Patent Application
20230149908
This disclosure relates generally to catalyst compositions, for example, containing cobalt. The disclosure also relates to methods of preparing and using such catalyst compositions for dehydrogenating light alkane gas (and/or light alkene gas).
Light alkenes, such as propene and ethene, are essential feedstocks for preparing a vast array of chemicals, such as polymers (e.g., polyethylene), oxygenates (e.g., ethylene glycol, acetaldehyde, and acetone) and chemical intermediates (e.g., ethylbenzene and propionaldehyde). In 2016, the global alkene market was valued at $250 billion and is expected to increase at an annual rate of about 6% over the next five years. These valuable intermediates are predominantly produced by steam-cracking or fluid catalytic cracking of crude oils and its by-products. However, growing demand for various petrochemicals coupled with decreasing petroleum reserves have shifted focus toward producing alkenes via alternate, but efficient and economical, methods.
On-purpose dehydrogenation of alkanes (e.g., propane and isobutane) has gained attention as an alternate route of producing alkenes. Such dehydrogenation methods are often based on natural/shale gas feedstocks. These feedstocks contain significantly fewer impurities and a higher hydrogen to carbon (H/C) ratio than reactants derived from crude oil, which also makes these methods more environmentally friendly. Alkane dehydrogenation technology is expected to produce more than 2×108 ton year−1 of light alkenes globally by the end of 2020.
Conventionally, alkane dehydrogenation has been practiced using supported platinum (Pt)-based and chromium-based (e.g., CrOx) catalysts. Two industrial processes for the production of light alkene using dehydrogenation are 1) the chromia-alumina-based Catofin® process; and 2) the Pt—Sn-based Oleflex™ process. However, the use of chromium (Cr) and platinum (Pt) based catalysts presents costs, environmental and health issues.
For example, platinum-based catalysts used for alkane dehydrogenation can include Pt deposited alone, or in combination with another material such as tin (Sn), on an inactive support. However, platinum-based catalysts are costly, sensitive to impurities, subject to deactivation and regenerable via a challenging regeneration process. The re-dispersion of Pt in spent catalysts often requires the addition of chlorine-based compounds during the catalyst regeneration process, which is ecologically harmful. Chromium-based catalysts containing hexavalent chromium (Cr(VI)) are toxic and present health issues. For example, according to the Occupational Safety and Health Administration (OSHA), human exposure to chromium (VI) may cause serious health issues such as lung cancer.
There is a need for methods and catalyst compositions that inhibit deactivation of the catalyst composition and at same time maintain a considerable dehydrogenation activity. There is a further need for catalyst compositions that are free of Cr and precious metals, such as Pt, and that increase the safety and sustainability of the dehydrogenation process. The use of such catalyst compositions in the dehydrogenation of light alkanes (and/or alkenes) could improve the total yield of dehydrogenation products within one cycle and require less frequent catalyst regenerations.
The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that different references to an or one embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.
According to embodiments, disclosed herein is a catalyst composition, comprising: a support comprising cobalt (II) (Co2+) cations, wherein the catalyst composition is free of at least one of chromium and a precious metal.
In further embodiments, disclosed herein is a method of preparing a catalyst composition, comprising: loading cobalt (II) (Co2+) cations onto a support, wherein the catalyst composition is free of at least one of chromium and a precious metal.
In yet further embodiments, disclosed herein is a method for dehydrogenating at least one of a light alkane gas and a light alkene gas, comprising: contacting the at least one light alkane gas and light alkene gas with a catalyst composition comprising a support comprising cobalt (II) cations (Co2+).
Further disclosed herein is a kit comprising: a catalyst composition according to embodiments herein; and instructions for using the catalyst composition according to embodiments herein.
Described herein are methods of using catalyst compositions for dehydrogenating light alkane gases (and/or light alkene gases). Also disclosed are catalyst compositions for such dehydrogenation reactions and methods of preparation thereof. It is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in a variety of ways.
Reference throughout this specification to one embodiment, certain embodiments, one or more embodiments or an embodiment means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as in one or more embodiments, in certain embodiments, in one embodiment or in an embodiment in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.
As used herein, the singular forms a, an, and the include plural references unless the context clearly indicates otherwise. Thus, for example, reference to a catalyst material includes a single catalyst material as well as a mixture of two or more different catalyst materials.
As used herein, the term about in connection with a measured quantity, refers to the normal variations in that measured quantity as expected by one of ordinary skill in the art in making the measurement and exercising a level of care commensurate with the objective of measurement and the precision of the measuring equipment. In certain embodiments, the term about includes the recited number ±10%, such that about 10 would include from 9 to 11.
The term at least about in connection with a measured quantity refers to the normal variations in the measured quantity, as expected by one of ordinary skill in the art in making the measurement and exercising a level of care commensurate with the objective of measurement and precisions of the measuring equipment and any quantities higher than that. In certain embodiments, the term at least about includes the recited number minus 10% and any quantity that is higher such that at least about 10 would include 9 and anything greater than 9. This term can also be expressed as about 10 or more. Similarly, the term less than about typically includes the recited number plus 10% and any quantity that is lower such that less than about 10 would include 11 and anything less than 11. This term can also be expressed as about 10 or less.
Unless otherwise indicated, all parts and percentages are by weight except that all parts and percentages of gas are by volume. Weight percent (wt %), if not otherwise indicated, is based on an entire composition free of any volatiles, that is, based on dry solids content. Volume percent (vol %), if not otherwise indicated, is based on the total volume of the gas.
Although the disclosure herein is with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the compositions and methods without departing from the spirit and scope of the invention. Thus, it is intended that the invention include modifications and variations that are within the scope of the appended claims and their equivalents.
