Improved carbon molecular sieve adsorbent

Abstract

This paper discloses a rapid cyclic pressure swing adsorption (PSA) method for separating O2 from N2 and / or Ar. The method uses a carbon molecular sieve (CMS) adsorbent with a driving force of 1 atma and 86 atma, as indicated by a linear driving force model. o F measures at least 5% O2 / N2 and / or O2 / Ar kinetic selectivity and at least 0.2000% O2 adsorption rate (1 / s).

Description

Technical Field

[0001] This invention relates to a method for rapid cyclic pressure swing adsorption (PSA) to separate O2 from N2 and / or Ar using carbon molecular sieve (CMS) adsorbents. Background Technology

[0002] The PSA method has long been used to separate air components. For decades, carbon molecular sieve (CMS) adsorbents have been known for separating various gas mixtures. Walker, Jr., PL,"Molecular Sieves", Mineral Industries, 1966 ).

[0003] Carbon molecular sieve (CMS) adsorbents are typically derived from processing various raw materials, such as plant products (waste wood, coconut shells, walnut shells, fruit kernels), mineral coal, waste mineral oil, waste resin, etc. (US patent). No. 3,801,513 US Patent No. 4,458,022; Nakao, Y., "Control of Micro-pores of Molecular Sieving Carbon by Impregnation of Hydrocarbons and Heat Treatment”, Presented at 20 th Spring Chemical Industrial Convention, 1987 In this process, the micropores are eventually partially blocked by fine carbon particles, which narrow the pores or alter the pore size distribution, thereby changing the molecular sieving properties. Selecting suitable raw materials, providing the initial microporous structure, and maintaining appropriate operating parameters (binder type, carbonization time and temperature, hydrocarbon type and final cracking concentration, cracking time and temperature, addition of inert gas flow during cooling, etc.) are key factors in obtaining CMS adsorbents suitable for size-selective separation.

[0004] US 4,742,040 discloses several methods for manufacturing carbon molecular sieves with improved capacity and selectivity for separating nitrogen from air. US 5,098,880 describes a two-step method for preparing carbon molecular sieves with faster oxygen kinetics and higher oxygen kinetic selectivity than nitrogen. US 5,164,355 describes a method for preparing high-capacity, high-density carbon molecular sieve adsorbents that can be used as host materials for further modification to produce efficient oxygen-selective carbon molecular sieves. US 5,972,834 discloses a method for manufacturing carbon molecular sieves suitable for separating oxygen and nitrogen from air, primarily involving halogenation and dehalogenation treatments followed by pore conditioning treatment on carbonized charcoal (derived from or derived from coconut shells) using thermally decomposable hydrocarbons (selected from benzene or toluene). US 6,916,358 discloses several carbon molecular sieve adsorbents for separating nitrogen from mixtures containing nitrogen and oxygen.

[0005] Therefore, as mentioned above, methods for producing carbon molecular sieve (CMS) adsorbents and for “tuning” the properties of CMS to exhibit high kinetic selectivity for oxygen in nitrogen or oxygen in argon have been established. Selective micropores are introduced into the adsorbent, where the pore opening controls the kinetics of oxygen, nitrogen, or argon. Therefore, this pore opening or inlet is considered the critical size for diffusion. Such micropores can exhibit very high selectivity, but this is usually achieved at the expense of the overall adsorption rate. Therefore, the adsorption rate in CMS adsorbents is inversely proportional to the kinetic selectivity. This behavior can be explained by the model proposed by Nguyen and Do (…). Nguyen, C.; Do, DD, "Dual Langmuir kinetic model for adsorption in Carbon molecular sieves”, Langmuir, volume 16, pages 1868-1873, 2000 ).

[0006] Recently, there has been considerable interest in intensifying separation processes. In recycling units such as PSA and TSA, reducing cycle time is a primary means of achieving greater production from a given amount of material. However, as cycle time decreases, recycling units typically face challenges such as reduced per-cycle operating capacity of the component of interest, decreased product recovery, and increased pressure drop.

[0007] Recent developments in PSA methods involve the use of complex structured adsorbents, such as relatively fast kinetically selective laminated adsorbent structures, to improve productivity. For example, US 7,645,324 discloses a rotary PSA method that uses laminated adsorbents to dynamically separate gases. US 7,645,324 teaches that using kinetically selective laminated materials can improve productivity; however, to avoid masking the kinetic selectivity through macroporous mass transfer resistance, the macroporous structure within the adsorbent layer should be as open as possible; i.e., the macroporous porosity should be relatively high. However, a problem in this regard is that high pore volumes often impair product recovery. Therefore, it can be expected that this improvement in productivity achievable through the use of such a laminated structure will again come at the cost of reduced product recovery. Furthermore, when commercially available formed CMS adsorbents are milled to produce powder for generating the laminated structure, most of the selective properties introduced by carbon deposition (non-uniform distribution) are lost, leaving behind a lower / non-selective CMS with faster kinetics. Therefore, preparing structured packings in CMS-based laminated forms for PSA methods seems impractical.

[0008] Therefore, it is clear from the existing technology that there is a trade-off between product recovery and process productivity. Steps taken to improve product recovery often harm process productivity, and vice versa.

