Light hydrocarbon aromatization method

Abstract

The invention discloses a light hydrocarbon aromatization method, which is characterized in that an aromatization reaction is carried out in a reaction system taking one or more of C4-C7 alkanes as raw materials under aromatization reaction conditions and in the presence of a ZnO / HZSM-5 molecular sieve catalyst, CO is introduced into the reaction system, the molar ratio of CO to C4-C7 alkanes is at most 0.9, the molar ratio of CO to C4-C7 alkanes is at most 0.9, the molar ratio of CO to C4-C7 alkanes is at most 0.9, the molar ratio of CO to C4-C7 alkanes is at most 0.9, and the molar ratio of CO to C4-C7 alkanes is at most 0.9. In the ZnO / HZSM-5 molecular sieve catalyst, based on the mass of the HZSM-5 molecular sieve, the loading amount of ZnO is 1-4% by mass. According to the method, the generation of methane and ethane with low value in aromatization reaction can be effectively inhibited by using a small amount of CO, and the selectivity of propane and butane is improved, so that the yield of valuable products is improved.

Description

Technical Field

[0001] This invention relates to a method for converting light hydrocarbons, and more specifically, to a method for converting light hydrocarbons to produce aromatic hydrocarbons. Background Technology

[0002] Currently, steam cracking and catalytic reforming using naphtha as feedstock are the main aromatics production processes. However, with the increasing deterioration of feedstock quality and the growing scarcity of naphtha resources, traditional aromatics production technologies centered on catalytic reforming face the problem of rising feedstock costs. Furthermore, with the maturation of shale gas extraction technologies, steam cracking feedstocks are gradually shifting towards lighter materials. Ethane and propane will be ideal feedstocks for steam cracking processes in the future, leading to a significant reduction in by-product aromatics.

[0003] With the continuous expansion of refining scale and the increasing depth of processing, low-value light hydrocarbon resources by-products in the refining process are in surplus. Currently, there is a lack of efficient utilization methods for these light hydrocarbon resources, especially low-carbon alkanes. Therefore, converting light alkanes into high-value aromatic products through light hydrocarbon aromatization technology is of considerable significance.

[0004] Despite the rapid development of light hydrocarbon aromatization technology, the high selectivity for methane and ethane remains a problem. The following reports address how to reduce the selectivity for methane and ethane during light hydrocarbon aromatization:

[0005] US8946107B2 and US8809608B2 disclose a light hydrocarbon aromatization method that uses Ge to limit the hydrogenolysis activity of a Pt-modified ZSM-5 molecular sieve catalyst, thereby reducing methane formation.

[0006] The method for aromatizing n-alkanes disclosed in CN111604086A uses Group IVA elements and rare earth ions or alkaline earth metals to achieve appropriate control of the electronic properties of Pt on Pt / KL molecular sieve catalysts, thereby suppressing the occurrence of hydrogenolysis or secondary hydrogenolysis reactions.

[0007] The literature "Enhanced Dehydrogenation Aromatization of Propane by Incorporating Fe and Pt into the Zn / HZSM-5Catalyst" (Industrial & Engineering Chemistry Research, 2018, 57, 16246-16256) reports a propane aromatization catalyst that utilizes the FePt bimetallic sites to promote the recombination and desorption of H atoms during dehydrogenation, thereby reducing the dry gas generated by the hydrogenolysis reaction.

[0008] In summary, existing light hydrocarbon aromatization technologies mostly employ metal promoters to modify catalysts, thereby increasing the recombination and desorption rate of activated hydrogen at metal sites, reducing the occurrence of hydrogenolysis reactions, and achieving the goal of reducing the selectivity of methane and ethane. However, these technologies require the use of additional metal promoters, which is costly. Therefore, it is necessary to develop a low-cost method to reduce the selectivity of methane and ethane in light hydrocarbon aromatization products. Summary of the Invention

