AU2009323821A1

AU2009323821A1 - Process for gas separation

Info

Publication number: AU2009323821A1
Application number: AU2009323821A
Authority: AU
Inventors: Patrizia Broccia; Angela Carati; Liberato Giampaolo Ciccarelli; Caterina Rizzo; Marco Tagliabue
Original assignee: Eni SpA
Current assignee: Eni SpA
Priority date: 2008-12-01
Filing date: 2009-11-30
Publication date: 2011-07-07
Also published as: IT1392165B1; HRP20110442A2; WO2010064121A8; WO2010064121A3; ITMI20082126A1; WO2010064121A2

Abstract

The present invention relates to a process for the separation of gases which comprises putting a mixture of gases in contact with a porous material, containing a silica matrix in which one or more metal oxides are possibly uniformly dispersed, which are selected from transition metals or from metals of groups IIIA, IVA and VA, having a surface area larger than 500 m2/g, a pore volume between 0.3 and 1.3 ml/g, a pore diameter smaller than 40 Angstrom and a XRD powder spectrum which does not have a crystalline structure, does not show any peak, and has a single broad diffraction line, or, in any case, a wide¬ spread scattering at angular values not higher than 2θ = 5° with CuKa radiation, without any other scattering phenomena coherent for higher angular values. By means of the process of the present invention, the selective adsorption is obtained of at least one of the gases forming the gaseous mixture. These adsorbing materials are regenerable and are particularly suitable for bulk removal operations of acid gases from natural gas.

Description

WO 2010/064121 PCT/IB2009/007618 PROCESS FOR GAS SEPARATION DESCRIPTION The present invention relates to a process for the separation of gases comprising putting a mixture of gases 5 in contact with a particular porous material, containing a silica matrix in which one or more metal oxides are possibly uniformly dispersed, said metal oxides being se lected from transition metals or from metals of groups IIIA, IVA and VA. This material has a surface area larger 10 than 500 m 2 /g, a pore volume between 0.3 and 1.3 ml/g, a pore diameter smaller than 40 Angstrom and an XRD powder spectrum which does not have a crystalline structure, does not show any peak, and has a single broad diffrac tion line, or, in any case, a widespread scattering at 15 angular values not higher than 20 = 50 with CuKa radia tion, without any other scattering phenomena coherent for higher angular values. By means of the process of the present invention, the selective adsorption of at least one of the gases forming the gaseous mixture, is ob 20 tained. The process is particularly suitable for the sweet ening of natural gas, mainly to remove carbon dioxide, hydrogen sulphide or mixtures thereof, from natural gas. The process can also be used in the separation of hydro 25 gen from blends containing carbon dioxide, carbon monox -1- WO 2010/064121 PCT/IB2009/007618 ide, hydrogen sulphide, water and hydrocarbons, such as, for example, gaseous effluents from steam methane reform ing. In this case, hydrogen is the non-adsorbed compo nent. 5 The separation of gases in a blend can be effected using various methods. For the removal of nitrogen from natural gas, for example, cryogenic processes, adsorption processes or membrane systems, can be used. In all these processes, the gas is produced at low pressure and must 10 therefore be recompressed to be delivered. The cryogenic processes are also carried out at low temperatures and therefore require pre-treatment to re move the components present in the natural gas which so lidify under these conditions. 15 In order to separate acid gases such as CO 2 and H 2 S from natural gas, systems respectively based on the use of amines, solvents, alkaline solutions of inorganic salts or mixtures thereof, can be used. The acid gases are then eliminated from the solvent by means of high 20 temperature stripping or depressurization. These tech nologies are typically used for large gas volumes to be treated. Technologies based on semi-permeable membranes have been proposed for gas separation. In Guoqing Guan et al., 25 Journal of Chemical Engineering of Japan, vol.34, No.8, -2- WO 2010/064121 PCT/IB2009/007618 pp. 990-997, 2001, for example, the separation of nitrogen from oxygen is described, using membranes containing zeo lites of the FAU type. In the case of the purification of natural gas, mem 5 brane systems are used for separating carbon dioxide: the membranes consist of polymer films without pores and ex tremely dense, in which the carbon dioxide dissolves and is conveyed by diffusion. In US 3,616,607, the use is de scribed of a membrane based on polyacrylonitrile for the 10 separation of N 2