[0009] Therefore, there is still a need for PSA methods that offer high process productivity while maintaining high product recovery rates. Invention Overview The inventors have discovered that using a “fast” kinetically selective CMS adsorbent to separate O2 from N2 and / or Ar in a fast cyclic pressure swing adsorption (PSA) process can surprisingly improve process productivity while still maintaining high product recovery rates compared to the productivity and recovery rates achievable with “slower” but more selective and higher-capacity CMS adsorbents.

[0010] Several preferred aspects of the method according to the invention are outlined below.

[0011] Aspect 1: A method for rapid cyclic pressure swing adsorption (PSA) for separating O2 from N2 and / or Ar, wherein the method uses multiple adsorption beds comprising carbon molecular sieve (CMS) adsorbents having a linear driving force model at 1 atma and 86 atma. o F measures at least 5% O2 / N2 and / or O2 / Ar kinetic selectivity and at least 0.20% O2 adsorption rate (1 / s), and the method comprises subjecting each of the plurality of beds to a rapid PSA cycle, including a feed step, at least one depressurization step, a purging step and at least one repressurization step, wherein the duration of the feed step is 60 seconds or less.

[0012] Aspect 2: The rapid cycle PSA method of aspect 1, wherein the duration of the feeding step is 3 to 45 seconds.

[0013] Aspect 3: The rapid cycle PSA method of aspect 1, wherein the duration of the feeding step is 6 to 45 seconds.

[0014] Aspect 4: The rapid cycle PSA method of aspect 1, wherein the duration of the feeding step is 6 to 36 seconds.

[0015] Aspect 5: The rapid cyclic PSA method of any one of Aspects 1 to 4, wherein the cycle time of the PSA cycle is 100 seconds or less. Aspect 6: A rapid cyclic PSA method of any one of Aspects 1 to 4, wherein the cycle time of the PSA cycle is 30 to 100 seconds.

[0016] Aspect 7: A rapid cyclic PSA method of any one of Aspects 1 to 4, wherein the cycle time of the PSA cycle is 30 to 70 seconds.

[0017] Aspect 8: A rapid cyclic PSA method of any one of Aspects 1 to 7, wherein the method uses 2 to 4 adsorption beds.

[0018] Aspect 9: A rapid cyclic PSA method of any one of Aspects 1 to 7, wherein the method uses two adsorption beds.

[0019] Aspect 10: Fast cyclic PSA method for any of Aspects 1 to 9, wherein the linear driving force model is used at 1 atma and 86 o F determined that the CMS exhibited O2 / N2 kinetic selectivity of 5 to 30.

[0020] Aspect 11: Fast cyclic PSA method for any of Aspects 1 to 9, wherein the linear driving force model is used at 1 atma and 86 o F determined that the CMS exhibited an O2 / N2 kinetic selectivity of 10 to 25.

[0021] Aspect 12: Fast cyclic PSA method for any of Aspects 1 to 9, wherein the linear driving force model is used at 1 atma and 86 o F determined that the CMS exhibited an O2 / N2 kinetic selectivity of 15 to 20.

[0022] Aspect 13: Fast cyclic PSA method for any of Aspects 1 to 12, wherein a linear driving force model is used at 1 atma and 86 o F determined that the CMS exhibited O2 / Ar kinetic selectivity ranging from 5 to 40. Aspect 14: A rapid cyclic PSA process of any one of Aspects 1 to 13, wherein the adsorbent bed comprises a CMS adsorbent in the form of random packing material.

[0023] Aspect 15: The rapid cycling PSA process of aspect 14, wherein the adsorbent is densely loaded and fixed in place by a permeable compression system.

[0024] Aspect 16: A rapid cycle PSA process according to any one of Aspects 1 to 15, wherein the feeding step is approximately 0 o F to approximately 125 o The process is carried out at a temperature of F.

[0025] Aspect 17: A rapid cycle PSA process according to any one of Aspects 1 to 15, wherein the feeding step is approximately 20 o F to approximately 100 o The process is carried out at a temperature of F.

[0026] Aspect 18: A rapid cycle PSA process according to any one of Aspects 1 to 15, wherein the feeding step is approximately 20 o F to approximately 40 o The process is carried out at a temperature of F.

[0027] Aspect 19: A rapid circulation PSA method of any one of Aspects 1 to 18, wherein the method is a rotating bed rapid circulation PSA method.

[0028] Aspect 20: A rapid cycle PSA method of any one of Aspects 1 to 16, wherein the method is a rotary valve rapid cycle PSA method.

[0029] Aspect 21: Use of carbon molecular sieve (CMS) adsorbents in the separation of O2 from N2 and / or Ar in a fast cyclic pressure swing adsorption (PSA) process, wherein CMS has the capability of separating O2 from N2 and / or Ar via a linear driving force model at 1 atma and 86 atma. o F measures at least 5% O2 / N2 and / or O2 / Ar kinetic selectivity and at least 0.20% O2 adsorption rate (1 / s).

[0030] Aspect 22: Application of Aspect 19, where a linear driving force model is used at 1 atma and 86 o F-measures showed that CMS exhibited O2 / N2 kinetic selectivity ranging from 5 to 30.

