CN107930643A - A kind of catalyst and its application for preparation of low carbon olefines by synthetic gas - Google Patents

Abstract

The invention discloses a catalyst for producing low-carbon olefins from synthesis gas. The catalyst uses activated carbon as a carrier, iron as an active metal component, and potassium and manganese as auxiliary agents; the loading of the iron is 5-20 wt%. , the loading of the potassium is 2-5wt%, and the loading of the manganese is 10-30wt%; the active phase of the prepared catalyst has a higher degree of dispersion and a smaller particle size, and has a higher activity It is selective to low-carbon olefins and has good stability. After 100 hours of reaction, it still maintains a high reactivity, which solves the problem of effective activity caused by migration and polymerization of metal active particles in traditional carbon-supported iron-based catalysts under high temperature and high pressure reaction conditions. The number of bits is reduced, there are many by-products, and the selectivity of low-carbon olefins is low, and it has a good industrial application prospect.

Description

Catalyst for producing low-carbon olefins from syngas and its application

Technical field:

The invention relates to the technical field of catalysts, in particular to a catalyst for producing low-carbon olefins from synthesis gas and its application.

Background technique:

Low-carbon olefins such as ethylene, propylene, and butene are important chemical raw materials in petrochemical energy, important platform molecules for the synthesis of polymer compounds such as plastics, rubber, and artificial fibers, and are also the most produced chemicals in the world. Ethylene is the basic chemical raw material for synthetic fibers, synthetic rubber, synthetic plastics (polyethylene and polyvinyl chloride), synthetic ethanol (alcohol), and is also used to manufacture vinyl chloride, styrene, ethylene oxide, acetic acid, acetaldehyde, and ethanol And explosives, etc., and further can be made into pipes, film products, packaging bags, cosmetics, high-poly fibers and other products, which are closely related to our daily life. As a major petrochemical fuel, propylene can be used to prepare chemical products such as acrylonitrile, propylene oxide, and acetone, while butene can be used to prepare butadiene, butylene oxide, butene polymers, and various plastics. Low-carbon olefins are one of the largest chemical products in the world and play an important role in the national economy. The world has taken ethylene propylene production as one of the important symbols to measure the development level of a country's petrochemical industry. In recent years, with the rapid development of the economy, the consumption and output of ethylene propylene in my country have increased year by year. According to statistics from the National Bureau of Statistics, my country's ethylene production has reached 17.81 million tons in 2016, and it has become the second largest producer of ethylene in the world after the United States. big country. Although my country's ethylene output, production scale and technical level have made great progress, it is also facing great challenges. For example: my country's output accounts for only 92.8% of apparent consumption, and its dependence on imports is relatively high. Larger production scale still cannot meet the growing demand. Crude oil cracking, as the main technology for the production of low-carbon olefins, is highly dependent on oil imports, has low production efficiency, and causes serious environmental pollution. It is obviously difficult to achieve sustainable development if my country still uses a single crude oil cracking technology to obtain low-carbon olefins.

China has a vast land area and a wide range of sources of biomass raw materials. After pyrolyzing biomass as a raw material to obtain synthesis gas with main components of _H2 and CO, the technical route of synthesizing low-carbon olefins by one-step Fischer-Tropsch synthesis has rich sources of raw materials. , Environmental friendliness, the advantages of less energy consumption in the production process. Using biomass as raw material can reduce environmental pollution caused by straw burning, and make full use of agricultural and forestry waste to achieve "zero" emission of carbon dioxide. Fischer-Tropsch synthesis is the catalytic conversion of synthesis gas ( _H2 and CO) into hydrocarbon oxides under high temperature and pressure, including methane, gaseous low-carbon hydrocarbons and liquid hydrocarbons. Commonly used catalysts for Fischer-Tropsch synthesis of low-carbon olefins are mainly iron-based catalysts, while traditional bulk iron-based catalysts have disadvantages such as easy breakage, low life, and low conversion rate per unit mass of iron. The use of carbon carrier-supported iron catalysts can effectively improve the dispersion of the active phase on the surface of the carrier, thereby increasing the conversion rate of the reaction, and compared with carriers such as silica, molecular sieves, and metal oxides, the carbon carrier has a weaker active phase and The interaction between the supports is beneficial to the reduction of the catalyst to form the active phase iron carbide. However, the presence of metal active particles in traditional carbon-supported iron-based catalysts is prone to migration polymerization under high temperature and high pressure reaction conditions, resulting in a decrease in the number of effective active sites, many by-products, and low selectivity for low-carbon olefins.