Propane dehydrogenation (PDH) reactions can be conducted in the presence of Co-based catalysts on a support (e.g., SiO2 and Al2O3 supports). The term “support” as used herein refers to a solid phase structure on which or into which a material is deposited or impregnated, respectively. Single-site Co2+ materials on silica supports (Co2+/SiO2) have been formed using chloride (Cl) and an ammonia (NH3)-based Co3+ precursor (Co(NH3)6Cl3). Such materials have an initial PDH rate (per mass) of 12.8 mol·kgcat−1·h−1 at 923 K, which upon deactivation over 20 h, decreases to a rate of 6.6 mol·kgcat−1·h−1. Mesoporous Co—Al spinel catalysts have been formed by an intricate and complex procedure involving pluronic-123 (P123) as a soft template, and also may experience deactivation of the initial PDH rate (per mass) of 5.2 mol·kgcat−1·h−1 to a PDH rate (per mass) of 1.1 mol·kgcat−1·h−1 at 873 K after 5 h. Frequent regenerations under several oxidative conditions may destroy the well-defined mesoporous structure resulting from the templating surfactant. Prior Co-based catalysts for PDH reactions, have not improved the robustness and stability of the catalyst compositions and the catalysts have experienced rapid deactivation, for example, resulting in a half-life of 21 h for Co2+/SiO2 and 2.5 h for Co—Al spinels, or from an initial PDH rate of 4 mol·kgcat−1·h−1 to 1.6 mol·kgcat−1·h−1 at 823 K after 10 h with a half-life of 7.5 h for a Co-catalyst supported on SiO2.
According to embodiments, disclosed herein are catalyst compositions comprising Co2+ cations. The cations may be dispersed on a support. In embodiments, the catalyst compositions may be prepared via a low-cost, one-step synthesis procedure using earth-abundant non-toxic and non-corrosive reagents. The method prepares catalyst compositions having highly dispersed cobalt (II) (Co2+) cations, for example, in the form of cobalt (II) oxide, on a support. The resulting catalyst compositions are stable against further reduction under the high temperature and highly reducing conditions of an alkane dehydrogenation catalysis. The catalyst compositions are also efficient in the conversion of light alkanes to corresponding alkenes (or alkenes to butadienes). The catalyst compositions and structures can be designed for specific applications and alkane (or alkene) feedstocks.
In embodiments, the catalyst compositions convert light alkanes (e.g., propane) to alkenes (e.g., propene), or light alkenes to butadienes, with high selectivity and efficient reaction rates. According to embodiments, the dehydrogenation reaction is in the absence of oxygen.
In embodiments, the one-step synthesis may be a one-step grafting method that allows systematic variations of the surface density of active cobalt (Co) sites on a wide range of support materials that enable structure-activity relationships. This simple grafting method is well suited for scale-up and uses earth-abundant material. The grafting method allows systematic variations in the surface density of active sites on different supports as a tool to understand the nature and reactivity of the active sites and to develop an efficient and robust catalyst for dehydrogenation reactions. For example, a catalyst composition formed by the grafting method can have cobalt (II) (Co2+) cations on a silicon dioxide (SiO2) support. In embodiments, the resulting catalyst composition has a cobalt surface density of 0.4 atoms nm−2 on SiO2 and provides a highly-stable propane dehydrogenation rate of 10 mol·Kgcat−1·h−1 (after 20 hours of slow-activation) with a selectivity (rd/rh=rate ratio of dehydrogenation products over hydrogenolysis products) of 10. In embodiments, the catalyst composition is re-usable up-to at least 10 cycles at 873 K demonstrating high-efficiency. The catalyst composition can be used in multiple catalytic cycles and regeneration steps without any noticeable loss in its alkane (or alkene) dehydrogenation rate demonstrating excellent robustness.
According to various embodiments, the Co2+ cations provide the active sites of the catalyst compositions. Optimally, the surface density of isolated Co2+ cations is high on the catalyst surface to increase the dehydrogenation rate (per mass). During the Co2+ grafting procedure, when no vicinal hydroxyl groups are present on the support, CoOx crystallites start to form. The formation of such crystallites inhibits the dehydrogenation rate of the catalyst composition with increasing loading of Co2+ on the support because the Co-species that do not belong to the surface, do not contribute to the dehydrogenation rate. Controlling the surface density of isolated Co2+ species helps optimize performance of the catalyst composition.
Without being bound by any particular theory, it is believed that the presence of cobalt (III) (Co−3) cations leads to the formation of Co0 during dehydrogenation reaction conditions (e.g., both H2 and light alkanes are reducing agents). Additionally, the formation of deactivating carbonaceous deposits during the dehydrogenation reaction causes deactivation of the catalyst.
According to embodiments, disclosed herein are methods of preparing a catalyst composition where such methods increase and optimize the isolated Co2+ surface density with increasing Co loading on a support, while minimizing vicinal hydroxyl groups (required for Co grafting) on the support. Increasing the surface density of isolated Co2+ on the support, results in an increase in dehydrogenation rate per mass of the catalyst composition. High selectivity and catalyst stability predominantly depend on the minimization of Co3+ in the catalyst composition, which can be achieved by forming isolated Co2+ on support. Controlling the grafting of isolated Co2+ on supports together with minimizing the formation of Co3+, minimizes the formation of both Co0 and deactivating carbonaceous deposits during a dehydrogenation reaction. The resulting catalyst compositions can have undetected deactivation for at least 40 ks (for Co/SiO2 catalyst with 0.2-0.4 Co nm−2) under dehydrogenation reaction conditions.
Catalyst compositions as described herein are useful in dehydrogenation reactions, for example, to dehydrogenate light alkane gases to form alkenes. In embodiments, the catalyst compositions can also be used to dehydrogenate light alkene gases to form alkadienes. According to embodiments, the catalyst compositions can comprise cobalt (II) (Co2+) cations, for example, in the form of cobalt (II) oxide. The Co2+ cations are the active catalyst material in the dehydrogenation reactions according to various embodiments disclosed herein.
The catalyst compositions may also be free of at least one of chromium and a precious metal. Non-limiting examples of precious metals include platinum (Pt), gold (Au), silver (Ag), copper (Cu), palladium (Pd) and combinations thereof In embodiments, the catalyst composition is free of both chromium and platinum. Catalyst compositions as described herein may present fewer risks to human health and the environment than other known catalysts, e.g., chromium- and platinum-based catalysts, used for dehydrogenation.
