Claims:1. A two-step spray impregnation process for preparing a catalyst for hydrodesulfurization of hydrocarbon fuels selected from Naphtha, Gasoline or Diesel, wherein, the process comprising steps of:
a first impregnation step of preparing a P-Mo-Alumina complex by loading a first spray solution on a calcined alumina support, wherein, the first spray solution comprises Molybdenum (Mo), Phosphorous (P) and at least one chelating agent; and
a second impregnation step of preparing a P-Mo-Ni loaded alumina by loading a second spray solution on the said P-Mo-Alumina complex, wherein, the said second spray solution comprises Nickel (Ni) and at least one chelating agent.

2. The process as claimed in claim 1, wherein, the first impregnation step further comprises aging the said P-Mo-Alumina complex at ambient room conditions for 1-5 hours, and drying at 90°C.

3. The process as claimed in claim 2, wherein, the said P-Mo-Alumina complex is calcined at 500°C.

4. The process as claimed in claim 1, wherein, the loading of the first spray solution on a calcined alumina support is done at a pH of 5-5.2.

5. The process as claimed in claim 1, wherein, the second impregnation step further comprises drying the P-Mo-Ni loaded alumina.

6. The process as claimed in claim 1, wherein, the at least one chelating agent is selected from an organic acid having -COOH functional group, amino carboxylic acid –NH2-COOH, phosphino carboxylic acid –PO4-COOH, thio phospho amino carboxylic acid –SH-NH2-COOH, hydroxamic acid -NOH-C=O or thio amino carboxylic acid –SH-NH2-COOH, or a combination thereof.

7. The process as claimed in claim 6, wherein, the at least one chelating agent is selected from acid group having citric acid (CA), nitrilo triacetic acid (NTA), phosphino carboxylic acid, phospho serine, aceto hydroxamic acid, thio L-aspartic acid, or a combination thereof.

8. The process as claimed in claim 7, wherein, the at least one chelating agent is selected from citric acid (CA), or a combination of citric acid (CA) with at least one acid selected from nitrilo triacetic acid (NTA), phosphino carboxylic acid, phospho serine, aceto hydroxamic acid, thio L-aspartic acid.

9. The process as claimed in claim 1, wherein, the Molybdenum (Mo) is selected from one of ammonium heptamolybdate, molybdophosphic acid, molybdenum oxide, molybdenum chloride, or a combination thereof.

10. The process as claimed in claim 1, wherein, the Phosphorous (P) is selected from Phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, hypophosphoric acid, or a combination thereof.

11. The process as claimed in claim 1, wherein, the Nickel (Ni) is selected from Nickel acetate, nickel sulfate, nickel acetylacetonate, nickel chloride, nickel carbonate, or a combination thereof.

12. A dispersed hydrotreating catalyst comprising:
phosphorous oxide in the range of 4-9 weight percentage with respect to the total weight of the catalyst;
molybdenum oxide in the range of 10-30 weight percentage with respect to the total weight of the catalyst;
nickel oxide in the range of 1-8 weight percentage with respect to the total weight of the catalyst;
at least one chelating agent in the range of 0.5-5 weight percentage with respect to the total weight of the catalyst; and
Al2O3 support in the range of 40-65 weight percentage with respect to the total weight of the catalyst, wherein, the said hydrotreating catalyst results 4ppm-9ppm product sulfur from a diesel feed having 20000 ppm sulfur content.

13. The dispersed hydrotreating catalyst as claimed in claim 12, wherein, at least one chelating agent stabilizes the formation of a Molybdenum-Phosphorous (Mo-P) heteropoly acid complex over the said Al2O3 support.

14. The dispersed hydrotreating catalyst as claimed in claim 12 to 13, wherein, the at least one chelating agent is selected from an organic acid having -COOH functional group, amino carboxylic acid –NH2-COOH, phosphino carboxylic acid –PO4-COOH, thio phospho amino carboxylic acid –SH-NH2-COOH, hydroxamic acid -NOH-C=O or thio amino carboxylic acid –SH-NH2-COOH, or a combination thereof.

15. The dispersed hydrotreating catalyst as claimed in claim 12 to 14, wherein, the at least one chelating agent is selected from acid group having citric acid (CA), nitrilo triacetic acid (NTA), phosphino carboxylic acid, phospho serine, aceto hydroxamic acid, thio L-aspartic acid, or a combination thereof.

