A pretreatment method for a catalyst for synthesizing alpha-olefins

Abstract

The present invention relates to a pretreatment method for a catalyst for synthesizing alpha-olefins, and its purpose is to solve the problems of low alpha-olefin selectivity and poor catalyst stability in a conventional synthesis gas conversion process. The pretreatment method comprises the following steps: sequentially undergoing the three steps of reduction, carbonylation, and re-reduction, wherein the reduction and re-reduction conditions are the same or different, wherein the reduction and re-reduction refer to a reduction atmosphere containing hydrogen at 250-500°C, 0.01-5.0MPa, and a reducing atmosphere space velocity of 1000-50000ml·h ‑1 ·gCat ‑1 The catalyst is reduced under the conditions of 2 to 30 hours; the carbonylation refers to the carbonylation under the atmosphere containing CO at 250 to 450 ° C, 0.01 to 5.0 MPa, and a gas space velocity of 500 to 50000 ml·h ‑1 ·gCat ‑1 The carbonylation catalyst is reacted under the conditions of 3 to 50 hours.

Description

Technical Field

[0001] The invention relates to a pretreatment method of a catalyst for synthesizing alpha-olefins, in particular to a pretreatment method of an iron-based catalyst for synthesizing high-carbon-number linear alpha-olefins. Background Art

[0002] Linear alpha-olefins (LAO) refer to alpha-olefins whose alkyl groups connecting the C=C bonds are linear alkyl groups. LAO can be widely used in many fields such as comonomers, surfactants, additives, etc., among which linear alpha-olefins with carbon numbers of 6-15 are the most widely used. At present, alpha-olefins are mainly produced by petroleum routes. With the development of petroleum resources, the shortage of liquid fuels has gradually become one of the important factors restricting my country's economic development. The production of alpha-olefins from non-petroleum resources has become a research direction that has attracted much attention.

[0003] As an important process for producing α-olefins from non-petroleum resources, syngas-to-α-olefins has attracted much attention. The route that has been studied the most is the production of α-olefins from syngas by Fischer-Tropsch synthesis, but the distribution of product hydrocarbons is affected by the distribution of ASF, and the carbon number distribution of olefin products is relatively wide, and the selectivity of both low-carbon olefins and high-carbon olefins is low. How to improve the carbon number distribution of Fischer-Tropsch synthesis hydrocarbon products and improve the distribution of target product olefins is the goal of current research on the syngas-to-α-olefin process, and catalyst research and development has always been one of the main ways to improve this goal. Among the many catalysts studied, iron-based catalysts, as the most studied and cheapest Fischer-Tropsch catalysts, are naturally ideal candidates for the development of syngas-to-α-olefin catalysts. However, the iron-based catalysts for syngas-to-α-olefins currently studied still have the characteristics of low α-olefin selectivity and insufficient catalyst stability. Improving the α-olefin selectivity and catalytic stability of iron-based catalysts for syngas-to-α-olefins is a challenging problem in this study.

[0004] On this basis, the present invention proposes a reduction pretreatment method for an iron-based catalyst for synthesizing α-olefins from syngas. The iron-based catalyst treated by this method can achieve high selectivity in synthesizing LAO from syngas, especially LAO with a carbon number of 6-15. Summary of the invention

[0005] The object of the present invention is to provide a method for pretreating a catalyst for synthesizing α-olefins, in particular, a method for reducing and pretreating an iron-based catalyst for preparing α-olefins from synthesis gas. The iron-based catalyst pretreated by this process exhibits high selectivity for synthesizing LAO from synthesis gas and good catalytic stability.

