NL2033800B1 - Method for obtaining a CH4-enriched gas fraction - Google Patents

Abstract

The present invention relates to a method for obtaining a CH4-enriched gas fraction from a gas mixture comprising C02 and CH4, an aluminum phyllosilicate material for use in the 5 same, and an adsorbent comprising the aluminum phyllosilicate material. The aluminum phyllosilicate material is characterized by the intercalating moieties and basal spacing, allowing the selectivity in adsorption. 36

Description

P36030NLOO/RLA

Title: Method for obtaining a CHs-enriched gas fraction

TECHNICAL FIELD

The present invention relates to a method of gas separation and purification using aluminum phyllosilicate adsorbents, in particular suitable for biogas upgrading.

BACKGROUND OF THE INVENTION

Limiting global warming requires, in addition to reducing fossil fuel consumption, exploring sources of renewable energy. One source is gas produced via the anaerobic digestion of organic compounds (organic waste, manure, landfill waste, etc.), known as biogas. After being stripped of minor contaminants as H2S, H2O, Nz, Oz, Hz, NHs, CO, and/or siloxanes in a biogas cleaning or purification process, biogas contains mostly methane (CHa4, 50-70%) and carbon dioxide (CO:, 30-50%). Although the cleaned biogas can be used directly for electricity and heat generation, separation of both gases (known as biogas upgrading) increases the calorific value of the methane stream and can produce a high-purity CO: stream. The pure methane stream can then be used as a vehicle fuel, injected directly into the existing natural gas grid, or used to produce chemicals, while simultaneously preventing methane emissions to the atmosphere. The pure CO: stream can be utilized, for example, in greenhouses, for algae cultivation, or for synthetic fuel or chemical production, or sequestered. The recovery and, after upgrading, utilization of biogas can therefore play a significant role in the energy transition and the reduction of greenhouse gas emission.

There are several existing methods for biogas upgrading. The main methods include absorption (e.g., water-, chemical-, or organic scrubbing), membrane separation, and adsorption (most often pressure swing adsorption). These methods can be effective under appropriate circumstances, but often suffer from high investment- and/or operational cost (including chemicals), high energy consumption, and/or technological limitations.

Furthermore, in the adsorption method, the performance depends strongly on the adsorbent material used. The adsorption method is based on different adsorption affinities (equilibrium separation) or adsorption time scales (kinetic separation) between the to-be-separated species and the adsorbent. In short, this method requires a reactor column packed with the adsorbent material through which the gas mixture flows. The strongly or quickly adsorbed 1 species (i.e., COy) are then retained in the column, whereas the weakly adsorbing species (i.e., CH.) are collected in the effluent.

Ideal adsorbents should have a high (equilibrium or kinetic) CO2/CHs selectivity for high CH4 and CO: output purity and recovery, they should adsorb CO: quickly and be easy to regenerate, and they should have a high working capacity to limit the required amount of adsorbent and equipment size. In addition, they should be readily available, stable, and safe.

Typical adsorbents include zeolites and activated carbon, and carbon molecular sieves (CMS; kinetic-based separation. Adversely, these materials often suffer from a trade-off between high CO./CHs selectivity and easy regeneration. For example, Zeolite 13X, which has a high

CO2/CHa4 selectivity, also has a high isosteric heat of CO, adsorption (43 — 55 kJ mol-1) and steep CO: adsorption isotherms. It thus requires high energy input and a relatively high temperature and/or a low vacuum pressure for complete regeneration. On the other hand, materials that weakly bind CO, e.g., activated carbon, typically have low CO2/CH selectivity.

Furthermore, kinetic based adsorbents (may) demonstrate relatively slow CO; adsorption and desorption kinetics as compared to equilibrium-based sorbents.

Itis thus imperative to find low-cost adsorption method with high CO2/CHa4 selectivity that can rapidly adsorb and desorb CO:. It is an object of the present invention provide such as method.

SUMMARY OF THE INVENTION

The inventors have achieved the above object of the invention by discovering that cation- exchanged aluminum phyllosilicate clays with appropriately sized (optionally hydrated) cations and basal spacing may be used for separation of CO2/CHs with high selectivity.

The effectiveness of the adsorbent clays of the invention relates to the combination of high selectivity and fast adsorption and desorption kinetics of the adsorbents. This is achieved by providing an aluminum phyllosilicate material with one or more intercalating moieties selected from the group consisting of the alkali metal cations, the alkaline-earth metal cations, and (substituted) ammonium cations, to thereby preferably provide a basal spacing in the range of 10-15A, 2

The adsorbent clays of the invention show improved performance in CO2/CH, separation compared to other known adsorbents. In particular, the inventors found surprisingly higher selectivity in CO2/CH, adsorption compared to activated carbon and higher release of the captured CO: (e.g. faster and/or under milder condition) than Zeolite. It furthermore was found that adsorption on the aluminum phyllosilicate particles can be at least as fast as, and appears faster than adsorption on equally-sized carbon molecular sieve particles. The fast

CO: adsorption and desorption kinetics allow for short cycle times and hence increased productivity. Overall, the method of the invention is particularly suitable under conditions relevant for biogas upgrading, that is, a (partial) pressure below 10 bar CO: and a temperature above 0°C.

On the process side, aluminum phyllosilicate adsorbents of the invention are particularly suitable for (near-)ambient pressure conditions and desorption can be performed without the input of external heat, which (i) reduces the energy demand of the setup, and (ii) simplifies the setup and hence reduces capital and operational costs, compared to reactors that use higher pressures and/or external heating. Furthermore, the diffusional transport into the clay adsorbents of the invention is fast, which allows for the use of relatively large sorbent particles. The latter may allow a higher throughput or flow, which is particularly beneficial for application at an industrial scale.

In an aspect, the present invention relates to a method for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO. and CH., the method comprising contacting the gas mixture with an adsorbent and obtaining a CHs-enriched gas fraction, wherein the adsorbent comprises an aluminum phyllosilicate material with one or more intercalating moieties selected from the group consisting of an alkali metal cation, an alkaline- earth metal cation, and an ammonium cation, to thereby preferably provide a basal spacing in the range of 10 - 15 A.

The method is preferably applied in a reactor, allowing for good contacting between gas and sorbent, more preferably a fixed-bed type of contactor. Sorbent regeneration can be done by temperature swing, (partial) pressure swing or a combination thereof. Preferably, (partial- or system-) pressure swing methods are applied. .

In an aspect, the present invention relates to an aluminum phyllosilicate material for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO, and CHa, wherein the aluminum phyllosilicate material has one or more intercalating moieties selected from the group consisting of an alkali metal cation, an alkaline-earth metal cation, and an 3 ammonium cation, to thereby preferably provide a basal spacing in the range of 10 - 15 A, wherein the aluminum phyllosilicate material has a selectivity in CO2/CHa4 adsorption of at least 2.

In an aspect, the present invention relates to a use of an aluminum phyllosilicate material as disclosed herein for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO» and CHa.

The use is preferably in biogas and/or landfill gas upgrading.

In an aspect, the present invention relates to an adsorbent for obtaining a CH4-enriched gas fraction from a gas mixture comprising CO: and CH, the adsorbent comprising the aluminum phyllosilicate material as disclosed herein.

In an aspect, the present invention relates to device for obtaining a CH4-enriched gas fraction from a gas mixture comprising CO. and CHg, the device comprising the aluminum phyllosilicate material and/or the adsorbent as disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The method of the invention pertains to containing a gas mixture comprising carbon dioxide (i.e. CO2) and methane (i.e. CH4) with an adsorbent, thereby obtaining a CH4-enriched gas fraction and/or a CO2-enriched gas fraction.

In general, the method preferably involves: providing a feed gas mixture (e.g. flue gas, biogas, landfill gas, natural gas) comprising carbon dioxide and methane; and/or contacting the feed gas mixture with an adsorbent; and/or allowing carbon dioxide from the feed gas mixture to adsorb onto the adsorbent, thereby removing at least some of the carbon dioxide from the feed gas mixture to yield a methane- enriched gas stream, wherein the methane-enriched gas stream preferably has a lower concentration of carbon dioxide and a higher concentration of methane than the feed gas mixture.

The method may further comprise regenerating the adsorbent, thereby desorbing at least some of the carbon dioxide to obtain a carbon dioxide-enriched gas stream, wherein the carbon dioxide-enriched gas fraction preferably has a higher concentration of carbon dioxide 4 and/or a lower methane concentration than the feed gas mixture and/or the methane-enriched gas stream.

In an embodiment, the method of the invention involves adsorbing CO: from the gas mixture (i.e. the first gas stream) on the adsorbent, wherein selective adsorption of CO2 over CH, may provide the CHa4-enriched gas. The gas mixture may be contacted with the adsorbent as a flow, such as generated by a blower or a compressor. The gas mixture may be heated or cooled in order to obtain the appropriate temperature. The gas mixture may include water. At least some of the water can be removed from the gas mixture before contacting with the adsorbent.

The adsorbent may be packed in any suitable column, vessel, or alike (e.g. steel such as stainless steel, plastic, concrete etc.), and the method may involve passing the gas mixture through the column.

