BIFUNCTIONAL CATALYST FOR DEEP DESULFURIZATION AND GASOLINE QUALITY IMPROVEMENT AND PREPARATION METHOD THEREFOR

Abstract

Provided are a bifunctional catalyst for deep desulfurization and gasoline quality improvement and a preparation method therefore and a use thereof. The bifunctional catalyst includes a modified catalyst and a loaded active metal, where the modified catalyst carrier is a γ-Al.sub.2O.sub.3 modified with a rare earth element, or the modified catalyst carrier is a composite carrier prepared by mixing and calcinating γ-Al.sub.2O.sub.3 and an acid molecular sieve through a binder, and then modifying with the rare earth element. The bifunctional catalyst for deep desulfurization and gasoline quality improvement can achieve deep desulfurization of high-sulfur fluid catalytic cracking gasoline, and ensure no significant loss of octane number under relatively mild conditions.

Claims

1. A hydrodesulfurization catalyst comprising a modified catalyst carrier and a loaded active metal, wherein the modified catalyst carrier is a γ-Al.sub.2O.sub.3 carrier modified with a rare earth element, or, the modified catalyst carrier is a composite carrier prepared by mixing and calcinating γ-Al.sub.2O.sub.3 and an acid molecular sieve through a binder, and then modifying with the rare earth element.

2. The hydrodesulfurization catalyst according to claim 1, wherein a content of the rare earth element in the hydrodesulfurization catalyst is 0.5-5 wt % based on a weight of an oxide of the rare earth element with respect to a weight of the hydrodesulfurization catalyst.

3. The hydrodesulfurization catalyst according to claim 1, wherein the rare earth element is selected from at least one of La, Ce, Pr, and Y.

4. The hydrodesulfurization catalyst according to claim 2, wherein the rare earth element is selected from at least one of La, Ce, Pr, and Y.

5. The hydrodesulfurization catalyst according to claim 1, wherein the hydrodesulfurization catalyst is obtained by loading the active metal on the modified catalyst carrier using an impregnation method, and then aging and drying.

6. The hydrodesulfurization catalyst according to claim 2, wherein the hydrodesulfurization catalyst is obtained by loading the active metal on the modified catalyst carrier using an impregnation method, and then aging and drying.

7. The hydrodesulfurization catalyst according to claim 3, wherein the hydrodesulfurization catalyst is obtained by loading the active metal on the modified catalyst carrier using an impregnation method, and then aging and drying.

8. The hydrodesulfurization catalyst according to claim 4, wherein the hydrodesulfurization catalyst is obtained by loading the active metal on the modified catalyst carrier using an impregnation method, and then aging and drying.

9. The hydrodesulfurization catalyst according to claim 1, wherein a mass ratio of γ-Al.sub.2O.sub.3 to the acid molecular sieve is (9-1): 1; and/or, the acidic molecule sieve is selected from one or more of ZSM-5, MCM-41, SAPO-34, and Bata molecular sieve.

10. The hydrodesulfurization catalyst according to claim 1, wherein the active metal is selected from more than two elements of VIB Group and VIII Group in the Periodic Table of Elements.

11. A preparation method of the hydrodesulfurization catalyst according to claim 1, characterized by comprising steps of: loading a rare earth element on γ-Al.sub.2O.sub.3 by an impregnation method, then aging, drying, and calcinating to obtain a modified catalyst carrier; or mixing and calcinating γ-Al.sub.2O.sub.3 and an acid molecular sieve through a binder to prepare a composite carrier, and then loading the rare earth element on the composite carrier by the impregnation method, and then aging, drying, calcining to obtain the modified catalyst carrier; loading an active metal on the modified catalyst carrier by the impregnation method, and then aging, drying, and calcinating to obtain the hydrodesulfurization catalyst.

12. The preparation method according to claim 11, wherein the modified catalyst carrier is obtained by loading an impregnation solution containing a rare earth compound on γ-Al.sub.2O.sub.3 or the composite carrier by an equal volume impregnation method, then aging at room temperature for 6-12 h, drying at 100-160° C. for 4-8 h, and calcining at 500-700° C. for 4-8 h; a calcination atmosphere is nitrogen, argon, or helium.