[0006] To this end, the present invention provides a pretreatment method for a catalyst for synthesizing α-olefins. The pretreatment method is performed before the iron-based catalyst performs a synthesis reaction, and comprises the following steps: sequentially performing the three steps of reduction, carbonylation, and re-reduction, wherein the conditions of the reduction and the re-reduction are the same or different, wherein:

[0007] (1) The reduction and re-reduction are carried out under a reducing atmosphere containing hydrogen at 250 to 500°C, 0.01 to 5.0 MPa, and a reducing atmosphere space velocity of 1000 to 50000 ml·h -1 ·gCat -1 Reducing the catalyst under the conditions of 2 to 30 hours;

[0008] (2) The carbonylation is carried out in an atmosphere containing CO at 250 to 450°C, 0.01 to 5.0 MPa, and a gas space velocity of 500 to 50,000 ml·h -1 ·gCat -1 The carbonylation catalyst is reacted under the conditions of 3 to 50 hours.

[0009] In the process of synthesizing α-olefins, Fe and FeO formed during the reduction and reaction of iron-based catalysts x 、FeC x Iron species are the active species of the Fischer-Tropsch synthesis reaction. The existence forms and proportions of these iron species are different, and the reaction performance and hydrocarbon product selectivity are different. Iron-based catalysts generally undergo a reduction pretreatment process before the synthesis gas conversion to α-olefins. The reduction pretreatment process has an important influence on the generation of reactive iron species, and the difference in reactive iron species directly affects the catalytic performance of the catalyst, the distribution of olefin products, etc.

[0010] The present invention provides a reduction pretreatment method for an iron-based catalyst for synthesizing α-olefins by converting synthesis gas. The method refers to a method in which the iron-based catalyst is subjected to a three-step pretreatment process of reduction, carbonylation, and re-reduction in sequence before the reaction. The reduction process and re-reduction process of the pretreatment process refer to a process in which the catalyst is subjected to a reduction atmosphere containing hydrogen at 250 to 500°C, 0.01 to 5.0 MPa, and a reducing atmosphere space velocity of 1000 to 50000 ml·h -1 ·gCat -1 The process of reducing the iron-based catalyst for 2 to 30 hours under the conditions of . The reducing atmosphere and conditions of the reduction process in the pretreatment process and the re-reduction process may be the same or different. The carbonylation process in the pretreatment process refers to the process of reducing the iron-based catalyst under the conditions of 250 to 450°C, 0.01 to 5.0 MPa, and a gas space velocity of 500 to 50000 ml·h in an atmosphere containing CO. -1 ·gCat -1 The process of carbonylation of iron-based catalyst for 3 to 50 hours under the conditions of.

[0011] In the method for pretreating the catalyst for synthesizing α-olefins of the present invention, it is preferred that the reducing atmosphere is composed of 5-100% hydrogen and the remainder of an inert gas that does not react with the catalyst.

[0012] In the method for pretreating a catalyst for synthesizing α-olefins of the present invention, it is preferred that the CO-containing atmosphere is composed of 30-100% CO gas and the remainder of an inert gas that does not react with the catalyst.

[0013] In the pretreatment method for the catalyst for synthesizing α-olefins of the present invention, it is preferred that the content of CO gas in the CO-containing atmosphere is 50 to 100%, and more preferably 75 to 100%.

[0014] The pretreatment method of the catalyst for synthesizing α-olefins of the present invention is preferably that the conditions of the reduction and re-reduction processes are: 300-450°C, 0.05-2.0MPa, and a reducing atmosphere space velocity of 2000-10000ml·h -1 ·gCat -1 The reduction time is 4 to 24 hours.

[0015] The pretreatment method of the catalyst for synthesizing α-olefins of the present invention is preferably that the carbonylation conditions are: 300-400°C, 0.05-2.0MPa, and a gas space velocity of 500-5000ml·h -1 ·gCat -1 , the catalyst carbonylation time is 6 to 30 hours.

[0016] The pretreatment method of the catalyst for synthesizing α-olefins described in the present invention is preferably that the iron-based catalyst uses iron oxide and / or iron-containing carbide as active components, wherein the iron content is 10-85% based on the total mass of the oxide and the carbide, more preferably 30-70%, and the remainder is an additive and / or a carrier, wherein the additive includes an alkali metal additive and a transition metal additive, and the carrier is an inorganic oxide.

