Methods for recycling a chromia-alumina based alkane dehydrogenation catalyst

Abstract

The disclosure provides a method of recycling a spent chromia-alumina alkane dehydrogenation catalyst for the preparation of a refreshed chromia-alumina alkane dehydrogenation catalyst, and further relates to a refreshed catalyst prepared from and including such recycled spent catalyst. The method of preparation utilizes a partial recycling approach, incorporating spent catalyst into the refreshed chromia-alumina catalyst.

Description

METHODS FOR RECYCLING A CHROMIA-ALUMINA BASED ALKANE DEHYDROGENATION CATALYSTTECHNICAL FIELD

[0001] The present disclosure generally relates to a method of preparing a refreshed chromia- alumina alkane dehydrogenation catalyst.BACKGROUND

[0002] Catalytic dehydrogenation is an important process for the production of olefins from alkanes. For example, catalytic dehydrogenation may be used to form isobutylene and propylene from their corresponding alkanes (isobutane and propane, respectively). Generally, catalytic dehydrogenation is performed in a fixed bed dehydrogenation unit. Such units typically comprise three or more parallel fixed bed reactors and a catalyst regeneration system. When the fixed bed dehydrogenation unit is in operation, one or more reactors are on-line (in dehydrogenation mode), and one or more fixed bed reactors are in regeneration mode. A fixed bed reactor in dehydrogenation mode first dehydrogenates the hydrocarbon feed for a period of time. Then, the fixed bed reactor is purged with steam. In a subsequent regeneration mode, heated air is blown through to decoke the catalyst disposed in the fixed bed reactor. The reactor is in turn evacuated and the catalyst in the reactor undergoes reductive regeneration. After catalyst reduction, the reactor is placed back on-line for performing dehydrogenation. The same sequence is sequentially repeated automatically for each fixed bed reactor using a programmable logic controller (PLC) to ensure continuous production of the entire dehydrogenation unit.

[0003] In atypical fixed bed dehydrogenation process, an aliphatic hydrocarbon (e.g., propane, isobutane, n-butane, 1 -butene, or isopentane) passes through a dehydrogenation catalyst bed and is dehydrogenated to a complementary olefin. The product (dehydrogenated hydrocarbon) of the fixed bed dehydrogenation unit may comprise, for example, propylene, isobutylene, pentene, isoprene, butadiene, or combinations thereof. The dehydrogenation reactions may include reactions (i) and / or (ii) as follows, where "n" in reactions (i) and (ii) is the number of carbon atoms in a hydrocarbon molecule, and "n" is less than 5:(i) CnH2n+2<-^CnH2n+H2, and / or(ii) CnH2n<"^CnH2n-2+H2.

[0004] Such fixed bed reactors commonly use a chromia-alumina based catalytic system to catalyze the dehydrogenation reaction. The catalytic system undergoes thousands of redox cycles of reaction and regeneration before eventually becoming deactivated, with a typical lifetime of 1.5 to 3 years for fixed bed dehydrogenation process technology. At the end of the catalytic life, these catalytic systems are typically discarded. The current disposal practice is removal to a landfill, which is not an environmentally friendly solution. Accordingly, there is a need in the art to provide an alternative solution to landfill disposal of such catalysts.SUMMARY

[0005] The present technology is generally directed to a method of preparing a chromia- alumina alkane dehydrogenation catalyst from a spent chromia-alumina alkane dehydrogenation catalyst. The method utilizes a partial recycling approach, incorporating the spent catalyst into a refreshed chromia-alumina catalyst. Surprisingly, it has been found according to the present disclosure that such refreshed catalyst exhibits comparable activity to newly manufactured commercial catalyst. The method is advantageous in avoiding both the economic and the environmental consequences of catalyst disposal.

[0006] Surprisingly, it has been found according to the present disclosure that the refreshed chromia-alumina alkane dehydrogenation catalyst prepared according to the disclosed method, in some embodiments, exhibits catalytic dehydrogenation performance comparable to that of a fresh commercial catalyst as determined by isobutane conversion, isobutylene selectivity, and / or isobutylene yield.

[0007] The present disclosure includes, without limitation, the following embodiments.

[0008] Embodiment 1 : A method of preparing a refreshed chromia-alumina alkane dehydrogenation catalyst from a spent chromia-alumina alkane dehydrogenation catalyst (already used), the method comprising: reducing a particle size of the spent chromia-alumina alkane dehydrogenation catalyst to provide a spent catalyst powder; mixing the spent catalyst powder with aluminum hydroxide, optionally in the bayerite polymorphic form, to form a mixture;adding to the mixture an aqueous solution of an acid to form an extrudable mixture; extruding the extrudable mixture to form an extrudate; drying the extrudate; calcining the dried extrudate to form a catalyst carrier; impregnating the catalyst carrier, optionally by incipient wetness, with a solution comprising a water-soluble chromium compound and a source of alkali metal ions, to form an impregnated catalyst carrier; drying the impregnated catalyst carrier; and calcining the dried impregnated catalyst carrier to provide a refreshed chromia- alumina alkane dehydrogenation catalyst.

[0009] Embodiment 2: The method of Embodiment 1, further comprising adding a source of lanthanum ions to the mixture, such as by adding the source of lanthanum ions to the aqueous solution of the acid.