13. The preparation method according to claim 11, wherein the active metal is loaded on the modified catalyst carrier by an equal volume impregnation method, and an impregnation solution used contains an organic complexing agent, and the organic complexing agent is selected from at least one of citric acid, tartaric acid, and ethylenediaminetetraacetic acid.

14. A method for hydrodesulfurization of gasoline using the hydrodesulfurization catalyst according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 is a Py-FTIR diagram of hydrodesulfurization catalysts provided by Examples 1-3 and Comparative Example 1;

[0042] FIG. 2 is a XPS diagram of Mo3d of hydrodesulfurization catalysts provided by Examples 1-3 and Comparative example 1; and

[0043] FIG. 3 shows hydrogenation reaction results of hydrodesulfurization catalysts provided by Examples 1-3 and Comparative example 1 to North China heavy fraction gasoline.

DESCRIPTION OF EMBODIMENTS

[0044] In order to make the objectives, technical solutions and advantages of embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and comprehensively in combination with the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are a part rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by persons of ordinary skill in the art without creative work belong to the protection scope of the present application.

Example 1

[0045] The present example provides a hydrodesulfurization catalyst as follows: [0046] 1. preparing a certain concentration of a rare earth element impregnation solution by deionized water, and then impregnating the rare earth element impregnation solution on γ-Al.sub.2O.sub.3 by an equal volume impregnation method, adding a certain amount of ammonia water to improve dispersion of the impregnation solution during the impregnation process, after the impregnating is completed, aging at room temperature for about 12 h, drying at 120° C. for about 8 h, and calcinating at 540° C. for about 4 h to obtain a carrier modified with the rare earth (named as GZ carrier). [0047] 2. taking an appropriate amount of water, stirring and heating to 40° C., adding citric acid CA (CA/Co=1.5), and stirring until completely dissolved; then adding 2.5 g cobalt carbonate, and stirring until no bubble; slowly raising the temperature of a solution to a boiling state to dissolve all materials (no bubble forms), stopping heating, cooling down to room temperature, then stopping stirring; adding ammonia water to 85% of a final volume, then slowly adding ammonium heptamolybdate and stirring until completely dissolved, supplementing ammonia water to the final volume so as to obtain an active metal impregnation solution, sealed storing and reserving. [0048] 3. loading the active metal impregnation solution prepared in the step 2 on the AZ composite carrier prepared in the step 1 by the equal volume impregnation method, and then stirring for 10 min after saturation, ageing at room temperature for 12 h, drying at 100° C. for 8 h, calcinating at 540° C. for 4 h, to obtain the catalyst modified with the rare earth element, named as GZ-1, and its specific components are shown in Table 1.

Comparative Example 1

[0049] The present Comparative Example provides a CoMo/γ-Al.sub.2O.sub.3 catalyst, its preparation method is as follows: γ-Al.sub.2O.sub.3 is not treated, the preparation process of an active metal impregnation solution and an equal volume impregnation method are the same as those in the steps 2-3 of Example 1, respectively, the components of this catalyst are shown in Table 1.

Example 2

[0050] The present example provides a hydrodesulfurization catalyst, and the preparation steps are basically the same as those in Example 1, except that: the loading amount of the rare earth element Ce is increased by 50% compared with Example 1, and the obtained catalyst is named as GZ-2. The specific components of this catalyst are shown in Table 1.

Example 3

[0051] The present example provides a hydrodesulfurization catalyst, and the preparation steps are basically the same as those in Example 1, except that: the rare earth element Ce is changed to La, the loading amount of the rare earth element La is basically consistent with that of Ce in Example 2, and the obtained catalyst is named as GZ-3.