[0009] The inventors performed CO-TPD characterization on HZSM-5 molecular sieve, ZnO / HZSM-5 molecular sieve, and nano-ZnO. They found that the spectrum of HZSM-5 molecular sieve showed a strong CO desorption peak only at 200℃, while the spectrum of ZnO / HZSM-5 molecular sieve showed a distinct shoulder peak in the range of 300–550℃. Figure 1 The spectral analysis of nano-ZnO reveals that the shoulder peak is attributed to the adsorption of CO by ZnO on ZnO / HZSM-5. Furthermore, due to the higher dispersion of ZnO on ZnO / HZSM-5, the desorption temperature of CO from these highly dispersed ZnO sites is also higher, thus demonstrating that the ZnO species on the ZnO / HZSM-5 molecular sieve have an adsorption capacity for CO. Under aromatization reaction conditions, co-feeding a certain proportion of CO with C4-C7 feedstock and utilizing the adsorption of CO by ZnO can suppress the adsorption of intermediate products on ZnO active sites and further hydrogenolysis reactions, thereby reducing the formation of methane and ethane during the aromatization of light hydrocarbons. Based on this, the present invention is formed.

[0010] Therefore, the object of this invention is to provide a low-cost method for aromatizing light hydrocarbons to reduce the selectivity of methane and ethane.

[0011] To achieve the above-mentioned objective, the present invention provides a light hydrocarbon aromatization method, which involves an aromatization reaction in a reaction system using one or more C4-C7 alkanes as raw materials under aromatization reaction conditions and in the presence of a ZnO / HZSM-5 molecular sieve catalyst. The method is characterized in that CO is introduced into the reaction system, the molar ratio of CO to the C4-C7 alkanes is at most 0.9, and the ZnO loading in the ZnO / HZSM-5 molecular sieve is 1-4% by mass, based on the mass of the HZSM-5 molecular sieve.

[0012] The light hydrocarbon aromatization method provided by this invention has the following characteristics and advantages:

[0013] 1. The CO feed rate is lower than that of hydrocarbons, which reduces the amount of CO circulating in the unit, improves production efficiency, and reduces energy consumption;

[0014] 2. A small amount of CO can effectively suppress the formation of low-value methane and ethane in the aromatization reaction, improve the selectivity of propane and butane, and thus increase the yield of valuable products. Attached Figure Description

[0015] Figure 1 CO-TPD spectra of HZSM-5 molecular sieve, ZnO / HZSM-5 molecular sieve, and nano ZnO.

[0016] Figure 2 Zn 2p for ZnO / HZSM-5 molecular sieve catalyst 3 / 2 XPS diagram. Detailed Implementation

[0017] The light hydrocarbon aromatization method provided by this invention involves an aromatization reaction in a reaction system using one or more C4-C7 alkanes as raw materials, under aromatization reaction conditions and in the presence of a ZnO / HZSM-5 molecular sieve catalyst. The method is characterized in that CO is introduced into the reaction system, the molar ratio of CO to the C4-C7 alkanes is at most 0.9, and the ZnO / HZSM-5 molecular sieve has a ZnO loading of 1–4% by mass, based on the mass of the HZSM-5 molecular sieve.

[0018] In the method provided by the present invention, the molar ratio of CO to C4-C7 alkane is preferably 0.05 to 0.9, more preferably 0.08 to 0.9:1.

[0019] In the method provided by the present invention, the ZnO loading in the HZSM-5 molecular sieve catalyst is preferably 1.2 to 3.5% by mass, more preferably 1.5 to 3.0% by mass, and most preferably 1.6 to 2.8% by mass, based on the mass of the HZSM-5 molecular sieve.

[0020] In the method provided by this invention, the zinc species in the ZnO / HZSM-5 molecular sieve catalyst is Zn 2+ and [Zn-O-Zn] 2+ Two structures exist, Zn 2+ In Zn 2+ and [Zn-O-Zn] 2+ The proportion of Zn in the preferred form is greater than 40% by mass. 2+ In Zn 2+ and [Zn-O-Zn] 2+ The proportion of Zn in the content is 45% to 60%, more preferably 49% to 59% by mass. 2+ The percentage data comes from XPS characterization, and the ZnO loading data comes from XRF characterization.