In an embodiment, the gas (e.g. gas mixture, CO:-enriched gas and/or CH:-enriched gas) comprises at least 5%, or 10%, or 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 95% CO: and/or CHa4, calculated on the gas. In an embodiment, the gas comprises no more than 95%, or 90%, or 85%, or 80%, or 75%, or 70%, or 65%, or 60%, or 55%, or 50%, or 45%, or 40%, or 35%, or 30%, or 25%, or 20%, or 15%, or 10%, or 5% CO: and/or

CHa, calculated on the gas mixture.

In a preferred embodiment, the gas mixture comprises 10 - 60% CO: and/or 35 — 85% CHa, preferably 20 - 50% CO: and/or 45 — 75% CHa, more preferably 30 - 40% CO: and/or 55 — 65% CHa4, calculated on the gas mixture.

In a preferred embodiment, the CH:-enriched gas comprises 0 - 40% CO: and/or 60 — 100%

CHa, preferably 1 — 30% CO: and/or 70 — 95% CH, more preferably 5 - 20% CO: and/or 80 — 90% CHa, calculated on the gas mixture.

In a preferred embodiment, the COz-enriched comprises 0 - 40% CHa4 and/or 60 — 100% CO», preferably 1 — 30% CH, and/or 70 — 95% CO:, more preferably 5 — 20% CHa and/or 80 — 90%

COa, calculated on the gas mixture.

As used herein, the percentage (%) of a gas is expressed as the volume % (vol.%).

The present inventors found that the method of the invention is particularly suitable to be performed at (near-) ambient pressure and/or temperature. This may reduce the energy demand of the setup and may simplify the setup, and hence reduces capital and operational costs. In an embodiment, the adsorption pressure during the adsorbing step is at a CH4 and/or CO: partial pressure of 0.01 — 100 bar, preferably 0.05 - 20 bar, more preferably 0.1 — 10 bar, even more preferably 0.5 — 5 bar {e.g. 0.7 -3 bar or 1-2 bar). In an embodiment, the 5 adsorption temperature during the adsorption step is at a temperature (of the gas) of -20 °C - 100 °C, preferably -10 - 90 °C, more preferably 0 - 70 °C, even more preferably 10 °C - 50 °C. The gas separation is preferably according to a pressure swing adsorption method.

In an embodiment, the method of the invention involves a step of regenerating the adsorbent.

The regeneration of the adsorbent preferably desorbs the carbon dioxide. The prevent inventors found that the desorption surprisingly can be performed without the input of external heat, which is therefore a preferred embodiment of the invention.

The “regenerating” step may involve one or more a temperature-swing, a pressure-swing, a concentration-swing, a humidity swing, or a combination thereof. The “regenerating” step preferably uses a lower pressure that in the adsorbing step. In an embodiment, the “regenerating” step involves subjecting the adsorbent to a vacuum, e.g. thereby allowing to obtain a CO--enriched gas fraction with (essentially) pure CO: (e.g. more than 90%, or 95%, or 99%, or 100% CO:2).

The aluminum phyllosilicate material of the invention pertains to a material for obtaining a

CHa-enriched gas fraction.

The adsorbent preferably comprises an aluminum phyllosilicate material with one or more intercalating moieties selected from the group consisting of an alkali metal cation, an alkaline- earth metal cation, and a (substituted) ammonium cation, to thereby preferably provide a basal spacing in the range of 10 - 15 A.

The term “aluminum phyllosilicate” as used herein means any (clay) mineral comprising Si,

Al and O and typically with additional metal cations, characterized by Al in octahedral coordination with O(H) that are bound to one (1:1) or two (2:1) sheets of Si in tetrahedral coordination with O, e.g. forming parallel aluminosilicate sheets. In addition or alternatively, the term “aluminum phyllosilicate” as used herein can mean any (clay) mineral composed on parallel aluminosilicate sheets. The “aluminum phyllosilicate” according to the invention are also typically referred to as “layer aluminosilicate” or “layered aluminosilicate” and therefore encompassed in the term. The “aluminum phyllosilicate” material in the context of the current invention is preferably cation-exchanged, meaning that one or more cations in the aluminum phyllosilicate is interchanged, preferably one or more interlayer cations and/or cations on any negatively charged particle (e.g. clay mineral). The term “aluminum phyllosilicate material” encompasses natural materials and materials that are not found as such in nature, for example when subjected to cation-exchange with one or more (intercalating) moieties not naturally found in the material. Aluminum phyllosilicate materials encompass materials 6 subjected to a “doping” or “loading” step with the aim of introducing (controlled amounts) of intercalating moieties such as intercalating cations. The aluminum phyllosilicate material in the context of the current invention thus also includes “doped aluminum phyllosilicate” and/or “loaded aluminum phyllosilicate”. The aluminum phyllosilicate material in the context of the current invention encompasses a clay subjected to exfoliation, thus being exfoliated, meaning that the layers are spatially separated by a delamination process and preferably leading to increased basal spacing. The term “aluminum phyllosilicate” preferably excludes non-layered aluminosilicates such as zeolite. The “aluminum phyllosilicate” material in the context of the current invention in addition or alternatively encompasses “activated” material, meaning any many treated physically and/or chemically to adsorb (e.g. stronger and/or with higher selectivity). The various aluminum phyllosilicate materials are known to the skilled person, e.g. from the “Handbook of clay science” (1st Edition - May 9, 2006, Editors: Faiza Bergaya,

B.K.G. Theng, G. Lagaly), and these aluminum phyllosilicate materials are suitable in the context of the current invention. The term “aluminum phyllosilicate” encompasses materials synthesized in a reactor.

Preferably, the aluminum phyllosilicate is (derived from) a clay material provided from a natural source such as from a mine. This for instance allows the material to be provided in sufficient quantities and at desirable low cost. Preferably, the aluminum phyllosilicate is found and/or comprised in a naturally occurring material such as bentonite and/or Fuller's earth. The clay material from a natural source may or may not have been activated already, or processed otherwise, prior to subjecting to an exchange a to achieve the aluminum phyllosilicate material according to the invention. For example, the clay material from a natural source encompasses commercially-available clays derived from a natural source which are for instance activated with an alkaline-earth metal cation and/or alkali metal cation (e.g. Na-activated montmorillonite-rich bentonite clay, such as Wyoming MMT (SWy-3)), prior to (further) cation exchange according to the invention.

In an embodiment, the aluminum phyllosilicate is a smectite-containing and/or a vermiculite- containing material. The aluminum phyllosilicate, preferably the smectite-containing and/or the vermiculite-containing material as disclosed herein, may comprise one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, saponite, sauconite, and hectorite, preferably montmorillonite. In addition or alternatively, the smectite as disclosed herein can be one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, saponite, sauconite, and hectorite, preferably montmorillonite. The term “smectite” as used herein preferably means a clay mineral with a 2:1 layer silicate structure and having 2 tetrahedral sheets surrounding a central octahedral 7 sheet that can expand and contract upon wetting and drying, e.g. which can include illite/mica, chlorite, and vermiculite groups.

In a preferred embodiment, the aluminum phyllosilicate material as disclosed herein is a smectite- and/or vermiculite-containing material. In a preferred embodiment, the smectite- containing material is bentonite. In a preferred embodiment, the smectite-containing material is Fuller's earth. In a preferred embodiment, the vermiculite-containing material is bentonite.

In a preferred embodiment, the vermiculite-containing material is Fuller's earth. In a preferred embodiment, the smectite is montmorillonite and/or comprises montmorillonite.

The term “intercalated moiety” as used herein means any moiety (e.g. cation or hydrated cation) inserted in between the aluminosilicate sheets and/or inserted to interact electrostatically with one or more negatively charged basal planes of the aluminosilicate sheets.

The “cation” in the context of the current invention encompasses hydrated cations (i.e. a cation surrounding by a hydration shell and/or with water molecules arranged around it), most preferably a hydrated metal cation, more preferably a hydrated alkaline-earth metal cation, most preferably hydrated calcium cation (Ca®) or hydrated magnesium (Mg?) cation.

In a preferred embodiment, the cation is a hydrated cation.

In a preferred embodiment, the alkaline-aarth metal cation is hydrated calcium {(Ca®") cation.

In a preferred embodiment, the alkaline-earth metal cation is hydrated magnesium (Mg*") cation.

The alkali metal cation as disclosed herein may be one or more selected from the group consisting of Lit, Nat, kK, Rb’, Os’, and Fr’ cation.

In a preferred embodiment, the alkali metal cation is Cs* (i.e. caesium, cesium) cation.

In a preferred embodiment, the alkali metal cation is K* cation.

The alkaline-earth metal cation as disclosed herein may be one or more selected from the group consisting of Be“, Mg?’ Ca®, Sr, Ba?’ and Ra” cation.

In a preferred embodiment, the alkaline-earth metal cation is Mg?’ cation.

In a preferred embodiment, the alkaline-earth metal cation is Ca®* cation.

The ‘ammonium cation” in the context of the current invention encompasses substituted ammonium cation, meaning ammonium cation wherein one or more hydrogen atoms are 8 substituted with another organic group, such as an C1-C4 alkyl, most preferably a methyl group.

In an embodiment, the ammonium cation is alkyl ammonium cation and/or C1-C4 alkyl ammonium cation. In an embodiment, the alkyl ammonium cation and/or C1-C4 alkyl ammonium cation is methylammonium, dimethylammonium, trimethylammonium, or tetramethylammonium cation, preferably methylammonium cation and/or tetramethylammonium cation.

In a preferred embodiment, the ammonium cation is methylammonium cation.

In a preferred embodiment, the ammonium cation is tetramethylammonium cation.

