Methods of regeneration of rhenium oxide-coated gamma-alumina-based catalysts and uses thereof

Abstract

Provided here are regeneration processes for rhenium oxide-coated γ-alumina-based catalysts. These regenerated catalysts can be used in the conversion of butenes in an operational metathesis reactor.

Description

METHODS OF REGENERATION OF RHENIUM OXIDE-COATED GAMMA-ALUMINA- BASED CATALYSTS AND USES THEREOFCross-Reference to Related Application

[0001] This application claims priority to, and the benefit of European Application No. 24155947.5, filed February 6, 2024. The contents of the referenced application are incorporated into the present application by reference.Technical Field

[0002] The disclosure relates to rhenium oxide-coated y-alumina-based catalysts, methods of their regeneration, and methods for their use in metathesis reactors.Background

[0003] The demand for propene is growing. Out of various on-purpose propene production routes, such as propane dehydrogenation, metathesis, olefin cracking, methanol to olefins, and high severity fluid catalytic cracking, olefin metathesis provides an opportunity to achieve olefin interconversion of excess ethene or butenes into required propene. However, current commercial metathesis processing of excess ethene and butenes into propene expends high value ethene.

[0004] Rhenium oxide-coated y-alumina-based catalysts show metathesis activity over a wide range of temperatures, such as from room temperature to temperatures greater than 150 degrees Celsius (°C). Presence of impurities leads to oligomer formation and also reductive elimination of metallacyclobutene intermediates, which leads to reduction in rhenium oxidation state. Both the processes can be major root causes for the catalyst deactivation after specified time duration of activity. The catalyst is also deactivated due to coke formation with prolonged use of the catalyst.Summary

[0005] Applicant has identified needs for regeneration of the deactivated catalyst and a proper regeneration protocol to gain back a structure and stability similar to that of the fresh catalyst for multiple reaction and regeneration cycles. Provided here are compositions and methods to address these shortcomings of the art and provide other additional or alternative advantages. Embodiments include regeneration processes of the highly selective and stable catalysts for metathesis reactions of butenes to propene and other olefins. Examples of methods for preparation and regeneration ofrhenium oxide-coated y-alumina-based catalysts and methods for use of these resulting compositions in metathesis reactions are provided here. In certain examples, these methods for metathesis reactions of butenes exclude additional consumption of ethene.

[0006] Examples include methods of preparing a rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of calcining a y-alumina-based support to form a calcined y- alumina-based support at a temperature ranging from about 450 Celsius (°C) to about 550 °C and treating the calcined y-alumina-based support with an aqueous rhenium-containing mixture in a rotating drum impregnation unit to form a rhenium-coated y-alumina-based support. In certain examples, the aqueous rhenium-containing mixture is a rhenium oxide solution. In certain examples, the impregnation unit is rotated at a speed ranging from about 15 revolutions per minute (rpm) to about 35 rpm to form a rhenium-coated y-alumina-based support. The method also includes the steps of aging the rhenium- coated y-alumina-based support to form a rhenium oxide-coated y-alumina- based catalyst containing a rhenium coating ranging from about 150 micrometers (pm) to about 250 pm in thickness, drying the rhenium oxide-coated y-alumina-based catalyst immediately after aging, and calcining the rhenium oxide-coated y-alumina-based catalyst at a temperature ranging from about 450°C to about 550 °C. In certain examples, the step of aging the rhenium oxide-coated y-alumina- based support is conducted for a time less than 5 minutes thereby to form a rhenium oxide-coated y- alumina-based catalyst. In certain examples, the step of drying the rhenium oxide-coated y-alumina- based catalyst immediately after aging at a temperature ranges from about 140 °C to about 160 °C.

[0007] Examples include methods of preparing an activated rhenium oxide-coated y-alumina- based catalyst. One such method includes the steps of treating the rhenium oxide-coated y-alumina- based catalyst under air at a temperature from about 500 °C to about 550 °C to produce an activated rhenium oxide-coated y-alumina-based catalyst, purging nitrogen into the activated rhenium oxidecoated y-alumina-based catalyst to displace the air, and cooling the activated rhenium oxide-coated y-alumina-based catalyst to a temperature of about 50 °C. In certain examples, the step of treating the rhenium oxide-coated y-alumina-based catalyst under air is conducted for about 4 hours to about 24 hours to produce an activated rhenium oxide-coated y-alumina-based catalyst. In certain examples, the step of treating the rhenium oxide-coated y-alumina-based catalyst under air is conducted for about 6 hours.