[0010] Embodiment 3: The method of Embodiment 1 or 2, wherein the catalyst carrier comprises one or more of the following: a) from 10 wt.% to 39 wt.%, preferably 20 wt.% to 35 wt.%, preferably 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier; b) from 60 wt.% to 89 wt.%, preferably 65 wt.% to 75 wt.%, preferably 65 wt.% or more of alumina, based on the total weight of the catalyst carrier; and / or c) from 1 wt.% to 5 wt.%, preferably 2 wt.% to 4 wt.%, preferably 2 wt.% or more of lanthanum oxide, based on the total weight of the catalyst carrier.

[0011] Embodiment 4: The method of any one of Embodiments 1-3, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst comprises one or more of the following: a) from 15 wt.% to 30 wt.%, preferably 17 wt.% to 25 wt.%, preferably 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; b) from 0.1% to 1 wt.%, preferably 0.3 wt.% to 0.7 wt.%, preferably 0.3 wt.% or more of an alkali metal oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; and / orc) from 65 wt.% to 85 wt.%, preferably 70 wt.% to 80 wt.%, preferably 70 wt.% or more of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

[0012] Embodiment 5: The method of any one of Embodiments 1-4, wherein the spent catalyst powder has an average particle size of from 45 microns to 10 microns, preferably from 40 microns or less, or from 25 microns to 40 microns.

[0013] Embodiment 6: The method of any one of Embodiments 2-5, wherein the source of lanthanum ions is a lanthanum salt soluble in aqueous nitric acid at a temperature of 25 °C; such as wherein the source of lanthanum ions is lanthanum nitrate; and / or wherein the aqueous solution comprising a source of lanthanum ions further comprises nitric acid.

[0014] Embodiment 7: The method of any one of Embodiments 1-6, wherein drying the extrudate and / or drying the impregnated carrier comprises exposing the extrudate or impregnated carrier in air to a series of increasing temperatures in a range from 25°C to 150°C; and / or wherein calcining the dried extrudate comprises heating the dried extrudate to a temperature in a range from 600°C to 900°C.

[0015] Embodiment 8: The method of any one of Embodiments 1-7, wherein the water-soluble chromium compound comprises chromium trioxide, chromium (III) nitrate, or a combination thereof, and optionally, an alkali metal hydroxide, an alkali metal hydroxide nitrate, an alkali metal chromate, an alkali metal dichromate, or a combination thereof.

[0016] Embodiment 9: The method of any one of Embodiments 1-8, further comprising dividing the dried extrudate into pellets, such as pellets having a length of from 4 mm to 10 mm, or from 6 mm to 8 mm.

[0017] Embodiment 10: A refreshed chromia-alumina alkane dehydrogenation catalyst prepared by the method of any one of Embodiments 1 to 9.

[0018] Embodiment 11 : A refreshed chromia-alumina alkane dehydrogenation catalyst comprising a water-soluble chromium compound impregnated within a catalyst carrier, the catalyst carrier comprising a mixture of a spent chromia-alumina alkane dehydrogenation catalyst and alumina, optionally further comprising lanthanum oxide.

[0019] Embodiment 12: The refreshed chromia-alumina alkane dehydrogenation catalyst of Embodiment 11, wherein the catalyst carrier comprises one or more of the following:a) from 10 wt.% to 39 wt.%, preferably 20 wt.% to 35 wt.%, preferably 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier; b) from 60 wt.% to 89 wt.%, preferably 65 wt.% to 75 wt.%, preferably 65 wt.% or more of alumina, based on the total weight of the catalyst carrier; and / or c) from 1 wt.% to 5 wt.%, preferably 2 wt.% to 4 wt.%, preferably 2 wt.% or more of lanthanum oxide, based on the total weight of the catalyst carrier.

[0020] Embodiment 13: The refreshed chromia-alumina alkane dehydrogenation catalyst of Embodiment 11 or 12, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst comprises one or more of the following: a) from 15 wt.% to 30 wt.%, preferably 17 wt.% to 25 wt.%, preferably 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; b) from 0.1 wt.% to 1 wt.%, preferably 0.3 wt.% to 0.7 wt.%, preferably 0.3 wt.% or more of an alkali metal oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; and / or c) from 65 wt.% to 85 wt.%, preferably 70 wt.% to 80 wt.%, preferably 70 wt.% or more of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

[0021] Embodiment 14: The refreshed chromia-alumina alkane dehydrogenation catalyst of any one of Embodiments 11-13, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst is in the form of a plurality of pellets, such as pellets having a length of from 4 mm to 10 mm, or from 6 mm to 8 mm; and / or wherein a surface area of the refreshed chromia-alumina alkane dehydrogenation catalyst is in a range from 60 m2 / g to 120 m2 / g, as measured by nitrogen adsorption.

[0022] Embodiment 15: Use of the refreshed chromia-alumina alkane dehydrogenation catalyst of any one of Embodiments 11 to 14 in alkane dehydrogenation.

