A method for preparing a catalyst for synthesizing low-carbon olefins by one-step synthesis gas

Abstract

The application belongs to the field of catalysis technology and relates to a preparation method of a catalyst for synthesizing low-carbon olefins by a one-step method of synthesis gas. Fe2O3 is prepared by grinding, drying and calcining iron nitrate and oxalic acid, a composite active component Fe2O3-CoO is obtained by mixing the prepared Fe2O3 and CoO, then a modifier is added to prepare modified Fe2O3-CoO-SiO2, and finally the modified active component is centrifuged, dried, pressed, broken and sieved for standby use. The application can inhibit the WGS reaction on the Fischer-Tropsch synthesis catalyst by silanization hydrophobic modification, and reduce the generation of C1 by-products. The catalyst and the acidic zeolite molecular sieve are beneficial to the cracking of long-chain hydrocarbons due to the acidic centers, so that the selectivity and yield of C2-C4 olefins are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalysis technology, and particularly relates to a preparation method of a catalyst for synthesizing low-carbon olefins by one-step method of synthesis gas. BACKGROUND

[0002] Low-carbon olefins (especially ethylene, propylene, butene, etc.) are the most basic and important organic chemical raw materials, and the traditional production process is heavily dependent on oil. According to the resource situation of "relatively rich in coal, lack of oil, and less gas" in China, producing low-carbon olefins by "coal" instead of "oil" is one of the important ways to realize clean and efficient utilization of coal and ensure national energy security. Therefore, developing the technology of producing low-carbon olefins from coal-based synthesis gas has important strategic significance and practical application value.

[0003] The technology of producing low-carbon olefins from synthesis gas by indirect method includes two steps. At present, the technology of producing low-carbon olefins by indirect method is relatively mature, such as the MTO process developed by UOP Company of the United States and the DMTO new process developed by Dalian Institute of Chemical Physics of Chinese Academy of Sciences. However, the indirect method process has complex reaction steps, which will bring huge energy consumption and additional cost. Compared with the indirect method process, the one-step method for producing low-carbon olefins has the advantages of less energy consumption, low cost, and short process, etc., and has attracted more and more attention.

[0004] At present, the main catalysts for the synthesis of low carbon olefins from syngas are as follows: (1) modified F-T catalysts Dent et al. found that cobalt-based catalysts can be used for the synthesis of low carbon olefins with high selectivity, such as CoCu / Al2O3, Fe-Co / C, Co-Fe / SiO2, Co-Ni / MnO2, Fe-Co alloy, etc. Among them, the modified F-T catalyst developed by Lurgi Company has better results. By adding components such as Mn or Ti to the Fe-ZnO-K2O catalyst and using high-speed gas circulation, the CO conversion rate is 80% and the selectivity of low carbon olefins is 70%; (2) ultrafine particle catalysts Venter et al. obtained high-dispersion K-FeMn catalyst supported by activated carbon by carbonyl complex decomposition method. The catalyst has very high activity, and C2-C4 olefins account for 85-90% in the product, and methane is the only other product detected. Cupta et al. prepared FexSiyCz powder with catalytic activity by laser pyrolysis, with CO conversion rate of 40% and C2-C4 selectivity of 87%, only a small amount of methane. Zhang Bing et al. of Shanxi Coal Research Institute successfully developed a new type of practical ultrafine particle Fe / Mn catalyst by using the degradation method of organic salt complex, with CO conversion rate of more than 95% and C2-C4 olefins of more than 80% in the product. Zhang Jingchang of Beijing University of Chemical Technology prepared highly dispersed amorphous ultrafine iron and carbon powder by laser pyrolysis, and successfully prepared F-T synthesis active new species Fe3C by solid-state reaction. Fe-C, Fe-C-Mn-K, Fe-C-Mn, etc. nanocatalysts with Fe3C as the main body were prepared, with CO conversion rate of 90% and olefin selectivity of more than 80%; (3) amorphous synthesis catalysts Yokoyama et al. used amorphous Fe 40 Ni 40 P 16 B4 compounds, with CO conversion rate of 50% and C2-C5 hydrocarbon selectivity of 65%, while the crystalline catalyst mainly generates methane; (4) zeolite catalyst system, such as Co-A, Co-Y, Fe-Y, etc. Ballivet-Tketchenko et al. prepared zeolite-supported iron catalyst with high dispersion, with low carbon olefin selectivity of 88-98% in the range of C2-C4, such as ZSM-5, mordenite, and 13X zeolite as the carrier of iron catalyst also showed low carbon olefin selectivity.