[0017] The pretreatment method of the catalyst for synthesizing α-olefins of the present invention is preferably such that the composition of the synthesis gas used for synthesizing α-olefins is: 2 / CO=1-5:1,CO 2 :1~10%; Synthesis reaction conditions: reaction temperature 250-380℃, reaction pressure: 0.1-5.0MPa, raw gas space velocity 1000-20000mL·h -1 ·gCat -1 .

[0018] The pretreatment method of the catalyst for synthesizing α-olefins of the present invention is preferably that the synthesis gas contains 0-10% of inert gas, and the inert gas comprises Ar, He, N 2 , CH 4 At least one of .

[0019] In the pretreatment method of the catalyst for synthesizing α-olefins of the present invention, it is preferred that the carbon number of the α-olefin is greater than or equal to 4, more preferably greater than or equal to 6, and even more preferably 6-15.

[0020] The iron-based catalyst for the synthesis gas to α-olefin reaction used in the present invention can be prepared by the following method, which is described in detail as follows:

[0021] Mix Fe(III) salt and Fe(II) salt with water in a mass ratio of 1:8 to 8:1 to form an iron salt solution, and add a certain amount of 3-13 mol / L HCl solution. At 60°C, add 1-10% NH 3 ·H 2 O solution, the acidic pH value of the solution is adjusted to about pH 10. After the addition is completed, the solution is stirred at a constant temperature for 1-8 hours and cooled to room temperature. After the reaction is completed, the deposited product is separated by magnetic field adsorption, washed with deionized water to neutrality, and dried for use, referred to as Fe-Cat.

[0022] Weigh 5 g of the Fe-Cat sample prepared by the above method, and prepare the corresponding K and Mn salt solutions according to the required auxiliary agent content. Immerse an equal volume of 5 g of the iron catalyst Fe-Cat sample in the above-prepared salt solution and stir, then let it stand for 3-20 hours, dry at 60-100°C, and roast at 500-850°C for 3-10 hours. Finally, grind, tablet and sieve (20-40 mesh) before use to obtain.

[0023] The iron component of the iron-based catalyst prepared by this method is mainly iron oxide, with Fe 3 O 4 and Fe 2 O 3 The final Fe-Cat containing additives is K-Mn-Fe 2 O 3 .

[0024] The evaluation method of the iron-based catalyst for the synthesis gas to α-olefin reaction used in the present invention is as follows:

[0025] The catalyst performance evaluation was carried out in a stainless steel fixed bed reactor (with an inner diameter of 14 mm), the iron-based catalyst particle size used was 20-40 mesh, and the catalyst bed was located in the constant temperature section of the heating furnace. Before the reaction, the catalyst was treated by the reduction pretreatment process (reduction-carbonylation-re-reduction) of the present invention: at 250-500°C, 0.01-5.0MPa, and a reducing atmosphere space velocity of 1000-50000ml·h -1 ·gCat -1 The iron-based catalyst is reduced under the conditions of 2 to 30 hours. After the reduction is completed, the reduction conditions are switched to carbonylation conditions (containing CO atmosphere, 250 to 450°C, 0.01 to 5.0 MPa, and the reducing atmosphere space velocity is 500 to 50000 ml·h -1 ·gCat -1 ) for 3 to 50 hours of carbonylation treatment of the catalyst, and then re-reduction of the catalyst (250-500°C, 0.01 to 5.0 MPa, reducing atmosphere space velocity of 1000 to 50000 ml·h -1 ·gCat -1 The iron-based catalyst was reduced under the conditions of 2 to 30 hours). After the catalyst was pre-treated by reduction, it was adjusted to the reaction temperature at a rate of 1°C / min and switched to the reaction raw gas (H 2 / CO / N 2 Mixed gas, N 2 As an internal standard, H 2 The reaction product is analyzed online by gas chromatography, and the reaction tail gas is directly fed into the first gas chromatograph after heat preservation for online analysis of all organic products. Then the product is cooled by cold trap and fed into the second gas chromatograph for N 2 , CO 2 , CO, CH 4 The reaction data were obtained after the reaction was stable. 2 The internal standard method is used for calculation. The selectivity of hydrocarbon products is calculated by using the area normalization method using the chromatographic peak areas after correction. The specific calculation method is as follows:

[0026] The CO conversion rate is calculated as follows:

[0027]

[0028] CO 2 The selectivity calculation formula is as follows:

[0029]

[0030] The product hydrocarbon selectivity is calculated as follows:

[0031]

[0032] In the above formula, CO in and CO out represent the molar fractions of CO at the reactor inlet and outlet, CO 2out Represents the CO in the reactor outlet 2 The mole fraction of .

[0033] The beneficial effects of the present invention are as follows:

[0034] The pretreated catalyst of the present invention is applied to the direct conversion of synthesis gas to produce linear alpha-olefins, which not only improves the selectivity of high-carbon linear alpha-olefins, but also greatly improves the stability of the catalytic reaction. DETAILED DESCRIPTION

[0035] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and process are given, but the protection scope of the present invention is not limited to the following embodiments. The experimental methods in the following embodiments without specifying specific conditions are usually carried out under conventional conditions.

[0036] The present invention provides a pretreatment method for a catalyst for synthesizing α-olefins. The pretreatment method is performed before the iron-based catalyst performs a synthesis reaction, and comprises the following steps: sequentially performing the three steps of reduction, carbonylation, and re-reduction, wherein the conditions of the reduction and the re-reduction are the same or different, wherein:

[0037] (1) The reduction and re-reduction are carried out under a reducing atmosphere containing hydrogen at 250 to 500°C, 0.01 to 5.0 MPa, and a reducing atmosphere space velocity of 1000 to 50000 ml·h -1 ·gCat -1 Reducing the catalyst under the conditions of 2 to 30 hours;

[0038] (2) The carbonylation is carried out in an atmosphere containing CO at 250 to 450°C, 0.01 to 5.0 MPa, and a gas space velocity of 500 to 50,000 ml·h -1 ·gCat -1 The carbonylation catalyst is reacted under the conditions of 3 to 50 hours.

[0039] In the process of synthesizing α-olefins, Fe and FeO formed during the reduction and reaction of iron-based catalysts x 、FeC xIron species are the active species of the Fischer-Tropsch synthesis reaction. The existence forms and proportions of these iron species are different, and the reaction performance and hydrocarbon product selectivity are different. Iron-based catalysts generally undergo a reduction pretreatment process before the synthesis gas conversion to α-olefins. The reduction pretreatment process has an important influence on the generation of reactive iron species, and the difference in reactive iron species directly affects the catalytic performance of the catalyst, the distribution of olefin products, etc.

[0040] The present invention provides a reduction pretreatment method for an iron-based catalyst for synthesizing α-olefins by converting synthesis gas. The method refers to a method in which the iron-based catalyst is subjected to a three-step pretreatment process of reduction, carbonylation, and re-reduction in sequence before the reaction. The reduction process and re-reduction process of the pretreatment process refer to a process in which the catalyst is subjected to a reduction atmosphere containing hydrogen at 250 to 500°C, 0.01 to 5.0 MPa, and a reducing atmosphere space velocity of 1000 to 50000 ml·h -1 ·gCat -1 The process of reducing the iron-based catalyst for 2 to 30 hours under the conditions of . The reducing atmosphere and conditions of the reduction process in the pretreatment process and the re-reduction process may be the same or different. The carbonylation process in the pretreatment process refers to the process of reducing the iron-based catalyst under the conditions of 250 to 450°C, 0.01 to 5.0 MPa, and a gas space velocity of 500 to 50000 ml·h in an atmosphere containing CO. -1 ·gCat -1 The process of carbonylation of iron-based catalyst for 3 to 50 hours under the conditions of.

