Claims:WE CLAIM:
1. A process for preparing a dehydrogenation catalyst, said process comprising the following steps:
(a) obtaining alpha alumina particles;
(b) coating said alpha alumina particles with activated alumina to form a component comprising a layer of the activated alumina over the alpha alumina particles;
(c) hydrating said component to form a hydrated component;
(d) calcining said hydrated component in the presence of air at a pre-determined temperature to allow morphological changes in said layer of activated alumina to obtain core-shell particles comprising a core of said alpha alumina and a shell layer comprising kappa alumina in an amount in the range of 4 wt.% to 6 wt.% of the shell layer and theta alumina in an amount in the range of 15 wt.% to 25 wt.% of the shell layer;
(e) impregnating the shell layer of the core-shell particles with at least one metal to obtain metal impregnated core-shell particles having a metal impregnated shell layer over said core; and
(f) drying and calcining the metal impregnated core-shell particles to obtain the dehydrogenation catalyst.

2. The process as claimed in claim 1, wherein said alpha alumina particles have a diameter in the range of 1.4 mm to 1.6 mm, or wherein said alpha alumina particles are obtained from alpha alumina powder having an average particle size in the range of 10 nm to 12 nm.
3. The process as claimed in claim 1, wherein said coating is carried out by using a binder and activated alumina powder, wherein said binder is at least one selected from the group consisting of water, polyvinyl alcohol, dextrose, and lignin.
4. The process as claimed in claim 1, wherein said hydration is carried out by mixing said component with water.
5. The process as claimed in claim 1, wherein in step (d), said hydrated component is calcined at a ramp rate in the range of 2.5 °C/min to 3.5 °C/min, or wherein said hydrated component is calcined for a time period in the range of 5 hours to 7 hours, or wherein said pre-determined temperature in step (d) of calcination is in the range of 1020 °C to 1060 °C.
6. The process as claimed in claim 1, wherein prior to step (e) of the impregnation, said core-shell particles are gradually cooled, at a rate in the range of 4 °C/min to 10 °C/min.
7. The process as claimed in claim 1, wherein step (e) of impregnation is done by contacting the shell layer of the core-shell particles with a solution of said at least one metal.
8. The process as claimed in claim 1, wherein in step (e) of impregnation, the shell layer of the core-shell particles is impregnated with a plurality of metals by contacting the shell layer of said core-shell particles with a solution of the plurality of metals.
9. The process as claimed in claim 1, wherein the shell layer of the core-shell particles is impregnated with a plurality of metals by reiterating the steps (e), and (f) to impregnate at least one metal of the plurality of metals in the shell layer in each iteration.
10. The process as claimed in claim 1, wherein said metal is at least one selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal, and group V metal.
11. The process as claimed in claim 1, wherein the shell layer of the core-shell particles is impregnated with at least one element of group VIA selected from the group consisting of sulfur, selenium and tellurium, or wherein the shell layer of the core-shell particles is impregnated with at least one halogen element selected from the group consisting of fluorine, chlorine, bromine and iodine.
12. The process as claimed in claim 1, wherein in step (f), the metal impregnated core-shell particles are dried in the presence of air and calcined at a temperature in the range of 600 °C to 700 °C for a time period in the range of 3 hours to 5 hours.
13. A dehydrogenation catalyst comprising metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina, wherein the metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt% to 6 wt% of the shell layer and theta alumina in an amount in the range of 15 wt% to 25 wt% of the shell layer, and wherein the metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal, and group V metal.
14. The catalyst as claimed in claim 13, wherein said core has a diameter in the range of 1.4 mm to 1.6 mm.
15. The catalyst as claimed in claim 13, wherein the metal impregnated shell layer of the catalyst has a thickness in the range of 0.2 mm to 0.4 mm, and wherein the crystallinity of the metal impregnated shell layer is in the range of 80% to 90%.
16. The catalyst as claimed in claim 13, the metal impregnated shell layer of the core shell particles further comprises gamma alumina in an amount in the range of 3 wt.% to 5 wt.% and delta alumina in an amount in the range of 1 wt.% to 3 wt.% with respect to the shell layer.
17. The catalyst as claimed in claim 13, wherein said alkali metal is at least one selected from the group consisting of sodium, lithium and potassium; wherein said alkaline earth metal is at least one selected from the group consisting of magnesium, calcium and barium; wherein said group VIII metal is at least one selected from the group consisting of platinum, nickel and palladium; wherein said group IVA metal is selected from tin and germanium; and wherein said group V metal is selected from niobium and tantalum.
18. The catalyst as claimed in claim 13, wherein the metal impregnated shell layer further comprises at least one element of group VIA selected from the group consisting of sulfur, selenium and tellurium, or wherein the metal impregnated shell layer further comprises at least one halogen element selected from the group consisting of fluorine, chlorine, bromine and iodine.