[0031] Aspect 23: Application of Aspect 19, where a linear driving force model is used at 1 atma and 86 o F-measures showed that CMS exhibited O2 / N2 kinetic selectivity ranging from 10 to 25.

[0032] Aspect 24: Application of Aspect 19, where a linear driving force model is used at 1 atma and 86 o F-measures showed that CMS exhibited O2 / N2 kinetic selectivity of 15 to 20.

[0033] Aspect 25: Application of Aspect 19, where a linear driving force model is used at 1 atma and 86 o F-measures showed that CMS exhibited O2 / Ar kinetic selectivity ranging from 5 to 40. Brief description of the attached diagram The invention will now be described with reference to the accompanying drawings, wherein the same numerals denote the same elements: Figure 1 The operation of a two-bed multi-step PSA cycle is shown.

[0034] Figure 2a Is it for display use Figure 1 The 2-bed multi-step cycle shown is used for switching from 7.80 atma and 100 o Normalized process performance curves of feed-to-product ratios for fast (414-02) and slow (414-04) CMS adsorbents producing N2 (containing 4500ppm O2) from air at F.

[0035] Figure 2b Is it for display use Figure 1 The graph shown illustrates the normalized process performance as a function of cycle time for the productivity of fast (414-02) and slow (414-04) CMS adsorbents used in a 2-bed multi-step cycle to produce N2 (containing 4500 ppm O2) from air at 7.80 atma and 100°F.

[0036] Figure 3a Is it for display use Figure 1 The data presented in the document is for values ​​from 7.80 atma and 100 atma. o A graph showing the normalized process performance of a 2-bed multi-step cycle of F-type air-generated N2 (containing 4500 ppm O2) as a function of the cycle time of the fast (414-02) and slow (414-04) CMS adsorbents, representing the feed-to-product ratio.

[0037] Figure 3b Is it for display use Figure 1 The 2-bed multi-step cycle shown is used for switching from 7.80 atma and 100 o A graph showing the normalized process performance of the CMS adsorbents for producing N2 (containing 4500 ppm O2) in air at F as a function of cycle time, using the rates of rapid (414-02) and slow (414-04) production.

[0038] Figure 4a Is it for display use Figure 1 The 2-bed multi-step cycle shown is used for from 7.80 atma and 30 o A graph showing the normalized process performance as a function of cycle time for the feed-to-product ratio of fast (414-02) and slow (414-04) CMS adsorbents that produce N2 (containing 4500 ppm O2) in air.

[0039] Figure 4b Is it for display use Figure 1 The 2-bed multi-step cycle shown is used for switching from 7.80 atma and 30 o A graph showing the normalized process performance of the CMS adsorbents for producing N2 (containing 4500 ppm O2) in air at F as a function of cycle time, using the rates of rapid (414-02) and slow (414-04) production. Invention Details The following detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the subsequent detailed description of preferred exemplary embodiments will provide those skilled in the art with a feasible description of how to implement these preferred exemplary embodiments. Various changes may be made to the function and arrangement of the elements without departing from the spirit and scope of the invention as set forth in the appended claims.

[0040] When applied to any feature in the embodiments of the invention described in the specification and claims, the articles “a” and “an” as used herein mean one or more. Unless specifically stated otherwise, the use of “a” and “an” does not limit the meaning of a single feature. The article “the” preceding a singular or plural noun or noun phrase indicates a particular feature or specific characteristic and may have a singular or plural meaning depending on the context in which it is used.

[0041] As used herein, "first," "second," "third," etc., are used to distinguish multiple steps and / or features and do not indicate a total number, or relative position in time and / or space, unless explicitly stated otherwise.

[0042] As used in this article, the term "comprising" means being included by or comprising.

[0043] As used herein, the phrase “and / or” placed between the first entity and the second entity includes any of the following meanings: (1) only the first entity, (2) only the second entity, and (3) both the first entity and the second entity. The term “and / or” placed between the last two entities in a list of three or more entities means at least one entity in the list, including any particular combination of entities in the list. For example, “A, B and / or C” has the same meaning as “A and / or B and / or C” and includes the following combinations of A, B and C: (1) only A, (2) only B, (3) only C, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A and B and C.

[0044] This document discloses a “fast” kinetically selective carbon molecular sieve (CMS) adsorbent for use in a fast cyclic pressure swing adsorption (PSA) method for separating O2 from N2 and / or Ar. This document also discloses a fast cyclic pressure swing adsorption (PSA) method for separating O2 from N2 and / or Ar, utilizing multiple adsorption beds comprising the said fast kinetically selective CMS adsorbent.

[0045] The fast-cycling PSA method described in this paper, using the disclosed fast CMS adsorbent to separate O2 from N2 or Ar, surprisingly provides improved process productivity while maintaining high product recovery. Furthermore, it has been found that the fast-cycling PSA method using the fast CMS adsorbent requires less purge gas.