[0041] In some embodiments, the reducing atmosphere is composed of 5-100% hydrogen and the remainder is an inert gas that does not react with the catalyst.

[0042] In some embodiments, the CO-containing atmosphere is composed of 30-100% CO gas and the remainder of an inert gas that does not react with the catalyst.

[0043] In some embodiments, the CO content of the CO-containing atmosphere is 50-100%, and more preferably 75-100%.

[0044] In some embodiments, the conditions of the reduction and re-reduction processes are: 300-450°C, 0.05-2.0 MPa, and a reducing atmosphere space velocity of 2000-10000 ml·h -1 ·gCat -1 The reduction time is 4 to 24 hours.

[0045] In some embodiments, the carbonylation conditions are: 300-400°C, 0.05-2.0 MPa, gas space velocity of 500-5000 ml·h -1 ·gCat -1, the catalyst carbonylation time is 6 to 30 hours.

[0046] In some embodiments, the iron-based catalyst uses iron oxide and / or iron-containing carbide as active components, wherein the iron content is 10-85% based on the total mass of the oxide and carbide, more preferably 30-70%, and the remainder is additives and / or carriers, wherein the additives include alkali metal additives and transition metal additives, and the carrier is an inorganic oxide.

[0047] In some embodiments, the composition of the synthesis gas used to synthesize α-olefins is: 2 / CO=1-5:1,CO 2 :1~10%; Synthesis reaction conditions: reaction temperature 250-380℃, reaction pressure: 0.1-5.0MPa, raw gas space velocity 1000-20000mL·h -1 ·gCat -1 .

[0048] In some embodiments, the synthesis gas contains 0-10% inert gas, and the inert gas includes Ar, He, N 2 , CH 4 At least one of .

[0049] In some embodiments, the carbon number of the α-olefin is greater than or equal to 4, more preferably greater than or equal to 6, and even more preferably 6-15.

[0050] In some embodiments, the iron-based catalyst is prepared by the following preparation method, which is described in detail as follows:

[0051] Mix Fe(III) salt and Fe(II) salt with water in a mass ratio of 1:8 to 8:1 to form an iron salt solution, and add a certain amount of 3-13 mol / L HCl solution. At 60°C, add 1-10% NH 3 ·H 2 O solution, the acidic pH value of the solution is adjusted to about pH 10. After the addition is completed, the solution is stirred at a constant temperature for 1-8 hours and cooled to room temperature. After the reaction is completed, the deposited product is separated by magnetic field adsorption, washed with deionized water to neutrality, and dried for use, referred to as Fe-Cat;

[0052] Weigh 5g of the Fe-Cat sample prepared by the above method, and prepare the corresponding K and Mn salt solutions according to the required additive content. Immerse 5g of the Fe-Cat sample in the above-prepared salt solution in equal volume and stir, then stand for 3-20h, dry at 60-100°C, roast at 500-850°C for 3-10h, and finally grind, tablet and sieve (20-40 mesh) before application to obtain;

[0053] The iron component of the iron-based catalyst prepared by this method is mainly iron oxide, with Fe 3 O 4 and Fe 2 O 3 The final Fe-Cat containing additives is K-Mn-Fe 2 O 3 .