[0023] Embodiment 16: A refreshed chromia-alumina alkane dehydrogenation catalyst comprising a water-soluble chromium compound impregnated within a catalyst carrier, the catalyst carrier comprising a mixture of a spent chromia-alumina alkane dehydrogenation catalyst and alumina, optionally further comprising lanthanum oxide;wherein the catalyst carrier comprises one or more of the following: a) from 10 wt.% to 39 wt.%, preferably 20 wt.% to 35 wt.%, preferably 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier; b) from 60 wt.% to 89 wt.%, preferably 65 wt.% to 75 wt.%, preferably 65 wt.% or more of alumina, based on the total weight of the catalyst carrier; and / or c) from 1 wt.% to 5 wt.%, preferably 2 wt.% to 4 wt.%, preferably 2 wt.% or more of lanthanum oxide, based on the total weight of the catalyst carrier.

[0024] Embodiment 17: The refreshed chromia-alumina alkane dehydrogenation catalyst of Embodiment 16, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst comprises one or more of the following: a) from 15 wt.% to 30 wt.%, preferably 17 wt.% to 25 wt.%, preferably 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; b) from 0.1 wt.% to 1 wt.%, preferably 0.3 wt.% to 0.7 wt.%, preferably 0.3 wt.% or more of an alkali metal oxide, based on the total weight of the refreshed chromia- alumina alkane dehydrogenation catalyst; and / or c) from 65 wt.% to 85 wt.%, preferably 70 wt.% to 80 wt.%, preferably 70 wt.% or more of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

[0025] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable, unless the context of the disclosure clearly dictates otherwise.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Having thus described aspects of the disclosure in the foregoing general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale.

[0027] FIG. 1 is a flow chart illustrating a method of preparing a chromia-alumina alkane dehydrogenation catalyst from a spent chromia-alumina alkane dehydrogenation catalyst according to a non-limiting embodiment of the disclosure.

[0028] FIG. 2 is a schematic representation of a dehydrogenation reactor system according to a non-limiting embodiment of the present disclosure.DETAILED DESCRIPTION

[0029] The present disclosure will now be described more fully hereinafter with reference to example embodiments thereof. These example embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0030] Although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. Embodiments of systems and methods have been described in considerable detail with specific reference to the illustrated embodiments. However, it will be apparent that various modifications and changes can be made within the spirit and scope of the embodiments of systems and methods as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.

[0031] The following includes definitions of various terms and phrases used throughout this specification.

[0032] The use of the words "a" or "an" when used with the term "comprising," "including," "containing," or "having" in the claims or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0033] The words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and anyform of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. The process of the present disclosure can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc., disclosed throughout the specification.

[0034] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, such as within 5%, or within 1%, or within 0.5%.

[0035] The terms "wt.%," "vol%," or "mol%" refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0036] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0037] The present disclosure is directed to a refreshed chromia-alumina alkane dehydrogenation catalyst and a method of preparing such catalyst. It has been discovered according to the present disclosure that spent chromia-alumina alkane dehydrogenation catalyst which would otherwise be sent for disposal within a landfill, may instead be processed to provide a refreshed catalyst. Surprisingly, such refreshed catalyst has substantially the same catalytic activity toward alkane dehydrogenation as fresh commercial catalyst.Method of preparing a chromia-alumina alkane dehydrogenation catalyst

[0038] In one aspect there is provided a method of preparing a chromia-alumina alkane dehydrogenation catalyst from a spent chromia-alumina alkane dehydrogenation catalyst. The method generally comprises forming a catalyst carrier from spent catalyst; impregnating the catalyst carrier with a solution comprising a water-soluble chromium compound and a source of alkali metal ions to form an impregnated catalyst carrier and drying and calcining the impregnated catalyst carrier to provide a refreshed chromia-alumina alkane dehydrogenation catalyst. Reference to a “refreshed” catalyst herein refers to a chromia-alumina alkane dehydrogenation catalyst prepared using a spent (previously used) catalyst as a component thereof, and which exhibits a dehydrogenation catalytic activity greater than the spent catalyst, as explained in further detail below. Each of the individual operations is described further herein below.Reducing particle size

[0039] The method according to a non-limiting embodiment is schematically illustrated in FIG. 1. With reference to FIG. 1, the method 100 comprises step 110, in which a particle size of a spent chromia-alumina alkane dehydrogenation catalyst is reduced to provide a spent catalyst powder. By "spent" catalyst is meant catalyst that has been in service for a period of time such that it exhibits a significant loss in catalytic activity after a typical regeneration cycle. The low activity renders such spent catalyst no longer suitable for dehydrogenation due to low conversion efficiency. Generally, over time, pores in the catalyst become blocked by coking, reducing access of alkane to the catalytic sites.

[0040] Typically, the chromia-alumina alkane dehydrogenation catalyst is utilized in pellet form. Accordingly, to begin catalyst recycling, the pellets are crushed, ground, or the like to reduce particle size (i.e., powdered), and optionally sieved to provide the desired particle size for further processing. In some embodiments, the spent catalyst, once powdered, has an average particle size of about 45 microns or less. In some embodiments, the average particle size is about 40 microns or less, about 30 microns or less, or about 25 microns or less. In some embodiments, the average particle size is from about 10 microns to about 45 microns, or from about 25 microns to about 40 microns. Within the context of the present disclosure, the term "average particle size" is synonymous with D50, meaning half of the population of particles has a particle size above this point, and half below. Particle size may be measured by laser light scattering techniques or by microscopic techniques. Formation of the powder can be performed by any suitable method or apparatus, such as through use of conical mills, hammer mills, and the like.