16. The dispersed hydrotreating catalyst as claimed in claim 12 to 15, wherein, the at least one chelating agent is selected from citric acid (CA), or a combination of citric acid (CA) with at least one acid selected from nitrilo triacetic acid (NTA), phosphino carboxylic acid, phospho serine, aceto hydroxamic acid, thio L-aspartic acid.

17. The dispersed hydrotreating catalyst as claimed in claim 12 to 13, wherein, the said Al2O3 support have uniform dispersion of Molybdenum (Mo) and Phosphorous (P).
, Description:FIELD OF THE INVENTION:
The present invention describes a two-step spray impregnation process for preparing a dispersed hydrotreating catalyst useful in the hydrocarbon fuel refineries. The dispersed hydrotreating catalyst is useful for hydrodesulfurization of hydrocarbon fuels like Naphtha, Gasoline and Diesel. The two-step process is economic, simple with reduced number of preparation steps and having a catalyst with enhanced homogeneous dispersion of Mo atoms.

BACKGROUND OF THE INVENTION:
Refining the hydrocarbon fuels from the crude oil involves many steps such as separation, distillation, purification, and removal of elemental impurities such as sulphur, nitrogen, and heavy metals. Further, different process stages require different types of catalysts such as catalyst for cracking of larger chain hydrocarbons into smaller chain hydrocarbons, catalyst for converting vegetable oils into to aviation fuels and catalyst for hydrotreating/hydrodesulphurization of hydrocarbon fuels.

The conventional hydrotreating/hydrodesulphurization catalysts for diesel are mostly prepared by multistep synthesis approach by impregnation of active metals on the support materials such as ?-Al2O3. Mostly, such catalysts contain of Mo, W promoted with Ni or Co along with Phosphorous supported on ?-Al2O3. Various methodologies, such as controlling promoters, tuning active phase and tailoring the structure of supports (Al2O3) have been utilized to enhance the performance of such Hydrodesulphurization catalyst. Some of the known state of the art catalyst as used in the hydrotreating/hydrodesulphurization are explained hereinbelow.

CN101439292A discloses a catalyst for oxidative dehydrogenation and process of preparing the same. The catalyst comprises of main materials and additives; the main materials are the compound material of phosphor molybdenum heteropoly acid alkali metal salt and nickel oxide or the compound material of phosphor molybdenum heteropoly acid alkali soil metal salt and nickel oxide; the contents of the additives account for 0 to 10 percent of the total weight of the solid catalyst.

CN102600913B discloses a dipping aqueous solution of a catalyst for a hydrotreatment and a method for preparing molybdenum, nickel and phosphorus dipping aqueous solution. The method comprises the steps of firstly, preparing a soluble molybdenum, nickel and phosphorus aqueous solution, adding the complex or the organic acid, fully dissolving the complex or the organic acid and then adding residual nickel, and heating till boiling to completely dissolve a mixture.

CN106732776B discloses a hydrodesulfurization catalyst based on heteropoly acid clusters as precursors. The method includes firstly, adding nickel sulfate to a Ba3/2PMo12O40 solution, and then adding phosphomolybdenum heteropoly acid clusters after filtering, and filtering Then take the filtrate to evaporate and crystallize to obtain nickel-molybdenum phosphorous heteropolyacid clusters, which are then formulated into an impregnating solution, and ?-alumina support is added for impregnation to obtain the catalyst precursor. The precursor is vulcanized in a tube furnace.
KR1751923B1 discloses a hydrodesulfurization catalyst and a method for manufacturing the same. D4 further discloses a catalyst disposes a crystal of a metal oxide containing nickel-molybdenum-phosphorus as an active component in an alumina support. D4 further discloses steps of preparation, in step 1 molybdenum (Mo) precursor compound and phosphoric acid (H3PO4) are added to the purified water and stirred at 110 to 150°C, followed by filtration at 40 to 70°C, followed by distillation under reduced pressure to crystallize the molybdenum-phosphorus-containing metal oxide crystals prepared in step ii) and nickel (Ni) precursor compound to purified water, stirring the mixture at 70 to 100°C, filtering at 40 to 70°C, and then crystallizing the nickel-molybdenum-phosphorus to form a crystal of a metal oxide having a compositional ratio of the following formula (1).