[0021] In the method provided by the present invention, the HZSM-5 molecular sieve has a molar ratio of silicon oxide to aluminum oxide of 20 to 100, preferably 25 to 80, and more preferably 40 to 60.

[0022] In the method provided by this invention, the aromatization reaction conditions are: temperature 460–550 °C, pressure 0.05–1 MPa, and the calculated mass hourly space velocity (HHSV) for C4–C7 alkanes is 0.1–3 h⁻¹. -1 The preferred reaction conditions are: temperature 500–530℃, pressure 0.08–0.5 MPa, and calculated mass hourly space velocity (MHV) of C4–C7 alkanes of 0.1–1 h⁻¹. -1 .

[0023] The ZnO / HZSM-5 molecular sieve catalyst provided in this invention can be prepared by an impregnation method, including steps of molecular sieve forming, impregnation, drying, and calcination. The impregnation includes adding an impregnation solution dropwise into the molecular sieve, the impregnation solution containing a ZnO precursor. The ZnO precursor in the impregnation solution is Zn(NO3)2, with a concentration of 16.0–80.0 mg / ml (based on ZnO). The drying temperature is 100–150°C for 8–24 h; the calcination temperature is 500–580°C for 3–6 h. For example, the preparation of the ZnO / HZSM-5 molecular sieve catalyst can involve forming an HZSM-5 molecular sieve, crushing and sieving it to obtain a block sample of 10–20 mesh size, then adding the impregnation solution dropwise into the molecular sieve, followed by drying and calcination. The catalyst prepared using the method provided in this invention is beneficial for reducing the selectivity of methane and ethane in the aromatization reaction of light hydrocarbons.

[0024] In a preferred embodiment of the present invention, the molar ratio of CO to the C4-C7 alkane is 0.1 to 0.9, and the ZnO / HZSM-5 molecular sieve, based on the mass of the HZSM-5 molecular sieve, has a ZnO loading of 1.0 to 3.0% by mass, and a ZnO loading of 1.0% to 3.0% by mass. 2+ In Zn 2+ and [Zn-O-Zn] 2+ The proportion of silica in the HZSM-5 molecular sieve is 50%–60% by mass, and the molar ratio of silica to alumina is 45–55. The aromatization reaction conditions are: temperature 510–525℃, pressure 0.08–0.4 MPa, and the calculated mass hourly space velocity (HSV) for C4–C7 alkanes is 0.2–0.9 h⁻¹. -1 .

[0025] The method provided by this invention can be carried out in reaction devices such as fixed beds, moving beds, or fluidized beds. Those skilled in the art can select a suitable reactor according to actual production needs.

[0026] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0027] In the example, the ZnO / HZSM-5 molecular sieve catalyst was prepared as follows:

[0028] Take 8g of HZSM-5 molecular sieve powder with a silica / alumina molar ratio of 47, and compress the powder into tablets using a tablet press. Crush and sieve the tablets to obtain molecular sieve samples with a size of 10-20 mesh. Weigh 1.1mL of Zn(NO3)2 aqueous solution (calculated as ZnO, its concentration is 75.7mg / mL, the same below) and add it dropwise to 4.2mL of deionized water. After stirring evenly, add the solution dropwise to the 10-20 mesh molecular sieve samples and stir to ensure full adsorption. Then let it stand for 4h. After standing, transfer the sample to an oven at 100℃ and dry for 2h, then calcine it in a muffle furnace at 550℃ for 4h to obtain ZnO / HZSM-5 molecular sieve catalyst A1.

[0029] With other preparation conditions unchanged, only the amounts of Zn(NO3)2 aqueous solution and deionized water were changed. The amount of Zn(NO3)2 aqueous solution was changed from 1.1 mL to 3.0 mL, 3.5 mL, and 5.3 mL, respectively, and the amount of deionized water was changed from 4.2 mL to 2.3 mL, 1.8 mL, and 0 mL, respectively, to prepare the corresponding ZnO / HZSM-5 molecular sieve catalysts, which were numbered A2, A3, and A0, respectively.