19. The catalyst as claimed in claim 13 or claim 18, wherein the total amount of metals in the dehydrogenation catalyst is in the range of 0.05 wt.% to 2.0 wt.% of the catalyst, or wherein the amount of the halogen element in the dehydrogenation catalyst is in the range of 0.1 wt.% to 1 wt.% of the catalyst, or wherein the amount of group VIA element is in the range of 0.1 wt.% to 1 wt.% of the catalyst.
20. The catalyst as claimed in claim 13, wherein the catalyst has a surface area in the range of 20 m2/g to 30 m2/g, a surface acidity in the range of 0.30 to 0.40 µmol per g of ammonia, and a pore diameter in the range of 320 A° to 380 A°.
21. A process for dehydrogenation of hydrocarbons, said process comprising treating a stream of hydrocarbons with a dehydrogenation catalyst in a reactor, at a temperature in the range of 450 °C to 500 °C in the presence of hydrogen, to obtain a stream of unsaturated hydrocarbons and a spent catalyst, wherein the dehydrogenation catalyst comprises metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina, wherein the metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt% to 6 wt% of the shell layer and theta alumina in an amount in the range of 15 wt% to 25 wt% of the shell layer, and wherein the metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal, and group V metal.
22. The process as claimed in claim 21, wherein the molar ratio of the hydrocarbon to hydrogen is in the range of 1:5 to 1:7.
23. The process as claimed in claim 21, wherein the coke content in said spent catalyst is in the range of 0.01 wt.% to 0.10 wt.% of the spent catalyst, or wherein the spent catalyst is recycled and reused.
, Description:FIELD
The present disclosure relates to a process for preparation of a dehydrogenation catalyst and the catalyst obtained therefrom.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.
Bromine number refers to the amount of bromine in grams absorbed by 100 grams of a sample, indicating the degree of unsaturation.
Alpha (a) alumina refers to the most stable phase/form of alumina that has the least chemical activity amongst other phases of alumina.
Gamma (?) alumina, delta (d) alumina, theta (?) alumina or kappa (?) alumina refer to meta-stable forms of alumina that have relatively higher chemical activity than alpha alumina.
Activated alumina refers to relatively active form of alumina that comprises meta-stable phases/forms such as Gamma (?) alumina, Delta (d) alumina, Theta (?) alumina or Kappa (?) alumina.
Core-shell particles refer to a core of alpha alumina surrounded by a shell layer comprising a mixture of metastable forms of alumina such as kappa alumina, theta alumina, delta alumina and gamma alumina .
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Dehydrogenation of hydrocarbons is an important chemical reaction for manufacture of valuable intermediates such as unsaturated hydrocarbons, aromatics and high octane gasoline. Conventionally, gamma-alumina support impregnated with metals is used as a catalyst for dehydrogenation. However, these catalysts tend to get deactivated early due to the formation of coke which masks the active metals in the catalyst. One of the primary reasons for the coke formation is the tendency of carbon-carbon (C-C) bonds to break, primarily due to the acidic nature of the catalyst support. This not only reduces the overall yield of the reaction but also lowers the stability and the activity of the catalyst.
There is, therefore, felt a need for a process for preparing dehydrogenation catalyst that mitigates the drawbacks mentioned hereinabove.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a catalyst for dehydrogenation that has comparatively better stability and activity than conventional catalysts.
Still another object of the present disclosure is to provide a recyclable catalyst with comparatively lesser surface acidity than conventional catalysts.
Yet another object of the present disclosure is to provide a simple and economical process for the preparation of a dehydrogenation catalyst.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a process for preparing a dehydrogenation catalyst. The process comprises obtaining alpha alumina particles and then coating the alpha alumina particles with activated alumina to form a component comprising a layer of the activated alumina over the alpha alumina particles. The component is hydrated to form a hydrated component. The hydrated component is calcined in the presence of air at a predetermined temperature to allow morphological changes in the layer of activated alumina to obtain core-shell particles comprising a core of the alpha alumina and a shell layer comprising kappa alumina in an amount in the range of 4 wt.% to 6 wt.% of the shell layer and theta alumina in an amount in the range of 15 wt.% to 25 wt.% of the shell layer. The shell layer of the core-shell particles is impregnated with at least one metal to obtain metal impregnated core-shell particles having a metal impregnated shell layer over the core. The metal impregnated core-shell particles are dried and calcined to obtain the dehydrogenation catalyst.
The present disclosure further provides a dehydrogenation catalyst comprising metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina, wherein the metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt% to 6 wt% of the shell layer and theta alumina in an amount in the range of 15 wt% to 25 wt% of the shell layer and, wherein the metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal, and group V metal.