/CH

4 with a high selectivity, but low permeability. US 6,565,626 describes a process with or ganic membranes permeable to CO 2 , H 2 0, H 2 S, N 2 , but with a low permeability to CH 4 . The SPREX process allows the extraction of hydrogen 15 sulphide from natural gas streams containing at least 10% by volume of H 2 S by cooling the gaseous feeding stream to -300C or -60 0 C (Hydrocarbon Processing: Gas Processes 2006, Gulf Publishing Company). A stream rich in H 2 S is thus produced, suitable for 20 being injected again into the gas well, together with a stream rich in CH 4 , destined for washing with amines for the abatement of the residual acid gases until the speci fication required. Adsorption/desorption cycles are also known, such as, 25 for example, those of the "pressure swing" (PSA), "thermal -3- WO 2010/064121 PCT/IB2009/007618 swing" (TSA), "vacuum swing" (VSA), "pressure-thermal swing" (PTSA), "pressure-vacuum swing" (PVSA) type. In particular, gas separation by "pressure swing ad sorption" (PSA) is well-known to experts in the field and 5 allows the selective adsorption and separation of the com ponents of a gaseous mixture. The desired product is nor mally only one of the components. PSA-type processes sub stantially comprise the following steps: - a first step in which a gaseous mixture containing 10 two or more gases is put in contact, at high pres sure, with an adsorbing material and one or more of the gases forming the mixture are selectively ad sorbed; the adsorption normally takes place in short times, in the order of 30 seconds to 5 minutes; 15 - a subsequent step wherein the adsorbed gas or gases are desorbed by means of one or more of the follow ing systems: pressure lowering, washing with gas. The gas desorption is obtained in this way, and the gas is recovered by regenerating the same adsorbent; 20 - and a last step, which concludes the cycle, in which the adsorbing bed is pressurized with the gas fed. Many processes of this type use zeolites as adsorbing material. US 2,882,243, for example, describes the use of zeolite A as adsorbing agent for separating nitrogen and 25 oxygen. US 3,140,933 describes the use of zeolite X, for -4- WO 2010/064121 PCT/IB2009/007618 the same type of separation. In US 4,925,460, a chabazite exchanged with lithium is used for gas separation. EP 758561 describes a process for nitrogen adsorption from gaseous streams containing it, by using suitably ex 5 changed zeolites, selected from chabazite, offretite, eri onite, levinite, mordenite, zeolite A, zeolite T, EMC-2, ZSM-3, ZSM-18, ZK-5, zeolite L and zeolite beta. The sepa ration of nitrogen from mixtures containing it together with methane is effected in US 6,068,682, using a new mo 10 lecular sieve containing titanium. Engelhard Corporation (now BASF Catalysts) applied this material in a process called Molecular Gate, capable of separating nitrogen from methane (US 6,197,092, US 6,444,012). The Molecular Gate process can also be applied 15 to the removal of carbon dioxide from methane (US 6,610,124). EP 1,254,694 describes the use of zeolite X for separating CO 2 and H 2 0 from air. If necessary, the de sorption phase of gases from the adsorber can be effected by thermal treatment (TSA), or by means of a vacuum (VSA). 20 A process is described in WO 2008/00380 for the separation of gases which includes putting a gas mixture in contact with an ESV-type zeolite in order to obtain the selective adsorption of at least one of the gases forming the gase ous mixture. 25 "Carbogenic" adsorbents are also mentioned for gas -5- WO 2010/064121 PCT/IB2009/007618 separation. In US 4, 521, 221 a process based on "carbon molecular sieves" (CMS) is described for the purification of gaseous mixtures containing methane. In separation processes based on adsorption/desorption 5 cycles many variables are involved and determine their ef ficacy. The characteristics of the adsorbing material (ex.

composition, porosity, surface properties) are at the ba sis of the separation capacity of the different gas compo nents. Other variables can be important: for example the 10 sensitivity of the adsorbent to humidity can influence the surface reactivity (the hydroxylation degree, for ex ample) or the porosity, or an insufficient stability can prevent the thermal regeneration of the material to elimi nate the accumulation of the adsorbed gas. Low recoveries 15 of the desired gas require onerous internal recycling. It has now been unexpectedly found that certain mate rials having a high surface area and a narrow pore dis tribution can be used as adsorbents for the separation of gaseous mixtures providing very high selectivities, even 20 such as to allow the direct use of the gas without re quiring subsequent recycling treatment or further purifi cation steps. These materials can be completely regenerated by means of isothermal depressurization. They are also par 25 ticularly stable and can therefore undergo thermal treat -6- WO 2010/064121 PCT/IB2009/007618 ment with the aim of restoring their adsorbing character istics. In particular, they have proved to be particu larly suitable for "bulk removal" operations of acid gases from natural gas. "Bulk removal" operations spe 5 cifically consist in the massive removal of pollutants present in natural gas, without necessarily reaching the required specifications, possibly passed on to subsequent "polishing" or finishing treatment (R. Wagner, B. Judd, Gas Sweetening Fundamentals, Proceedings of the 5 6 th 10 Laurance Reid Gas Conditioning Conference, Norman, OK, 2006, 1) . The in situ regenerability for many cycles is therefore a main requirement for adsorbents to be used in "bulk removal" operations. Specifically as a result of the high quantities of pollutants to be removed from 15 natural gas, the use of poorly regenerable adsorbers (which are such as to require frequent substitutions) cannot be proposed. A first object of the present invention therefore re lates to a process for gas separation comprising putting 20 a mixture of gas in contact with a porous material in or der to obtain the selective adsorption of at least one of the gases forming the gaseous mixture, wherein said mate rial comprising a silica matrix in which one or more metal oxides are possibly uniformly dispersed, selected 25 from transition metals or from metals belonging to groups -7- WO 2010/064121 PCT/IB2009/007618 IIIA, IVA and VA, characterized by a surface area larger than 500 m 2 /g, a pore volume ranging from 0.3 to 1.3 ml/g, a pore diameter lower than 40 Angstrom, an XRD pow der spectrum which does not have a crystalline structure, 5 does not reveal any peak, and has a single broad diffrac tion line, or, in any case, a widespread "scattering", at angular values not larger than 20 = 50 with CuKa radia tion, without any other scattering phenomena coherent for larger angular values. 10 The remaining gases forming the mixture pass through the adsorbing bed and can therefore be separated. The ad sorbed gas(es) are subsequently recovered and/or removed by desorption. The material used in the process of the present in 15 vention, comprising a silica matrix in which one or more metal oxides selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA and having the aforementioned characteristics, are possi bly uniformly dispersed, is called ERS-8 and is described 20 in EP 691305, EP 736323 and EP 812804. These materials preferably have a surface area larger than 800 m 2 /g and a pore volume preferably between 0.3 and 0.6 ml/g. A particular aspect of the present invention is that 25 the metal oxide dispersed in the silica matrix is alumin -8- WO 2010/064121 PCT/IB2009/007618 ium oxide: these silico-aluminas of the ERS-8 type pref erably have a SI0 2 /A1 2 0 3 molar ratio higher than 50, even more preferably ranging from 100 to 500. In accordance with the IUPAC terminology, "Manual of 5 Symbols and Terminology" (1972), Appendix 2, Part I Coll. Surface Chem. Pure Appl. Chem., Vol. 31, page 578, in which pores with a diameter smaller than 20 Angstrom are called micropores, those with a diameter of between 20 and 500 Angstrom are defined mesopores, those with a di 10 ameter larger than 500 Angstrom, macropores, the materi als of the ERS-8 type used in the present invention and, in particular, silica-aluminas of the ERS-8 type, are mi cro-mesoporous materials and preferably substantially mi croporous. 15 The materials of the ERS-8 type, and in particular silica-aluminas of the ERS-8 type and their preparation are described in EP 691305, EP 736323 and in EP 812804, whose content is incorporated herein as reference, in G. Perego et al. "ERS-8: a new class of microporous alumi 20 nosilicates" H. Chon, S. K. Ihm and Y.S. Uh (Editors) Progress in Zeolite and Microporous Materials, Studies in Surface Science and Catalysis, Vol. 105, 1997 Elsevier Science B.V. and in C.Rizzo et al., "Synthesis and tex tural properties of amorphous silica-aluminas", Studies 25 in Surface Science and Catalysis Volume 128, 2000, Pages -9- WO 2010/064121 PCT/IB2009/007618 613-622. In accordance with what is described in EP 691305, for example, the materials of the ERS-8 type of the pre sent invention can be prepared as follows: 5 (A) a solution of a tetra-alkyl orthosilicate in al cohol is subjected to hydrolysis and gelification with an aqueous solution of a hydroxide of tetra-alkyl ammonium having the formula:

R'

4 N-OH 10 wherein R' represents a C 3

-C

7 alkyl group or one or more soluble or hydrolyzable compounds of one or more met als selected from transition metals or from metals belong ing to groups IIIA, IVA and VA; the quantity of the constituents of the above solution 15 being such as to respect the following molar ratios:

H

2 0/SiO 2 = 5-30 R-OH/SiO 2 = 5-10

R'

4 N*/SiO 2 = 0.05 - 0.5 metal oxides/SiO 2 = 0 - 0.05, 20 whereas the H 2 0/R' 4 N' ratio varies with a variation in the number of carbon atoms in the alkyl chain R' according to the values shown in Table 1 below: 25 -10- WO 2010/064121 PCT/IB2009/007618

R'

4 N-OH H 2 0/R' 4 N* Tetra-hexyl-ammonium-hydroxide < 133 Tetra-pentyl-ammonium-hydroxide < 100 Tetra-butyl-ammonium-hydroxide < 73 5 Tetra-propyl-ammonium-hydroxide < 53 10 Table 1 operating at a temperature close to the boiling point, at atmospheric pressure, of the alcohol used in the solution of tetra-alkyl-orthosilicate and of any alcohol formed as by-product of the above hydrolysis reaction, with no 15 elimination, or without any substantial elimination of said alcohols from the reaction environment, preferably at a temperature ranging from 20 to 80OC; (B) subjecting the gel in step (a) to drying and cal cination. 20 The tetra-alkyl orthosilicate can be selected from tetramethyl-, tetraethyl-, tetrapropyl-, tetra-isopropyl orthosilicate, and tetra-ethyl-orthosilicate (TEOS) is preferred. The alcohol used for solubilizing the above mentioned tetra-alkyl orthosilicate is preferably ethanol. 25 The soluble or hydrolyzable compounds of one or more met als are selected from the salts or hydrosoluble or hydro -11- WO 2010/064121 PCT/IB2009/007618 lysable acids of the same metals. Among these, aluminium tripropoxide and triisopropoxide are preferred. In the case of liquid aluminium alkoxides, it is possible to dis solve these alkoxides in the alcohol solution instead of 5 in the aqueous solution. Preparations of materials of the ERS-8 type are also described in EP 736323 and EP 812804. In particular, preparations are preferred in which the hydrolysis and gelification step is effected at atmospheric pressure, 10 using reactors equipped with reflux condensers and in the presence of a tetra-alkyl ammonium hydroxide in which at least one of the alkyl substituents contain 6 or 7 carbon atoms. The materials of the ERS-8 type, in particular 15 silico-aluminas of the ERS-8 type, can be used in the process of the present invention in the form bound with an inorganic binder, selected, for example, from alumina, silica, clay. Binding processes which can be used are those well-known to experts in the field, such as press 20 ing, extrusion, granulation, drop coagulation, atomiza tion techniques. In the final bound product, the material of the ERS-8 type and, in particular, the silico-alumina of the ERS-8 type, is contained in proportions of between 50 and 100% by weight with respect to the total weight of 25 the product, wherein the proportion of 100% refers to a -12- WO 2010/064121 PCT/IB2009/007618 formation in the absence of a binder. In the final bound product, the material of the ERS-8 type and, in particu lar, the silico-alumina of the ERS-8 type, is preferably contained in a proportion higher than 80% by weight with 5 respect to the total weight of the product. The process for the separation of gases of the present invention, which comprises putting a mixture of gases in contact with a material of the ERS-8 type, preferably a silico-alumina of the ERS-8 type, so as to have the selec 10 tive adsorption of at least one of the gases forming the gas mixture, can be effected by means of adsorp tion/desorption cycles. According to this latter technology, the gaseous mix ture to be fractionated is put in contact with the mate 15 rial of the ERS-8 type, preferably a silico-alumina of the ERS-8 type, in order to selectively adsorb one or more components of the same mixture. The non-adsorbed component is collected as pure product and the adsorbed components are periodically desorbed, for example by means of reduc 20 tion in the pressure and/or washing, and/or temperature increase, so as to avoid saturation of the adsorbing bed. Among processes based on adsorbing/desorbing cycles, those of the "pressure swing" (PSA), "thermal swing" (TSA), "vacuum swing" (VSA), "pressure-vacuum swing" 25 (PVSA) or "pressure-thermal swing" (PTSA) type (D.M. Ruth -13- WO 2010/064121 PCT/IB2009/007618 ven, S. Farooq, K.S. Knaebel, Pressure Swing Adsorption (1994) Wiley - VCH) can'be well used in the present inven tion. In the first case, "pressure swing adsorption", after 5 adsorption at high pressure of at least one of the gases forming the mixture, and the separation of the remaining components of the mixture, the pressure is reduced to de adsorb the adsorbed gas and regenerate the adsorbing bed containing the material of the ERS-8 type, preferably a 10 silico-alumina of the ERS-8 type. In the case of a TSA process the desorption step is effected, instead of by reducing the pressure, by raising the temperature of the adsorbing bed containing the mate rial of the ERS-8 type, preferably a silico-alumina of the 15 ERS-8 type. - In the case of a PTSA process, the adsorption step is carried out at high pressure, whereas the desorption step is effected by increasing the temperature of the adsorbing bed, containing the material of the ERS-8 type, preferably 20 a silico-alumina of the ERS-8 type, and reducing the pres sure. In the case of a VSA process, the adsorption step is carried out at atmospheric pressure, or slightly higher, whereas the desorption step is effected by reducing the 25 pressure to vacuum. -14- WO 2010/064121 PCT/IB2009/007618 In the case of a PVSA process, the adsorption step is carried out at high pressure, whereas the desorption step is effected by reducing the pressure to vacuum. A process of the PVSA type is therefore a particular case of the PSA 5 process, in which the desorption is effected under vacuum. In cases in which the use of a vacuum is not envis aged, the desorption can be facilitated by the contempora neous washing of the adsorbing bed containing, for exam ple, silico-alumina, by partial recycling of the pure com 10 ponent, not adsorbed, or with inert gas not contained in the feeding. The process of the present invention is preferably ef fected by means of "pressure swing adsorption" (PSA) o "pressure-thermal swing adsorption" (PTSA). 