Invention content:

The purpose of the present invention is to provide a catalyst for producing low-carbon olefins from syngas and its application. The prepared catalyst has higher dispersion and smaller particle size, and has higher activity and low-carbon olefin selectivity , good stability, and still maintain high reactivity after 100 hours of reaction, which solves the problem that the metal active particles in traditional carbon-supported iron-based catalysts are prone to migration and polymerization under high temperature and high pressure reaction conditions, resulting in a decrease in the number of effective active sites and side effects. There are many products, and the selectivity of low-carbon olefins is low.

The present invention is achieved through the following technical solutions:

A catalyst for producing low-carbon olefins from synthesis gas, the catalyst uses activated carbon as a carrier, iron as an active metal component, and potassium and manganese as auxiliary agents; the loading of the iron is 5-20 wt%, and the potassium The load of manganese is 2-5wt%, and the load of manganese is 10-30wt%. The auxiliary agents potassium and manganese are fixed on the support by pretreating the activated carbon support with potassium permanganate aqueous solution and modifying the surface groups The active component iron is loaded onto the treated activated carbon carrier by an equal volume impregnation method, and obtains a loaded iron-based catalyst pretreated with potassium permanganate after drying and calcining. The preparation method of the catalyst comprises the following steps:

1) Boil and wash the activated carbon with deionized water to remove ash and impurities in the activated carbon, then disperse it in the nitric acid solution and heat it to reflux, then wash it with deionized water until the filtrate pH=7 to remove the residual metal ions in the activated carbon ;Washed and acid-washed activated carbon is then dispersed into potassium permanganate aqueous solution, the mass ratio of potassium permanganate to activated carbon is controlled between 0.2-1.1, magnetically stirred at 50-100°C for 20-40min, and then filtered Wash with deionized water until the filtrate is colorless, and dry overnight in an oven at 120°C to obtain a pretreated activated carbon carrier;

2) Prepare ferric nitrate aqueous solution according to the load of 5-20wt%, disperse the pretreated activated carbon carrier in the ferric nitrate solution, place it in a 120°C oven to dry overnight after magnetic stirring at room temperature for 24 hours, and grind Raise the temperature to 200-500° C. at a rate of 2° C./min under nitrogen atmosphere and calcinate for 3-5 hours to obtain the target catalyst.

Preferably, the potassium permanganate aqueous solution has a concentration of 0.02mol/L-0.1mol/L.

Preferably, the temperature at which the potassium permanganate aqueous solution treats the activated carbon is 70°C.

Preferably, the loading amount of iron in the catalyst is 5-10wt%.

Preferably, the catalyst loaded with iron is calcined at a temperature of 300° C. in a nitrogen atmosphere, and the calcined time is 3 hours.

Preferably, the volume of the ferric nitrate aqueous solution is 2 ml, which is equal to the total pore volume of the activated carbon used.

The present invention also protects the application of the catalyst for producing low-carbon olefins from syngas, comprising the following steps:

Mix the above catalyst with quartz sand evenly, and load it into a fixed bed reactor; in situ reduction at 300°C under normal pressure for 12 hours under a synthesis gas atmosphere with a molar ratio of _H2 and CO of 1 to 3, the reaction temperature is 280 ~360°C, reaction pressure 1.0~3.0MPa, reaction gas volume space velocity 1500~15000h ^-1 , the synthesis gas contacts with the catalyst in the fixed bed reactor to generate light olefins mainly containing C2~C4, and at the same time By-products such as C ₅₊ and other gasoline segment long-chain hydrocarbon products.

Preferably, the reaction temperature is 300-320°C, the reaction pressure is 2MPa, the molar ratio of the reaction gas is H ₂ :CO=1, and the volume space velocity of the reaction gas is 1500-3000h ^-1 .