[0046] As used herein, a “fast” kinetically selective CMS adsorbent (also referred to herein as a “fast” CMS adsorbent) refers to an adsorbent with an O2 / N2 and / or O2 / Ar kinetic selectivity of at least 5 and which is obtained by a linear driving force model at 1 atma and 86 oThe CMS adsorbent has an O2 adsorption rate (1 / s) of at least 0.20 as determined at F. More preferably, the fast CMS adsorbent has an O2 adsorption rate (1 / s) of at least 0.21, at least 0.22, at least 0.23, at least 0.24, at least 0.25, at least 0.26, at least 0.27, at least 0.28, at least 0.29, or at least 0.30, determined by 1 atma and 86 o The linear driving force model of F is determined.

[0047] As used herein, a “slow” kinetically selective CMS adsorbent (also referred to herein as a “slow” CMS adsorbent) refers to an adsorbent with an O2 / N2 and / or O2 / Ar kinetic selectivity of at least 5 and an O2 kinetic selectivity of 1 atm and 86 atm via a linear driving force model. o CMS adsorbents with an O2 adsorption rate (1 / s) of at least 0.20 as measured at F.

[0048] The linear driving force (LDF) model is a well-known model for determining adsorption rates from experimental absorption curves and can be used to calculate the adsorption rate of a particular adsorbent to a particular adsorbent pair, as well as the resulting kinetic selectivity of the adsorbent to the particular adsorbent pair.

[0049] More specifically, the adsorption rate of adsorbates (e.g., O2, N2, or Ar) on the adsorbent was evaluated using a standard volumetric adsorption apparatus. The experiment involved initially applying the adsorbate to a vacuum and at 303 K (86... o The adsorbent sample at F) was exposed to a measured amount of adsorbate at 1 atma (760 Torr / 101 kPa) at the same temperature. Pressure changes were recorded as a function of time. Then, using the same weight of quartz beads instead of the adsorbent sample, the pressure-to-time data were subtracted from a similar pressure history to obtain a graph of the amount of adsorbed gas as a function of time, also known as the absorption curve. The adsorption rate of the adsorbate was then extracted using the LDF model in reverse time (1 / s) of the uptake curve. The kinetic selectivity of the adsorbent for a specific adsorbate pair can be determined individually by the ratio of the calculated adsorption rates of the two adsorbates. The analytical form of this model is given by the following equation (also in the literature Sircar, S. and Hufton, JR, “Why Does the Linear Driving Force Model for Adsorption Kinetics Work”). (Listed in Table 1 of Adsorption 2000, 6, 137-147), where f(t) is the fractional uptake, k is the LDF mass transfer coefficient, α is the correction factor for constant volume experiments, and t is time.

[0050] When this method is used to separate O2 from N2, the fast CMS adsorbent preferably has an O2 / N2 kinetic selectivity of 5 to 30, 10 to 25, or 15 to 20, determined by a linear driving force model at 1 atm and 86 °F. When this method is used to separate O2 from Ar, the fast CMS adsorbent may preferably have an O2 / Ar kinetic selectivity of 5 to 40. The fast CMS adsorbent may have any suitable adsorption capacity. For example, by using a linear driving force model at 1 atm and 86 °F... o The standard isotherm measurement at F indicates that its adsorption capacity at equilibrium can be between 0.2 and 0.4 mmol / g.

[0051] As is well known, the PSA process involves subjecting each adsorption bed used in the process to a PSA cycle, which includes at least a feed step (also known as an adsorption step), at least one depressurization step, a purging step, and at least one repressurization step. In the feed step, a feed stream is introduced and passed through the bed to adsorb one or more readily adsorbable components (O2 in this example) from the feed stream, thereby generating a product stream exiting the bed, which is depleted of the adsorbed components and enriched with the remaining components (N2 and / or Ar in this example). In the depressurization step, the bed is depressurized from the feed pressure during the feed step until a lower purging pressure is reached. The depressurization step typically includes at least one depressurization equalization step (whereby the pressure of the bed is reduced by venting some gas from the bed and sending said gas to another bed undergoing equalization and repressurization, thereby at least partially balancing the pressure between the two beds), and a countercurrent depressurization or “drain” step, which typically occurs after the depressurization equalization step, in which gas enriched with more readily adsorbable components is vented from the bed (typically in a countercurrent direction). In the purging step, purging gas (typically some product gas generated in the adsorption step) is passed through a bed (usually countercurrently) now at the aforementioned purging pressure to remove residual adsorbed components, which in turn causes the component-rich gas stream to exit the bed. Finally, in the repressurization step, the bed is pressurized back to the feed pressure. The repressurization step typically includes at least one repressurization equalization step (whereby the bed pressure is increased by receiving gas from another bed undergoing equalization depressurization), and at least one step of repressurizing the bed with either the feed gas or the product gas (or preferably both), with the feed gas typically introduced in a co-current flow and the product gas introduced countercurrently. It is well known that this cycle can also include other steps occurring between any of the above steps.

[0052] As used herein with respect to the PSA cycle, a “co-current” step refers to a step in which gas flows into and / or out of the bed undergoing the step in the same direction as the gas flow direction during the feed step. Similarly, a “counter-current” step refers to a step in which gas flows into and / or out of the bed in the opposite direction to the gas flow direction during the feed step. Likewise, as used herein, the “inlet” or “inlet” end of the bed refers to the inlet or end of the bed through which the feed gas enters during the feed step, and the “outlet” or “outlet” end of the bed refers to the outlet or end of the bed through which the product gas exits during the feed step.