Example 4

[0052] The present example provides a hydrodesulfurization catalyst modified with a rare earth element and an acid molecular sieve, and its preparation process is as follows: [0053] 1. mixing γ-Al.sub.2O.sub.3 and ZSM-5 in a mass ratio of about 8:1, and then adding PVP to mix evenly, where the mass of PVP is twice of a sum of the mass of γ-Al.sub.2O.sub.3 and ZSM-5, and then drying at 120° C. for 8 h and calcining at 500° C. for 4 h, to obtain a γ-Al.sub.2O.sub.3/ZSM-5 composite carrier. [0054] 2. impregnating the rare earth element Ce on the composite carrier according to the steps of Example 1, and the loading amount of Ce is the same as that in Example 1, and the prepared catalyst is named as GZ-4.

[0055] FIG. 1 is a Py-FTIR diagram of the hydrodesulfurization catalysts provided by the above Examples 1-3 and Comparative Example 1, in which FIG. 1(a) obtained at 200° C. is used to calculate a total acid content of the hydrodesulfurization catalysts, and FIG. 1(b) obtained at 350° C. is used to calculate a medium strong acid content of the hydrodesulfurization catalysts.

[0056] The hydrodesulfurization catalysts in the above Examples 1-3 and Comparative Example 1 are taken to put in a fixed bed reactor having an inner diameter of 8 mm, and the hydrodesulfurization catalysts are subjected to prevulcanization by 3 wt % CS.sub.2 solution as a prevulcanization solution. Prevulcanization reaction conditions are as follows: T=340° C., P=2.5 MPa, hydrogen to oil ratio (H/O)=300, space velocity=2 h.sup.−1, and a prevulcanization time is 6 h. Samples of the hydrodesulfurization catalysts after prevulcanization and before reaction are characterized and tested. The XPS results are shown in FIG. 2.

[0057] After the prevulcanization reaction is completed, the hydrodesulfurization performance of the hydrodesulfurization catalysts is tested on North China heavy fraction gasoline (distillation range 102-194° C., sulfur content 1,538 ppm, research octane number RON=88.9), Jingbo heavy fraction gasoline (distillation range 104-185° C., sulfur content 2,276 ppm, RON=87.8), and Golmud heavy fraction gasoline (distillation range 86-180° C., sulfur content 1,854 ppm, RON=90.2) as feedstocks. The reaction conditions are as follows: T=260° C., P=2 MPa, hydrogen to oil ratio (H/O)=300, space velocity=3.5 The hydrogenation reaction results of the North China heavy fraction gasoline are shown in FIG. 3.

[0058] According to reports, the characteristic peaks near 1,450 cm.sup.−1 and 1,622 cm.sup.−1 are the characteristic absorption peaks of Lewis acid (L acid for short), and the characteristic absorption peak near 1,542 cm.sup.−1 is the characteristic absorption peak of Bronsted acid (B acid for short). It can be seen from FIG. 1 that the hydrodesulfurization catalysts provided by Examples 1-3 have a clear distinction from the unmodified CoMo/γ-Al.sub.2O.sub.3 catalyst of Comparative Example 1 in physicochemical properties, which especially shows that the introduction of different types of rare earth elements will lead to a significant decrease in the peak strength of the characteristic peaks of L-acid of the hydrodesulfurization catalysts. This may be due to the reaction between the rare earth element and Al—OH on the surface of the carrier during the preparation of the hydrodesulfurization catalyst, resulting in neutralization of a part of L-acid.

[0059] In addition, after the CoMo/γ-Al.sub.2O.sub.3 catalyst is modified with the rare earth element Ce (GZ-1 and GZ-2), the characteristic absorption peak of B-Acid is observed in the spectrogram obtained at 200° C., which indicates that there are a certain amount of L acid and B acid distributed on the surface of the CoMo/γ-Al.sub.2O.sub.3 catalyst modified with the rare earth element Ce. Compared with GZ-1, GZ-2 has a stronger B acid center. Previous studies have shown that the presence of B acid site is conducive to the fracture of the C—S bond in a thiophene sulfide, thereby promoting the occurrence of DDS (direct desulfurization) pathway and improving hydrodesulfurization reaction efficiency. Therefore, it can be concluded from this that GZ-2 should have better hydrodesulfurization performance than GZ-1, which can be confirmed from Table 2.