In an embodiment, the metal impregnated shell layer further comprises at least one element of group VIA selected from the group consisting of sulfur, selenium and tellurium. In an embodiment, the metal impregnated shell layer further comprises at least one halogen element selected from the group consisting of fluorine, chlorine, bromine and iodine.
The present disclosure still further provides a process for dehydrogenation of hydrocarbons, wherein the process comprises a step of treating a stream of hydrocarbons with the dehydrogenation catalyst in a reactor, at a temperature in the range of 450 °C to 500 °C in the presence of hydrogen, to obtain a stream of unsaturated hydrocarbons and a spent catalyst, wherein the dehydrogenation catalyst comprises metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina, wherein the metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt% to 6 wt% of the shell layer and theta alumina in an amount in the range of 15 wt% to 25 wt% of the shell layer, and wherein the metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal, and group V metal.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1(A) illustrates the Transmission Electron Microscopic (TEM) image of catalyst A, prepared in accordance with the present disclosure;
Figure 1(B) illustrates the TEM image of reference catalyst B; and
Figure 2 illustrates the graph for the change in bromine number after 1 hour and 2 hours of dehydrogenation reaction using catalysts prepared with alumina support, calcined at different temperatures, in accordance with the present disclosure.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
The conventional catalysts used for dehydrogenation of hydrocarbons comprise gamma alumina impregnated with metals. However, the acidic nature of the gamma alumina leads to side-reactions such as carbon-carbon (C-C) bond breaking, thereby leading to the formation of coke. The coke thus formed tends to mask the active metals in the catalyst, thus impacting the stability and the performance of the catalyst.
The present disclosure provides a dehydrogenation catalyst and a process for preparing the same. The process is simple and leads to the formation of an efficient catalyst that has comparatively high selectivity and leads to comparatively lesser formation of coke than conventional catalysts.
In one aspect, the present disclosure provides a process for preparing a dehydrogenation catalyst. The process is described in detail herein below. Firstly, alpha alumina particles are obtained.
The alpha alumina particles are obtained from alpha alumina powder having an average particle size in the range of 10 nm to 12 nm. In an embodiment, the alpha alumina powder has an average particle size of 11 nm.
In an embodiment, the alpha alumina particles have a spherical shape.
Typically, the alpha alumina particles have a diameter in the range of 1.4 mm to 1.6 mm. In an embodiment, the diameter of the alpha alumina particles is 1.5 mm.
In the next step of the process, the alpha alumina particles are coated with activated alumina to form a component comprising a layer of the activated alumina over the alpha alumina particles.
Typically, the layer of activated alumina has a thickness in the range of 0.2 mm to 0.4 mm. In an embodiment, the thickness of the layer is 0.3 mm.
The alpha (a) alumina is the most stable phase/form of alumina but also has the least chemical activity amongst other phases of alumina, whereas the activated alumina is relatively active form of alumina that comprises meta-stable phases/forms such as Gamma (?) alumina, Delta (d) alumina, Theta (?) alumina or Kappa (?) alumina. The alpha alumina is relatively more chemically inert which is used as a support material for the core, whereas the activated alumina is relatively more chemically active, which forms the outside layer.
The step of coating is carried out by using a binder and activated alumina powder. The binder is at least one selected from the group consisting of water, polyvinyl alcohol, dextrose, and lignin. In an exemplary embodiment, the binder is water. In an embodiment, the coating is carried out by simultaneous spraying of activated alumina powder and an aqueous binder solution, over the alpha alumina particles.
The so obtained component is hydrated to form a hydrated component. The hydrated component is calcined in the presence of air at a pre-determined temperature to allow morphological changes in the layer of activated alumina to obtain core-shell particles. The core shell particles comprise a core of the alpha alumina and a shell layer comprising kappa alumina in an amount in the range of 4 wt.% to 6 wt.% of the shell layer and theta alumina in an amount in the range of 15 wt.% to 25 wt.% of the shell layer.
The hydration of the component is necessary for improving the mechanical strength of the final catalyst. The hydration is carried out by mixing the so-obtained component with water.
In an embodiment, the pre-determined temperature is calcined in the range of 1020 °C to 1060 °C. In an exemplary embodiment, the step of calcining the hydrated component is carried out at 1050 °C.
The calcination process changes the morphology of the activated alumina such that kappa alumina (?-Al2O3) and theta alumina (?-Al2O3) are formed in the shell layer. Theta alumina and kappa alumina are relatively inert and more crystalline in nature in comparison to other phases of alumina which allows better dispersion of metals in the matrix and higher stability during the sintering process. The formation of kappa alumina is an indication that, theta alumina formed is not further completely converted to alpha alumina. In addition, the formation of kappa alumina and theta alumina result in a catalyst with shell layer having relatively lesser surface acidity, thereby ensuring less cracking of the C-C bonds and hence formation of relatively lesser amount of coke.