[0041] Without wishing to be bound by any particular theory, it is believed that decreasing the particle size of the spent catalyst increases the relative amount of spent catalyst that can be incorporated into the refreshed catalyst while still maintaining the desired catalytic activity of the final refreshed catalyst material.Forming mixture with aluminum hydroxide

[0042] With continued reference to FIG. 1, the method 100 comprises step 120, in which the spent catalyst powder is mixed with aluminum hydroxide to form a mixture. Aluminum hydroxide (Al(0H)3) is commercially available in several polymorphic forms. In some embodiments, the aluminum hydroxide is in the bayerite polymorphic form. The mixing can be performed by any suitable method or apparatus.Forming an extrudable mixture

[0043] With continued reference to FIG. 1, method 100 comprises step 130, in which an aqueous solution of an acid is added to the mixture to form a mixture. The acid is generally a mineral acid, and the concentration of the acid in water may vary. For example, in some embodiments, the acid is nitric acid and the concentration is from about 5 vol% to about 90 vol% in water. In some embodiments, the aqueous solution of acid is 10 vol% to 50 vol% nitric acid in water. The quantity of aqueous acid added to form the mixture may vary based on the acid, concentration thereof, and scale on which the mixing is performed. The mixture is typically extrudable, meaning that the mixture is capable of being extruded using standard extruding machinery, such as screw extruders. However, "extrudable" is not intended to be limiting with respect to the actual processing of the mixture but is merely descriptive of the nature of the mixture (i.e., of a dough-like consistency). In some embodiments, the mixture may actually be processed by extrusion, but other processing methods are contemplated as described below.

[0044] In some embodiments, the method further comprises adding a source of lanthanum ions to the mixture. In some embodiments, the source of lanthanum ions is a lanthanum salt soluble in aqueous acid, for example, a lanthanum salt exhibiting substantial solubility in aqueous nitric acid at a temperature of about 25 °C. In some embodiment, the aqueous solution comprises a source of lanthanum ions and further comprises nitric acid. In particular embodiments, the source of lanthanum ions is lanthanum nitrate.Extruding

[0045] With continued reference to FIG. 1, method 100 comprises step 140, in which the mixture formed in step 130 is extruded. Reference to extruding the mixture is not intended to be limited solely to extrusion, and the mixture may be processed in any manner such as to put the mixture into a format which can subsequently provide a pellet-like form. In some embodiments, the extrudable mixture is extruded. The extrusion can be carried out using extruders such as screw, sieve, basket, roll, and ram-type extruders, extruding the mixture through suitably sized pierced screens. Any suitable extrudate shape may be used. In some embodiments, the mixture is extruded into rods.

[0046] In some embodiments, method 100 further comprises dividing the dried extrudate into pellets. In some embodiments, the extrudate is in rod form, and the rods are divided into individual shorter rod-shaped pieces (e.g., pellets). This may conveniently be performed within step 140,prior to drying, but may also be performed at other stages (e.g., following drying or calcining). In some embodiments, the pellets so produced have a length of about 4 mm to about 10 mm, or about 6 mm to about 8 mm.Drying and calcining

[0047] With continued reference to FIG. 1, method 100 comprises step 150, in which the extrudate is dried. In some embodiments, drying comprises exposing the extrudate in air to a series of increasing temperatures. In some embodiments, drying comprises exposing the extrudate in air to a series of increasing temperatures in a range from about 25 °C to about 150 °C, such as from about 25 °C, about 30 °C, about 35 °C, about 40 °C, about 45 °C, about 50 °C, about 55 °C, or about 60 °C, to about 65 °C, about 70 °C, about 75 °C, about 80 °C, about 85 °C, about 90 °C, about 95 °C, about 100 °C, about 110 °C, about 120 °C, about 130 °C, about 140 °C, or about 150 °C. The temperature may be increased in various increments and with various hold times at one or more temperatures within the range of increasing temperatures. The overall length of time for the drying will vary based on the temperatures utilized, the moisture content of the extrudate, and the air flow conditions during drying. Generally, the drying is conducted for a period ranging from a few hours to a few days. In certain embodiments, the length of the drying period is determined by monitoring change in weight of the material being dried. When the weight of the material stops changing, drying can be stopped.

[0048] Following the drying, in step 160 of method 100 the dried extrudate is calcined to form a catalyst carrier. Generally, the calcining comprises heating the dried extrudate to a temperature in a range from about 600 °C to about 900 °C for a period ranging from a less than an hour to a few days. Following the calcining, the catalyst carrier is obtained.

[0049] The composition of the carrier may vary based on the relative amounts of spent catalyst and alumina which have been utilized. In some embodiments, the catalyst carrier comprises about 10% or more of the spent chromia-alumina alkane dehydrogenation catalyst. In some embodiments, the catalyst carrier comprises about 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst. In some embodiments, the catalyst carrier comprises about 10 wt.% to about 40 wt.% of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier. In some embodiments, the catalyst carrier comprises about 20 wt.% to about 35 wt.% of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier. As described herein above, it is believed that smalleraverage particle size of the spent catalyst allows greater levels of inclusion of the spent catalyst relative to aluminum hydroxide.