US20200290025 discloses a hydrotreatment catalysts and a process for preparing said catalysts advantageously usable in the hydrotreatment processes, for example in hydrodesulphurization, hydrodenitrogenation, hydrodearomatization processes of hydrocarbons. The said process comprises steps of mixing at least one soluble source of W and at least one soluble source of Mo into a suitable volume of water, until obtaining a clear aqueous solution. Then optionally, adding at least one source of at least one element Me to the solution obtained in step 1. Then adding at least one source of Ni to the mixture obtained in the previous step. Then subjecting the mixture obtained in step 3 to a first heat treatment at temperatures comprised between 50° and 80° C., under stirring. Then adding to the mixture obtained in step 4, at least one soluble, hydrolysable or dispersible source of Al, and at least one polymer organic compound. Subjecting the mixture obtained in the previous step to a second heat treatment at temperatures comprised between 80° C. and 95° C., under stirring, obtaining a suspension. Subjecting the suspension obtained in step 6 to drying, obtaining in such a way a solid phase. Finally, calcining said solid phase obtained in the previous step, obtaining the mixed oxide of formula (I). The present invention further relates to said hydrotreatment catalysts and a hydrotreatment process wherein said catalysts are used.

US10058852B2 discloses a hydrotreatment catalyst comprising an alumina-based support, at least one metal from group VIB, at least one metal from group VIII and phosphorus. The said catalyst is prepared by impregnation of the metals from group VIB, group VIII and phosphorus onto the support in order to obtain an impregnated catalyst precursor, then drying said impregnated catalyst precursor at a temperature of less than 200°C and without subsequent calcining. Then impregnating the dry catalyst as obtained with an impregnation solution comprising at least one organic compound containing oxygen and/or nitrogen in order to obtain a doped catalyst precursor. Optionally, allowing the doped catalyst precursor as obtained to mature.

US10118160B2 discloses a process for preparing a hydrotreating catalyst comprising of from 5 wt% to 50 wt% of molybdenum of from 0.5 wt% to 20 wt% of nickel and of from 0 to 5 wt % of phosphorus, all based on total dry weight of catalyst. The process comprises impregnating an alumina carrier with an impregnation solution, consisting essentially of a phosphorus compound, a molybdenum component, a nickel component, and gluconic acid that is present in the impregnation solution in such an amount to provide a ratio of weight of gluconic acid to the total weight of nickel and molybdenum of from 0.1 to 5, and a phosphorus compound, to thereby provide an impregnated carrier. Then drying the impregnated carrier at a temperature of from 40°C to 200°C followed by calcining the impregnated carrier at a temperature of from 200°C to 650° C to obtain a calcined impregnated carrier. And sulphiding the calcined impregnated carrier to obtain the hydrotreating catalyst.

US9321041B2 discloses a process for preparing a catalyst comprising at least one metal from group VIII, at least one metal from group VIB and at least one support formed from at least one oxide. The said process comprising at least one step for bringing at least one pre-catalyst comprising at least said metal from group VIII, at least said metal from group VIB and at least said support into contact with at least one organic compound formed from at least one cyclic oligosaccharide composed of at least 6 a-(1,4)-bonded glucopyranose subunits. Then at least one step for bringing at least said support into contact with at least one solution containing at least one precursor of at least said metal from group VIII, at least one precursor of at least said metal from group VIB and at least one organic compound formed from at least one cyclic oligosaccharide composed of at least 6 a-(1,4)-bonded glucopyranose subunits. Thereafter, at least one first step for bringing at least said support into contact with at least one organic compound formed from at least one cyclic oligosaccharide composed of at least 6 a-(1,4)-bonded glucopyranose subunits followed by at least one second step for bringing the solid derived from said first step into contact with at least one precursor of at least said metal from group VIII and at least one precursor of at least said metal from group VIB. Further, the process also includes at least one drying step, and at least one heat treatment step to decompose said organic compound.

IN202041005951 discloses a hydrodesulfurization (HDS) catalyst and a process for preparing the said catalyst, the process comprises (a) impregnating a phosphorus oxide precursor on at least one porous support, followed by drying and calcination to obtain a first precursor; (b) dispersing a molybdenum oxide precursor on the first metal precursor in presence of at least one chelating agent, followed by ageing, drying, and calcination to obtain a second precursor; and (c) impregnating a nickel oxide precursor on the second precursor in the presence of at least one chelating agent, followed by drying to obtain the catalyst.

From the state of the art, it is observed that the hydrotreating/hydrodesulphurization catalyst preparation involves multistep reaction processes. Such multistep reaction processes are time consuming, requires many costly reagents and thus increases the overall cost of the catalysts.

Further, it is also observed that there is continuous improvement in hydrotreating/hydrodesulphurization catalysts with respect to enhancing their catalytic properties by providing more active metal sites.

Further, it is also observed that for industrial scale production of hydrotreating/hydrodesulphurization catalyst, the production steps should be simple and less time consuming.

Accordingly, for industrial scale production of hydrotreating catalyst, there is a requirement for preparing a hydrotreating catalyst with minimum process steps and having a catalyst with enhanced active metal dispersion.

OBJECTIVE OF THE PRESENT INVENTION:
The objective of the present invention is to provide simple two-step spray impregnation process for preparing a catalyst for hydrotreating/hydrodesulfurization of hydrocarbon fuels.

The main objective of the present invention is two-step spray impregnation process for preparing an improved nickel-molybdenum-phosphorus-alumina catalyst suitable for hydrogenating reactions.

The specific objective of the present invention is to provide a dispersed hydrotreating catalyst having enhanced catalytic activity due to enhanced homogeneous dispersion of active metal atoms on the catalytic support.

SUMMARY OF THE INVENTION:
The present invention discloses a two-step process for preparing a catalyst useful in the hydrocarbon fuel refineries. The catalyst is useful for hydrotreating/hydrodesulfurization of hydrocarbon fuels. The process comprising a first step of preparing a P-Mo-Alumina complex by loading molybdenum and phosphorus on a calcined alumina support. The loading of molybdenum and phosphorus is done along with at least one chelating agent. The said P-Mo-Alumina complex is aged at ambient room conditions for 1-5 hours and dried at 90°C. Then the said P-Mo-Alumina complex is calcined at 500°C.

The molybdenum is selected from one of an ammonium heptamolybdate, molybdophosphic acid, molybdenum oxide, molybdenum chloride, or a combination thereof. The phosphorus is selected from phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, hypophosphoric acid, or a combination thereof.

Further, the said process comprises a second step of preparing a P-Mo-Ni loaded alumina by loading a Nickel (Ni) along with at least one chelating agent on the said P-Mo-Alumina complex, and then drying to get the said final catalyst. The Nickel (Ni) is selected from Nickel acetate, nickel sulfate, nickel acetylacetonate, nickel chloride, nickel carbonate, or a combination thereof.

Further, the at least one chelating agent is selected from an organic acid having -COOH functional group, amino carboxylic acid –NH2-COOH, phosphino carboxylic acid –PO4-COOH, thio phospho amino carboxylic acid –SH-NH2-COOH, hydroxamic acid -NOH-C=O or thio amino carboxylic acid –SH-NH2-COOH, or a combination thereof.

DESCRIPTION OF THE DRAWINGS:
To further clarify advantages and aspects of the invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing(s). It is appreciated that the drawing(s) of the present invention depicts only typical embodiments of the invention and are therefore not to be considered limiting of its scope.
Figure 1: illustrates the H2-TPR of two different types of catalysts prepared by two different process.
Figure 2: illustrates the UV spectra of three different types of catalysts each prepared by using different process steps.

DETAILED DESCRIPTION OF THE INVENTION:
For promoting an understanding of the principles of the present disclosure, reference will now be made to the specific embodiments of the present invention further illustrated in the drawings and specific language will be used to describe the same. The foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated composition, and such further applications of the principles of the present disclosure as illustrated herein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinarily skilled in the art to which this present disclosure belongs. The methods, and examples provided herein are illustrative only and not intended to be limiting.

In the present invention, active metal and non-metals which includes Ni, Mo and P are loaded on the alumina support. The novel two-step process is invented for loading these metals on the alumina support.

The present invention provides a two-step process for preparing a catalyst useful for hydrotreating/hydrodesulfurization of hydrocarbon fuels. The process comprising a first step of preparing a P-Mo-Alumina complex by loading molybdenum and phosphorus on a calcined alumina support. The loading of molybdenum and phosphorus is done along with at least one chelating agent.

Then the said P-Mo-Alumina complex is aged at ambient room conditions for 1-5 hours and dried at 90°C. Finally, the said P-Mo-Alumina complex is calcined at 500°C.

The molybdenum is selected from one of ammonium heptamolybdate, molybdophosphic acid, molybdenum oxide, molybdenum chloride, or a combination thereof. The phosphorus is selected from phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, hypophosphoric acid, or a combination thereof.

