Method for preparing aromatic hydrocarbon with carbon dioxide hydrogenation

Abstract

A method for preparing aromatic hydrocarbons with carbon dioxide hydrogenation, comprising: directly converting a mixed gas consisting of carbon dioxide and hydrogen with the catalysis of a composite catalyst under reaction conditions of a temperature of 250-450 C., a pressure of 0.01-10.0 MPa, a feedstock gas hourly space velocity of 500-50000 mL/(h.Math.g.sub.cat) and a H.sub.2/CO.sub.2 molar ratio of 0.5-8.0, to produce aromatic hydrocarbons. The composite catalyst is a mixture of a first component and a second component. The first component is an iron-based catalyst for making low-carbon olefin via carbon dioxide hydrogenation, and the second component is at least one of metal modified or non-modified molecular sieves which are mainly used for olefin aromatization. In the method, CO.sub.2 conversion per pass may be above 33%, the hydrocarbon product selectivity may be controlled to be above 80%, the methane content is lower than 8%, C.sub.5+ hydrocarbon content is higher than 65% and the proportion of the aromatic hydrocarbons in C.sub.5+ hydrocarbons may be above 63%.

Claims

1. A method for preparing aromatic hydrocarbon with carbon dioxide hydrogenation comprising: directly converting a mixed gas which comprises carbon dioxide and hydrogen, used as feed gas, with the catalysis of a composite catalyst to produce aromatic hydrocarbons, wherein the composite catalyst is a mixture of a first component and a second component, the first component is an iron-based catalyst for making low-carbon olefin via carbon dioxide hydrogenation, and the second component is at least one of metal modified or non-modified molecular sieves which are mainly used for olefin aromatization; and the mass ratio of the first component to the second component is 1:10-10:1; the iron-based catalyst comprises one or more of FeO, Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4 as at least one main active component and optionally an auxiliary; the iron-based catalyst has reverse water gas conversion function and olefin production function with CO hydrogenation; the auxiliary is an oxide, and the content of the auxiliary is 0-20% of the total mass of the iron-based catalyst; and the second component is a molecular sieve containing ten-membered ring porous structure.

