WO2017031635A1

WO2017031635A1 - Iron-based catalyst prepared by using coprecipitation-melting method, preparation method therefor, and application thereof

Info

Publication number: WO2017031635A1
Application number: PCT/CN2015/087810
Authority: WO
Inventors: 陈艳平; 朱文良; 刘中民; 刘勇; 刘红超; 倪友明
Original assignee: 中国科学院大连化学物理研究所
Priority date: 2015-08-21
Filing date: 2015-08-21
Publication date: 2017-03-02

Abstract

Disclosed is an iron-based catalyst prepared by using a coprecipitation-melting method. The catalyst comprises the iron element Fe, a metallic element A, and a metallic element B. The metallic element A is selected from at least one of aluminium and/or a transition metal; and the metallic element B is selected from at least one of an alkali metal and/or an alkaline earth metal. Each metal element exists in a form of a single metal and/or a metallic oxide. Accounting by using that the total amount of the metal elements comprised in the catalyst is 100 wt%, the metal element Fe in the catalyst accounts for 50 wt% to 99 wt%, the metal element A in the catalyst accounts for 0.1 wt% to 50 wt%, and the metal element B in the catalyst accounts for 0.01 wt% to 40 wt%. In the one-stage preparation of light olefins from syngas, the catalyst has features of high activity, high mechanical stability, and low carbon deposit in reaction, thereby preventing the catalyst from pulverization, and presenting relatively high light-olefin selectivity.

Description

Iron-based catalyst prepared by coprecipitation-melting method, preparation method and application thereof

Technical field

The invention relates to an iron-based catalyst prepared by a coprecipitation-melting method, a preparation method thereof and an application thereof in the reaction of preparing a low-carbon olefin in a synthesis gas, and belongs to the field of chemistry and chemical engineering.

Background technique

Ethylene and propylene are bulk chemical raw materials. The industrial development level and market supply and demand balance directly affect the development level and industrial scale of the entire petrochemical industry. For coal-based syngas in China's rich coal, oil-deficient and low-gas energy structure characteristics. Conversion to lower olefins can effectively reduce dependence on petroleum resources. Traditionally, the production of olefins from syngas is primarily the conversion of synthesis gas to methanol followed by conversion of methanol to lower olefins (MTO). In contrast, the direct preparation of low-carbon olefins from syngas has the advantages of simple operation and simple process route, which is attracting great attention. Iron-based catalysts are the focus of research on the direct preparation of low-carbon olefins from coal-based syngas. They are inexpensive, allow a wide range of operating temperatures, and have greater flexibility in product selection.

At present, iron-based catalysts are mainly divided into bulk iron catalysts and supported iron catalysts. The supported iron catalysts have low space-time yield due to low iron loading, which is not conducive to industrial production, and bulk iron catalysts have high catalytic efficiency. It is the catalyst of choice for the direct preparation of low-carbon olefins from syngas. The bulk iron catalyst is mainly prepared by co-precipitation method. The co-precipitated iron catalyst has higher selectivity for low-carbon olefins when the reaction temperature is higher than 300 °C, but the higher reaction temperature leads to the formation of a large amount of carbon deposits. Powdering, mechanical strength is reduced, and the catalytic bed and separation equipment are severely blocked in industrial applications.

Summary of the invention

According to an aspect of the present application, there is provided an iron-based catalyst prepared by a coprecipitation-melting method, which has high activity and high mechanical stability, and reduces carbon deposition generated by a catalyst in a process for directly preparing a low-carbon olefin from a synthesis gas. The amount inhibits the pulverization of the catalyst, thereby preventing the active site from being clogged or covered, improving the utilization of the active site, thereby regulating the product distribution of the Fischer-Tropsch synthesis and improving the selectivity of the lower olefin.

The iron-based catalyst prepared by the coprecipitation-melting method, characterized in that the catalyst contains iron element Fe, metal element A and metal element B; and the metal element A is selected from at least aluminum and/or transition metal One; the metal element B is selected from at least one of an alkali metal and/or an alkaline earth metal;

Each metal element is present in the form of a metal element and/or a metal oxide;

The content of the metal element Fe in the catalyst is 50% by weight to 99% by weight based on the total amount of the metal element contained in the catalyst, and the content of the metal element A in the catalyst is 0.1% by weight to 50% by weight, the metal element B The content in the catalyst is from 0.01% by weight to 40% by weight.