[0060] In addition, it can be seen from FIG. 1 that the hydrodesulfurization catalyst modified with the rare earth element La (GZ-3) does not show obvious characteristic peak of B acid. It is speculated that the improvement of its hydrodesulfurization activity is mainly due to that the introduction of La reduces the interaction between the carrier and the active metal, thereby facilitating the formation of more MoS.sub.2 active phase. It is precisely because the effect of the introduction of La on the acidity of the hydrodesulfurization catalyst is mainly reflected on the reduction of the content of L acid, and there is no obvious effect on the formation of B acid, therefore, the hydrodesulfurization performance of GZ-3 is not as good as that of GZ-2 catalyst, which can also be confirmed from Table 2.

[0061] As shown in FIG. 2, it can be seen from XPS results by X-ray photoelectron spectroscopy that the Mo.sub.3d spectrums of the sulfurized catalysts contain the following three double-peaks: a double peak with bind energy of 229.1±2 and 232.3±1 eV are the characteristic peak of MoS.sub.2 species; a double-peak with a binding energy of 231.2±0.1 and 235.2±0.1 eV is the characteristic peak of MoS.sub.xO.sub.y species; a double-peak with a bind energy of 233.2±1 and 236±0.1 eV is the characteristic peak of Mo.sup.6+ species. It can be seen from FIG. 2 that under the same prevulcanization conditions, the sulfurization degree of the hydrodesulfurization catalysts modified with rare earth elements is higher, with more MoS.sub.2 active phase. Taking the comparison of the Comparative Example 1 and Example 3 as an example, the content of MoS.sub.2 active phase in the unmodified CoMo/γ-Al.sub.2O.sub.3 catalyst in Comparative Example 1 is 45.2%, and the relative content of MoS.sub.xO.sub.y species (an incomplete sulfurized product) is 25.1% which is the highest; the content of the MoS.sub.2 active phase in the hydrodesulfurization catalyst modified with the rare earth element La in Example 3 is 61.9%, and the relative content of MoS.sub.xO.sub.y species is 15.5%. It can be concluded that the introduction of the rare earth element can promote sulfidation and reduction of Mo species, and is conducive to the formation of more MoS.sub.2 active phase, thereby enhancing hydrodesulfurization effect of the hydrodesulfurization catalyst.

TABLE-US-00001 TABLE 1 Components of catalyst (mass fraction, wt %) γ-Al.sub.2O.sub.3 ZSM-5 La.sub.2O.sub.3 CeO.sub.2 CoO MoO.sub.3 Comparative 79.7 — — — 3.5 13.6 Example1 GZ-1 78.9 — — 0.75 3.7 13.4 GZ-2 78.1 — — 1.50 3.8 13.4 GZ-3 78.2 — 1.50 — 3.6 13.5 GZ-4 70.4 8.9 — 0.75 3.5 13.3 Note: “—” represents none; the sun of components of the above catalysts is less than 100% due to that the industrial grade γ- Al.sub.2O.sub.3 used has a certain amount of impurities.

TABLE-US-00002 TABLE 2 Hydrogenation performance of different catalysts North China heavy Jingbo heavy Golmud heavy fraction gasoline gasoline fraction fraction gasoline (1,538 ppm) (2,276 ppm) (1,854 ppm) Sulfur Desulfurization Sulfur Desulfurization Sulfur Desulfurization content rate content rate content rate (ppm) (%) (ppm) (%) (ppm) (%) Comparative 178 88.4 269 88.2 142 92.3 Example 1 GZ-1 13 99.2 21 99.1 18 99.0 GZ-2 6 99.6 10 99.6 10 99.5 GZ-3 22 98.5 34 98.5 23 98.7 GZ-4 39 97.5 52 97.9 43 97.7