The reaction temperature is more preferably 320°C, and the reaction gas volume space velocity is 3000h ^-1 .

The beneficial effects of the present invention are as follows:

1. The catalyst of the present invention is a loaded catalyst prepared by an equal-volume impregnation method. The average particle size of the iron active particles is small, and the dispersion degree on the surface of the activated carbon carrier is high, which is conducive to greatly improving the activity of the catalytic reaction;

2. The carrier of the catalyst of the present invention is pretreated with potassium permanganate aqueous solution at 50-100°C and then impregnated with the active phase precursor. On the one hand, during the treatment process, potassium permanganate and activated carbon undergo oxidation-reduction reactions. The oxygen-containing groups on the surface of the carrier have been improved, which is conducive to the increase of surface defect sites, and can effectively improve the dispersion of the iron precursor and the electronic effect of the activated carbon carrier; on the other hand, the additives manganese and potassium are introduced into the catalyst carrier at the same time , which is conducive to the generation of active phase and the improvement of the selectivity of low-carbon olefins. At the same time, it has good catalyst stability. After 100 hours of reaction, it still maintains high reactivity and the selectivity of the target product low-carbon olefins, which solves the problem of traditional carbon Supported iron-based catalysts have the problems that metal active particles are prone to migration polymerization under high temperature and high pressure reaction conditions, resulting in a decrease in the number of effective active sites, and there are many by-products, and the selectivity of low-carbon olefins is low.

3. The catalyst prepared by the method of the present invention has low raw material cost, simple and easy-to-control preparation method, higher conversion rate and low-carbon olefin selectivity, and good industrial application prospect.

4. The application of the catalyst of the present invention for the production of low-carbon olefins from syngas. The proposed reaction system is firstly reduced in situ at 300°C under normal pressure and then adjusted to a suitable reaction pressure and temperature for Fischer-Tropsch synthesis to produce low-carbon olefins. The in situ reduction process can effectively shorten the induction time of the initial stage of the catalyst reaction, which is beneficial to the generation of active phase iron carbide. Under the reaction conditions, low-carbon olefins can be stably and efficiently produced continuously, and at the same time, C ₅₊ and other gasoline and diesel long-chain hydrocarbon products are by-produced.

Description of drawings:

Fig. 1 is the graph of the reactivity of the catalyst Fe-10MnK-AC of Example 1 as a function of time.

FIG. 2 is a transmission electron microscope image of the catalyst in Example 1 after reacting for 100 h.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

Example 1:

Include the following steps:

1. Boil an appropriate amount of activated carbon with deionized water and wash it with water to remove ash and impurities in the activated carbon, then disperse it in a 10wt% nitric acid solution, reflux it in an oil bath at 80°C for 5 hours, and then wash it with deionized water until the filtrate pH=7, to remove residual metal ions in the activated carbon, the filter cake was placed in an oven at 60°C and dried overnight; 3 g of activated carbon washed with water and acid washed were dispersed into an aqueous potassium permanganate solution with a concentration of 0.1 mol/L, Control the mass ratio of potassium permanganate to activated carbon between 0.2-1.1, stir magnetically at 70°C for 30 minutes, then filter and wash with deionized water until the filtrate is colorless, and dry overnight in an oven at 120°C to obtain the pre- Treated activated carbon carrier;

2. Prepare an aqueous ferric nitrate solution with a loading capacity of 10 wt%, disperse the pretreated activated carbon carrier in the ferric nitrate solution, and remove the solvent by magnetic stirring at room temperature for 24 hours, so that the iron precursor is evenly adsorbed on the surface of the activated carbon. Place it in an oven at 120°C and dry it overnight. After grinding, raise the temperature to 300°C at a rate of 2°C/min under nitrogen atmosphere and calcinate for 3 hours. The obtained catalyst is designated as Fe-10MnK-AC;

3. Mix the catalyst obtained in step 2 with quartz sand (60-80 mesh) and fill it into a fixed-bed reaction device, and reduce it in situ at 300°C under normal pressure under a synthesis gas atmosphere of H ₂ /CO=1:1 After 12 hours, adjust the pressure to 2 MPa (gauge pressure), adjust the temperature to 320°C, and catalyze the Fischer-Tropsch synthesis reaction of synthesis gas to prepare light olefins. The volume space velocity of the reaction gas is 3000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components in the gas phase hydrocarbon products are alkanes and olefins below C5, and the main components in the oil phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection all pass the standard Quantitative analysis is carried out with the external standard method of sample calibration, and the carbon balance of all the products and raw gas obtained is kept above 95%.

Example 2:

With reference to Example 1, the difference is that the concentration of potassium permanganate aqueous solution in step 1 is 0.05mol/L, and the catalyst obtained is denoted as Fe-5MnK-AC; Others are the same as in Example 1.

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Example 3:

With reference to Example 1, the difference is that the concentration of potassium permanganate aqueous solution in step 1 is 0.02mol/L, and the catalyst obtained is denoted as Fe-2MnK-AC; Others are the same as in Example 1.

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Example 4:

Referring to Example 1, the difference is that the volume space velocity of the reaction gas in step 3 is 1500h ^-1 . Others are the same as in Example 1.

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Example 5:

Referring to Example 1, the difference is that the volume space velocity of the reaction gas in step 3 is 9000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Embodiment 6:

Referring to Example 1, the difference is that the reaction gas volume space velocity in step 3 is 15000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Embodiment 7:

Referring to Example 1, the difference is that in step 3, the catalytic reaction temperature is adjusted to 280° C., and the Fischer-Tropsch synthesis reaction of catalytic synthesis gas occurs to prepare light olefins.

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Embodiment 8:

Referring to Example 1, the difference is that in step 3, the temperature is adjusted to 360° C., and the Fischer-Tropsch synthesis reaction of catalytic synthesis gas occurs to prepare light olefins.

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Comparative example 1:

With reference to Example 1, the difference is that the activated carbon washed and pickled in step 1 is not redispersed in the potassium permanganate aqueous solution for processing;

Include the following steps:

1. Disperse an appropriate amount of activated carbon in deionized water, treat it in an oil bath at 100°C for 2 hours, filter it and wash it with deionized water, then disperse it in a 10wt% nitric acid solution, reflux it in an oil bath at 80°C for 5 hours, and then use Washing with deionized water until the pH of the filtrate = 7, and drying the filter cake in an oven at 60°C overnight to obtain a pretreated activated carbon carrier;

2. Prepare an aqueous ferric nitrate solution at a load of 10 wt%, disperse the pretreated activated carbon carrier in the ferric nitrate solution, stir magnetically at room temperature for 24 hours to remove the solvent, place it in an oven at 120°C to dry overnight, and grind Afterwards, it was raised to 300°C at a heating rate of 2°C/min under a nitrogen atmosphere and calcined for 3 hours, and the obtained catalyst was designated as Fe-AC;

3. Mix the catalyst obtained in step 2 with quartz sand and fill it into a fixed-bed reaction device. Under the synthesis gas atmosphere of H ₂ /CO = 1:1, reduce in situ at 300°C under normal pressure for 12 hours, and adjust the pressure to to 2MPa (gauge pressure), the temperature is adjusted to 320°C, and the catalytic synthesis gas undergoes Fischer-Tropsch synthesis reaction to prepare light olefins. The gas volume space velocity of the reaction gas is 3000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Comparative example 2:

Include the following steps:

1. Disperse an appropriate amount of activated carbon in deionized water, treat it in an oil bath at 100°C for 2 hours, filter it and wash it with deionized water, then disperse it in a 10wt% nitric acid solution, reflux it in an oil bath at 80°C for 5 hours, and then use Washing with deionized water until the pH of the filtrate = 7, and drying the filter cake in an oven at 60°C overnight to obtain a pretreated activated carbon carrier;

2. According to the load of Fe is 10wt%, the load of K is 5wt% to prepare a mixed aqueous solution of ferric nitrate and potassium nitrate, disperse the pretreated activated carbon carrier in the solution, and magnetically stir at room temperature for 24 hours to remove the solvent , put it in an oven at 120°C to dry overnight, grind it up to 300°C at a rate of 2°C/min under nitrogen atmosphere after grinding and calcined for 3 hours, the obtained catalyst is designated as Fe-10K-AC;

3. Mix the catalyst obtained in step 2 with quartz sand and fill it into a fixed-bed reaction device. Under the synthesis gas atmosphere of H ₂ /CO = 1:1, reduce in situ at 300°C under normal pressure for 12 hours, and adjust the pressure to to 2MPa (gauge pressure), the temperature is adjusted to 320°C, and the catalytic synthesis gas undergoes Fischer-Tropsch synthesis reaction to prepare light olefins. The gas volume space velocity of the reaction gas is 3000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Comparative example 3:

With reference to Example 1, the difference is that gac is not washed and pickled in step 1, and the mass ratio of potassium permanganate and gac in the process is 3.2, comprising the following steps:

1. Take 1g of activated carbon and disperse it in an aqueous potassium permanganate solution with a concentration of 0.1mol/L, stir magnetically at 70°C for 30 minutes, then filter and wash with deionized water until the filtrate is colorless, and dry it in an oven at 120°C overnight, to obtain pretreated activated carbon carrier;

2. Prepare an aqueous ferric nitrate solution at a load of 10 wt%, disperse the pretreated activated carbon carrier in the ferric nitrate solution, stir magnetically at room temperature for 24 hours to remove the solvent, place it in an oven at 120°C to dry overnight, and grind Afterwards, it was raised to 300°C at a heating rate of 2°C/min under a nitrogen atmosphere and calcined for 3 hours. The obtained catalyst was designated as Fe-30MnK-AC;

3. Mix the catalyst obtained in step 2 with quartz sand and fill it into a fixed-bed reaction device. Under the synthesis gas atmosphere of H ₂ /CO = 1:1, reduce in situ at 300°C under normal pressure for 12 hours, and adjust the pressure to to 2MPa (gauge pressure), the temperature is adjusted to 320°C, and the catalytic synthesis gas undergoes Fischer-Tropsch synthesis reaction to prepare light olefins. The gas volume space velocity of the reaction gas is 3000h ^-1 .

After the reaction is stable, the gas obtained from the reaction is directly passed into gas chromatography (FID, TCD) to detect and analyze its components on-line, and the liquid components (water phase and oil phase) obtained from the reaction are collected by cold traps connected to the fixed bed , The liquid components were taken out and weighed every 24 hours, wherein the hydrocarbon content in the water phase product was extremely low and negligible, and the oil phase product was analyzed by off-line gas chromatography. The main components of gas-phase hydrocarbon products are alkanes and olefins below C5, and the main components of oil-phase hydrocarbon products are long-chain alkanes and olefins above C5 and their isomers, alcohols and other substances. The chromatographic detection is all carried out quantitative analysis by the external standard method calibrated by the standard sample, and the carbon balance of all the obtained products and the raw material gas is kept above 95%.

Table 1 shows the comparative results of the catalyst reaction conditions, the conversion rate of raw materials and the selectivity of light olefins in Examples 1-8 and Comparative Examples 1-3.

Table 1

From the comparison of the results of Example 1 with Comparative Examples 1 and 2, it can be seen that under the same reaction conditions, potassium effectively suppressed the generation of by-product methane as a base additive, and compared with the Fe without additive simultaneously. -AC, the proportion of C ₂ -C ₄ alkanes decreased, indicating that the potassium promoter inhibited the hydrogenation reaction activity of CO and light alkenes in the process of Fischer-Tropsch synthesis of light alkenes, reducing the selectivity of alkanes. Catalyst Fe-10MnK-AC has higher CO conversion rate among the embodiment 1, illustrates as commonly used Fischer-Tropsch synthesis additive, on the one hand manganese has improved the dispersibility of iron active phase, has improved the adsorption capacity of catalyst to CO; On the one hand, manganese weakens the C=O double bond in the carbon monoxide molecule, making it easier for the CO molecule adsorbed on the active site to dissociate and participate in the reaction. Catalyst Fe-10MnK-AC has higher low-carbon olefin selectivity among the embodiment 1, and C ₅₊ product has only 29.7%, illustrates that manganese additive suppresses further hydrogenation and chain growth of reaction in reaction process, by Anderson- The chain growth factor of the product calculated by the Schulz-Flory model is 0.73, indicating that the catalyst in Example 1 can concentrate the hydrocarbons in the product below C ₅ .