[0053] As used herein, the term "fast" PSA cycle refers to a PSA cycle in which the total duration of the feeding step of the cycle is 60 seconds or less. Preferably, the total duration of the feeding step of the cycle is at least 3 seconds. More preferably, the total duration of the feeding step is 3 to 45 seconds, or 6 to 45 seconds, or 6 to 36 seconds.

[0054] The rapid PSA cycle preferably also has a cycle time of 100 seconds or less, which is the amount of time taken to complete a complete set of steps in the PSA cycle (i.e., the feeding step, at least one depressurization step, purging step, at least one repressurization step, and any other steps that may exist in the cycle). More preferably, the PSA cycle time is 30 to 100 seconds, or 30 to 70 seconds.

[0055] A rapid cyclic PSA method employs multiple adsorption beds, each containing a rapid CMS adsorbent. Any suitable number of beds can be used, but in some embodiments, the method uses only 2 to 4 adsorption beds, or even just 2 beds. In this regard, it should be noted that, as used herein, the term "adsorption bed" or "bed" refers to one or more adsorbent containers, each simultaneously undergoing each step of the PSA cycle. Thus, a process using 2 beds has a first container or set of containers simultaneously undergoing each step of the PSA cycle (this represents one of the beds), and a second container or set of containers simultaneously undergoing each step of the PSA cycle (this represents another bed), however, the timing of the PSA cycle in the first container or set of containers is staggered from the timing of the PSA cycle in the second container or set of containers, such that each step of the PSA cycle in the first container or set of containers does not begin and end simultaneously with the start and end of the corresponding step of the PSA cycle in the second container or set of containers.

[0056] The adsorption bed can be filled with any suitable form of fast CMS adsorbent, but preferably contains CMS adsorbent in the form of random packing. The adsorbent should preferably be dense and held in place by a permeable compression system, such as a porous plate with a wire mesh facing the CMS to accommodate it and downward pressure applied, for example, by a spring. A dense load prevents additional settling, thus relieving the spring. A dense load can be achieved by methods known in the art, such as a snowfall-type load.

[0057] The feeding step is usually around 0 o F to approximately 125 o The procedure is carried out at a temperature of F, more preferably at about 20°C. o F to approximately 100 o F or approximately 20 o F to approximately 40 o The process is carried out at a temperature of F. As used herein, the temperature of the feed step refers to the temperature at which the feed gas is introduced into the adsorption bed, as measured at the inlet of the adsorption bed. Surprisingly, the inventors have discovered that in the methods described and disclosed herein, at lower temperatures (e.g., about 30°C), the process can be more efficient. o Performing the feed step at F) increases process productivity while maintaining or improving product recovery, unlike known PSA systems. Performing the feed step at such lower temperatures may be particularly advantageous, where the feed gas is already available at temperatures below room temperature (e.g., in the case of a method for separating oxygen and / or nitrogen from a crude argon stream derived from a distillation column), and where significant cooling of the feed gas to the required temperature for the feed step is not necessary.

[0058] Any suitable feed pressure can be used during the feeding step. For example, the pressure during the feeding step, measured at the inlet of the adsorption bed, can be from about 5 to about 12 atmospheres absolute.

[0059] This method for rapid cyclic PSA can be performed using any suitable apparatus. Conventional switching valves can achieve a certain degree of efficiency. However, preferably, the method is a rapid cyclic PSA using a rotating bed PSA apparatus (where the adsorption bed is mounted in a rotor located between and rotating relative to the feed and product stator assemblies, each stator assembly containing a stator plate that acts as a valve plate for switching the bed between cyclic PSA steps), or a rapid cyclic PSA using a rotary valve PSA apparatus (in contrast, the adsorption bed is located in a fixed bed assembly and is switched between PSA steps by rotating the feed and product valves known in the art).

[0060] As an example only, the following will now be referenced. Figure 1 An exemplary dual-bed multi-step PSA cycle suitable for the method of the present invention is described. The cycle timetable is shown in tabular form. Figure 1 In this table grid, each row represents all the distinct cycle steps a given bed undergoes throughout the cycle, while a column of the grid indicates which bed runs which cycle step at a specific unit time step. The total cycle time is the sum of all individual unit time steps for a given row. Note that in the cycle plan, there is a highlighted section, often called a “unit block,” within which all steps are run by a single multi-bed (Mehrotra et al., 2011). The number of repeating unit blocks is the same as the number of beds. Typical cycle planning methods can be found in the literature: “Mehrotra, A.; Ebner, AD; Ritter, JA Simplified Graphical Approach for ComplexPSA Cycle Scheduling, Adsorption ,2011, 17 337-345. Figure 1 The salient features of all the loop designs presented are summarized below.

