FIELD OF INVENTION

This invention generally relates to the fields of organic chemistry and inorganic chemistry, dealing with the preparation of impregnating solution for a catalyst preparation comprising molybdenum ( Mo) and group VIII metal for the synthesis of catalysts for hydrodesulfurization (HDS) process.

BACKGROUND OF THE INVENTION

Many countries are now producing and using environmentally friendly fuels. As a result, improvements in fuel quality standards have become more stringent. Hence, a reduction of sulfur content in the fuel is even more important. In 2024, Thailand will change the diesel quality standard from Euro 4 to Euro 5, reducing the sulfur content in the fuel from 50 to 10 ppm. Thus, Thailand’ s fuel quality standards will gradually continue to reduce 1he amount of sulfur content in the fuel following the trend of fuel standards in other countries around the world.

To reduce the sulfur content in a diesel fuel, the petroleum refinery uses a process of sulfur compounds removal with hydrogen gas (Hydrodesulfurization, HDS) in a diesel fuel to the amount not exceeding the value set by diesel fuel standards. Hydrogen gas reacts with sulfur compounds in a diesel fuel at a temperature of 320- 400 degrees Celsius, at a pressure of 3-7 MPa. This results in a hydrocarbon-based product containing sulfur atom in the range that does not exceed the value specified in diesel fuel standards. Sulfur atoms are removed as hydrogen sulfide gas ( H2S) . This HDS process requires a catalyst to accelerate the reaction. As a result of Thailand’s requirement to improve the diesel fuel quality standards to meet 1he world’ s demand of more environmentally friendly fuel has urged a higher demand for this type of catalyst for both quantity and cost value.

This HDS process has been shown to effectively remove sulfur from sulfur-containing compounds. However, when considering the structure of the sulfur compounds in diesel fuel, a complex sulfur compound is also co-existing in the fuel, most of which are dibenzothiophene derivatives (Dibenzothiophenes, DBTs) with one or two alkyl groups at positions 4 and / or 6. This is a structure of sulfur compounds which are difficult to get rid of by this process since the binding of alkyl groups hinders the bonding between the sulfur molecules and the active sites on the catalyst.

Therefore, a reduction of the sulfur content in diesel fuel to less than 10 ppm via the HDS process is imperative to react at high temperatures with a large amount of hydrogen gas and catalyst. This is because the sulfur residues in a diesel fuel are complex and difficult to react with hydrogen gas in the regular conditions used in a HDS process in accordance with Euro 4 fuel standard. Hence, there is a need for an innovative catalyst with higher efficiency to be able to reduce the amount of the sulfur compounds in a diesel fuel to meet the requirements of the Euro 5 fuel quality standard with HDS process at regular reaction temperature and pressure. This is due to a limitation of the plant equipment which can tolerate only at a regular operating condition.

The catalysts for HDS processes which are commonly used in the refinery and petrochemical industries are nickel- molybdenum sulfide on gamma alumina (Ni-Mo- S/y- AI2O3) or cobalt-mo lybdenum sulfide on gamma alumina (CO-MO-S/Y-AI2O3). Depending on the patent formula, the catalyst efficiency can be improved through different processes, such as the selection of active metal types, types of additives and improvement of synthesis methods which may include the change in the chemical composition of the solution used for preparing the catalyst (Impregnating solution) . In addition, support improvements such as improvement of the porous structure of the supports, catalyst baking improvement (Drying step) and improvement of the catalyst activation process, also reflected in the efficiency of the catalyst to be more efficient in removing sulfur compounds in a diesel fuel. Details of 1he catalyst enhancement from the patent review are shown below.

Patent No. JP-A-61 -114737 describes the synthesis of catalyst using a solution containing nitrogen organic compounds (Nitrogen Containing Ligand) and active metals on the alumina or silica support. Followed by catalyst drying at a temperature not exceeding 200°C.

Patent No. US 6,329,314 describes the activating process of a catalyst containing group VIII and group VI metals by mixing it with petroleum- based liquids containing thiophene and nitrogen compounds under specific conditions.

Patent No . US 5,032,565 describes the reduction process of a catalyst containing group VIII metals by reacting with a reducing agent such as alcohol or poly alcohol. Patent No. US 6,540,908 describes the preparation of sulfide catalysts which consists of the process of mixing alumina with organic compounds containing nitrogen and carbonyl group. This is followed by a procedure to convert the catalyst into the sulfide form.

Patent No. US 3,114,701 describes a multiple- cycle immersion of alumina in nickel nitrate and ammonium molybdate solution aqueous solvent until the final catalyst reaches 4— 10% nickel by weight and 19-30% molybdenum by weight.

Patent No. US 6,872,678 describes a synthesis of a catalyst containing group VI B metal compounds, group VIII metal compounds and organic sulfur additives. The catalyst is then activated with petroleum-based organic liquids in combination with hydrogen gas, or in a continuous process.

From the above patent review, it is mainly related to the catalyst synthesis process aiming to improve the catalyst efficiency. However, in the synthesis of the catalyst, the solution used to prepare the catalyst (Impregnating Solution) is one of the most important part of the catalyst synthesis. Since the impregnating solution used for the preparation of the catalyst contains the active species which provide the main function of the catalyst when 1he synthesis is complete. From a patent review, details of an impregnating solution used to prepare the catalyst are disclosed as follows:

Patent No. US 3,232,887 describes an impregnating solution for a catalyst preparation containing acidic organic or acidic inorganic compounds which act as a stabilizer such as phosphoric acid whose molar ratio of phosphorus to molybdenum (P/Mo) is in the range of 0.25-2.5.

Patent No. US 3,840,472 describes an impregnating solution for a catalyst preparation containing molybdic oxide, at least one compound from group VIII metal, and phosphoric acid dissolved in water at a molar ratio of P/Mo in the range of 0.065-2.5.

Patent No. US 5,332,709 describes an aqueous solution for a catalyst preparation. It consists of group VI B metal, group VIII metal, phosphorus- containing inorganic acid, and a reducing agent in sufficient quantities to dissolve group VI B metal and group VIII metal and stabilize the solution. The reducing agent can be selected from hydrazine and hydroxylamine compounds.

Patent No. US 9,364,816 describes an aqueous impregnating solution for catalyst preparation containing phosphorus compounds, group VI metal and group VIII metal compounds with a concentration of group VI metal greater than 5.6 mol/L. From the above patent review, most of them mention the preparation of the catalytic impregnating solution, focusing on the different types and ratios of each compound for each patent. A very small number of patents are available to discuss a control of the active species structure to have a certain specific structure in an impregnating solution to increase the efficiency of the catalyst. From the patent review in this matter, the similarity was found in Patent No. US 7,427,578 which discusses howto control the structure of the active species in the impregnating solution via the control of pH of the impregnating solution in the range of 2-5 by using phosphoric acid. Therefore, when the impregnating solution is examined using Raman spectroscopy technique, the Raman spectrum of the solution appears at the position of the wavelength between 965-975 cm ¹ .

However, only the Raman spectrum position of the solution does not indicate the specific structure of active species in the impregnating solution used in a catalyst preparation. This is because the active species structure is very important for the properties of the impregnating solution, hence, affecting the catalyst efficiency synthesized from this impregnating solution. Therefore, this invention has focused on the control of the structure of heptamolybdate ion ( Mo O^ ⁶ ' ) which decays, both qualitatively and quantitatively by controlling the pH and the potential difference of the redox reaction (Eh) in a specific range. The structure of the active species in the impregnating solution would then be achieved as described above. The Raman spectrum height ratio obtained from the impregnating solution for the catalyst preparation compared with the spectrum height of the ammonium heptamolybdate ( NH4) 6MO7O24 must also be in the control range. Moreover, various compounds in the impregnating solution must be controlled within the specific range to increase the catalytic efficiency of the catalyst prepared from the impregnating solution according to this invention for use in the removal of sulfur compounds with hydrogen gas process.

SUMMARY OF THE INVENTION

The invention is related to the solution, which consists of molybdenum (Mo) and group 8 transition metals used for a catalyst preparation for the hydrodesulfurization process. By using water as a solvent, the solution is a mixture of molybdenum trioxide, compounds of group 8 transition metals carbonate, phosphoric acid, reducing agent and organic acid. The invention provides the solution preparation method for high performance catalyst synthesis which is used to reduce sulfur compounds in diesel following Euro 5 standard The structure of active species inside the impregnation solution and the interaction among the solution compounds which consist of molybdenum (Mo) , cobalt (Co), phosphorus (P) , organic acid and the specific ratio of reducing agent during the solution preparation melhod must be controlled. In specific, during the preparation, the pH and oxidation reduction potential (Eh) of impregnating solution must be controlled. Redox potential (Eh) is a measure of the tendency for a chemical species to accept electrons (Reduction) or to donate electrons (Oxidation). These controlled factors greatly affect the quality of impregnating solution and the performance of the synthesized catalyst using this solution prepared by this invention.

The catalyst synthesized by using this solution invention is the Co-Mo catalyst which shows a small interaction with the support leading to very low deactivation rate during the catalyst lifetime and high catalytic performance for hydrodesulfurization reaction. In term of energy efficiency aspect, the start of run temperature is lower than the other commercial Co- Mo catalysts and the range between the start of run until the end of run temperature can be extended to increase the catalyst life period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Raman Spectroscopy spectrum of the reference standard solution ammonium hepta-molybdate tetrahydrate (NHOGMO O^ • 4H1O) 25.3 gin distilled water 50 mL, pH 0.5 adjustment using citric acid.

FIG. 2 Sulfur content in hydrodesulfurization diesel at various temperatures from 1he catalyst synthesized by using this solution invention.

FIG. 3 1/ Io ratio of the solution at various pH and sulfur content in hydrodesulfurization diesel at 350 °C from the catalyst synthesized by using the solution at various pH.

FIG. 4 I/Io ratio and viscosity of the solution at various reduction oxidation potential (Eh)

FIG. 5 Catalytic stability test in hydrodesulfurization process: ( a) the catalyst synthesized by using this solution invention (b) the commercial catalyst. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the impregnating solution for catalyst preparation, which is used in a hydrodesulfurization process. The impregnating solution consists of molybdenum trioxide, carbonate compound of group-VIII metal, phosphoric acid, reducing agent, organic acid and water as a solvent. Properties of the impregnating solution are listed as follows.

• Molar ratio of molybdenum (Mo) per group-VIII metal is in the range of 2.00-2.22

• Molar ratio of phosphorous (P) per group-VIII metal is in the range of 0.20- 0.40

• Molar ratio of organic acid per group-VIII metal is in the range of 1.00-1.08

• pH value of the impregnating solution is in the range of 0.5 - 1

• Redox potential value (Eh) of the impregnating solution is in the range of 500 - 530 mV, which is controlled by using a reducing agent in which ascorbic acid is selected from this group

• Structure of active clusters in the impregnating solution can be investigated using Raman spectroscopy, which shows the Raman spectrum at wavenumber around 945 cm ¹ . The intensity ratio at this position of the impregnating solution is from 0.04-0.06, when compared with the Raman spectrum at this position of the reference standard of ammonium hepta-molybdate solution ((NH^eMo O^) at equivalent mole of molybdenum to the impregnating solution.

Preferably, carbonate compound of group-VIII metal for the impregnating solution of the present disclosure is selected from cobalt carbonate, nickel carbonate or mix of these compounds.

Preferably, organic acid for the impregnating solution of the present disclosure is selected from citric acid, malic acid or mix of these acids.

Preferably, redox potential value (Eh) for the impregnating solution of the present disclosure is in the range of 515-520 mV. Another aspect of the invention, the present invention also relates to catalyst preparation by impregnation method using the impregnating solution on inorganic porous oxide as a catalyst support.

Preferably, inorganic porous oxide as a catalyst support of the present disclosure is selected from alumina, silica, silica-alumina, zeolite or mix of these materials.

Preferably, pore size of the inorganic porous oxide as a catalyst support of the present disclosure is in the range of 85-160 angstrom.

Structural control of active clusters in the impregnating solution is the key concept to construct the specific structure of active clusters for a catalyst preparation in the present invention. The specific structure of active clusters in the impregnating solution enhances a superior performance of the synthesized catalyst from this invention, compared to the same type of conventional catalysts.

Experimental data show that the control of pH and Eh of impregnating solution in 1he specific ranges as well as the molar ratio of Group-VIII metal, phosphoric acid and organic acid as disclosed in the present invention can enhance the performance of a catalyst for hydrodesulfurization process. Figure 1 shows the Raman spectrum of ammonium heptamolybdate (25.3 g) dissolved in distilled water (50 mL), in which the pH is controlled at 0.5 by using citric acid from High Resolution Raman Microscope Spectrometer (HORIBA). The impregnating solution was dropped on the sample holder then measured the Raman spectrum. The Raman spectrum at wavenumber around 945 cm ¹ comes from the symmetric stretching vibration of molybdenum and oxygen bonding (vs (Mo=O)) while the spectrum at wavenumber around 900 cm ¹ comes from the asymmetric stretching vibration of molybdenum and oxygen bonding (VAS (MO=O)) of Mo C^ ⁶ '. The Raman spectrum of impregnating solution from the present invention also shows the spectrum at these two positions but much lower intensity than that of ammonium heptamolybdate solution, which imply a partial decomposition of Mo C^ ⁶ ' structure to a lower valency of molybdenum structure in the impregnating solution. Therefore, the impregnating solution from the present invention consists of various valency molybdenum structure along with the majority of MO7O24 ⁶ ' structure. The present invention focuses on the control of the decomposed molybdenum structure in terms of quality and quantity as well as the mix of various valency molybdenum structure in the impregnating solution. The reduction of Raman spectrum intensity at wavenumber around 945 and 900 cm ¹ of the impregnating solution from this invention imply the changes of molybdenum structure as follows.

1. Structural transformation from Mo=O of Mo C^ ^6- to Mo-O-organic acid leads to a closer Mo O^ ⁶ ' and Group-VIII metal, which results in higher opportunity for a clustering of Mo, Group-VIII metal and organic acid. This highly stabilized cluster will be transformed to be the dispersed active sites on the catalyst after impregnation process. Thus, a reduction of the spectrum intensity at wavenumber around 945 and 900 cm ¹ implies an increment of active sites on the catalyst, which enhances the performance of the synthesized catalyst from this invention.

2. Partial decomposition of Mo C^ ⁶ ' structure to the lower valency of molybdenum structure leads to an improvement of M0S2 dispersion on the catalyst after sulfidation process.

3. Reducing agent used in the impregnating solution leads to partial transformation of Mo=O in MO7O24 ⁶ ' to Mo-OH, which increases the electron density of molybdenum structure to contain more anions. This phenomenon can strengthen the electrostatic interaction between molybdenum structure and positively charged gamma alumina support in the acidic aqueous solution, which enhances the fixing of Mo, Group-VIII metal and organic acid clusters on gamma alumina support.

As mentioned above that the position and intensity of Raman spectrum of the impregnating solution is significant for the quantity and dispersion of active sites on the catalyst. More active sites along with well dispersion on the catalyst lead to the outstanding performance of a catalyst. Therefore, a control of position and intensity of Raman spectrum of the impregnating solution is the crucial factor for a catalytic hydrodesulfurization performance of the synthesized catalyst from this invention.

The control of pH and Eh of the impregnating solution are also important for a partial transformation of Mo C^ ^6- , which can be evaluated from the intensity ratio (I/IQ) of Raman spectrum at wavenumber around 945 cm ¹ of the impregnating solution (I) and ammonium heptamolybdate solution (Io) as a reference standard. The catalytic hydrodesulfurization performance of the synthesized catalyst from this invention is demonstrated as the example in the detailed description section. The quantity of the decomposed Mo O^ ⁶ ' structure to be various valency molybdenum structures along with the majority of Mo C^ ⁶ ' structure in the impregnating solution from the present invention is controlled by controllingpH and Eh of the impregnating solution along with the quantity of compounds at specific values as disclosedin this invention.

Example 1 A catalyst is prepared in accordance with the invention. 64.17 g of molybdenum trioxide (produced by Merck) and 26.7 g of cobalt (II) carbonate (produced by ACROS Organics, A Thermo Fisher Scientific Brand) were added in 300 mL of distillated water. Further, 3.75 mL of 85% phosphoric acid (produced by Merck) and 50 g of citric acid (produced by Merck) were added. The solution was heated at 85°C during agitation. After 1 hours and 30 min, 0.63 g of ascorbic acid (produced by VETEC) was added, followed by natural ambient cooling to room temperature. The volume of the final solution was 156 mL.

This final solution was impregnated with alumina support (JGC Catalysts and Chemicals Ltd.) to prepare a HDS catalyst. This support had a surface area, a pore volume, and a pore diameter of 302 m ² /g, 0.83 mL/gand 10.2 nm, respectively. This catalyst was used to perform HDS experiments by using Straight Run Gas Oil ( SRGO) as a feed. The sulfur and nitrogen concentration in SRGO were 6,670 and 100 ppm, respectively. The hydrogen partial pressure was 44 bars and H2 to SRGO ratio was 205 by volume. Liquid hourly space velocity (LHSV) of SRGO was 1 h ¹ . The experiment was performed for 9 days. Sulfur contents of produced oils collected at reaction temperatures of 340 °C, 350 °C, and 360 °C were analyzed.

Figure 2 presents sulfur contents of produced oils collected at each reaction temperature. The result clearly indicates that the catalyst according to the present invention has a high performance for hydrodesulfurization reaction. The diesel with sulfur content less than 10 ppm (EURO 5 standard) is produced at 350 °C. Additionally, the high sulfur level in the first three days at reaction temperature of 340 °C probably results from the change of catalyst structure which is the nature of this non-calcined catalyst.

Example 2 The effect of the solution pH on Mo7O24 ^6- structure in impregnating solution according to the present invention and HDS activity of obtained catalyst is clarified. The impregnating solution containedMo/group (VIII) metal molar ratio of 2.0, P/group (VIII) metal molar ratio of 0.25 and organic acid/group (VIII) metal molar ratio of 1.08. The pH of the solution was varied from 0.5, 2 and 3 (913 pH meter, Metrohm), which caused the change of the redox potential ( Eh, RM-3 OP ORP meter, DKK-TO A) from 529, 379 and 31 1 mV, respectively. Figure 3 clearly indicates the effect of pH on I/Io ratio of the solution and HDS activity of obtained catalyst at 350 °C. The Mo C^ ^6- structure in impregnating solution is not significantly affected by pH as I/Io ratio value is not much changed. Considering the HDS activity, the solution with pH less than 1 has higher performance than that with pH of 2 and 3 . Thus, to obtain a good HDS catalyst, the pH of the impregnating solution should be controlled to be less than 1.

Example 3 Effect of the redox potential (Eh) on Mo O^ ⁶ ' structure in impregnating solution according to the present invention. The concentration of Mo, group (VIII) metal and P in the solution were the same as described in Example 2 while the pH was controlled to less than 1. The redox potential ( Eh) of solution was varied in the range of 500 - 800 mV. Figure 4 exhibits the effect of the redox potential (Eh) on I/Io ratio of the solution. Table 1 shows 1he sulfur content in the diesel product at 350 °C with the difference of the redox potential (Eh) of impregnating solution.

Table 1 Sulfur content in the product after Hydrodesulfurization at 350 °C by using catalyst in which different Eh in solution was controlled.

From the results, it is clearly seen that the reduction of the redox potential (Eh) lowers the height of Raman spectroscopypeak at945 cm ¹ . This results in the decreasing of I/Io ratio. It implies that the redox potential (Eh) significantly affects the Mo C^ ⁶ ' structure. Considering the HDS activity, the performance of catalyst strongly depends on the redox potential (Eh) as shown in Table 1 To obtain the great impregnating solution with proper Mo C^ ⁶ ' structure, the redox potential (Eh) and I/Io ratio should be in the range of 500 - 530 mV and 0.04 - 0.06, respectively. The catalyst prepared within this controlled solution will have high HDS activity. The impregnating solution with the redox potential (Eh) out of this range results in the catalyst with lower HDS activity. However, the solution viscosity increases with the decreasing of 1he redox potential (Eh). Thus, the viscosity of solution with the redox potential (Eh) less than 500 mV and pH less than 1 is too high to be prepared into a catalyst.

Example 4 Effect of molar ratio of the components in the impregnating solution for this invention

Apart from the pH and Eh for the redox potential values, the components in the impregnating solution are also crucial in the catalyst preparation, as they affect the structures of active species in the impregnating solution. The suitable amount of component is needed as stated in the detailed description to obtain the proper structure of active species for 1he catalyst preparation.

Table 2 Effect of molar ratio of components in the impregnating solution and Sulfur content in the product which were treated by hydrodesulfurization process with hydrogen gas at 340, 350, and 360 degree Celsius by using the prepared catalyst from the impregnating solution.

Table 2 shows the effect of molar ratio of components in the impregnating solution and sulfur content which were treated by hydrodesulfurization process with hydrogen gas at 340 , 350 , and 360 degrees Celsius by using the prepared catalyst from the impregnating solution. The results show that the molar ratio of component in the impregnating solution must be controlled in the specified range only to obtain a high performance catalyst. If the molar ratio of components are too high or too low, the catalyst performance will be dropped.

Example 5 Stability test of this prepared HDS catalyst from example comparing with the commercial catalyst in 110 days to identify the deactivation rate in the actual condition, the reaction temperature was increased by maintaining the sulfur content in the product to be less than 10 ppm.

Figure 5 shows that the temperatures of both catalysts started at 340 degree Celsius and then the reaction temperature were increased to maintain the level of sulfur in the product to be less than 10 ppm by following the Euro 5 standard. The Start of Run (SOR) of this invented catalyst was at 340 degree Celsius but it had relatively high deactivation rate at the start which was a typical behavior of this catalyst type II. Then the reaction temperature was increased to 350 degree Celsius after 7 days. On the other hand, the Start of Run of the commercial catalyst started at 354 Degree Celsius.

From the result, it can be concluded that this invented catalyst has high performance, comparing with the commercial catalyst. However, after passing 110 days, the reaction temperature was up to 356 Degree Celsius. The calculated deactivation rate was at 1.6 degree Celsius/month in 110 days. However, it will be much lower in the overall life-time (approximately more than2 years). The lower deactivationrate reduces the number of catalyst changing. This is one of the opportunities to reduce the production cost of Euro 5 standard diesel.

The best method of invention is as described in detailed description of the invention.