From the comparison of the results of Example 1 with Comparative Examples 1 and 3, it can be seen that the synergistic effect of water washing, pickling and potassium permanganate treatment in step 1 of the present invention produces unexpected technical effects. Compared with Comparative Example 1 and Comparative Example 3, the conversion rate of CO has been greatly improved, indicating that the surface of activated carbon has more oxygen-containing groups after water washing, pickling and potassium permanganate pretreatment, which is beneficial to improve the reaction rate. activity. Compared with Comparative Example 3, it can be seen that the high content of manganese and potassium inhibits the conversion rate of CO and the selectivity of low-carbon olefins to a certain extent, indicating that there is a mass of potassium permanganate and activated carbon in the treatment process. The optimal range of ratio.

Examples 1-3 compared the reaction effects of catalysts prepared by using activated carbon carriers pretreated with different concentrations of potassium permanganate aqueous solutions, and the mass ratio of potassium permanganate to activated carbon was between 0.2-1.1. It can be seen from the XRF characterization results that the mass ratios of iron and manganese in the three catalysts are 1:3, 1:2 and 1:1, respectively. By comparing the CO conversion rate of the reaction, it can be concluded that the catalyst with higher manganese content has lower reactivity. It shows that the combination of manganese and iron causes a slight reduction of active sites. The catalyst with higher manganese content shows higher selectivity of low carbon olefins, because manganese has a competitive adsorption effect on _H2 , and only enough manganese exists around the iron active phase to reduce the surface that can participate in the hydrogenation reaction. H ₂ content, thereby inhibiting the secondary hydrogenation of olefins. At the same time, manganese is not an active site in the Fischer-Tropsch synthesis reaction. A sufficient amount of manganese can effectively isolate adjacent active sites and increase the distance of C ^* adsorbed on adjacent active sites microscopically, making It is difficult for further carbon chain growth to occur.

Example 1 and Examples 4-6 compared the reaction effects of Fe-10MnK-AC at different space velocities. It can be clearly seen that the conversion rate of CO decreases with the increase of space velocity, indicating that the shorter the residence time of raw materials CO and _H2 on the catalyst surface, the less complete the reaction. Comparing the selectivity of light olefins at 1500h ^-1 , 3000h ^-1 , 9000h ^-1 and 15000h ^-1 , it can be seen that the selectivity of light olefins is the highest when the reaction space velocity is 3000h ^-1 .

Example 1 and Examples 7-8 compared the reaction effects of Fe-10MnK-AC at different temperatures. It can be seen that the conversion rate of CO at 280° C. is only 17.1%, indicating that the catalyst has low reactivity at low temperature. By comparing the distribution of hydrocarbons in the products, it can be seen that high temperature is conducive to the migration of products to low-carbon hydrocarbons, but too high temperature (360 ° C) will cause the intensification of chain growth reactions.

Based on the above examples, the optimized reaction conditions for the synthesis gas to low-carbon olefins catalyst are: temperature 320°C, space velocity 3000h ^-1 , and the optimized preparation conditions are 0.1mol/L potassium permanganate aqueous solution for pretreatment of activated carbon carrier. During the continuous reaction of the optimized catalyst Fe-10MnK-AC for 100 h under the optimized reaction conditions (Figure 1), the reaction activity of the catalyst remained stable, and the CO conversion rate remained above 80%, indicating that the catalyst had no obvious deactivation Phenomenon. The transmission electron microscope image of the catalyst in Example 1 after 100 hours of reaction is shown in Figure 2. It can be seen that the iron particles still maintain a good degree of dispersion on the surface, and the particle size distribution is mainly concentrated at about 13nm, which also shows that pickling and high manganese Potassium acid pretreatment helps to improve the stability of catalyst active sites. The ratio (O/P) of C ₂ -C ₄ olefins to alkanes is stable at 4-5, and the selectivity of low-carbon olefins remains basically unchanged (about 40%). In a word, the catalyst for producing low-carbon olefins from synthesis gas according to the present invention has the advantages of simple and pollution-free preparation process and low raw material price, and the catalyst shows higher reactivity and higher selection of low-carbon olefins during the reaction process. properties and good stability, it has a good prospect of industrial application.