[0054] Example 1

[0055] Preparation of iron-based catalysts:

[0056] 26.35 g FeCl 3 6H 2 O and 10.45 g FeCl 2 ·4H 2 O was mixed with 80 mL of water to form an iron salt solution, and 4.25 mL of 12.1 mol / L HCl solution was added. At 60 °C, under stirring, about 300 mL of 5% NH 3 ·H 2 O solution. Within about 2 hours, the acidic pH value of the solution is adjusted to a pH value of about 10. After the dropwise addition is completed, stir at a constant temperature for 1 hour and cool to room temperature. After the reaction is completed, the deposited product is separated by magnetic field adsorption, washed with deionized water to neutrality, and dried for use. Weigh 5g of the iron sample prepared by the above method, and prepare the corresponding K and Mn salt solutions according to the required auxiliary agent content. Immerse an equal volume of 5g of the iron sample in the above-prepared salt solution, stir, stand for 15 hours, dry at 60°C, roast at 500°C for 3 hours, and finally grind, press and sieve (20-40 mesh) before use to obtain K-Mn-Fe-Cat.

[0057] Nickel-based catalyst preparation:

[0058] Weigh 2.5g γ-Al 2 O 3 The sample is prepared into a corresponding Ni salt solution according to the required Ni content. 2.5g γ-Al 2 O 3 An equal volume was immersed in the Ni salt solution prepared above, stirred, allowed to stand for 15 h, dried at 60 ° C, calcined at 500 ° C for 3 h, and finally ground, pressed and sieved (20-40 mesh) to obtain Ni-Cat.

[0059] Catalyst pretreatment and evaluation:

[0060] The K-Mn-Fe-Cat and Ni-Cat catalysts were respectively loaded into the reactor in a ratio of 1:1. The catalyst loading amount was 1 g, and the atmosphere was pure H2 at normal pressure. 2, at 350℃, reducing atmosphere space velocity 6000ml·h -1 ·gCat -1 The mixture was reduced for 4 h under normal pressure, CO atmosphere, 300 °C, 2000 ml·h -1 ·gCat -1 Treat for 4 hours; finally, pressurize and reduce the atmosphere to pure H 2 , at 300℃, 6000ml·h -1 ·gCat -1 Restore for another 8 hours.

[0061] After the reduction was completed, the temperature was adjusted to 300 °C at a rate of 1 °C / min and the reaction raw gas (H 2 / CO / N 2 Mixed gas, N 2 As an internal standard, H 2 The volume ratio of N / CO is 2 / 1, 2 :4%), and the back pressure was 2.0MPa, the catalyst was at 300℃, 2.0MPa, 4000ml·gCat -1 ·h -1 The reaction performance test was carried out under the following conditions. The performance of the direct synthesis of linear α-olefins from synthesis gas for 5 hours is listed in Table 1.

[0062] Comparative Example 1

[0063] The steps of catalyst preparation, pretreatment and evaluation are the same as those in Example 1, except that the catalyst reduction pretreatment process is changed to normal pressure, pure hydrogen at 350°C, 6000ml·h -1 ·gCat -1 The reduction was carried out for 8 hours. The reaction performances tested are listed in Table 1.

[0064] Table 1. Effect of catalyst pretreatment on the reaction performance of the catalyst

[0065]

[0066] From the results in Table 1, we can see that the 2 Compared with the reduction process, the H 2 -CO-H 2 The iron-based composite catalyst in the reduction pretreatment process can improve the selectivity of hydrocarbon products in the reaction products while maintaining the CO conversion rate, and maintain the olefin linearity (LAO in C 6-15 ) to increase the C content of olefin products 6-15 Olefin content.

[0067] Example 2 and Comparative Example 2

[0068] The catalyst preparation, pretreatment and evaluation steps of Example 2 are the same as those of Example 1. The catalyst preparation, pretreatment and evaluation steps of Comparative Example 2 are the same as those of Comparative Example 1, except that the stability performance of the iron-based composite catalyst in the two reduction pretreatment processes is tested. The test conditions are: 300°C, 2.0MPa, 4000ml·gCat -1 ·h -1 The test results show that within the 50-hour reaction time of the test, the product selectivity of the two pretreatment processes did not change significantly, but the catalytic activity comparison results of the two changed significantly, and the results are listed in Table 2.