[0050] In some embodiments, the catalyst carrier comprises about 60 wt.% or more of alumina. In some embodiments, the catalyst carrier comprises about 65 wt.% or more. In some embodiments, the catalyst carrier comprises about 60 wt.% to about 89 wt.% or about 65 wt.% to about 75 wt.% of alumina, based on the total weight of the catalyst carrier.

[0051] In some embodiments, the catalyst carrier comprises about 1 wt.% or more of lanthanum oxide. In some embodiments, the catalyst carrier comprises about 2 wt.% or more of lanthanum oxide. In some embodiments, the catalyst carrier comprises about 1 wt.% to about 5 wt.% or about 2 wt.% to about 4 wt.% of lanthanum oxide, based on the total weight of the catalyst carrier.Impregnating the carrier

[0052] With continued reference to FIG. 1, method 100 comprises step 170, in which the carrier is impregnated with a water-soluble chromium compound. The impregnating may be performed by any suitable method. In some embodiments, the impregnating comprises performing incipient wetness impregnation. Incipient wetness impregnation techniques, also called capillary impregnation or dry impregnation, are commonly used for the synthesis of catalysts. Typically, a catalyst precursor (e.g., a water-soluble chromium compound, as disclosed herein) is dissolved in an aqueous solution and the solution is added to the material to be impregnated (e.g., the catalyst carrier), and which contains the same pore volume as the volume of the solution that was added. Capillary action draws the solution into the pores of the material. Solution added in excess of the material pore volume causes the solution transport to change from a capillary action process to a diffusion process, which is much slower. The impregnated material is then be dried and calcined to remove the volatile components within the solution, depositing the active species (e.g., the chromium compound) on the surface of the carrier material. The maximum loading is limited by the solubility of the precursor in the solution. The concentration profile of the impregnated material depends on the mass transfer conditions within the pores during impregnation and drying.

[0053] The water-soluble chromium compound may vary. Generally, the water-soluble chromium compound(s) may be one or more water-soluble chromium compounds which, when subjected to the calcining described below, are converted to chromia (chromium (III) oxide; Cr20s). In some embodiment, the water-soluble chromium compound comprises chromiumtrioxide (CrCh), chromium (III) nitrate (CrfNCh) ), or a combination thereof. In some embodiments, the solution utilized for impregnation comprises chromium trioxide, chromium (III) nitrate, or a combination thereof, and further comprises one or more of a chromate (CrCU2') salt, a dichromate (C^Ch2') salt, an alkali metal hydroxide, an alkali metal nitrate, or a combination thereof. Alkali metals include, but are not limited to, lithium, sodium, and potassium. In some embodiments, the solution utilized for impregnation further comprises sodium dichromate or potassium dichromate.Drying and calcining

[0054] With continued reference to FIG. 1, method 100 comprises step 180, in which the impregnated carrier is dried. In some embodiments, drying comprises exposing the impregnated carrier in air to a series of increasing temperatures. In some embodiments, drying comprises exposing the impregnated carrier in air to a series of increasing temperatures in a range from about 25 °C to about 150 °C, such as from about 25 °C, about 30 °C, about 35 °C, about 40 °C, about 45 °C, about 50 °C, about 55 °C, about 60 °C, about 65 °C, about 70 °C, about 75 °C, or about 80 °C, to about 85 °C, about 90 °C, about 95 °C, about 100 °C, about 110, °C about 120 °C, about 130 °C, about 140 °C, or about 150 °C. The temperature may be increased in various increments and with various hold times at one or more temperature within the range of increasing temperatures. The overall length of time for the drying will vary based on the temperatures utilized, the moisture content of the impregnated carrier, and the air flow conditions during drying. Generally, the drying is conducted for a period ranging from a few hours to a few days. Generally, as noted above, the drying is carried out for a period of time sufficient to provide a stable weight of the carrier when measured at several time points during the course of drying (i.e., no more moisture is being lost).

[0055] Following the drying, the dried impregnated carrier is calcined (step 190) to form the refreshed catalyst. Generally, the calcining comprises heating the dried impregnated carrier to a temperature in a range from about 600 °C to about 900 °C for a period ranging from less than an hour to a few days. Following the calcining, the refreshed catalyst is obtained.

[0056] The composition of the refreshed chromia-alumina alkane dehydrogenation catalyst may vary based on, e.g., the relative amounts of spent catalyst, alumina, and chromium compound incorporated. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 15 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst. In some embodiments, therefreshed chromia-alumina alkane dehydrogenation catalyst comprises about 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 15 wt.% to about 30 wt.% or about 17 wt.% to about 25 wt.% of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

[0057] In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 0.1 wt.% or more of an alkali metal oxide. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 0.3 wt.% or more of an alkali metal oxide. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 0.1 wt.% to about 1 wt.% or about 0.3 wt.% to about 0.7 wt.% of an alkali metal oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst. In some embodiments, the alkali metal oxide is sodium oxide. In some embodiments, the alkali metal oxide is potassium oxide.