Further, the temperature range of 1020 °C to 1060 °C for calcination of the hydrated component is significant because below 1020 °C, the crystallinity of the shell layer is relatively reduced, whereas above 1060 °C, the amount of kappa alumina and theta alumina in the shell layer decreases considerably, thus increasing the amount of alpha alumina, which is not desirable with respect to the present disclosure. Further, the catalyst obtained by the calcination of alumina at the temperature range of 1020 °C to 1060 °C, has desired properties such as mechanical integrity, pore texture, pore size, surface acidity and morphology. The calcination done beyond 1060 °C tends to reduce the crushing strength and pore volume of the catalyst.
The calcination is carried out in the presence of air to eliminate the binder used during the coating step, to generate relatively higher porosity and to prevent sintering.
In an exemplary embodiment, the shell layer of the core-shell particles comprises 5 wt.% of kappa alumina and 19 wt% of theta alumina, with respect to the shell layer.
Typically, the hydrated component is calcined for a time period in the range of 5 hours to 7 hours.
In an exemplary embodiment, the hydrated component is calcined at 1050 °C for 6 hours.
Typically, the hydrated component is calcined at a ramp rate in the range of 2.5 °C/min to 3.5 °C/min. In an exemplary embodiment, the hydrated component is calcined at a ramp rate of 3 °C/min until a temperature of 1050 °C is attained.
In the next step of the process, the shell layer of the core-shell particles are impregnated with at least one metal to obtain metal impregnated core-shell particles. The metal impregnated core-shell particles have a metal impregnated shell layer over the core.
Typically, the metal impregnation of the shell layer of the core-shell particles is done by contacting the shell layer of the core-shell particles with a solution of the metal. In an embodiment, the metal impregnation of the shell layer of the core-shell particles is done by using wet impregnation technique.
The metal is at least one selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal and group V metal.
In an embodiment, the alkali metal is at least one selected from the group consisting of sodium, lithium and potassium; the alkaline earth metal is at least one selected from the group consisting of magnesium, calcium and barium; the group VIII metal is at least one selected from the group consisting of platinum, nickel and palladium; the group IVA metal is selected from tin and germanium and the group V metal is selected from niobium and tantalum.
In an exemplary embodiment, the alkali metal is sodium, wherein the precursor is sodium chloride (NaCl).
In an exemplary embodiment, the alkaline earth metal is magnesium, wherein the precursor is magnesium nitrate (MgNO3).
In an embodiment, the group VIII metal is platinum, wherein the precursor is hexachloroplatinic acid.
In an embodiment, the group IVA metal is tin, wherein the precursor is tin chloride (SnCl2).
In an embodiment, the group V metal is niobium, wherein the precursor is niobium chloride (NbCl3).
In an exemplary embodiment, the shell layer of the core-shell particles is impregnated with metals comprising magnesium, niobium, platinum, tin and sodium.
In an embodiment, the shell layer of the core-shell particles is further impregnated with at least one element of group VIA selected from the group consisting of sulfur, selenium and tellurium. In an exemplary embodiment, the group VIA element is sulfur, wherein the precursor of element of group VIA is thiomalic acid.
In an embodiment, the shell layer of the core-shell particles is impregnated with at least one halogen element selected from the group consisting of fluorine, chlorine, bromine and iodine. In an exemplary embodiment, the halogen element is chlorine.
In an embodiment, prior to the step of impregnation, the core-shell particles are gradually cooled, at a rate in the range of 4 °C/min to 10 °C/min. In an exemplary embodiment, the core-shell particles are cooled at a rate of 5 °C/min.
The metal impregnated core-shell particles are dried and calcined to obtain the dehydrogenation catalyst.
The metal impregnated core-shell particles are dried in the presence of air and calcined at a temperature in the range of 600 °C to 700 °C for a time period in the range of 3 hours to 5 hours. In an exemplary embodiment, the calcination of the metal impregnated core-shell particles is done at 640 °C for 4 hours.
In one embodiment, the shell layer of the core-shell particles are impregnated with a plurality of metals by contacting the shell layer of the core-shell particles with a solution of the plurality of metals.
In another embodiment, the shell layer of the core-shell particles are impregnated with a plurality of metals by reiterating the steps of impregnation of the metal, drying and calcination, to impregnate at least one metal of the plurality of metals in the shell layer, in each iteration.
In an exemplary embodiment, the shell layer of the core-shell particles are impregnated with a solution of magnesium nitrate by wet impregnation. The magnesium impregnated core-shell particles are dried and then calcined at 640 °C for 4 hours. In a second step of impregnation, the magnesium impregnated core-shell particles are impregnated with a solution of niobium chloride by wet impregnation, followed by drying and calcination at 640 °C for 4 hours. In a third step of impregnation, magnesium and niobium impregnated core-shell particles are impregnated with a mixture of salt solutions of platinum, tin, sodium, sulfur and chloride to obtain metal impregnated core-shell particles, wherein the shell layer is impregnated with sodium, magnesium, niobium, tin, platinum, sulfur and chlorine. The metal impregnated core-shell particles are dried in air and calcined at 640 °C for 4 hours, to obtain the dehydrogenation catalyst.
