Carbon molecular sieve monolith and preparation method thereof

Abstract

A method for forming a monolith of carbon molecular sieves includes loading a resin into an extruder; heating the resin to form a polymer melt; introducing the polymer melt into a microcapillary film die to form microcapillaries in the polymer melt; quenching the polymer melt to form a microcapillary film; generating a microcapillary film layer; laminating the layers or placing the microcapillary film layers into a mold; heating the microcapillary film layers to a temperature of 50 DEG C to 350 DEG C to form a polymer monolith; pyrolyzing the polymer monolith by heating the polymer monolith to a temperature of 500 DEG C to 1700 DEG C to form the carbon molecular sieve monolith; and activating the carbon molecular sieve monolith using one or more oxidizing agents.

Description

[0001] Cross-reference to related applications This application claims the benefit of U.S. Provisional Application Serial No. 63 / 592,792, filed on October 24, 2023, the contents of which are incorporated herein by reference.

[0002] Background technology. Technical Field

[0003] This specification relates generally to carbon molecular sieve bulk materials for gas separation. Specifically, this specification relates to carbon molecular sieve bulk materials for gas separation and methods for preparing carbon molecular sieve bulk materials for gas separation. Technical Background Carbon molecular sieves and carbon molecular sieve membranes have been used for gas separation. Carbon molecular sieves can be prepared from various resins pyrolyzed at different temperatures and / or under different conditions. Pyrolysis reduces the resin to carbon, but retains at least some porosity in the pyrolysis products in the form of micropores. Subsequently, the resulting carbon molecular sieves can be used in conventional gas separation equipment (such as packed beds, chromatographic columns, etc.) employing specific gas adsorption, where the micropore size determines which gases in the gas mixture are adsorbed and which are not. Separation can be achieved by alternating adsorption and desorption techniques according to, for example, conventional pressure swing adsorption (PSA) or temperature swing adsorption (TSA) methods.

[0005] Structured adsorbents can reduce the adsorbent bed size and capital cost of PSAs by using shorter cycle operations without causing pressure drop and mass transfer problems.

[0006] Therefore, there is a need for structured adsorbents and methods for preparing structured adsorbents for gas separation. Summary of the Invention

[0007] According to one embodiment, a method for forming a carbon molecular sieve monolith includes loading resin into an extruder; heating the resin to form a polymer melt; introducing the polymer melt into a microcapillary membrane die to form microcapillaries in the polymer melt; quenching the polymer melt to form a microcapillary membrane; producing a microcapillary membrane layer; laminating the microcapillary membrane layer or placing the microcapillary membrane layer into a die; heating the microcapillary membrane layer to a temperature of 50°C to 350°C to form a polymer monolith; pyrolyzing the polymer monolith by heating it to a temperature of 500°C to 1700°C to form a carbon molecular sieve monolith; and activating the carbon molecular sieve monolith using one or more oxidants.

[0008] In another embodiment, the carbon molecular sieve assembly includes a first end and a second end opposite to the first end; two or more sheets of carbon microcapillary membrane arranged in parallel such that the first axial ends of the two or more sheets of carbon microcapillary membrane are positioned at the first end of the carbon molecular sieve assembly, and the second axial ends of the one or more sheets of carbon microcapillary membrane are arranged at the second end of the carbon molecular sieve assembly; and a microcapsule extending from the first end of the one or more sheets of carbon microcapillary membrane to the second end of the one or more sheets of carbon microcapillary membrane, wherein the outer surfaces of the one or more sheets of carbon microcapillary membrane are joined together to form the carbon molecular sieve assembly, and the pore density of the carbon molecular sieve assembly is greater than or equal to 300 pores / square inch.

[0009] Further features and advantages will be set forth in the detailed description below, and will be apparent in part from the detailed description or to those skilled in the art by practicing the embodiments described herein (including the detailed description below, the claims and the drawings).

[0010] It should be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and characteristics of the claimed subject matter. Drawings are included to provide a further understanding of the various embodiments, and these drawings are incorporated in and form a part of this specification. The drawings illustrate the various embodiments described herein and, together with the specification, serve to explain the principles and operation of the claimed subject matter. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a carbon molecular sieve assembly according to the embodiments disclosed and described herein.

[0012] Figure 2 This is an enlarged photograph of the cross-section of a carbon molecular sieve substrate according to the embodiments disclosed and described herein.

[0013] Figure 3 This is an enlarged photograph of the cross-section of a carbon molecular sieve substrate according to the embodiments disclosed and described herein.

[0014] Figure 4 This is a graph showing the capacity of a carbon molecular sieve stock at various pressures on different dates, based on the embodiments disclosed and described herein.

[0015] Figure 5 This is a graph showing the capacity of a carbon molecular sieve stock at various pressures on different dates, based on the embodiments disclosed and described herein.

[0016] Figure 6This is a graph showing the capacity of a carbon molecular sieve stock at various pressures on different dates, based on the embodiments disclosed and described herein. Detailed Implementation

[0017] Reference will now be made in detail to embodiments of carbon molecular sieve monoliths and methods for preparing carbon molecular sieve monoliths. In one embodiment, a method for forming a carbon molecular sieve monolith includes loading resin into an extruder; heating the resin to form a polymer melt; introducing the polymer melt into a microcapillary membrane die to form microcapillaries in the polymer melt; quenching the polymer melt to form a microcapillary membrane; producing microcapillary membrane layers; laminating these layers or placing these microcapillary membrane layers into a die; heating the microcapillary membrane layers to a temperature of 50°C to 350°C to form a polymer monolith; pyrolyzing the polymer monolith by heating it to a temperature of 500°C to 1700°C to form a carbon molecular sieve monolith; and activating the carbon molecular sieve monolith using one or more oxidants.

[0018] In another embodiment, the carbon molecular sieve assembly includes a first end and a second end opposite to the first end; two or more sheets of carbon microcapillary membrane arranged in parallel such that the first axial ends of the two or more sheets of carbon microcapillary membrane are positioned at the first end of the carbon molecular sieve assembly, and the second axial ends of the one or more sheets of carbon microcapillary membrane are arranged at the second end of the carbon molecular sieve assembly; and a microcapsule extending from the first end of the one or more sheets of carbon microcapillary membrane to the second end of the one or more sheets of carbon microcapillary membrane, wherein the outer surfaces of the one or more sheets of carbon microcapillary membrane are joined together to form the carbon molecular sieve assembly, and the pore density of the carbon molecular sieve assembly is greater than or equal to 300 pores / square inch. The carbon molecular sieve assembly according to the embodiment will now be described with reference to the accompanying drawings.