[0069] Table 2. Effect of catalyst pretreatment on the reaction stability of the catalyst

[0070]

[0071] From the results in Table 2, we can see that the traditional H 2 Compared with the reduction process, the H 2 -CO-H 2 The pretreatment process significantly improves the stability of the catalyst. Within 50 hours of reaction, the CO conversion rate is still maintained at more than 80%, while the conversion rate of the catalyst in the conventional reduction process under the same conditions has dropped to 55% after 50 hours of reaction. This difference in reaction stability is related to the fact that the reduction pretreatment process of the present invention changes the formation mode of the iron active species in the conventional catalyst reduction process.

[0072] Example 3

[0073] The steps of catalyst preparation, pretreatment and evaluation were the same as those in Example 1, except that the conditions of catalyst reduction pretreatment were changed to 2.0 MPa, 5% H 2 (H 2 -Ar mixed gas) 300℃, 10000ml·h -1 ·gCat -1 Reduction 12h, 2.0MPa, 50%CO(CO-N 2 Mixed gas), 350℃, 500ml·h -1 ·gCat -1 30h treatment, 5.0MPa pure H 2 400℃、3000ml·h -1 ·gCat -1 After 4 h of reduction, the raw gas was switched to test the reaction performance of the catalyst. The reaction test conditions were changed to: syngas raw gas (H 2 / CO / N 2 Mixed gas, N 2 As an internal standard, H 2 The volume ratio of N / CO is 3 / 1,2 :6%), 350℃, 1.0MPa, 8000ml·gCat -1 ·h -1 The measured reaction results are listed in Table 3.

[0074] Example 4

[0075] The steps of catalyst preparation, pretreatment and evaluation were the same as those in Example 1, except that the conditions of catalyst reduction pretreatment were changed to 5.0 MPa, 30% H 2 (H 2 -Ar mixed gas) 400℃, 2000ml·h -1 ·gCat -1 Reduction 24h, 5.0MPa, 75%CO(CO-N 2 Mixed gas), 400℃, 5000ml·h -1 ·gCat -1 Treatment for 6h, 2.0Mpa, 5%H 2 (H 2 -Ar mixed gas) 400℃, 3000ml·h -1 ·gCat -1 After 12 hours of reduction, the raw gas was switched to test the reaction performance of the catalyst. The reaction test conditions were changed to: syngas raw gas (H 2 / CO / N 2 Mixed gas, N 2 As an internal standard, H 2 The volume ratio of N / CO is 1 / 1. 2 :6%), 280℃, 3.0MPa, 4000ml·gCat -1 ·h -1 The measured reaction results are listed in Table 3.

[0076] Comparative Example 3

[0077] The steps of catalyst preparation, pretreatment and evaluation are basically the same as those in Example 4, except that the re-reduction step of catalyst pretreatment is removed and only the reduction-carbonylation step of catalyst pretreatment is retained. The reaction performance test results are listed in Table 3.

[0078] Table 3. Reaction performance of iron-based catalysts for synthesis gas to α-olefins

[0079] Example Example 3 Example 4 Comparative Example 3 CO conversion rate (mol%) 98.8 93.6 25.0 Hydrocarbon product selectivity (C%) 68.3 60.2 55.0 Olefin / Hydrocarbon Products (C%) 60.3 72.2 25.0 Olefin products (C%) <![CDATA[C 2-3 ＝ ]]> 29.0 23.4 56.0 <![CDATA[C 4-5 ＝ ]]> 29.5 26.4 43.0 <![CDATA[C 6-15 ＝ ]]> 41.5 47.7 1.0 <![CDATA[C 16-18 ＝ ]]> --- 2.5 --- <![CDATA[C 18+ ＝ ]]> --- --- --- <![CDATA[LAO in C 6-15 ＝ ]]> 70.0 63.6 ---

[0080] As can be seen from Table 3, the iron-based composite catalyst exhibits good catalytic performance for the conversion of synthesis gas to α-olefins under different conditions of the pretreatment process of the present invention. Compared with the reduction process of Comparative Example 3, the results show that the re-reduction step in the pretreatment process of the iron-based composite catalyst has a more obvious effect on the reaction performance of the treated catalyst.