[0008] Examples include a rhenium oxide-coated y-alumina-based catalyst, also referred to as an egg-shell catalyst. The rhenium oxide-coated y-alumina-based catalyst can be spherical or an extrudate. One such rhenium oxide-coated y-alumina-based catalyst has y-alumina-based spherical particles of a diameter ranging from about 1.2 mm to about 3 mm and a rhenium coating ranging from about 150 pm to about 250 pm in thickness. Other examples include y-alumina-based extrudate particles of a size ranging from 1.2 mm to about 3 mm in diameter and from about 4 mm to about 12 mm in length, with the rhenium coating ranging from about 150 pm to about 250 pm in thickness. In certain examples, the rhenium oxide-coated y-alumina-based catalyst contains rhenium in an amount ranging from about 4.8 wt.% to about 5.6 wt.%.

[0009] The rhenium oxide-coated y-alumina-based catalyst can facilitate conversion of one or more of: (trans / cis (t / c)) but-2-ene with but-l-ene to propene and (t / c) pent-2-ene, but-l-ene with but- 1-ene to ethene and (t / c) hex-3-ene, ethene with (t / c) but-2-ene to propene and propene, but-l-ene with (t / c) pent-2-ene to propene and (t / c) hex-3-ene, and (t / c) pent-2-ene and (t / c) pent-2-ene to (t / c) but-2-ene and (t / c) hex-3-ene in an operational metathesis reactor. In certain examples, the rhenium oxide-coated y-alumina-based catalyst can be functional for at least 300 days in the operational metathesis reactor. Based on regeneration times, the catalyst can be functional for about 1000 days or longer. In certain examples, the catalyst is regenerated for greater than 50 times in the operational metathesis reactor.

[0010] Examples include processes for regeneration of the rhenium oxide-coated y-alumina-based catalyst. The regeneration processes are affected by one or more of the includes several process conditions such as feed concentration, weight hourly space velocity (WHSV), temperature, and time duration for each step to regenerate the egg-shell shaped Re2O7 / AhO3 catalyst. The proposed regeneration protocol allows to maintain the catalyst stability and activity for long term by not affecting the coating or the egg-shell structure and not allowing the rhenium particle to undergo agglomeration process. By following the proposed regeneration protocol, the catalyst is regenerated multiple times without any loss in its activity and stability.

[0011] Examples include processes for regeneration of the rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of purging a reactor with a spent rhenium oxide-coated y-alumina-based catalyst bed with nitrogen at a temperature of about 50 °C and at a pressure of 6 barg, releasing the pressure in the reactor to atmosphere pressure; and purging the catalyst bed withnitrogen by increasing the temperature from 50 °C to 300 °C and holding at 300 °C. In some examples, the temperature from 50 °C to 300 °C is increased at a rate of 1 °C / min. In some examples, 99.99 mol.% pure nitrogen is supplied to the reactor for purging the catalyst bed at a temperature at about 50 °C. In some examples, the catalyst bed is maintained at a temperature of 300 °C for a time period ranging from 2 hours to 10 hours during purging of the catalyst bed. The hydrocarbon content in a purged stream from the reactor can be less than 100 ppm. The method further includes the step of supplying air containing oxygen (ranging from about 1 mol.% to about 3 mol.%) to the catalyst bed and increasing temperature of the catalyst bed to a temperature of 550 °C, and then supplying air containing oxygen (ranging from about 15 mol.% to about 25 mol.%) to the catalyst bed and maintaining the catalyst bed at a temperature of 550 °C. In some examples, air containing 2 mol.% oxygen is supplied to the catalyst bed and temperature of the catalyst bed is increased to a temperature of 550 °C. In some examples, the temperature is increased to 550 °C at a ramp rate of 0.5 °C / min when the air containing 2 mol.% of oxygen is supplied to the catalyst bed. In some examples, air containing 20.9 mol.% oxygen is supplied to the catalyst bed and the catalyst bed is maintained at a temperature of 550 °C. In certain examples, the catalyst bed is maintained at a temperature of 550 °C for a time period ranging from 4 hours to 24 hours when the air containing 20.9 mol.% of oxygen is supplied to the catalyst bed. The method further includes the step of reducing temperature of the catalyst bed to a temperature ranging from about 35 °C to about 100 °C; and supplying nitrogen to the catalyst bed to regenerate a rhenium oxide-coated y-alumina-based catalyst bed.

[0012] Examples include processes for regeneration of the rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of purging a reactor with a spent rhenium oxide-coated y-alumina-based catalyst bed with nitrogen at a temperature at 50 °C and at a pressure of 6 barg and releasing the pressure in the reactor to atmosphere pressure. The method further includes the steps of purging the catalyst bed with nitrogen by increasing the temperature from 50 °C to 300 °C at the rate of 1 °C / min and holding at 300 °C. In certain examples, the catalyst bed is maintained at a temperature of 300 °C for 3 hours. The method further includes the steps of supplying air containing 2 mol.% of oxygen to the catalyst bed and increasing temperature of the catalyst bed to a temperature of 550 °C at the ramp rate of 0.5 °C / min, and then supplying air containing 20.9 mol.% of oxygen to the catalyst bed and maintaining the catalyst bed at a temperature of 550 °C. In certain examples, the catalyst bed is maintained at a temperature of 550 °C for 5 hours when the air containing 20.9 mol.% of oxygen is supplied to the catalyst bed. The method further includes the steps of reducing temperature of thecatalyst bed to a temperature ranging from about 35 °C to about 100 °C, and supplying nitrogen to the catalyst bed to regenerate rhenium oxide-coated y-alumina-based catalyst bed. In certain examples, the hydrocarbon content in a purged stream from the reactor is less than 100 ppm.Brief Description of the Drawings