[0019] Now for reference Figure 1The carbon molecular sieve monolith 100 according to an embodiment includes a first end 110 and a second end 120 opposite to the first end 110. The carbon molecular sieve monolith includes two or more sheets 210 and 220 of carbon microcapillary membranes. For example, the carbon molecular sieve monolith may include a first sheet 210 and a second sheet 220. The first sheet 210 and the second sheet 220 are arranged in parallel such that a first axial end 213 of the first sheet 110 and a first axial end 223 of the second sheet 220 are positioned at the first end 110 of the carbon molecular sieve monolith 100, and a second axial end 217 of the first sheet 210 and a second axial end 227 of the second sheet 220 are arranged at the second end 120 of the carbon molecular sieve monolith 100. The carbon molecular sieve monolith 100 includes microcapillaries 300 extending from the first end 110 to the second end 120. The outer surfaces 215 of the first sheet 210 and the outer surfaces 225 of the second sheet 220 are joined together to form the carbon molecular sieve monolith 100. It should be understood that, Figure 1 The carbon molecular sieve 100 does not specify all the microcapillaries 300.

[0020] like Figure 1 As illustrated in the embodiment, the carbon molecular sieve monolith 100 is formed by bonding the outer surfaces 215 and 225 of sheets 210 and 220 together to form the carbon molecular sieve monolith 100. The method for bonding the outer surfaces 215 and 225 of sheets 210 and 220 to form the carbon molecular sieve monolith 100 will be described in more detail herein.

[0021] like Figure 1 As depicted in the embodiments, the outer surfaces 215 and 225 of sheets 210 and 220 are in physical contact and are joined together by forming a monolithic carbon molecular sieve 100 according to the embodiments disclosed and described herein. According to the embodiments, the outer surfaces 215 and 225 are in physical contact and joined together, such as by fusion, such that the physically contacting outer surfaces 215 and 225 are joined and form an interface that prevents gas from bypassing the microcapillary channels. Thus, the individual sheets 210 and 220 are joined together to form a monolithic carbon molecular sieve. By joining the individual sheets 210 and 220 as disclosed and described herein, the monolithic carbon molecular sieve 100 of the embodiments is easy to transport and maintains its shape and integrity during use.

[0022] In one embodiment, the carbon molecular sieve substrate 100 comprises 10 or more sheets of carbon microcapillary membrane. In another embodiment, the carbon molecular sieve substrate 100 comprises 5 or more sheets of carbon microcapillary membrane, 10 or more sheets of carbon microcapillary membrane, 50 or more sheets of carbon microcapillary membrane, 100 or more sheets of carbon microcapillary membrane, 200 or more sheets of carbon microcapillary membrane, or 500 or more sheets of carbon microcapillary membrane. In yet another embodiment, the carbon molecular sieve substrate 100 comprises 2 to 5000, 2 to 1000, or 2 to 500 sheets of carbon microcapillary membrane.

[0023] In one embodiment, the carbon molecular sieve stock 100 may have a height of 0.5 mm to 1.5 m, wherein the height is measured perpendicular to the edge of the microcapillary membrane layer. In another embodiment, the carbon molecular sieve stock 100 may have a height of 0.5 mm to 1.5 m, 1 mm to 1 m, or 5 mm to 0.5 m, wherein the height is measured perpendicular to the edge of the microcapillary membrane layer.

[0024] In the implementation plan, the adsorbent loading in the carbon molecular sieve substrate is at least 0.1 g / cm³. 3 As used herein, "adsorbent loading" refers to the amount of adsorbent per unit volume of bulk material. For example, according to the embodiments described herein, it has a loading of 0.1 g / cm³. 3 The carbon molecular sieve stock with an adsorbent loading will have 0.1 g of adsorbent solids per cubic centimeter of carbon molecular sieve stock. In the embodiment, the adsorbent loading in the carbon molecular sieve stock is at least 0.1 g / cm³. 3 At least 0.2g / cm 3 At least 0.3g / cm 3 Or at least 0.4 g / cm 3 In the implementation plan, the adsorbent loading in the carbon molecular sieve substrate is 0.1 g / cm³. 3 Up to 1.5g / cm 3 0.1g / cm 3 Up to 1g / cm 3 or 0.2g / cm 3 Up to 0.75 g / cm 3 .

[0025] In one embodiment, the carbon molecular sieve stock 100 has a microcapillary density of 300 pores per square inch or greater, also referred to as pore density. In some embodiments, the pore density of the carbon molecular sieve stock 100 is from 300 pores per square inch to 3000 pores per square inch. The number of pores per square inch is measured at a first end 110 or a second end 120 of the carbon molecular sieve stock 100 and indicates the number of microcapillaries 300 on the surface cross-section. In the implementation scheme, the pore density of the carbon molecular sieve 100 is greater than 300 pores / square inch, such as greater than or equal to 400 pores / square inch, greater than or equal to 500 pores / square inch, greater than or equal to 750 pores / square inch, greater than or equal to 1000 pores / square inch, greater than or equal to 1100 pores / square inch, greater than or equal to 1250 pores / square inch, greater than or equal to 1500 pores / square inch, greater than or equal to 1750 pores / square inch, greater than or equal to 2000 pores / square inch, greater than or equal to 2250 pores / square inch, greater than or equal to 2500 pores / square inch, greater than or equal to 2750 pores / square inch, or even greater than or equal to 3000 pores / square inch. In the implementation scheme, the pore density of the carbon molecular sieve 100 is greater than or equal to 1,000 pores / square inch to less than 5,000 pores / square inch, greater than or equal to 1,000 pores / square inch to less than 3,000 pores / square inch, or greater than or equal to 1,500 pores / square inch to less than 3,000 pores / square inch.