In another aspect, the present disclosure provides a dehydrogenation catalyst comprising metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina. The metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt.% to 6 wt.% of the shell layer and theta alumina in an amount in the range of 15 wt.% to 25 wt.% of the shell layer. The metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal and group V metal.
Typically, the core of the catalyst has a diameter in the range of 1.4 mm to 1.6 mm. In an embodiment, the core of the catalyst has a diameter of 1.5 mm.
In an embodiment, the shell layer of the catalyst has a thickness in the range of 0.2 mm to 0.4 mm, wherein the crystallinity of the shell layer is in the range of 80 % to 90 %. In an exemplary embodiment, the shell layer of the catalyst has a thickness of 0.3 mm. In an exemplary embodiment, the crystallinity of the shell layer is 83%.
The catalyst has a surface area in the range of 20 m2/g to 30 m2/g, a surface acidity in the range of 0.30 to 0.40 µmol per g of ammonia, and a pore diameter in the range of 320 A° to 380 A°.
In an exemplary embodiment, the catalyst has the surface area of 21 m2/g, the surface acidity of 0.35 µmol per g of ammonia, and the pore diameter of 373 A°.
In an embodiment, the shell layer of the core shell particles comprises at most 75 wt.% of alpha alumina, with respect to the shell layer. In an exemplary embodiment, the shell layer of the core shell particles comprises 71 wt.% of alpha alumina, with respect to the shell layer.
In an embodiment, the shell layer of the core shell particles further comprises gamma alumina in an amount in the range of 3 wt.% to 5 wt.% and delta alumina in an amount in the range of 1 wt.% to 3 wt.% with respect to the shell layer. In an exemplary embodiment, the shell layer of the core shell particles further comprises gamma alumina in an amount of 4 wt.% with respect to the shell layer and delta alumina in an amount of 1 wt.% with respect to the shell layer.
The alkali metal is at least one selected from the group consisting of sodium, lithium and potassium. In an exemplary embodiment, the alkali metal is sodium.
The alkaline earth metal is at least one selected from the group consisting of magnesium, calcium and barium. In an exemplary embodiment, the alkaline earth metal is magnesium.
The group VIII metal is at least one selected from the group consisting of platinum, nickel and palladium. In an exemplary embodiment, the group VIII metal is platinum.
The group IVA metal is selected from tin and germanium. In an exemplary embodiment, the group IVA metal is tin.
The group V metal is selected from niobium and tantalum. In an exemplary embodiment, the group V metal is niobium.
In an embodiment, the metal impregnated shell layer of the dehydrogenation catalyst comprises magnesium, niobium, platinum, tin and sodium.
The metal impregnated shell layer further comprises at least one element of group VIA selected from the group consisting of sulfur, selenium and tellurium. In an exemplary embodiment the metal impregnated shell layer comprises sulfur.
In an embodiment, the metal impregnated shell layer further comprises at least one halogen element selected from the group consisting of fluorine, chlorine, bromine and iodine.
The total amount of metals in the dehydrogenation catalyst is in the range of 0.05 wt.% to 2.0 wt.% of the catalyst. In an exemplary embodiment, the total amount of metals are 1.7 wt.% of the catalyst.
In an embodiment, the amount of the halogen element in the dehydrogenation catalyst is in the range of 0.1 wt.% to 1 wt.% of the catalyst. In an exemplary embodiment, the amount of halogen element is 0.3 wt.% of the catalyst.
In an embodiment, the amount of group VIA element is in the range of 0.1 wt.% to 1 wt.% of the catalyst. In an exemplary embodiment, the amount of group VIA element is 0.5 wt.% of the catalyst.
In yet another aspect, the present disclosure provides a process for dehydrogenation of hydrocarbons. The process comprises treating a stream of hydrocarbons with a dehydrogenation catalyst in a reactor, at a temperature in the range of 450 °C to 500 °C in the presence of hydrogen, to obtain a stream of unsaturated hydrocarbons and a spent catalyst, wherein the dehydrogenation catalyst comprises metal impregnated core-shell particles having a metal impregnated shell layer over a core of alpha alumina, wherein the metal impregnated shell layer comprises kappa alumina in an amount in the range of 4 wt% to 6 wt% of the shell layer and theta alumina in an amount in the range of 15 wt% to 25 wt% of the shell layer, and wherein the metal impregnated shell layer comprises at least one metal selected from the group consisting of alkali metal, alkaline earth metal, group VIII metal, group IVA metal and group V metal.
In one embodiment, the hydrocarbon is n-decane. In another embodiment, the hydrocarbon is n-dodecane.