Preferably, the metal element A is at least one selected from the group consisting of Mn, Co, Cu, Zn, Ti, Al, Cr, Ni, Ce, and Zr.

Preferably, the metal element B is at least one selected from the group consisting of Li, Na, K, Mg, and Ca.

According to still another aspect of the present application, there is provided a method of preparing an iron-based catalyst by a coprecipitation-melting method, characterized in that it comprises at least the following steps:

a) mixing a solution I containing a source of Fe and source A with a coprecipitant at a temperature of 20 ° C to 80 ° C and a pH of 7 to 11 for coprecipitation;

b) after the completion of the precipitation, the resulting precipitate is filtered, washed, and mixed with a solution containing B source II to obtain a mixture I;

c) After the mixture I obtained in the step b) is dried, it is melt-treated at a temperature of 600 ° C to 1600 ° C for 2 hours to 10 hours to obtain the iron-based catalyst.

Preferably, the coprecipitating agent is at least one selected from the group consisting of ammonia water, aqueous sodium carbonate solution, and aqueous potassium carbonate solution.

Preferably, the solution I containing the Fe source and the A source in the step a) is co-precipitated by cocurrently mixing with the coprecipitant.

The mixing method of the solution I containing the Fe source and the A source in the step a) and the coprecipitant may be positive addition, reverse addition or cocurrent mixing. Preferably, the solution I containing the Fe source and the A source in the step a) is mixed with the coprecipitant by cocurrent addition.

As an embodiment of the present application, the step a) is to pass the solution I containing the Fe source and the A source and the coprecipitant through the co-current at a temperature of 20 ° C to 80 ° C and a pH of 7-11. The mixing method is mixed, coprecipitation is carried out, and stirring is continued during the coprecipitation.

Preferably, said washing in said step b) means washing to a pH of the filtrate in the range of from 6 to 8.

Preferably, in the step b) of the solution II containing the B source, the mass percentage of the B source is from 1% by weight to 20% by weight.

Preferably, the step b) is performed after the precipitation is completed, and is aged at a temperature of 30 ° C to 80 ° C for 2 hours to 24 hours, filtered, washed until the pH of the filtrate is in the range of 6-8, and then the precipitate is contained. 1 wt% to 20 wt% of the solution II of the B source is mixed to obtain a mixture I.

Preferably, the washing process in the step b) uses deionized water.

Preferably, the mixture I obtained in the step b) is dried at a temperature of 30 ° C to 150 ° C for 12 hours to 36 hours, and further melted at a temperature of 600 ° C to 1600 ° C for 2 hours to 10 hours. That is, the iron-based catalyst is obtained.

Further preferably, the step c) is to dry the mixture I obtained in the step b) at a temperature of 30 ° C to 150 ° C for 12 hours to 36 hours, and then to roast at a temperature of 400 ° C to 600 ° C for 2 hours to 10 hours. In the hour, it is further melt-treated at a temperature of 600 ° C to 1600 ° C for 2 hours to 10 hours to obtain the iron-based catalyst.

Preferably, the temperature of the melt treatment in the step c) is 800 ° C to 1300 ° C, and the time of the melt treatment is 4 hours to 6 hours.

According to still another aspect of the present application, a method for producing a lower olefin from a synthesis gas is provided, characterized in that the catalyst is at least one of the above iron-based catalysts and/or an iron-based catalyst prepared according to any of the above methods. At least one of the catalysts; after the reduction treatment, the catalyst is used for syngas to produce low-carbon olefins; the synthesis gas to produce low-carbon olefins has a reaction temperature of 200 ° C to 450 ° C, a reaction pressure of 0.5 MPa to 5 MPa, and a synthesis gas. CO and H ₂ in volume ratio H ₂ /CO=0.5~3, space velocity GHSV = 500h ^{^-1} ~ 8000h ^-1.

According to the iron-based catalyst obtained by the embodiment of the present application, the catalyst needs to be subjected to a reduction treatment before the reaction, and can be used for the reaction of syngas to produce a low-carbon olefin. Preferably, before the reaction of the synthesis gas to produce a low-carbon olefin, the catalyst needs to be reduced. The reduction temperature of the catalyst is 200-650 ° C, the pressure is reduced at normal pressure, the reduction time is 5 hours to 20 hours, and the reducing gas is H ₂ and / or CO.

In the present application, the lower olefin refers to an olefin having a carbon number of not more than 4.

The beneficial effects that can be produced by the present application include but are not limited to:

1) The iron-based catalyst prepared by the coprecipitation-melting method provided by the present application has both high activity and high mechanical stability.