[0026] In the implementation, the cross-sectional diameter of the microcapillary is less than or equal to 1000µm, such as less than or equal to 750µm, less than or equal to 500µm, less than 400µm, less than 300µm, less than 250µm, less than 200µm, or less than 150µm. In the implementation scheme, the cross-sectional diameter of the microcapillaries is 10µm to 1000µm, 100µm to 1000µm, 200µm to 1000µm, 300µm to 1000µm, 400µm to 1000µm, 500µm to 1000µm, 600µm to 1000µm, 700µm to 1000µm, 800µm to 1000µm, 900µm to 1000µm, 10µm to 900µm, 100µm to 900µm, 200µm to 900µm, 300µm to 900µm, 40µm to 900µm. 0µm to 900µm, 500µm to 900µm, 600µm to 900µm, 700µm to 900µm, 800µm to 900µm, 10µm to 800µm, 100µm to 800µm, 200µm to 800µm, 300µm to 800µm, 400µm to 800µm, 500µm to 800µm, 600µm to 800µm, 700µm to 800µm, 10µm to 700µm, 100µm to 700µm, 200µm to 700µm, 300µm to 700µm 0µm, 400µm to 700µm, 500µm to 700µm, 600µm to 700µm, 10µm to 600µm, 100µm to 600µm, 200µm to 600µm, 300µm to 600µm, 400µm to 600µm, 500µm to 600µm, 10µm to 500µm, 100µm to 500µm, 200µm to 500µm, 300µm to 500µm, 400µm to 500µm, 10µm to 500µm, 100µm to 500µm, 200µm to 500µm µm to 500µm, 300µm to 500µm, 400µm to 500µm, 10µm to 400µm, 100µm to 400µm, 200µm to 400µm, 300µm to 400µm, 10µm to 300µm, 100µm to 300µm, 200µm to 300µm, 300µm to 300µm, 10µm to 300µm, 100µm to 300µm, 200µm to 300µm, 10µm to 200µm, 100µm to 200µm or 10µm to 100µm. It should be understood that the smaller diameter microcapillary 300 provides more efficient separation by providing a larger contact area, but if the cross-sectional diameter of the microcapillary 300 is too small, the pressure drop on the carbon molecular sieve bulk 100 will increase to an undesirable level.

[0027] In some embodiments, the void fraction of the carbon molecular sieve bulk 100 is 10 v.% to 90 v.%, where the void fraction is the volume of gas absorbed by the microcapillaries. In some embodiments, the void fraction of the carbon molecular sieve bulk 100 is 10 v.% to 90 v.%, 15 v.% to 75 v.%, or 20 v.% to 50 v.

[0028] According to embodiments, two or more sheets of carbon microcapillary membrane are made from any melt-extrudeable carbon-forming precursor. Suitable melt-extrudeable carbon-forming precursors may include one or more of polyimide, polyvinylidene chloride, polyetherimide, and polyphenylene ether, or combinations thereof. Thus, in embodiments, two or more microcapillary membrane layers comprise, are substantially composed of, or are composed of, polyvinylidene chloride, polyimide, polyetherimide, polyphenylene ether, or combinations thereof. Examples of suitable polyvinylidene chloride are disclosed in U.S. Patent No. 10,239,043 (the entire contents of which are incorporated herein by reference) and are also described below. Examples of suitable polyimides that may be used to form the membrane of the embodiments include BTDA-DAPI (Matrimid) described in U.S. Patent No. 8,911,534, the entire contents of which are incorporated herein by reference. Examples of suitable polyetherimides may be marketed under the trade name Ultem. ® Acquired and disclosed in Fuertes, AB; Centeno, TA, Carbon molecular sieve membranes from polyetherimide. Microporous Mesoporous Mat. 1998, 26 (1), 23-26), which is incorporated herein by reference in its entirety. Examples of suitable polyphenylene ethers are disclosed in Yoshimune, M.; Fujiwara, I.; Haraya, K., Carbonmolecular sieve membranes derived from trimethylsilyl substituted poly(phenylene oxide) for gas separation. Carbon 2007, 45 (3), 553-560, which is incorporated herein by reference in its entirety.

[0029] Typically, the embodiments provide a carbon molecular sieve feedstock suitable for various separations. Such separations may include, but are not necessarily limited to, the following gas pairs, wherein at least one molecule and, in some embodiments, two molecules have representative molecular diameters falling within the range of 3.0 Å to 5.0 Å: ethylene (C2H4) and ethane (C2H6); propylene (C3H6) and propane (C3H8); carbon dioxide (CO2) and nitrogen (N2); carbon dioxide (CO2) and hydrogen (H2), hydrogen (H2) and methane (CH4), N2 and methane (CH4); and n-butane (n-C4H4). 10 ) and isobutane (i-C4H 10 The implementation scheme of carbon molecular sieve bulk material can be readily used in typical separation systems, especially those based on principles such as pressure or temperature fluctuations.

[0030] The carbon molecular sieve feedstock of the embodiment can be prepared from a vinylidene chloride copolymer, which includes vinylidene chloride monomer and at least one additional comonomer. The comonomer can be selected from a variety of materials, and in a particular embodiment includes vinyl monomers, vinyl chloride monomers, acrylate monomers, methacrylate monomers, styrene monomers, acrylonitrile, methacrylonitrile, itaconic acid, trifluorochloroethylene, and combinations thereof. In the embodiment, examples of vinyl monomers include vinyl chloride, vinyl acetate, acrylonitrile, and combinations thereof. Exemplary acrylate monomers include methyl acrylate, ethyl acrylate, butyl acrylate, and combinations thereof. More specific examples of methacrylate monomers include methyl methacrylate, butyl methacrylate, and combinations thereof. An example of a styrene monomer is styrene itself.

[0031] In the embodiments, the vinylidene chloride-based copolymer comprises at least 60% by weight of vinylidene chloride based on the total weight of the copolymer, such as at least 70% by weight. However, it is further desirable that, in the embodiments, the vinylidene chloride comprises at most 97% by weight of vinylidene chloride, and therefore, in the embodiments, it comprises at least 3% by weight of a comonomer or a combination of comonomers, such as 3% to 40% by weight, 3% to 30% by weight, or 3% to 20% by weight.

[0032] In one embodiment, based on the total weight of vinylidene chloride, the vinylidene chloride contains 3% to 30% by weight, such as 3.5% to 15% by weight or 4% to 12% by weight, of acrylate comonomers (such as methyl acrylate, ethyl acrylate, butyl acrylate, or combinations thereof). In one or more embodiments, the vinylidene chloride used contains 3% to 30% by weight, such as 7% to 28% by weight or 9% to 25% by weight, of vinyl chloride monomer. In another embodiment, the total weight-average molecular weight (Mw) of the vinylidene chloride copolymer can be in the range of 10,000 Mw to 250,000 Mw, such as 50,000 Mw to 200,000 Mw, or 60,000 Mw to 150,000 Mw.

