Graphene Modified Iron-Based Catalyst and Preparation and Application Thereof for Use in Fischer-Tropsch Reaction

Abstract

The present disclosure disclosures a graphene modified iron-based catalyst and preparation and application thereof for use in Fischer-Tropsch reaction, belonging to the technical field of catalytic conversion of synthesis gas. The catalyst consists of, by mass percent, 0.01-30% of graphene, 0-20% of promoter and 60-99.99% of iron oxide powder. The preparation process of the catalyst is as follows: the graphene, the iron oxide powder and the promoter are sequentially placed in an aqueous solution for ultrasonic treatment and stirring, and then rotary evaporation, drying and calcining are conducted. The preparation method is simple. The catalyst shows excellent activity in the Fischer-Tropsch reaction, and maintains a high CO conversion rate of 90% or above for a long time at a very high reaction space velocity; meanwhile, the alkane content in a product is low, and an olefin-alkane ratio can reach 14, thus having an extremely high industrial application value.

Claims

1. A method for preparing a graphene modified iron-based catalyst, wherein raw materials comprise 0.01-30 parts by mass of graphene, 0-20 parts by mass of promoter and 60-99.99 parts by mass of iron oxide, the method comprising the following steps: (1) dispersing the graphene in an aqueous solution at 10-80 C. to form a suspension, ultrasonically dispersing for 0.5-5 h, and then stirring for 1-24 h; (2) adding the iron oxide into the suspension formed in the step (1) according to a stoichiometric ratio, and continuously stirring for 0.5-24 h; (3) adding a precursor of the promoter into the suspension formed in the step (2) according to a stoichiometric ratio, and continuously stirring for 1-24 h; and (4) conducting rotary evaporation on a solution obtained in the step (3) to dryness, drying an obtained solid at 80-120 C. for 1-24 h, and then calcining in a gas of nitrogen, helium or argon at 250-800 C. for 1-24 h to obtain the graphene modified iron-based catalyst, and wherein when the promoter is 0 part by mass, the step (3) is omitted.

2. The method according to claim 1, wherein the precursor is selected from soluble compounds containing promoter elements.

3. The method according to claim 2, wherein the precursor is one selected from a group consisting of nitrate, carbonate, acetate, molybdate, sulfide, and any combination thereof.

4. The method according to claim 1, wherein the iron oxide is one selected from a group consisting of ferroferric oxide, ferric oxide, ferrous oxide, and any combination thereof; and the iron oxide has a particle size of 50-1000 nm.

5. The method according to claim 4, wherein the particle size is 100-500 nm.

6. The method according to claim 1, wherein the promoter is one selected from a group consisting of K, Na, Mn, Cu, Zn, Mo, Co, S, and any combination thereof.

7. The method according to claim 3, wherein the promoter is one selected from a group consisting of K, Na, Mn, Cu, Zn, Mo, Co and S, and any combination thereof.

8. A graphene modified iron-based catalyst prepared by the method according to claim 1.

9. A method of conducting Fischer-Tropsch reaction by using the graphene modified iron-based catalyst according to claim 8, comprising applying the catalyst to catalyze the Fischer-Tropsch reaction of synthesis gas, wherein the catalyst is pre-reduced with H.sub.2 for a certain period of time before the reaction, and then the catalyst is cooled to a reaction temperature to perform catalytic reaction.

10. The method according to claim 9, the further comprising pressing the catalyst at a pressure of 5.5 MPa, crushing the catalyst, and sieving the catalyst through a 40-60 mesh sieve.

11. The method according to claim 9, wherein the catalyst is placed in a continuous flow reactor to catalyze continuous reaction.

12. The method according to claim 10, wherein the catalyst is placed in a continuous flow reactor to catalyze continuous reaction.

Description

BRIEF DESCRIPTION OF FIGURES

[0022] FIG. 1 is an SEM image of ferric oxide powder in Examples 1 and 2.

[0023] FIG. 2 is an SEM image of ferroferric oxide powder in Examples 3 and 4.