15 A particular aspect of the present invention is there fore a process for the separation of gases of the PSA type comprising the following steps: a) putting a mixture of gases in contact, under high pressure, with a porous material to selectively ad 20 sorb at least one of the gases forming the mixture and collecting or discharging the remaining gaseous components of the mixture, wherein said material includes a silica matrix in which one or more metal oxides selected from among transition metals or from among metals belonging to 25 groups IIIA, IVA and VA, are possibly uniformly dispersed, -15- WO 2010/064121 PCT/IB2009/007618 characterized by a surface area larger than 500 m 2 /g, a pore volume between 03 and 1.3 ml/g, an average pore di ameter smaller than 40 Angstrom, an XRD powder spectrum which does not have a crystalline structure, does not show 5 any peak and has a single, broad diffraction line, or in any case, a widespread scattering at angular values not larger than 20 = 50 with CuKa radiation, without any other scattering phenomena coherent for higher angular values; b) interrupting the flow of the gaseous mixture and 10 possibly reducing the pressure; c) desorbing the gas(es) adsorbed in step (a), by reduction of the partial pressure of the gas(es) adsorbed and collecting them or discharging them; d) re-pressurizing the system with the gas mixture 15 fed. Accessory operations such as recycling of the prod ucts, partial depressurization (in equi- and/or counter current with respect to the feed), rinsing of the adsorb ing bed, well-known to experts in the field, can be added 20 to phases (a) -(d). According to a preferred aspect, the material of the ERS-8 type used in step (a) is a silico alumina of the ERS-8 type. The adsorbing step (a) can be carried out at a tem perature ranging from 0 to 400C, preferably at room tem 25 perature, and at an adsorbing pressure of 10 to 90 bara, -16- WO 2010/064121 PCT/IB2009/007618 preferably 10 to 40 bara. In step (c) the desorption pressure can be selected from 0.1 to 10 bara, whereas the temperature ranges from 0 to 400C and is preferably room temperature. When in step 5 (c) the desorption is chosen to be effected under vacuum, the process will be in particular of the PVSA type. When the process of the present invention is effected by means of PTSA, the adsorption step (a) is carried out under the same conditions described above, whereas the de 10 sorption step (c) is effected by means of an increase in the temperature of the adsorbing bed containing the mate rial of the ERS-8 type, preferably a silico-alumina of the ERS-8 type, and a reduction in the pressure: it is there fore preferable to operate at a pressure ranging from 0.1 15 to 10 bara and a temperature of 50 to 250*C, even more preferably between 60 and 1000C. In both PSA and PTSA cases the desorption process and therefore the regeneration of the adsorbing bed containing the material of the ERS-8 type, are favoured by gas rins 20 ing, such as, for example, N 2 , CH 4 , air or hydrogen. The process of the present invention can be success fully used, in particular, for the purification of natural gas from pollutants selected from C0 2 , H 2 S, water and mix tures thereof, wherein the water is in a quantity, at the 25 most, equal to the saturation of the gaseous mixture. The -17- WO 2010/064121 PCT/IB2009/007618 contaminants are preferably adsorbed with respect to meth ane. According to a preferred aspect, the process of the present invention is used for the purification of natural gas from CO 2 and/or H 2 S. In accordance with the above, a 5 particularly preferred aspect of the present invention is a process of the PSA type for the separation of carbon di oxide, H 2 S or mixtures thereof from a gaseous mixture con taining them together with methane, comprising the follow ing steps: 10 a) putting said gaseous mixture in contact with a po rous material, at high pressure, in order to selectively adsorb carbon dioxide, H 2 S or their mixture, and collect ing the remaining gaseous component containing methane, wherein said material comprises a silica matrix in which 15 one or more metal oxides selected from transition metals or metals belonging to groups IIIA, IVA and VA, are possi bly uniformly dispersed, characterized by a surface area larger than 500 m 2 /g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter smaller than 40 Ang 20 strom, an XRD powder spectrum which does not have a crys talline structure, does not show any peak, and has a sin gle broad diffraction line, or, in any case, a widespread scattering at angular values not higher than 20 = 50 with CuKoa radiation, without any other scattering phenomena 25 coherent for higher angular values. -18- WO 2010/064121 PCT/IB2009/007618 b) interrupting the flow of the gaseous mixture and possibly reducing the pressure; c) desorbing carbon dioxide, H 2 S or their mixture, adsorbed in step (a), by reduction of the partial pres 5 sure of the gas or gases adsorbed, collecting or dis charging them; d) re-pressurizing the system with the gas mixture fed. In step (a) , a silico-alumina is preferably used as 10 adsorbing material of the ERS-8 type. If the separation of carbon dioxide, H 2 S or a mixture thereof, from a gase ous mixture containing them together with methane, is carried out by means of PTSA, the desorption step (c) is effected by an increase in the temperature of the adsorb 15 ing bed containing the material of the ERS-8 type, pref erably a silico-alumina of the ERS-8 type, and reduction of the pressure. The same general pressure and temperature conditions described above are applied to the separation of natural 20 gas from pollutants selected from C0 2 , H 2 S, water and mix tures thereof, by means of a process of the PSA or PTSA type. In particular, by using a material of the ERS-8 type, preferably a silico-alumina of the ERS-8 type in a PSA 25 process, it is possible to abate the content of acid -19- WO 2010/064121 PCT/IB2009/007618 gases in natural gas from 20% by volume to less than 2% by volume, with a methane recovery, expressed as CH 4 in the stream of sweetened gas, referred to the quantity of