[0030] In catalysts A1, A2, A3, and A0, the ZnO loadings, as characterized by XRF, were 1.69 wt%, 2.69 wt%, 3.25 wt%, and 4.93 wt%, respectively.

[0031] Figure 2 Zn 2p for catalysts A1, A2, A3, and A0 3 / 2 XPS spectra, Zn characterization 2+ In Zn 2+ and [Zn-O-Zn] 2+ The percentages were 57%, 50%, 48%, and 44%, respectively.

[0032] Catalysts A4 and A5 were prepared using the same method as catalyst A2, with the only difference being that the HZSM-5 molecular sieve with a silica / alumina molar ratio of 47 was replaced with HZSM-5 molecular sieves with silica / alumina molar ratios of 30 and 70, respectively.

[0033] In catalysts A4 and A5, the ZnO loadings, as characterized by XRF, were 2.71 wt% and 2.75 wt%, respectively.

[0034] In catalysts A4 and A5, Zn was characterized by XPS.2+ The percentages were 53% and 46%, respectively.

[0035] Example 1

[0036] 8g of catalyst A1 was loaded into the reactor and the reactor was heated at 520℃, 0.1MPa, and a mass hourly space velocity (H₂Sv). -1 (Based on n-pentane), under the condition that the molar ratio of CO to n-pentane is 0.1:1, CO and n-pentane are introduced into the reactor to react with the catalyst, and the results are shown in Table 1.

[0037] Example 2

[0038] Example 2 uses the same reaction conditions as Example 1, except that catalyst A1 is replaced with catalyst A2, and the molar ratio of CO to n-pentane in the feed is changed from 0.1:1 to 0.43:1. The results are shown in Table 1.

[0039] Example 3

[0040] Example 3 uses the same reaction conditions as Example 2, except that the molar ratio of CO to n-pentane in the feed is changed from 0.43:1 to 0.9:1. The results are shown in Table 1.

[0041] Example 4

[0042] Example 4 uses the same reaction conditions as Example 1, except that catalyst A1 is replaced with catalyst A4, and the molar ratio of CO to n-pentane in the feed is changed from 0.1:1 to 0.25:1. The results are shown in Table 1.

[0043] Example 5

[0044] The reaction conditions in Example 5 were the same as in Example 4, except that catalyst A4 was replaced with catalyst A5. The results are shown in Table 1.

[0045] Comparative Example 1

[0046] The reaction conditions for Comparative Example 1 were the same as those for Example 2, except that pure pentane was used as the feed and reacted with the catalyst in the reactor. The results are shown in Table 1.

[0047] Comparative Example 2

[0048] Comparative Example 2 was performed under the same reaction conditions as Example 3, except that catalyst A2 was replaced with catalyst A0. The results are shown in Table 1.

[0049] Table 1

[0050]

[0051] In Table 1:

[0052] C1+C2 represents methane and ethane, and the C1+C2 selectivity = the mass fraction of methane in the product + the mass fraction of ethane in the product;

[0053] C3+C4 represents propane and butane, and the C3+C4 selectivity = the mass fraction of propane in the product + the mass fraction of butane in the product;

[0054] A represents aromatic hydrocarbons, and A selectivity = the sum of the mass fractions of benzene, toluene, xylene, and C9+ aromatic hydrocarbons in the product;

[0055] As shown in Table 1, compared with Comparative Example 1, the mass selectivity of methane and ethane decreased in Examples 2 and 3, indicating that CO effectively suppressed the formation of methane and ethane during the reaction, while the selectivity of valuable products such as propane, butane, and aromatics increased. Compared with Comparative Example 2, Example 3 shows that the zinc oxide loading in the catalyst was too high, which was detrimental to the reduction in the mass selectivity of methane and ethane and the improvement in the selectivity of valuable products such as propane, butane, and aromatics.