In an embodiment, the temperature maintained during the dehydrogenation reaction is 475 °C.
The pressure during the dehydrogenation reaction is in the range of 1 atm to 2 atm.
The stream of hydrocarbons is introduced into the reactor at a flow rate of 350 mL/min to 400 mL/min. In an exemplary embodiment, the flow rate is 380 mL/min.
The dehydrogenation reaction is carried out for a time period in the range of 1 hour to 8 hours. In an exemplary embodiment, the dehydrogenation reaction is carried out for 7 hours.
The molar ratio of the hydrocarbon to the hydrogen is in the range of 1:1.5 to 1:7. In one exemplary embodiment, the molar ratio is 1:6. In another exemplary embodiment, the ratio is 1:2.
In an embodiment, the spent catalyst is recycled and reused. The deactivation of the catalyst of the present disclosure is lesser than conventional catalysts, indicating better stability and lower coke content.
The coke content in the spent catalyst is in the range of 0.01 wt.% to 0.10 wt.% of the spent catalyst. In an exemplary embodiment, the coke is formed in an amount of 0.08 wt. % of the spent catalyst.
The process of the present disclosure provides a catalyst that leads to comparatively lesser coke formation during the dehydrogenation reaction than conventional catalysts. The catalyst is stable, active and is also recyclable, and is prepared by a simple and effective process.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
Experiment 1: Preparation of catalyst A
Step 1a: Preparation of core-shell particles
Alpha alumina powder having average particle size of 11 nm, was used to obtain spherical particles having an average diameter of 1.5 mm (as determined by SEM). The alpha alumina particles (100 g) were coated with activated alumina by simultaneous spraying of aqueous solution of binder (polyvinyl alcohol) (0.5 wt.% mixed with 106 mL of distilled water) and activated alumina powder (70g). The coating was carried out in a rotating pan till 0.3 mm thick layer of the activated alumina (as determined by SEM) was obtained over the alpha alumina particles to form a component. The component was hydrated by mixing the component with water to obtain a hydrated component. The hydrated component was then calcined to attain a temperature of 1050 °C in presence of air, at a ramp rate of 3 °C/min. The attained temperature was maintained for 6 hours to obtain core-shell particles comprising a core of alpha alumina coated with a shell layer comprising kappa alumina in an amount of 5 wt.% of the shell layer and theta alumina in an amount of 19 wt.% of the shell layer. The core-shell particles so obtained were gradually cooled.
Step 1b: Preparation of catalyst A comprising metal impregnated core-shell particles
The core-shell particles, as obtained in Experiment 1 (Step 1a) were subjected to impregnation of metals by using the incipient wetness technique. In the first step of impregnation, a solution of magnesium nitrate (MgNO3) was employed to impregnate the core-shell particles by wet impregnation. Thereafter the core-shell particles thus impregnated was dried and then calcined at 640° C for 4 hours. The second impregnation was carried out by using a solution of Niobium chloride (NbCl3) followed by drying and then calcining at 640° C for 4 hours. The third impregnation was carried out with the salt solutions of platinum (Pt), tin (Sn) and sodium (Na), by using the precursors including H2PtCl6, SnCl2, NaCl, HCl and Thiomalic acid (TMA), to obtain the metal impregnated core-shell particles. The metal impregnated core-shell particles so obtained were dried and then calcined at 640° C for 4 hours, to obtain a dehydrogenation catalyst.
The metal concentration in the catalyst A, along with other elements (or precursors), are depicted in Table 1.
Table 1: Amount of metals or elements (precursors) in catalyst A
Amount of metals/precursors Pt (wt%) Sn (wt%) Na (wt%) Mg (wt%) Nb
(wt%) Cl
(wt %) TMA (wt%)
Catalyst A 0.17 0.21 0.30 0.50 0.05 0.3 0.5

Experiment 2: Preparation of reference catalyst B
The procedure as given in Experiment 1 was repeated except that the hydrated component, after hydration, was calcined at 700 °C, instead of 1050 °C, to obtain a reference catalyst B.
Commercial catalyst C
A commercial catalyst C was used for comparison of properties.
The data related to the catalyst properties are depicted in Table 2.
