Method for catalyzing high-selectivity synthesis of light aromatic hydrocarbon from CO2 coupled pentane by using Ga / Ga-MFI (Ga / Ga-MFI)

Abstract

The invention provides a method for high-selectivity synthesis of light aromatic hydrocarbon by using Ga / Ga-MFI to catalyze CO2 coupled pentane. The molecular sieve is tabletted, ground and sieved, and sieved molecular sieve particles are selected as a catalyst. The method comprises the following steps: loading a catalyst into a constant-temperature area of a fixed bed reactor, pretreating with H2, conveying pentane to the fixed bed reactor, continuously bringing pentane steam vaporized in the constant-temperature area into a catalyst bed layer through carrier gas CO2 and inert gas, pressurizing the reaction, and monitoring the product on line by gas chromatography. A CO2 insertion path on an H-ZMS-5 reaction catalyst in the prior art is abandoned, the reasonable design of the catalyst provides a new CO2 coupled pentane aromatization path, and the path has higher atom economy and environmental influence advantages, and is more beneficial for connecting the whole reaction in series so that CO2 is efficiently coupled with pentane to prepare light aromatic hydrocarbon with high selectivity. Ga / Ga-MFI is adopted as the catalyst, so that the activity and the stability of the light aromatic hydrocarbon prepared by coupling the CO2 with the pentane are improved, and the light aromatic hydrocarbon can be recycled.

Description

A method for highly selective synthesis of light aromatics from pentane using Ga / Ga-MFI catalysis coupled with CO2. Technical Field

[0001] This invention relates to a method for producing light aromatic hydrocarbons by catalytically coupling CO2 with pentane dehydrogenation using Ga / Ga-MFI, belonging to the field of CO2-coupled alkane conversion technology and also to the field of molecular sieve applications. Background Technology

[0002] Light aromatic hydrocarbons (BTX) are mainly derived from catalytic reforming and catalytic cracking oils from fossil fuels, and their production is limited. Pentane, as a widely available hydrocarbon product in the petrochemical industry, is an effective means of increasing resource added value and supplementing light aromatic hydrocarbons through aromatization.

[0003] CO2 is a major component of greenhouse gases, and its massive emissions in recent years have caused a severe greenhouse effect, triggering global climate change. The CO2 hydrogenation reaction is exothermic, and low temperature is a crucial condition for the reaction. Pentane aromatization, on the other hand, is endothermic; the coupling of these two steps can drive the reaction forward. Furthermore, the combination of CO2 with the hydrogen produced during pentane aromatization, converting it into highly beneficial byproducts, can effectively utilize the large amounts of CO2 emitted from the excessive use of fossil fuels, reducing dependence on fossil fuels.

[0004] Currently, in CO2-coupled pentane aromatization to produce aromatics, HZSM-5 molecular sieves combined with metallic Zn are often used. However, this method suffers from deactivation of Al active sites due to carbon deposition and Zn migration, ultimately yielding approximately 40% BTX product. Furthermore, the CO2-pentane coupling pathway is a CO2 insertion pathway, resulting in low efficiency. In addition, the CO2 reduction conversion process involves a counter-current water-gas competition reaction, severely impacting CO2 conversion efficiency and becoming a major factor limiting the reaction's high efficiency. Therefore, optimizing the active sites of CO2-coupled pentane to enhance the activity of molecular sieves in pentane aromatization to produce light aromatics and developing new reaction pathways are of great significance for CO2-coupled pentane aromatization reactions. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing light aromatic hydrocarbons by Ga / Ga-MFI-catalyzed pentane dehydrogenation coupled with CO2 hydrogenation.