The present inventors found that it was particularly beneficial if the cation disclosed herein has an ionic radius in appropriate range. In an embodiment, the cation as disclosed herein has an ionic radius of 150 — 350 pm, or 160 — 330 pm, or 170 — 320 pm.

The present inventors found that an appropriate amount of the intercalating cations is beneficial in terms of the materials’ conformation {e.g. basal spacing} and/or sorption properties, in particular when the adsorbent comprises smectite, most preferably montmorillonite, as aluminum phyllosilicate material.

In a preferred embodiment, the (amount of the one or more of intercalating moieties in the aluminosilicate material is 0.1 — 3 mEq, preferably 0.2- 2 mEq, more preferably 0.4 — 1.2 mEq, most preferably 0.6 — 1.0 mEq, all per g aluminum phyllosilicate material, wherein the weight (g) is preferably the dry weight.

In an embodiment, the amount of cation in the aluminosilicate material is 0.1 — 3 mEq, preferably 0.2- 2 mEq, more preferably 0.4 — 1.2 mEq, most preferably 0.6 — 1.0 mEq, all per g aluminum phyllosilicate material, wherein the weight (g) is preferably the dry weight, wherein the cation is Cs*, K*, Ca?*, Mg?*, hydrated Ca?*, hydrated Mg?*, methylammonium, or tetramethylammonium cation.

The amount of the one or more of intercalating moieties in the aluminum phyllosilicate material may be at least 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.8, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.8, 2.7, 2.8, 2.9, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 46, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 54, 5.5,56,5.7,5.8, 5.9, 5.9, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 10, 11, 12, 13, 14, or 15 mEq per g aluminum phyllosilicate material, wherein the weight (g) is preferably the dry weight. In addition or alternatively, the amount of the one or more of intercalating moieties in the 9 aluminum phyllosilicate material may be no more than 15, 14, 13, 12, 11, 10, 9, 8.5, 8.0, 7.5, 7.0,6.5,6.0,59.,58,57,56,55,54,53,52,51,50,49,48,47,46,45,44,43 4.2, 41,40,3.9 3.8, 37,36,35,34,33,32,31,30,29,28,27,26,25,24,23,22,21, 20,19,18,17,16,15,14,13.12,1.1.1.0,0.9,08,0.7,0.6,0.5,04,0.3,02,0.1, or 0.05 mEq per g aluminum phyllosilicate material, wherein the weight (g) is preferably the dry weight.

In the context of the current invention, the amount of the one or more intercalating moieties in the aluminum phyllosilicate material can be determined by any suitable analytical technique for the elemental analysis or chemical characterization of a sample known to the skilled person. In a preferred method, Energy-Dispersive X-ray spectroscopy (also known as EDX,

EDXA, or EDS) provides a wt.% of a certain atom type, from which the milliequivalents (mEq) value can be derived. In an example, for a Cs-activated clay, only one EDX measurement can be sufficient, and reflects the amount of intercalated Cs cations. In addition or alternatively, the amount of the intercalating moieties in the aluminum phyllosilicate material can be determined from the difference in the chemical composition of the material before and after exchange. In an example, an increase in Cs mass in the material after exchange with Cs may correspond to the number of Cs intercalating moieties, whereas changes in mass percentage moieties other than Cs can similarly be derived from the chemical characterization of the material before and after Cs exchange.

In an embodiment, the aluminum phyllosilicate and/or adsorbent as disclosed herein is “anhydrous”. The term “anhydrous” as used herein to describe a material means that there is (essentially) no free interlayer water. In addition or alternatively, a material is herein considered to be “anhydrous” when it has a (free and/or non-adsorbed) water no more than the content it would have if 10 g of the material is dried at 60 °C under dry nitrogen for at least 24 h. In addition or alternatively, an “anhydrous material” can mean a material with less than 5 wt. %, or less than 1 wt.%, or less than 0.1 wt.%, or less than 0.01 wt.%, or less than 0.001 wt.%, or less than 0.0001 wt.% (free and/or non-adsorbed) water, calculated per weight of the material.

The present inventors found that for certain cations, particularly certain alkaline-earth metal cations such as Ca?" and/or Mg?" | the selective CO,/CH, adsorption is especially high when the aluminum phyllosilicate comprises a threshold amount of water, for instance a water content in the range of 0.5 — 5 wt.%. Without being bound by theory, the threshold amount of water may facilitate the basal spacing and/or the hydration of cations in the context of the current invention. 10

In an embodiment, the aluminum phyllosilicate and/or adsorbent as disclosed herein comprises water, allowing to open up the interlayer space. In an embodiment, the aluminum phyllosilicate and/or adsorbent comprises 0.1 — 15 wt.%, preferably 0.2 — 10 wt.%, more preferably 0.5 — 5 wt.%, even more preferably 1 — 3 wt.% water, wherein the water is preferably adsorbed and/or associated with one or more hydrated cations.

The present inventors found that the aluminum phyllosilicate material has a surprisingly high selectivity in CO2/CHa4 adsorption, which is particularly seen for a basal spacing of the aluminum phyllosilicate material in the range of 10 — 15 A.

In a preferred embodiment, the aluminum phyllosilicate material has a basal spacing in the range of 9 — 16 A (angstroms), preferably 10 — 15 A, more preferably 10.5 — 14.5 A, even more preferably 11 - 14 A, most preferably 11.5 —13. A.

The term “basal spacing” as used in the context of the current invention means the distance between two layers (i.e. the interlayer distance) plus thickness of a single layer.

The basal spacing can be measured by x-ray reflectivity. For instance, the (001) reflection under (powder) X-ray diffraction can be measured, from which the Basal spacing can be calculated using Braggs Law, known to the skilled person. The material can be optionally first hydrated (e.g. in 90% RH nitrogen) and then equilibrated (e.g. in 10% RH nitrogen).

In the context of the current invention, the basal spacing is preferably measured under 1 or 10 bar CO2 and at 20 °C.

In a preferred embodiment, the aluminum phyllosilicate material has a selectivity in CO2/CH4 adsorption of at least 2, preferably at least 5, more preferably at least 10, even more preferably at least 20, for example 2-40, or 3-30, or 2-20, or 5-10. The selectivity in CO2/CH4 adsorption in the context of the invention is preferably defined as the ratio in CO2/CH. adsorption capacity measured at a total pressure of 1 bar and at 20 °C for a 50/50% CO2/CHa gas mixture.

In a preferred embodiment, the aluminum phyllosilicate material has a CO: adsorption capacity of at least 0.4 mmol g’t, preferably at least 0.8 mmol gt, even more preferably at least 1.0 mmol g’t, most preferably at least 1.5 mmol gt, such as for example 0.4 — 4.0 mmol gt, 0r0.8-3.0 mmol gt, or1.0-2.0 mmol g'. The CO: adsorption capacity is preferably measured at a pressure of 10 bar and at 20 °C for pure CO:. 11

In an embodiment, the aluminum phyllosilicate material and a CH. adsorption capacity of no more than 0.05 mmol gt, preferably of no more than 0.1 mmol gt, even more preferably of no more than 1 mmol g, most preferably of no more than 2 mmol g’í The CH, adsorption capacity is preferably measured at a pressure of 10 bar and at 20 °C for pure CHa.

The adsorption capacity in the context of the present invention can be measured according to the Sievert’s technique which is common to the skilled person. The Example illustrates a preferred protocol to determine the adsorption capacity with a Sieverts apparatus. In determining the adsorption capacity, adsorbed quantity of CO, or CH, can be calculated using the Van der Waals equation (e.g. to account for non-ideality of the gases). In addition or alternatively, the adsorption capacity can be measured by any gravimetric analysis method suitable in the art.

The present inventors found that the adsorbent composition, in particular the inclusion of a clay binder and/or particle size may influence the CO: and/or CH, sorption capacity.

The adsorbent as disclosed herein may comprise one or more binder materials (i.e. “binder”), meaning any material that is added primarily for agglomerating or compacting individual elements in the adsorbent. In addition or alternatively, the binder in the context of the current invention may enhance the mechanical properties (e.g. higher strength} or stability of the adsorbent. In addition or alternatively, the one or more binders may improve the plasticity of the adsorbent for shaping into a body (i.e. the binder then being a plasticizing binder). In addition or alternatively, the binder may increase the overall porosity of the adsorbent. The binder as disclosed herein may be a clay binder, preferably an aluminum phyllosilicate, preferably a non-cation-exchanged or non-activated aluminum phyllosilicate and/or an aluminum phyllosilicate from a natural source activated in another way (e.g. when commercially available) than according to the present invention. For example, the adsorbent of the invention may comprise activated aluminum phyllosilicate (e.g. activated bentonite, smectite, vermiculite and/or montmorillonite) and a further non-activated aluminum phyllosilicate (e.g. non-activated bentonite, smectite, vermiculite and/or montmorillonite) and/or an aluminum phyllosilicate from a natural source activated in another way (e.g. when commercially available) than according to the present invention, wherein the non-activated aluminum phyllosilicate in the adsorbent may be the same or a different material than the activated aluminum phyllosilicate material in the adsorbent. The binder as disclosed herein may be any known {plasticizing) organic binder, such as cellulose ether type binders and/or their derivatives some of which are thermally gellable. Typical organic binders that may be suitable in the context of the current invention may be one or more selected from the group 12 consisting of methylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose, hydroxybutyl methylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, and sodium carboxy methylcellulose, and mixtures thereof.