2. The method according to claim 1 wherein the iron-based catalyst comprises Fe.sub.3O.sub.4 as an active component, and the method comprises one of the following processes to make the iron-based catalyst: A. the catalyst is prepared by a one-step synthesis method which comprises the following steps: (1) mixing soluble Fe (II) salt and soluble Fe (III) salt to form a salt solution or mixing soluble Fe (II) salt, soluble Fe (III) salt and auxiliary salt to form a salt solution in accordance with a catalyst composition ratio, the concentration of Fe (III) in the salt solution being 0.02-0.8 mol/L; adding HCl solution with a concentration of 3-12.1 mol/L; regulating a pH value to 0-3, wherein the molar ratio of Fe(III) to Fe(II) in the salt solution is 2:(0.8-2.8); wherein the soluble Fe (II) salt and the soluble Fe (III) salt are water-soluble salt compounds; and the auxiliary salt is a water-soluble salt compound; (2) adding aqueous alkali to (1); gradually regulating the pH value of the solution to 0-3 until the alkaline pH value is 9-12; after completing dripping, ageing for 1-10 h, wherein the aqueous alkali is an alkali solution with an adjustable pH value; the concentration of the aqueous alkali is 0.1-8 mol/L, wherein R refers to an organo-functional group and comprises C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkenyl or C.sub.6-C.sub.20 aryl; (3) after completing the reaction, separating deposited products from (2) through magnetic field absorption, centrifugal or sucking filtration method; adequately washing the deposited products with deionized water, drying, optionally roasting at a roasting temperature of 200-600 C. for a roasting time of 2-10 h, to prepare the iron-based catalyst containing the auxiliary; B. or the catalyst is prepared by a one-step synthesis method which comprises the following steps: (1) mixing soluble Fe (II) salt and soluble Fe (III) salt to form a salt solution in accordance with a catalyst composition ratio, the concentration of Fe (III) in the salt solution being 0.02-0.8 mol/L; adding HCl solution with a concentration of 3-12.1 mol/L; and regulating a pH value to 0-3, wherein the molar ratio of Fe(III) to Fe(II) in the salt solution is 2:(0.8-2.8); (2) adding aqueous alkali containing Na or K in A method to (1); gradually regulating the pH value of the solution to 0-3 until the alkaline pH value is 9-12; and after completing dripping, ageing for 1-10 h; (3) after completing the reaction, separating deposited products from (2) through magnetic field absorption, centrifugal or sucking filtration method; washing the deposited products with deionized water; controlling the content of remaining Na or K in the catalyst by controlling washing times and water consumption per washing; drying, roasting or not roasting at a roasting temperature of 200-600 C. for a roasting time of 2-10 h, to prepare the iron-based catalyst containing the auxiliary; C. or the catalyst is prepared by synthesizing Fe.sub.3O.sub.4 through a coprecipitation method and adding the auxiliary through an immersion method, comprising the following steps: (1) mixing soluble Fe (II) salt and soluble Fe (III) salt to form a salt solution in accordance with a catalyst composition ratio, the concentration of Fe (III) in the salt solution being 0.02-0.8 mol/L; adding HCl solution with a concentration of 3-12.1 mol/L; and regulating a pH value to 0-3, wherein the molar ratio of Fe(III) to Fe(II) in the salt solution is 2:(0.8-2.8); (2) adding the aqueous alkali in A method to (1); gradually regulating the pH value of the solution to 0-3 until the alkaline pH value is 9-12; and after completing dripping, ageing for 1-10 h; (3) after completing the reaction, separating deposited products from (2) through magnetic field absorption, centrifugal or sucking filtration method; adequately washing the deposited products with deionized water, and drying, to prepare the active component Fe.sub.3O.sub.4; (4) combining the auxiliary salt with the active component through the immersion method to form a catalyst, which comprises: computing the amount of theoretically required auxiliary salt according to the required auxiliary content to prepare an aqueous solution of the auxiliary salt; immersing equal volume of Fe.sub.3O.sub.4 obtained in preparation of (3) into the solution; stirring, standing, drying and roasting at a roasting temperature of 200-600 C. for a roasting time of 2-10 h, to prepare the iron-based catalyst containing the auxiliary.

3. The method according to claim 1, wherein during modification of the molecular sieve, the metal component is supported by the molecular sieve through one of the following two methods: (1) preparing through an isometric immersion method, which comprises: computing the amount of theoretically required metal salt according to the required metal content to prepare an aqueous solution of the metal salt, wherein the metal salt is selected from the group consisting of: nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate and benzoate; immersing equal volume of molecular sieve that needs modification treatment into the solution; stirring, standing, drying and roasting at a roasting temperature of 300-700 C. for a roasting time of 2-10 h, to prepare a metal modified molecular sieve; (2) preparing through an ion exchange method, which comprises: computing the amount of theoretically required metal salt according to the required metal content to prepare an aqueous solution of the metal salt, wherein the metal salt is selected from the group consisting of: nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate and benzoate; mixing the molecular sieve that needs modification treatment with a mass ratio of solid to liquid of 1:(10-200); conducting ion exchange for 2-24 h; and washing, drying and roasting at a roasting temperature of 300-700 C. for a roasting time of 2-10 h, to prepare a metal modified molecular sieve.

4. The method according to claim 1 comprising mixing the two components of the composite catalyst through one of the following two modes: (1) particle mixing mode: respectively weighing iron-based catalyst and molecular sieve catalyst powder; respectively tableting, shaping and screening; and uniformly mixing particles according to a required mass ratio to form a composite catalyst; (2) layered packing mode: successively packing required mass of the iron-based catalyst and the molecular sieve catalyst on catalyst bed layers in a top-to-bottom sequence of reactors, wherein two catalyst bed layer components contain or do not contain an isolation layer of inert material, and the mass ratio of the isolation layer of inert material to the active component of the composite catalyst is 0.01-10.

5. The method according to claim 1, wherein the reaction temperature is 250-450 C.; the reaction pressure is 0.01-10.0 MPa; feedstock gas hourly space velocity is 500-50000 mL/(h.Math.gcat) and H.sub.2/CO.sub.2 molar ratio in the feed gas is 0.5-8.0.

6. The method according to claim 1, wherein the carbon dioxide is present in at least one of industrial waste gas, automobile exhaust, coal waste gas, atmosphere and seawater.

7. The method of claim 1 wherein the mass ratio of the first component to the second component is 1:3-3:1.

8. The method of claim 1 wherein the iron-based catalyst comprises Fe.sub.3O.sub.4 as the main active component.

9. The method of claim 1 wherein the content of the auxiliary in the iron-based catalyst is 0.5-10% of the total mass of the iron-based catalyst.

10. The method of claim 1 wherein the second component is at least one of ZSM-5, ZSM-22, ZSM-23 and MCM-22 molecular sieves.

11. The method of claim 1 wherein the second component is at least one of ZSM-5 and MCM-22 molecular sieves.

12. The method of claim 1 wherein the second component has a silica alumina ratio of 20-200.

13. The method of claim 1 wherein the metal modified molecular sieves comprise at least one metal element selected from the group consisting of Mo, Ga, Cr, La, Cu and Zn in an amount of 0.1%-20% based on the mass of the metal modified molecular sieves.

14. The method of claim 1 wherein the metal modified molecular sieves comprise 0.5%-10% of at least one metal element based on the mass of the metal modified molecular sieves.

15. The method of claim 1 wherein the auxiliary is at least one of K oxide, Na oxide, Cu oxide, Mn oxide, V oxide, Zr oxide, Zn oxide, and Ce oxide.

16. A method for preparing aromatic hydrocarbon with carbon dioxide hydrogenation comprising: directly converting a mixed gas which comprises carbon dioxide and hydrogen, used as feed gas, with the catalysis of a composite catalyst to produce aromatic hydrocarbons, wherein the composite catalyst is a mixture of a first component and a second component, the first component is an iron-based catalyst for making low-carbon olefin via carbon dioxide hydrogenation, and the second component is at least one of metal modified or non-modified molecular sieves which are mainly used for olefin aromatization; and the mass ratio of the first component to the second component is 1:10-10:1; and the method comprises mixing the two components of the composite catalyst through one of the following two modes: (1) particle mixing mode: respectively weighing iron-based catalyst and molecular sieve catalyst powder; respectively tableting, shaping and screening; and uniformly mixing particles according to a required mass ratio to form a composite catalyst; (2) layered packing mode: successively packing required mass of the iron-based catalyst and the molecular sieve catalyst on catalyst bed layers in a top-to-bottom sequence of reactors, wherein two catalyst bed layer components contain or do not contain an isolation layer of inert material, and the mass ratio of the isolation layer of inert material to the active component of the composite catalyst is 0.01-10.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

(1) The technical details of the present invention are described in detail through the following embodiments. It should be indicated that listed embodiments are only used to further illustrate technical features of the present invention, not to limit the present invention.

Embodiment 1

(2) Steps: mixing 15.81 g of FeCl.sub.3.6H.sub.2O and 6.27 g of FeCl.sub.2.4H.sub.2O with 80 mL of water to form a malysite solution, and adding 3.5 mL of 9.0 mol/L HCl solution; under stirring at 60 C., adding about 180 mL of 1.5 mol/L NaOH solution at uniform speed; within about 1.5 h, adjusting the pH value of the solution to about 10; after completing dripping, keeping the temperature and continuing to stir for 1 h, and finally cooling to room temperature; after completing the reaction, separating deposited products through magnetic field absorption; washing the deposited products once with 400 mL of deionized water, and drying at 60 C., to prepare a NaFe.sub.3O.sub.4 catalyst sample which can be used later after ground, tableted and screened.