Table 2: Comparison of properties of catalyst A, reference catalyst B and commercial catalyst C
Properties Catalyst A
(Present disclosure) Reference Catalyst B Commercial
Catalyst C Criterion/technique (Standard method or Instrument used)
Pore Volume (in cc/g) 0.51 0.54 0.25 Water pore volume (Vacuum pump and desiccator)
Bulk Density (g/cc) 0.80 0.77 0.81 Tap Bulk Density (Tap Density Apparatus TD1025)
Crushing Strength (in kg) 1.40 1.60 3.20 Single Pellet (Crush Strength Equipment PCS 100402)
Attrition loss (in %) 0.24 0.30 0.20 Tumbling method (ASTM 4058)
BET Surface Area (in m2/g) 21 47 34 Nitrogen Adsorption (ASAP2010)
BJH desorption cumulative pore volume (in cm3/g) 0.22 0.35 0.15 Nitrogen Adsorption (ASAP2010)
BJH desorption avg. pore diameter (4V/A) (in A°) 373 232 150 Nitrogen Adsorption (ASAP2010)
Platinum Metal Dispersion (in %) 55 32 59 Hydrogen chemisorption (Chemisorption Unit)
Surface acidity (in µmol of NH3/g) 0.35 0.44 0.47 NH3 Chemisorption/desorption (Chemisorption Unit)
Coke content in spent catalyst, wt % 0.08 0.19 0.29 CHNS analyser (Vario Macro Cube)

It could be observed from Table 2 that the catalyst A, prepared in accordance with the present disclosure, has comparatively lower surface acidity than the reference catalysts B and C. The coke content after reaction is also lower in Catalyst A as compared to the reference catalysts B and C (as observed in Table 2). Lower acidity is a crucial factor in reducing the coke formation during the dehydrogenation of hydrocarbons.
Further, the pore diameter was also higher for catalyst A in comparison to the reference catalysts B and C. A higher pore diameter resulted in better control over distribution of platinum solution over alumina surface during impregnation stage. This ultimately resulted in better metal dispersion than the catalyst B (as observed in Table no. 2), which is suitable for better accessibility of reactant molecules during dehydrogenation reaction of alkanes.
Further, the crushing strength and attrition loss indicate the mechanical strength of the catalyst. The crushing strength and attrition loss of catalyst A are comparable with that of catalyst B.

Experiment 3: Study of effect of calcination temperature on the morphology of the shell layer of catalyst
The hydrated component [prior to calcination in experiment 1 (step 1a)] was subjected to calcination at different temperatures, to study the formation of various phases in the activated alumina after calcination. The phase composition (percentage of each type of alumina) was understood by using XRD technique. The resulting trend observed and the corresponding surface properties are provided in Table 3.
Table 3: Change in morphology of the activated alumina in the hydrated component at various calcination temperatures
Calcination temperature of the hydrated component
(in °C) Crystallinity (in %) ?-Al2O3 (%) ?-Al2O3 (%) ?-Al2O3 (%) ?- Al2O3 (%) a-Al2O3 (%) BET SA* (m2/gm) BJH PV** (cm3/gm) BJH Pore Diameter (Å)
700 67 42 17 13 7 20 48 0.34 231
880 67 28 10 27 9 26 50 0.36 221
1000 73 3 5 28 11 52 41 0.39 297
1025 80 4 1 20 5 70 23 0.22 340
1050 83 4 1 19 5 71 21 0.25 373
1075 87 2 0 13 4 82 17 0.16 362
1150 90 0 0 3 0 97 7 0.04 431
1350 93 0 0 0 0 100 4 0.01 265
* BET SA - Brunauer-Emmett-Teller (BET) surface area measurements
**BJH PV - Barrett-Joyner-Halenda (BJH) pore volume measurements

It was observed that the activated alumina in the hydrated component, when calcined at high temperatures around 1050 °C, show comparatively higher crystallinity, greater surface area and higher percentage of theta and kappa alumina, in comparison to the catalysts calcined at relatively lower temperatures (around 700 °C). The activated alumina in the hydrated component [experiment 1 (step 1a)] is morphologically altered to form kappa alumina in an amount of 5 wt.% of the shell layer and theta alumina in an amount of 19 wt.% of the shell layer.
Experiment 4: Transmission electron microscope (TEM) analysis
The catalysts A, B and C were subjected to TEM analysis using Transmission Electron Microscope Titan 60-300. The TEM images for catalysts A and B are provided in Figures 1A and 1B respectively. It could be observed that the catalyst A has less number of larger particles, comparatively better dispersion and improved hydrothermal sintering ability than catalyst B, thereby indicating that the catalyst A has better characteristics than catalyst B.
Experiment 5: Measurement of sintering stability
The catalysts A, B and C were tested for the sintering stability by exposing fresh catalyst to 40000 ppm of moisture for one week. The catalyst thus obtained was compared for its activity with the corresponding fresh catalyst. The results obtained are as shown in Table 4.
Table 4: Comparison of sintering stability of catalyst A with reference catalysts B and C
Bromine number in terms of activity Catalyst A
(Present disclosure) Reference Catalyst B Commercial
Catalyst C
Before sintering (fresh catalyst) 21.6 20.4 21.5
After sintering 19.6 15.6 16.5
Drop in sintering stability (in %) 9 24 23

As observed in Table 4, the catalyst of the present disclosure (catalyst A), exhibits better sintering stability than the reference catalysts B and C.