[0033] According to one or more embodiments, additives may also be included in vinylidene chloride. Commonly used additives may include, but are not limited to, epoxidized oil stabilizers, such as epoxidized soybean oil, epoxidized linseed oil, and diglycidyl ether of bisphenol A. Liquid plasticizers, such as aliphatic and aromatic esters, are also frequently used, including, for example, dibutyl sebate, acetyl tributyl citrate, dioctyl phthalate, and combinations thereof. Other commonly used additives may include lubricants, such as polyethylene wax, paraffin wax, oxidized polyethylene wax, and combinations thereof. Lubricants may optionally be included, and may include, for example, high-density polyethylene, acrylate copolymers, and silicone polymers and combinations thereof. Another group of additives that may be included are acid scavengers, such as epoxy compounds, magnesium hydroxide, magnesium oxide, tetrasodium pyrophosphate, calcium phosphate, magnesium phosphate, DHT 4A (a synthetic hydrotalcite-like halogen scavenger available from Kyowa Chemical Industry), calcium oxide, calcium carbonate, and combinations thereof. Antioxidants, such as phenolic resins, may also be combined. Any or a combination of all these types of additives can be included in vinylidene chloride.

[0034] According to the implementation scheme, the total amount of all additives shall not exceed 8 wt%, such as not exceeding 3 wt%. However, in the implementation scheme, a combination of at least 2 wt% of all additives may be used, and therefore its use is preferably from 2 wt% to 8 wt%, and more preferably from 2 wt% to 3 wt%. Those skilled in the art will recognize the use of such additives and their indications and contraindications, and no further guidance is required herein.

[0035] Various means and methods for preparing copolymers can be used to form vinylidene chloride in the embodiments. However, any typical or conventional polymerization method can generally be used, including but not limited to bulk polymerization, suspension polymerization, and emulsion polymerization, and suspension polymerization or emulsion polymerization is preferred. In the embodiments, polymerization is carried out at temperatures that ensure the degradation of all vinylidene chloride components is avoided, such as 10°C to 120°C, 20°C to 100°C, or 30°C to 90°C.

[0036] In the implementation scheme, the peak melting temperature of vinylidene chloride is within the following ranges: 100°C to 200°C, 110°C to 200°C, 120°C to 200°C, 130°C to 200°C, 140°C to 200°C, 150°C to 200°C, 160°C to 200°C, 170°C to 200°C, 180°C to 200°C, 190°C to 200°C, 100°C to 190°C, 110°C to 190°C. ℃, 120℃ to 190℃, 130℃ to 190℃, 140℃ to 190℃, 150℃ to 190℃, 160℃ to 190℃, 170℃ to 190℃, 180℃ to 190℃, 100℃ to 180℃, 110℃ to 180℃, 120℃ to 180℃, 130℃ to 180℃, 140℃ to 180℃, 150℃ to 180℃, 160℃ to 180℃, 17 0℃ to 180℃, 100℃ to 170℃, 110℃ to 170℃, 120℃ to 170℃, 130℃ to 170℃, 140℃ to 170℃, 150℃ to 170℃, 160℃ to 170℃, 100℃ to 160℃, 110℃ to 160℃, 120℃ to 160℃, 130℃ to 160℃, 140℃ to 160℃, 150℃ to 160℃, 100℃ to 1 50℃, 110℃ to 150℃, 120℃ to 150℃, 130℃ to 150℃, 140℃ to 150℃, 100℃ to 140℃, 110℃ to 140℃, 120℃ to 140℃, 130℃ to 140℃, 100℃ to 130℃, 110℃ to 130℃, 120℃ to 130℃, 100℃ to 120℃, 110℃ to 120℃, 100℃ to 110℃.

[0037] In this embodiment, vinylidene chloride is formed into a resin. The resin is loaded into an extruder and heated to form a polymer melt. The resin can be heated to a temperature of 100°C to 200°C to form a polymer melt. The resin can be heated to temperatures of 100°C to 200°C, 125°C to 180°C, 150°C to 175°C, or 155°C to 170°C to form a polymer melt.

[0038] A polymer melt is introduced into a microcapillary membrane die to form microcapillaries within the polymer melt. In one embodiment, the microcapillary membrane die has a split design. In another embodiment, the microcapillary membrane die includes an insert. The insert may be an air manifold insert or any other fluid (water, liquid fluid, low-carbon yield polymer, such as polyethylene) that can open the capillary after heat treatment. The width of the insert and the die slit opening may be 0.5 inches to 100 inches, 1 inch to 90 inches, 3 inches to 80 inches, or 5 inches to 75 inches. In another embodiment, the insert includes parallel hollow pins positioned near the outlet of the microcapillary membrane die. The insert may include 2 to 2000 hollow pins, 10 to 1500 hollow pins, or 25 to 1000 hollow pins. The parallel hollow pins are used to introduce air into the polymer melt to form microcapillaries within the polymer melt. In another embodiment, the parallel hollow pins are used to introduce air into the polymer melt. The ratio of air flow rate to volumetric polymer melt flow rate will determine the void fraction of the microcapillary membrane and the bulk material. The microcapillary size and wall thickness will be determined by the ratio of polymer to air flow rate. In embodiments, the air feed pressure can be from 1 psig to 100 psig, such as 5 psig to 75 psig, 10 psig to 50 psig, or 20 psig to 40 psig. In embodiments, the air flow rate can be from 1 standard cubic centimeter per minute (sccm) to 2000 sccm, such as 5 sccm to 500 sccm, 10 sccm to 250 sccm, or 15 to 200 sccm. The polymer flow rate can be within the same range as the air flow rate.

[0039] After introducing the polymer melt into a microcapillary membrane die to form microcapillaries within the polymer melt, the polymer melt is then quenched to form a microcapillary membrane. Quenching the polymer melt may include passing the polymer melt through a water bath. The water bath may be at temperatures ranging from 1°C to 80°C, such as room temperature (approximately 22°C).