2) The iron-based catalyst prepared by the coprecipitation-melting method provided by the present application effectively solves the phenomenon of carbon deposition of the catalyst, and provides an effective way for improving the life of the iron-based catalyst.

3) The method for preparing the iron-based catalyst prepared by the coprecipitation-melting method provided by the present application, by first coprecipitating and then performing a certain degree of melting treatment, the catalyst is introduced into the dense structure of the molten iron on the basis of the coprecipitated iron, and the inhibition is carried out. The formation of carbon deposits increases the life of the catalyst.

4) The iron-based catalyst provided by the present application is used for the synthesis of low-carbon olefins in the synthesis gas, which can effectively inhibit the carbon deposition of the catalyst, and the amount of carbon deposition makes the active sites less likely to be blocked or covered, thereby improving the active site utilization of the iron-based catalyst. The rate, thereby increasing the catalytic activity of the synthesis gas to produce low-carbon olefins, while also regulating the product distribution of the Fischer-Tropsch synthesis, and improving the selectivity of the low-carbon olefins.

DRAWINGS

1 is a scanning electron micrograph of a sample C1 ^# obtained in Example 1.

2 is a scanning electron micrograph of sample D1 ^# obtained in Comparative Example 1.

detailed description

The present application is described in detail below with reference to the embodiments and the drawings, but the application is not limited to the embodiments.

In the examples, the SEM topography analysis was performed using a SU8020 scanning electron microscope from the Scientific Instrument Factory of the Chinese Academy of Sciences.

Sample composition was analyzed by X-ray diffraction (XRD) at X'Pert of PANalytical Measured on a PRO X-ray diffractometer.

The amount of carbon deposited on the sample after the reaction was measured by thermogravimetry (TG) and measured on a SDT Q600 thermal analyzer of TA Company, USA.

The reaction product was analyzed by on-line gas chromatography. The gas chromatograph is Agilent's 7890A, the detector uses TCD and FID, the TCD analysis uses packed column TDX-01 (2m × 2mm), the carrier gas is high purity helium; FID analysis uses capillary column HP-PLOT/Q (30m × 0.32mm). The column temperature was programmed to be raised from 40 ° C to 150 ° C at a heating rate of 20 ° C / min for 5 min, and then raised to 240 ° C at a heating rate of 30 ° C / min for 5 min.

Example 1 Preparation of Catalyst Samples

20.0 g of iron nitrate nonahydrate and 10.1 g of manganese nitrate hexahydrate were dissolved in 200 ml of deionized water to obtain a solution I, the coprecipitant was a 25% by mass aqueous ammonia, and the solution I and the coprecipitant were continuously mixed by a cocurrent method. The mixing ratio was controlled to keep the pH of the solution at 7, and the temperature during the coprecipitation was kept at 20 ° C, and the mixture was continuously stirred during the precipitation. After the coprecipitation was completed, it was aged at a temperature of 30 ° C for 10 h, filtered, washed with deionized water until neutral, and the filter cake was re-slurryed by adding 190 g of a 1 wt% potassium carbonate solution (solution II) to obtain a mixture I. The mixture I was dried at a temperature of 50 ° C for 12 h, and then calcined at a temperature of 500 ° C in an air atmosphere for 10 h. Further, it was melt-treated at a temperature of 1200 ° C in an air atmosphere for 10 hours. That is, the desired catalyst was prepared and recorded as sample C1 ^# .

The specific preparation procedure for sample C2 ^{# is} the same as sample C1 ^# except that the aging step has not been performed, as shown in Table 1. Raw materials and other conditions are shown in Tables 1 and 2.

The specific preparation procedure of sample C3 ^{# is} the same as sample C1 ^# except that the calcination step has not been performed, as shown in Table 2. Raw materials and other conditions are shown in Tables 1 and 2.

The specific preparation steps of the samples C4 ^# to C15 ^# are the same as those of the sample C1 ^# . The Fe source, the source type and amount of the solution I, the coprecipitation conditions, the amount of the solution II, and the concentration of the B source in the specific preparation are shown in Table 1. The conditions for drying, calcining and melting treatment of the mixture I are shown in Table 2. The elemental composition of the final samples C1 ^# to C15 ^# was analyzed by XRF, and the results are shown in Table 1.

Table 1 Catalyst preparation raw materials, coprecipitation conditions and elemental composition

Table 2 Conditions for drying, calcining and melting of mixture I

Comparative Example 1 Catalyst prepared by coprecipitation

The preparation method of the raw material and the coprecipitation was the same as that of the sample C1 ^# , as shown in Table 1. The difference was that after drying at 120 ° C for 12 h and then baking at 500 ° C for 5 h, it was recorded as sample D1 ^# .

Comparative Example 2 Catalyst prepared by molten iron method

The raw material was the same as the sample C1 ^# except that the raw materials were directly mixed and dried and melted without coprecipitation, and as a catalyst, the sample D2 ^{# was used} .

Example 2 Scanning Electron Microscopy Characterization

The sample C1 ^# obtained in Example 1 and the sample D1 ^# obtained in Comparative Example 1 were subjected to scanning electron microscopic analysis, and the results are shown in Figs. 1 and 2.

2 is a surface topography of the coprecipitated iron catalyst sample D1 ^# . It can be seen from the figure that the coprecipitated iron catalyst is composed of particles of 10 to 20 nm. Figure 1 shows the surface morphology of the coprecipitated-melted iron catalyst sample C1 ^# . It can be seen that after the melting section treatment, the particle size is obviously increased, the particle size is 50-200 nm, and there is adhesion between the particles, which is due to the melting treatment. High-temperature melting of metal particles, this structural feature can greatly improve the mechanical strength of the catalyst, but also reduce the amount of carbon deposition, especially to prevent catalyst powdering caused by carbon deposition and other factors, greatly extending the life, while at the same time Maintain adequate reactivity and selectivity.

Example 3 Sample C1 ^# to sample C15 ^# and sample D1 ^# , sample D2 ^# synthesis gas to produce low carbon olefin reaction performance test

2 g of sample C1 ^{# was} charged into the reaction tube, and the catalyst was placed in a constant temperature section in combination with a liner, quartz wool, and quartz sand. The reaction tube was placed in a fixed bed apparatus with the thermocouple in the catalyst bed. The reduction treatment was carried out by using H ₂ , and the reduction conditions were as follows: the reduction temperature was 350 ° C, the atmospheric pressure was reduced, and the reduction time was 6 h. The reduced catalyst is used in a synthesis gas to prepare a low-carbon olefin, the reaction condition is 350 ° C, the reaction pressure is 4 MPa, the volume ratio of the raw material gas is H _{2 /} CO = 0.5, and the space velocity GHSV is 1000 h ^-1 . At the same time, set the valve box temperature, line insulation and chromatographic line insulation to 150 °C. The reaction product was subjected to on-line chromatography every 30 min. The reaction time is 24 h, the CO conversion rate is 97%, the olefin selectivity of carbon atoms is 2 to 4 (C ₂ -C ₄ ) is 46%, the carbon number is 2 to 4 olefins, and the alkane molar ratio is olefin/alkane ratio is 7. The selectivity of CH _{4 is} 16%, the hydrocarbon (C ₅ ⁺ ) having a carbon number of more than 5 has a selectivity of 31%, and the CO ₂ selectivity is 42%. After the completion of the reaction, the catalyst was taken out and the amount of carbon deposited on the catalyst was measured by a thermogravimetric analyzer, and the amount of carbon deposited was 30%.

Other catalysts are used in the synthesis of low-carbon olefins in syngas. The specific reduction and reaction conditions are shown in Table 3. The reaction results are shown in Table 4.

Table 3 Synthesis of low carbon olefins by synthesis gas and reaction conditions

Table 4 Synthesis of low-carbon olefins by synthesis gas

Comparative Example 3 Preparation of a low-carbon olefin from the synthesis gas of sample D1 ^#

The sample D1 ^# was used to prepare a low-carbon olefin reaction, and the reduction conditions and reaction conditions were identical to those of the sample C1 ^# in Example 3 except that the sample C1 ^{# was} changed to the sample D1 ^# . The reaction time is 24 h, and the reaction results are: 95% CO conversion, 20% olefin selectivity of 2 to 4 carbon atoms, 2 to 4 carbon atoms, olefin/alkane molar ratio of 0.8, and CH ₄ selectivity of 30%. The C ₅ ⁺ selectivity is 25%, the CO ₂ selectivity is 41%, and the carbon deposition amount is 80%. It can be seen that the coprecipitated iron catalyst has low reactivity and selectivity due to the high carbon deposition amount.