In embodiments, the catalyst composition can include at least about 0.1 wt % cobalt, at least about 0.5 wt % cobalt, at least about 1.0 wt % cobalt, at least about 2.0 wt % cobalt, at least about 5.0 wt % cobalt, at least about 7.5 wt % cobalt, at least about 10 wt % cobalt, at least about 15 wt % cobalt, or at least about 20 wt % cobalt. In embodiments, the catalyst composition can include about 0.1 wt % to about 20 wt % cobalt, or about 0.25 wt % to about 16 wt % cobalt, or about 0.5 wt % to about 12 wt % cobalt, or about 1.0 wt % to about 10 wt % cobalt, or about 2.0 wt % to about 8.0 wt % cobalt, or about 2.0 wt % cobalt, or about 5.0 wt % cobalt, or about 7.5 wt % cobalt, or about 10 wt % cobalt, or about 15 wt % cobalt, or about 20 wt % cobalt. The amount of cobalt can be determined by calculating how much of CoO will form on a support after degrading from a given number of impregnated Co(II) acetate. The weight (after mass loss) of the supports can be similarly determined when heat treated under conditions of catalyst preparation. The following equation can be used to determine the % wt. of cobalt in each catalyst: (Wt. of CoO in g)/(Wt. of CoO+support in g)).
Catalyst compositions according to embodiments herein contain a plurality of active sites. In embodiments, the active sites are formed by Co2+ cations on the surface of a support. The support may be a nominally inert support. The term nominally inert support means that the support provides little or no measurable catalytic activity. In embodiments, the catalytic activity of the support (e.g., in mol/s) is less than about 5% of the catalytic activity of the Co2+ cations (e.g., in mol/s). In embodiments, the catalytic activity of the support (e.g., in mol/s) is less than about 4% of the catalytic activity of the Co2+ cations (e.g., in mol/s). In further embodiments, the catalytic activity of the support (e.g., in mol/s) is less than about 3% of the catalytic activity of the Co2+ cations (e.g., in mol/s). In yet further embodiments, the catalytic activity of the support (e.g., in mol/s) is less than about 2.5%, or less than about 1%, or less than about 0.5% of the catalytic activity of the Co2+ cations (e.g., in mol/s). In further embodiments, the catalytic activity of the support (e.g., in mol/s) is less than 0.1% of the catalytic activity of the support (e.g., in mol/s). In embodiments, the support has no measurable catalytic activity. The catalytic activity of the support and of the catalyst composition, for example, as measured in mol/s, is dependent on the type of material (e.g., homogenous, heterogeneous, etc.) as would be understood by those of ordinary skill in the art. According to embodiments, the support comprises a surface density of about 0.1 Co atoms/nm2 to about 20 Co atoms/nm2. In embodiments, the support comprises a surface density of about 0.25 Co atoms/nm2 to about 18 Co atoms/nm2. In further embodiments, the support comprises a surface density of about 0.5 Co atoms/nm2 to about 15 Co atoms/nm2. In yet further embodiments, the support comprises a surface density of about 1.0 Co atoms/nm2 to about 10 Co atoms/nm2, or about 2.0 Co atoms/nm2 to about 8.0 Co atoms/nm2. The Co surface density=(% wt. of CoO×6.023×1023)/(Surface area×74.9×1018). When he % wt. of CoO is known, the surface area is measured by N2 physisorption uptakes (e.g., Praxair, 99.999%)) at its normal boiling point in a Quantasorb unit (Quantasorb 6 Surface Analyzers, Quantachrome Corp.) after degassing the samples for 2 h at 423 K.
According one or more embodiments, the support can be a high surface area powder (e.g., gamma, delta or theta alumina powder) comprised of particles, granules and/or spheres (e.g., alumina microspheres or nanospheres in amorphous or colloidal form), which may be referred to herein as supports. In embodiments, the support comprises at least one of silicon dioxide (SiO2), aluminum oxide (Al2O3), fumed Al2O3, aluminum oxyhydroxide (AlOx(OH)3-2x) and silicon oxyhydroxide (SiOx(OH)2-x). In embodiments, the support comprises at least one of gamma-Al2O3, delta-Al2O3 and theta-Al2O3.
In embodiments, alumina supports can be activated or transition aluminas. These activated aluminas can be identified by their ordered structures observable by their X-ray diffraction patterns (e.g., measured using a Siemens D5000 unit at ambient temperature with Cu Kα radiation and a scan rate of 0.033° s−1 to determine the crystalline structure of the catalyst composition), which indicate a mixed phase material containing minimal to no low surface area or crystalline phase alpha alumina. Alpha alumina is identified by a defined crystalline phase by x-ray diffraction. The higher surface area activated aluminas are often defined as a gamma alumina phase, but the phase transitions can be a continuum of varying percentages of multiple mixed phases such as, but not limited to, delta and theta phases based on the chosen calcination temperature to achieve the desired support surface area.
According to embodiments, the catalyst compositions are comprised of Co2+ oxides dispersed onto SiO2 and/or Al2O3 support materials. As will be discussed in more detail below, an aqueous solution of a Co2+ precursor (e.g., cobalt acetate; Co(OAc)2) may be used to graft Co2+ cations onto the SiO2 and/or γ-Al2O3 supports. To maximize performance and achieve the intrinsic activity of the surface Co2+ sites, it is important to minimize and/or eliminate surface contamination.
In further embodiments, the catalyst compositions comprising Co2+ cations can be dispersed on oxy-hydroxide supports. Without being bound by any particular theory, it is believed that the higher surface density of hydroxyl groups (e.g., as compared to corresponding oxide supports) can increase the surface density of isolated Co2+ sites with increasing Co loading.
The Brunauer, Emmett and Teller (BET) surface area of the catalyst composition can be measured using nitrogen (N2) physisorption uptake at its normal boiling point in a surface analyzer (e.g., a Quantasorb® 6 Surface Analyzer by Quantachrome® Corp.). The BET surface area can be measured as set forth in Otroshchenko, et al., Zro2-Based Unconventional Catalysts for Non-Oxidative Propane Dehydrogenation: Factors Determining Catalytic Activity, J. of Catalysis, 348, 282-290 (2017), which is incorporated herein by reference in its entirety. Another suitable method of measuring the BET surface area is set forth in ASTM D3663-03(2008), which is incorporated by reference herein in its entirety. Catalyst compositions comprising Co2+ as described herein can have a BET surface area of about 1 m2 g−1 to about 100 m2 g−1, or about 10 m2 g−1 to about 90 m2 g−1, or about 20 m2 g−1 to about 80 m2 g−1, 30 m2 g−1 to about 70 m2 g−1, 40 m2 g−1 to about 60 m2 g−1, or about 40 m2 g−1, or about 45 m2 g−1, or about 50 m2 g−1, or about 75 m2 g−1 to about 355 m2 g−1, or about 1 m2 g−1 to about 400 m2 g−1 as measured by a surface analyzer as described above.