[0040] A microcapillary membrane layer can be generated after the polymer melt is quenched to form a microcapillary membrane. In some embodiments, the microcapillary membrane layer can be generated while the microcapillary membrane is in a water bath. In one embodiment, generating a microcapillary membrane layer includes stacking a single microcapillary membrane on itself. In another embodiment, generating a microcapillary membrane layer includes stacking a plurality of microcapillary membranes. In yet another embodiment, generating a microcapillary membrane layer includes both stacking a single microcapillary membrane on itself (e.g., by folding a single microcapillary membrane) and stacking a plurality of microcapillary membranes; in such embodiments, layers of the same microcapillary membrane may be referred to as a first sheet of microcapillary membrane and a second sheet of microcapillary membrane. In another embodiment, the microcapillary membrane layers may be arranged in parallel such that a first axial end of each microcapillary membrane is positioned at a first end of the carbon molecular sieve bulk material, and a second axial end of each microcapillary membrane is aligned at a second end of the carbon molecular sieve bulk material, and microcapillaries extend from the first end of each microcapillary membrane to the second end of each microcapillary membrane.

[0041] In this embodiment, the microcapillary membrane is stretched during the formation of the microcapillary membrane layer. The thickness of the stretched microcapillary membrane ranges from 10 µm to 1000 µm, such as 20 µm to 500 µm, or 50 µm to 200 µm. In this embodiment, such stretching can particularly effectively induce faster crystallization and increase, and thus improve the arrangement of polyvinylidene chloride microcrystals. Ideally, the stretching ratio ranges from 1 to 8, such as 1 to 6, 1 to 4, or 2 to 4.

[0042] It has been found that ensuring a given level of crystallinity within a specified range helps achieve the desired average micropore size and average micropore volume in the final carbon molecular sieve after pyrolysis. It should be noted that homopolymer polyvinylidene chloride typically exhibits an initial polymerization crystallinity greater than 75%, and it has been found that it is important that polyvinylidene chloride be copolymerized either with a sufficient amount of at least one of the listed monomers, or melt-extruded (stretched or unstretched), or both, to ensure the specified level (i.e., 25% to 75%) of precursor (i.e., pre-pyrolysis) crystallinity specified herein. Therefore, including comonomers generally helps to reduce precursor crystallinity to ensure the desired range and also helps to lower the melt temperature, thereby improving the processability of the resulting copolymer. Generally, including monomers with larger volumes can tend to reduce the overall copolymer crystallinity to a greater extent compared to including monomers with smaller volumes. Thus, for example, butyl acrylate will tend to reduce crystallinity more significantly compared to, for example, methyl acrylate or ethyl acrylate, assuming that methyl acrylate and / or ethyl acrylate are used in the same molar percentage (mol%) based on the final copolymer composition.

[0043] In some embodiments, the microcapillary membrane layers can be laminated after their formation. The microcapillary membrane layers can be laminated by placing multiple softened microcapillary membrane layers adjacent to each other and cooling them for 1 minute to 48 hours to form a laminate. The microcapillary membrane layers can be laminated at temperatures between 1°C and 60°C, for example at room temperature (25°C). The microcapillary membrane layers can be laminated for 1 minute to 48 hours, 1 minute to 36 hours, 1 minute to 24 hours, 2 minutes to 24 hours, 5 minutes to 24 hours, 30 minutes to 24 hours, 1 hour to 24 hours, 4 hours to 24 hours, or 8 hours to 24 hours. After the microcapillary membrane layers are formed, they are at least partially crystallized. Cooling the microcapillary membrane layers to form a laminate allows for complete crystallization of the microcapillary membrane layers. The time required for the microcapillary membrane layer to fully crystallize and form a laminate depends on several factors, including the temperature to which the layer is cooled and the degree to which the microcapillary membrane is stretched during formation and quenching. Cooling the microcapillary membrane layer to form a laminate stabilizes the structure of the microcapillary membrane layer.

[0044] In some embodiments, the microcapillary membrane layer is placed in a mold. The mold has the desired shape of the carbon molecular sieve. The mold can be made of any material capable of withstanding the processing pressures and temperatures described below. In some embodiments, the mold may be lined with a gasket that prevents or mitigates adhesion of the microcapillary membrane layer to the mold. In some embodiments, the mold may be treated with a coating that prevents or mitigates adhesion of the microcapillary membrane layer to the mold. In one or more embodiments, the mold may be ceramic.

[0045] In this embodiment, after the microcapillary membrane layers have been loaded into the mold, the mold in which the microcapillary membrane layers are placed is heated to a temperature that softens the microcapillary membrane layers, such as, for example, at or above the softening point or glass transition temperature of the microcapillary membrane layers. Because the microcapillary membrane layers are constrained by the mold, when the microcapillary membrane layers are heated to a temperature at or above the softening point or glass transition temperature of the microcapillary membrane layers, the microcapillary membrane layers soften and bond with adjacent microcapillary membrane layers in physical contact with them, thereby forming a polymer monolith. Heating the mold containing the microcapillary membrane layers stabilizes or “locks in” the structure of the microcapillary membrane layers before they carbonize. Therefore, as used herein, the term “polymer monolith” refers to two or more microcapillary membranes bonded together to form a monolithic structure that is not easily separated.

[0046] In the implementation scheme, the laminated microcapillary membrane layer or the microcapillary membrane layer placed in a mold can be heated to the following temperatures: 50°C to 350°C, 75°C to 350°C, 100°C to 350°C, 125°C to 350°C, 150°C to 350°C, 175°C to 350°C, 200°C to 350°C, 225°C to 350°C, 250°C to 350°C, 275°C to 350°C, 300°C to 350°C, 325°C to 350°C, 50°C to 325°C, 75°C to 325°C, 100°C to 325°C, 125°C to 325°C, 150°C to 325℃, 175℃ to 325℃, 200℃ to 325℃, 225℃ to 325℃, 250℃ to 325℃, 275℃ to 325℃, 300℃ to 325℃, 50℃ to 300℃, 75℃ to 300℃, 100℃ to 300℃, 125℃ to 300℃, 150℃ to 300℃, 175℃ to 300℃, 200℃ to 300℃, 225℃ to 300℃, 250℃ to 300℃, 275℃ to 300℃, 50℃ to 275℃, 75℃ to 275℃, 100℃ to 275℃, 125℃ to 275℃, 1 50℃ to 275℃, 175℃ to 275℃, 200℃ to 275℃, 225℃ to 275℃, 250℃ to 275℃, 50℃ to 250℃, 75℃ to 250℃, 100℃ to 250℃, 125℃ to 250℃, 150℃ to 250℃, 175℃ to 250℃, 200℃ to 250℃, 225℃ to 250℃, 50℃ to 225℃, 75℃ to 225℃, 100℃ to 225℃, 125℃ to 225℃, 150℃ to 225℃, 175℃ to 225℃, 200℃ to 225℃, 50℃ to 200℃ ℃, 75℃ to 200℃, 100℃ to 200℃, 125℃ to 200℃, 150℃ to 200℃, 175℃ to 200℃, 130℃ to 160℃, 50℃ to 175℃, 75℃ to 175℃, 100℃ to 175℃, 125℃ to 175℃, 150℃ to 175℃, 50℃ to 150℃, 75℃ to 150℃, 100℃ to 150℃, 125℃ to 150℃, 50℃ to 125℃, 75℃ to 125℃, 100℃ to 125℃, 50℃ to 100℃, 75℃ to 100℃, or 50℃ to 75℃.