[0081] In summary, the pretreated catalyst of the present invention is applied to the direct conversion of synthesis gas to linear α-olefins, which not only improves the selectivity of high-carbon linear α-olefins, but also greatly improves the stability of the catalytic reaction.

[0082] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the present invention.

Claims

1. A pretreatment method for a catalyst for synthesizing α-olefins, the pretreatment method being performed before a synthesis reaction of an iron-based composite catalyst, wherein the iron-based composite catalyst is composed of an iron-based catalyst and a nickel-based catalyst in a ratio of 1:1, characterized in that: The following steps are involved: After three steps of reduction, carbonylation and re-reduction, (1) The reduction and re-reduction refer to the conditions of 250-500°C, 0.1-5.0 MPa and a reducing atmosphere space velocity of 1000-50000 ml·h in a reducing atmosphere containing hydrogen. -1 ·gCat -1 The catalyst is reduced under the conditions of , the reduction time is 2 to 30 hours, and the re-reduction time is 4 to 12 hours; (2) The carbonylation is carried out in a CO-containing atmosphere at 250-450°C, 0.1-5.0 MPa, and a gas space velocity of 500-50000 ml·h -1 ·gCat -1 The carbonylation catalyst is used for 3 to 50 hours under the conditions of ; The reducing atmosphere is composed of 5-100% hydrogen and the remainder of an inert gas that does not react with the catalyst; the CO-containing atmosphere is composed of 30-100% CO gas and the remainder of an inert gas that does not react with the catalyst; The iron-based catalyst uses iron oxide and / or iron-containing carbide as active components, wherein the iron content is 10-85% based on the total mass of the oxide and the carbide, and the remainder is an additive and / or a carrier, wherein the additive includes an alkali metal additive K and a transition metal additive Mn, and the carrier is an inorganic oxide. The preparation process of the nickel-based catalyst comprises the following steps: An equal volume of 2.5 g γ-Al2O3 was immersed in a Ni salt solution, stirred, allowed to stand for 15 h, dried at 60 °C, calcined at 500 °C for 3 h, and finally ground, tableted and sieved with a sieve mesh of 20-40 to obtain a nickel-based catalyst.

2. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The content of CO gas in the CO-containing atmosphere is 50-100%.

3. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 2, characterized in that: The content of CO gas in the CO-containing atmosphere is 75-100%.

4. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The conditions of the reduction and re-reduction processes are: 300-450°C, 0.1-2.0 MPa, and a reducing atmosphere space velocity of 2000-10000 ml·h -1 ·gCat -1 .

5. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The time of the reduction step is 4 to 24 hours.

6. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The carbonylation conditions are: 300-400°C, 0.1-2.0 MPa, and a gas space velocity of 500-5000 ml·h -1 ·gCat -1 , the catalyst carbonylation time is 6 to 30 hours.

7. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: In the iron-based catalyst, the content of iron is 30-70% based on the total mass of oxides and carbides.

8. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The composition of the synthesis gas used to synthesize α-olefins is: H2 / CO = 1-5:1, CO2: 1~10%; the synthesis reaction conditions are: reaction temperature 250-380℃, reaction pressure: 0.1-5.0MPa, raw gas space velocity 1000-20000 mL·h -1 ·gCat -1 .

9. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The synthesis gas contains 0-10% of inert gas, and the inert gas includes at least one of Ar, He, N2, and CH4.

10. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 1, characterized in that: The α-olefin has 4 or more carbon atoms.

11. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 10, characterized in that: The α-olefin has 6 or more carbon atoms.

12. The pretreatment method of the catalyst for synthesizing α-olefins according to claim 11, characterized in that: The α-olefin has a carbon number of 6 to 15.

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