[0058] In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 65 wt.% or more of the catalyst carrier. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 70 wt.% or more of the catalyst carrier. In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst comprises about 65 wt.% to about 85 wt.% or about 70 wt.% to about 80 wt.% of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

[0059] In some embodiments, the refreshed chromia-alumina alkane dehydrogenation catalyst has a surface area in a range from about 60 m2 / g to about 120 m2 / g. In some embodiments, the surface area is from about 60 m2 / g, about 70 m2 / g, about 80 m2 / g, or about 90 m2 / g, to about 100 m2 / g, about 110 m2 / g, or about 120 m2 / g.Surface area expressed in m2 / g, is a measure of the total surface area of a porous material per unit of mass. Unless otherwise stated, "surface area" refers to surface area according to the Brunauer- Emmett-Teller (BET) method for determining surface area by N2 adsorption measurements.Dehydrogenation System

[0060] The refreshed catalyst as disclosed herein may be utilized for alkane dehydrogenation, for example, in a fixed bed catalytic dehydrogenation system. The dehydrogenation process canbe run as an adiabatic, cyclic process where each cycle includes a catalyst reduction step and a dehydrogenation step, and typically further includes a step to purge the remaining hydrocarbon from the reactor, and finally a regeneration step with air. Following this, the cycle begins again with the catalyst reduction step.

[0061] The reactors in dehydrogenation processes operate under vacuum during various steps of the reaction process, such as during dehydrogenation and during catalyst reduction. The evacuation of the reactors is accomplished using a quench system in combination with a vacuum pump as described in greater detail below. The final reactor pressure after evacuation is typically about 0.6 bar or less, such as about 0.2 bar to about 0.6 bar (Absolute; bara).

[0062] FIG. 2 provides a schematic diagram for a non-limiting embodiment of a fixed bed dehydrogenation unit, illustrating different reactors at different points in the process cycle. With reference to FIG. 2, the fixed bed dehydrogenation unit 200 may include a fixed bed reactor 201 in purge mode, a fixed bed reactor 202 in dehydrogenation mode, and a fixed bed reactor 203 in regeneration mode. Each of the fixed bed reactors comprises a catalyst bed comprising a chromia- alumina catalyst as described herein.

[0063] The inlet of fixed bed reactor 202 in dehydrogenation mode may be connected to a heater 210 that is configured to heat a hydrocarbon feed to a reaction temperature, and the outlet of fixed bed reactor 202 in dehydrogenation mode may be connected to a heat exchanger 208 to cool down the effluent from fixed bed reactor 202 in dehydrogenation mode. The combined hydrocarbon stream 13 from a hydrocarbon feed stream 11 and a recycled hydrocarbon stream 12 may be vaporized and heated to a reaction temperature by heater 210. The reaction temperature is typically from about 540 °C to about 750 °C. The reaction pressure may be in a range from about 0.2 bara to about 1.2 bara, such as about 0.2 bara to about 0.6 bara.

[0064] Fixed bed dehydrogenation unit 200 may further include a regeneration air system comprising an air compressor 204 configured to blow air into fixed bed reactor 203 in regeneration mode, a regeneration air heater 205 configured to heat the air from air compressor 204, a fuel injector 206 configured to inject fuel gas into fixed bed reactor 203 in regeneration mode, and a heat exchanger 207 configured to cool down the effluents from fixed bed reactor 203 in regeneration mode and fixed bed reactor 201 in purge mode. The effluent from the reactor in purge mode may be configured to be cooled in either of heat exchanger 207 or 208 with a suitable condensate recovery system. Fuel injector 206 may be disposed between air compressor 204 andregeneration air heater 205. A stream 16 leaving fixed bed reactor 203 in regeneration mode may be used for generating steam via heat exchanger 207. The regenerating conditions can include a regenerating pressure of about 0.1 bar to about 10 bar. The regenerating conditions can include a regenerating period that may be in a range of about 7 minutes to about 18 minutes.

[0065] Fixed bed dehydrogenation unit 200 may further include a compression and recovery system 209 to recover and purify a dehydrogenated hydrocarbon obtained from fixed bed reactor 202 in dehydrogenation mode. Specifically, an effluent stream 14 from fixed bed reactor 202 in dehydrogenation mode may be cooled, recovered, and purified through compression and recovery system 209. Purified dehydrogenated hydrocarbons may flow in stream 17. Recovered unreacted hydrocarbon may be recycled back to combined hydrocarbon stream 13 via recycled hydrocarbon stream 12.

[0066] Fixed bed dehydrogenation unit 200 may further include a purge gas source 20 (e.g., steam) in fluid communication with each reactor for use in the purge step and a reducing gas source 22 (e.g., hydrogen) in fluid communication with each reactor to reduce the catalyst.

[0067] The process sequence can be controlled, for example, using programmable logic controllers. See, for example, the programmable logic controllers set forth in US Pat. No. 11,370,729 to Ansari et al. and US Pat. Publ. No. 2022 / 0055002 to Bodas et al, which are incorporated by reference herein in their entirety.