According to various embodiments, the catalyst composition comprising Co2+ can further include a rare earth metal. In embodiments, the rare earth metal can include at least one lanthanide metal, an oxide thereof and combinations thereof. According to embodiments, the rare earth metal can be at least one of yttrium (Y), erbium (Er), cerium (Ce), dysprosium (Dy), gadolinium (Gd), lanthanum (La), neodymium (Nd), samarium (Sm), ytterbium (Yb), oxides thereof and mixtures thereof. In embodiments, the catalyst composition can include about 0.5 wt % to about 50 wt %, or about 1 wt % to about 40 wt %, or about 2 wt % to about 30 wt %, or about 3 wt % to about 25 wt %, or about 4 wt % to about 20 wt %, or about 5 wt % to about 15 wt %, or about 1 wt % to about 12 wt %, or about 2 wt % to about 10 wt % of the rare earth metal, an oxide thereof or mixtures thereof. In certain embodiments, the catalyst composition can include yttrium, for example, in the form of yttrium oxide. In embodiments, the rare earth metal increases the surface area of catalyst composition. Such catalyst compositions can comprise about 0.1 wt % to about 20.0 wt % cobalt and about 0.05 wt % to about 15 wt % Y2O3 and/or an atomic ratio of the rare earth element to cobalt of greater than 0 to about 0.2. The catalyst composition comprising the Co2+ together with the rare earth metal can have a BET surface area of about 40 m2 g−1 to about 110 m2 g−1.
According to various embodiments, the catalyst composition comprising Co2+ can be treated with a pretreatment gas. Pretreating the catalyst composition can increase the number of active sites on the catalyst, which can result in higher catalytic activity during the dehydrogenation reaction (e.g., at the beginning of the reaction). In embodiments, a pretreated catalyst composition containing Co2+ comprises more active sites than a catalyst composition containing Co2+ that has not been pretreated.
In embodiments, the pretreated catalyst composition can be formed by contacting the catalyst composition with a pretreatment gas under certain conditions. The pretreatment gas can include a reducing agent comprising at least one of H2, carbon monoxide (CO), ammonia and methane (CH4). In embodiments, the pretreatment gas can further include an inert gas comprising at least one of nitrogen (N2), helium (He) and Argon (Ar). In embodiments, the pretreatment gas can comprise the reducing agent at a concentration of about 1 mol % to about 10 mol %, or about 2 mol %, or about 4 mol %, or about 6 mol %, or about 8 mol %, or about 10 mol %. In certain embodiments, the pretreatment gas is H2 and can include about 1 mol % to about 10 mol % H2, or about 2 mol % H2, or about 4 mol % H2, or about 6 mol % H2, or about 8 mol % H2, or about 10 mol % H2.
During the pretreatment, the pretreatment gas and/or the catalyst composition can be at a temperature of at least about 500 K, or at least about 600 K, or at least about 700 K, or at least about 850 K, or at least about 860 K, or at least about 870 K, or at least about 873 K, or at least about 880 K, or at about 870 K, or at about 871 K, or at about 872 K, or at about 873 K, or at about 874 K, or at about 875 K. The pretreatment gas can be in contact with the catalyst composition for about 0.1 h to about 24 h, or about 0.5 h to about 24 h, or about 1.0 h to about 24 h, or about 2 h to about 22 h, or about 3 h to about 20 h, or about 5 h to about 15 h, or about 8 h to about 12 h, or about 0.1 h, or about 0.5 h, or about 1 h, or about 2 h, or about 3 h, or about 4, hour or about 5 h.
According to various embodiments, catalyst compositions as disclosed herein can be in the form of a plurality of units. The plurality of units can include, but are not limited to, particles, powder, extrudates, tablets, pellets, agglomerates, granules and combinations thereof. The plurality of units can have any suitable shape known to those of ordinary skill in the art. Non-limiting examples of shapes include round, spherical, spheres, ellipsoidal, ellipses cylinders, hollow cylinders, four-hole cylinders, wagon wheels, regular granules, irregular granules, multilobes, trilobes, quadrilobes, rings, monoliths and combinations thereof. In embodiments, the shape of the plurality of units may contributed to the performance of the catalyst composition, for example, by increasing the surface area providing the catalytic activity.
The plurality of units can be formed by any suitable method known to those of ordinary skill in the art. Non-limiting examples of methods for shaping and forming a plurality of units (e.g., from a mixture of catalyst materials) include, extrusion, spray drying, pelletization, agglomeration, oil drop, and combinations thereof In one embodiment, the plurality of units can be formed by pressing a powder into wafers (e.g., at about 690 bar, for about 0.05 h), crushing the wafers and then sieving the resulting aggregates to retain a mean aggregate size of about 100 μm to about 250 or about 1.5 mm to about 5 mm, or about 80 mesh to about 140 mesh.
In certain embodiments, the plurality of units can have a size of less than about 1,000 μm, or less than about 750 μm, or less than about 500 μm, or less than about 300 μm, or less than about 250 μm, or less than about 225 μm, or less than about 200 μm, or less than about 190 μm, or less than about 180 μm, or less than about 150 μm, or less than about 100 μm, or less than about 10 μm as measured by any suitable method known to those of ordinary skill in the art. In embodiments, the plurality of units can have a size of about 170 μm to about 250 μm, or about 80 mesh to about 140 mesh. In further embodiments, the plurality of units have a mean size of about 1.5 mm to about 15.0 mm, or about 1.5 mm to about 12 mm, or about 1.5 mm to about 10 mm, or about 1.5 mm to about 8.0 mm, or about 1.5 mm to about 5.0 mm. Particle size can be measured using any suitable method known to those of ordinary skill in the art. For example, particle size can be measured using ASTM D4438-85(2007) and ASTM D4464-10, both of which are incorporated herein by reference in their entirety.