[0024] FIG. 3 is an SEM image of ferroferric oxide powder in Example 5.

DETAILED DESCRIPTION

[0025] Definition and calculation formula of conversion rate:

[00001]$X_{\mathrm{CO}}.Math..Math.\left(\%\right)=\frac{{\left[\mathrm{CO}\right]}_{i.Math..Math.n}-{\left[\mathrm{CO}\right]}_{\mathrm{out}}}{{\left[\mathrm{CO}\right]}_{i.Math..Math.n}}100.Math.\%,$

[0026] wherein [CO].sub.in represents the molar concentration of CO in inlet gas of a reactor, and [CO].sub.out represents the molar concentration of CO in outlet gas of the reactor.

[0027] Definition and calculation formula of selectivity:

[00002]$S_{\mathrm{CH}.Math..Math.4}.Math..Math.\left(\%\right)=\frac{{\left[{\mathrm{CH}}_4\right]}_{\mathrm{out}}}{{\left[\mathrm{CO}\right]}_{i.Math..Math.n}-{\left[\mathrm{CO}\right]}_{\mathrm{out}}}100.Math.\%,$

[0028] wherein [CO].sub.out represents the molar concentration of CO.sub.2 in the outlet gas of the reactor, and [CH.sub.4].sub.out represents the molar concentration of CH.sub.4 in the outlet gas of the reactor.

[0029] Selectivity S.sub.Cn of hydrocarbons with a carbon number of n in products, and selectivity S.sub.Cnn+k of hydrocarbons with carbon numbers ranging from n to n+k in the products:

[00003]$S_{\mathrm{Cn}}.Math..Math.\left(\%\right)=\frac{{\left[\mathrm{Cn}\right]}_{\mathrm{out}}}{{\left[{\mathrm{CH}}_4\right]}_{\mathrm{out}}}{S}_{\mathrm{CH}.Math..Math.4},.Math.S_{\mathrm{Cn}-n+k}.Math..Math.\left(\%\right)=\underset{i=n}{\overset{i=n+k}{.Math.}}.Math.S_{\mathrm{Ci}},$

[0030] wherein [Cn].sub.out represents the molar concentration of hydrocarbons with a carbon number of n in the outlet gas of the reactor.

Examples 1-4 Preparation of Graphene Modified Iron-Based Catalyst

Example 1

[0031] 0.677 g graphene oxide and 3.112 g ferric oxide powder were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst A with a graphene content of 17.8% and a ferric oxide content of 82.2%, wherein the average particle diameter of ferric oxide in the catalyst was 120 nm, as shown in FIG. 1.

Example 2

[0032] 0.325 g graphene oxide, 2.876 g ferric oxide powder and 0.0715 g potassium carbonate were respectively taken, dispersed and dissolved in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst B with a graphene content of 10%, a ferric oxide content of 88.5%, and a potassium oxide content of 1.5%, wherein the average particle diameter of ferric oxide in the catalyst was 120 nm, as shown in FIG. 1.

Example 3

[0033] 0.551 g graphene oxide and 4.052 g ferroferric oxide powder were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst C with a graphene content of 12% and a ferroferric oxide content of 88%, wherein the average particle diameter of ferroferric oxide in the catalyst was 290 nm, as shown in FIG. 2.

Example 4

[0034] 0.861 g graphene oxide, 4.001 g ferroferric oxide powder, and 0.435 g potassium nitrate were respectively taken, dispersed and dissolved in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst D with a graphene content of 17%, a ferroferric oxide content of 79%, and a potassium oxide content of 4%, wherein the average particle diameter of ferroferric oxide in the catalyst was 290 nm, as shown in FIG. 2.

Example 5

[0035] 0.861 g graphene oxide, 4.001 g ferroferric oxide powder, and 0.435 g potassium nitrate were respectively taken, dispersed and dissolved in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst G with a graphene content of 17%, a ferroferric oxide content of 79%, and a potassium oxide content of 4%, wherein the average particle diameter of ferroferric oxide in the catalyst was 610 nm, as shown in FIG. 3.