(3) Respectively roasting HMCM-22 (SiO.sub.2/Al.sub.2O.sub.3=30) purchased from Molecular Sieve Plant of Nankai University, HZSM-5 molecular sieves with silica alumina ratios SiO.sub.2/Al.sub.2O.sub.3 of 27, 50, 150 and 300 and HZSM-23 (SiO.sub.2/Al.sub.2O.sub.3=80) molecular sieve synthesized by the laboratory for 4 h at 500 C., and grinding, tabletting and screening the samples for later use.

(4) Weighing the above prepared 0.5 g NaFe.sub.3O.sub.4 catalyst particles and uniformly mixing with 0.5 g HMCM-22, HZSM-5 and HZSM-23 molecular sieve particles for use in evaluation of CO.sub.2 hydrogenation reaction in a fixed bed reactor.

(5) Reducing Conditions:

(6) Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 320 C., a pressure of 3.0 MPa, and an hourly space velocity of 4000 mL/(h.Math.g.sub.cat). The influence of the molecular sieve type on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/zeolite catalyst is inspected. The result (see Table 1 and Table 2) indicates that, compared with an individual iron-based catalyst, after the molecular sieve is added as the second component to mix with the iron-based catalyst, the C.sub.5+ content in the hydrocarbon product and aromatic hydrocarbon content in C.sub.5+ are greatly increased. ZSM-5 molecular sieve has a three-dimensional ten-membered ring porous channel matched with the molecular dimension of aromatic hydrocarbons and appropriate acid strength, and thus has excellent aromatization performance.

(7) TABLE-US-00001 TABLE 1 Influence of Molecular Sieve Type on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/Zeolite Composite Catalyst Hydrocarbon Conversion Distribution Aromatic Rate Selectivity (C-mol %) Hydrocarbon Content Molecular Sieve CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ in C.sub.5+ (C-mol %) .sub.a 33.7 14.3 11.7 48.4 39.9 1.0 HZSM-23 33.7 14.7 10.6 37.8 51.6 20.0 HMCM-22 34.8 13.4 11.0 31.3 57.7 31.0 HZSM-5 (300) 33.0 15.0 8.6 23.2 68.2 41.0 HZSM-5 (150) 33.6 15.0 7.9 18.4 73.7 56.1 HZSM-5 (50) 33.3 14.7 7.4 23.9 68.7 61.0 HZSM-5 (27) 33.6 13.9 7.3 24.5 68.1 63.1 .sup.aPacking NaFe.sub.3O.sub.4 catalyst only, not packing molecular sieve.

(8) TABLE-US-00002 TABLE 2 Aromatic Hydrocarbon Distribution of CO.sub.2 Hydrogenation Reaction Products on NaFe.sub.3O.sub.4/Zeolite Composite Catalyst Aromatic Aromatic Hydrocarbon Hydrocarbon HMCM-22 HZSM-5(300) HZSM-5(150) HZSM-5(27) C.sub.6 Benzene 0.6 0.5 0.9 2.3 C.sub.7 Toluene 3.8 4.9 8.5 18.7 C.sub.8 Ethylbenzene 1.7 2.4 3.1 4.6 Xylene 19.0 21.8 25.3 34.2 C.sub.9 Propylbenzene 1.4 1.3 0.8 0.3 Methyl Ethylbenzene 8.7 23.8 22.8 17.4 Trimethylbenzene 22.1 12.3 13.5 5.5 C.sub.10 Diethylbenzene 2.3 4.6 2.9 1.4 Monomethyl 5.4 5.1 2.4 1.1 Propylbenzene Dimethyl 9.0 11.6 11.9 4.1 Ethybenzene Tetramethylbenzene 10.2 1.0 1.2 0.2 C.sub.11 11.4 7.3 5.3 2.7 C.sub.12+ 4.3 3.2 1.5 7.6

Embodiment 2

(9) Steps: respectively weighing the NaFe.sub.3O.sub.4 catalyst and HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve prepared through the method of embodiment 1 in accordance with different mass ratios to form a particle mixed catalyst with a total mass of 1.0 g; and uniformly mixing for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h.

(10) Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 320 C., a pressure of 3.0 MPa, and an hourly space velocity of 4000 mL/(h.Math.g.sub.cat). The influence of the mass ratio of the two components on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/HZSM-5 catalyst is inspected. The result (see Table 3) indicates that, the composite catalyst has double functions, and the two components have synergy. As the two components are changed in scale, when the ratio of the two components Fe/ZSM is 1:1, the performance of the composite catalyst is best and the aromatic hydrocarbon selectivity is highest.

(11) TABLE-US-00003 TABLE 3 Influence of Mass Ratio of Two Components on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/HZSM-5 (150) Composite Catalyst Aromatic Hydrocarbon Hydrocarbon Conversion Distribution Content in Fe/ZSM Rate Selectivity (C-mol %) C.sub.5+ (wt/wt) CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) 1:7 29.0 19.4 6.7 22.9 69.4 49.9 1:3 32.9 15.4 7.1 20.6 72.3 54.3 1:1 33.6 15.2 7.9 18.4 73.7 56.1 3:1 35.0 14.5 9.2 20.4 70.4 51.3 7:1 35.8 14.0 10.0 24.0 66.0 46.8

Embodiment 3

(12) Steps: respectively weighing 0.5 g of NaFe.sub.3O.sub.4 catalyst prepared through the method in embodiment 1 and 0.5 g of HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve; uniformly mixing particles for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 280-380 C., a pressure of 3.0 MPa, and an hourly space velocity of 2000 mL/(h.Math.g.sub.cat). The influence of the reaction temperature on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/HZSM-5 catalyst is inspected. The result (see Table 4) indicates that, as the reaction temperature is increased, the CO.sub.2 conversion rate is gradually increased, and the C.sub.5+ selectivity is increased and then decreased. The catalyst always presents excellent CO.sub.2 aromatization performance within an inspected temperature range.

(13) TABLE-US-00004 TABLE 4 Influence of Reaction Temperature on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/HZSM-5 (150) Composite Catalyst Hydrocarbon Aromatic Conversion Distribution Hydrocarbon Reaction Rate Selectivity (C-mol %) Content in C.sub.5+ Temperature ( C.) CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) 280 25.2 14.3 9.8 22.1 68.1 41.2 300 34.5 9.1 8.7 22.0 69.3 48.0 320 40.1 8.2 8.0 21.6 70.4 54.0 340 44.1 9.2 8.6 25.1 66.3 54.3 360 46.3 10.5 9.2 27.1 63.7 54.7 380 48.4 11.9 12.0 30.3 57.7 54.3

Embodiment 4

(14) Steps: respectively weighing 0.5 g of NaFe.sub.3O.sub.4 catalyst prepared through the method in embodiment 1 and 0.5 g of HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve; uniformly mixing particles for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 320 C., a pressure of 1.0-5.0 MPa, and an hourly space velocity of 2000 mL/(h.Math.g.sub.cat). The influence of the reaction pressure on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/HZSM-5 catalyst is inspected. The result (see Table 5) indicates that, as the reaction pressure is increased, the CO.sub.2 conversion rate is gradually increased, and the CO selectivity is gradually decreased. The C.sub.5+ selectivity is increased and then decreased. The catalyst always presents excellent CO.sub.2 aromatization performance within an inspected pressure range.

(15) TABLE-US-00005 TABLE 5 Influence of Reaction Pressure on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/HZSM-5 (150) Composite Catalyst Aromatic Hydro- Hydrocarbon carbon Reaction Conversion Distribution Content in Pressure Rate Selectivity (C-mol %) C.sub.5+ (MPa) CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) 1.0 31.2 24.3 8.9 28.4 62.7 46.0 2.0 33.8 16.5 9.5 24.4 66.1 50.1 3.0 38.6 10.4 8.5 21.0 70.5 54.0 4.0 40.7 8.0 10.4 22.9 66.7 46.7 5.0 42.2 7.1 12.7 24.8 62.5 45.1

Embodiment 5

(16) Steps: respectively weighing 0.5 g of NaFe.sub.3O.sub.4 catalyst prepared through the method in embodiment 1 and 0.5 g of HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve; uniformly mixing particles for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 320 C., a pressure of 3.0 MPa, and an hourly space velocity of 1000-10000 mL/(h.Math.g.sub.cat). The influence of the feedstock gas hourly space velocity on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/HZSM-5 catalyst is inspected. The result (see Table 6) indicates that, as the feedstock gas hourly space velocity is increased, the CO.sub.2 conversion rate is gradually decreased, and the C.sub.5+ selectivity is increased and then decreased, and is maximum when the hourly space velocity is 4000 mL/(h.Math.g.sub.cat). The catalyst always presents excellent CO.sub.2 aromatization performance at the hourly space velocity of 10000 mL/(h.Math.g.sub.cat).

(17) TABLE-US-00006 TABLE 6 Influence of Feedstock Gas Hourly Space Velocity on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/HZSM-5 (150) Composite Catalyst Hydrocarbon Aromatic Hourly space Conversion Distribution Hydrocarbon velocity (mL .Math. g Rate Selectivity (C-mol %) Content in C.sub.5+ 1 .Math. h 1) CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) 1000 43.1 9.4 10.5 25.4 64.1 51.5 2000 37.2 11.2 8.3 21.3 70.4 54.0 4000 33.2 17.0 7.8 19.0 73.3 56.1 6000 31.7 19.0 8.0 20.2 71.9 54.0 8000 30.3 22.3 8.2 20.6 71.2 49.2 10000 28.7 25.0 10.5 24.2 65.3 47.0

Embodiment 6

(18) Steps: respectively weighing 0.5 g of NaFe.sub.3O.sub.4 catalyst prepared through the method in embodiment 1 and 0.5 g of HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve; uniformly mixing particles for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=1.0-6.0, a temperature of 320 C., a pressure of 3.0 MPa, and an hourly space velocity of 2000 mL/(h.Math.g.sub.cat). The influence of the hydrogen-carbon ratio of the feedstock gas on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/HZSM-5 catalyst is inspected. The result (see Table 7) indicates that, as the hydrogen-carbon ratio of the feedstock gas is increased, the CO.sub.2 conversion rate is obviously increased. The aromatic hydrocarbon content in C.sub.5+ always keeps higher value within the inspected hydrogen-carbon ratio range.

(19) TABLE-US-00007 TABLE 7 Influence of Hydrogen-Carbon Ratio of Feedstock Gas on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/HZSM-5 (150) Composite Catalyst Aromatic Hydro- Hydrogen- Hydrocarbon carbon Carbon Conversion Distribution Content in Ratio Rate Selectivity (C-mol %) C.sub.5+ H.sub.2/CO.sub.2 CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) 1.0 22.0 17.6 4.3 19.5 76.2 60.5 2.0 27.1 16.5 6.5 20.3 73.3 57.9 3.0 36.0 13.1 8.6 20.8 70.7 54.0 4.0 45.0 9.7 10.5 21.3 68.2 53.0 5.0 53.1 7.4 11.5 21.4 67.1 52.1 6.0 59.5 5.7 12.9 22.2 64.9 51.2

Embodiment 7

(20) Steps: weighing 0.72 g of Ga(NO.sub.3)3.9H.sub.2O, adding about 7.2 mL of deionized water to prepare Ga(NO.sub.3).sub.3 solution, then weighing 6.0 g of HZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=150) molecular sieve and immersing equal volume of the molecular sieve in the above Ga(NO.sub.3).sub.3 solution, stirring, standing for 12 h, drying at 60 C., roasting for 4 h at 500 C. and finally grinding, tabletting and screening for later use. Other metal modified molecular sieves are prepared by the similar method.