According to embodiments, catalyst compositions as described herein may be comprised in a kit. The kit can include the catalyst composition as described above and instructions for pretreating the catalyst composition. The instructions can comprise the following elements: 1) place the catalyst composition in a chamber and/or reactor; 2) heat the pretreatment gas, the chamber, the reactor and/or the catalyst composition to a temperature of at least about 850 K, or at least about 860 K, or at least about 870 K, or at least about 873 K, or at least about 880 K, or at about 870 K, or at about 871 K, or at about 872 K, or at about 873 K, or at about 874 K, or at about 875 K; 3) introduce the pretreatment gas into the chamber and/or reactor and contact the catalyst composition with the pretreatment gas for about 0.1 h to about 24 h, or about 0.5 h to about 22 h, or about 1.0 h to about 20 h, or about 2.5 h to about 15 h, or about 5 h to about 12 h, or about 0.1 h, or about 0.2 h, or about 0.5 h, about 1 h, or about 2 h, or about 3 h, or about 4, hour or about 5 h.
According to embodiments, the kit may include the catalyst composition together with instructions for using the catalyst composition in a light alkane (or light alkene) dehydrogenation process. The catalyst composition can be pretreated or may not be pretreated in accordance with embodiments herein. If not pretreated, the kit can further include instructions for pretreating the catalyst composition as described above. The instructions for using the catalyst composition can comprise the following elements: 1) place the catalyst composition in a reactor; 2) introduce the light alkane gas (and/or light alkene gas) together with H2 into the reactor; and 3) contact the light alkane gas (and/or light alkene gas) and the H2 with the catalyst composition. Optionally, the instructions may further include 4) recover the dehydrogenated (i.e., alkene or alkadiene) gas.
The kits discussed above can include suitable details and instructions for using the catalyst composition safely and productively. Non-limiting examples of such details and instructions can include how to load the catalyst composition into the reactor, how to pre-treat the catalyst composition, if necessary, before starting the reaction, the starting temperatures and gas composition for bringing the catalyst composition on-stream, the regeneration procedures, how to unload the catalyst composition from the reactor and combinations thereof.
According to various embodiments, disclosed herein are methods of preparing catalyst compositions as described above. A catalyst composition comprising Co2+ can be prepared by loading cobalt (II) (Co2+) cations onto a support. In embodiments, loading the Co2+ onto the support can be by at least one of grafting, doping, co-precipitating and impregnating the Co2+ cations onto (or within) the support. In embodiments, the loading includes contacting the support with an aqueous solution of at least one of a cobalt (II) carboxylate, a cobalt (II) glycolate and a cobalt (II) citrate. In embodiments, the cobalt (II) carboxylate comprises cobalt (II) acetate tetrahydrate. In embodiments, the aqueous solution is free of a nitrate, CoSO4 and CoCl2. Without being bound by any particular theory, it is believed that using a nitrate solution may lead to the formation of Co3O4 (of 33.7 nm diameter), possibly because of poor grafting of Co2+ on supports, which may result in faster catalytic deactivation (with a deactivation constant (kd) of 2.5 h-1) during a dehydrogenation reaction. It is further believed that CoSO4 and CoCl2 may poison the Co-based sites by their respective anions.
The aqueous solution can be at a concentration of about 10 wt % up to the solubility of the at least one of cobalt (II) carboxylate, cobalt (II) glycolate and cobalt (II) citrate in the solution. In embodiments, the aqueous solution is at a concentration of about 10 wt % to about 100 wt %, about 15 wt % to about 90 wt %, about 20 wt % to about 80 wt %, about 25 wt % to about 75 wt %, about 30 wt % to about 60 wt %, or about 40 wt % to about 50 wt % of the at least one of cobalt (II) carboxylate, cobalt (II) glycolate and cobalt (II) citrate by weight of the solution.
In embodiments, the aqueous solution can be at a temperature of about 100 K to about 500 K, or about 150 K to about 450 K, or about 100 K to about 400 K, or about 288 K to about 353 K. The contacting can occur for about 1 h to about 36 h, or about 5 h to about 32 h, or about 10 h to about 24 h, or about 12 h to about 20 h, or about 18 h, or about 19 h, or about 20 h, or about 21 h, or about 22 h.
According to various embodiments, the method further includes, for example, after contacting the support with the aqueous solution, drying the support in ambient air. The drying can be at a temperature of about 350 K to about 450 K, or about 360 K to about 440 K, or about 370 K to about 430 K, or about 380 K to about 420 K, or about 380 K, to about 410 K, or about 390 K to about 400 K, or about 391 K, or about 392 K, or about 393 K, or about 394 K, or about 395 K. In embodiments, the drying can be for about 1 h to about 24 h, or about 2 h to about 22 h, or about 3 h to about 20 h, or about 4 h to about 18 h, or about 5 h to about 16 h, or about 6 h to about 15 h, or about 8 h to about 12 h, or about 9 h to about 10 h.
Following the contacting and/or drying, the support can be heat-treated. The heat-treating can include flowing dry air over the support at a rate of about 1 cm3/s to about 3 cm2/s, about 1.5 cm3/s to about 2.5 cm3/s, or about 2.0 cm3/sec. The heat treating can be at a temperature of about 300 K to about 500 K, or about 325 K to about 450 K, or about 350 K to about 400 K, or about 380 K, or about 381 K, or about 382 K, or about 383 K, or about 384 K, or about 385 K, for a period of about 6 h to about 24 h, or about 8 h to about 22 h, or about 10 h to about 20 h, or about 12 h to about 18 h.
In embodiments, the resulting heat-treated support having the Co2+ thereon, can be calcined according to any suitable method known to those of ordinary skill in the art. For example, the heat-treated support can be calcined in flowing dry air (e.g., zero grade) at a flow rate of about 0.5 cm3 s−1 to about 2.00 cm3 s−1, or about 1.67 cm3 s−1 and a temperature of about 700 K to about 1,000 K, or about 750 K to about 950 K, or about 800 K to about 900 K, or about 870 K, or about 871 K, or about 872 K, or about 873 K, or about 874 K, or about 875 K, or about 923 K, for about 1 h to about 6 h, or about 3 h.