CH

4 in the stream of gas to be treated, of at least 80%. 5 The material of the ERS-8 type, preferably a silico alumina of the ERS-8 type, when used in the present gas adsorption process, in particular when used for the re moval of acid gas, can be completely regenerated by iso thermal depressurization and a particularly preferred as 10 pect of the present invention is therefore to effect the desorption step of the adsorbed gases by reducing the partial pressure of the adsorbed gas(es), at a constant temperature. The materials of the ERS-8 type, used in the separa 15 tion process of the present invention and preferably silico-aluminas of the ERS-8 type, unexpectedly prove to be capable of contemporaneously satisfying the following requirements, with particular reference to C0 2 : a) maximum quantity of adsorbable CO 2 at 5 bara and 20 300C, higher than 50 Nml/g; b) ratio between the maximum quantity of adsorbable

CO

2 and CH 4 at 5 bara and 300C, higher than 3.5: c) maximum quantity of CO 2 that can be released by isothermal depressurization from 5 bara to 0.5 bara at 25 300C, equal to at least 75% of the maximum quantity ad -20- WO 2010/064121 PCT/IB2009/007618 sorbable at 5 bara. With particular reference to H 2 S, the materials of the ERS-8 type and, preferably, a silico-alumina of the ERS-8 type, used in the separation process of the present in 5 vention are capable of contemporaneously satisfying the following requirements: a) maximum quantity of adsorbable H 2 S at 5 bara and 30 0 C, higher than 120 Nml/g; b) ratio between the maximum quantity of adsorbable 10 H 2 S and CH 4 at 5 bara and 30 0 C, higher than 8.5: c) maximum quantity of H 2 S that can be released by isothermal depressurization from 5 bara to 0.5 bara at 300C, equal to at least 75% of the maximum quantity ad sorbable at 5 bara. 15 The process of the present invention can also be used for the separation of hydrogen from mixtures containing carbon dioxide, carbon monoxide and hydrocarbons, such as, for example, gaseous effluents from "steam methane reform ing". In this case, hydrogen is the non-adsorbed compo 20 nent. In the following examples, according to the present invention, the results of the experimental tests are ex pressed by using, as measurement parameter of the adsorb ing properties of a material, the adsorption capacity at 25 equilibrium q(Nml/g), expressed as the quantity of ad -21- WO 2010/064121 PCT/IB2009/007618 sorbed gas at equilibrium under certain conditions (T, P) and referring to the weight of the adsorbing material (specific capacity) . The function q(Nml/g) = f(T, p) is commonly referred to as adsorption/desorption isotherm. 5 The following examples have the sole 'purpose of de scribing the present invention in greater detail and should not be interpreted as limiting the objectives of the same. Example 1 - synthesis of ERS-8 silico-alumina 10 669.2 g of tetra-hexyl ammonium hydroxide at 40% by weight in aqueous solution are diluted with 928.4 g of wa ter and charged into a reactor equipped with a condenser. A solution containing 1667.0 g of tetra-ethyl orthosili cate, 2944.0 g of ethanol and 13.2 g of aluminium sec 15 butoxide are added at room temperature, and the whole mix ture is maintained under stirring for 3 hrs. A limpid sol is obtained which is concentrated in a rotavapor until a gel is formed. The gel is dried under vacuum at 800C and calcined at 5500C for 8 hrs. 20 The material obtained was characterized by adsorption of N 2 at -196 0 C: - specific surface area (BET method): 1260 m 2 /g; - pore volume (Gurvitsch rule) : 0.6 cm 3 /g; - average pore diameter (DFT method): 16 Angstrom. 25 Example 2 - Absorption test with ERS-8 silico-alumina -22- WO 2010/064121 PCT/IB2009/007618 The adsorbing material of Example 1 was pre-treated under vacuum at 3500C for 16 hrs and the adsorp tion/desorption isotherms were acquired on it for H 2 S, C0 2 , CH 4 at 30 -C. The results are shown in Figure 1. 5 From Figure 1 it can be seen that the adsorbing material synthesized according to Example 1 preferably adsorbs the acid gases (H 2 S and C0 2 ) with a high selectivity with re spect to CH 4 , within a wide pressure range. A high selectivity prevents the co-adsorption of 10 various components on the same adsorbing material, thus increasing the efficiency of the separation process. In the case of the sample of Example 1, the quanti ties of C0 2 , H 2 S and CH 4 adsorbed at 5 bara and 30 0 C are 57 Nml/g, 132 Nml/g and 14 Nml/g respectively. It follows 15 that the ratio between the maximum quantity of CO 2 and