[0061] Figure 1The PSA cycle shown includes a product and feed repressurization step (F1 / RP1), feed (F2, F3), co-current depressurization (CoD), co-current and dual equilibrium depressurization (EQD1, DEQD2, DEQD3), counter-current depressurization (CnD1, CnD2), product purging (PU1, PU2), product repressurization (RP2, RP3), counter-current and dual equilibrium repressurization (EQR1, DEQR2, DEQR3), and several idle steps (I1, I2, I3). In the product and feed repressurization (F1 / RP1) step, the bed is pressurized to the highest pressure level of the cycle by adding a primary product (e.g., N2-rich) and a feed gas (e.g., air) from the top and bottom of the bed, respectively. During this step of the cycle, no product is removed from the bed. Next, in the feed step (F2 and F3 represent stages of the same feed step), feed gas continues to be introduced until the mass transfer zone of the preferentially adsorbed component (i.e., O2) reaches the outlet end of the bed without substantially disrupting it, and unadsorbed gas (e.g., purified N2) is discharged from the outlet end of the bed as the main product. Then, in the co-current depressurization (CoD) step, the feed flow is stopped and the bed pressure is reduced to a first intermediate level by extracting the product from the top of the bed. Then, in the co-current equalization depressurization (EQD1) step, the bed is connected to the bed that has undergone the counter-current equalization repressurization (EQR1) step, and a portion of the voids and desorbed gas are transferred from the product end of the bed that underwent EQD1 to the product end of the bed that underwent EQR1. Thus, at the end of this step, the pressure is partially equalized between the two beds and the bed pressure in the bed is reduced to the second intermediate level of EQD1. Next, in the double-end equalization depressurization step (DEQD2), more co-adsorbed gas and void gas are extracted from the top and bottom of the bed that has undergone the previous step, reducing the pressure in the bed to the third intermediate level. The gas extracted from the top and bottom of the bed is then sent back to the top and bottom of the bed, respectively, for a double equalization repressurization step (DEQR2). Next, double-end equalization depressurization continues in step (DEQD3 / CnD1), but some of the depressurization step gas extracted in the countercurrent is used as secondary products (i.e., O2-rich gas) instead of being used to repressurize another bed. This step further reduces the bed pressure to the fourth intermediate level. Then, in the countercurrent depressurization step (CnD2), the bed is countercurrently depressurized to the minimum operating pressure and purged at the minimum operating pressure in purging steps (PU1 and PU2) to produce further secondary products. Subsequently, in the countercurrent repressurization steps (RP2 and RP3), the bed is countercurrently repressurized with the primary product gas. Following the repressurization steps (RP2 and RP3), the column is further pressurized through pressure equalization repressurization steps (EQR1, DEQR2 and DEQR3) to bring the bed back to the pressure level for initiation and repetition of the cycle.Note that the three idling steps (I1, I2, and I3) are also incorporated into the cycle time, during which the bed undergoing the idling step is isolated and the valve is turned off. Example

[0062] Choose as Figure 1 The two-bed multi-step pressure swing adsorption (PSA) process cycle shown uses fast (414-02) and slow (414-04) carbon molecular sieve (CMS) adsorbents to separate nitrogen from air. Process performance indicators are evaluated based on feed-to-product ratio and specific productivity. The feed-to-product ratio is inversely related to recovery; therefore, a lower ratio indicates higher recovery, and vice versa. In other words, a lower feed-to-product ratio means lower compressor power requirements. The oxygen and nitrogen rates, kinetic selectivity, and equilibrium capacity on the fast (414-02) and slow (414-04) CMS adsorbents, as well as the characteristics of the adsorption beds, are summarized in Tables 1 and 2. Note that the oxygen absorption rate differs by only 30% between the fast and slow CMS adsorbents, but the selectivity differs by a factor of two.

[0063] For different N2 product purities (containing 4500 ppm and 45,000 ppm O2) and using different feed step temperatures (100... o F and 30 o F), the PSA process performance results, in terms of product ratio and productivity, are summarized in Figures 2 (a and b), 3 (a and b), and 4 (a and b) for both fast (414-02) and slow (414-04) CMS adsorbents. In these figures, the feed-to-product ratio and productivity were normalized by dividing by representative values ​​for 414-04 under the conditions given in Table 3, and these normalized values ​​were plotted as a function of cycle time. For each adsorbent, the PSA process parameters were individually optimized to produce these figures. In Table 3, for 100 o At F, 4500ppm, the cycle time for both 414-02 and 414-04 is 60 seconds. o F, 45,000ppm, cycle time is 50 seconds. For 30 o For comparison, 414-02 ran with a cycle time of 90 seconds, and 414-04 ran with a cycle time of 190 seconds. In all cases, the pressure during the feed step, measured at the adsorption bed inlet, was 7.80 atma.

[0064] As shown in Figures 2 to 4, for all N2 product purities (containing varying amounts of O2) and temperatures, the optimal cycle time for fast CMS (414-02) was equal to or faster than that for slow CMS (414-04). A surprising characteristic of fast CMS (414-02) is that, compared to slow CMS (414-04), it maintained significantly better productivity (100%) at similar recoveries (i.e., similar feed-to-product ratios) for all product purities and temperatures considered here. o F, at 4500ppmO2, is 34.5%, 100 o F, at 45,000 ppm O2, is 23.2%, 30 o (F, 95.4% at 4500 ppm O2), even though the kinetic selectivity and equilibrium capability of fast CMS are much lower than those of slow CMS. This means that using fast carbon molecular sieves in the PSA process can reduce bed size, thereby reducing capital costs.