(21) Steps: weighing 0.5 g of NaFe.sub.3O.sub.4 catalyst prepared through the method in embodiment 1 and 0.5 g of 2% M/ZSM-5 molecular sieve prepared; uniformly mixing particles for use in CO.sub.2 hydrogenation reaction. Reducing conditions: Normal pressure, pure H.sub.2 (25 mL/min), 350 C. and reduction time of 8 h. Reaction conditions: H.sub.2/CO.sub.2=3.0, a temperature of 320 C., a pressure of 3.0 MPa, and an hourly space velocity of 4000 mL/(h.Math.g.sub.cat). The influence of different metal modification on CO.sub.2 hydrogenation performance of the NaFe.sub.3O.sub.4/M-ZSM-5 catalyst is inspected. The result (see Table 8 and Table 9) indicates that, the influence of different metal modified molecular sieves on CO.sub.2 conversion rate is low, but after metal modification, product compositions are obviously changed and C.sub.5+ selectivity is reduced to different degrees.

(22) TABLE-US-00008 TABLE 8 Influence of Metal Modification on CO.sub.2 Hydrogenation Performance of NaFe.sub.3O.sub.4/M-ZSM-5 (150) Composite Catalyst Hydrocarbon Aromatic Conversion Distribution Hydrocarbon Metal Rate Selectivity (C-mol %) Content in C.sub.5+ M CO.sub.2 (%) CO (%) CH.sub.4 C.sub.2~C.sub.4 C.sub.5+ (C-mol %) .sub.a 33.6 15.2 7.9 18.4 73.7 56.1 Mo 33.6 16.8 7.9 18.8 73.3 55.8 Ga 35.6 14.0 7.9 20.2 71.9 55.2 Cr 35.0 14.3 8.4 20.5 71.1 48.9 La 35.7 13.8 8.6 20.7 70.7 48.0 Cu 35.9 13.6 8.1 24.1 67.8 47.9 Zn 35.0 13.9 8.6 22.8 68.5 41.9 .sub.aUnmodified molecular sieve.

(23) TABLE-US-00009 TABLE 9 Aromatic Hydrocarbon Distribution of CO.sub.2 Hydrogenation Reaction Products on NaFe.sub.3O.sub.4/M-ZSM-5 (150) Composite Catalyst Aromatic Hydrocarbon Mo Ga Cr La Cu Zn C.sub.6 0.9 0.8 1.1 0.7 0.7 0.9 0.5 C.sub.7 8.5 8.6 10.4 7.6 7.2 9.1 5.6 C.sub.8 28.4 28.3 30.8 29.2 29.5 31.1 23.5 C.sub.9 37.0 36.8 35.1 38.1 39.3 37.1 36.4 C.sub.10 18.4 17.9 15.2 19.3 19.4 17.1 25.4 C.sub.11 5.3 5.5 3.0 4.7 3.7 4.2 7.2 C.sub.12+ 1.5 2.1 4.5 0.5 0.3 0.5 1.4

(24) In the method, CO.sub.2 conversion per pass may be above 33%, the hydrocarbon product selectivity may be controlled to be above 80%, the methane content is lower than 8%, C.sub.5+ hydrocarbon content is higher than 65% and the proportion of the aromatic hydrocarbon in C.sub.5+ hydrocarbon may be above 63%. The present invention develops a new route for producing aromatic hydrocarbon from carbon dioxide.