Experiment 6: Dehydrogenation of n-decane using catalyst A, reference catalysts B and C
A stream of n-decane was introduced in a fixed bed reactor comprising catalyst A of the present disclosure at a flow rate of 380 mL/min, in the presence of hydrogen. The molar ratio of hydrogen to hydrocarbon (n-decane) was 6. The stream of n-decane was converted into a mixture of mono-olefins, diolefins and aromatic compounds at a reaction temperature of 475 °C and pressure of 1 atm. The samples of the reaction mixture were withdrawn at several reaction times and the bromine number was measured in terms of catalyst activity for 1 and 2 hours respectively as given in Table 5. Figure 2 illustrates the graph for the change in bromine number after 1 hour and 2 hours of dehydrogenation, using catalysts prepared with alumina that are calcined at different temperatures. It could be seen from Figure 2, that maximum activity is attained when calcination of alumina is done at 1050 °C.
Table 5: Comparison of properties of catalyst A, B and C
Bromine number after Catalyst A
(Present disclosure) Reference Catalyst B Commercial
Catalyst C
1st hour 24.1 21.5 22.1
2nd hour 23.5 19.5 20.1
As observed in Table 5, in case of the catalyst A, the product mixture obtained after dehydrogenation has higher bromine number, in comparison to the product mixture obtained by using the reference catalysts B and C. Bromine number is the amount of bromine in grams absorbed by 100 grams of a sample, indicating the degree of unsaturation. The higher bromine number obtained by using catalyst A represents higher amounts of unsaturated products formed, thereby indicating greater transformation of n-decane to unsaturated products. As the reaction proceeds under optimum process conditions, the activity decreases with time. Due to that, the bromine number decreases for all the catalysts (A, B and C) after the second hour, although the drop in bromine number after the second hour is relatively lesser in case of catalyst A than reference catalysts B and C.
The above conclusion was further confirmed by measuring the composition of the product mixture obtained after dehydrogenation of n-decane (as described in Experiment 3) is as illustrated in Table 6.
Table 6: Product obtained after dehydrogenation of n-decane
Hours Percentage conversion after first hour Percentage conversion after second hour
Composition Mono-olefins Di olefin Aromatics Mono-olefins Di olefin Aromatics
Catalyst A 81.9 13.9 4.3 79.9 15.3 5.0
Catalyst B 74.0 14.8 10.9 71.0 16.6 12.5
Commercial Catalyst C 78.2 14.9 7.0 78.7 16.3 5.2

It was observed from Table 6 that the desired mono-olefins selectivity of catalyst A was significantly better in comparison to the reference catalyst B and the commercial catalyst C.
The formation of aromatics is one of the reasons for the catalyst deactivation during the dehydrogenation reaction. It was observed that catalyst A was deactivated lesser than catalysts B and C, as indicated by relatively lesser amount of aromatics formed when catalyst A is used.
Experiment 7: Dehydrogenation of n-dodecane and measurement of bromine number and deactivation constant
In order to study catalyst deactivation, the operating parameters such as hydrogen to hydrocarbon ratio was kept relatively low and the reaction temperature was maintained relatively high. The catalysts A, B and C were evaluated in the dehydrogenation reaction of n-dodecane, in a fixed bed reactor for 7 hours. The molar ratio of hydrogen to n-dodecane was 2, the reaction temperature was 490 °C, pressure was 1.3 atm and the flow rate (LHSV) was 26 per hour.
Bromine number evaluated for sample withdrawn after each hour, is provided in Table 7. The deactivation rate was obtained from the value of bromine number drawn after 1st hour and 7th hour.
Table 7: Bromine number evaluated after dehydrogenation of n-dodecane
Bromine number Catalyst A Reference catalyst B Commercial catalyst C
After 1st hour 33.4 30.9 30.1
After 3rd hour 30.8 25.9 25.4
After 5th hour 28.9 24.4 20.4
After 7th hour 27.7 22.9 19.3
Drop in bromine number 5.7 8 10.8
Deactivation constant (in %) 17.1 25.9 35.9

As observed in Table 7, the deactivation constant of the catalyst A of the present disclosure was relatively low in comparison to the reference catalysts B and C, thereby indicating that the catalyst A has relatively better stability than catalysts B and C.
Thus, the catalyst A prepared in accordance with the present disclosure has comparatively higher activity, better mono olefin selectivity and better stability. The catalyst of the present disclosure performs better even under severe process conditions and leads to lower coke formation.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing a dehydrogenation catalyst:
• that is simple and economical;
• that provides a dehydrogenation catalyst having improved characteristics, better activity and stability than conventional catalysts; and
• that provides a dehydrogenation catalyst having comparatively lesser surface acidity that leads to lesser coke generation during dehydrogenation in comparison to the conventional catalysts.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation