TECHNICAL FIELD:

The present invention relates to the method of preparation of a material composed of metal oxide on zinc oxide by co-precipitation method. The said materials shall be applied for removal of sulfur from hydrocarbon fuels, particularly naphtha, diesel.

BACKGROUND AND PRIOR ART:

In view of the environmental concerns & regulatory norms, the utilization of ultra-low Sulphur fuels has been mandated globally. Refineries all around the globe are being modified/revamped to produce fuels with less than 10 ppm of Sulphur content. Conventionally, Hydro- Desulfurization (HDS) is the primary desulphurization process to reduce the sulfur compounds from refinery streams. In HDS, the liquid hydrocarbon stream is contacted with the hydrogen gas over a supported catalyst to remove sulphur in the form of H2S. Hydrodesulfurization can efficiently remove sulfur from sterically less hindered sulphur compounds such as sulphides, disulphides and thiols, however, it requires severe process conditions to remove aromatic sulfur compounds such as di-benzothiophene (DBT) and 4,6 dimethyl-di-benzothiophene (4,6- DMDBT) due to the steric hindrance. In order to achieve ultra-deep desulfurization through HDS requires high temperature, high hydrogen partial pressure, high hydrogen consumption, large reactors and high cost. With Naphtha desulphurization, there is an additional drawback is the octane loss due to the saturation of olefins. To address these drawbacks, several nonhydrogenating technologies have been explored to produce ultra-deep desulfurized fuels.

Reactive Adsorptive Desulfurization (RADS) is alternative approach to ultra-deep desulfurization because it combines the advantages of HDS and Adsorptive Desulfurization (ADS), low hydrogen consumption, could remove refractory sulfur compounds.

S-Zorb process by Conoco Philips Petroleum Company is based on reactive adsorptive desulphurisation, which utilizes an adsorbent containing transition metals loaded on support of metal oxide.

U.S. Pat. No. 4,894,185 discloses a method for manufacturing a zinc oxide based powder by coprecipitation method. Prepared aqueous solution of soluble salts of zinc and at least one other metal element selected from the group of antimony, cobalt, manganese, nickel, chromium, lead and aluminum. Prepared NH3/NH4 ⁺ based aqueous buffer solution and used to precipitate.

U.S. Pat. No. 9,663,725 discloses a catalytic composition of adsorbent comprised of highly dispersed crystals of ZnO, CuO and optionally CeCh by co-precipitation method. Alkaline solution at least one of (Nkk CCh, Na2CO3 and NH4HCO3 used to precipitate and combined the precipitate with binder selected from the group consisting of poly-ethylene oxide, polyvinyl alcohol, a sol of aluminum pseudoboehmite and silica gel to form an extrudate mixture.

U.S. Pat. No. 9,663,724 discloses a method for synthesis of alumina/NiO/ZnO and Alumina/ZnO via a novel modified hydrothermal method. Specifically, the document discloses an alumina/NiO/ZnO and an alumina/ZnO composite, a method in which the composites are obtained, and a method in which the composites are used as adsorbents in a method of desulfurization of diesel fuel. The method for desulfurizing a hydrocarbon composition, include contacting an alumina/NiO/ZnO material with the hydrocarbon composition to adsorb one or more sulfur compounds present in the hydrocarbon composition on the alumina/NiO/ZnO material, wherein the alumina/NiO/ZnO material has a surface area of 10-15 m2/g.

U.S. Pat. No. 8,623,220 discloses a simple, room temperature method for producing CuO-doped zinc oxide nanoparticles by reacting with zinc nitrate hexahydrate, copper nitrate trihydrate and cyclo-hexylamine at room temperature.

Further, several literatures on preparation of zinc oxide based adsorbent powder material have been reported. Andrey Ryzhikov et al., 2008, Applied Catalysis B: Environmental 84 (2008) 766-772, title “Reactive adsorption of thiophene on Ni/ZnO: Role of hydrogen pretreatment and nature of the rate determining step” discloses that the reduction of NiO/ZnO in H2 (360°C, 6h) results in the formation of Ni-Zn alloyed particles and leads to a decrease of the sulfidation rate in comparison with the unreduced sample. Concerning the mechanism of the reaction, it was found that H2S is absent in the gas phase during sulfidation in a fixed bed reactor for both reduced and unreduced solids, showing that all produced H2S is rapidly absorbed by ZnO. However, the document used very low molar concentrations of metal solution (0.0221 M of Zn & 0.0054 M of Ni) and long aging time for getting high surface area.

Lichung Huang et al. (2010), Ind. Eng. Chem. Res. 2010, 49, 10, 4670-4675, title “A Detailed Study on the Negative Effect of Residual Sodium on the Performance of Ni/ZnO Adsorbent for Diesel Fuel Desulfurization”. The document discloses that that Desulfurization of diesel fuel was conducted via reactive adsorption over a coprecipitated Ni/ZnO adsorbent. A negative effect of the residual sodium in Ni/ZnO adsorbent on its adsorption performance was observed. The desulfurization ability of Ni/ZnO adsorbent is markedly weakened with the increase in the residual sodium content. This negative effect can be attributed to the fact that the residual sodium decreases the adsorbent surface area and pore volume, suppresses the interaction between Ni and ZnO, and leads to an increase in the crystallite size of the active species. Moreover, the residual sodium is enriched on the adsorbent surface upon calcination and reduction treatment, which may promote the formation of the catalytically inactive Ni-Zn and NaZn(OH)3 species. Further, the document discloses that the powder adsorbent of Nickel-Zinc oxide is prepared by using 0.25 M concentration of metal solution and refluxing the precipitation at 90 °C for 3 hours.

Mingxing Tang et al. (2015), Catalysis Communications Volume 61, 10 February 2015, Pages 37-40 “A novel reactive adsorption desulfurization Ni/MnO adsorbent and its hydrodesulfurization ability compared with Ni/ZnO”. The document discloses that IM of metal solution is used with reflux at 70 °C for 0.5 hours to obtain the nickel-zinc oxide with low surface area.

Aihua Kong et al., 2013, Frontiers of Chemical Science and Engineering volume 7, pagesl70- 176 (2013), title “Reactive adsorption desulfurization over a Ni/ZnO adsorbent prepared by homogeneous precipitation”. Eichung Huang et al., 2018 Russian Journal of Applied Chemistry volume 91, pages 833-838 (2018), title “Desulfurization of Diesel over Ni/ZnO Adsorbent Prepared by Coprecipitation”. These documents also reported the preparation of nickel oxide/zinc oxide adsorbent by co-precipitation method. The adsorbent materials, mentioned in the previous literatures, are prepared under a higher temperature of precipitation, with a longer aging time of precipitate, with the usage of additive/templating agent, and at low metal solution concentration to get high surface area. Preparation method and conditions significantly influence the adsorbent properties like surface area, pore volume, and pore width and particle size.

Accordingly, there is a need of a method for preparation of mesoporous adsorbent at less aging time, high metal solution concentration and without addition of any additive or a templating agent to obtain high mesoporous surface area of the adsorbent.

BRIEF SUMMARY OF INVENTION

The present invention describes the method for preparation of mesoporous adsorbent by temperature assisted co-precipitation method and their use for adsorptive desulfurization of hydrocarbon fuels using mesoporous adsorbent.

The method includes the steps of preparing a first solution by dissolution of a zinc salt in a deionized water and preparing a second solution by dissolution of a metal salt selected from group consisting of nitrates, sulphates, chlorides of Cu, Ni, Fe and Mn, wherein, the dissolution is carried out in deionized water. Then preparing a metal salt solution by mixing the first solution and the second solution under a set of mixing conditions. Then preparing an alkali carbonate solution by dissolution of alkali carbonate in deionized water. Thereafter, precipitating the metal salt solution by mixing the metal salt solution with the alkali carbonate solution to prepare a slurry. Followed by aging of the slurry, followed by filtration and thermal treatments of the precipitate obtained after the mixing to obtain the said adsorbent material.

In one embodiment, the precipitation is performed at lower temperature, between 25-50 °C, by addition of a precipitating solution to the metal salt solution until the pH of the resultant solution reaches to 8 and it is completed in 45 minutes and a slurry is prepared. Wherein, the precipitating solution is an alkali carbonate solution prepared by dissolving alkali carbonate in deionized water. The total metal oxide content on a dry basis in the final slurry is maintained at about 2.4 wt. %.

In another embodiment, the precipitation is performed at elevated temperature of 50-90 °C by addition of precipitating solution to the metal salt solution until the pH of the resultant solution reaches 8 and it is completed in 40 minutes and a slurry is prepared. Wherein, the precipitating solution is an alkali carbonate solution prepared by dissolving alkali carbonate in deionized water. The total metal oxide concentration on a dry basis in the final slurry is maintained at about 2.6 wt. %.

In another embodiment, the precipitation is performed at temperature between 25-50 °C, by addition of precipitating solution to the metal salt solution containing moles of Ni/Zn until the pH of the resultant solution reaches to 8 and it is completed in 30 minutes and a slurry is prepared. Wherein, the precipitating solution is an alkali carbonate solution prepared by dissolving alkali carbonate in deionized water. The total metal oxide concentration on dry basis in the slurry is maintained at 2.5 wt. %. The temperature of the mixture solution is raised to an elevated temperature between 50-90 ° C. The total metal oxide concentration on dry basis in the final slurry is maintained at 3.6 wt. %.

In accordance with the embodiments, the adsorbents were tested at batch scale for desulphurization of hydrocarbons. The adsorbent has to be reduced under hydrogen atmosphere followed by adsorptive desulphurization. The hydrocarbon feed can be any hydrocarbon stream with boiling point less than 350 °C.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present disclosure will become apparent from the following detailed description of the subject matter when considered in conjunction with the accompanying drawings. For the purpose of illustrating the subject matter, there is shown in the drawings embodiments that are presently preferred, it being understood, however, that the subject matter is not limited to the specific instrumentalities disclosed.

FIG 1 illustrates Powder X-ray diffraction patterns of the adsorbent materials; and

FIG 2 illustrates H2-Temperature Programmed Reduction Profile of the adsorbent material 3.

DETAILED DESCRIPTION

The present invention relates to the method of preparation of mesoporous adsorbent by modified co-precipitation method. The mesoporous adsorbent material is used for the desulfurization of hydrocarbon stream. The method includes the steps of preparing a first solution by dissolution of a zinc salt in a deionized water and preparing a second solution by dissolution of a metal salt selected from group consisting of nitrates, sulphates, chlorides of Cu, Ni, Fe and Mn, wherein, the dissolution is carried out in deionized water. Then preparing a metal salt solution by mixing the first solution and the second solution under a set of mixing conditions.

Then preparing an alkali carbonate solution by dissolution of alkali carbonate in deionized water. Thereafter, precipitating the metal salt solution by mixing the metal salt solution with the alkali carbonate solution to prepare a slurry. The mixing of the metal salt solution with the alkali carbonate solution is carried out until a resultant solution reaches at a pH of 5-8.

Followed by aging of the slurry, wherein the aging is carried out at 30-50 °C for a period of 1-12 hours. Followed by filtration and thermal treatments of the precipitate obtained after the mixing to obtain the said adsorbent material.

The set of mixing conditions are selected from mixing of the metal salt solution with the alkali carbonate solution is carried out by using a two-step mixing process with a temperature variation of 20-50 °C difference between a first step mixing and a second step mixing of the two-step mixing process. The concentration of zinc and other metal oxides on dry basis in the slurry obtained after first step mixing is 1 to 3 wt.%. The concentration of zinc and other metal oxides on dry basis in the final slurry obtained after second step mixing is 1 to 5 wt.%.

In an embodiment, the first solution is prepared by using one zinc salt selected from the group consisting of zinc nitrate, zinc acetate, zinc chloride and zinc sulphate. The second solution is prepared by dissolution of a metal salt selected from group consisting of nitrates, sulphates, chlorides of Cu, Ni, Fe and Mn. In the first solution, the zinc salt is more preferably zinc nitrate and zinc chloride and most preferably it is zinc nitrate. In the second solution, the metal salt is more preferably nickel nitrate and nickel acetate and more preferably, it is nickel nitrate.

The individual metal salt solutions are prepared in a concentration of 0.2 to 2 M, more preferably 0.2 to 1.5 M, most preferably 0.25 to 1 M. In the mixed metal salt solution, the mole ratio of metal to zinc is maintained at 0.1 to 0.6, more preferably 0.15 to 0.5 and most preferably 0.2 to 0.45. The second solution contains a metal to zinc mole ratio of 0.1 to 0.6.

Further, an alkali carbonate solution is prepared by dissolving alkali carbonate in deionized water and named as precipitating solution. Wherein, the alkali carbonate solution contains carbonate salts of sodium and/or potassium and/or ammonium. The carbonate salt is preferably mix of sodium and potassium more preferably sodium carbonate. The solution is maintained at water to alkali carbonate mole ratio of 30 to 100 more preferably 35 to 80 and most preferably 40 to 75.

The mixing of metal salt solution and the alkali carbonate solution is done using two-step mixing with a temperature variation of 20-50 °C difference between the two steps. The first step mixing is done at a temperature of 25 to 50 °C, until pH of the resultant solution reaches to 5-9 more preferably 6-8 and most preferably 7-8. The first step resultant slurry contains zinc and other metal oxides on dry basis in is 1 to 4 wt. % more preferably 1 to 3.5 wt. % most preferably 1.5 to 3 wt. %. The temperature is raised to a temperature of 50 to 90 °C more preferably 50 to 80 °C most preferably 50 to 70 °C and the concentration of zinc and other metal oxides on dry basis in the resultant slurry is maintained at 1.5 to 6 wt.% more preferably 2 to 5.5 wt.% by addition of metal salt solution and precipitating solutions. The final pH of the solution is 8 to 9 or more preferably 8-8.5.

The slurry is aged for a period of 1 to 12 hours more preferably 1 to 8 hours most preferably 1 to 5 hours at a temperature of 30 to 80 °C more preferably at 40 to 70 °C, most preferably at 40 to 60 °C. After filtration and washing, the solid material is subjected to thermal treatments at 80 to 700 °C for period of 10 to 16 hours more preferably 80 to 600 °C for a period of 10 to 15 hours most preferably 90 to 550 °C for a period of 10 to 14 hours.

The present invention also provides an adsorbent material for desulfurization of hydrocarbons, wherein, the adsorbent material has a surface area of 25-80 m2/g, and a pore volume of 0.1-0.4 cc/g. Further, the adsorbent material has a surface area of 25-80 m2/g, and wherein a mesoporous surface area is at least 98% of the total surface area. The adsorbent material removes at least 90% sulfur from the hydrocarbons. Wherein, the hydrocarbons are selected from diesel, naphtha, or any hydrocarbon stream with boiling range of <350 °C.

The present disclosure is further supported by lab-scale experiments which are set forth for illustration purposes only and not to be construed as limiting the scope of the disclosure. The following batch scale experiment can be scaled up to industrial/commercial scale. The adsorbent is loaded in the batch reactor and reduced under a continuous hydrogen pressure of 20-70 bar & at a temperature between 400-550 °C, preferably 450-500 °C. After the reduction of the adsorbent, the hydrocarbon feed is added to maintain the adsorbent to feed ratio within 0.2 to 0.01. The feed can be any hydrocarbon stream with a boiling point of <350 °C with refractory sulfur. The adsorptive desulphurization of the hydrocarbon feed is conducted at a pressure of 20- 70 bar, preferably 50-60 bar and a temperature of 300-400 °C, preferably 330-360 °C.

EXAMPLE 1

The preparation of Example 1 adsorbent material includes the initial preparation of the metal salt solution and precipitating solution. The metal salt solution is prepared by dissolving Zn(NO3)2.6H2O and Ni(NO3)2.6H2O in 263 ml of deionized water to maintain a Ni/Zn mole ratio of 0.32. The precipitating solution is prepared by dissolving alkali carbonate in deionized water, which is maintained at a water to alkali carbonate mole ratio of 55.5. The co-precipitation is performed at a temperature of 25 °C by addition of precipitating solution to the metal salt solution until the pH of the resultant solution reaches to 8 and it is completed in 45 minutes. The total metal oxide content on dry basis in the final slurry is maintained at 2.4 wt. %. The resultant slurry is aged at room temperature for 60 minutes followed by filtration and washing with deionized water. The resultant solid mass is subjected to thermal treatments at 120 °C for 10 hours followed by 500 °C for 4 hours. The properties of the adsorbent are presented in Table 1.

TABLE 1 EXAMPLE 2:

The preparation of Example 2 adsorbent material includes the initial preparation of the metal salt solution and precipitating solution. The metal salt solution is prepared by dissolving Zn(NO3)2.6H2O and Ni(NO3)2.6H2O in 263 ml of deionized water to maintain a Ni/Zn mole ratio of 0.32. The precipitating solution is prepared by dissolving alkali carbonate in deionized water, which is maintained at a water to alkali carbonate mole ratio of 55.5. The co-precipitation is performed at 50 °C by addition of precipitating solution to the metal salt solution until the pH of the resultant solution reaches to 8 and it is completed in 40 minutes. The total metal oxide concentration on dry basis in the final slurry is maintained at 2.6 wt. %. The resultant slurry is aged at 50 °C for 60 minutes followed by filtration and washing with deionized water. The resultant solid mass is subjected to thermal treatments at 120 °C for 10 hours followed by 500 °C for 4 hours. The properties of the adsorbent are presented in Table 2.

TABLE 2

EXAMPLE 3:

The preparation of Example 3 adsorbent material includes the initial preparation of the metal salt solution and precipitating solution. The metal salt solution is prepared by dissolving Zn(NO3)2.6H2O and Ni(NO3)2.6H2O in 132 ml of deionized water to maintain a Ni/Zn mole ratio of 0.32. The precipitating solution is prepared by dissolving alkali carbonate in deionized water, which is maintained at a water to alkali carbonate mole ratio of 55.5. The co-precipitation is performed at a temperature of 25 °C by addition of precipitating solution to the metal salt solution containing moles of Ni/Zn until the pH of the resultant solution reaches to 8 and it is completed in 30 minutes. The total metal oxide concentration on dry basis in the slurry is maintained at 2.5 wt. %. To this slurry, add another 132 ml of metal salt solution containing Zn(NO3)2.6H2O and Ni(NO3)2.6H2O with Ni/Zn mole ratio of 0.32. The pH of the mixture is at 5. The temperature of the mixture solution is raised to 50 °C, co-precipitation is performed by addition of precipitating solution to the mixture solution until the pH of the resultant solution reaches to 8, and it is completed in 30 minutes. The total metal oxide concentration on dry basis in the final slurry is maintained at 3.6 wt. %. The resultant slurry is aged at 50 °C for 60 minutes followed by filtration and washing with deionized water. The resultant solid mass is subjected to thermal treatments at 120 °C for 10 hours followed by 500 °C for 4 hours. The properties of the adsorbent are presented in Table 3.

TABLE 3

EXAMPLE 4:

The adsorbent material mentioned in the Examples 1, 2 and 3 are tested for desulfurization of diesel. Prior to the reaction, the adsorbent material was reduced under H2 environment at 500 °C for 240 minutes. The desulfurization of diesel was performed using 3 wt. % of adsorbent material with respect to feed at 300°C at H2 pressure of 60 bar for residence time of 30 minutes. After the reaction, the liquid product was collected and analyzed. The activity results are presented in Table 4 and 5.

TABLE 4 TABLE 5