Further, the said process comprises a second step of preparing a P-Mo-Ni loaded alumina by loading a Nickel (Ni) along with at least one chelating agent on the said P-Mo-Alumina complex, and then drying to get the said final catalyst. The Nickel (Ni) is selected from Nickel acetate, nickel sulfate, nickel acetylacetonate, nickel chloride, nickel carbonate, or a combination thereof.

The at least one chelating agent is selected from an organic acid having -COOH functional group, amino carboxylic acid –NH2-COOH, phosphino carboxylic acid –PO4-COOH, thio phospho amino carboxylic acid –SH-NH2-COOH, hydroxamic acid -NOH-C=O or thio amino carboxylic acid –SH-NH2-COOH, or a combination thereof.

Specifically, the present invention disclosed a novel two-step process for preparing a dispersed hydrotreating catalyst. The said process comprising two-step spray impregnation process/technique. In the first impregnation step, a first spray solution is prepared by mixing a phosphoric acid with a molybdenum salt. The mixing of the phosphoric acid with molybdenum salt results in the formation of heteropoly acid structures (Dawson or Keggin structures). Further, at least one chelating agent is added in the said first spray solution. Wherein, the addition of at least one chelating agent along with these heteropoly acid structures stabilizes the heteropoly acid complex formation during impregnation which apparently enhances the uniform dispersion of Molybdenum (Mo) and Phosphorous (P). Further, the first impregnation step includes spray loading of the first spray solution on a calcined alumina support at pH of 5-5.2 to get a Phosphorous-Molybdenum (P-Mo) loaded Alumina complex. The obtained material is aged at room temperature and dried at 90°C. The obtained final material is calcined at 500°C.

In the second impregnation step, a nickel salt solution along with at least one chelating agent is deposited on the said Phosphorous-Molybdenum (P-Mo) loaded alumina complex. After loading nickel (Ni) along with chelating agents, the final dispersed hydrotreating catalyst is only dried with avoiding final calcination step.

Specifically, the at least one chelating agent is selected from acid group having Citric acid (CA), Nitrilo triacetic acid (NTA), Phosphino carboxylic acid, phospho serine, Aceto hydroxamic acid, thio L- aspartic acid, or a combination thereof.

More specifically, the at least one chelating agent is selected from the Citric acid (CA), or a combination of Citric acid (CA) with at least one acid selected from Nitrilo triacetic acid (NTA), Phosphino carboxylic acid, phospho serine, Aceto hydroxamic acid, thio L-aspartic acid, or a combination thereof.

Further, the present invention provides a dispersed hydrotreating catalyst having phosphorous oxide in the range of 4-9 weight percentage, molybdenum oxide in the range of 10-30 weight percentage, nickel oxide in the range of 1-8 weight percentage, at least one chelating agent in the range of 0.5-5 weight percentage; and Al2O3 support in the range of 40-65 weight percentage. Wherein, the said hydrotreating catalyst results 4ppm-9ppm product sulfur from a hydrocarbon feed having 20000 ppm sulfur content.

Further, the novel two-step process of the present invention can be applied for the synthesis of hydrodesulphurization catalysts, hydrotreating catalysts, hydrodeoxygenation catalysts and hydrocracking catalysts for various refinery applications. Furthermore, the novel two-step process of the present invention can be applied to prepare catalysts for the vegetable oil conversion to aviation fuels.

The present invention enhances the usefulness of the dispersed hydrotreating catalyst as prepared by increasing its catalytic activity due to uniform dispersion of Molybdenum (Mo) and Phosphorous (P). Thus, the active metal centres are relatively high when compared to the known prior art catalyst, thus this leads to the increased catalytic activity.

Experimental Results:
The Fig. 1 illustrates the H2-TPR of two different types of catalysts prepared by two different process. Wherein the curve (i) indicates catalyst prepared using three step spray deposition (as disclosed in IN202041005951) and curve (ii) indicates catalyst as prepared using current invention using two-step spray deposition/ impregnation. Wherein, the Tmax reduction temperature of catalysts are in the order i.e., (i) > (ii).

It is evident from figure 1 that catalysts as prepared with two step spray impregnation technique having chelating agents selected from a combination of Citric acid (CA) and Nitrilo triacetic acid (NTA) forms MoS2 at lower temperature during sulfidation when compared to other three step spray impregnation techniques. Because of strong interaction between active phase and support for multiple impregnation technique, the MoS2 formation slows down and shits to higher temperature which eventually affects the MoS2 dispersion in the final catalysts.

The Fig. 2 illustrates the UV spectra of three different types of catalysts each prepared by using different process steps. Wherein, curve (i) indicates catalyst prepared by three step wet impregnation (as disclosed in IN202041005951).