Claims (7)

1. a kind of catalyst for preparation of low carbon olefines by synthetic gas, it is characterised in that the catalyst is using activated carbon as carrier, with iron As active metal component, potassium and manganese are as auxiliary agent；The load capacity of the iron is 5-20wt%, and the load capacity of the potassium is 2- 5wt%, the load capacity of the manganese is 10-30wt%, and auxiliary agent potassium and manganese are by absorbent charcoal carrier potassium permanganate solution Pretreatment is fixed on carrier and surface group is modified, and active component iron is to load to processing by equi-volume impregnating On the absorbent charcoal carrier crossed, the load-type iron-based catalyst of permanganate pretreatment, the catalyst are obtained after drying, calcining Preparation method comprise the following steps：

1) activated carbon is boiled and washed with deionized water, redisperse is heated to reflux into salpeter solution, uses deionized water afterwards To filtrate pH=7, redisperse controls the mass ratio of potassium permanganate and activated carbon in 0.2- into potassium permanganate solution for washing Between 1.1, the magnetic agitation 20-40min at 50-100 DEG C, filtered afterwards and deionized water wash to filtrate be it is colourless, It is dried overnight in 120 DEG C of baking ovens, obtains pretreated absorbent charcoal carrier；

2) iron nitrate aqueous solution is prepared by the load capacity of 5-20wt%, it is molten that pretreated absorbent charcoal carrier is dispersed in ferric nitrate In liquid, when magnetic agitation 24 is small at normal temperatures after be placed in 120 DEG C of baking ovens and be dried overnight, after grinding under nitrogen atmosphere with The heating rate of 2 DEG C/min rise to 200-500 DEG C and calcine 3-5 it is small when obtain final catalyst.

2. the catalyst according to claim 1 for preparation of low carbon olefines by synthetic gas, it is characterised in that the potassium permanganate Concentration of aqueous solution is 0.02mol/L-0.1mol/L.

3. the catalyst according to claim 1 or 2 for preparation of low carbon olefines by synthetic gas, it is characterised in that the Gao Meng The temperature of sour aqueous solutions of potassium processing activated carbon is 70 DEG C.

4. the catalyst according to claim 1 or 2 for preparation of low carbon olefines by synthetic gas, it is characterised in that the catalysis The load capacity of iron is 5-10wt% in agent.

5. the catalyst according to claim 1 or 2 for preparation of low carbon olefines by synthetic gas, it is characterised in that after load iron Catalyst under nitrogen atmosphere calcining heat be 300 DEG C, calcination time for 3 it is small when.

6. the application of the catalyst for preparation of low carbon olefines by synthetic gas in claim 1-5 described in any one claim, It is characterised in that it includes following steps：Catalyst is uniformly mixed with quartz sand, is filled in fixed bed reactors；In H₂With It is 280~360 in reaction temperature after when the lower 300 DEG C of normal pressure in-situ reducings 12 of synthesis gas atmosphere that the molar ratio of CO is 1~3 are small DEG C, reaction pressure is 1.0~3.0MPa, and reacting gas volume space velocity is 1500~15000h^-1Under conditions of, synthesis gas and fixation The catalyst contact of bed reactor, generates the mainly low-carbon alkene containing C2~C4, while by-product C₅₊Gasoline segment length's chain hydrocarbon products.

7. the application of the catalyst according to claim 6 for preparation of low carbon olefines by synthetic gas, it is characterised in that reaction temperature Spend for 300-320 DEG C, reaction pressure 2MPa, the molar ratio of reaction gas is H₂:CO=1, reacting gas volume space velocity are 1500 ~3000h^-1。