[0047] According to the implementation scheme, the heating is performed for a certain duration sufficient to reduce the weight of the microcapillary membrane layer by at least 5%, at least 7%, at least 10%, at least 12%, at least 15%, at least 17%, or at least 20%. Therefore, in the implementation scheme, the heating is performed for a certain duration sufficient to reduce the weight of the microcapillary membrane layer by 5% to 20%, 7% to 20%, 10% to 20%, 12% to 20%, 15% to 20%, 17% to 20%, 5% to 17%, 7% to 17%, 10% to 17%, 12% to 17%, 15% to 17%, 5% to 15%, 7% to 15%, 10% to 15%, 12% to 15%, 5% to 12%, 7% to 12%, 10% to 12%, 5% to 10%, 7% to 10%, and 5% to 7%.

[0048] According to one embodiment, after the mold in which the microcapillary membrane layers are placed has been heated to a temperature that bonds the microcapillary membrane layers to adjacent microcapillary membrane layers, the mold in which the microcapillary membrane layers are placed may optionally be returned to room temperature. This cooling allows the mold in which the microcapillary membrane layers are placed to be easier to handle and transport. However, in one embodiment, the mold in which the microcapillary membrane layers are placed does not need to be cooled to room temperature before further processing. Additionally, in one embodiment, the polymer monolith may optionally be removed from the mold before further processing to form a carbon molecular sieve monolith (such as the further processing described below). However, in one or more embodiments, the polymer monolith is not removed from the mold before further processing to form a carbon molecular sieve monolith.

[0049] Heating the mold containing the microcapillary membrane layer will cause the microcapillary membrane layer to undergo at least 10% dehydrochlorination. As used herein, the term "at least 10% dehydrochlorination" means that the microcapillary membrane layer has been treated by removing hydrogen chloride to a point where the copolymer precursor no longer melts and effectively begins to become infusible. It is acknowledged in the art that such changes in molecular dynamics begin at the point of approximately 10% dehydrochlorination and are completed or maintained beyond that point as the level of dehydrochlorination increases.

[0050] For convenience, heating of the microcapillary membrane can be carried out in air, but other atmospheres, such as N2 and other inert or oxidizing gases (such as CO2) or combinations thereof, can also be used, since only low levels of copolymer oxidation are generally expected within a given temperature range.

[0051] The microcapillary membrane layer can be heated as needed for 1 hour to 48 hours (e.g., 1 to 24 hours or 1 to 12 hours) to reach at least a 10% dehydrochlorination point, at which the copolymer begins to become infusible (i.e., can no longer be melted). The degree of dehydrochlorination can vary from 10% to 100% depending on temperature and time. While it is expected that substantially all copolymers will be dehydrochlorinated to the desired degree, it should be recognized that the presence of small amounts, and expected to be less than 2% by weight, of precursors that have not undergone at least 10% dehydrochlorination is acceptable. If further visual confirmation of the onset of infusibility is desired, additional confirmation of the percentage of dehydrochlorination can be obtained, for example, by thermogravimetric analysis (TGA), using standard and well-known methods and equipment.

[0052] After heating the mold containing the microcapillary membrane layer, the resulting polymer monolith is pyrolyzed to form a carbon molecular sieve monolith. Pyrolysis can result in the carbonization of at least 90 wt% (e.g., at least 95 wt% or at least 99 wt%) of the copolymer. This pyrolysis can also be referred to as “carbonization” because the result is that the copolymer is transformed into a carbon-only or near-carbon-only skeleton of its copolymer structure (i.e., all or almost all atoms except carbon are removed, but the carbon-carbon bonds remain essentially intact), and the carbon molecular sieve monolith can now be referred to as “carbon-containing.” Therefore, once the polymer monolith is pyrolyzed, the microcapillary membrane becomes a carbon microcapillary membrane because the microcapillary membrane becomes carbonized.

[0053] Pyrolysis can be carried out using any method commonly known to those skilled in the art, but can be carried out at the highest temperatures within the following ranges: 600°C to 1500°C, 700°C to 1500°C, 800°C to 1500°C, 900°C to 1500°C, 1000°C to 1500°C, 1100°C to 1500°C, 1200°C to 1500°C, and 1300°C to 1500°C. 1400℃ to 1500℃, 600℃ to 1400℃, 700℃ to 1400℃, 800℃ to 1400℃, 900℃ to 1400℃, 1000℃ to 1400℃, 1100℃ to 1400℃, 1200℃ to 1400℃, 1300℃ to 1400℃, 600℃ to 1300℃, 700℃ to 1300℃, 800℃ to 1300℃ 900℃ to 1300℃, 1000℃ to 1300℃, 1100℃ to 1300℃, 1200℃ to 1300℃, 600℃ to 1200℃, 700℃ to 1200℃, 800℃ to 1200℃, 900℃ to 1200℃, 1000℃ to 1200℃, 1100℃ to 1200℃, 600℃ to 1100℃, 700℃ to 1100℃ 800℃ to 1100℃, 900℃ to 1100℃, 1000℃ to 1100℃, 600℃ to 1000℃, 700℃ to 1000℃, 800℃ to 1000℃, 900℃ to 1000℃, 600℃ to 900℃, 700℃ to 900℃, 800℃ to 900℃, 600℃ to 800℃, 700℃ to 800℃, or 600℃ to 700℃.