CH

4 which can be adsorbed by the sample of Example 1 (at 5 bara and 300C) is equal to 4, whereas the ratio between the maximum quantity of H 2 S and CH 4 which can be adsorbed by the sample of Example 1 (at 5 bara and 300C) is equal 20 to 9.5. It can also be noted that the quantity of acid gas

(H

2 S and C0 2 ) which can be adsorbed by the adsorbing ma terial is strongly correlated with the pressure. This makes these adsorbing materials easily regenerable by de 25 pressurization and/or washing with gas (CH 4 , N 2 , for ex -23- WO 2010/064121 PCT/IB2009/007618 ample) . Regenerability is a necessary characteristic for an adsorbing material to be used in a cyclic separation process. In the case of the sample of ERS-8 silico-alumina of 5 Example 1, by depressurization to 0.5 bara under isother mal conditions, the adsorbing material releases about 80% of the acid gas (H 2 S and C0 2 ) adsorbed at 5 bara at 300C. Example 3 In this example, the behaviour is described of the ad 10 sorbing material synthesized as described in Example 1, in the competitive adsorption of CO 2 . A tubular adsorber was charged with the adsorbing ma terial granulated at 20-40 mesh. The adsorber was degassed in situ at 3500C under vac 15 uum for 16 hrs. After waiting for the system to be cooled to stabili zation of the pre-established temperature, a gaseous mix ture having a composition of CH 4

/CO

2

/N

2 = 60/27/13 (% vol.), was fed to the adsorber. 20 The following adsorption operative conditions were used: T = 27C p = 30 barg. Gas-chromatographic analyses effected on the effluent 25 from the adsorber revealed a reduction of the CO 2 content -24- WO 2010/064121 PCT/IB2009/007618 to less than 2.5% by volume for more than 20 minutes and the re-establishment of a CO 2 concentration identical to that in the feeding after about 35 minutes. On the whole, the CO 2 adsorption, referring to the 5 weight of adsorbing material, proved to be equal to 90 Nml/g. This value is comparable to the equilibrium value (ob tained from the measurements described in Example 2, car ried out with pure CO 2 ) and indicates the selectivity of 10 the adsorbing material. Also in the presence of a large excess of CH 4 in the feeding gas, in fact, it tends to preferably adsorb C0 2 .' Example 4 In this example, the regeneration of the adsorbing ma 15 terial synthesized as described in Example 1 is indicated, by means of depressurization and washing of the adsorbing bed with CH 4 . After an adsorption under pressure carried out accord ing to the procedure described in Example 2, the adsorbing 20 bed was regenerated in situ. The operation was carried out by depressurization and subsequent sweeping of the adsorbing bed with CH 4 . The following operative conditions were adopted for the regeneration: 25 T = 27 0 C -25- WO 2010/064121 PCT/IB2009/007618 p = 3 barg. In order to 'evaluate the regenerability of the adsorb ing bed, 5 adsorption/desorption cycles were repeated ac cording to the above-mentioned procedures. 5 Table 2 shows the quantities of CO 2 adsorbed (refer ring to the weight of the adsorbing material) during the cycles. Example 5 This example describes the effect of the thermal re 10 generation of the adsorbing material synthesized as de scribed in Example 1. At the end of the 5 adsorption/desorption cycles, men tioned in Example 4, the adsorbing material saturated with