In embodiments, a catalyst composition comprising the Co2+ cations and a rare earth metal can be prepared according to any suitable method known to those of ordinary skill in the art. For example, a support (e.g., comprising alumina or formed of alumina) can be impregnated with Co2+ cations and La(NO3)3. Optionally, the impregnated support can be calcined at 600° C. for about 2 hours.
According to embodiments, methods of preparing the catalyst composition can further include pretreating the catalyst composition in a pretreatment gas as discussed above. For example, the catalyst composition can be subjected to a reductive pretreatment, for example, with a pretreatment gas comprising at least one of H2, carbon monoxide (CO), light alkanes, propane (C3H8), alkenes, propene (C3H6) and H2 species present as reactant and products of the dehydrogenation reaction. In embodiments, the catalyst composition can be pretreated with H2 at a temperature of about 800 K to about 1,000 K, or about 850 K to about 900 K, or about 873 K. The pretreated catalyst composition can include more surface-active sites (e.g., Zrcus surface-active sites) than a catalyst composition that has not been pretreated.
Further described are methods of using catalyst compositions comprising Co2+ according to embodiments. In embodiments, the catalyst compositions can be used in the dehydrogenation of hydrocarbons, for example, light alkane gas to form alkenes. In embodiments, the methods can also be used in the dehydrogenation of light alkene gas to form alkadienes. The Co2+ present in the catalyst compositions is the active catalyst material in the dehydrogenation reactions as disclosed herein.
In embodiments, when preparing to dehydrogenate a light alkane gas, the catalyst composition can be placed within a reactor (e.g., at a weight hourly space velocity of about 5.5 h−1 to about 0.05 h−1, or about 5.4 h−1 to about 0.054 h−1, or about 2.7 h−1 to about 1.8 h−1, or about 5.0 h−1 to about 0.1 h−1) and held at an about constant temperature using a furnace and a temperature controller (e.g., a Watlow Series 96). The reactor can be any suitable reactor known to those of ordinary skill in the art. Non-limiting examples include a U-shape quartz reactor (e.g., with an inner diameter of about 11.0 mm), a packed tubular reactor, a catofin-type reactor, a fluidized bed reactor, a fixed bed reactor and a moving bed reactor. The furnace may be any suitable furnace known to those of ordinary skill in the art. Non-limiting examples include a single zone furnace (e.g., by National Element Inc., Model No. BA-120), a batchwise furnace or a quartz tube furnace.
Prior to dehydrogenation, the catalyst composition can be treated in a flowing oxygen gas (O2) and helium (He) mixture at a molar ratio of O2 of about 20:1 to about 30:1, or about 22:1 to about 28:1, or about 24:1 and heating the flowing gas mixture to a temperature of about 800 K to about 1,000 K, or about 850 K to about 900 K, or about 873 K at a rate of about 0.1 K s−1 to about 1 K s−1, or about 0.167 K s−1. Treating the catalyst composition with the flowing O2 and He gas mixture can be for a period of about 0.5 h to about 8 h, or about 1 h to about 4 h, or about 1 h, or about 2 h. Subsequently, the reactor can be purged with flowing inert gas (as defined above), steam, or by vacuum (e.g., 2 cm3 g−1 s−1, ultra-high purity) to remove residual O2 within the reactor.
The light alkane gas (and/or light alkene gas) can be introduced to the reactor in the presence of the catalyst composition. According to embodiments, the light alkane gas (and/or light alkene gas) can comprise any one of a C2 to C5 straight or branched alkane and mixtures thereof In embodiments, the light alkane gas (and/or light alkene gas) can comprise at least one of ethane, propane, n-butane, isobutane, pentane and mixtures thereof. In embodiments, a portion of the effluent from the reactor can be recycled to the gas inlet and combined with fresh feed gas. The effluent can comprise alkenes, for example, at least one of ethene, pentene, butene, isobutene and pentene, and unreacted light alkanes comprising at least one of ethane, propane, n-butane, isobutane and pentane. In embodiments, the light alkane gas (and/or light alkene gas) can be mixed with an inert gas (e.g., steam, He, N2, Ar) at a molar ratio of about 1:2 to about 2:1, or about 1:1. In embodiments, for example, during a Catofin process, a vacuum pump can be used to lower the pressure of the reactants while maintaining the total pressure above, for example, 1 bar, to allow convective flow when the exit pressure is atmospheric.
Methods of dehydrogenating light alkane gas (and/or light alkene gas) can include co-feeding H2 with the light alkane gas (and/or light alkene gas) in the presence of the catalyst composition. The catalyst composition can comprise Co2+ according to various embodiments described herein. Adding or co-feeding the H2 with the light alkane gas (and/or light alkene gas) can include introducing the H2 at a pressure of about 1 kPa to about 100 kPa, or about 5 kPa to about 75 kPa, or about 10 kPa to about 50 kPa, or about 30 kPa to about 50 kPa while dehydrogenating the light alkane gas. In embodiments, the H2 can be added to the light alkane gas (and/or light alkene gas) at a molar ratio of H2 to light alkane gas (and/or light alkene gas) of about 1:100 to about 1:1. In embodiments, the H2 and/or reactor can be at a temperature of about 500 K to about 1000 K, or about 550 K to about 950 K, or about 600 K to about 900 K, or about 700 K to about 900 K.