In an embodiment, the adsorbent comprises 0.5- 60 wt.% of the binder material and 40-99.5 wt.% of the aluminum phyllosilicate material, for instance1- 40 wt.% of the binder material and 60-99 wt.% of the aluminum phyllosilicate material, or 5 - 30 wt.% of the binder material and 70-95 wt.% of the aluminum phyllosilicate material, or 10 - 20 wt.% of the binder material and 80-90 wt.% of the aluminum phyllosilicate material, all calculated on the weight of the binder material and the aluminum phyllosilicate material, wherein the weight is preferably the dry weight.

The adsorbent as disclosed herein may be in one or more forms selected from the group consisting of a powder, a film, a fiber, a coating, a self-supporting structure, a monolith, and particles (e.g. granules, beads, pellets}, with or without binder.

When the binder is in the form of particles, the particles preferably have an average diameter of 0.1 — 50 mm, more preferably 0.5 — 20 mm, even more preferably 1.0 — 10 mm, most preferably 1.5 — 5.5 mm.

The “gas mixture” as disclosed can be any mixture of gases comprising CO2/CH.. In a preferred embodiment, the gas mixture is biogas, meaning a gas produced from raw materials such as one or more of agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. In addition or alternatively, biogas can mean any gas produced by anaerobic digestion with anaerobic organisms or methanogen inside an anaerobic digester, biodigester or a bioreactor. Biogas typically is a saturated gas mixture mainly of methane, carbon dioxide, and furthermore may contain hydrogen sulfide and/or siloxanes. In a preferred embodiment, the gas mixture landfill gas, meaning a type of biogas that originates from the decomposition of organic waste in a landfill. The use as disclosed herein encompasses the “upgrading” of the gas mixture, meaning that the gas is enriched in methane and carbon dioxide is (sufficiently) removed to for instance obtain bio-methane.

One aspect of the invention may relate to a method for preparing the aluminum phyllosilicate material.

In an embodiment, the method for preparing the aluminum phyllosilicate material involves a step of cation exchange, preferably by contacting the aluminum phyllosilicate with a solution 13 comprising a salt of the desired cation, more preferably a fluoride, a bromide, a chloride, an iodide, a nitrate, a sulfate, a phosphate, a hydroxide or a carbonate may be used. In an embodiment, the cation-exchange is performed at alkaline pH, e.g. pH 7-12, or 8-11, or 9-10, and the pH of the solution may be adjusted accordingly by adding a pH-adjusting compound.

In an embodiment, the cation-exchange is performed at acidic pH, e.g. pH 2-7, or 3-6, or 4-5, and the pH of the solution may be adjusted accordingly by adding a pH-adjusting compound.

For cation-exchange a batch method or column flow method can be employed, wherein the batch method may be more suitable for uniform cation-exchanging. The cation-exchange can be performed at any temperature, including at room temperature. The present inventors found under certain conditions the cation-exchange is improved at elevated temperature such as 50 - 70°C. The temperature during cation-exchanging may be also from 30 - 100°C, or 40 - 80°C, or 50 - 70°C. In an embodiment, the salt or cation is present in the solution in a concentration of 0.01 - 2 M (i.e. 0.01-2 mmol/ml) per gram aluminum phyllosilicate, preferably 0.5-15M (i.e. 0.5-15mmol/ml) per gram aluminum phyllosilicate, more preferably 1 — 10 M (ie. 1-10 mmol/ml) per gram aluminum phyllosilicate, even more preferably 1.5 -5 M (i.e. 1.5-5 mmol/ml) per gram aluminum phyllosilicate. If two or types of cations are introduced into the aluminum phyllosilicate material, the aluminum phyllosilicate may be brought into contact with the different types of cations simultaneously, separately and/or successively to allow cation exchange. For instance, the aluminum phyllosilicate may be immersed in a first solution comprising a first type of cation, before being immersed in a second and possibly further solution comprising a further type of cation. After each ion exchange procedure the aluminum phyllosilicate can be suitably washed and dried.

In an embodiment, the aluminum phyllosilicate can be provided in a dialysis membrane to remove solutes and/or to equilibrate the solution in a new buffer.

In an embodiment, the concentration of one or more cations in the solution can be in a concentration of 0.5 — 20 times, preferably 1- 15 times, more preferably 2-10 times, even more preferably 3-6 times, the cation exchange capacity (CEC, in mEqg/g) of the aluminum phyllosilicate. An example is provided for Cs-exchanged montmorillonite: considering a CEC of montmorillonite of 0.8 mEq/g, one may mix 1 gram of montmorillonite with 1 mmol of Cs(Cl) {~168 mg), and any desirable amount of water (e.g. 10 mL of water per gram clay). The skilled person knows the CEC of aluminum phyllosilicates. For example, the cation exchange capacity of montmorillonite is described in the “Data Handbook for Clay Materials and Other

Non-Metallic Minerals (Van Olphen, H. and Fripiat, J.J., 1979, Pergamon Press, Oxford).

In an embodiment, the aluminum phyllosilicate can be provided in the solution for a time chosen as to achieve the desired cation-exchange and/or for at least 24 h, preferably at least 7 days, more preferably at least 14 days, more preferably at least 21 days, even more preferably at least 28 days, such as 1 — 10 weeks, or 2 — 8 weeks, or 4 — 6 weeks. 14

In an embodiment, the method for preparing the aluminum phyllosilicate material can involve a step of washing after the cation exchange.

In an embodiment, the method for preparing the aluminum phyllosilicate material involves a step of removing (excess) salt during and/or after cation exchange. In an embodiment, the removal of (excess) salt involves providing the aluminum phyllosilicate, preferably in a dialysis membrane, in water such as distilled water or ultra-pure water.

The cation exchange may be performed before or after adding an optional binder material as disclosed herein.

In an embodiment, the method for preparing the aluminum phyllosilicate material involves a step of drying the aluminum phyllosilicate material after cation-exchange and/or salt-removal.

The drying may be performed at for example 40-100°C, or 50-80 °C, or 55 - 80 °C. The drying may be performed as long needed to achieve the amount of (free) water, or the absence thereof, in the aluminum phyllosilicate. In an embodiment, the drying is performed as to achieve an anhydrous aluminum phyllosilicate as disclosed herein.

One aspect of the invention may relate to a method for preparing the adsorbent. In an embodiment, the adsorbent consists of the cation-exchanged aluminum phyllosilicate. In an embodiment, the adsorbent comprises the cation-exchanged aluminum phyllosilicate without a further binder. In an embodiment, the adsorbent comprises the cation-exchanged aluminum phyllosilicate with a binder.

In an embodiment, the adsorbent is prepared by combining the cation-exchanged aluminum phyllosilicate with a binder in necessary amounts (e.g. mass ratios), as to achieve the adsorbent of the invention. For example, the cation-exchanged aluminum phyllosilicate may be combined with as-received and/or non cation-exchanged aluminum phyllosilicate serving as binder in a mass ratio of 1:0.01 —1:2, or 1:0.05-1:1, or 1:0.5 - 1:0.1. The method for preparing the adsorbent may optionally comprise adding a solvent (e.g. water or other aqueous medium) to the aluminum phyllosilicate and binder, followed by mixing the components (e.g. by kneading or agglomerating). The preparation of the binder may involve a step of drying the adsorbent after combing the cation-exchanged aluminum phyllosilicate and the binder, for example at 40-100°C, or 50-80 °C, or 55 - 80 °C. The drying of the adsorbent may be performed as long needed to achieve the amount of (free) water, or the absence thereof, in the adsorbent. In an embodiment, the drying is performed as to achieve an anhydrous adsorbent.

The use of the invention pertains to a use of the aluminum phyllosilicate material disclosed herein in a process for obtaining a CH4-enriched gas fraction from a gas mixture comprising

CO: and CHa. 15

In a preferred embodiment, the (further) use is in biogas and/or landfill gas upgrading.

The device of the invention pertains to a device comprising the aluminum phyllosilicate material according to the invention and/or the adsorbent according to the invention. In an embodiment, the device according to the invention is adsorption reactor, preferably a swing adsorption reactor. In an embodiment, the device is a fixed-bed reactor. In an embodiment, the device is a pressure swing fixed-bad reactor.

General definitions - The terms ‘comprising’ or ‘to comprise’ and their conjugations, as used herein, refer to a situation wherein said terms are used in their non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. It also encompasses the more limiting verb ‘to consist essentially of and ‘to consist of’. - Reference to an element by the indefinite article ’a’ or ‘an’ does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article ‘a’ or ‘an’ thus usually means ‘at least one’. - The terms ‘to increase’ and ‘increased level’ and the terms ‘to decrease’ and ‘decreased level (or to reduce” and “reduced level”) preferably refer to a change of at least 5%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% higher or lower, respectively, than the corresponding level in a control or reference. In addition or alternatively, a level in a sample may be increased or decreased when it is statistically significantly increased or decreased compared to a level in a control or reference, irrespective of the size of change.