Comparative Example 4 Preparation of a low carbon olefin reaction from the synthesis gas of sample D2 ^#

The sample D2 ^# was used to prepare a low-carbon olefin reaction, and the reduction conditions and reaction conditions were identical to those of the sample C1 ^# in Example 3 except that the sample C1 ^{# was} changed to the sample D2 ^# . The reaction time is 24 h, and the reaction results are: 40% CO conversion, 25% olefin selectivity of 2 to 4 carbon atoms, 2 to 4 carbon atoms, alkane molar ratio of olefin/alkane of 1.5, and CH ₄ selectivity of 30. %, C ₅ ⁺ selectivity 32.5%, CO ₂ selectivity 42%, carbon deposition 40%. It can be seen that although the molten iron catalyst has a low carbon deposition amount, the reactivity and selectivity are poor.

The above description is only a few examples of the present application, and is not intended to limit the scope of the application. However, the present application is disclosed in the preferred embodiments, but is not intended to limit the application, any person skilled in the art, It is within the scope of the technical solution to make a slight change or modification with the technical content disclosed above, which is equivalent to the equivalent embodiment, without departing from the technical scope of the present application.

Claims

An iron-based catalyst prepared by a coprecipitation-melting method, characterized in that the catalyst contains iron element Fe, metal element A and metal element B; and the metal element A is selected from at least aluminum and/or transition metal One; the metal element B is selected from at least one of an alkali metal and/or an alkaline earth metal;

Each metal element is present in the form of a metal element and/or a metal oxide;

The content of the metal element Fe in the catalyst is 50% by weight to 99% by weight based on the total amount of the metal element contained in the catalyst, and the content of the metal element A in the catalyst is 0.1% by weight to 50% by weight, the metal element B The content in the catalyst is from 0.01% by weight to 40% by weight.
The iron-based catalyst according to claim 1, wherein the metal element A is at least one selected from the group consisting of Mn, Co, Cu, Zn, Ti, Al, Cr, Ni, Ce, and Zr.
The iron-based catalyst according to claim 1, wherein the metal element B is at least one selected from the group consisting of Li, Na, K, Mg, and Ca.
A method for preparing an iron-based catalyst by a coprecipitation-melting method, characterized in that it comprises at least the following steps:

a) mixing a solution I containing a source of Fe and source A with a coprecipitant at a temperature of 20 ° C to 80 ° C and a pH of 7 to 11 for coprecipitation;

b) the resulting precipitate is filtered, washed, and mixed with a solution containing B source II to obtain a mixture I;

c) after the mixture I obtained in the step b) is dried, at a temperature of from 600 ° C to 1600 ° C The iron-based catalyst is obtained by melt treatment for 2 hours to 10 hours.
The method according to claim 4, wherein the coprecipitating agent is at least one selected from the group consisting of ammonia water, aqueous sodium carbonate solution, and aqueous potassium carbonate solution.
The method according to claim 4, wherein the solution I containing the Fe source and the A source in the step a) is co-precipitated by cocurrently mixing with the coprecipitant.
The method according to claim 4, wherein the step b) is performed after the precipitation is completed, and is aged at a temperature of 30 ° C to 80 ° C for 2 hours to 24 hours, filtered, and washed until the pH of the filtrate is 6-8. Within the range, the precipitate is then mixed with a solution II containing 1% by weight to 20% by weight of a B source to obtain a mixture I.
The method according to claim 4, wherein the step c) is to dry the mixture I obtained in the step b) at a temperature of 30 ° C to 150 ° C for 12 hours to 36 hours, at 400 ° C to 600 ° C. The iron-based catalyst is obtained by calcining at a temperature of 2 hours to 10 hours and further at a temperature of 600 ° C to 1600 ° C for 2 hours to 10 hours.
The method according to claim 4, wherein the temperature of the melt treatment in the step c) is from 800 ° C to 1300 ° C, and the time of the melt treatment is from 4 hours to 6 hours.
A method for producing a lower olefin from a synthesis gas, characterized in that the catalyst is at least one of the iron-based catalysts according to any one of claims 1 to 3 and/or according to any one of claims 4 to 9. At least one of the iron-based catalysts prepared by the method;

After the catalyst is subjected to reduction treatment, it is used in synthesis gas to produce low-carbon olefins;

The reaction temperature for the production of low-carbon olefins from syngas is 200 ° C to 450 ° C, the reaction pressure is 0.5 MPa to 5 MPa, the volume ratio of H 2 to CO in the synthesis gas is H 2 /CO = 0.5 to 3 , and the space velocity GHSV is 500 to 8000 h. -1 .