IN SITU BIFUNCTIONAL CATALYST FOR DEEP DESULFURIZATION AND INCREASING OCTANE NUMBER OF GASOLINE AND PREPARATION METHOD THEREOF

Abstract

Provided are an in situ bifunctional catalyst for deep desulfurization and increasing octane number of gasoline, and its preparation method and application. The bifunctional catalyst includes a modified catalyst carrier and a loaded active metal, where the modified catalyst carrier is a composite carrier prepared through mixing γ-Al.sub.2O.sub.3 and an acidic molecular sieve by a binder and calcining. When the bifunctional catalyst provided by the present application is used for hydrodesulfurization of gasolines, deep desulfurization, olefin reduction and octane number preservation can be realized simultaneously, thereby obtaining a high-quality oil product.

Claims

1. A bifunctional catalyst for hydrodesulfurization coupled with isomerization, comprising a modified catalyst carrier and a loaded active metal, wherein the modified catalyst carrier is a composite carrier prepared by mixing γ-Al.sub.2O.sub.3 and an acidic molecular sieve by a binder and calcining.

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

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

4. The bifunctional catalyst according to claim 1, wherein the catalyst for hydrodesulfurization is obtained by loading an active metal onto the modified catalyst carrier via an impregnation method, then aging, drying, and calcining.

5. A preparation method of the bifunctional catalyst for hydrodesulfurization coupled with isomerization according to claim 1, comprising: mixing γ-Al.sub.2O.sub.3 and an acidic molecular sieve by a binder and calcining, to prepare a modified catalyst carrier; and loading an impregnation solution containing an active metal onto the modified catalyst carrier by an impregnation method, then aging, drying, calcining, to obtain the bifunctional catalyst.

6. The preparation method according to claim 5, further comparing a step of preparing the impregnation solution: mixing a compound containing the active metal, an organic complexing agent and water to obtain the impregnation solution; wherein the organic complexing agent includes at least two carboxyl groups in its molecular structure, and the organic complexing agent is soluble in water.

7. The preparation method according to claim 6, wherein the organic complexing agent is selected from at least one of citric acid, tartaric acid, nitrilotriacetic acid and amino sulfonic acid.

8. The preparation method according to claim 5, wherein after the impregnation solution containing the active metal is loaded onto the modified catalyst carrier, aging at room temperature for 6-12 h, drying at 100-120° C. for 6-12 h, and calcining at 450-600° C. for 4-8 h to obtain the bifunctional catalyst.

9. A hydrodesulfurization method of gasoline, adopting a bifunctional catalyst for hydrodesulfurization coupled with isomerization, wherein the bifunctional catalyst comprises a modified catalyst carrier and a loaded active metal, wherein the modified catalyst carrier is a composite carrier prepared by mixing γ-Al.sub.2O.sub.3 and an acidic molecular sieve by a binder and calcining.

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

11. The hydrodesulfurization method according to claim 9, wherein the active metal is selected from two or more of VIB Group and VIII Group elements in the Periodic Table of Elements.

12. The hydrodesulfurization method according to claim 9, wherein the catalyst for hydrodesulfurization is obtained by loading an active metal onto the modified catalyst carrier via an impregnation method, then aging, drying, and calcining.

13. The hydrodesulfurization method according to claim 9, wherein during an operation, a temperature is controlled to 250-300° C., a pressure is 1.5-3.0 MPa, a volume space velocity is 3-8 h.sup.−1, and a volume ratio of hydrogen to oil is 150-350.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0044] FIG. 1 is a Py-FTIR diagram of the total acid amount of catalysts provided by Examples 1-3 and Comparative example of the present application;

[0045] FIG. 2 is a H.sub.2-TPR diagram of catalysts prepared by Examples 1-3 and Comparative example of the present application;

[0046] FIG. 3 is a HRTEM diagram of the sulfurized state of catalysts prepared by Examples 1-3 and Comparative example of the present application after hydrodesulfurization reaction; and

[0047] FIG. 4 is a variation diagram of hydrodesulfurization rate and olefin isomerization conversion rate as a function of BAS/LAS ratio.

DESCRIPTION OF EMBODIMENTS

[0048] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to drawings in the embodiments of the present application. Obviously, the described embodiments are part of embodiments of the present application, but not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by skilled in the art without creative work belong to the protection scope of the present application.

Example 1

[0049] The present example provides the preparation method of a bifunctional catalyst for hydrodesulfurization coupled with isomerization, including the following steps:

[0050] 1. Weighing 16 g of γ-Al.sub.2O.sub.3, and then mixing γ-Al.sub.2O.sub.3 and ZSM-5 in a mass ratio of 7.8:1, adding 28.6 g of sesbania powders and 12 ml dilute nitric acid (3%), drying at 120° C. for about 8 h and calcining at 500° C. for 4 h, to obtain the γ-Al.sub.2O.sub.3/ZSM-5 as a composite carrier.