[0054] Following pyrolysis, the carbon molecular sieve concentrate can be activated using any method commonly known to those skilled in the art. In embodiments, the carbon molecular sieve concentrate can be activated using one or more oxidants. Oxidants may include steam, carbon dioxide, air, or combinations thereof. In embodiments, activation of the carbon molecular sieve concentrate can result in a loss of 1% to 30% by weight. In embodiments, activation of the carbon molecular sieve concentrate can result in a loss of 0% to 50% by weight, 0.5% to 40% by weight, 0.75% to 35% by weight, or 1% to 30% by weight. Activation of the carbon molecular sieve concentrate will introduce additional microporosity, which will increase the adsorption capacity of the carbon molecular sieve concentrate. Furthermore, activation of the carbon molecular sieve concentrate can enlarge the micropore size, which will increase the adsorption rate.

[0055] After activation, the carbon molecular sieve formulation has an average micropore size in the range of 3.0 Å to 6.0 Å. In a particular embodiment, the average micropore size is 4.0 Å to 4.3 Å, thus allowing propylene molecules to pass through while excluding propane molecules. In another embodiment, the average micropore size is in the range of 3.7 Å to 4.1 Å, thus allowing ethylene molecules to pass through while removing ethane molecules. In an embodiment, the average micropore size is in the range of 3.64 Å to 3.8 Å, thus allowing nitrogen molecules to pass through while removing methane molecules. In an embodiment, the average micropore size is in the range of 3.0 Å to 3.64 Å, thus allowing carbon dioxide molecules to pass through while removing nitrogen molecules. In an embodiment, the average micropore size is in the range of 4.3 Å to 5.0 Å, thus allowing n-butane molecules to pass through while removing isobutane molecules. Therefore, the compositions of the present invention are particularly desirable for these specific separations, but in other non-limiting embodiments, they can be used for certain other separations.

[0056] Example The following embodiments are provided by way of illustration and are presented in a manner that would be recognized by those skilled in the art, and are not intended to limit the whole of this disclosure or the appended claims.

[0057] SARAN 711 (a commercially available polyvinylidene chloride containing approximately 8.5% by weight methyl acrylate, sourced from SK Global SARAN) was loaded into the extruder. The extruder was a 0.75-inch diameter single-screw extruder with a three-barrel temperature zone. The extruder featured a microcapillary die. The microcapillary die had a simple split design with a two-inch wide air manifold insert containing 42 parallel hollow pins positioned near the die outlet. The air feed pressure was approximately 30 psig, and the flow rate was approximately 17 sccm. A bend adapter positioned the microcapillary die to guide the extrudate into a water bath.

[0058] First, the bend and die are heated using metal heating elements clamped in place. The temperature of the three zones of the extruder, bend, and die is increased from 155°C to 170°C until no unmelted resin is visible in the extruded film. The microcapillary membrane die is used to introduce air into the polymer melt, thereby forming microcapillaries. The extruder is fed through a hopper and operates at approximately 50 rpm. The airflow velocity through the pins in the die is 17 sccm. Polyethylene (PE) resin is periodically fed into the extruder to flush away accumulated carbon.

[0059] After extrusion from the die, the microcapillary membrane is quenched to room temperature (approximately 22°C) in a water bath and wound onto guide rollers at the bottom of the water bath. The membrane is then pulled out of the water bath at 10.5 rpm using a winding machine to achieve a film thickness of approximately 10 mils (250 µm). The winding machine also stretches the membrane near the die exit, reducing both the width and thickness. The membrane is then wound onto a 5-inch outer diameter winding roller using the winding machine. To prepare the laminate, approximately 10 layers of the microcapillary membrane are wound onto the winding roller and allowed to cool for approximately 10 minutes.

[0060] The individually extruded microcapillary membrane layers were cut into 5 cm long sheets to form strips. The laminates were also cut into 5 cm long sheets to form strips. The membrane width was approximately 1.4 cm.

[0061] The belt is then placed between two honeycomb ceramic plates. Two sheets of Whatman 1003-125 filter paper are placed between the belt and the honeycomb ceramic plates to provide cushioning. The belt / filter paper / honeycomb ceramic plate assembly is then placed in an oven and continuously purged with air at a rate of 2 liters per minute (L / min) throughout the processing cycle. The oven is then heated to 130°C at a heating rate of 1°C / min and maintained at 130°C for 24 hours. After 24 hours, the oven is allowed to cool, and the resulting polymer concentrate is removed from the oven once it has cooled to below 60°C.

[0062] The polymer stock was then placed into a quartz tube furnace. The quartz tube furnace had a diameter of six inches and a length of 24 inches. Once the polymer stock was loaded into the quartz tube furnace, it was continuously purged with nitrogen at a rate of 5 L / min. The quartz tube furnace was then heated to 250 °C at a heating rate of 0.1 °C / min. The quartz tube furnace was then heated to the pyrolysis temperature shown in Table 1 (600 °C or 900 °C, depending on the sample) at a heating rate of 3 °C / min. The quartz tube was held at the pyrolysis temperature for 120 minutes. The quartz tube was then cooled, and the resulting carbon molecular sieve stock was removed from the quartz tube after the quartz furnace had cooled to below 60 °C. Adsorption was performed using a magnetically levitated balance (MSB). Solid carbon molecular sieve samples ranging from 300 mg to 500 mg were loaded into the pores of the MSB. A vacuum pretreatment was performed by raising the temperature to 100 °C and maintaining it for 4 hours under vacuum conditions to desorb any pre-adsorbed material. At the end of the 4-hour vacuum period, the stability of the mass readings was checked to ensure the desorption step was complete. The temperature was then set to an adsorption temperature of 50 °C. The pressure was then gradually increased to measure the adsorption amount at different pressures. Between tests, the carbon adsorbent was stored in laboratory air. Repeated adsorption was performed after the same 100 °C vacuum pretreatment step outlined above to check the recyclability of the material.

[0063] Figure 2 A cross-section of Example 1 is shown. Figure 3 A cross-section of Example 3 is shown. In Examples 1 and 3, regular microcapillaries (170 μm major axis, 93 μm minor axis) are uniformly distributed. The interlayer void space is negligible, indicating good lamination, and showing that in Example 3, only one microcapillary is available for distributing the feed fluid for adsorption.

