System and method for separating complex feedstocks

Abstract

The present invention relates to the field of separation processes, and in particular to a process for separating light hydrocarbons using membranes of microporous molecular sieves. The process of the present invention relies on a membrane system comprising at least two membrane units arranged in series, each membrane unit comprising a membrane wherein molecular sieves are tightly embedded in channels perpendicular to the membrane surface, and the membrane comprises a polymeric matrix, and the membrane allows separation of a target compound from a mixture of at least 3 compounds. The present invention also provides a novel membrane system.

Description

[0001] This invention relates to the field of separation processes, and more particularly to a process for separating light hydrocarbons from complex feed streams using membranes of microporous molecular sieves. The invention provides a novel membrane system capable of separating such target compounds from complex feed streams. Furthermore, the invention provides a method relying on a membrane system comprising at least two sequentially arranged membrane units, each membrane unit comprising a membrane in which different molecular sieves are closely embedded in channels perpendicular to the membrane surface, and said membranes comprising a polymer matrix.

[0002] Many chemical manufacturing and refining processes involve separating a desired product compound from a fluid mixture containing two or more other compounds whose physical properties are very similar to those of the product compound. Examples of such separation include the separation of propylene from other components, such as other alkanes, alkenes, hydrogen, CO2, and nitrogen.

[0003] On an industrial scale, these separations are carried out by distillation. However, because the boiling points of the compounds being separated are very close, distillation of such compounds requires tall distillation columns and significant amounts of heating to achieve satisfactory separation. Distillation separation consumes a large amount of energy. For example, the distillation separation of ethylene and propylene (two of the world's most produced chemicals) from ethane and propane alone is estimated to consume 0.3% of global energy use.

[0004] On an industrial scale, because traditional separation techniques are uneconomical, mixed streams containing valuable product compounds, such as propylene, are often burned.

[0005] At the research and development scale, fluid separation via membranes has been described. Stark et al. (WO2017 / 207424) described membranes comprising MOFs embedded in a channel-like structure within a polymer matrix. These membranes have numerous applications, including the separation of binary gas mixtures. Liu et al. (US2019 / 0381449) described a multi-stage membrane system and method for processing binary gas streams, particularly CO2 / CH4. In an embodiment, the multi-stage membrane system comprises a combination of microporous zeolite inorganic membranes and polymer membranes. It should be noted that the membranes disclosed in this literature do not combine the polymer and zeolite in the same membrane. Furthermore, the multi-stage membrane system disclosed in this literature is suitable for separating binary systems but not for separating the feed stream into three product streams. Lai et al. (US2012 / 0310018) described a zeolite imidazole ester framework (ZIF) membrane that can be used to separate binary mixtures, such as separating C2 hydrocarbons from C3 hydrocarbons. Pinnau et al. (US6361582) described the use of C2-resistant... 3+Membranes are used for gas separation of hydrocarbons. Kinoshita et al. (DE112021002379) disclosed a separation system for fluids such as gases. An inorganic membrane with a support 11 and a zeolite membrane 12 was disclosed. The use of polymer membranes was not mentioned in this literature. None of these separation methods have progressed from research and development to industrial scale. The cited literature discloses methods for separating binary mixtures.

[0006] However, none of the disclosed separation methods allow for the separation of the target compound from complex feeds, i.e., feeds containing at least two other compounds in addition to the target compound.

[0007] There is a persistent need in the art to provide separation methods that can replace existing technologies. Furthermore, there is a significant need for improved separation techniques to address one or more of the well-known drawbacks in the art, particularly in separating a target product (target molecule) from a complex feed stream containing the target molecule. More modular and flexible separation methods are also required. In particular, there is a need for separation methods that are more energy efficient than conventional distillation.

[0008] Therefore, the object of the present invention is to mitigate at least some of the disadvantages of the prior art. In particular, the object of the present invention is to provide an improved method for hydrocarbon separation. Another object is to provide an improved membrane system suitable for this method.

[0009] These objectives are achieved by the method defined according to claim 1 and the membrane defined according to claim 9. Other aspects of the invention are disclosed in the specification and independent claims, and preferred embodiments are disclosed in the specification and dependent claims. Therefore, the invention relates to:

[0010] ● In the first aspect, it relates to membrane systems (10);

[0011] ● In a second aspect, the invention relates to a method for separating gaseous hydrocarbons (particularly propylene) from a mixture of at least three gaseous hydrocarbons (particularly a mixture comprising alkanes and alkenes) using a membrane system (10); and

[0012] ● In the third aspect, the use of membrane systems in complex petrochemical applications and separation methods is discussed.

[0013] The invention will now be described in more detail. It should be understood that the various embodiments, preferred embodiments, and scopes provided / disclosed in this specification can be combined arbitrarily. Furthermore, depending on the specific embodiment, the selected definitions, embodiments, or scopes may not apply.

[0014] Unless otherwise stated, the following definitions apply to this specification:

[0015] As used herein, the absence of a quantifier before an element, and similar terms used in the context of this invention (especially in the context of the claims), shall be construed as covering both singular and plural forms, unless otherwise stated herein or the context clearly contradicts this. As used herein, the terms “comprising,” “containing,” and “including” are used in their open, non-limiting sense. Unless otherwise stated, percentages in this specification refer to mass % (weight %).

[0016] Membrane: This term is known in the art and refers to a device that acts as a selective barrier due to the presence of pores / channels. Membranes can exist in the form of flat sheets or hollow fibers. In each case, such a membrane is defined by two surfaces and channels / pores perpendicular to the membrane surfaces.

[0017] Flat sheets are typically manufactured continuously, with widths ranging from 0.25 meters to 1.5 meters and thicknesses from 10 micrometers to 200 micrometers. Hollow fibers are typically manufactured continuously, with outer diameters ranging from 0.1 mm to 5 mm and wall thicknesses ranging from 10 micrometers to 500 micrometers.

[0018] In the context of this invention, the polymer pore size / channel size of the membrane can cover a wide range, typically from 20 nm to 3000 nm, preferably from 100 nm to 500 nm.

[0019] A membrane is "self-supporting" if it is freestanding and / or can be manually operated without a support structure. Furthermore, the membrane can be part of a layered structure, i.e., it includes additional layers such as support layers or cover layers. These additional layers can improve the membrane's stability, thus allowing for reliable manufacturing and / or use at higher pressures.

[0020] MOFs and / or zeolites (both described in further detail below) are embedded in these pores / channels, particularly in channels perpendicular to the membrane plane. Unbound by theory, MOFs are believed to significantly improve membrane selectivity.

[0021] The portion of feed that passes through the membrane is called "permeate," while the portion that does not pass through the membrane is called "residue." Therefore, these terms do not limit the steps of the method, but rather describe the function of the membrane and membrane system.

[0022] The term "ideal selectivity" is defined as the ratio of the permeability of a smaller compound (higher permeability) through the membrane to the permeability of a larger compound (lower permeability) through the membrane, and it is a measure of the membrane's ability to separate two compounds. (See, for example, Baker, Richard W., "Membrane Technology and Applications", pp. 290-291, McGraw-Hill, New York, 2000).

[0023] The selectivity of a membrane to a given fluid component can also be evaluated by considering Knudsen diffusion. Assuming a simple, non-size-selective pore / channel, diffusion depends on the pore radius and molecular mass. The separation of compounds by Knudsen diffusion can be calculated using the following formula, where α is the selectivity of compound A relative to compound B, and M... a and M b These are their respective molar masses.

[0024]

[0025] For example, the value for the propylene / propane pair is 1.023, and the value for the ethylene / ethane pair is 1.035. The membranes of the present invention exhibit values ​​far exceeding the Knudsen limit, particularly a selectivity of at least 10 for the propylene / propane pair and at least 5 for the ethylene / ethane pair. This finding indicates that the MOF incorporated into the membrane significantly affects the membrane's selectivity. On the other hand, membranes exhibiting selectivity within the Knudsen limit clearly possess simple pores / channels that only provide moderate selectivity, i.e., selectivity unaffected by molecular sieving. To distinguish them from simple membranes exhibiting selectivity within the Knudsen limit, the term "closely embedded MOF" is chosen.

[0026] The term "pore size range" is known in the art and can be determined by measuring the permeability of reference gas molecules of various sizes. A range of selectivity for the membrane can be discovered by measuring continuously from very small compounds, i.e., H2, to larger compounds, i.e., propane. The effective pore size range of the membrane is then determined to be between the sizes of two consecutive compounds whose permeability difference is at least 5 times.

[0027] Metal-organic framework (MOF): The term MOF is known in the art and refers to a chemical entity comprising a metal ion (including clusters) nucleus and ligands (also referred to as "pillars"). The ligands have at least two coordination sites. In the context of this invention, MOFs do indeed form three-dimensional networks with open pores.

[0028] Zeolite: The term zeolite is known in the art and specifically refers to microporous aluminosilicate minerals, including both natural and synthetic ones. Unlike MOFs, they do not contain organic ligands.

[0029] Hydrocarbon: The term hydrocarbon is known in the art to refer to a molecule composed of hydrogen and carbon. Therefore, the term hydrocarbon includes alkanes, alkenes (including those with multiple double bonds, such as dienes), and alkynes. Furthermore, it includes aliphatic and cyclic molecules. C n Hydrocarbons are hydrocarbons composed of n carbon atoms. Therefore, C n+ Hydrocarbons are defined as hydrocarbons consisting of at least n carbon atoms. In accordance with convention in this field, the term hydrocarbon should not include aromatic molecules.

[0030] The invention will be better understood by referring to the accompanying drawings.

[0031] Figure 1 illustrates the separation method of the present invention described herein.

[0032] List of reference numerals in the attached diagram:

[0033] (10) A membrane system having a sensor (11, not shown) and a control unit (12, not shown).

[0034] Membrane separation units (20) and (20'), arranged in sequence, have membrane modules (21, 21') comprising one or more membranes (22, 22') (modules not shown).

[0035] (1) Feeding

[0036] (3) Permeate I

[0037] (4) Residue I

[0038] (5) Permeate II

[0039] (7) Exudate II

[0040] (21) Components

[0041] (30) Compressor

[0042] (In) Feed Inlet

[0043] (Per) Permeate outlet

[0044] (Ret) Residue outlet

[0045] Figure 2 schematically outlines an embodiment of a suitable membrane (22), wherein

[0046] Figure 2a An embodiment with a backing layer (28) is shown;

[0047] Figure 2b An embodiment without a backing layer is shown.

[0048] List of reference numerals in the attached diagram:

[0049] (22) Membrane

[0050] (23) Molecular sieves;

[0051] (24) Polymer matrix;

[0052] (25) A first functional layer [comprising a polymer matrix (24) having channels (26) and a molecular sieve (23) tightly embedded in the channels (26)];

[0053] (26) Channels perpendicular to the membrane surface.

[0054] (28) A backing layer connected to the first functional layer (25) [improves pressure resistance and tear resistance].

[0055] Figure 3 Another embodiment of the separation method of the present invention described herein is outlined, wherein a single component 22 is replaced by a combination of components 22a and 22b in parallel mode.

[0056] In a first aspect, the present invention relates to membrane systems (10) and production equipment including the membrane systems described herein. These membrane systems are capable of separating complex gas mixtures, i.e., gases containing at least three components, wherein typically one component is the target component. This aspect of the invention will be described in further detail below:

[0057] Membrane system (10):

[0058] According to the present invention, the membrane system (10) includes at least two membrane units (20, 20') arranged in sequence. The membrane system may include known membranes, membrane modules, and membrane units. As shown in FIG1, feed passes through the first membrane unit (20) to obtain permeate I and effluent I. Permeate I (e.g.) Figure 1A (as shown) or permeate I (such as Figure 1B As shown, the membrane passes through a second membrane unit (20') to obtain effluent II and permeate II. Depending on the selected membrane and the starting material used, effluent II or permeate II is the desired product. The combination of the two membrane units provides both high flexibility and high selectivity. The membrane of the present invention is described in detail below. Careful selection of the molecular sieve pore size PS is considered an important feature of the membrane system to allow reliable separation of complex gas flows as defined below.

[0059] The suitable pore sizes of the molecular sieves (23, 23') for membranes 22 and 22' are as follows:

[0060] 2.9Å≤PS 23 ≤4.46 angstroms, and

[0061] 2.9Å≤PS 23' ≤4.50 angstroms, and

[0062] The pore size difference ΔPS between the molecular sieves is 0.1 angstroms to 1.5 angstroms.