[0068] In one aspect of the present disclosure, a method of alkane dehydrogenation using the refreshed catalyst is provided. The method can include contacting a hydrocarbon feed (e.g., an aliphatic hydrocarbon such as propane, isobutane, n-butane, 1 -butene, or isopentane) with the refreshed catalyst in a reactor to produce a dehydrogenated hydrocarbon, such as propylene, isobutylene, pentene, isoprene, butadiene, or combinations thereof, and withdrawing the dehydrogenated hydrocarbon product from the reactor. Thereafter, the product can be subjected to downstream processing to purify the dehydrogenated hydrocarbon product, recycle unreacted hydrocarbon feed, and the like.EXPERIMENTALExample 1. Preparation of carrier composition

[0069] A spent chromia / alumina catalyst extrudate from an isobutane dehydrogenation plant after approximately 2 years of operation was processed into a carrier composition. The spent catalyst extrudate was powdered and the powder passed through a 38-micron sieve. Aluminum hydroxide (Bay erite; Pural® BT, Sasol) powder was added to the spent catalyst powder and mixed uniformly. To this solid mixture was added dropwise with mixing an aqueous 25 wt.% nitric acid solution containing dissolved lanthanum nitrate hexahydrate until the solid mixture formed an extrudable mixture. The obtained extrudable mixture was extruded through dies having a circular opening of 3.5 mm diameter. The obtained wet extrudate was maintained at 25 °C for two hours and at 70 °C for about 12 hours. The extrudate was then broken to lengths of 6 to 8 mm and heated at 90 °C for 12 hours and at 120 °C for 12 hours. The dried extrudate was then placed in a quartz tray and calcined by heating at 120 °C for 4 hours followed by heating at 800 °C for 2 hours. The calculated composition of the prepared carrier was 72 wt.% alumina, 25 wt.% spent catalyst, and 3 wt.% lanthanum oxide.Example 2. Preparation of catalyst

[0070] A chromia / alumina dehydrogenation catalyst was prepared by incipient wetness impregnation of the carrier composition of Example 1 using an aqueous solution of chromium trioxide and sodium dichromate dihydrate. The impregnated carrier was shaken intermittently and kept at 25 °C for about 12 hours. The impregnated carrier was then heated in an oven at 70 °C for about 12 hours and at 120 °C for about 12 hours. The dried impregnated carrier was placed in a quartz tray and calcined in air at 750 °C for 2 hours. The obtained catalyst had a surface area of 102.5 m2 / g and a calculated composition of 21 wt.% Cr20s, 0.5 wt.% Na?O, and 78.5 wt.% carrier composition.Example 3. Catalyst Testing

[0071] The dehydrogenation activity of the prepared catalyst of Example 2 was measured in a tubular fixed-bed quartz reactor. The reactor internal diameter was 16 mm and the outer diameter was 19 mm. Isobutane (99.9 vol%) was used as the feed. The catalyst weight was 8.5 g, and the particle size was in a range of about 3 to 3.2 mm. Inert quartz chips (8.5 g) having particle size in a range of about 0.4 mm to 0.5 mm were mixed with the catalyst. Quartz chips having a size of 1.0 mm to 1.4 mm were loaded above the catalyst bed. A nitrogen purge was employed betweendehydrogenation, catalyst regeneration / oxidation, and reduction with hydrogen. The total feed flow in the dehydrogenation step corresponded to GHSV of 600 ml / hr / g. The reactor outlet gases were analyzed by an online gas chromatograph (Agilent 6890) equipped with a flame ionization detector for hydrocarbon analysis and a thermal conductivity detector for hydrogen analysis. The reactant and product flow rates were measured using a Ritter-type wet gas flow meter. The reactor was operated at atmospheric pressure and in a cyclic mode with the following steps: 1) catalyst oxidation with air at a start temperature of 650 °C for 20 min.; 2) purge with nitrogen at 650 °C for 3 min.; 3) reduce with H2 at a start temperature of 650 °C for 6 min.; 4) cool from 650 °C to 585 °C under nitrogen and maintain a temperature of 585 °C for 30 min.; 5) dehydrogenation of isobutane at a start temperature of 585 °C for 21 min.; 6) analyze the reactor outlet gas composition with gas chromatography at the 20thminute from the start of the isobutane feed. Steps 1 to 6 were repeated 30 times and the isobutane conversion was stabilized in 10 cycles. The average catalyst performance of 20 cycles of reaction after stabilization is provided in Table 1 below.Example 4. Evaluation of commercial dehydrogenation catalyst (reference)

[0072] A fresh commercially available isobutane dehydrogenation catalyst was tested according to the protocol of Example 3. The average catalyst performance of 20 cycles of reaction after stabilization is provided in Table 1. The results provided in Table 1 show that the performance of the inventive prepared catalyst was comparable to that of the commercial catalyst.Table 1. Catalyst performance

[0073] Other objects, features and advantages of the disclosure will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the disclosure, are given by way of illustration only and are not meant to be limiting. Additionally, itis contemplated that changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

Claims

CLAIMSWhat is claimed is:

1. A method of preparing a refreshed chromia-alumina alkane dehydrogenation catalyst from a spent chromia-alumina alkane dehydrogenation catalyst, the method comprising: reducing a particle size of the spent chromia-alumina alkane dehydrogenation catalyst to provide a spent catalyst powder; mixing the spent catalyst powder with aluminum hydroxide, optionally in the bayerite polymorphic form, to form a mixture; adding to the mixture an aqueous solution of an acid to form an extrudable mixture; extruding the extrudable mixture to form an extrudate; drying the extrudate; calcining the dried extrudate to form a catalyst carrier; impregnating the catalyst carrier, optionally by incipient wetness, with a solution comprising a water-soluble chromium compound and a source of alkali metal ions, to form an impregnated catalyst carrier; drying the impregnated catalyst carrier; and calcining the dried impregnated catalyst carrier to provide a refreshed chromia-alumina alkane dehydrogenation catalyst.