[0051] 2. Taking an appropriate amount of water, stirring and heating to 40° C., adding citric acid (CA), and stirring until completely dissolved; then adding 2.5 g of cobalt carbonate (CA/Co=1.5) and stirring until no bubble is generated; slowly heating the solution to a boiling state so as to dissolve all materials (no bubble is generated), stopping heating, and stopping stirring when the temperature is reduced to room temperature; adding ammonia to 85% of a final volume, then adding slowly 6.2 g of ammonium heptamolybdate, stirring until completely dissolved, supplementing ammonia to the final volume, sealing and storing, ready for use.

[0052] 3. Loading an impregnation solution prepared in step 2 onto the AZ composite carrier prepared in step 1 by anisometric impregnation method, and then stirring for 10 min after saturation, ageing at room temperature for 8 h, drying at 120° C. for 6 h, and performing temperature programmed calcination: firstly calcining at 200° C. for 50 min, then calcining at 300° C. for 30 min, and finally calcining at 500° C. for 4 h to obtain the bifunctional catalyst, recorded as AZ-1, a specific composition of the bifunctional catalyst AZ-1 is shown in Table 1.

COMPARATIVE EXAMPLE

[0053] The present Comparative example provides a traditional CoMo/γ-Al.sub.2O.sub.3 catalyst, its preparation method is as follows: no treatment is done for γ-Al.sub.2O.sub.3, a preparation process of the impregnation solution and the isometric impregnation method are the same as those in steps 2-3 of Example 1, respectively. The composition of CoMo/γ-Al.sub.2O.sub.3 catalyst is shown in Table 1.

Example 2

[0054] The present example provides a preparation method of a bifunctional catalyst for hydrodesulfurization coupled with isomerization, and the process steps are basically the same as those in Example 1, except that: the mass ratio of γ-Al.sub.2O.sub.3 to ZSM-5 is about 4.1:1, and the obtained bifunctional catalyst is named as AZ-2, and its specific composition is shown in Table 1.

Example 3

[0055] The present example provides a preparation method of a bifunctional catalyst for hydrodesulfurization coupled with isomerization, and the process steps are basically the same as those in Example 1, except that: ZSM-5 molecular sieve used in Example 1 is replaced by MCM-41 molecular sieve, the mass ratio of γ-Al.sub.2O.sub.3 to ZSM-5 is about 7.9:1, and the obtained bifunctional catalyst is named as AM, and its specific composition is shown in Table 1.

[0056] A pyridine adsorption infrared spectrum (Py-FTIR) diagram of total acid amounts of catalysts provided by Examples 1-3 and the Comparative example is shown in FIG. 1, and a H.sub.2-TPR diagram is shown in FIG. 2.

[0057] The desulfurization effect and olefin isomerization of the catalysts provided by Examples 1-3 and Comparative example were evaluated, specifically as follows:

[0058] 3.2 g of catalyst was taken and put into a temperature constant zone of a fixed bed reactor with an inner diameter of 8 mm and the quartz sand is filled above and below the catalyst. The catalyst was pre-sulfurized by 3 wt % of CS.sub.2 solution as a pre-sulfurization solution. The reaction conditions of pre-sulfurization were as follows: temperature 300° C., pressure 2.5 MPa, H/0=300, volume space velocity 3 h.sup.−1, time of pre-sulfurization 6h.

[0059] After the pre-sulfurization reaction was completed, the hydrogenation reaction performance of each catalyst was tested using model oil (olefin content is 19.3 wt %, thiophene sulfur content is 996 ppm, solvent is N-heptane) and North China heavy fraction gasoline (above 100° C., sulfur content is 1,078 ppm, composition of group is shown in Table 2) as raw materials. The process conditions of the hydrogenation reaction were as follows: temperature 270° C., pressure 2 MPa, H/0=300, volume space velocity 3.5 h.sup.−1. The hydrogenation reaction results of the model oil and the North China heavy fraction gasoline by each catalyst were shown in Table 3-1 and Table 3-2 respectively. The catalyst samples after reaction were taken for characterizing and testing. The obtained HRTEM results were shown in FIG. 3.