[0063] Furthermore, the suitable pore sizes of the molecular sieves (23, 23') for membranes 22 and 22' are as follows:

[0064] 2.9Å≤PS 23 ≤4.7 angstroms, and

[0065] 2.9Å≤PS 23' ≤4.7 angstroms, and

[0066] The pore size difference ΔPS between the molecular sieves is 0.1 angstroms to 1.5 angstroms.

[0067] Depending on the specific separation task, a molecular sieve (23, 23') can be selected to meet a ΔPS preferably of 0.1 Å to 0.3 Å, more preferably 0.1 Å to 0.15 Å. It has been found that the membrane used in the system of the present invention allows for adjustment to this specific pore size.

[0068] Therefore, in this invention, the combination of two types of membranes arranged in a specific manner allows for the separation of compounds of interest (i.e., target compounds such as propylene) from complex feeds (e.g., gas streams containing propylene and at least two other gaseous components).

[0069] Furthermore, multiple first membrane units (20) can be connected in parallel within the membrane system (10). Conversely, it is also contemplated that multiple second membrane units (20') be connected in parallel within the membrane system (10). This implementation can accommodate different feed volumes (according to...) Figure 1A 1, 4, or according to Figure 1B The permeability in 1, 3) or a single membrane (22, 22'). This embodiment is as follows Figure 3 As shown, the membrane unit (20) is replaced by two membrane units (20a, 20b).

[0070] According to the invention, the membrane system (10) comprises at least two membrane units (20, 20') arranged in sequence. The membrane system is further described in detail below. Furthermore, the membrane system may include one or more sensors (11, 11') and a control unit (12), said sensors (11, 11') adapted to measure and transmit the properties of the feed (1), residual material (4, 7), and / or permeate (3, 5), and said control unit (12) adapted to receive such signals. These properties may be the concentration of one or more components in the corresponding flow, the mass flow rate of said flow, the temperature of said flow, and / or the pressure of said flow. This embodiment allows for prediction of process performance and maintenance, for example, by interpreting differences in properties measured over time, or by comparing these differences to predetermined values.

[0071] Furthermore, one or more compressors (30) may be included in the membrane system, preferably located between 20 and 20'. The presence of the compressor can improve the performance of the membrane system and / or facilitate the integration of the membrane system of the present invention into larger devices.

[0072] In an embodiment, the present invention relates to a membrane system (10) as described herein, wherein the pore size of the molecular sieve (23, 23') increases from the first unit to the second unit (PS).23' PS 23 ), and the inlet of the second membrane unit (In 20' ) and the second outlet (Ret) of the permeate from the first membrane unit 20 Fluid connectivity. This implementation scheme is as follows: Figure 1A As shown.

[0073] In an embodiment, the present invention relates to a membrane system (10) as described herein, wherein the pore size of the molecular sieve (23, 23') decreases from the first membrane unit to the second membrane unit (PS). 23' <PS 23 ), and the inlet of the second membrane unit (In 20' ) and the first outlet of the permeate from the first membrane unit (Per 20 Fluid connectivity. This implementation scheme is as follows: Figure 1B As shown.

[0074] The following embodiments describe particularly preferred membrane systems (10), wherein in each case, ideal selectivity and pore size are determined by measuring the flow rate of a specified gas in a test cell; and wherein in each case, the membrane is available from UniSieve AG under the trade name given below:

[0075] Implementation plan 1, wherein:

[0076] ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.9 Å (due to the molecular sieve being tightly embedded in the polymer channel: Uni 5-3.9), and an ideal selectivity of at least 10, preferably at least 20, when using ethylene and propylene as reference gases; and

[0077] ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 to 4.5 angstroms (due to the molecular sieve being tightly embedded in the polymer channel: UniS-4), and an ideal selectivity of at least 10, preferably at least 20, when propylene and propane are used as reference gases.

[0078] This implementation scheme is particularly suitable for separating propylene, the target compound, from other gases, especially from propane and ethylene.

[0079] Implementation plan 2, in which:

[0080] ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 to 3.5 angstroms (due to the molecular sieve being tightly embedded in the polymer channel: UniS-3), and an ideal selectivity of at least 20, preferably at least 30, when using N2 and propylene as reference gases; and

[0081] ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 to 4.5 angstroms (due to the molecular sieve being tightly embedded in the polymer channel: UniS-4), and an ideal selectivity of at least 10, preferably at least 20, when propylene and propane are used as reference gases.

[0082] This implementation scheme is particularly suitable for separating propylene as a target compound from other gases, especially from N2 and propane.

[0083] Implementation plan 3, in which:

[0084] ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.2 Å (due to the molecular sieve being tightly embedded in the polymer channel: UniS-2), and an ideal selectivity of at least 20, preferably at least 30, when using H2 and propylene as reference gases; and

[0085] ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 to 4.5 angstroms (due to the molecular sieve being tightly embedded in the polymer channel: UniS-4), and an ideal selectivity of at least 10, preferably at least 20, when propylene and propane are used as reference gases.

[0086] This implementation scheme is particularly suitable for separating propylene, the target compound, from other gases, especially from hydrogen and propane.

[0087] Implementation plan 4, in which:

[0088] ● The first membrane unit (20) includes a membrane (22) with a pore size of 4.1 Å to 4.4 Å (due to the molecular sieve being tightly embedded in the polymer channel: 1812 UniS-4), and an ideal selectivity of at least 20, preferably at least 30, when using cis-2-butene and trans-2-butene as reference gases; and

[0089] ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.3 to 4.7 Å (due to the molecular sieve being tightly embedded in the polymer channel: 1812 UniS-5) and an ideal selectivity of at least 10 when 1-butene and cis-2-butene are used as reference gases.

[0090] This implementation scheme is particularly suitable for separating linear butene as the target compound from a mixture of linear butenes.

[0091] Membrane (22, 22'):

[0092] Unbound by theory, the membranes (22, 22') described herein are believed to play a crucial role in the successful implementation of the continuous process described herein. In particular, the combination of the polymer matrix (24), the channels (26), and the molecular sieve (23) is important. The molecular sieve (23) is held within the channels (26) during use, i.e., during the fabrication of the membrane module and in use. To distinguish it from a simple (and removable) coating of the molecular sieve on the membrane surface, the term "tightly embedded" is used.

[0093] As described below, membranes (22, 22') are assembled in membrane modules (21, 21'), which are key components of membrane units (20, 20'). According to the invention, at least two membrane units are combined to form a membrane system (10). The use of such a membrane system (10) allows for large-scale improvements in the separation of specific products from feed, avoids the need for distillation, and ensures long-term reliable separation and high flexibility.