CO

2 was treated at 3500C under a stream of CH 4 , in situ. 15 At the end of the thermal regeneration, after cooling the system to room temperature, the sequence of 5 adsorp tion/desorption cycles was repeated with the same proce dures described in Example 4. 20 -26- WO 2010/064121 PCT/IB2009/007618 Example 4 Example 5 Cycles CO 2 Ads. CO 2 Ads. [Nml / g] [Nml / g] 5 1 90 89 2 89 91 3 90 90 4 91 90 5 90 90 10 Table 2 From Table 2 the following can be observed: - the adsorbing material synthesized as described in Example 1 can be regenerated by depressurization and sweeping with CH 4 . No significant decrease in 15 the specific capacity for CO 2 is revealed during the 1-5 cycles. - the adsorbing material synthesized as described in Example 1, can be regenerated by thermal treatment. No significant decrease in the specific capacity 20 for CO 2 is revealed passing from the 5 cycles of Example 4 to the 5 cycles of Example 5. Example 6 (comparative) - Adsorption test with a commer cial adsorbent. An adsorbing test is carried out on a sample of com 25 mercial adsorbing material (Grace Davison SG125 silica) -27- WO 2010/064121 PCT/IB2009/007618 whose morphological characteristics (determined by ad sorption of N 2 at -1960C) are indicated hereunder: - specific surface area (BET method) : 725 m 2 /g; - pore volume (Gurvitsch rule): 0.38 cm 3 /g; 5 - average pore diameter (DFT method): 16 Angstrom. The adsorbing material was pretreated under vacuum at 3500C for 16 hrs and the adsorption/desorption isotherms of H 2 S and CO 2 were acquired on this at 30 *C. The re sults are indicated in Figure 2. 10 From the data shown in Figure 2 it can be seen that the specific capacity, respectively for H 2 S and C0 2 , of the commercial material is lower than that indicated in Figure 1 for the silico-alumina of the ERS-8 type . The specific capacity represents a fundamental char 15 acteristic for an adsorbing material to be used in a cy clic separation process. In particular, high specific ca pacities allow less frequent regenerations of the adsorb ing material used. Example 7 20 This example describes the behaviour of the adsorb ing material synthesized as described in example 1, in the competitive adsorption of H 2 S. A tubular adsorber was charged with the adsorbing material granulated at 20-40 mesh. 25 The adsorber was degassed in situ at 3500C under vac -28- WO 2010/064121 PCT/IB2009/007618 uum for 16 hrs. After waiting for the system to be cooled to stabili zation of the pre-established temperature, a gaseous mix ture having a composition of CH 4

/H

2 S = 90/10 (% vol.), was 5 fed to the adsorber. The following adsorption operative conditions were used: T = 27 0 C p = 30 barg. 10 Gas-chromatographic analyses effected on the effluent from the adsorber revealed a reduction of the H 2 S content to less than 500 ppmv in the phases preceding the satura tion of the bed. On the whole, the H 2 S adsorption, referring to the 15 weight of the adsorbing material, proved to be equal to 90 Nml/g. This value is comparable to the equilibrium value (ob tained from the measurements described in Example 2, car ried out with pure H 2 S) and indicates the selectivity of 20 the adsorbing material. Also in the presence of a large excess of CH 4 in the feeding gas, in fact, it tends to preferably adsorb H 2 S. Example 8 This example indicates the regeneration of the adsorbing 25 material synthesized as described in Example 1 by means -29- WO 2010/064121 PCT/IB2009/007618 of depressurization and washing of the adsorbing bed with

CH

4 . After an adsorption under pressure carried out accord ing to the procedure described in Example 7, the adsorbing 5 bed was regenerated in situ. The operation was carried out by depressurization and subsequent sweeping of the adsorbing bed with CH 4 . The following operative conditions were adopted for the regeneration: 10 T = 270C p = 3 barg. In order to evaluate the regenerability of the adsorb ing bed, 5 adsorption/desorption cycles were repeated ac cording to the above-mentioned procedures. 15 Table 3 indicates the quantities of H 2 S adsorbed (re ferring to the weight of the adsorbing material) during the cycles. Example 8 Cycles H 2 S Ads. [Nml / g] 1 90 2 89 3 89 4 91 5 90 Table 3 -30- WO 2010/064121 PCT/IB2009/007618 From the data indicated in Table 3 it can be deduced that the adsorbing material synthesized as described in Example 1, can be regenerated by depressurization and sweeping with CH 4 . No significant decrease in the spe 5 cific capacity of H 2 S is observed within the sequence of the cycles 1-5. In addition, the regeneration carried out without the application of vacuum, allows the possible costs due to the recompression of the stream rich in acid gas, to be limited, in the possibility of re-injection 10 into the well, related to "enhanced hydrocarbon recovery" operations. 15 20 25 -31-

Claims

1) Process for the separation of gases comprising placing a gaseous mixture in contact with a porous material to obtain the selective adsorption of at least one of the gases making up the gaseous mixture, wherein said material comprising a silica matrix in which one or more metal oxides are possibly dispersed, in a uniform manner, selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA, characterised by a surface area greater than 500 m²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crystalline structure, does not show any peak, and has a single broad diffraction line, or in any case a wide- spread "scattering", at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scattering" phenomena coherent for greater angular values.

2) Process according to claim 1 comprising a desorption step of the adsorbed gases.

3) Process according to claim 1 wherein the pore volume of the porous material is in the range of 0.3 - 0.6 ml/g.

4) Process according to claim 1 wherein the surface area of the porous material is greater than 800 m²/g. 5) Process according to one or more of the preceding claims wherein the metal oxide dispersed in the silica matrix, contained in the porous material, is aluminium oxide . 6) Process according to the preceding claim wherein the molar ratio between the aluminium oxide and the silica of the matrix contained in the porous material is greater than 50.

7) Process according to one or more of the preceding claims wherein the porous material is in a bound form with an inorganic binder.

8) Process according to claim 1 implemented through adsorption cycles.

9) Process according to claim 8 implemented through ad- sorption cycles of the pressure swing adsorption (PSA) , thermal swing adsorption (TSA) , vacuum swing adsorption (VSA) , pressure-thermal swing adsorption (PTSA) , or pressure-vacuum swing adsorption (PVSA) type.

10) Process according to claim 9 implemented through ad- sorption cycles of the PSA or PTSA type.