[0060] In the Py-FTIR diagram, the characteristic peaks near 1450 and 1622 cm.sup.−1 are the characteristic absorption peaks of Lewis acid (L acid for short). It can be seen from FIG. 1 that, compared with the traditional CoMo/γ-Al.sub.2O.sub.3 catalyst provided by the Comparative example, the bifunctional catalysts provided by Examples 1-3 have more acid centers and higher B/L value, thus giving the bifunctional catalysts more excellent acid catalytic activity. In the hydrotreating process of FCC gasoline, it is more conducive to promoting hydrocarbon isomerization reaction, which can also be directly confirmed from Table 3-1 and Table 3-2.

[0061] Moreover, compared with the bifunctional catalysts in Example 1 and Example 2, AZ-2 has stronger acidic center and better isomerization performance. However, since the decrease in the proportion of γ-Al.sub.2O.sub.3 in the composite carrier will lead to a large reduction on hydrogenation active sites, the hydrodesulfurization performance of AZ-2 is lower than that of AZ-1, which can also be confirmed from Table 3-1 and Table 3-2.

[0062] According to the H.sub.2-TPR results of catalyst in oxidized state (FIG. 2), compared to the conventional CoMo/γ-Al.sub.2O.sub.3 catalyst provided by the Comparative example, low temperature characteristic peaks (Mo.sup.6+.fwdarw.H.sub.xMoO.sub.3.fwdarw.Mo.sup.4+) of Mo species of the bifunctional catalyst provided by Examples 1-3 are decreased from 553° C. to 542° C. (AZ-1), 536° C. (AZ-2) and 538° C. (AM), respectively. This indicates that Mo species in high valence state of the bifunctional catalyst is more readily reduced to a sulfurized product MoS.sub.2 having a higher degree of sulfurization, which is beneficial for the hydrodesulfurization reaction.

[0063] According to the results of a high resolution transmission electron microscope (HRTEM) (FIG. 3, a scale in the drawing is 5 nm), an average length L of MoS.sub.2 active phase of the conventional CoMo/γ-Al.sub.2O.sub.3 catalyst is 2.9 nm and the average number N of stacking layers is 2.04. While, an average length L of MoS.sub.2 active phase of the bifunctional catalyst provided by Example 1 is 3.6 nm, and the average number N of stacking layers is 2.87; an average length L of MoS.sub.2 active phase of the bifunctional catalyst provided by Example 2 is 3.34 nm, and the average number N of stacking layers is 2.11; an average length L of MoS.sub.2 active phase of the bifunctional catalyst provided by Example 3 is 3.15 nm, and the average number N of stacking layers is 2.41. The average length L and average number of stacking number N of MoS.sub.2 active phases of AZ and AM bifunctional catalysts are higher than those of the corresponding catalyst of Comparative example. This indicates that an interaction between the composite carrier and the active metal of the bifunctional catalysts is weak and more MoS.sub.2 active phases are formed, so the bifunctional catalyst has stronger hydrodesulfurization effect than Comparative example.

[0064] Moreover, AM bifunctional catalyst has more B acid centers than AZ-1 and AZ-2 bifunctional catalysts, and thus shows the strongest isomerization performance. However, too many acidic sites have occupied original hydrogenation active sites, resulting in the hydrodesulfurization activity of AM bifunctional catalyst decreased compared with AZ-1 and AZ-2 bifunctional catalysts, which can also be confirmed from Table 3-1 and Table 3-2.

TABLE-US-00001 TABLE 1 Composition of catalysts (wt %) γ-Al.sub.2O.sub.3 ZSM-5 MCM-41 CoO MoO.sub.3 Comparative example 77.4 — — 3.3 13.2 Example 1(AZ-1) 68.9 8.8 — 3.4 13.3 Example 2(AZ-2) 62.4 15.3  — 3.3 13.1 Example 3(AM) 68.1 — 8.6 3.5 13.3 Note: “—” stands for not present; the composition of the catalyst also includes unavoidable impurities introduced by the industrial grade raw material γ-Al.sub.2O.sub.3 used.

TABLE-US-00002 TABLE 2 Composition of North China heavy fraction gasoline group N- Ole- Cyclo- Aromatic Carbon alkane Isoalkane fin alkane hydrocarbon Total number (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 7 0.60 1.04 6.27 1.79 7.38 17.08 8 1.83 11.38 11.49 3.68 22.12 50.51 9 1.04 8.34 5.12 1.93 8.93 25.36 10 0.33 3.47 0.83 0.29 0.67 5.58 11 0.18 0.68 0.19 0.01 0.00 1.05 Total 3.98 24.91 23.80 7.70 43.10 100.0

