating adsorption process for gas purification, characterized in that each cycle takes place in five stages which comprises: a) feeding at least one column containing the two layers of adsorbent material, at high pressure with the gas to be separated ; b) depressurising the mixture to an intermediate pressure in a range between 20 and 600 kPa; c) countercurrent evacuation; d) countercurrent product purge; and e) pressurizing with countercurrent product in a range between 200 and 1500 kPa, preferably between 400 and 800 kPa. A process according to the preceding claim, characterized in that the feed pressure is in the range of 200 to 1500 kPa, preferably 400 to 800 kPa. A process according to claims 4-5, characterized in that the intermediate depressurising of the column takes place at a pressure lower than that of the feed. Process according to Claims 4-6, characterized in that the counter-current evacuation is carried out with the outlet of the closed column, the column being then connected to a line with lower pressure, in a range between 100 and 1 kPa of total pressure . 3 Process according to Claims 4-7, characterized in that the purging with counter-current product is carried out by introducing all or only part of the product, being carried out at the minimum pressure of the system, ie in a range between 200 and 1 kPa of total pressure in the column. A pressure modulating adsorption process for gas purification according to claims 5,8 characterized in that the pressurizing is carried out with all or only part of the product and the gas coming from the depressurising, the pressure of the column being increased from the minimum pressure to the maximum pressure, ie from 1 to 200 kPa at 250 to 2000 kPa of total pressure. A pressure modulating adsorption process for gas purification according to claims 4-9, characterized in that it is carried out continuously by the use of multiple separation columns and a new cycle is initiated, the maximum pressure value referred to in the preceding claim is obtained. A pressure modulating adsorption process for gas purification according to claims 4-10, characterized in that it is developed in continuous or individual cycles. Use of the separation column described in claims 1-3 by the process described in claims 4-11, which is applicable to the purification of mixtures of CH 4 -CO 2. Use of the separation column according to the preceding claim, characterized in that it is applicable in the removal of CO 2 from currents of 0-4-400 existing in natural gas, biogas and landfill gas. Use of the separation column according to the preceding claim, which is applicable in the removal of CO 2 from CH 4 -CO 2 streams whose CO 2 mole fractions may range from 0.15 to 0.85, preferably from 0.45 to 0.55. Lisbon, August 12, 2010.