CLAUSES

Herein, clauses are embodiments of the invention. Features of clauses (embodiments) herein can be combined. 1. Method for obtaining a CH4-enriched gas fraction from a gas mixture comprising

CO: and CH, the method comprising contacting the gas mixture with an adsorbent and obtaining a CHs-enriched gas fraction, wherein the adsorbent comprises an aluminum phyllosilicate material with one or more intercalating moieties selected from the group consisting of an alkali metal cation, an alkaline-earth metal cation, and an ammonium cation, to thereby provide a basal spacing in the range of 10 - 15 A. 16

2. Method according to clause 1, wherein CO: from the gas mixture is adsorbed on the adsorbent.

3. Method according to clause 1 or 2, further comprising a step of regenerating the adsorbent.

4, Method according to clause 3, wherein the regenerating comprises a step wherein the CO: is desorbed from the adsorbent to provide a CO:z-enriched gas fraction.

5. Method according to any one of the previous clauses, wherein the aluminum phyllosilicate is a smectite- and/or vermiculite-containing material.

6. Method according to clause 5, wherein the smectite-containing material and/or the vermiculite-containing material is bentonite and/or Fuller's earth.

7. Method according to clause 5 or 8, wherein the smectite-containing material comprises one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, hectorite, saponite, and sauconite.

8. Method according to clause 7, wherein the smectite-containing material comprises montmorillonite.

9. Method according to any one of the previous clauses, wherein the cation is a hydrated cation.

10. Method according to any one of the previous clauses, wherein the alkali metal cation is Cs* and/or K* cation.

11. Method according to any one of the previous clauses, wherein the alkaline-earth metal cation is Ca?’ and/or Mg?* cation.

12. Method according to any one of the previous clauses, wherein the alkaline-earth metal cation is hydrated Ca?" cation.

13. Method according to any one of the previous clauses, wherein the alkaline-earth metal cation is hydrated Mg?* cation. 17

14. Method according to any one of the previous clauses, wherein the ammonium cation is C1-C4 alkyl ammonium cation.

15. Method according to clause 14, wherein the C1-C4 alkyl ammonium cation is methylammonium cation and/or tetramethylammonium cation.

16. Method according to any one of the previous clauses, wherein the amount of the one or more of intercalating moieties in the aluminum phyllosilicate material is 0.1 — 3 mEq per g aluminum phyllosilicate material.

17. Method according to clause 16, wherein the amount of the one or more of intercalating moieties in the aluminum phyllosilicate material is 0.4 — 1.2 mEq per g aluminum phyllosilicate material.

18. Method according to any one of the previous clauses, wherein the adsorbent comprises 1- 40 wt.% of a binder material and 60-99 wt.% of the aluminum phyllosilicate material, calculated on weight of the binder material and the aluminum phyllosilicate material.

19. Method according to clause 18, wherein the binder material is a non-activated aluminum phyllosilicate material and/or a plasticizing organic binder.

20. Method according to any one of the previous clauses, wherein the adsorbent is provided in one or more forms selected from the group consisting of a powder, a film, a fiber, a coating, a self-supported structure, a monolith and particles.

21. Method according to clause 20, wherein the particles have an average diameter of 0.1- 50 mm.

22. Method according to any one of the previous clauses, wherein the gas mixture is contacted with the adsorbent at a CO: partial pressure of 0.1 - 10 bar.

23. Method according to any one of the previous clauses, wherein the gas mixture is contacted with the adsorbent at a temperature 0-70°C.

24. Method according to any one of the previous clauses, wherein the gas mixture comprises 30 — 60 vol.% CO: and 40 — 70 vol.% CHa, calculated on the gas 18 mixture. 25. Method according to any one of the previous clauses, wherein the CHs-enriched gas fraction comprises 1 — 30 vol.% CO: and 70-95 vol.% CHa, calculated on the

CHgs-enriched gas fraction. 26. Aluminum phyllosilicate material for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO: and CHa, wherein the aluminum phyllosilicate material has one or more intercalating moieties selected from the group consisting of an alkali metal cation, an alkaline- earth metal cation, and an ammonium cation, to thereby provide a basal spacing in the range of 10 - 15 A, wherein the aluminum phyllosilicate material has a selectivity in CO2/CH, adsorption of at least 2, wherein selectivity in CO2/CH, adsorption is defined as the ratio in CO./CH4 adsorption capacity measured at a total pressure of 1 bar and at °C for a 50/50 vol.% CO2/CH4 gas mixture. 27. Aluminum phyllosilicate material according to clause 26, wherein the aluminum phyllosilicate material has a CO: adsorption capacity of at least 0.8 mmol g*, 20 measured at a pressure of 10 bar and at 20 °C for pure CO.. 28. Aluminum phyllosilicate material according to clause 26 or 27, wherein the aluminum phyllosilicate material is a smectite- and/or vermiculite-containing material. 29. Aluminum phyllosilicate material according to clause 28, wherein the smectite- containing material and/or the vermiculite-containing material is bentonite and/or

Fuller's earth. 30. Aluminum phyllosilicate material according to any one of clauses 26-29, wherein the smectite-containing material comprises one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, hectorite, saponite, and sauconite. 31. Aluminum phyllosilicate material according to clause 30, wherein the smectite- containing material comprises montmorillonite. 19

32. Aluminum phyllosilicate material according to any one of clauses 26-31, wherein the cation is a hydrated cation. 33. Aluminum phyllosilicate material according to any one of clauses 26-32, wherein the alkali metal cation is Cs* and/or K* cation. 34. Aluminum phyllosilicate material according to any one of clauses 28-33, wherein the alkaline-earth metal cation is Ca?* and/or Mg?* cation. 35. Aluminum phyllosilicate material according to any one of clauses 26-34, wherein the alkaline-earth metal cation is hydrated Ca?* cation. 36. Aluminum phyllosilicate material according to any one of clauses 26-35, wherein the alkaline-earth metal cation is hydrated Mg?* cation. 37. Aluminum phyllosilicate material according to any one of clauses 26-36, wherein the ammonium cation is C1-C4 alkyl ammonium cation. 38. Aluminum phyllosilicate material according clause 37, wherein the C1-C4 alkyl ammonium cation is methylammonium cation and/or tetramethylammonium cation. 39. Aluminum phyllosilicate material according to any one of clauses 26-38, wherein the amount of the one or more of intercalating moieties in the aluminum phyllosilicate material is 0.1 — 3 mEq per g aluminum phyllosilicate material. 40. Aluminum phyllosilicate material according to clause 39, wherein the amount of the one or more of intercalating moieties in the aluminum phyllosilicate material is 0.4 — 1.2 mEq per g aluminum phyllosilicate material. 41. Use of an aluminum phyllosilicate material for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO: and CH. wherein the aluminum phyllosilicate material is as defined in any one of clauses 26-40. 42. Use according to clause 41, wherein a further use is in biogas and/or landfill gas upgrading. 43. Adsorbent for obtaining a CH4-enriched gas fraction from a gas mixture comprising

CO: and CH, the adsorbent comprising the aluminum phyllosilicate material as 20 defined in any one of clauses 26-40. 44. Adsorbent according to clause 43, comprising 1- 40 wt.% of a binder material and 60-99 wt.% of the aluminum phyllosilicate material, calculated on weight of the binder material and the aluminum phyllosilicate material. 45. Adsorbent according to clause 44, wherein the binder material is a non-activated aluminum phyllosilicate material and/or a plasticizing organic binder. 46. Adsorbent according to any one of clauses 43-45, wherein the adsorbent is provided in one or more forms selected from the group consisting of a powder, a film, a fiber, a coating, a self-supported structure, a monolith and particles. 47. Device for obtaining a CH:-enriched gas fraction from a gas mixture comprising

CO: and CH, the device comprising the aluminum phyllosilicate material as defined in any one of clauses 26-40 and/or the adsorbent as defined in any one of clauses 43-46. 48. Device according to clause 47, wherein the device is a fixed-bed reactor.

FIGURE LEGENDS

Figure 1: BET surface area (powder) as a function of number of cations per gram clay during exchange. For comparison, the MMTs and bentonite particles are also shown. Samples in the green area were used in the remainder of experiments. The CEC of MMT and the BET surface areas of non-exchanged MMT and bentonite are indicated by the vertical line, black dotted horizontal line, and black solid horizontal line, respectively.

Figure 2: Adsorption isotherms of CO; and CH, on a) non-exchanged bentonite, b) Cs bentonite, c) MMA-bentonite, and d) TMA-bentonite powders.

Figure 3: CO2/CHa4 adsorption selectivity for a binary (50/50) mixture of CO, and CHa4 on a)

Cs-bentonite, b) MMA-bentonite, and c) TMA-bentonite.

Figure 4: CO; adsorption (1 bar, room temperature) normalized by the CO: adsorption after 30 minutes, on Cs-bentonite, MMA-bentonite, and TMA-bentonite particles and powder. The 21 approximate CO; concentration is indicated by the gray solid line.

Figure 5: Breakthrough curves for a binary (50/50) mixture of CO; and CH. (dark shade: 0.40

L min”', light shade: 0.20 L min?) on a) Cs-bentonite, b) MMA-bentonite, and c) TMA bentonite (Multiple repetitions are shown).

Figure 6: Regeneration of a,b} Cs-bentonite, c,d) MMA-bentonite, and e,f) TMA-bentonite, with a,c,d) in a 0.60 L min”! N2 stream and b,d.f) in a 0.30 L min”? N2 stream. Note the different scales of the ordinates. The inset of Panel d) shows the data on a log-log scale.

Figure 7: Adsorption-desorption cycles of a,b) Cs-bentonite, and c,d) TMA-bentonite. Panels a) and c) show the cycles consecutively, whereas in panels b) and d), cycles are shifted on top of each other.