[0013] Examples will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements or procedures in a method. Examples are illustrated by way of example and not by way of limitation in the accompanying drawings. The present disclosure can be better understood by referring to the following figures. These drawings illustrate the principles of the disclosure and no limitation of the scope of the disclosure is thereby intended.

[0014] FIG. 1A is a graphical representation of the catalyst bed temperature during a regeneration protocol and FIG. IB is a zoomed-in version during exotherm.

[0015] FIG. 2A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIG. 2B is a zoomed-in version during exotherm.

[0016] FIG. 3A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIGs. 3B and 3C are zoomed-in versions during exotherm.

[0017] FIG. 4A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIGs. 4B and 4C are the zoomed-in versions during exotherm.

[0018] FIG. 5 is a graphical representation of the multiple runs of reaction by following the regeneration protocol-4.

[0019] FIG. 6 is a graphical representation of the comparison of catalytic activity of fresh and 2000 hours of time on stream and 8 times of regenerated catalyst by following the regeneration protocol-4.Detailed Description

[0020] The present disclosure describes various examples related to rhenium oxide-coated y- alumina-based catalyst compositions, methods for of use in metathesis reactions, and methods of regeneration of the spent rhenium oxide-coated y-alumina-based catalyst compositions.

[0021] In the following description, reference is made to the accompanying drawings that form a part of this disclosure and numerous details are set forth in order to provide a thorough understanding of the various examples. In other instances, well-known processes, devices, and systems may not been described in particular detail in order not to unnecessarily obscure the various examples. Additionally, illustrations of the various examples may omit certain features or details in order to not obscure the various examples. The drawings may provide an illustration of some of the various examples in which the subject matter of the present disclosure may be practiced. Other examples may be utilized, and logical changes may be made without departing from the scope of this disclosure.

[0022] The description may use the phrases “in some examples,” “in various examples,” “in an example,” or “in examples,” which may each refer to one or more of the same or different examples. 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 any form 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.

[0023] The term “about” refers to a range of values including the specified value, which a person of ordinary skill in the art would consider reasonably similar to the specified value. In examples, “about” refers to values within a standard deviation using measurements generally acceptable in the art. In one non-limiting example, when the term “about” is used with a particular value, then “about” refers to a range extending to ±10% of the specified value, alternatively ±5% of the specified value, or alternatively ±1% of the specified value, or alternatively ±0.5% of the specified value. In examples, “about” refers to the specified value.

[0024] Methods of preparation of these rhenium oxide-coated y-alumina-based catalysts include the steps of calcining a y-alumina support to form a calcined y-alumina-based support at a temperature ranging from about 450 °C to about 550 °C, treating the calcined y-alumina-based support with an aqueous rhenium solution in an impregnation unit, and aging the rhenium-coated y-alumina-based support to form a rhenium-coated y-alumina-based support. In certain examples, the rotating drum impregnation unit is operated at a speed ranging from about 15 rpm to about 35 rpm to form a rhenium-coated y-alumina-based support. In certain examples, the method also includes the step of aging the rhenium-coated y-alumina-based support for a time less than 5 minutes. In certain examples,the rhenium oxide-coated y-alumina-based catalyst contains a rhenium coating ranging from about 150 m to about 250 pm in thickness. The method also includes the steps of drying the rhenium- coated y-alumina-based catalyst immediately, and calcining the rhenium oxide-coated y-alumina- based catalyst at a temperature ranging from about 450°C to about 550 °C. The step of drying the catalyst after aging may be conducted at a temperature ranging from about 140 °C to about 160 °C. In the example, the particle size of the y-alumina-based support ranging from about 1.2 mm to about 3 mm.

[0025] The particle size of the y-alumina-based support can range from about 1.2 millimeters (mm) to about 3 mm. For example, the diameter of a spherical or a cylindrical y-alumina-based support can range from about 1.2 mm to about 3 mm. In certain examples, the y-alumina-based support has a pore volume ranging from about 0.5 milliliter per gram (ml / g) to about 0.65 ml / g. In certain examples, the y-alumina-based support has a pore diameter ranging from about 75 Angstroms (A) to about 110 A. In certain examples, the y-alumina-based support has a total acidity ranging from about 0.58 millimole per gram (mmolNH3 / g) to about 0.62 mmolNH3 / g. In certain examples, the rhenium oxide-coated y- alumina- based catalyst can contain rhenium in an amount ranging from about 4.8 weight percent (wt.% ) to about 5.6 wt.% . The rhenium oxide-coated y-alumina-based catalyst can have a surface area ranging from about 200 square meters per gram (m2 / g) to about 270 m2 / g. The rhenium oxidecoated y-alumina-based catalyst can be spherical in shape or an extrudate. An extrudate can be cylindrical or lobed or of other shapes. In certain examples, the rhenium particles in the coating have a particle size ranging from about 0.3 nanometer (nm) to about 1.5 nm.