[0065] Another surprising feature of the fast CMS (414-02) is the ability to achieve higher productivity at cold operating temperatures while still maintaining similar or better recovery rates (i.e., lower feed-to-product ratios). For example, at a bed pressure of 7.80 atma and a product stream of 4500 ppm O2, the normalized feed-to-product ratio and normalized productivity are 30%. o F was 0.979 and 1.954 at the operating temperature and 90-second cycle time, respectively. Even at the same operating pressure and product O2 purity of 100... o At F and a cycle time of 60 seconds, the standardized feed-to-product ratio of 414-02 was only 1.6% higher than that of 414-04, while the standardized productivity of 414-02 was still 34.5% higher than that of 414-04. Slow CMS (414-04) reduced productivity by approximately 26%, from 100 o F to 30 o The recovery rate increased by approximately 12% with increasing feed temperature. In comparison, the productivity of fast CMS (414-02) increased by 6.7%, from 100 o F to 30 o The feed temperature of F recovered by 16%. The comparison results can be found in Table 3 and Figures 2 (a and b) and 4 (a and b).

[0066] Using fast CMS (414-02) to produce medium-purity nitrogen via PSA, the amount of purge gas required for effective bed regeneration is surprisingly low, even though its selectivity is lower than that of 414-04. Even with lower purge gas, the process performance metrics of fast CMS are significantly better than those of slow CMS. Table 3 provides an overview of the purge-to-feed ratio (in terms of ACF ratio) for different product purities (containing different amounts of O2) and temperatures for fast and slow CMS adsorbents. For fast CMS, the purge-to-feed ratio is significantly lower than that of slow CMS adsorbent at 100... o At F, it decreased by about 43%, and at 30 o At F, it decreases by approximately 8%. Note that a portion of the primary products rich in slower-diffusing components (nitrogen during PSA air separation based on CMS) is used in the low-pressure countercurrent bleed-out step (such as... Figure 1 After steps CnD1 and CnD2 (as shown), a countercurrent purging step is performed (e.g., Figure 1 (See steps PU1 and PU2 shown). The purging step is necessary to ensure the bed is clean enough to produce a primary product of a certain purity in the production steps.

[0067] As previously mentioned, the uptake rates of all diffuse components on fast CMS (414-02) are faster than those on slow CMS (414-04). The fast CMS adsorbents considered in these studies are approximately 25% faster than the slow CMS adsorbents, but have 58% lower selectivity (based on kinetic selectivity) than the slow CMS adsorbents (Table 1). However, in rapid cycling, the fast CMS adsorbents not only offer higher specific productivity (which is likely due to their faster uptake rates), but also achieve this goal with no / minimum recovery loss (i.e., similar feed to product ratios) despite their lower selectivity, as shown in Table 3.

[0068] The improvement in specific productivity with no / minimal recovery loss is quite surprising, as it contradicts what was previously known in the art. In a study by Schork et al. (1993), it was noted that productivity increases with increasing uptake, but the maximum available recovery decreases. Table 4 (data from Schork et al.) summarizes the effects of the total rate constants of O2 and N2 on the process performance parameters (recovery and productivity) of the carbon molecular sieve adsorbents from that study, clearly demonstrating that increased productivity is detrimental to product recovery.

[0069] Although the principles of the invention have been described above in conjunction with preferred embodiments, it should be clearly understood that this description is by way of example only and is not intended to limit the scope of the invention.

[0070] Table 1. Summary of the results at 1 atma and 86 oLinear driving force (LDF) model based on O2 rate constant and the effect of O2 on N2 kinetic selectivity for different carbon molecular sieve adsorbents under F.

[0071] Table 2 summarizes the adsorbent and bed characteristics of fast (414-02) and slow (414-04) carbon molecular sieve adsorbents.

[0072] Table 3 summarizes the purging requirements (in terms of purging-to-feed ratio) for fast (414-02) and slow (414-04) CMS adsorbents at different operating temperatures and product O2 purging ... Figure 1 The two-bed multi-step cycle presented in the paper is used for evaluation.

[0073] Table 4 summarizes the effects of the total rate constants of O2 and N2 on the process performance parameters (recovery and productivity) of the carbon molecular sieve adsorbents. The rate constants are multiplied by a single factor, therefore the kinetic selectivity is the same as the baseline case in all cases. Results are taken from "Schork, JM; Srinivasan, R.; Auvil, SR Shortcut Computational Method for Designing Na PSA Adsorbents, Ind. Eng. Chem. Res., 1993, 32, 2226-2235”.