Example 6

[0036] 0.677 g graphene oxide and 3.112 g ferric oxide powder were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 5 h; then rotary evaporation to dryness at 85 C. and dry at 120 C. for 12 h were conducted; and then calcined at 600 C. for 3 h in a nitrogen atmosphere to obtain a catalyst H with a graphene content of 17.8% and a ferric oxide content of 82.2%, wherein the average particle diameter of ferric oxide in the catalyst was 120 nm.

Examples 7-10 Application of Graphene Modified Iron-Based Catalyst in Synthesis Gas Conversion

[0037] A prepared catalyst was pressed at a pressure of 5.5 MPa, crushed and sieved to obtain a 40-60 mesh sample; and 0.15 g catalyst was taken and placed in a continuous flow reactor, the catalyst was pre-reduced with H.sub.2 for a certain period of time before reaction, and then cooled to a reaction temperature to perform continuous reaction. The reaction gas was composed of 47.5 vol % CO, 47.5 vol % H.sub.2 and 5 vol % Ar, wherein Ar was used as the internal standard gas to calculate the conversion rate of CO. The products were analyzed on-line at atmospheric pressure after being cooled in a cold trap by a gas chromatography equipped with TCD and FID detectors.

Example 7

[0038] The catalysts A, G and H were placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and reaction temperatures of 300 C., 320 C. and 340 C., so as to investigate the influence of the reaction temperatures. The results of the conversion rate of CO and olefin selectivity are shown in Table 1.

Example 8

[0039] The catalyst B was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction temperature of 300 C., and reaction space velocities of 10000 h.sup.1, 20000 h.sup.1 and 40000 h.sup.1, so as to investigate the influence of the reaction space velocities. The results of the conversion rate of CO and olefin selectivity are shown in Table 1.

Example 9

[0040] The catalyst C was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 1.

Example 10

[0041] The catalyst D was placed in a pressurized fixed bed reactor, a fluidized bed reactor and a slurry bed reactor respectively, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup., and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 1. This result was used to compare the reaction results of the catalyst in different reactors.

Comparative Example 1

[0042] 3.88 g ferric oxide powder and 0.176 g potassium carbonate were respectively taken, dispersed and dissolved in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst E with a ferric oxide content of 97% and a potassium oxide content of 3%, wherein the average particle diameter of ferric oxide in the catalyst was 120 nm, as shown in FIG. 1. The catalyst was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup., and reaction temperatures of 300 C. and 340 C., so as to investigate the influence of the reaction temperatures. The results of the conversion rate of CO and olefin selectivity are shown in Table 2.

Comparative Example 2

[0043] 0.506 g activated carbon, 4.948 ferroferric oxide powder and 0.248 g potassium carbonate were respectively taken, dispersed and dissolved in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst F with an activated carbon content of 9%, a ferroferric oxide content of 89% and a potassium oxide content of 3%, wherein the average particle diameter of ferroferric oxide in the catalyst was 290 nm, as shown in FIG. 2. The catalyst was placed in a pressurized fixed bed reactor and a fluidized bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 2.

Comparative Example 3

[0044] 0.677 g graphene oxide and 15.716 g iron nitrate nonahydrate were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst I with a graphene content of 17.8% and a ferric oxide content of 82.2%. The catalyst was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 2.

Comparative Example 4

[0045] 2.568 g graphene oxide and 3.112 g ferric oxide powder were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst J with a graphene content of 45.2% and a ferric oxide content of 54.8%, wherein the average particle diameter of ferric oxide in the catalyst was 120 nm, the same as that in Example 1. The catalyst was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 2.