[0026] In some embodiments, the impregnation unit is a rotating drum impregnator. The y- alumina- based support is placed in the drum and the drum is rotated at about 15 rpm to 35 rpm. An aqueous rhenium solution is sprayed on to y-alumina-based support using a spray gun into the rotating drum. In some examples, the rhenium containing impregnating solution is a rhenium oxide (HReO-i) solution having a pH of 1.5. The rhenium oxide solution can be present in an amount that corresponds to the pore volume of the y-alumina support. In certain examples, the calcined y- alumina spheres are sprayed with the rhenium oxide solution at 2 barg of pressure and at rate of 31.5 milliliters per minute (ml / min) over the course of 12 minutes for 700 grams of the rhenium oxide-coated y-alumina-based support.

[0027] Example of the rhenium oxide-coated y-alumina-based catalysts include spherical particles or extrudate particles. The spherical rhenium oxide-coated y-alumina-based catalysts include y- alumina- based spherical particles of a diameter ranging from about 1.2 mm to about 3 mm and a rhenium coating ranging from about 150 pm to about 250 pm in thickness. The extrudate rhenium oxide-coated y-alumina-based catalysts include y-alumina-based extrudate particles of a size ranging from 1.2 mm to about 3 mm in diameter and from about 4 mm to about 12 mm in length and the rhenium coating ranging from about 150 pm to about 250 pm in thickness.

[0028] Examples of uses of the foregoing catalysts include the metathesis of butenes to propene and internal olefins. Methods of use of these catalysts in the metathesis reaction involve treating and purging of the rhenium oxide-coated y-alumina-based catalysts prior to introduction of the butenes at the reaction temperature. Certain examples include treating the rhenium oxide-coated y-alumina- based catalyst under air at a temperature from about 500 °C to about 550 °C for about 6 hours to produce an activated rhenium oxide-coated y-alumina-based catalyst and purging nitrogen into the activated rhenium oxide-coated y-alumina-based catalyst to displace the air and cooling the activated rhenium oxide-coated y-alumina-based catalyst. Certain examples include activating the rhenium oxide-coated y-alumina-based catalyst under air for about 6 hours. Certain examples include cooling the activated rhenium oxide-coated y-alumina-based catalyst to a temperature of about 50 °C. These catalysts exhibit high selectivity to the foregoing propene and internal olefins production.

[0029] Stability of the rhenium oxide-coated y-alumina-based catalyst can depend on the coating thickness. When the rhenium oxide-coated y-alumina-based catalyst has a coating thickness greater than 250 pm, it can lead to unavailability or low availability of all of the rhenium particles for a metathesis reaction. Such catalysts may deactivate fast and be a low stability catalyst. With regards to rhenium oxide-coated y-alumina-based catalyst having a thickness of less than 150 pm and the rhenium particle size being less than 1.5 nm, such as due to fast drying practices, the availability of rhenium particles on the surface can be low.

[0030] In certain examples, the rhenium oxide-coated y-alumina-based catalyst is spherical or an extrudate. In certain examples, the rhenium oxide-coated y-alumina-based catalyst contains rhenium in an amount from about 4.8 wt.% to about 5.6 wt.% . In other examples, the rhenium oxide-coated y-alumina-based catalyst has a surface area ranging from about 200 m2 / g to about 270 m2 / g. The physical and mechanical properties of the rhenium oxide-coated y-alumina-based catalyst arepresented in Table 1.

[0031] Table- 1: Physical and mechanical properties of metathesis catalyst.

[0032] The rhenium oxide-coated y-alumina-based catalyst can facilitate conversion of one or more of: (trans / cis (t / c)) but-2-ene with but-l-ene to propene and (t / c) pent-2-ene, but-l-ene with but- 1-ene to ethene and (t / c) hex-3-ene, ethene with (t / c) but-2-ene to propene and propene, but-l-ene with (t / c) pent-2-ene to propene and (t / c) hex-3-ene, and (t / c) pent-2-ene and (t / c) pent-2-ene to (t / c) but-2-ene and (t / c) hex-3-ene in an operational metathesis reactor. In certain examples, the rhenium oxide-coated y-alumina-based catalyst can be functional for at least 300 days in the operational metathesis reactor. Based on regeneration times, the catalyst can be functional for about 1000 days or longer. In certain examples, the catalyst is regenerated for greater than 20 or 30 times in the operational metathesis reactor. In certain examples, the catalyst is regenerated for greater than 50 times in the operational metathesis reactor.