According to embodiments, the method of dehydrogenating the light alkane gas (and/or light alkene gas) in the presence of the catalyst composition as described herein can provide a dehydrogenation rate per mass of the catalyst composition of about 0.5 mol to about 10.0 mol kg−1 h−1, or about 0.6 mol kg−1 h−1 to about 8.3 mol kg−1 h−1. The light alkane gas (and/or light alkene gas) dehydrogenation rate and cracking rate can be determined by analyzing the effluent stream from the reactor using gas chromatography (e.g., by an Agilent® 1540A gas chromatograph) with flame ionization detection (FID) (e.g., a GC fitted with a GS-GASPRO column) after chromatographic separation. In embodiments, the light alkane gas (and/or light alkene gas) dehydrogenation rate and the cracking rate can be normalized by the mass of the catalyst composition (e.g., in mol kg−1 h−1). In embodiments, the light alkane gas (and/or light alkene gas) dehydrogenation rate and cracking rate can be determined at a temperature of 873 K and 823 K. The temperature can be measured using any suitable method known to those of ordinary skill in the art. In embodiments, the temperature can be measured with a thermocouple (e.g., a K-type thermocouple by Omega®) and the reactor temperature can be determined from a thermocouple placed in contact with an outer tube surface (e.g., made of metal, quartz, etc.) at the catalyst bed midpoint.
In embodiments, when used in a dehydrogenation reaction as described above, catalyst compositions as disclosed herein can provide improved stability over other known catalyst compositions for the dehydrogenation of light alkanes (and/or light alkenes). The half-life of the catalyst composition in the dehydrogenation reaction can be measured using any suitable method known to those of ordinary skill in the art. In embodiments, the term half-life of the catalyst composition can refer to the number of days or hours after which the catalyst device has a dehydrogenation rate (DR) that is 50% lower than an initial or maximum dehydrogenation rate (DR) value produced by the catalyst composition at the start (or soon after the start upon stabilization) of the catalyst composition's operation (e.g., the half-life of the catalyst composition can be based on the dehydrogenation reaction rate as a function of time). In embodiments, the half-life of the catalyst composition is related to the weight hourly space velocity (WHSV), which is the hourly mass feed flow rate per catalyst mass (h−1) in the reactor. In embodiments, the catalyst composition can have a half-life of about 1 h to about 50 h, or about 6 h to about 46 h when the WHSV is about 5.4 h−1 to about 0.054 h−1.
The half-life of the catalyst composition can also be evaluated when aging the composition under different conditions. The DR can be calculated based on Formula I:
DR=60·(ke−kn)·V Formula I
wherein ke represents the total decay constant, kn represents natural decay constant, V represents the chamber volume in m3, and (ke−kn) is calculated based on Formula II:
(ke−kn)·t=−ln(Ct/C0) Formula II
wherein t represents the total testing time, Ct represents the concentration at time t in mg/m3, and C0 represents the concentration at time t=0 in mg/m3.
To determine the half-life of the catalyst composition, testing can begin by obtaining the DR value produced by the catalyst composition at the start of the catalyst composition's operation or soon after the start of the catalyst composition's operation once the DR has stabilized (t=0), also known as DR0. Subsequently, the catalyst composition can be optionally subjected to an Acceleration Test. An Acceleration Test refers to an extreme condition that may impact or deteriorate the efficacy of the catalyst composition more rapidly, such as no H2 gas co-feed or pre-treatment, co-feeding with O2, introducing a pollutant or continuous generation of pollutants. The optional Acceleration Test results can allow the estimation of the catalyst composition's life span under real-life conditions. Following the optional Acceleration Test, the catalyst composition is then aged under real-life conditions.
After the catalyst composition is aged for eight hours under real-life conditions, another sample is taken to obtain the DR value at t=n, also known as DRn. If the DRn value is greater than 50 percent of the DR0 value, then the catalyst composition is considered as still operable and the testing continues by repeating the optional acceleration test, aging the catalyst device under real-life conditions, and measuring the DRn value after each subsequent cycle. Once the DRn value is lower or equal to 50 percent of the DR0 value, the life span of the catalyst device is deemed to have ended and the overall alkene mass (AM) generated by the catalyst composition is calculated.
The above-described methods of using the catalyst compositions to dehydrogenate light alkane gas, can also be used to dehydrogenate a light alkene gas to form alkadienes. A light alkene gas can include C2-C5 branched or straight alkenes. In embodiments, two reactors can be configured in series, the first for dehydrogenating light alkane gas and the second for dehydrogenating the light alkene gas.
Catalytic dehydrogenation reactions can be classified into two categories, based on the presence of dioxygen in the reaction environment; they are denoted as oxidative and non-oxidative dehydrogenation processes. Oxidative dehydrogenation reactions occur in the presence of oxygen-containing gases and form combustion side products along with alkenes; non-oxidative dehydrogenations occur in the absence of oxygen-containing gases and form hydrogenolysis side products and carbonaceous residues that tend to block active sites.
According to embodiments, the method of using the catalyst composition comprising Co2+ as described herein is a process for non-oxidative dehydrogenation of light alkane (or light alkenes) in the presence of hydrogen (H2) to produce corresponding alkenes using SiO2 and Al2O3 supported Co-based catalyst compositions. The catalyst compositions can be synthesized in a single step as described above to provide cobalt in its intermediate oxidation state (Co2+), which is active for the non-oxidative dehydrogenation processes. In embodiments, any gas containing oxygen (O2) was avoided during propane dehydrogenation in order to eliminate the possibility of hydrocarbon oxidation to CO or CO2. In embodiments, no catalyst deactivation was detected for at least 40 ks (when performed on Co/SiO2 catalyst with 0.2-0.4 Co nm−2). The dehydrogenation rate (per mass) can increase with time (for a prolonged period of time) showing no indication of decrease. This is applicable for materials with low cobalt content (up to around 0.5 Co nm−2) and may not be observed for materials with higher cobalt loading.
In embodiments, the dehydrogenation of straight or branched light alkanes with catalyst compositions as described herein can provide higher dehydrogenation rates than other known Co-based catalysts, with higher selectivity and stability, and with the robustness required for occasional oxidative regenerations. Such catalyst compositions can be formed, for example, using SiO2 and γ-Al2O3 supported Co(II)-based catalysts, in the presence of hydrogen (H2) at the high temperatures required by the thermodynamics of these very exothermic dehydrogenation reactions.
CoOx/SiO2 catalysts were prepared by impregnating SiO2 (Sigma-Aldrich, high-purity grade, 293 m2 g−1) with an aqueous solution of cobalt (II) acetate tetrahydrate (Sigma-Aldrich, 99.99%). Samples were then dried at 393 K in ambient air for 9 h and treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923 K for 3 h.