[0006] The main concept of this invention is as follows:

[0007] A method for synthesizing light aromatics from pentane via Ga / Ga-MFI-catalyzed pentane dehydrogenation coupled with CO2 hydrogenation, the method comprising:

[0008] Molecular sieves are compressed, ground, and sieved to select the sieved molecular sieve particles as catalysts. The catalysts are placed in the isothermal zone of a fixed-bed reactor for reduction pretreatment. The raw materials CO2 and liquid pentane are delivered to the fixed-bed reactor at a certain flow rate through gas cylinders and constant flow pumps, respectively. The raw material vapors, which are rapidly vaporized in the vaporization chamber, are continuously carried into the catalyst bed by CO2 gas and inert gas. The reaction is pressurized and the products are finally analyzed online by gas chromatography.

[0009] The catalyst is any one of Ga-MFI, H-ZSM-5, Ga / S-1, or Ga / Ga-MFI.

[0010] The Si / Al molar ratio in the H-ZSM-5 catalyst is 40-120, preferably 80.

[0011] The Si / Ga molar ratio in the Ga-MFI catalyst is 40-120, preferably 40.

[0012] The catalyst has a Ga loading of 1–15 wt.%, preferably 5 wt.%.

[0013] The catalyst particles are 20-80 mesh, preferably 40-60 mesh.

[0014] The reduction pretreatment is performed in an H2 atmosphere with a concentration of 10-100%, preferably 100%.

[0015] The pentane liquid flow rate is 0.5 to 1.25 mL / h, preferably 0.5 mL / h.

[0016] The flow rates of CO2 gas and N2 inert gas are 11-22 mL / min, preferably 18 mL / min.

[0017] The reaction pressure is 0.1 to 3 MPa, preferably 2 MPa.

[0018] The temperature of the constant temperature zone is 450-550℃, preferably 550℃.

[0019] The volume ratio of CO2 gas to N2 inert gas is 0:5, 2:3 or 4:1, preferably 2:3.

[0020] The molecular sieve-catalyzed CO2 hydrogenation coupled with pentane dehydrogenation to drive the synthesis of light aromatics from pentane showed the best conversion effect between pentane and CO2 when the pentane flow rate was 0.5 mL / h, the isothermal temperature was 550℃, and the CO2 and nitrogen (volume ratio CO2:N2 = 2:3) flow rates were 18 mL / min. The pentane conversion rate reached 99%, the CO2 conversion rate was 3.8%, the total aromatics selectivity reached 85%, and the light aromatics selectivity reached 80%.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] By abandoning the existing CO2 insertion pathway into pentane, the Ga / Ga-MFI catalyst used in this invention enables the control of the reaction pathway, and the reaction steps are simple.

[0023] The reaction pathway used in this invention has a high raw material conversion rate and exhibits superior activity and a 99% conversion rate of pentane in CO2 coupled pentane aromatization tests.

[0024] The catalyst Ga / Ga-MFI prepared by this invention has a simple process, high reproducibility, and can be produced on a large scale. Attached Figure Description

[0025] Figure 1 shows the activity-time variation of the Ga-supported Ga-MFI-40 catalyst.

[0026] Figure 2 shows a comparison of the activity of the Ga / Ga-MFI-40 catalyst at different pentane flow rates.

[0027] Figure 3 shows a comparison of the activity of the Ga / Ga-MFI-40 catalyst under different CO2 and N2 volume ratios.

[0028] Figure 4 shows a comparison of the activity of the Ga / Ga-MFI-40 catalyst at different temperatures.

[0029] Figure 5 shows a comparison of the activities of Ga-MFI molecular sieve catalysts with different Si / Ga molar ratios in Ga / S-1.

[0030] Figure 6 shows a comparison of the activities of Ga / H-ZSM-5-80 and H-ZSM-5 molecular sieve catalysts with different Si / Al molar ratios. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific examples and accompanying drawings. These examples will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. Furthermore, it is noted that for those skilled in the art, the optimal data in this invention are only applicable to this invention, and reasonable adjustments and improvements made without departing from the concept of the invention are all within the scope of protection of this invention.