[0033] Examples include processes for regeneration of the rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of purging a reactor with a spent rhenium oxide-coated y-alumina-based catalyst bed with nitrogen at a temperature of about 50 °C and at a pressure of 6 barg, releasing the pressure in the reactor to atmosphere pressure; and purging the catalyst bed with nitrogen by increasing the temperature from 50 °C to 300 °C and holding at 300 °C. In some examples, the temperature from 50 °C to 300 °C is increased at a rate of 1 °C / min. In some examples, the temperature is raised from about 50 °C to about 350 °C and held at about 350 °C. In some examples, 99.99 mol.% pure nitrogen is supplied to the reactor for purging the catalyst bed at a temperature at about 50 °C. The hydrocarbon content in a purged stream from the reactor can be less than 100 ppm. In some examples, the catalyst bed is maintained at a temperature of 300 °C for a time period ranging from 2 hours to 10 hours. This time is adjusted as required to reduce the hydrocarbon content in thepurged stream to less than 100 ppm. The method further includes the step of supplying air containing oxygen (ranging from about 1 mol.% to about 3 mol.%) to the catalyst bed and increasing temperature of the catalyst bed to a temperature of 550 °C, and then supplying air containing oxygen (ranging from about 15 mol.% to about 25 mol.%) to the catalyst bed and maintaining the catalyst bed at a temperature of 550 °C. In some examples, air containing 2 mol.% oxygen is supplied to the catalyst bed and temperature of the catalyst bed is increased to a temperature of 550 °C. In some examples, the temperature is increased to 550 °C at a ramp rate of 0.5 °C / min when the air containing 2 mol.% of oxygen is supplied to the catalyst bed. In some examples, air containing 20.9 mol.% oxygen is supplied to the catalyst bed and the catalyst bed is maintained at a temperature of 550 °C. In certain examples, the catalyst bed is maintained at a temperature of 550 °C for about 4 hours to about 24 hours. The method further includes the step of reducing temperature of the catalyst bed to a temperature ranging from about 35 °C to about 100 °C; and supplying nitrogen to the catalyst bed to regenerate a rhenium oxide-coated y-alumina-based catalyst bed.

[0034] In certain embodiments, a reactor containing the rhenium oxide-coated y-alumina-based catalyst is supplied with a pure nitrogen stream to purge impurities from the spent rhenium oxidecoated y-alumina-based catalyst. In some examples, nitrogen is supplied to the catalyst bed at a WHSV between about 0.4 / hr to about 5.0 / hr. The temperature at this stage can be from about 35 °C to about 100 °C. The pressure can be from 4 barg to about 30 barg. In some examples, nitrogen is supplied to the catalyst bed at a WHSV of 0.6 / hr at a temperature ranging from about 35 °C to about 75 °C and at pressures ranging from 4 barg to about 10 barg. At a subsequent step, the pressure in the reactor is reduced to atmosphere pressure, and then the catalyst bed is purged with nitrogen at a WHSV between about 0.6 / hr to about 5.0 / hr. Then, the temperature of the catalyst bed is increased to about 300 °C and is held at about 300 °C for about 2 hours to about 10 hours. This time is adjusted as required to reduce the hydrocarbon content in the purged stream to less than 100 ppm. Air containing about 2 mol.% oxygen is subsequently introduced into the catalyst bed. In certain examples, this air can contain about 1 -3 mol.% oxygen. The air can be introduced at a WHSV between about 0.4 / hr to about 5.0 / hr. In certain examples, the temperature of the catalyst bed is raised to about 350 °C to about 550 °C at the ramp rate of 20 °C / hr to about 45 °C / hr. Then, air containing about 20.9 mol.% oxygen is subsequently introduced into the reactor at about 0.4 / hr to about 5.0 / hr of WHSV. In certain examples, this air can contain about 15-25 mol.% oxygen. Here, the temperature of the catalyst bed is maintained at 550 °C for about 4 hours to about 24 hours. Finally, the air flow isstopped and a nitrogen stream is supplied to the catalyst bed at a WHSV that is between about 0.4 / hr to about 5.0 / hr and the catalyst bed temperature is cooled to a reaction temperature of about 35 °C to about 100 °C.