[0056] Example 6

[0057] The above-mentioned 8g of catalyst A3 was loaded into a reactor and heated at a temperature of 500℃, a pressure of 0.1MPa, and a space velocity of 0.3h. -1 (Based on n-pentane), under the condition that the molar ratio of CO to n-pentane is 0.9:1, the raw materials are introduced into the reactor to react with the catalyst, and the results are shown in Table 2.

[0058] Example 7

[0059] The reaction conditions in Example 7 are the same as in Example 6, except that catalyst A3 is replaced with catalyst A2 and the molar ratio of CO to n-pentane in the feed is changed from 0.9:1 to 0.25:1. The results are shown in Table 2.

[0060] Comparative Example 3

[0061] Comparative Example 3 was reacted under the same conditions as Example 7, except that it was fed with pure pentane and reacted with the catalyst in the reactor. The results are shown in Table 2.

[0062] Example 8

[0063] The above-mentioned 8g of catalyst A2 was loaded into a reactor and subjected to a temperature of 525℃, a pressure of 0.3MPa, and a space velocity of 0.8h. -1 (Based on n-pentane), under the condition that the molar ratio of CO to n-pentane is 0.9:1, the raw materials are introduced into the reactor to react with the catalyst, and the results are shown in Table 2.

[0064] Comparative Example 4

[0065] Comparative Example 4 was reacted under the same conditions as Example 8, except that it was fed with pure pentane and reacted with the catalyst in the reactor. The results are shown in Table 2.

[0066] Table 2

[0067]

[0068] As shown in Table 2, compared with Comparative Example 3 in Example 7 and Comparative Example 4 in Example 8, the mass selectivity of methane and ethane decreased, indicating that CO effectively suppressed the formation of methane and ethane during the reaction, and improved the selectivity of valuable products such as propane, butane, and aromatics.

Claims

1. A light hydrocarbon aromatization method, which is an aromatization reaction in a reaction system in which one or more of C4 to C7 alkanes is used as a raw material in the presence of an aromatization reaction condition and a ZnO / HZSM-5 molecular sieve catalyst, characterized by, The molar ratio of the CO to the C4-C7 alkane in the reaction system is at most 0.9, and the ZnO loading in the ZnO / HZSM-5 molecular sieve catalyst is 1-4% by mass based on the mass of the HZSM-5 molecular sieve.

2. The aromatization process according to claim 1, characterized in that, The aromatization reaction conditions are temperature 460-550°C, pressure 0.05-1 MPa, and mass space velocity of C4-C7 alkanes 0.1-3 h -1 .

3. The aromatization process of claim 1 wherein, The ZnO loading in the ZnO / HZSM-5 molecular sieve catalyst is 1.5-3.5% by mass based on the mass of the HZSM-5 molecular sieve.

4. The aromatization method according to claim 1 or 3, characterized by, In the ZnO / HZSM-5 molecular sieve catalyst, Zn 2+ In Zn 2+ and [Zn-O-Zn] 2+ is greater than 40 mass%.

5. The aromatization method according to claim 1 or 3, characterized by, The ZnO / HZSM-5 molecular sieve catalyst has Zn 2+ In the Zn 2+ and [Zn-O-Zn] 2+ The content of Zn in the ZnO / HZSM-5 molecular sieve catalyst is 45% to 60% by mass, preferably 49% to 59% by mass.

6. The method of aromatization according to claim 1, characterized in that, The HZSM-5 molecular sieve has a molar ratio of silicon oxide to aluminum oxide of 20-100.

7. The method of aromatization according to claim 1, characterized in that, The HZSM-5 molecular sieve has a molar ratio of silicon oxide to aluminum oxide of 25-80.

8. The method of aromatization according to claim 1, characterized in that, The molar ratio of the CO to the C4-C7 alkane in the reaction system is 0.05-0.9:

1.

9. The method of aromatization according to claim 1, characterized in that, The molar ratio of the CO to the C4-C7 alkane in the reaction system is 0.08-0.9:

1.

10. The method of aromatization according to claim 1, characterized in that, The ZnO / HZSM-5 molecular sieve catalyst is prepared by an impregnation method.

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