[0064] Table 2 shows the characteristics of Example 3. The pore density is 18,700 pores / square inch (cpsi). The porosity of Example 3 is approximately 37%, which provides a good path for fluid flow. Since the entire wall is made of carbon adsorbent (i.e., there is no carrier occupying the entire volume), the flow rate is 0.76 g / cm³. 3 A very high adsorbent loading was achieved. Figure 4 and Figure 5 The results of multi-cycle CO2 adsorption tests for Examples 1 and 2 are shown separately. Example 2 exhibited a stable isotherm throughout the entire three cycles and after one month of storage in a laboratory atmosphere. Example 1 showed a significant decrease in adsorption capacity over time. Without being bound by theory, it is believed that a higher pyrolysis temperature in Example 2 produces a more stable carbon material.

[0065] Figure 6 A comparison of the CO2 isotherms in Example 2 and Comparative Examples 1 and 2 is shown. Example 2 exhibits a higher capacity than existing carbon adsorbents. Even higher CO2 adsorption capacity is expected after further activation of Example 2.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the specification and appended claims, the singular forms “a / an” and “the” are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0067] It should be noted that the terms "substantially" and "about" are used herein to indicate the degree of inherent uncertainty attributable to any quantitative comparison, value, measurement, or other representation. These terms are also used herein to indicate the extent to which a quantitative representation may differ from the stated reference without causing a fundamental change in the basic function of the subject matter. The term "substantially" is also used herein to indicate the extent to which a quantitative representation may differ from the stated reference without causing a fundamental change in the basic function of the subject matter. Therefore, it is used to indicate the degree of inherent uncertainty that may be attributable to any quantitative comparison, value, measurement, or other representation relating to an arrangement of elements or features that, while theoretically expected to exhibit precise correspondences or behaviors, may in practice be less precise.

[0068] It should be noted that one or more of the appended claims use the term "wherein" as a transitional expression. For the purpose of defining this technology, it should be noted that this term is introduced in the claims as an open transitional phrase used to introduce a description of a series of features of the structure, and should be interpreted in a similar manner to the more commonly used open prepositional term "comprising".

[0069] It should be understood that when a first component is described as "comprising" or "including" a second component, it is contemplated that in some embodiments, the first component is "composed of" or "substantially composed of" the second component. Furthermore, the term "substantially composed of" is used in this disclosure to refer to a quantitative value that does not materially affect the essential and novel characteristics of this disclosure.

[0070] It should be understood that any two quantitative values ​​assigned to a certain characteristic or measurement can constitute a range of that characteristic or measurement, and this disclosure considers all combinations of ranges formed by all stated quantitative values ​​of a given characteristic or measurement.

[0071] Although specific embodiments have been described and illustrated herein, it should be understood that various other changes and modifications may be made without departing from the scope of the claimed subject matter. Furthermore, while various aspects of the claimed subject matter have been described herein, such aspects need not be used in combination. Therefore, the appended claims are intended to cover all such changes and modifications within the scope of the claimed subject matter.

Claims

1. A method for forming a carbon molecular sieve bulk material, the method comprising: Load the resin into the extruder; The resin is heated to form a polymer melt; The polymer melt is introduced into a microcapillary membrane die to form microcapillaries in the polymer melt; The polymer melt is rapidly cooled to form a microcapillary membrane; Generates a microcapillary membrane; The microcapillary membrane layer is laminated or the microcapillary membrane layer is placed in a mold; The microcapillary membrane layer is heated to a temperature of 50°C to 350°C to form a polymer monolith. The polymer bulk material is pyrolyzed by heating it to a temperature of 500°C to 1700°C to form the carbon molecular sieve bulk material; as well as The carbon molecular sieve material is activated using one or more oxidants.

2. The method according to claim 1, wherein the method further comprises stretching the microcapillary membrane near the outlet of the microcapillary membrane die.

3. The method according to claim 1 or claim 2, wherein generating the microcapillary membrane layer comprises stacking a single microcapillary membrane on itself.

4. The method according to claim 1 or claim 2, wherein generating the microcapillary membrane layer comprises stacking a plurality of microcapillary membranes.

5. The method according to any one of claims 1 to 4, wherein the method further comprises cooling the microcapillary membrane layer for 1 minute to 48 hours to form a laminate.

6. The method according to any one of claims 1 to 5, wherein the resin comprises polyvinylidene chloride.

7. The method according to any one of claims 1 to 6, wherein heating the resin to form a polymer melt comprises heating the resin to a temperature of 155°C to 170°C.

8. The method according to any one of claims 1 to 7, wherein the pyrolysis step comprises heating the polymer bulk to a temperature of 600°C to 1500°C.

9. The method according to any one of claims 1 to 8, wherein heating the mold containing the microcapillary membrane comprises heating the mold containing the microcapillary membrane to a temperature of 130°C to 160°C.

10. A carbon molecular sieve feedstock, comprising: A first end and a second end opposite to the first end; Two or more sheets of carbon microcapillary membrane, the two or more sheets being arranged in parallel such that the first axial ends of the two or more sheets of carbon microcapillary membrane are positioned at the first end of the carbon molecular sieve material, and the second axial ends of one or more sheets of carbon microcapillary membrane are arranged at the second end of the carbon molecular sieve material. as well as Microcapillaries extending from a first end of one or more sheets of the carbon microcapillary membrane to a second end of one or more sheets of the carbon microcapillary membrane, wherein... The outer surfaces of two or more sheets of the carbon microcapillary membrane are joined together to form the carbon molecular sieve assembly, and The pore density of the carbon molecular sieve is greater than or equal to 300 pores per square inch.

11. The carbon molecular sieve assembly according to claim 10, wherein two or more sheets of the carbon microcapillary membrane are made of polyvinylidene chloride.

12. The carbon molecular sieve composition according to any one of claims 10 or 11, wherein the void fraction of the carbon molecular sieve composition is from 10 v.% to 90 v.%.

13. The carbon molecular sieve stock according to any one of claims 10 or 12, wherein the carbon molecular sieve stock comprises 10 or more sheets of carbon microcapillary membrane.

14. The carbon molecular sieve stock according to any one of claims 10 to 13, wherein the pore density of the carbon molecular sieve stock is from 300 pores / square inch to 3000 pores / square inch.

15. The carbon molecular sieve substrate according to any one of claims 10 to 14, wherein the adsorbent loading in the carbon molecular sieve substrate is at least 0.1 g / cm³. 3 .

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