CoOx/Al2O3 catalysts were prepared by impregnating fumed γ-Al2O3 (Catalox SBA-90 Alumina, 110 m2 g−1) with an aqueous solution of cobalt (II) acetate tetrahydrate (Sigma-Aldrich, 99.99%). Samples were dried at 393 K in ambient air for 9 h and treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923 K for 3 h.
AlOx(OH)3-2x supports (121 m2 g−1) were prepared by the hydrolysis of an aqueous solution of 0.5 M Al(NO3)3 (Aldrich Chemicals, >98%) pH 10, controlled by 14 N NH4OH (Aldrich Chemicals, >98%). The precipitate was washed thoroughly by an aqueous solution of NH4OH (pH 10) until residual Cl− ions were removed, tested by adding the filtrate to a 3 M AgNO3 solutions which forms white AgCl precipitate in the presence of Cl− ions at a concentration at and above 10 ppm). The AlOx(OH)3-2x precipitate was then dried at 393 K for 12 h prior to further treatments to preparing the catalyst.
CoOx/AlOx(OH)3-2x catalysts were prepared by impregnating AlOx(OH)3-2x (121 m2 g−1) with an aqueous solution of cobalt (II) acetate tetrahydrate (Sigma-Aldrich, 99.99%). Samples were dried at 393 K in ambient air for 9 h and treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923 K for 3 h. All samples were additionally treated before catalytic reactions using the procedures described below.
All catalysts were treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923 K for 3 h before the BET surface area and powder X-ray diffractogram measurements. The BET surface area of the catalysts was measured using N2 physisorption uptakes (Praxair, 99.999%)) at its normal boiling point in a Quantasorb unit (Quantasorb 6 Surface Analyzers, Quantachrome Corp.) after degassing the samples for 2 h at 423 K.
Powder X-Ray diffractograms (PXRD) were measured with a Siemens D5000 diffractometer at ambient temperature using Cu Kα radiation with a scan rate of 2° min−1. The Co surface density, the number of Co atoms per nm2 of surface area (Co atoms nm−2) of the catalyst was obtained by the equation:
Co surface density=(% wt. of CoO×6.023×1023)/(Surface area×74.9×1018),
where, the unit of the surface area is m2g−1. The BET surface areas of all Al2O3 and SiO2 supported materials (treated in flowing dry air at 923 K for 3 h) have been summarized in Table 1 and Table 2, respectively.
aAll catalysts were treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923K for 3 h.
aAll catalysts were treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) at 923K for 3 h.
The rates and selectivities of non-oxidative dehydrogenation of propane on SiO2 and Al2O3 supported CoOx catalysts (0.1-0.2 g), sieved to 180-250 μm aggregates, were measured at different temperatures between 673-923 K in a tubular quartz reactor with plug-flow hydrodynamics. The temperature of the reactor was set using an electrical furnace, coupled with a temperature controller (Watlow, series 988), and was measured by a K-type thermocouple (Omega) inserted into the furnace and positioned in the dimple of the reactor wall.
Reactant mixtures contained C3H8 (Praxair, 49.3%, balance He) and H2 (Praxair, 99.999%) and He (Praxair, 99.999%). All gases were metered using mass flow controllers (parker-porter instruments) at flow rates adjusted to get desired C3H8 and H2 pressures (0-60 kPa).
Catalysts were treated in flowing dry air (Praxair, zero grade, 1.67 cm3 s−1) for 0.5 h at 873 K and then in He (Praxair, ultra-high pure, 1.67 cm3 s−1) for 0.5 h at the same temperature to remove residual O2. Followed by this, Propane (50% C3H8 balanced with He, Praxair), Hydrogen (UHP, Praxair), and He (UHP, Praxair) were introduced to the reactor for catalytic measurements.
Reactant and product concentrations were measured by gas chromatography (Agilent 6890) using a methyl siloxane capillary column (HP-1, 50 m×0.32 mm×1.05 μm) connected to a flame ionization detector. Methane (CH4), ethane (C2H6), Ethylene (C2H4), propene (C3H6), and propane (C3H8) were the only products detected.
Dehydrogenation rates of propane (normalized by per mass (kg−1) or atom (Co nm−2)) were defined by the rates of propene formation (rd=rpropene) and the hydrogenolysis rates (rh) were determined from the rates of methane, ethane and ethylene formation (rh=rmethane/3+2 (rethane+rethylene)/3). Reactions using pure SiO2 and Al2O3 showed that the reaction rates were negligible in the absence of CoOx species. The gas-phase reactions contributing towards the dehydrogenation and hydrogenolysis reactions, were minimized by decreasing the dead-volume of the reactor using quartz tubes and measured using a catalyst-free reactor; and the dehydrogenation and hydrogenolysis rates (mol h−1) obtained in the presence of the catalyst were subtracted by their corresponding gas-phase values prior to normalizing them by the mass or atoms of the catalyst used.
The initial increment in the PDH rate (per mass) with increasing CoOx surface density is associated with the formation of increasing amounts of isolated Co2+ on support. Beyond a certain surface density, no more isolated Co2+ forms with increasing Co loading because of the absence of vicinal hydroxyl (—OH) groups on the support, leading to the formation of two-dimensional structures and then three-dimensional clusters of CoOx (CoOx crystallites), which keeps the active sites beneath the surface layer inaccessible to the reactants, and that in turn, causes the formation of the plateaus as observed in
According to
The CoSi and CoAl materials with highest PDH rates (per mass) (that is 1.5 CoSi and 1 CoAl) were compared with the CoAl material reported earlier and other Ga+, Cr3+, and Pt-based catalysts. Support of each system has been mentioned in
2. C3H8+2 H2→3CH4
3. C3H8→C3H6
From 1 and 2: rCH4=rc+3 rh=(kc+3 kh PH22)PC3H8
From 1: rC2H4=kc PC3H8
From 1: rCH4/rC2H4=(kc+3 kh PH22)/kc=1+(3 kh)/kc PH22=1+K PH22
The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present invention.
Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/018692 | 2/19/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62993878 | Mar 2020 | US |