[0035] Examples include processes for regeneration of the rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of purging a reactor with a catalyst bed with nitrogen at a temperature at 50 °C and at a pressure of 6 barg and releasing the pressure in the reactor to atmosphere pressure. The method further includes the steps of purging the catalyst bed with nitrogen by increasing the temperature from 50 °C to 300 °C at the rate of 1 °C / min and holding at 300 °C. In certain examples, the catalyst bed is maintained at a temperature of 300 °C for 3 hours. The method further includes the steps of supplying air containing 2 mol.% of oxygen to the catalyst bed and increasing temperature of the catalyst bed to a temperature of 550 °C at the ramp rate of 0.5 °C / min, and then supplying air containing 20.9 mol.% of oxygen to the catalyst bed and maintaining the catalyst bed at a temperature of 550 °C. In certain examples, the catalyst bed is maintained at a temperature of 550 °C for 5 hours when the air containing 20.9 mol.% of oxygen is supplied to the catalyst bed. The method further includes the steps of reducing temperature of the catalyst bed to a temperature ranging from about 35 °C to about 100 °C, and supplying nitrogen to the catalyst bed to regenerate rhenium oxide-coated y-alumina-based catalyst bed. In certain examples, the hydrocarbon content in a purged stream from the reactor is less than 100 ppm.EXAMPLES

[0036] Various examples provided herein illustrate selected aspects of the various examples of rhenium oxide-coated y-alumina-based catalyst, methods of manufacture of these catalysts, and methods of use of these catalysts in metathesis reactions.Example 1

[0037] Catalyst Testing. To characterize the activity of Re2O7 / y-AhO3 catalyst, the catalyst spheres were loaded into a tubular fixed bed reactor. The details of the catalyst loading are as follows: Catalyst weight of 50 g and catalyst in the shape of spheres (1.5 to 2 mm diameter). The catalyst spheres were accurately weighted and loaded into the reactor and maintained under the plug flow conditions. The thermowells were placed at top, middle, and bottom of the catalyst bed. Above the catalyst bed, a 13X molecular sieve was loaded to absorb the moisture from the feedstock prior to contact with the catalyst bed. Inert a-alumina was loaded below the catalyst bed. After loading, thecatalyst was used for metathesis of 2-butene with 1 -butene. The catalyst was activated under air at 550 °C for 6 hours, then purged with air containing nitrogen, and cooled to 50 °C under nitrogen. Once the catalyst bed reaches 50 °C, the feed (containing 1.14 mol.% n-butane, 54.6 mol.% trans 2- butene, 23 mol.% cis 2-butene, and 21 mol.% 1-butene) was supplied to the reactor. N-butane is used as an internal standard. The feed was fed to maintain the WHSV of 5 / hrs at 6 barg pressure. The reactor outlet gases were analyzed by online gas chromatography (Agilent 6890) equipped with a flame ionization detector for hydrocarbon analysis and thermal conductivity detector for ideal gases. The reactor and products molar flowrates were calculated using internal standard n-butane based on its molar flow rate as well as GC areas. The conversion with respect to 1-butene was initially 90% and dropped over the course of 5 days to 85% and the cycle time was 5 days. In addition, the propylene selectivity was 50% over the entire cycle time. When the cycle was completed, the catalyst was regenerated as provided by one of the following regeneration protocols.

[0038] Regeneration protocol- 1: The reactor was purged with nitrogen (purity of 99.99 mol.%) and maintain the WHSV of 0.6 / hr under same reaction and process conditions. The reactor pressure was released to atmospheric pressure and the reactor was purged with N2 (purity 99.99 mol.%) at a WHSV of 0.6 / hr by increasing the reactor temperature from 50 °C to 550 °C at the rate of 1 °C / min. Air containing 20.9 mol. % of oxygen was introduced at a WHSV of 0.6 / hr and the catalyst bed was maintained at a temperature of 550 °C for 5 hours. The airflow was stopped and N2 (purity 99.99 mol.%) was introduced at 30 standard liters per hour (SLPH) and the catalyst bed was cooled to reaction temperature ranging from about 35 °C to about 100 °C. FIG. 1A is a graphical representation of the catalyst bed temperature during a regeneration protocol and FIG. IB is a zoomed-in version during exotherm.Example-2

[0039] Fresh catalyst was loaded into a reactor and evaluated similar to Example 1, and after deactivation of the catalyst, the catalyst was regenerated as described in regeneration protocol-2.

[0040] Regeneration protocol-2: The reactor was purged with nitrogen (purity of 99.99 mol.%) at a flow rate of 30 SLPH under same reaction / process condition. The reactor pressure was released to atmosphere pressure and the reactor was purged with N2 (purity 99.99 mol.%) at a flow rate of 30 SLPH by increasing the reactor temperature from 50 °C to 550 °C at the rate of 1 °C / min. Air containing 10 mol.% of oxygen was introduced at a flow rate of 30 SLPH and the catalyst bed wasmaintained at a temperature of 550 °C for 60 minutes. Then, air containing 20.9 mol.% of oxygen was introduced at a flow rate of 30 SLPH and the catalyst bed was maintained at a temperature of 550 °C for 5 hours. The airflow was stopped and N2 (purity 99.99 mol.%) was introduced at 30 SLPH and the catalyst bed was cooled to reaction temperature ranging from about 35 °C to about 100 °C. FIG. 2A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIG. 2B is a zoomed-in version during exotherm.