TABLE-US-00003 TABLE 3-1 Hydrogenation reaction performance of different catalysts for model oil Sulfur Olefin N-alkane Isoalkane content Desulfurization content content content (ppm) rate (%) (wt %) (wt %) (wt %) Model oil 996 — 19.3 — — Comparative 132 86.7 8.2 11.2  1.3 example AZ-1 20 98.0 11.3 8.0 4.6 AZ-2 56 94.4 12.6 6.7 6.5 AM 78 92.2 13.2 6.1 7.1

TABLE-US-00004 TABLE 3-2 Hydrogenation reaction performance of different catalysts for North China heavy fraction gasoline Sulfur Olefin Isoalkane content Desulfurization content content Octane (ppm) rate (%) (wt %) (wt %) number North China 1,078 — 23.8 24.9 84.2 heavy fraction gasoline Comparative 269 75.1 9.6 25.2 81.5 example AZ-1 41 96.2 12.3 27.1 84.1 AZ-2 96 91.2 15.6 29.3 84.7 AM 112 89.6 13.8 30.7 85.2

[0065] It can be seen from Table 3-1 that, the bifunctional catalyst provided by Examples 1-3 of the present application has excellent hydrodesulfurization and isomerization performance for the mixed model oil of thiophene and olefin, with the desulfurization rate of more than 90%, even as high as 98%. Moreover, from the composition distribution of the product oil, the bifunctional catalysts provided by Examples 1-3 can significantly inhibit the olefin hydrogenation saturation reaction and greatly promote the olefin isomerization reaction. Therefore, the bifunctional catalysts provided by Examples 1-3 are significantly superior to Comparative example in hydrodesulfurization performance and olefin isomerization performance.

[0066] It can be seen from Table 2 and Table 3-2 that, the bifunctional catalyst provided by Examples 1-3 of the present application has excellent desulfurization and olefin reduction performance for North China heavy fraction gasoline, and meanwhile can ensure no loss or even slight increase of octane number. From the composition of the product oil, the bifunctional catalysts in Examples 1-3 have better desulfurization effect than the traditional catalyst in the Comparative example, where:

[0067] For Example 1, the desulfurization rate of AZ-1 bifunctional catalyst is as high as 96.2%, and the sulfur content in North China heavy fraction gasoline can be reduced to about 40 ppm after one desulfurization reaction. Moreover, a large number of branched alkanes are generated due to isomerization reaction. For the isomerization reaction of olefins, the higher the degree of branching, the greater the contribution to octane number. Therefore, the loss of octane number during hydrogenation is effectively alleviated, and the octane number of oil is protected. Specifically, for AZ-1, the loss of octane number after hydrogenation of gasoline is only 0.1 unit.

[0068] For Example 2, since the content of ZSM-5 molecular sieve was higher than that of Example 1, acidity of the composite carrier was further enhanced, and thus AZ-2 showed stronger isomerization effect than AZ-1. This is mainly reflected in two aspects: on the one hand, from the product distribution, a product oil for AZ-2 contains more isoalkanes; on the other hand, the octane number of the product oil for AZ-2 is 84.7, which is higher than that of AZ-1 (84.1), even 0.5 units higher than that of the raw material oil, This indicates that the outstanding isomerization activity of AZ-2 can ensure that the octane number of FCC gasoline does not reduce but increase during the hydrogenation reaction, which is more obvious for the AM bifunctional catalyst in Example 3.

[0069] After hydrogenation reaction by the AM bifunctional catalyst in Example 3, the octane number of the product oil increased by 1.0 units. However, the hydrodesulfurization activity of AM bifunctional catalyst is lower than that of AZ-1 and AZ-2 since too many acid centers on the surface of AM bifunctional catalyst replace the original hydrogenation active centers.

[0070] In view of the above, the bifunctional catalyst provided by the present application can be used to solve the problems of deep desulfurization, olefin reduction and octane number preservation in a process of quality upgrading of FCC gasoline.

[0071] Based on the performance study of the bifunctional catalysts obtained in the previous examples, the variation rules of hydrodesulfurization (HDS) rate (%) and conversion of isomerization (%) of olefin as a function of BAS/LAS ratio are summarized, roughly shown in FIG. 4. Specifically, within a certain range, with the increase of ratio of BAS/LAS of the surface of the bifunctional catalyst, the hydrodesulfurization rate and the conversion of isomerization showed an upward trend. This indicates that the increase of B acid centers on the surface of γ-Al.sub.2O.sub.3 and the decrease of L acid centers at the same time are conducive to the hydrogenation reaction and isomerization of gasoline, thus realizing deep desulfurization, olefin reduction and octane number preservation of gasoline, and finally obtaining high-quality gasoline products.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or equivalently replace some or all of the technical features therein; these modifications or substitutions do not make the essence of the corresponding technical solution depart from the scope of the technical solutions of the embodiments of the present application.