[0032] Example 1

[0033] 0.2g Ga / Ga-MFI-40 molecular sieve was compressed into tablets, ground, and sieved. The sieved 40-60 mesh molecular sieve particles were selected as the catalyst. The catalyst was placed in the isothermal zone of a fixed-bed reactor and reduced at 550℃ in a 100% H2 atmosphere for 2 hours. Liquid pentane was pumped to the vaporization chamber at a flow rate of 0.5mL / h using a constant flow pump. The rapidly vaporized raw material vapor was continuously carried into the catalyst bed by a mixture of CO2 and N2 (volume ratio CO2:N2 = 2:3) at a flow rate of 18mL / min. The reaction was carried out at 500℃ and pressurized to 2MPa. Finally, the products were analyzed online by gas chromatography. The activity-time change is shown in Figure 1.

[0034] Within 7 hours, with the catalyst being Ga / Ga-MFI-40, the conversion rate of pentane remained stable at 98%, the conversion rate of CO2 remained stable at 3.2%, the selectivity of aromatics remained stable at ~81%, and the selectivity of light aromatics remained stable at ~76%.

[0035] Experimental results show that Ga / Ga-MFI-40 has good activity for the CO2-coupled pentane dehydrogenation to produce light aromatics.

[0036] Example 2

[0037] For the Ga / Ga-MFI-40 catalyst, the CO2-coupled pentane dehydrogenation to light aromatics reaction was carried out using the same method as in Example 1, but the liquid pentane injection flow rate was changed to 0.75, 1.0, and 1.25 mL / h. The effect of the pentane injection flow rate on the CO2-coupled pentane dehydrogenation to light aromatics reaction of the Ga / Ga-MFI-40 catalyst is shown in Figure 2.

[0038] When the liquid pentane injection flow rate is 0.5 mL / h, the conversion rate of pentane is 98%, the CO2 conversion rate is 3.2%, the aromatic selectivity is 81%, and the light aromatic selectivity is 76%. When the pentane injection flow rate is 0.75 mL / h, the conversion rate of pentane is 99%, the CO2 conversion rate is 3.3%, the aromatic selectivity is 75%, and the light aromatic selectivity is 71%. When the pentane injection flow rate is 1.0 mL / h, the conversion rate of pentane is 99%, the CO2 conversion rate is 4.3%, the aromatic selectivity is 63%, and the light aromatic selectivity is 59%. When the pentane injection flow rate is 1.25 mL / h, the conversion rate of pentane is 99%, the CO2 conversion rate is 4.6%, the aromatic selectivity is 57%, and the light aromatic selectivity is 54%.

[0039] Experimental results show that the CO2-coupled pentane aromatization reaction to produce light aromatics is more active when the liquid pentane injection flow rate is reduced to 0.5 mL / h. This may be because the pentane aromatization reaction is a volume expansion process, and increased pressure is not conducive to the reaction.

[0040] Example 3

[0041] For the Ga / Ga-MFI-40 catalyst, the CO2-coupled pentane dehydrogenation to light aromatics reaction was carried out using the same method as in Example 1, but the volume ratio of the CO2 and N2 mixture was changed to 0:5 and 4:1. The effect of the CO2 proportion on the CO2-coupled pentane to light aromatics reaction of the Ga / Ga-MFI-40 catalyst is shown in Figure 3.

[0042] When the CO2:N2 volume ratio is 0:5, the conversion rate of pentane is 97%, the aromatic selectivity is 81%, and the light aromatic selectivity is 70%. When the CO2:N2 volume ratio is 2:3, the conversion rate of pentane is 98%, the CO2 conversion rate is 3.2%, the aromatic selectivity is 81%, and the light aromatic selectivity is 76%. When the CO2:N2 volume ratio is 4:1, the conversion rate of pentane is 96%, the CO2 conversion rate is 1.5%, the aromatic selectivity is 73%, and the light aromatic selectivity is 68%.

[0043] Experiments show that a CO2 concentration that is too low or too high in the gas mixture is detrimental to the CO2-coupled pentane-to-light aromatic hydrocarbon reaction. Therefore, the optimal CO2:N2 volume ratio is 2:3.