Comparative Example 5

[0046] 0.677 g graphene oxide and 3.112 g ferric oxide powder were respectively taken, dispersed in an aqueous solution at 40 C. in sequence, and continuously stirred for 12 h; then rotary evaporation to dryness at 85 C. and dry at 105 C. for 24 h were conducted; and then calcined at 400 C. for 5 h in a nitrogen atmosphere to obtain a catalyst K with a graphene content of 17.8% and a ferric oxide content of 82.2%, wherein the average particle diameter of ferric oxide in the catalyst was 10 nm. The catalyst was placed in a pressurized fixed bed reactor, heated to 380 C. at a rate of 5 C./min in an H.sub.2 atmosphere, and reduced for 10 h at atmospheric pressure and a space velocity of 1000 h.sup.1; and then the temperature was reduced, and reaction gases were introduced for reaction at a reaction pressure of 1.0 MPa, a reaction space velocity of 20000 h.sup.1, and a reaction temperature of 340 C. The results of the conversion rate of CO and olefin selectivity are shown in Table 2.

TABLE-US-00001 TABLE 1 Reaction Performance of Different Catalysts in Preparing Lower Olefins through Synthesis Gas Conversion Hydrocarbon product Reaction Reaction Conversion distribution temperature space rate of CO (C-mol %) Olefin-alkane Catalyst ( C.) velocity (h.sup.1) (%) CH.sub.4 C.sub.2+.sup.= C.sub.2+.sup.0 ratio (O/P) A 300 20000 65.2 9.7 83.4 6.9 12.1 A 320 20000 78.5 11.2 81.0 7.8 10.4 A 340 20000 90.2 13.8 79.0 7.2 10.9 B 320 10000 85.1 12.1 81.9 6.0 13.6 B 320 20000 79.2 11.2 82.7 6.1 13.5 B 320 40000 70.4 11.7 82.0 6.3 13.0 C 340 20000 92.1 14.2 80.0 5.8 13.7 D 340 20000 93.2 12.7 80.8 6.5 12.4 D* 340 20000 92.9 10.5 83.5 6.0 14.0 D** 340 20000 90.8 9.8 83.7 6.5 12.9 G 340 20000 80.3 11.8 76.6 11.6 6.6 H 340 20000 87.5 11.6 82.4 6.0 13.7 Reaction conditions: fixed bed reactor, 1.0 MPa, average data within 100-500 h of reaction. *Fluidized bed reactor; **Slurry bed reactor

TABLE-US-00002 TABLE 2 Experimental Results of Comparative Examples Hydrocarbon product distribution Reaction Reaction space Conversion (C-mol %) Olefin alkane Catalyst temperature ( C.) velocity (h.sup.1) rate of CO (%) CH.sub.4 C.sub.2+.sup.= C.sub.2+.sup.0 ratio (O/P) E 300 20000 12.3 34.5 24.6 40.9 0.6 E 340 20000 5.6 41.2 19.6 39.2 0.5 F 320 20000 8.9 37.7 25.7 36.6 0.7 F* 320 20000 11.1 32.9 25.2 41.9 0.6 I 340 20000 20.6 40.5 20.7 38.8 0.5 J 340 20000 1.2 60.7 6.8 32.5 0.2 K 340 20000 89.6 20.5 14.3 65.2 0.2 Reaction conditions: fixed bed reactor, 1.0 MPa, average data within 5-10 h. *Fluidized bed reactor

[0047] Comparing the experimental results in Table 1 and Table 2, it can be clearly seen that the graphene modified iron-based catalyst exhibits excellent catalytic performance, maintains a stable activity within 500 h of reaction, and still exhibits a very high CO conversion rate at a very high reaction space velocity. Even in the absence of promoter, olefin selectivity in the products is close to 50%, and olefin-alkane ratio can reach 13. However, iron-based catalysts without graphene modification or modified with other carbon materials quickly lose the activity within a few hours of reaction, and the products are mainly alkanes. The results show that the graphene modified iron-based catalyst has an excellent industrial application value.

[0048] Although the present disclosure has been disclosed in terms of preferred examples, the preferred examples are not intended to limit the present disclosure. Any person familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure should be as defined in the claims.