[0041] Example-3

[0042] Fresh catalyst was loaded into a reactor and evaluated similar to Example 1, and after deactivation of the catalyst, the catalyst was regenerated as described in regeneration protocol-3.

[0043] Regeneration protocol-3: The reactor was purged with nitrogen (purity of 99.99 mol.%) at a flow rate of 30 SLPH under same reaction / process condition. The reactor pressure was released to atmosphere pressure and the reactor was purged with N2 (purity 99.99 mol.%) at a flow rate of 30 SLPH by increasing the reactor temperature from 50 °C to 300 °C at the rate of 1 °C / min and holding at 300 °C for 3 hrs (or) until the hydrocarbon content in the purged stream reaches less than 100 ppm. Air containing 20.9 mol.% of oxygen was introduced at a flow rate of 30 SLPH and the catalyst bed was increased a temperature of 550 °C at the ramp rate of 0.5 °C / min and held for 5 hours at this condition. The airflow was stopped and N2 (purity 99.99 mol.%) was introduced at 30 SLPH and the catalyst bed was cooled to reaction temperature ranging from about 35 °C to about 100 °C. FIG. 3A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIGs. 3B and 3C are zoomed-in versions during exotherm.Example-4

[0044] Fresh catalyst was loaded into a reactor and evaluated similar to Example 1, and after deactivation of the catalyst, the catalyst was regenerated as described in regeneration protocol-4.

[0045] Regeneration Protocol-4: The reactor was purged with nitrogen (purity of 99.99 mol.%) at a flow rate of 30 SLPH under same reaction / process condition. The reactor pressure was released to atmosphere pressure and the reactor was purged with N2 (purity 99.99 mol.%) at a flow rate of 30 SLPH by increasing the reactor temperature from 50 °C to 300 °C at the rate of 1 °C / min and holding at 300 °C for 3 hrs (or) until the hydrocarbon content in the purged stream reaches less than 100 ppm. Air containing 2 mol.% of oxygen was introduced at a flow rate of 30 SLPH and the catalyst bed was increased to a temperature of 550 °C at the ramp rate of 0.5 °C / min. Then, air containing 20.9 mol.%of oxygen was introduced at a flow rate of 30 SLPH and the catalyst bed was maintained at a temperature of 550 °C for 5 hours. The airflow was stopped and N2 (purity 99.99 mol.%) was introduced at 30 SLPH and the catalyst bed was cooled to reaction temperature ranging from about 35 °C to about 100 °C. FIG. 4A is a graphical representation of the catalyst bed temperature during another regeneration protocol and FIGs. 4B and 4C are the zoomed-in versions during exotherm.

[0046] FIGS. 1A- 4C demonstrate how the catalyst bed temperature varies over the heating range and reactive gas (air) introduced. FIGS. 1A, 2A, 3A, and 4A represent the overall picture of the catalyst bed temperature and FIGS. IB, 2B, 3B, 3C, 4B, and 4C are the zoomed-in versions during exotherm where air is introduced in the catalyst bed. In all the cases, the thermocouple is placed at the center of the catalyst bed from top to bottom with the gap of 2.5 cm from top of the catalyst bed. Regeneration protocols- 1 and -2 show about a 80 °C raise in catalyst bed temperature, which may cause hotspot formation and make metal particles to agglomerate and leads to reduced catalyst stability. In the case of regeneration protocol-3, a slight reduction in the exotherm in comparison to regeneration protocol-1 and -2 was observed (about 50 °C). This reduction may be due to the introduction of oxygen at the low catalyst bed temperature. In the case of regeneration protocol-4, low exotherm was observed, which is necessary to avoid the hotspot and metal agglomeration. The low exotherm in protocol-4 may be due to low temperature and low oxygen content in the feed and that leads minimized damage to the coating or the egg-shell structure of the rhenium oxide-coated y- alumina-based catalyst and also no structural damage to the rhenium particle size, which was monitored in TEM analysis.

[0047] Based on the various regeneration protocols, the regeneration protocol-4 was selected for regeneration of the rhenium oxide-coated catalyst to maintain its shape, particle size, and alumina properties based on the various characterization. Therefore, the regeneration protocol-4 for multiple reactions and regeneration cycles were evaluated to validate whether the activity of the catalyst is maintained similar to that of fresh catalyst. First, the rhenium oxide-coated catalyst was subjected for WHSV-5 with reaction temperature of 50 °C and other process conditions are represented in the Table-2. FIG. 5 is a graphical representation of the multiple runs of reaction by following the regeneration protocol-4. Once the catalyst is deactivated as shown in FIG. 5, the regeneration protocol-4 was followed, then the same catalyst was subjected for another run. Likewise, 8 different runs were performed to evaluate the catalyst performance. The process conditions for different Runs are shown in Table 2.