EXAMPLES

The invention is illustrated by the following working Example that do not limit the scope of the invention.

The Example evaluates cation-exchanged MMT-rich bentonite for biogas upgrading via pressure-swing adsorption. Specifically, we study three different cation-exchanged bentonites of which the interlayer spacing is comparable to the molecular size of CO: and CHs. In order of increasing interlayer spacing, these are: cesium-bentonite (Cs-bentonite, with d-spacing d = 11 A (mono)methylammonium-bentonite, MMA-bentonite, d = 12 A, and tetramethylammonium-bentonite (TMA-bentonite, d = 14 A. Equilibrium adsorption isotherms of CO: and CHa4 (10 — 70°C, up to 10 bar) and breakthrough measurements of the mixture on (powders and particles of) the different bentonites demonstrate unambiguously their ability to separate both gases. Kinetic measurements of CO: adsorption and the breakthrough measurements show that diffusional transport into the particles is sufficiently fast for cation- exchanged bentonites.

Methods

Materials

MMT-rich Na-activated bentonite clay (Cebogel QSE) was purchased from Eijkelkamp Soil &

Water. Wyoming MMT (SWy-3) was purchased from the Clay Mineral Society Source Clay 22

Repository. To exchange their interlayer cations, the clays were suspended in a dialysis tube (SnakeSkin, 3.5 kDa MCOW) in a solution of the chloride salt of the desired cation (Sigma

Aldrich; MMACI and TMACI: synthesis grade; CsCl: 2 98%; unless specified otherwise, per gram clay, 3.2 mmol cations corresponding to ~4 times the cation exchange capacity of MMT, and 10 mL Milli-Q water) at room temperature for at least two weeks. Excess salt was washed off the cation-exchanged clay in multiple cycles by suspending the dialysis tube in

Milli-Q water until the supernatant conductivity was below < 100 HS cm™ (typically 6 — 8 cycles over ~1 week). Subsequently, the clays were dried in an oven at 60°C, ground manually to a powder using a mortar, and used for analysis without size fractioning and further purification.

For the measurements that require particles instead of powder, the clays were pelletized by mixing the exchanged bentonites with a suspension of the as-received bentonite (100 g L™) ina 1: 1.1 mass ratio of adsorbent to binder suspension (the water from the suspension is evaporated, and leaves a 1:0.1 ratio of adsorbent to dry binder material), where the as- received bentonite serves as a binder material. Particles (with particle diameter dp = 2 - 4 mm or dp = 2 cm) were hand-rolled from the resulting paste and dried in an oven at 60°C. The particles thus contain ~91% exchanged bentonite, and ~9% binder material.

Sample characterization

Nitrogen adsorption measurements at 77K were performed using a Gemini VII 2390t surface area analyzer. Prior to each measurement, the sample was outgassed at 150°C for 6 — 16 hours under a flow of dry Na.

Thermogravimetric analysis (TGA) was performed using a Netsch STA 449 F3 Jupiter thermal gravimetric analyzer. As the bentonite samples can contain a significant fraction of impurities, this analysis was performed on the MMT samples. Approximately 20 mg of clay powder was placed in an Al2O: crucible and heated from 0°C to 1000°C at a rate of 10°C min”! under Nz purge (50 mL min™). Outlet gases were analyzed using a Bruker Tensor 27 FT-IR spectrometer with a MCT (mercury-cadmium telluride} detector and a stainless steel light pipe gas cell at 200°C. IR spectra were recorded with a resolution of 4 cm”! and averaged over 32 scans in the range 4000 — 850 cm™ throughout the heating process.

Adsorption isotherms

CO: and CH, adsorption isotherms were measured using a homebuilt Sieverts apparatus.

The sample chamber was loaded with 10 — 15 g of clay powder (oven-dried at 150°C for approximately 20 hours) and immersed in a Julabo F25-HE refrigerated heating circulator.

Before each measurement, the sample chamber was evacuated at ~80°C for one hour.

During a measurement, the pressure in the sample chamber was increased stepwise 23

(equilibration time = 10 minutes) from vacuum to ~10 bar while continuously monitoring the pressure (two Gems 3100 digital pressure transducers; 0 — 25 bar; accuracy: 0.25% of full- scale) and temperature in the sample chamber and reservoir. The adsorbed quantity of CO; or CH4 was calculated using the Van der Waals equation to account for non-ideality of the gases.

Adsorption and desorption kinetics

Adsorption and desorption kinetics were measured gravimetrically on a scale (Adam

Equipment Nimbus NBL 254i) enclosed by a plastic container (V = 0.5 L). Approximately 5 g sample (ovendried at 150°C for approximately 20 hours) was placed on the scale in a glass petri dish. First, the chamber was saturated with Nz, then CO: was provided to the chamber for 30 min, and finally the particles were regenerated in N2 (all flow rates are 2 L min™ and controlled with a home built humidistat of which the “wet” channel was not used). At the gas switching points, no gas was provided for 30 s. A calibration measurement with an empty petri dish and an assumed linear drift as interpolated between begin- and endpoint were subtracted from each measurement.

Breakthrough measurements of CO, and CH,

Breakthrough measurements of a mixture of CO: and CH, (50 + 2%) were performed using a homebuilt fixed-bed reactor setup operating at room temperature and atmospheric pressure.

Approximately 50 gram of clay particles (oven-dried at 150°C for approximately 20 hours) were loaded in the cylindrical, stainless steel reactor (d = 1.3 cm, L = 60 cm, and V = 80 mL).

Supply of CO:, CHs, and/or Nz to the inlet of the reactor was controlled by two Brooks

SLA5800 Mass Flow Controllers that were calibrated volumetrically for the different gas types.

Atthe outlet of the reactor, the effluent was diluted with a 0.60 L min”! flow of N». The diluted effluent was analyzed using a SICK S710 gas analyzer with a detection range of 0 - 50%

CO: and CH. To study the regeneration of the sorbent, first the supply of the CO2 and CH4 mixture was stopped. Then, after 2 minutes, the dilution flow at the outlet of the reactor was stopped (or decreased to 0.30 L min”), and immediately thereafter a 0.60 L min"! (or 0.30 L min?) flow of N2 was supplied to the inlet of the reactor.

Results

Sample characterization

The surface areas and porous structure of the bentonite and MMT samples exchanged at various cation concentrations using nitrogen adsorption isotherms at 77K was assessed. All samples demonstrated mesoporous structures (Hs adsorption-desorption hysteresis), 24 microporous structures (no saturation in the limit p/p0 — 1), and external surface areas (t plot) that are nearly independent of the interlayer cation species and exchange concentration.

Yet, adsorption on surfaces and in micropores, including the interlayer space (i.e., the low partial-pressure domain), to which the BET surface area is a convenient proxy (Figure 1) increases (i) with increasing cation size, and (ii) with increasing cation concentration up to a saturation concentration. Given the similar external surface areas of all samples, the exchange with large(r) cations must facilitate the adsorption of Nz in the interlayer space. The saturation concentration can be interpreted as the concentration at which all interlayer spaces are opened up by sufficient cations. For Cs-bentonite and TMA-bentonite, this is ~1 mmol per g, close to the cation exchange capacity (CEC) of MMT (~0.8 mEq g°’). For MMA bentonite, this is ~3 mmol per g. Bentonites exchanged with 3.2 mmol cations per g are used in the remainder of the Examples.

To test the thermal stability of the clays, a TGA of the MMT samples was performed. For all MMTs, loss of water is observed at 90°C — 100°C. The MMA-MMT sample demonstrates a peak mass loss due to decomposition of the cations at ~345°C and a second peak at ~495°C.

For TMA-MMT, a single decomposition peak was observed at ~460°C that is well-segregated from water desorption. As expected, no ‘decomposition’ of Cs+ was found. Finally, dehydroxylation occurred at 610°C — 665°C for all MMT Ss.

Single component gas adsorption

The adsorption isotherms of the individual components (CO. and CH.) on the non-exchanged bentonite, Cs-bentonite, MMA-bentonite, and TMA-bentonite were analyzed (Figure 2). Non- exchanged bentonite, dominated by Na+ cations that are much smaller than the studied gas molecules, hardly sorbs either gas over the entire P (0 — 10 bar) and T-range (10 — 70°C) with a maximum adsorption capacity 0.23 mmol g~* and 0.08 mmol g™* for CO; and CHa, respectively. The measured capacities are in line with the adsorption capacity on (various types of) MMT and other smectites (e.g., hectorite) with small cations for CO; and for CH. in absence of interlayer water. In these cases the interlayer space is inaccessible to either gas and adsorption is limited to external surfaces.

The CO: adsorption capacity of bentonite exchanged with large cations is significantly larger than that of non-exchanged bentonite. It follows the order Cs bentonite > TMA-bentonite >

MMA-bentonite with maximum adsorption capacities at 10°C and 10 bar of ~1.25 mmol g*, ~1.16 mmol gt, and ~0.92 mmol g™*, respectively. All exchanged bentonites feature similarly- shaped isotherms that are curved in the low-pressure domain, followed by a domain of more gradual increase. The steepness of the isotherm in the low-pressure domain and the high- pressure capacity decrease with increasing adsorption temperature. A comparison between these results and CO: adsorption on non-exchanged bentonite, where adsorption is restricted 25 to an external surface of approximately equal size, suggests that the larger adsorption capacity of the cation-exchanged bentonites can be attributed to adsorption in the interlayer space that is now sufficiently opened up by the large cations.