11) Process of the PSA type according to claim 10 comprising the following steps: a) placing a gaseous mixture in contact, under high pressure, with a porous material to obtain the selective ad- sorption of at least one of the gases making up the gase- ous mixture and collecting or discharging the remaining gaseous components of the mixture, where said porous material comprises a silica matrix in which one or more metal oxides are possibly dispersed, in a uniform manner, selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA, characterised by a surface area greater than 500 m²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crystalline structure, does not show any peak, and has a single broad diffraction line, or in any case a widespread "scattering", at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scattering" phenomena coherent for greater angular val- ues; b) interrupting the flow of the gaseous mixture and possibly reducing the pressure; c) desorbing the gas or gases adsorbed in step (a) , by reducing the partial pressure of the adsorbed gas or gases, and collecting or discharging them; d) repressurizing the system with the gaseous mixture fed.

12) Process of the PTSA type according to claim 10 comprising the following steps: a) placing a gas mixture in contact, under high pressure, with a porous material to obtain the selective adsorption of at least one of the gases making up the gaseous mixture and collecting or discharging the remaining gaseous components of the mixture, where said porous material comprising a silica matrix in which one or more metal oxides are possibly dispersed, in a uniform manner, selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA, characterised by a surface area greater than 500 m²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crystalline structure, does not show any peak, and has a single broad diffraction line, or in any case a widespread "scattering", at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scattering" phenomena coherent for greater angular values ; b) interrupting the flow of the gaseous mixture and possibly reducing the pressure; c) desorbing the gas or gases adsorbed in step (a), by raising the temperature of the porous material and reducing the partial pressure of the adsorbed gas or gases, and collecting or discharging them; d) repressurizing the system with the gas mixture fed. 13) Process according to claim 1 wherein the gaseous mixture is natural gas containing one or more pollutants selected from among CO₂, H₂S, water, which are adsorbed.

14) Process according to claim 1 wherein the gaseous mixture is hydrogen containing carbon dioxide, carbon monoxide, hydrogen sulphide, water and hydrocarbons which are adsorbed.

15) Process according to claim 11 or 13 of the PSA type for separating a pollutants from a gaseous mixture which contains it together with methane, where said pollutant is CO₂, H₂S or their mixtures, comprising the following steps : a) placing said gaseous mixture in contact, under high pressure, with a porous material to selectively adsorb the pollutant, and collecting the remaining gaseous component containing methane, where said porous material comprising a silica matrix in which one or more metal oxides are possibly dispersed, in a uniform manner, selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA, characterised by a surface area greater than 500 m²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crystalline structure, does not show any peak, and has a sin- gle broad diffraction line, or in any case a widespread "scattering", at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scattering" phenomena coherent for greater angular values; b) interrupting the flow of the gaseous mixture and pos- sibly reducing the pressure; c) desorbing the pollutant adsorbed in step (a) , by reducing the partial pressure of the adsorbed gas or gases, and collecting or discharging them,- d) repressurizing the system with the gas mixture fed. 16) Process according to claim 12 or 13 of the PTSA type for separating a pollutants from a gaseous mixture which contains it together with methane, where said pollutants is CO₂, H₂S or their mixtures, comprising the following steps: a) placing said gaseous mixture in contact, under high pressure, with a porous material to selectively adsorb the pollutant, and collecting the remaining gaseous component containing methane, where said porous material comprises a silica matrix in which one or more metal ox- ides are possibly dispersed, in a uniform manner, selected from among transition metals or from among metals belonging to groups IIIA, IVA and VA, characterised by a surface area greater than 500 τn²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crys- talline structure, does not show any peak, and has a single broad diffraction line, or in any case a widespread "scattering", at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scatter- ing" phenomena coherent for greater angular values; b) interrupting the flow of the gaseous mixture and possibly reducing the pressure; c) desorbing the pollutants adsorbed in step (a) , by raising the temperature of the porous material and reduc- ing the partial pressure of the gas or the adsorbed gases, and collecting or discharging them,- d) repressurizing the system with the gas mixture fed.

17) Process according to claim 1, 11, 12, 15 or 16 wherein the adsorption is performed at a temperature in the range of 0 - 40⁰C and at a pressure in the range of 10 - 90 bara.

18) Process according to claim 17 wherein the adsorption is performed at an adsorption pressure in the range of 10 - 40 bara. 19) Process according to claim 2, 11 or 15 wherein the desorption stage is performed at a pressure in the range of 0.1 - 10 bars and at a temperature in the range of 0 - 40 ⁰C. 20) Process according to claim 2, 12 or 16 wherein the desorption stage is performed at a pressure in the range of 0.1 - 10 bara and heating at a temperature in the range of 50 - 250⁰C.

21) Process according to claim 20 wherein the temperature is in the range of 60 - 100 ⁰C. 22) Process according to claim 2, 11, 12, 15 or 16 wherein the desorption is followed by sweeping with a gas selected from among N₂, CH₄, air or hydrogen. 23) Process according to one or more of the claims wherein the porous material comprises a silica matrix in .which aluminium oxide is dispersed, and it is characterised by a surface area greater than 500 m²/g, a pore volume in the range of 0.3 - 1.3 ml/g, a pore diameter smaller than 40 Angstrom, an XRD spectrum from powders not having a crystalline structure, does not show any peak, and has a single broad diffraction line, or in any case a widespread "scattering" , at angular values not greater than 2Θ = 5° with CuKa radiation, without any other coherent "scattering" phenomena coherent for greater angular values . 24) Process according to claim 1 or 2 wherein the adsorbing porous material is completely regenerated through isothermal depressurization.