[0044] Example 4

[0045] For the Ga / Ga-MFI-40 catalyst, the CO2-coupled pentane dehydrogenation reaction to produce light aromatics was carried out using the same method as in Example 1, but the reaction temperature was changed to 400, 450, and 550 °C. The effect of temperature on the CO2-coupled pentane dehydrogenation reaction to produce light aromatics using the Ga / Ga-MFI-40 catalyst is shown in Figure 4.

[0046] At a reaction temperature of 400℃, the conversion rate of pentane is 88%, the CO2 conversion rate is 1.1%, the aromatic selectivity is 57%, and the light aromatic selectivity is 51%. At a reaction temperature of 450℃, the conversion rate of pentane is 94%, the CO2 conversion rate is 2.3%, the aromatic selectivity is 67%, and the light aromatic selectivity is 63%. At a reaction temperature of 500℃, the conversion rate of pentane is 98%, the CO2 conversion rate is 3.2%, the aromatic selectivity is 81%, and the light aromatic selectivity is 76%. At a reaction temperature of 550℃, the conversion rate of pentane is 99%, the CO2 conversion rate is 3.8%, the aromatic selectivity is 85%, and the light aromatic selectivity is 80%.

[0047] Experimental results show that as the reaction temperature increases, the pentane conversion rate increases to 99%, the CO2 conversion rate increases to 3.8%, the aromatic selectivity is 85%, and the light aromatic selectivity is 80%. Therefore, the Ga / Ga-MFI-40 catalyst at 550℃ exhibits good activity for the CO2-coupled pentane aromatization reaction to produce light aromatics.

[0048] Comparative Example 1

[0049] The process of CO2 coupled with pentane dehydrogenation to produce light aromatics was carried out using the same method as in Example 1, but the molecular sieve was changed to Ga / S-1 and Ga-MFI with different Si / Ga molar ratios. The effects of the state of Ga and the Ga-MFI catalyst with different Si / Ga molar ratios on the CO2 coupled with pentane dehydrogenation to produce light aromatics are shown in Figure 5.

[0050] When the catalyst is Ga / S-1, and a mixture of CO2 and N2 is continuously introduced with pentane at a flow rate of 0.5 mL / h at a flow rate of 18 mL / min, the conversion rate of pentane is 62%, the conversion rate of CO2 is 2.7%, the selectivity of aromatics is 65%, and the selectivity of light aromatics is 60%. When the catalyst is Ga-MFI-40, the conversion rate of pentane is 98%, the conversion rate of CO2 is 2.2%, the selectivity of aromatics is 77%, and the selectivity of light aromatics is 74%. When the catalyst is Ga-MFI-80, the mixture of CO2 and N2... When a mixture of CO2 and N2 is continuously injected with pentane at a flow rate of 0.5 mL / h, the conversion rate of pentane is 97%, the conversion rate of CO2 is 1.8%, the selectivity of aromatics is 60%, and the selectivity of light aromatics is 54%. When the catalyst is Ga-MFI-120, when a mixture of CO2 and N2 is continuously injected with pentane at a flow rate of 0.5 mL / h, the conversion rate of pentane is 93%, the conversion rate of CO2 is 1.5%, the selectivity of aromatics is 51%, and the selectivity of light aromatics is 45%.

[0051] Experiments show that Ga-MF-40 molecular sieve with a Si / Ga molar ratio of 40 has good activity for CO2 coupled pentane dehydrogenation to produce light aromatics, while Ga / S-1 produces more olefins and the pentane conversion rate is much lower than that of Ga-MFI, which illustrates the importance of Ga in the molecular sieve framework for pentane dehydrogenation aromatization.

[0052] Comparative Example 2

[0053] The process of CO2 coupled with pentane dehydrogenation to produce light aromatics was carried out using the same method as in Example 1, but the molecular sieve was changed to H-ZSM-5 with different Si / Al molar ratios and Ga-supported H-ZSM-5 (Ga / H-ZSM-5-80). The effects of the Si / Al molar ratio of H-ZSM-5 and the Ga loading on the catalytic CO2 coupled with pentane dehydrogenation to produce light aromatics are shown in Figure 6.