[0005] The main problems in the synthesis of low carbon olefins from syngas are as follows: the product distribution is limited by the low yield of low carbon olefins in F-T synthesis, resulting in low overall selectivity of low carbon olefins; due to the strong exothermic reaction of the reaction, local overheating is easy to occur, which promotes methanation and carbon deposition, and reduces the total olefin yield. Olefins are easy to be converted into saturated alkanes as an intermediate product.

[0006] Therefore, developing a catalyst for synthesizing low-carbon olefins from synthesis gas in one step, and preparing a catalyst with high activity, high selectivity, and good stability are important issues to be solved by researchers. SUMMARY

[0007] The purpose of the present application is to provide a catalyst preparation method for synthesizing low-carbon olefins from synthesis gas in one step, and to prepare a catalyst with high activity, high selectivity, and good stability.

[0008] The main technical solution of the present application is a catalyst preparation method for synthesizing low-carbon olefins from synthesis gas in one step, characterized in that Fe2O3 is obtained by grinding, drying, and calcining iron nitrate and oxalic acid, the composite active component Fe2O3-CoO is obtained by mixing Fe2O3 and CoO, the modified active component Fe2O3-CoO-SiO2 is obtained by adding a modifier, and the catalyst is obtained by mixing the modified active component and molecular sieve, centrifuging, drying, tabletting, crushing, and sieving.

[0009] Generally, the catalyst preparation method of the present application is prepared by the following steps:

[0010] 1) Fe2O3 is prepared by grinding, drying, and calcining iron nitrate and oxalic acid in a mortar using a solid-phase method;

[0011] 2) Fe2O3 prepared in step (1) is mixed with CoO in a proportion, dispersed in ethanol under ultrasonic conditions, and silicon tetraethoxide is added to the prepared solution under stirring, the pH is adjusted, and centrifugal washing is performed until neutral;

[0012] 3) the composite active component Fe2O3-CoO prepared in step (2) is dispersed in an ethanol solution under ultrasonic conditions, and a modifier is added to prepare the modified active component Fe2O3-CoO-SiO2;

[0013] 4) the modified active component Fe2O3-CoO-SiO2 prepared in step (3) is mixed with molecular sieve in a proportion, dispersed in ethanol under ultrasonic conditions, centrifuged, dried, tabletted, crushed, and sieved to prepare the catalyst.

[0014] Preferably, in step (1), grinding is performed for 30-40 min, drying is performed at 100-130 ℃ for 12-15 h, and calcination is performed at 550-850 ℃ for more than 2 h.

[0015] Preferably, in step (2), the molar ratio of Fe2O3 to CoO is 3-4.

[0016] Preferably, in step (2), the pH is adjusted by adding a base.

[0017] Further preferably, the base is one or more of ammonia water, ammonium carbonate, and ammonium bicarbonate.

[0018] Preferably, in step (3), the modifier is selected from one or more of hexadecyltrimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, vinyltrimethoxysilane, and gamma-aminopropyltriethoxysilane.

[0019] Preferably, in step (4), the molecular sieve is selected from one or more of molecular sieve SAPO-34, SAPO-18, ZSM-5, and MCM-41.

[0020] Preferably, in step (4), the mass ratio of the modified active component to the molecular sieve is (1-2):1.

[0021] The main advantages of the present application are:

[0022] (1) The hydrophobic modification by silanization can inhibit the WGS reaction on the Fe-based Fischer-Tropsch synthesis catalyst, reducing the generation of C1 byproducts.

[0023] (2) The combination of the Fe-based Fischer-Tropsch synthesis catalyst with the acidic zeolite molecular sieve can improve the selectivity of olefin products due to the acid centers that are conducive to the cracking of long-chain hydrocarbons. Embodiment

[0024] The present application will be described in detail below with reference to examples. Example 1

[0025] 8.08 g of iron nitrate nonahydrate and 3.79 g of oxalic acid dihydrate were ground in a mortar for 30 min, dried in an oven at 110°C for 15 h to obtain iron oxalate, and then calcined at 550°C for 2 h to obtain pure-phase Fe2O3. The prepared Fe2O3 was mixed with CoO in a ratio of 3:1, dispersed in 250 mL of ethanol under ultrasonic conditions for 20 min, and then 2.5 mL of tetraethyl orthosilicate was added while stirring for 4 h. Then, 5 mL of ammonium carbonate and 20 mL of deionized water were added, and stirring was continued for another 4 h. The mixture was washed by centrifugation until it was neutral, and then dried at 60°C. The above prepared composite active component was dispersed in 40 mL of a 75% ethanol solution, and then modified with 0.1 mL of hexadecyltrimethoxysilane per gram of composite active component at 70°C for 3 h to obtain the modified active component Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 in a ratio of 1:1, dispersed in ethanol under ultrasonic conditions, centrifuged, and dried. The obtained catalyst was then pressed, crushed, and sieved, and labeled as S-1. Example 2