All bentonites adsorb less CH4 than CO,. Cs-bentonite and MMA-bentonite hardly sorb CHa4 over the entire P and T-range (~0.18 mmol g-1 and ~0.27 mmol g7', respectively, at 10°C and bar), similar to non-exchanged bentonite. The CH4 adsorption isotherms of TMA-bentonite are moderately curved with a maximum adsorption capacity of ~0.76 mmol g™' at 10°C and 10 bar. A comparison of these results with CH4 adsorption on non-exchanged bentonite suggest that only the interlayer space of TMA-bentonite is readily accessible to CH4 and adsorption of 10 CHa on Cs-bentonite and MMA-bentonite is (mostly) restricted to external surfaces.

The adsorption isotherms were fit with the (multi-site) Langmuir adsorption isotherm: n;b;P q= Dir where n; is the number of adsorption sites of type i and bi is the equilibrium constant for sites of type i. When the gas is only adsorbed on the external surface, i = 1 (i.e., for CO: on non- exchanged bentonite, and CH4 on non-exchanged, Cs-, and MMA-bentonite). When the gas is adsorbed on the external surface and in the interlayer space, i € {1,2} (i.e, for CO: on Cs-,

MMA-, and TMA-bentonite, and CH4 on TMA-bentonite).

The CO2/CHa4 adsorption selectivity S of the materials that does not take into account competitive or synergistic effects can be determined from the Langmuir fit to the equilibrium

CO: and CH, adsorption isotherms (Figure 3). The selectivity follows the order Cs-bentonite > MMA-bentonite > TMA-bentonite, i.e., the selectivity decreases with increasing cation size.

At typical conditions for biogas upgrading (T = 30°C, feed pressure PCO: = PCH4 = 0.5 bar), the selectivity of Cs bentonite, MMA-bentonite, and TMA-bentonite is $ = 35, S= 23, and S= 4, respectively.

Adsorption and desorption kinetics

CO: adsorption and desorption kinetics are measured on the clay powders (to probe the ‘intrinsic’ adsorption) and the clay particles of two different sizes (to probe diffusional transport limitations) (Figure 4). CO: adsorption and desorption on all clay powders is fast and follows the approximate CO: concentration in the container (for which equilibration takes ~1 min).

CO: adsorption and desorption time scales of the small Cs- and TMA-bentonite particles (dp ~ 4 mm) are nearly identical to the adsorption and desorption time scales on the powder, suggestion that these particles are sufficiently porous to allow for fast diffusional transport of the gas species into the particle. Smaller particles (dp = 4 mm) of MMA bentonite display CO» adsorption and desorption time scales > 10 min. 26

Simultaneous CO2 and CH4 adsorption

The breakthrough measurements of the gas mixture in the fixed-bed reactor setup at high (0.40 L min™") and low (0.20 L min") flow rates (Figure 5) were considered. For Cs-bentonite and TMA-bentonite, after the biogas flow is switched to the reactor and the N: initially present in the reactor is displaced, first the signal of CHs4 grows rapidly while no CO: is detected. This implies that purified CHa, mixed with the N dilution gas, flows through the analyzer, with the

CO: retained in the bed. Once CO: adsorption in the bed progresses towards saturation, also

CO: is detected in the effluent. It was found that the time at which CH4 and CO: are first detected and the shape of the breakthrough curve depend on the material and the flow rate (a direct comparison of the Cs-bentonite and TMA-bentonite was made). For MMA-bentonite, on

CO: and CH, are first detected nearly simultaneously (Figure 4).

For Cs-bentonite, that has a high CO,/CHj4 selectivity and a limited CH. adsorption capacity,

CH, is first detected after approximately 19 s (0.40 L min™) and 37 s (0.20 L min™). This is approximately the time required for the displacement of the reactor void volume (~62 mL) by

CHa, indicating limited adsorption of CHa. In contrary, the first detection of CH4 on TMA- bentonite is at approximately 41 s and 90 s, respectively. Consequently, the TMA-bentonite must have adsorbed considerable CH.. Yet, immediately after breakthrough, the produced flow of CHs is larger in the system with TMA-bentonite than with Cs-bentonite, indicating that atleast part of the adsorbed CH4 on TMA-bentonite is desorbed again. This desorption may have two origins: (i) local concentration swings of CH4 due to the adsorption of CO, upstream followed by the progression of the CO: adsorption front, and (ii) competitive adsorption leading to the displacement of adsorbed CH4 by CO:.

In line with their nearly identical CO: adsorption capacity, CO: breakthrough on Cs- and TMA- bentonite occurs nearly simultaneously, after approximately 1.3 min (0.40 L min") and 3.6 min (0.20 L min™"). For Cs bentonite, temporal shifts in CO: breakthrough between different experiments was observed. These shifts correlate well with the temperature of the environment (~20 — 27°C), with accelerated breakthrough at higher temperature due to a lower adsorption capacity.

Comparing the experiments while normalized for their flow rates and as a function of the cumulative input biogas volume, it turns out that the measurements at different flow rates nearly overlap, apart from two distinct features. First, the sharpness of the breakthrough fronts of both CH4 and CO: decreases with increasing flow rate, likely due to enhanced axial dispersion at higher flow rates, and/or limitations in diffusional transport in the particles.

Second, the breakthrough of CO. is delayed with decreasing flow rate, likely due to thermal effects: a lower flow rate permits more time to dissipate the released adsorption heat, hence the sorbent can be utilized at a lower average temperature. 27

Sorbent regeneration

The regeneration of the bed with Nz after it has been fully saturated with the biogas mixture was considered. Regeneration experiments were performed at high (0.60 L min"*) and low (0.30 L min") flow rates (Figure 6). For all experiments, after the Nz flow is switched to the reactor, immediately a large flow of CO; and CH, is detected as a result of the biogas present in the void space of the reactor being displaced. For Cs-bentonite, no CHa4 is detected after approximately 24 s. For MMA-bentonite and TMA-bentonite, CHa is detected until approximately 3 min and 2 min, respectively. Based on the material selectivity and diffusional transport in the particles, it appears that this CH, originates (i) for MMA-bentonite mostly from

CH, that is slowly displaced from the particle void space, and (ii) for TMA-bentonite from CH4 that was desorbed from the interlayer space. The amount of desorbed CO: and the typical desorption time of CO: are, on all materials, clearly larger than for CHs. The typical CO2 desorption times for Cs-bentonite and TMA-bentonite are 5 min and 7 min (0.60 L min") and 8 min and 10 min (0.30 L min), respectively. For MMA-bentonite, CO: is still detected after 1 hr of desorption.

Comparison isotherm, adsorption and desorption

Table 1 summarizes CO: and CH, adsorption and desorption in the reactor, and the adsorption based on the single component isotherms under reactor conditions. With the sole exception of CH4 on TMA-bentonite, adsorption and desorption in the reactor is in reasonable agreement (overlapping error margin) with the single component isotherms, indicating that competitive and synergistic effects do not play a significant role here. It can be noted, however, that the relative error of, in particular, CH4 adsorption and desorption on Cs- and

MMA-bentonite in the reactor appears large. Regarding CH4 adsorption on TMA-bentonite, it appears that the adsorption capacity of CH decreases due to the competitive adsorption with

CO: in the interlayer space. Hence, the effective selectivity of TMA-bentonite is higher than its single component selectivity (S = 4) and estimated as 5 = 7.

Table 1: Adsorption capacity based on the single component isotherms, and as measured in the fixed bed reactor during adsorption and desorption (reported values in mmol gt). 2 At 0.5 bar, 23 °C. Interpolated from the isotherms in Figure 2 and multiplied by 0.91 to account for the binder material. 5 Gas volume in the void space is subtracted (assuming

Vvoid = 62 mL with ¢cC0O2 = cCH4 = 0.5). © The integration of the adsorption and desorption signals were cut after 20 min and 30 min, respectively, because of the slow adsorption and desorption kinetics. 28

Material | Single Adsorption Desorption

TT

[ae [aOR [aa [aG0F [aOR [aa [Go [ach

Cs 0.40 0.01 0.39 0.42 0.03 0.43 046+ |004¢

MMA 0.33 0.02 029+ |028+ [000+ [033+ [035+ [000%

TMA 0.40 0.12 0.35 0.40 0.05 0.34 0.39 0.04

Cyclic stability

The cyclic stability of Cs- and TMA-bentonite was considered (Figure 7). To this end, consecutive adsorption-desorption cycles were measured. Each cycle consisted of an adsorption time of 8 minutes with a 0.40 L min" biogas flow, followed by a desorption time of minutes with a 0.60 L min™ Nz flow. When switching between adsorption and desorption and vice versa, a waiting period of 1 minute was employed. The exchanged bentonite demonstrates excellent cyclic stability. 10 Concluding remarks

Cation-exchanged bentonite clay can be used for biogas upgrading in a pressure-swing fixed bed reactor. These clays can be highly selective compared to Activated Carbon (typically: S < 6) and are able to release the captured CO: faster and/or under milder conditions than, e.g.,

Zeolite 13X, in the latter case at the expense of selectivity. The comparison with CMS in terms of their kinetic performance is less straightforward. For example, adsorption time scales(0 — 90% of the capacity) of ~1 min (cylindrical particles with dp = 0.9 mm; CMS KP 407) and ~2 min (dp = 1.8 mm; Takeda CMS 3K) were reported. For TMA-bentonite with dp = 4 mm, this is ~1.2 min. Yet, (i) larger particles are intrinsically subject to longer mass diffusion times and slower dissipation of the adsorption heat, and (ii) the clays were studied under transient partial pressure (N2 — CO) with an equilibration time of ~1 min, whereas CMS were studied under transient absolute pressure. Without being bound by theory, it appears that adsorption on clay particles can be at least as fast as, and probably a few times faster than adsorption on equally-sized CMS particles. Despite the relatively small adsorption capacity of the clays compared to conventional sorbents, the fast CO, adsorption and desorption kinetics allow for short cycle times and hence increased productivity.