Claims

1. A method for rapid cyclic pressure swing adsorption (PSA) for separating O2 relative to N2 and / or Ar, wherein the method uses multiple adsorption beds comprising carbon molecular sieve (CMS) adsorbent, which have a linear driving force model at 1 atma and 86 o The method comprises determining at least 5 O2 / N2 and / or O2 / Ar kinetic selectivity and at least 0.20 O2 adsorption rate (1 / s) under F, and wherein the method comprises subjecting each of the plurality of beds to a rapid PSA cycle, which includes a feed step, at least one depressurization step, a purging step and at least one repressurization step, wherein the duration of the feed step is 60 seconds or less. in, The adsorption rate of the adsorbent for O2, N2, or Ar is determined by the following steps: Make the initial state in vacuum and 86 o The adsorbent sample at F was exposed to a measured amount of adsorbate O2, N2 or Ar at the same temperature and 1 atm. The pressure changes are recorded as a function of time; Subtract the pressure versus time data from a similar pressure history of a sample using quartz beads instead of adsorbent to obtain an absorption curve as a function of time for the amount of adsorbed gas; and A linear driving force model was used to extract the adsorption rate of the adsorbate in reverse time (1 / s) from the absorption curve; and The O2 / N2 or O2 / Ar kinetic selectivity of the adsorbent is determined individually by the ratio of the calculated adsorption rates of the two adsorbents. The adsorbent is densely loaded and secured in place using a permeable compression system.

2. The rapid cycle PSA method of claim 1, wherein the duration of the feeding step is 3 to 45 seconds.

3. The rapid cycle PSA method of claim 1, wherein the duration of the feeding step is 6 to 45 seconds.

4. The rapid cycle PSA method of claim 1, wherein the duration of the feeding step is 6 to 36 seconds.

5. The fast cyclic PSA method of claim 1, wherein the cycle time of the PSA cycle is 100 seconds or less.

6. The fast cyclic PSA method of claim 1, wherein the cycle time of the PSA cycle is 30 to 100 seconds.

7. The fast cyclic PSA method of claim 1, wherein the cycle time of the PSA cycle is 30 to 70 seconds.

8. The rapid cyclic PSA method of claim 1, wherein the method uses 2 to 4 adsorption beds.

9. The rapid cyclic PSA method of claim 1, wherein the method uses two adsorption beds.

10. The fast cyclic PSA method of claim 1, wherein a linear driving force model is used at 1 atma and 86 o The CMS was determined to have an O2 / N2 kinetic selectivity of 5 to 30 under F conditions.

11. The fast cyclic PSA method of claim 1, wherein a linear driving force model is used at 1 atma and 86 o The CMS was determined to have an O2 / N2 kinetic selectivity of 10 to 25 under F conditions.

12. The fast cyclic PSA method of claim 1, wherein a linear driving force model is used at 1 atma and 86 o The CMS was determined to have an O2 / N2 kinetic selectivity of 15 to 20 under F conditions.

13. The fast cyclic PSA method of claim 1, wherein a linear driving force model is used at 1 atma and 86 o The CMS was determined to have an O2 / Ar kinetic selectivity of 5 to 40 under F conditions.

14. The rapid cyclic PSA method of claim 1, wherein the adsorbent bed comprises a CMS adsorbent in the form of random packing material.

15. The rapid cycle PSA method of claim 1, wherein the feeding step is performed in about 0... o F to approximately 125 o The process is carried out at a temperature of F.

16. The rapid cycle PSA method of claim 1, wherein the feeding step is performed in about 20... o F to approximately 100 o The process is carried out at a temperature of F.

17. The rapid cycle PSA method of claim 1, wherein the feeding step is performed in about 20 minutes. o F to approximately 40 o The process is carried out at a temperature of F.

18. The rapid cyclic PSA method of claim 1, wherein the method is a rotating bed rapid cyclic PSA method.

19. The rapid cycle PSA method of claim 1, wherein the method is a rotary valve rapid cycle PSA method.

20. Use of carbon molecular sieve (CMS) adsorbents for the separation of O2 relative to N2 and / or Ar in rapid cyclic pressure swing adsorption (PSA), wherein a linear driving force model is used at 1 atma and 86 o The CMS was determined to have an O2 / N2 and / or O2 / Ar kinetic selectivity of at least 5 and an O2 adsorption rate of at least 0.20 (1 / s) under F conditions. in, The adsorption rate of the adsorbent for O2, N2, or Ar is determined by the following steps: Make the initial state in vacuum and 86 o The adsorbent sample at F was exposed to a measured amount of adsorbate O2, N2 or Ar at the same temperature and 1 atm. The pressure changes are recorded as a function of time; Subtract the pressure versus time data from a similar pressure history of a sample using quartz beads instead of adsorbent to obtain an absorption curve as a function of time for the amount of adsorbed gas; and A linear driving force model was used to extract the adsorption rate of the adsorbate in reverse time (1 / s) from the absorption curve; and The O2 / N2 or O2 / Ar kinetic selectivity of the adsorbent is determined individually by the ratio of the calculated adsorption rates of the two adsorbents. The adsorbent is densely loaded and secured in place using a permeable compression system.

21. The use as described in claim 20, wherein the linear driving force model is used at 1 atma and 86 o CMS was determined to have O2 / N2 kinetic selectivity of 5 to 30 under F conditions.

22. The use as described in claim 20, wherein the linear driving force model is used at 1 atma and 86 o CMS was determined to have O2 / N2 kinetic selectivity of 10 to 25 under F conditions.

23. The use as described in claim 20, wherein the linear driving force model is used at 1 atma and 86 o CMS was determined to have an O2 / N2 kinetic selectivity of 15 to 20 under F conditions.

24. The use as described in claim 20, wherein the linear driving force model is used at 1 atma and 86 o CMS was determined to have O2 / Ar kinetic selectivity of 5 to 40 under F conditions.

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