[0026] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-18 according to 1:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-2. Example 3

[0027] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-18 according to 1:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-2. Example 4

[0028] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve ZSM-5 according to 1:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-4. Example 5

[0029] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve ZSM-5 according to 1:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-4. Example 6

[0030] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-6. Example 7

[0031] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-6. Example 8

[0032] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to a ratio of 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-8. Example 9

[0033] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to a ratio of 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tableted, crushed, sieved, and labeled as S-8. Example 10

[0034] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to a ratio of 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tabletized, crushed, sieved, and labeled as S-10. Example 11

[0035] Fe2O3-CoO-SiO2. The prepared modified active component was mixed with molecular sieve SAPO-34 according to a ratio of 2:1, dispersed in ethanol under ultrasonic condition, centrifuged, dried, and the obtained catalyst was tabletized, crushed, sieved, and labeled as S-10.

[0036] Evaluation of catalyst performance

[0037] 10 ml of each of the catalyst samples S-1 to S-11 was loaded in a fixed bed reactor, and the selectivity and yield of low carbon olefins were investigated under the conditions of a reaction temperature of 250-400℃, a pressure of 1-2.5 MPa, a space velocity of 1000-10000 h-1, and n(H2) / n(CO)=1-1.5. The evaluation results are shown in Table 1. -1

[0038] Table 1​

[0039]

[0040] As shown in Table 1 above, samples S-1, S-2, S-4, S-4 examine the effects of catalysts prepared by mixing modified active component Fe2O3-CoO-SiO2 with five different molecular sieves SAPO-34, SAPO-18, MCM-41, ZSM-5 respectively, and the results show that the olefin selectivity and yield are general, among which the catalyst prepared with molecular sieve SAPO-34 has the best effect.

[0041] Samples S-1 and S-5 examine different catalysts prepared by using two different proportions of modified active component and molecular sieve SAPO-34, and the results show that when the mass ratio of modified active component to molecular sieve is 2:1, the catalytic effect is good.

[0042] Samples S-5, S-6, S-7, S-8, S-9 add five different modifiers hexadecyl trimethoxysilane, dimethyl diethoxysilane, trimethyl ethoxysilane, vinyl trimethoxysilane, γ-aminopropyl triethoxysilane respectively, and the results show that the catalyst modified by modifier hexadecyl trimethoxysilane has better catalytic effect.

[0043] Sample S-10 examines the effect of active component ratio on catalyst activity, and the results show that when the molar ratio of Fe2O3 to CoO is 4:1, the catalyst has the best effect.

[0044] Sample S-11 examines the effect of calcination temperature change on catalyst effect, and the results show that the calcination temperature has little effect on the catalyst.

[0045] In summary, when the molar ratio of Fe2O3 to CoO is 4:1, the catalyst is modified by modifier hexadecyl trimethoxysilane, and the mass ratio of modified active component Fe2O3-CoO-SiO2 to molecular sieve SAPO-34 is 2:1, the catalytic effect of sample S-10 is the best, the olefin selectivity is 65.8%, and the highest yield is 40.8%.

Claims

1. A method for preparing a catalyst for one-step synthesis of low-carbon olefins from syngas, characterized in that... It is prepared through the following steps: 1) Fe2O3 was prepared by grinding ferric nitrate and oxalic acid in a mortar for 30-40 min using a solid-state method, drying at 100-130 ℃ for 12-15 h, and calcining at 550-850 ℃ for more than 2 h. 2) Mix the Fe2O3 and CoO prepared in step (1) in a molar ratio of (3-4):1 and disperse them in ethanol under ultrasonic conditions; while stirring, add tetraethyl silicate to the prepared solution, adjust the pH, and centrifuge and wash until neutral. 3) The composite active component Fe2O3-CoO prepared in step (2) is dispersed in an ethanol solution under ultrasonic conditions, and the modifier hexadecyltrimethoxysilane is added to obtain the modified active component Fe2O3-CoO-SiO2; 4) The modified active component Fe2O3-CoO-SiO2 prepared in step (3) is mixed with molecular sieve SAPO-34 in a mass ratio of (1~2):1, ultrasonically dispersed in ethanol, centrifuged, dried, pressed into tablets, crushed, and sieved to obtain the catalyst.

2. The catalyst preparation method according to claim 1, characterized in that... In step (2), alkali is added to adjust the pH.

3. The catalyst preparation method according to claim 2, characterized in that, The alkali is one or more of ammonia, ammonium carbonate, and ammonium bicarbonate.

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