[0054] When the catalyst is H-ZSM-5-40, and a CO2 and N2 mixture is continuously injected with pentane at a flow rate of 0.5 mL / h at a flow rate of 18 mL / min, the pentane conversion rate is 99%, the CO2 conversion rate is 2.1%, the aromatic selectivity is 59%, and the light aromatic selectivity is 55%. When the catalyst is H-ZSM-5-80, and a CO2 and N2 mixture is continuously injected with pentane at a flow rate of 0.5 mL / h at a flow rate of 18 mL / min, the pentane conversion rate is 98%, the CO2 conversion rate is 1.5%, and the aromatic selectivity is 55%. The selectivity for pentane was 64%, and the selectivity for light aromatics was 58%. When the catalyst was H-ZSM-5-120, and a mixture of CO2 and N2 was continuously introduced with pentane at a flow rate of 0.5 mL / h at a flow rate of 18 mL / min, the conversion rate of pentane was 96%, the conversion rate of CO2 was 1.0%, the selectivity for aromatics was 57%, and the selectivity for light aromatics was 51%. When the catalyst was Ga / H-ZSM-5-80, the conversion rate of pentane was 98%, the conversion rate of CO2 was 3.0%, the selectivity for aromatics was 72%, and the selectivity for light aromatics was 62%.

[0055] Experiments show that H-ZSM-5-80 molecular sieve with a Si / Al molar ratio of 80 has low activity for the CO2-coupled pentane dehydrogenation to light aromatics reaction. The activity increases after Ga loading, and the CO2 conversion rate also increases. Therefore, the loaded Ga can not only promote pentane aromatization, but also serve as an active site for CO2 conversion.

Claims

1. A method for synthesizing light aromatic hydrocarbons from pentane via Ga / Ga-MFI catalysis and CO2 coupling, characterized in that... The reaction modules shown in (a) to (c) are: (a) the first module, which involves the dehydrogenation of pentane to benzene, toluene and H2; (b) the second module, which involves the aromatization of CO2 with pentane to remove H2 and produce methanol products; and (c) the third module, which involves the combination of methanol products with benzene and toluene for CC coupling to produce toluene and xylene. The three reaction modules are synergistically involved in the reaction by the Brønsted acid site and the Lewis acid site on Ga / Ga-MFI.

2. The method according to claim 1, characterized in that, Includes the following steps: The catalyst is pressed into tablets, ground, and sieved. The sieved molecular sieve particles are selected as the catalyst and loaded into the isothermal zone of a fixed-bed reactor. Pentane liquid is transported to the fixed-bed reactor by a constant flow pump. The pentane vapor after vaporization in the isothermal zone is continuously carried into the catalyst bed by a mixture of CO2 and N2 gas. Finally, the product is analyzed by gas chromatography after pressurization.

3. The method for preparing light aromatics by coupling CO2 with pentane using Ga / Ga-MFI molecular sieve catalysis according to claim 1, characterized in that, The catalyst is any one of H-ZSM-5, Ga-MFI, Ga / S-1, Ga / H-ZSM-5, or Ga / Ga-MFI.

4. A method for the highly selective synthesis of aromatic products from pentane using Ga / Ga-MFI catalysis coupled with CO2, characterized in that, Using the catalytic system described in claim 1, 2 or 3, the method includes the following steps: (1) pressing, grinding and sieving the molecular sieve; the selected molecular sieve particles are 20-80 mesh; (2) activating and pretreating the catalyst in a hydrogen atmosphere; the activation and pretreating temperature is 400-600℃; the activation and pretreating time is 2-10h; (3) adding the catalyst obtained in step (2) to the reactor, introducing the raw material gas, adjusting the reaction temperature to 400-550℃ and the reaction pressure to 0.1-3MPa for reaction; the raw material gas includes a mixture of CO2 and N2 and n-pentane, wherein the CO2:N2 volume ratio is 0.5-20, the flow rate is 20-50mL / min, and the n-pentane liquid flow rate is 0.5-1.25mL / h.

Images