[0094] The membrane (22) may be in the form of a flat sheet or fibers. According to the invention, the membrane (22) includes a first functional layer (25) and a backing layer (28) optionally connected to the first functional layer. The membrane (22) may also include a second functional layer (27) opposite to the backing layer (28).

[0095] First functional layer (25): This layer comprises a polymer matrix (24) and a molecular sieve (23), wherein the matrix (24) comprises channels perpendicular to the membrane surface, thereby connecting the two surfaces of the membrane, and wherein the molecular sieve (23) is located within the channels. Due to the position of the molecular sieve (23) within the channels, the molecular sieve is tightly embedded, and the membrane exhibits selectivity above the Knudsen limit for a given product / feed pair.

[0096] Matrix: A suitable polymer matrix (24) may be selected from a wide range of polymers, including cellulose acetate (CA), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polysulfone (PSf), polyacrylonitrile (PAN), polyimide (PI), polyamide-imide (PAI, e.g., TORLON), polyetheretherketone (PEEK), polylactic acid (PLA), polycarbonate (PC), polystyrene (PS), polyacrylate, and polyurethane (PU). PES is the preferred polymer for the matrix (24).

[0097] Molecular sieves: Molecular sieves (23) can be selected from a wide range of known molecular sieves, including molecular frameworks (MOFs) and optional zeolites. Suitable MOFs include ZIF-7, ZIF-8, ZIF-L, ZIF-20, ZIF-21, ZIF-22, ZIF-23, ZIF-67, ZIF-69, ZIF-71, ZIF-90, SIM-1, MIL-47, MIL-53, MOF-5, MIL-96, MIL-89, MIL-101, and HKUST-1 and combinations thereof; ZIF-8, ZIF-90, and ZIF-7 and combinations thereof are preferred. Suitable zeolites include AlPO-14, AlPO-18, AlPO-34, SAPO-34, SSZ-13, DD3R, ITQ-12, CDS-1, UZM-25, and combinations thereof. Molecular sieves are selected to provide suitable size exclusion for the separation task. Therefore, membrane (22) and membrane (22') are different; preferably, the molecular sieve is selected, and optionally, the pore size, matrix, backing layer or other parameters are also different.

[0098] Backing layer: A wide range of materials can be used. It should be understood that the backing layer is porous and will not negatively affect the selectivity of the functional layer (25). The backing layer (28) may include or be composed of a polyamide membrane. Advantageously, the membrane (22) includes or is composed of a first functional layer (25) and a backing layer (28).

[0099] Second functional layer: The second functional layer can further improve the performance of the membrane. If present, the second functional layer (27) may include or constitute a molecular sieve as defined herein.

[0100] Membrane morphology: Advantageously, the diameter of the channel-like structure (26) is from 50 nm to 10000 nm, preferably from 100 nm to 1000 nm. Advantageously, the channel-like structure (26) accounts for 0.5 vol% to 50 vol% of the membrane (22, 22'), preferably 20 vol% to 50 vol%.

[0101] In a preferred embodiment, the membrane (22, 22') includes a backing layer (28), preferably selected from polyamide membranes with a pore size greater than 3 micrometers; a first functional layer (25) includes a polymer matrix (24) and a molecular sieve (23), the functional layer (25) including channels (26) within the matrix (24), the channels (26) being perpendicular to the membrane surface to connect the two surfaces of the membrane, and wherein the molecular sieve (23) is located within the channels (26), the molecular sieve (23) being as defined above, and the polymer matrix (24) being as defined above. Advantageously, the backing layer (28) is selected from polyamide membranes with a pore size greater than 3 micrometers. Advantageously, the matrix (24) is a PES matrix. Advantageously, the molecular sieve (23) is ZIF-8.

[0102] Membrane module (21, 21'):

[0103] Typically, as is known in the art, one or more membranes (22, 22') are housed within a membrane module (21, 21'). Such membrane modules include spiral wound membrane modules, plate-and-frame modules, cylindrical modules, and potted hollow-fiber membrane modules. Spiral wound membrane modules comprising one membrane are preferred. The manufacture of all these types of modules is well known in the art. Because the membranes use conventional polymer materials, their preparation and loading into modules are relatively simple and inexpensive, especially compared to other types of membranes, such as pyrolytic carbon membranes or ceramic membranes.

[0104] Membrane unit (20, 20'):

[0105] The membrane unit itself is known; the membrane unit (20) includes one or more membrane modules (21, 21'). Each membrane module includes one or more membranes (22, 22'). The membrane unit also includes at least one inlet (In), one outlet (Ret) for residual waste, and one outlet (Per) for permeate.

[0106] The membrane unit (20) is adapted to elevated temperatures, such as 30°C to 100°C, and elevated pressures, such as 10 bar to 50 bar.

[0107] In a preferred embodiment, the membrane unit (20, 20') includes one or more components (21, 21') as described above, as well as a feed inlet, a permeate outlet, a residual product outlet, and one or more sensing elements (11) as described herein.

[0108] More generally, in a second aspect, the present invention relates to a method for separating a feed stream (1) into three or more product streams. By implementing this method, one of the product streams is obtained, wherein the concentration of the target compound is increased relative to the concentration of the compound in the feed stream (1). This aspect of the invention will be described in more detail below.

[0109] Overview:

[0110] The process is a continuous process, as indicated by the terms feed stream and product stream. This method can be implemented in existing manufacturing processes. The method is very versatile and can be implemented to separate a wide range of products from corresponding starting materials (feed stream (1)).

[0111] Membrane separation is a known technique. By passing the feed stream (1) through the membrane (22) of the membrane system (10), the feed is separated into a permeate stream and a residual stream. This step can be performed at a wide range of temperatures and pressures. Suitable parameters can be determined by those skilled in the art, taking into account the separation task, the type of membrane, and the type of membrane system. Suitable temperatures range from 0°C to 120°C, and suitable pressures range from 0 bar to 30 bar.

[0112] The resulting hydrocarbon stream can undergo other process steps, such as compression. Such steps are known in the art.

[0113] In an embodiment, the method is adapted to separate a feed stream (1) into three or more product streams, wherein the feed stream comprises a mixture of three or more gases selected from hydrogen, nitrogen, methane, C2 hydrocarbons, C3 hydrocarbons and C4 hydrocarbons; and the method includes the step of passing the feed stream (1) through a membrane system (10) as defined in the first aspect of the invention to obtain three product streams, wherein the concentration of a target compound contained in one of the product streams is increased relative to the feed stream (1).

[0114] The method of this invention utilizes the tunable pore size of the molecular sieve membranes outlined herein, enabling the separation of high-value hydrocarbons from complex hydrocarbon mixtures via size exclusion mechanisms. Compared to prior art, this membrane-assisted separation method can purify desired hydrocarbon compounds from complex mixtures using only membrane technology.

[0115] In the embodiments, the present invention therefore provides a separation method as described herein that does not involve a distillation step.

[0116] In the embodiments, the present invention therefore provides a separation method as described herein that does not involve an extraction step.

[0117] Therefore, the method of the present invention allows for the separation of unsaturated organic compounds from fluid mixtures without the presence of water during the separation process.

[0118] The method also differs from previous methods because the separation depends entirely on the molecular diameter of the compounds to be separated, and the mixture is separated according to the pore size of the selected molecular sieve.

[0119] Membrane systems and membranes:

[0120] Suitable membrane systems and membranes are specified in the first aspect of the invention described above. It has been found advantageous if the membrane (22, 22') comprises or consists of a backing layer (28); and a functional layer (25) comprising the polymer matrix (24) and the molecular sieve (23) located in the channel (26).

[0121] In embodiments, the polymer matrix (24) comprises or consists of: polysulfone, polyethersulfone, sulfonated polysulfone, sulfonated polyethersulfone, polyetherimide, cellulose polymer, polyimide, polyamide / imide, polyketone, polyetherketone, poly(aryloxide), poly(benzobenzimidazole), polyhydrazide, polyoxadiazole, polybenzoxazole, polytriazole, polybenzimidazole, polycarbodiimide, polyphosphazine, microporous polymers, and mixtures thereof. Advantageously, the polymer matrix is ​​composed of a PES polymer.

[0122] In the embodiments, the molecular sieve (23, 23') is selected from metal-organic frameworks (MOFs) and optionally zeolites; wherein the MOFs are preferably selected from ZIF-7, ZIF-8, ZIF-L, ZIF-20, ZIF-21, ZIF-22, ZIF-23, ZIF-67, ZIF-69, ZIF-71, ZIF-90, SIM-1, MIL-47, MIL-53, MOF-5, MIL-96, MIL-89, MIL-101 and HKUST-1 and mixtures thereof; and the zeolites are preferably selected from AlPO-14, AlPO-18, AlPO-34, SAPO-34, SSZ-13, DD3R, ITQ-12, CDS-1, UZM-25 and mixtures thereof.

[0123] Feed flow (1):

[0124] A wide range of starting materials (feed streams), including hydrocarbons as defined herein, can be used in the processes of this invention. Such starting materials include intermediate products from refineries or other chemical plants. They may contain hydrocarbons as defined herein, as well as other components such as CO, CO2, H2, N2, and rare gases.

[0125] In some embodiments, the feed stream is selected from the feed, overhead stream, or bottom stream of a hydrocarbon fractionation tower, particularly a C3 fractionation tower. In some embodiments, the feed stream is flue gas. In some embodiments, the feed stream is a flare stream. In some embodiments, the feed stream is a purge stream, such as purge gas from PP production. In some embodiments, the feed stream is a recirculated stream from a polypropylene reactor. The method of the present invention is tolerant of a wide variety of starting materials and is considered advantageous given the various combinations of streams that may occur in commercial production settings.

[0126] Product stream / target compound:

[0127] The product stream contains one or more target compounds, such as C2, C3, or C4 hydrocarbons, at a concentration higher than that of the corresponding compound in the feed (1). Therefore, the target compound is concentrated compared to the feed. The purity of the target compound depends on the intended use and is typically higher than 60% by weight, for example, higher than 90% by weight, higher than 95% by weight, higher than 99% by weight, higher than 99.5% by weight, and higher than 99.9% by weight. In one embodiment, the concentration is the chemical grade of the corresponding compound. In another embodiment, the concentration is the polymer grade of the corresponding compound.

[0128] The C2 product includes acetylene, ethylene, and ethane. The C3 product includes methylacetylene (H3C-CCH), propadiene (H2C=C=CH2), propylene, and propane. Propylene is a particularly preferred product.

[0129] The term C4 products include n-butane, isobutane, 1-butene, isobutene, butadiene, cis-2-butene, and trans-2-butene. A particularly preferred product is trans-2-butene.

[0130] Propylene separation:

[0131] Specifically, the method of the present invention allows for the separation of propylene as a target compound. In this embodiment, the feed (1) contains propylene, and one of the product streams contains a higher concentration of propylene than the feed (1). Preferably, the product stream contains refinery grade (RGP, about 60% to 70%), chemical grade (CGP, 92% to 96%), or polymer grade (PGP, >99.5%) propylene.

[0132] In the implementation, the feed stream (1) comprises (i) 1% to 99% by weight of propylene and (ii) 99% to 1% by weight of propane and (iii) 99% to 1% by weight of other gases selected from nitrogen, hydrogen and methane; and (i) + (ii) + (iii) total 100%.

[0133] In other embodiments, the feed stream (1) comprises 1% to 99% by weight of propylene and 99% to 1% by weight of other hydrocarbons, preferably selected from acetylene, ethylene, ethane, methylacetylene, propadiene, propane, n-butane, isobutane, 1-butene, isobutene, butadiene, cis-2-butene, and trans-2-butene.

[0134] This invention specifically provides the method described herein for separating the following gas pairs:

[0135] ■ C3H6 / C3H8 / ethylene;

[0136] ■ C3H6 / C3H8 / Nitrogen;

[0137] ■ C3H6 / C3H8 / Hydrogen;

[0138] ■ C3H6 / C3H8 / Methane;

[0139] ■ C3H6 / C3H8 / Methane + Hydrogen + Nitrogen + Ethylene.

[0140] Depending on the feed and the membrane used, the method of the present invention can be used in different ways to separate propylene. In a first embodiment, propylene is permeate I, while in a second embodiment, propylene is permeate I.

[0141] Butene separation:

[0142] Specifically, the method of the present invention allows for the separation of trans-2-butene, cis-2-butene, and 1-butene. To date, no commercially available method is known for these linear butenes, particularly no continuous separation method.

[0143] In this embodiment, the feed (1) contains trans-2-butene, and one of the product streams contains a higher concentration of trans-2-butene than the feed (1).

[0144] This invention specifically provides the method described herein for separating the following gas pairs:

[0145] ■ trans-2-butene / cis-2-butene / isobutane;

[0146] ■ trans-2-butene / 1-butene / isobutane;

[0147] ■ trans-2-butene / cis-2-butene / isobutene;

[0148] ■ trans-2-butene / 1-butene / isobutene;

[0149] Depending on the feed and the membrane used, the method of the present invention can be used in different ways to separate linear butene. In a first embodiment, cis-2-butene is permeate I. In an alternative second embodiment, cis-2-butene is permeate I.

[0150] Therefore, in a first embodiment, the present invention relates to a method wherein a first membrane unit (20) includes a membrane (22) that separates propylene and C 3+ Hydrocarbons (4, ret I) are separated from methane, ethane, ethylene, acetylene, hydrogen, CO, and CO2 (3, permeate I), and the second membrane unit (20') includes a membrane (22') that separates propylene (5, per II) from propane and some C 4+Hydrocarbon (7, ret II) separation. Advantageously, the membrane (22) has an ideal selectivity of at least 10, preferably at least 20. Advantageously, the membrane (22') has an ideal selectivity of at least 10, preferably at least 15. This embodiment is as follows: Figure 1A As shown. Suitably, the first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.9 Å, and an ideal selectivity of at least 10, preferably at least 20, for determination using ethylene and propylene as reference gases. Suitably, the second membrane unit (20') includes a membrane (22') with a pore size of 4.1 Å to 4.5 Å, and an ideal selectivity of at least 10 for determination using propylene and propane as reference gases.

[0151] Therefore, in the second embodiment, the present invention relates to a method wherein a first membrane unit (20) comprises a membrane (22) that separates methane, ethane, ethylene, acetylene, hydrogen, CO, CO2, and propylene (permeate I) from propane and C4+ hydrocarbons (residue I); and a second membrane unit (20') comprises a membrane (22') that separates propylene (7, residue II) from methane, ethane, ethylene, acetylene, H2, CO, and CO2 (per II). Advantageously, the membrane (22) has an ideal selectivity of at least 10, preferably at least 15. Advantageously, the membrane (22') has an ideal selectivity of at least 10, preferably at least 20. This embodiment is as follows Figure 1B As shown. Suitably, the first membrane unit (20) comprises a membrane (22) with a pore size of 2.9 Å to 3.5 Å, and an ideal selectivity of at least 20, preferably at least 30, determined using N2 and propylene as reference gases. Suitably, the second membrane unit (20') comprises a membrane (22') with a pore size of 4.1 Å to 4.5 Å, and an ideal selectivity of at least 10 (using propylene and propane as reference gases).

[0152] Therefore, in the third embodiment, the present invention relates to a method wherein a first membrane unit (20) comprises a membrane (22) that separates methane, ethane, ethylene, acetylene, hydrogen, CO, CO2, and propylene (permeate I) from propane and C4+ hydrocarbons (residue I); and a second membrane unit (20') comprises a membrane (22') that separates propylene (7, residue II) from methane, ethane, ethylene, acetylene, H2, CO, and CO2 (permeate II). Advantageously, the membrane (22) has an ideal selectivity of at least 20, preferably at least 30. Advantageously, the membrane (22') has an ideal selectivity of at least 10. This embodiment is as follows Figure 1BAs shown. Suitably, the first membrane unit (20) comprises a membrane (22) with a pore size of 2.9 Å to 3.2 Å, and an ideal selectivity of at least 20, preferably at least 30, for determination using N2 and propylene as reference gases. Suitably, the second membrane unit (20') comprises a membrane (22') with a pore size of 4.1 Å to 4.5 Å, and an ideal selectivity of at least 10 for using propylene and propane as reference gases.

[0153] Therefore, in the fourth embodiment, the present invention relates to a method wherein a first membrane unit (20) comprises a membrane (22) that separates trans-2-butene (permeate I) from cis-2-butene and 1-butene (residue I); and a second membrane unit (20') comprises a membrane (22') that separates cis-2-butene (7, residue II) from 1-butene (permeate II). Advantageously, the membrane (22) has an ideal selectivity of at least 10, preferably at least 20. Advantageously, the membrane (22') has an ideal selectivity of at least 5. This embodiment is as follows Figure 1A As shown. Suitably, the first membrane unit (20) comprises a membrane (22) with a pore size of 4.1 Å to 4.4 Å, and an ideal selectivity of at least 20, preferably at least 30, for determination using cis-2-butene and trans-2-butene as reference gases. Suitably, the second membrane unit (20') comprises a membrane (22') with a pore size of 4.3 Å to 4.7 Å, and an ideal selectivity of at least 10 for using 1-butene and cis-2-butene as reference gases.

[0154] In a third aspect, the present invention relates to the use of the membrane system (10) as described herein. This aspect of the invention will be described in further detail below:

[0155] The system described herein can be used to separate C2, C3, or C4 hydrocarbons from a feed stream containing such hydrocarbons as well as various other components / impurities, such as ternary or quaternary systems. The desired product can be obtained without distillation and the use of water. Furthermore, the desired product can be obtained with high purity, as defined in the second aspect of this invention.

[0156] Therefore, the present invention also provides the use of the membrane system (10) as described herein for C3H6 separation, i.e., removal of two or more byproducts / impurities from the desired product C3H6. This separation is particularly useful in the case of propylene polymerization. A typical propylene stream exhibits the purity described in the second aspect above. A typical feed stream is:

[0157] ■ C3H6 / C3 / ethylene;

[0158] ■ C3H6 / C3 / Nitrogen;

[0159] ■ C3H6 / C3 / Hydrogen;

[0160] ■ C3H6 / C3 / methane; and

[0161] ■ C3H6 / C3 / Methane + Hydrogen + Nitrogen + Ethylene.

[0162] Therefore, the present invention also provides the use of the membrane system (10) as described herein for the separation of linear butenes, i.e., providing separate streams rich in trans-2-butene, cis-2-butene, and 1-butene, respectively. This separation is particularly useful because it is the first time a membrane system has been used to separate these three difficult-to-separate gases in a continuous process.

[0163] To further illustrate the present invention, the following non-limiting embodiments are provided.

[0164] Example 1: Separation of propylene from propane and ethylene. The goal is to purify propylene from the feed stream by separating it from smaller and larger compounds of very similar size.

[0165] In this embodiment, two different molecular sieve membrane units are connected to obtain the above-described membrane system, and as follows: Figure 1A As shown. In this embodiment, the first membrane unit (22) includes a spiral wound assembly with a membrane area of ​​0.3 m². 2 The component used is '1812-UniS-3.9', available from UniSieve AG. In this embodiment, the second membrane unit (22') includes a spiral wound assembly with a membrane area of ​​0.05 m². 2 The component used was '1812-UniS-4', available from UniSieve AG. The feed was a hydrocarbon gas mixture containing ethylene, propylene, and propane. The kinetic diameters of ethylene were 3.9 Å, propylene 4.0 Å, and propane 4.2 Å. Specifically, a first membrane unit with a pore size of 3.9 Å separated ethylene (permeate I) from propylene and propane (residue I). A second membrane unit, connected to stream 4, with a pore size of 4.1 Å, effectively separated propylene (permeate II) from propane (residue II). In this embodiment, the feed pressure was 7 bar gauge pressure, the permeate pressure was 0 bar gauge pressure, and the temperature was ambient temperature. Mass flow rates were controlled and measured using a Coriolis mass flow controller. The gas composition of each stream was determined by gas chromatography using a flame ionization detector, and the results are summarized in the table below. Stream numbers correspond to... Figure 1A .

[0166]

[0167] In summary, this membrane system can effectively separate propylene from components with smaller kinetic diameters and components with larger kinetic diameters.

[0168] Example 2: Separation of propylene from hydrogen and propane

[0169] The goal is to purify propylene from the feed stream by separating it from smaller and larger compounds that are very similar in size.

[0170] In this embodiment, two different molecular sieve membrane units are connected to obtain the above-described membrane system, and as follows: Figure 1A As shown. In this embodiment, the first membrane unit (22) includes a spiral wound assembly, and the membrane area is 0.15m². 2 The component used is '1812-UniS-3', available from UniSieve AG. In this embodiment, the second membrane unit (22') includes a spiral wound assembly with a membrane area of ​​0.15 m². 2 The component used is '1812-UniS-4', which is available from UniSieve AG.

[0171] The feed is a gas mixture containing hydrogen, propylene, and propane. The kinetic diameter of hydrogen is 2.9 angstroms, that of propylene is 4.0 angstroms, and that of propane is 4.2 angstroms.

[0172] Specifically, a first membrane unit with a pore size of 3.0 Å separates hydrogen (permeate I) from propylene and propane (residue I). A second membrane unit, connected to stream 4, with a pore size of 4.0 Å, effectively separates propylene (permeate II) from propane (residue II). In this embodiment, the feed pressure is 5 bar gauge pressure, the permeate pressure is 0 bar gauge pressure, and the temperature is 30°C. Mass flow rate is controlled and measured using a Coriolis mass flow controller. The gas composition of each stream was determined by gas chromatography using a thermal conductivity detector, and the results are summarized in the table below. Stream number corresponds to... Figure 1A .

[0173]

[0174] In summary, this membrane system can effectively separate hydrogen and propane from propylene, with one component having a kinetic diameter smaller than that of propylene and the other component having a kinetic diameter larger than that of propylene.

[0175] Example 3: Separation of linear butene

[0176] The goal is to separate the C4 gas mixed in the feed stream.

[0177] In this embodiment, two different molecular sieve membrane units are connected to obtain the above-described membrane system, and as follows: Figure 1A As shown. In this embodiment, the first membrane unit (22) includes a spiral wound assembly, and the membrane area is 0.15m². 2The component used is '1812-UniS-4', available from UniSieve AG. In this embodiment, the second membrane unit (22') includes a spiral wound assembly with a membrane area of ​​0.15 m². 2 The component used is '1812-UniS-5', which is available from UniSieve AG.

[0178] The feed is a gas mixture containing multiple C4 gases, including trans-2-butene, cis-2-butene, and 1-butene. Specifically, a first membrane unit with a pore size of 4.4 Å separates trans-2-butene (permeate I) from 1-butene and cis-2-butene (residue I). A second membrane unit, connected to feed stream 4, with a pore size of 4.5 Å, effectively separates cis-2-butene (permeate II) from 1-butene (residue II). In this embodiment, the feed pressure is 5 bar gauge pressure, the permeate pressure is 0 bar gauge pressure, and the temperature is 70°C. Mass flow rate is controlled and measured using a Coriolis mass flow controller. The gas composition of each feed stream was determined by gas chromatography using a flame ionization detector, and the results are summarized in the table below. The feed stream number corresponds to... Figure 1A .

[0179]

[0180] In summary, this membrane system can effectively separate C4 gas mixtures such as trans-2-butene, cis-2-butene, and 1-butene from each other.

Claims

1. A membrane system (10) comprising a first membrane unit (20) and a second membrane unit (20') fluidly connected thereto; The membrane units (20, 20') are arranged in sequence, and the first membrane is arranged at the beginning facing the feed flow (1); Each membrane unit (20, 20') includes a membrane (22, 22'), at least one inlet (In), at least one first outlet for permeate (Per), and at least one second outlet for residue (Ret), characterized in that, ● The membrane (22, 22') comprises a polymer matrix (24) and a molecular sieve (23, 23'), and ● The membrane (22, 22') includes channels (26) within the matrix (24), the channels (26) being perpendicular to the membrane surface to connect the two surfaces of the membrane, and ● The molecular sieve (23, 23') is tightly embedded within the channel (26), and ● The molecular sieve (23, 23') ○ Each has a specified aperture PS 23 PS 23' ,in 2.9Å≤PS 23 ≤4.7 angstroms, and 2.9Å≤PS 23' ≤4.7 angstroms, and ○ The pore size difference ΔPS between the molecular sieves is 0.1 Å to 1.5 Å.

2. The membrane system (10) as defined in claim 1, further comprising: ● One or more sensors (11, 11') and a control unit (12), said sensors (11, 11') being adapted to measure and transmit the properties of feed (1), permeate (4, 7) and / or permeate (3, 5), said control unit (12) being adapted to receive such signals and to predict the performance and maintenance of said process by interpreting the differences in said properties measured over time; and / or ● Compressor (30), which is located between the first membrane unit and the second membrane unit.

3. The membrane system (10) according to any one of claims 1 to 2, wherein each membrane separation unit (20, 20') comprises one or more components (21, 21'), wherein said components are selected from... ● Spiral wound membrane module, ● Plate and frame membrane modules, ● Tube-type components, and ● Encapsulated hollow fiber membrane modules In each case, one or more membranes (22, 22') as defined in claim 1 are included.

4. The membrane system (10) according to any one of claims 1 to 3, wherein ● Two or more separate units (20a, 20b) are arranged in parallel, and / or ● Two or more separate units (20'a, 20'b) are arranged in parallel.

5. The membrane system (10) according to any one of claims 1 to 4, wherein ● The pore size of the molecular sieve (23, 23') increases from the first unit to the second unit (PS). 23' PS 23 ),and ● The inlet of the second membrane unit (In) 20' ) and the second outlet (Ret) of the first membrane unit for residual waste 20 Fluid connectivity.

6. The membrane system (10) according to any one of claims 1 to 4, wherein ● The pore size of the molecular sieve (23, 23') decreases from the first membrane unit to the second membrane unit (PS). 23' <PS 23 ),and ● The inlet of the second membrane unit (In) 20' ) and the first outlet (Per) of the first membrane unit for permeate 20 Fluid connectivity.

7. The membrane system (10) according to any one of claims 1 to 6, wherein In the first embodiment suitable for propylene separation: ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.9 Å and an ideal selectivity of at least 10, preferably at least 20 (using ethylene and propylene as reference gases); and ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 angstroms to 4.5 angstroms and an ideal selectivity of at least 10 (using propylene and propane as reference gases); In a second embodiment suitable for propylene separation: ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.5 Å and an ideal selectivity of at least 20, preferably at least 30 (N2 and propylene as reference gases); and ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 Å to 4.5 Å and an ideal selectivity of at least 10 (using propylene and propane as reference gases); or In the third embodiment suitable for propylene separation: ● The first membrane unit (20) includes a membrane (22) with a pore size of 2.9 Å to 3.2 Å and an ideal selectivity of at least 20, preferably at least 30 (H2 and propylene as reference gases); and ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.1 Å to 4.5 Å and an ideal selectivity of at least 10 (using propylene and propane as reference gases); or In a fourth embodiment suitable for separating linear butene: ● The first membrane unit (20) includes a membrane (22) with a pore size of 4.1 Å to 4.4 Å and an ideal selectivity of at least 20, preferably at least 30 (using cis-2-butene and trans-2-butene as reference gases); and ● The second membrane unit (20') includes a membrane (22') with a pore size of 4.3 Å to 4.7 Å and an ideal selectivity of at least 10 (using 1-butene and cis-2-butene as reference gases); and In each case, the flow rate of a specified gas is measured in a test cell to determine the ideal selectivity and the aperture.

8. A method for separating a feed stream (1) into three product streams, wherein The feed stream comprises a mixture containing three or more gases selected from methane, C2 hydrocarbons, C3 hydrocarbons and C4 hydrocarbons; The method includes the step of passing the feed stream (1) through a membrane system (10) as defined in any one of claims 1 to 7 to obtain three product streams.

9. The method according to claim 8, wherein ● The feed (1) contains propylene, and ● One of the product streams contains a higher concentration of propylene than the feed (1), preferably refinery-grade, chemical-grade, or polymer-grade propylene.

10. The method of claim 8, wherein The feed stream (1) comprises (i) 1% to 99% by weight of propylene, (ii) 99% to 1% by weight of propane, and (iii) 99% to 1% by weight of other gases selected from nitrogen, hydrogen, and methane; and (i) + (ii) + (iii) total 100%; or The feed stream (1) comprises (i) 1% to 90% by weight of 1-butene, (ii) 90% to 1% by weight of cis-2-butene, (iii) 90% to 1% by weight of trans-2-butene, and (iv) other gases selected from nitrogen, hydrogen, C3 alkanes, C3 olefins, C4 alkanes, and isobutene; and (i)+(ii)+(iii)+(iv) total 100%.

11. The method according to any one of claims 8 to 10, wherein the feed stream (1) is selected from... ● Hydrocarbon fractionation towers, especially C3 fractionation towers, including feed, overhead flow, or bottom flow; ● Flue gas; or ● Torch stream; or ● Purge airflow, especially purge air from PP production; or ● Recirculation flow in a polypropylene reactor.

12. The method according to any one of claims 8 to 11, wherein the membrane (22, 22') comprises or consists of: ● Backing layer (28); ● Functional layer (25), which includes the polymer matrix (24) and the molecular sieve (23) located in the channel (26).

13. The method according to any one of claims 1 to 5, wherein The polymer matrix (24) comprises or consists of: polysulfone, polyethersulfone, sulfonated polysulfone, sulfonated polyethersulfone, polyetherimide, cellulose polymer, polyimide, polyamide / imide, polyketone, polyetherketone, poly(arylene oxide), poly(benzobenzimidazole), polyhydrazide, polyoxadiazole, polybenzoxazole, polytriazole, poly(benzimidazole), polycarbodiimide, polyphosphazene, microporous polymers and mixtures thereof; and / or The molecular sieve (23, 23') is selected from metal-organic frameworks (MOFs) and optionally zeolites; The MOF is preferably selected from ZIF-7, ZIF-8, ZIF-L, ZIF-20, ZIF-21, ZIF-22, ZIF-23, ZIF-67, ZIF-69, ZIF-71, ZIF-90, SIM-1, MIL-47, MIL-53, MOF-5, MIL-96, MIL-89, MIL-101 and HKUST-1 and mixtures thereof; The zeolite is preferably selected from AlPO-14, AlPO-18, AlPO-34, SAPO-34, SSZ-13, DD3R, ITQ-12, CDS-1, UZM-25 and mixtures thereof.

14. Use of the membrane system (10) as defined in any one of claims 1 to 8 for carrying out a process selected from: ■ C3H6 / C3H8 / ethylene separation; ■ C3H6 / C3H8 / Nitrogen separation; ■ C3H6 / C3H8 / Hydrogen separation; ■ C3H6 / C3H8 / methane separation; ■ Separation of C3H6 / C3H8 / Methane + Hydrogen + Nitrogen + Ethylene In each case, a propylene stream with a purity of at least 90% by weight is obtained; or Used to implement processes selected from the following: ■ Separate 1-butene / cis-2-butene / trans-2-butene to obtain a product stream of each butene with a purity at least 5% by weight higher than that of the feed stream.

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