2. The method of claim 1, further comprising adding a source of lanthanum ions to the mixture, such as by adding the source of lanthanum ions to the aqueous solution of the acid.

3. The method of claim 1, wherein the catalyst carrier comprises one or more of the following: a) from 10 wt.% to 39 wt.%, preferably 20 wt.% to 35 wt.%, preferably 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier; b) from 60 wt.% to 89 wt.%, preferably from 65 wt.% to 75 wt.%, preferably 65 wt.% or more of alumina, based on the total weight of the catalyst carrier; and / orc) from 1 wt.% to 5 wt.%, preferably 2 wt.% to 4 wt.%, preferably 2 wt.% or more of lanthanum oxide, based on the total weight of the catalyst carrier.

4. The method of claim 1, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst comprises one or more of the following: a) from 15 wt.% to 30 wt.%, preferably 17 wt.% to 25 wt.%, preferably 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; b) from 0.1 wt.% to 1 wt.%, preferably 0.3 wt.% to 0.7 wt.%, preferably 0.3 wt.% or more of an alkali metal oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; and / or c) from 65 wt.% to 85 wt.%, preferably from 70 wt.% to 80 wt.%, preferably 70 wt.% or more of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

5. The method of claim 1, wherein the spent catalyst powder has an average particle size of from 45 microns to 10 microns, preferably 40 microns or less, , or from 25 microns to 40 microns.

6. The method of claim 2, wherein the source of lanthanum ions is a lanthanum salt soluble in aqueous nitric acid at a temperature of 25 °C; such as wherein the source of lanthanum ions is lanthanum nitrate; and / or wherein the aqueous solution comprising a source of lanthanum ions further comprises nitric acid.

7. The method of claim 1, wherein drying the extrudate and / or drying the impregnated carrier comprises exposing the extrudate or impregnated carrier in air to a series of increasing temperatures in a range from 25 °C to 150 °C; and / or wherein calcining the dried extrudate comprises heating the dried extrudate to a temperature in a range from 600 °C to 900 °C.

8. The method of claim 1, wherein the water-soluble chromium compound comprises chromium trioxide, chromium (III) nitrate, or a combination thereof, and optionally, an alkalimetal hydroxide, an alkali metal hydroxide nitrate, an alkali metal chromate, an alkali metal dichromate, or a combination thereof.

9. The method of claim 1, further comprising dividing the dried extrudate into pellets, such as pellets having a length of from 4 mm to 10 mm, or from 6 mm to 8 mm.

10. A refreshed chromia-alumina alkane dehydrogenation catalyst prepared by the method of any one of claims 1 to 9.

11. A refreshed chromia-alumina alkane dehydrogenation catalyst comprising a water- soluble chromium compound impregnated within a catalyst carrier, the catalyst carrier comprising a mixture of a spent chromia-alumina alkane dehydrogenation catalyst and alumina, optionally further comprising lanthanum oxide.

12. The refreshed chromia-alumina alkane dehydrogenation catalyst of claim 11, wherein the catalyst carrier comprises one or more of the following: a) from 10 wt.% to 39 wt.%, preferably 20 wt.% to 35 wt.%, preferably 25 wt.% or more of the spent chromia-alumina alkane dehydrogenation catalyst, based on the total weight of the catalyst carrier; b) from 60 wt.% to 89 wt.%, preferably 65 wt.% to 75 wt.%, preferably 65 wt.% or more of alumina, based on the total weight of the catalyst carrier; and / or c) from 1 wt.% to 5 wt.%, preferably from 2 wt.% to 4 wt.%, preferably 2 wt.% or more of lanthanum oxide, based on the total weight of the catalyst carrier.

13. The refreshed chromia-alumina alkane dehydrogenation catalyst of claim 11, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst comprises one or more of the following: a) from 15 wt.% to 30 wt.%, preferably 17 wt.% to 25 wt.%, preferably 20 wt.% or more of chromium (III) oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst;b) from 0.1 wt.% to 1 wt.%, preferably 0.3 wt.% to 0.7 wt.%, preferably 0.3 wt.% or more of an alkali metal oxide, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst; and / or c) from 65 wt.% to 85 wt.%, preferably 70 wt.% to 80 wt.%, preferably 70 wt.% or more of the catalyst carrier, based on the total weight of the refreshed chromia-alumina alkane dehydrogenation catalyst.

14. The refreshed chromia-alumina alkane dehydrogenation catalyst of claim 11, wherein the refreshed chromia-alumina alkane dehydrogenation catalyst is in the form of a plurality of pellets, such as pellets having a length from 4 mm to 10 mm or from 6 mm to 8 mm; and / or wherein a surface area of the refreshed chromia-alumina alkane dehydrogenation catalyst is in a range from 60 m2 / g to 120 m2 / g, as measured by nitrogen adsorption.

15. Use of the refreshed chromia-alumina alkane dehydrogenation catalyst of any one of claims 11 to 14 in alkane dehydrogenation.

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