TABLE-US-00003 TABLE 3 Changes of olefin and octane number (RON) on different catalysts North China heavy Jingbo heavy Golmud heavy fraction gasoline fraction gasoline fraction gasoline (O = 23.80 wt %) (O = 15.72 wt %) (O = 24.48 wt %) Olefin Olefin Olefin (wt %) ΔRON (wt %) ΔRON (wt %) ΔRON Comparative 5.51 −3.5 3.12 −2.8 4.08 −3.9 Example 1 GZ-1 11.87 −1.7 9.54 −1.5 10.02 −2.0 GZ-2 10.59 −1.9 8.61 −1.7 9.88 −2.0 GZ-3 9.43 −2.2 8.23 −1.7 8.97 −2.3 GZ-4 12.60 −1.2 9.89 −1.0 10.54 −1.6

[0062] It can be seen from Table 2 that the hydrodesulfurization catalyst modified with the rare earth using the method of the present application has very excellent desulfurization performance on high-sulfur FCC gasoline (the sulfur content is >1,500 ppm). Under relatively mild reaction conditions (T=260° C., P=2 MPa), the desulfurization rate can reach to more than 98.5%, and the sulfur content can fall to no more than 35 ppm, and the deep desulfurization is realized.

[0063] It can be seen from further comparison of GZ-1, GZ-2 and GZ-3 that the hydrodesulfurization effect of GZ-1 and GZ-2 obtained after being modified with the rare earth element Ce is better than that of GZ-3 obtained after being modified with the rare earth element La. According to the comparison result of GZ-1 and GZ-2, changing the content of the rare earth element has an very obvious influence on the hydrodesulfurization effect. Appropriately increasing the loading amounts of the rare earth element is conducive to the deep desulfurization of gasoline. For example, the sulfur content in the gasoline products could fall to no more than 10 ppm when GZ-2 is used.

[0064] In addition, according to the result of Example 4, when the rare earth element Ce and the acidic molecular sieve (ZSM-5 molecular sieve) are used together to modify the catalyst, the octane number protection ability of the obtained GZ-4 catalyst is better than the other three examples, but the desulfurization effect is lower than the other examples.

[0065] Moreover, as shown in Table 3, it can be seen from the composition of the product oils, the olefin contents of the product oils obtained after the high-sulfur FCCs are subjected to hydrodesulfurization using the hydrodesulfurization catalysts in Examples 1-3 are higher than that of the unmodified CoMo/γ-Al.sub.2O.sub.3 catalyst. This shows that the hydrodesulfurization catalysts modified with the rare earth element have more excellent olefin protection function than the unmodified CoMo/γ-Al.sub.2O.sub.3 catalyst. In the process of hydrodesulfurization, it is more prone to occur the hydrogenation removal reaction of sulfides, which reduces olefin saturation to a certain extent, thereby improving selectivity of hydrodesulfurization reaction/olefin hydrogenation saturation reaction.

[0066] It can be seen from Tables 2 and 3 and FIG. 3 that the hydrodesulfurization catalyst provided by the present application can not only meet deep desulfurization of high-sulfur FCC gasoline, at the same time but also reduce the loss of octane number. Taking the North China heavy fraction gasoline as an example, the loss of octane number caused by the unmodified CoMo/γ-Al.sub.2O.sub.3 catalyst thereto in Comparative Example 1 is up to 3.5 units. The loss of octane number caused by the hydrodesulfurization catalysts in Example 1-3 modified with the rare earth element is less than 2.5 units, especially the loss of octane number caused by the hydrodesulfurization catalysts (GZ-1 and GZ-2) modified with Ce is less than 2 units.

[0067] In conclusion, the hydrodesulfurization catalyst provided by the present application can realize deep desulfurization of high-sulfur FCC gasoline (the sulfur content is >1500 ppn) under mild process conditions. After the hydrogenation reaction once, the sulfur content can fall to 40 ppm or even no more than 10 ppm, and the hydrodesulfurization catalyst has more excellent olefin protection function, with the final octane number loss of no more than 3.5 units, even no more than 2 units.

[0068] Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solution of the present application other than limiting the present application. Although the present application is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments, or make equivalent substitutions to some or all of the technical features thereof. These modifications or substitutions do not make the essence of the corresponding technical solutions departs from the scope of the technical solutions of the embodiments of the present application.