[0048] Table 2 process conditions for different runs.

[0049] FIG. 6 shows the comparison of catalytic activity of fresh and 2000 hours of time on stream and 8 times of regenerated catalyst by following the regeneration protocol-4. FIG. 6 clearly indicates that the regenerated catalyst maintains its properties similar to that of the fresh catalyst.

[0050] When ranges are disclosed herein, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, reference to values stated in ranges includes each and every value within that range, even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0051] Other objects, features and advantages of the disclosure will become apparent from the foregoing drawings, detailed description, and examples. These drawings, detailed description, and examples, while indicating specific examples of the disclosure, are given by way of illustration only and are not meant to be limiting. In further examples, features from specific examples may be combined with features from other examples. In further examples, additional features may be added to the specific examples described herein. It should be understood that although the disclosure contains certain aspects, examples, and optional features, modification, improvement, or variation of such aspects, examples, and optional features can be resorted to by those skilled in the art, and that such modification, improvement, or variation is considered to be within the scope of this disclosure.

Claims

Claims1. A method of regenerating a spent rhenium oxide-coated y-alumina- based catalyst, the method comprising: purging a catalyst bed in a reactor with nitrogen at a temperature of 50 °C and at a pressure of 6 barg, the catalyst bed containing spent rhenium oxide-coated y-alumina-based catalyst; releasing the pressure in the reactor to atmosphere pressure; purging the catalyst bed with nitrogen and increasing the temperature from 50 °C to 300 °C and holding at 300 °C; supplying a first stream of air containing oxygen to the catalyst bed and increasing temperature of the catalyst bed to a temperature of 550 °C, the oxygen in the first stream ranging from 1 mol.% to about 3 mol.%; supplying a second stream of air containing oxygen to the catalyst bed and maintaining the catalyst bed at a temperature of 550 °C, the oxygen in the second stream ranging from 15 mol.% to 25 mol.%; reducing temperature of the catalyst bed to a temperature ranging from about 35 °C to about 100 °C; and supplying nitrogen to the catalyst bed to regenerate a rhenium oxide-coated y-alumina-based catalyst.

2. The method of Claim 1, wherein the catalyst bed is purged with 99.99 mol.% pure nitrogen at a temperature at 50 °C.

3. The method of Claim 1, wherein the temperature of the catalyst bed in the presence of nitrogen is increased from 50 °C to 300 °C at a rate of 1 °C / min.

4. The method of Claim 1, wherein the spent rhenium oxide-coated y-alumina-based catalyst bed is maintained at a temperature of 300 °C for a time period ranging from 3 to 10 hours.

5. The method of Claim 1, wherein hydrocarbon content in a purged stream from the reactor is less than 100 ppm.

6. The method of Claim 1, wherein air containing 2 mol.% oxygen is supplied to the spent rhenium oxide-coated y-alumina-based catalyst bed and temperature of the catalyst bed is increased to a temperature of 550 °C.

7. The method of Claim 6, wherein the temperature of the catalyst bed is increased to 550 °C at a ramp rate of 0.5 °C / min when the air containing 2 mol.% of oxygen is supplied to the spentrhenium oxide-coated y-alumina-based catalyst bed.

8. The method of Claim 1, wherein air containing 20.9 mol.% oxygen is supplied to the spent rhenium oxide-coated y-alumina-based catalyst bed and the catalyst bed is maintained at a temperature of 550 °C.

9. The method of Claim 8, wherein the spent rhenium oxide-coated y-alumina-based catalyst bed is maintained at a temperature of 550 °C for a time period ranging from 4 hours to 24 hours.

10. The method of Claim 1, wherein rhenium oxide-coated y-alumina-based catalyst in the catalyst bed comprises y-alumina-based spherical particles ranging from 1.2 millimeters (mm) to 3 mm in diameter.

11. The method of Claim 1, wherein rhenium oxide-coated y-alumina-based catalyst in the catalyst bed comprises y-alumina-based extrudate particles of a size ranging from 1.2 mm to about 3 mm in diameter and from 4 mm to 12 mm in length.

12. The method of Claim 10 or claim 11, wherein the rhenium oxide-coated y-alumina-based catalyst comprises a rhenium coating ranging from 150 micrometers (pm) to 250 pm in thickness.

13. The method of Claim 1, wherein rhenium oxide-coated y-alumina-based catalyst in the catalyst bed comprises rhenium particles in the coating with a particle size ranging from about 0.3 nanometers (nm) to about 1.5 nm.

14. The method of Claim 1, wherein rhenium oxide-coated y-alumina-based catalyst in the catalyst bed contains rhenium oxide in an amount ranging from 4.8 wt.% to 5.6 wt.%.

15. The method of Claim 1, wherein the rhenium oxide-coated y-alumina-based catalyst bed is regenerated for longer than fifty times.

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