The curve (ii) indicates catalyst prepared by two-step impregnation technique as provided in the present invention having citric acid as chelating agent. The curve (iii) indicates catalyst prepared by two step impregnation technique as provided in the present invention having citric acid and phosphino carboxylic acid as chelating agents.

It is evident from figure 2 that more amount of heptamolybdate [Mo7O24]6 formations in case of two step spray impregnation with citric acid and phosphino carboxylic acid.

Reaction Results:
The key reaction is desulphurization of sulfur containing molecules. Mercaptans, sulfides and disulfides react easily with hydrogen and produces corresponding saturated or aromatic compounds. When the sulfur is combined into cycles of aromatic structure, like thiophene, benzothiphene, dibenzothiophenes is more difficult to eliminate. These reactions are exothermic in nature and they produce hydrogen sulphide and consume hydrogen.

Reaction Example:
R-SH (Mercaptan) + H2 R-H + H2S
Thiophene + 4H2 C4H10 + H2S
Benzothiophene + 5 H2 Cyclohexyl Benzene + H2S

The below Table 1 illustrates the comparative performance study of three different types of catalysts each prepared by using different process steps. Wherein, the first catalyst is prepared by conventional three step wet impregnation. The second catalyst is prepared by two step impregnation technique as provided in the present invention having Citric acid as chelating agent. The third catalyst is prepared by two step impregnation technique as provided in the present invention having citric acid and phosphino carboxylic acid as chelating agents.

Table 1
Catalyst with three step impregnation method (IN202041005951) Present invention with two step synthesis using citric acid as chelating agent Present invention with two step synthesis using citric acid and phosphino carboxylic acid as chelating agents
Product sulfur ppm 15 ppm 9 ppm 4ppm
Operating conditions (WHSV: 1.0 hr-1, 330°C, H2/HC: 575 Nm3/m3, P: 80 Bar, Sulfur in Diesel feed- 20000 ppm.

The Table 1 indicates that the first catalyst as prepared by conventional three step wet impregnation have higher product sulfur i.e., 15 ppm. The second catalyst which is prepared by two step impregnation technique as provided in the present invention having Citric acid as chelating agent have low product sulfur i.e., 9 ppm which is much less when compared to the first catalyst. The third catalyst which is prepared by two step impregnation technique as provided in the present invention having citric acid and phosphino carboxylic acid as chelating agents have much lower product sulfur i.e., 4 ppm when compared to the first catalyst and the second catalyst. Hence, the second and third catalyst have much lower product sulfur content as compared to the catalyst prepared by conventional three step wet impregnation technique.

The below Table 2 illustrates the time on stream study of catalysts as prepared through two step impregnation technique as provided in the present invention by using citric acid and phosphino carboxylic acid as chelating agents.

Table 2
S. No. Time in hours Product Sulfur, ppm*
1. 50 4
2. 100 3
3. 200 4
4. 400 6
5. 600 4
6. 800 5
7. 1000 8
8. 1500 4
9. 2000 2
10. 2500 4
11. Average 4.4
*Operating conditions are, WHSV: 1.0 hr-1, H2/HC: 575 Nm3/m3, P: 80 Bar.

The Table 2 indicates that at 50 hours time on stream studies, the product Sulfur is 4ppm by using the catalyst which is prepared by two step impregnation technique as provided in the present invention having citric acid and phosphino carboxylic acid as chelating agent.

The hydrotreating/hydrodesulfurization catalyst as prepared by the novel two-step process of the present invention provides many advantages over the hydrotreating catalyst as prepared through conventional multistep process. Firstly, reduces the number of preparation steps and the spraying of heteropoly acid structural components on alumina surface enhances the homogeneous dispersion of Molybdenum (Mo) atoms during the calcination step.

The spray loading of Nickel along with complexation agents and uncalcined final catalyst can slows down the formation of NiS2 and apparently MoS2 forms first followed by nickel substitution at edges. Thus, this provides more active metal sites and thus enhanced catalytic activity.

Further, the present invention decreases the interaction between Nickel (Ni), Molybdenum (Mo) and Alumina which is evident in temperature programmed reduction. When compared to multi step spray impregnation, this interaction between support and active phase is less with the present spray impregnation along with chelating agent combination.

Further, the proportion of Heptamolybdate species on the catalyst can be increased by preparing a catalyst through the two-step spray impregnation technique as disclosed in the present invention.