On the process side, the clay sorbents work best for near-ambient pressure conditions (vacuum to pCO, S 1 bar) and desorption can be performed without the input of external heat, which (i) reduces the energy demand of the setup, and (ii) simplifies the setup and 29 hence reduces capital and operational costs, compared to reactors that do require higher pressures and/or external heating. Furthermore, the diffusional transport into the Cs- and

TMA-bentonite particles is fast, which allows for the use of relatively large sorbent particles.

This appears of relevance, as the pressure drop over the reactor length decreases with increasing particle size.

In conclusion, it is demonstrated that MMT-rich bentonite clays with appropriately sized cations can provide a viable alternative to conventional sorbents for biogas upgrading in a pressure-swing fixed bed reactor, in particular due to the combination high selectivity and fast adsorption and desorption kinetics of this sorbents.

Claims (1)

CONCLUSIONS 1. A method for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO: and CH, the method comprising contacting the gas mixture with an adsorbent and obtaining a CHy-enriched gas fraction, the adsorbent comprising an aluminium phyllosilicate material having one or more intercalating units selected from the group consisting of an alkali metal cation, an alkaline earth metal cation and an ammonium cation, thereby providing a basal spacing in the range of 10 - 15 Å. 2. A method according to claim 1, wherein CO: from the gas mixture is adsorbed onto the adsorbent. 3. The method of claim 1 or 2, further comprising a step of regenerating the adsorbent. 4. The method of claim 3, wherein the regeneration comprises a step of desorbing the CO2 from the adsorbent to provide a CO2-enriched gas fraction. 5. A method according to any preceding claim, wherein the aluminium phyllosilicate is a smectite- and/or vermiculite-containing material. 6. A method according to claim 5, wherein the smectite-containing material and/or the vermiculite-containing material is bentonite and/or Fuller's earth. 7. The method of claim 5 or 6, wherein the smectite-containing material comprises one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, hectorite, saponite and sauconite. 8. The method of claim 7, wherein the smectite-containing material comprises montmorillonite. 9. A method according to any preceding claim, wherein the cation is a hydrated cation. 10. A method according to any preceding claim, wherein the alkali metal cation is Cs" and/or K* cation. 31 11. A method according to any preceding claim, wherein the alkaline earth metal cation is Ca?* and/or Mg?* cation. 12. A method according to any preceding claim, wherein the alkaline earth metal cation is hydrated Ca?* cation. 13. A method according to any preceding claim, wherein the alkaline earth metal cation is hydrated Mg?* cation. 14. A method according to any preceding claim, wherein the ammonium cation is C1-C4 alkylammonium cation. 15. A method according to claim 14, wherein the C1-C4 alkylammonium cation is methylammonium cation and/or tetramethylammonium cation. A method according to any preceding claim, wherein the amount of the one or more intercalating units in the aluminium phyllosilicate material is 0.1 - 3 mEq per g of aluminium phyllosilicate material. 17. The method of claim 18, wherein the amount of the one or more intercalating units in the aluminium phyllosilicate material is 0.4 - 1.2 mEq per g of aluminium phyllosilicate material. 18. A method according to any preceding claim, wherein the adsorbent comprises 1-40 wt.% binder and 60-99 wt.% aluminium phyllosilicate material, calculated on the weight of the binder and the aluminium phyllosilicate material. 19. A method according to claim 18, wherein the binder is a non-activated aluminium phyllosilicate material and/or a plasticising organic binder. 20. A method according to any preceding claim, wherein the adsorbent is provided in one or more forms selected from the group consisting of a powder, a film, a fiber, a coating, a self-supporting structure, a monolith and particles. 21. A method according to claim 20, wherein the particles have an average diameter of 0.1-50 mm. 22. A method according to any preceding claim, wherein the gas mixture is contacted with the adsorbent at a CO: partial pressure of 0.1 - 10 bar. 32 23. A method according to any preceding claim, wherein the gas mixture is contacted with the adsorbent at a temperature of 0-70°C. 24. A method according to any preceding claim, wherein the gas mixture comprises 30-60 vol.% CO: and 40-70 vol.% CH4, calculated on the gas mixture. 25. A method according to any preceding claim, wherein the CHa-enriched gas fraction comprises 1 - 30 vol.% CO: and 70 - 95 vol.% CH4, calculated on the CHa4-enriched gas fraction. 26. Aluminium phyllosilicate material for obtaining a CHa4-enriched gas fraction from a gas mixture comprising CO: and CHa, wherein the aluminium phyllosilicate material comprises one or more intercalating units selected from the group consisting of an alkali metal cation, an alkaline earth metal cation and an ammonium cation, thereby providing a base distance in the range of 10 - 15 Å, wherein the aluminium phyllosilicate material has a selectivity in CO2/CH: adsorption of at least 2, wherein selectivity in CO2/CH adsorption is defined as the ratio in CO2/CH4 adsorption capacity measured at a total pressure of 1 bar and at 20 °C for a 50/50 vol.% CO:/CHs gas mixture. 27. Aluminium phyllosilicate material according to claim 26, wherein the aluminium phyllosilicate material has a CO2 adsorption capacity of at least 0.8 mmol g', measured at a pressure of 10 bar and at 20°C for pure CO2. 28. Aluminium phyllosilicate material according to claim 26 or 27, wherein the aluminium phyllosilicate material is a smectite- and/or vermiculite-containing material. 29. The aluminium phyllosilicate material of claim 28, wherein the smectite-containing material and/or the vermiculite-containing material is bentonite and/or Fuller's earth. 30. The aluminium phyllosilicate material of any one of claims 26 to 29, wherein the smectite-containing material comprises one or more selected from the group consisting of montmorillonite, beidellite, nontronite, volkonskoite, hectorite, saponite and sauconite. 33 31. The aluminum phyllosilicate material of claim 30, wherein the smectite-containing material comprises montmorillonite. 32. An aluminium phyllosilicate material according to any one of claims 26 to 31, wherein the cation is a hydrated cation. 33. An aluminium phyllosilicate material according to any one of claims 26 to 32, wherein the alkali metal cation is Cs* and/or K* cation. 34. An aluminium phyllosilicate material according to any one of claims 26 to 33, wherein the alkaline earth metal cation is Ca? and/or Mg? cation. 35. The aluminium phyllosilicate material of any one of claims 26 to 34, wherein the alkaline earth metal cation is hydrated Ca?" cation. 36. The aluminium phyllosilicate material of any one of claims 26 to 35, wherein the alkaline earth metal cation is hydrated Mg?* cation. 37. The aluminium phyllosilicate material of any one of claims 26 to 36, wherein the ammonium cation is C1-C4 alkylammonium cation. 38. The aluminium phyllosilicate material of claim 37, wherein the C1-C4 alkylammonium cation is methylammonium cation and/or tetramethylammonium cation. 39. The aluminium phyllosilicate material of any one of claims 26 to 38, wherein the amount of the one or more intercalating units in the aluminium phyllosilicate material is 0.1 to 3 mEq per g of aluminium phyllosilicate material. 40. The aluminium phyllosilicate material of claim 39, wherein the amount of the one or more intercalating units in the aluminium phyllosilicate material is 0.4 - 1.2 mEq per g of aluminium phyllosilicate material. 41. Use of an aluminium phyllosilicate material for obtaining a CHa- enriched gas fraction from a gas mixture comprising CO; and CH, wherein the aluminium phyllosilicate material is as defined in any one of claims 26 to 40. 42. Use according to claim 41, wherein a further use is the upgrading of biogas and/or landfill gas. 34 43. Adsorbent for obtaining a CHs-enriched gas fraction from a gas mixture comprising CO: and CH, wherein the adsorbent comprises the aluminium phyllosilicate material as defined in any one of claims 26 to 40. 44. An adsorbent according to claim 43 comprising 1-40 wt.% of a binder and 60-99 wt.% of the aluminium phyllosilicate material, based on the weight of the binder and the aluminium phyllosilicate material. 45. The adsorbent of claim 44, wherein the binder is a non-activated aluminum phyllosilicate material and/or a plasticizing organic binder. 48. The adsorbent of any one of claims 43 to 45, wherein the adsorbent is provided in one or more forms selected from the group consisting of a powder, a film, a fiber, a coating, a self-supporting structure, a monolith and particles. 47. Apparatus for obtaining a CH-enriched gas fraction from a gas mixture comprising CO: and CH,, the apparatus comprising the aluminium phyllosilicate material as defined in any one of claims 26-40 and/or the adsorbent as defined in any one of claims 43-46. 48. The apparatus of claim 47, wherein the apparatus is a fixed bed reactor.