Low-carbon alcohol catalyst as well as preparation method and application thereof

Abstract

The invention provides a low-carbon alcohol catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The CuZnM catalyst is prepared by adopting a complete liquid phase method, Al (NO3) 3.9 H2O or Ga (NO3) 3.xH2O is added in the preparation process and can play a role of a structural aid, and the content of oxygen vacancies in the CuZnM catalyst is increased, so that the selectivity of the catalyst to the low-carbon alcohol is improved, a good effect of catalyzing synthesis gas to prepare the low-carbon alcohol is achieved, and high-selectivity synthesis of the low-carbon alcohol is realized. In the process of preparing the CuZnM catalyst in a liquid phase, the liquid paraffin is added and then is subjected to heat treatment, so that the slurry catalyst is obtained, the liquid paraffin is used as a medium and is beneficial to forming the catalyst in the liquid phase, and the preparation method realizes direct conversion from a solution to slurry, so that the preparation process is simple, and the cost is low. The problem that the catalyst is inactivated when the solid powder catalyst is dispersed in an inert reaction medium for slurry bed reaction is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a lower alcohol catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Energy is an important material basis for the survival and sustainable development of human society. The development and utilization status of energy is an important symbol to measure a country's economic development and scientific and technological level, and is also directly related to the level of people's living standards. Therefore, the development and utilization of energy is particularly important. Coal, petroleum, and natural gas, as the three major energy systems, consume a large amount, and these primary energy sources are all non-renewable. Although new energy systems are being vigorously developed now, coal will still be the main body of energy consumption within the next 50 years. However, the carbon emissions generated by coal consumption account for almost 70% of all energy carbon emissions, and its utilization rate is low. In view of this, accelerating the realization of clean and efficient conversion and utilization of coal, and directing the synthesis gas derived from non-petroleum carbon resources such as coal, natural gas, biomass, or CO 2 and other non-petroleum carbon resources into lower alcohols is one of the effective ways to achieve clean and efficient utilization of coal and an important measure to alleviate the tense situation of energy supply.

[0003] Lower alcohols generally refer to the mixed alcohols of C 2 ~C 6 . They have a relatively high octane number, can be used as clean liquid fuels, or can be used as gasoline additives instead of methyl tert-butyl ether. The most important thing for synthesizing lower alcohols from syngas is a catalyst with high selectivity for lower alcohols. Currently, the main catalysts for synthesizing lower alcohols are divided into four categories: Rh-based catalysts, Mo-based catalysts, modified Fischer-Tropsch catalysts, and modified methanol catalysts. Rh-based catalysts are the only ones that show high selectivity for lower alcohols. This is because Rh-based catalysts have unique CO dissociation and non-dissociative adsorption properties. However, the high price and scarcity of Rh make Rh-based catalysts not conducive to industrialization. Mo-based catalysts have high sulfur resistance, but their catalytic activity is low. Therefore, Mo-based catalysts require higher reaction pressures, the reaction conditions are harsh, and the cost is high. At the same time, sulfur is easily introduced into the products during the reaction, making it difficult to handle. Modified Fischer-Tropsch catalysts have strong carbon chain growth ability, but the product type distribution is wide and difficult to separate, resulting in low product purity. Modified methanol catalysts are mainly represented by modified high-temperature Zn-Cr catalysts and modified low-temperature Cu-based catalysts. Among them, the reaction temperature and pressure of modified Zn-Cr catalysts are relatively high, resulting in high energy consumption and difficulty in industrialization. Although modified Cu-based catalysts have low cost, mild reaction conditions, high catalytic activity, and are easy to industrialize, the proportion of methanol in the products synthesized by modified Cu-based catalysts is relatively high while the proportion of lower alcohols is relatively low.

[0004] Therefore, how to improve the selectivity of the catalyst for lower alcohols and reduce the methanol proportion in the products has become a technical problem to be urgently solved in this field. Summary of the Invention

[0005] The object of the present invention is to provide a lower alcohol catalyst, a preparation method thereof and an application. The catalyst prepared by the preparation method provided by the present invention has high selectivity for lower alcohols and high conversion rate for CO at the same time.

[0006] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a lower alcohol catalyst, comprising the following steps:

[0008] (1) Mix citric acid, a structure assistant and water and conduct heat treatment to obtain a mixed solution; the structure assistant is Al(NO 3 ) 3 ·9H 2 O or Ga(NO 3 ) 3 ·xH 2 O;

[0009] (2) Add an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O to the mixed solution obtained in the step (1) to obtain a green sol;

[0010] (3) Age the green sol obtained in the step (2), then add liquid paraffin, and finally conduct heat treatment to obtain a lower alcohol catalyst.

[0011] Preferably, the mass ratio of citric acid, the mass of the structure assistant and the volume of water in the step (1) is (5-8) g:(4-10) g:(80-100) mL.

[0012] Preferably, the heat treatment in the step (1) is to first heat up to 45-60 °C and heat for 2-4 h, and then heat up to 90-100 °C and heat for 0.5-1 h.

[0013] Preferably, the Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O in the ethylene glycol solution of Cu(NO 3 ) 2· 3H 2 The mass of O, Zn(NO 3 ) 2 · 6H 2 The ratio of the mass of O and the volume of ethylene glycol is (50 - 80) g : (15 - 30) g : 100 mL.

[0014] Preferably, the aging time in step (3) is 5 - 20 days.

[0015] Preferably, the volume ratio of the water in step (1) to the liquid paraffin in step (3) is (80 - 100) : (200 - 400).

[0016] Preferably, the temperature of the heat treatment in step (3) is 300 - 400 °C, the time of the heat treatment is 6 - 10 h, and the atmosphere of the heat treatment is an inert atmosphere.

[0017] The present invention provides a lower alcohol catalyst prepared by the preparation method described in the above technical solution.

[0018] Preferably, in the lower alcohol catalyst, the Cu crystal grain size < 35 nm, the specific surface area of the lower alcohol catalyst is 60 - 70 m 2 / g, the pore volume of the lower alcohol catalyst is 0.20 - 0.25 cm 3 / g, and the pore diameter of the lower alcohol catalyst is 14 - 16 nm.

[0019] The present invention provides the application of the lower alcohol catalyst prepared by the preparation method described in the above technical solution or the lower alcohol catalyst described in the above technical solution in the synthesis of lower alcohols from syngas.

[0020] The present invention provides a preparation method of a lower alcohol catalyst, comprising the following steps: (1) Mixing citric acid, a structure assistant and water, and performing a heat treatment to obtain a mixed solution; the structure assistant is Al(NO 3 ) 3 · 9H 2 O or Ga(NO 3 ) 3 · xH 2 O; (2) Adding an ethylene glycol solution of Cu(NO 3 ) 2 · 3H 2 O and Zn(NO 3 ) 2 · 6H 2 O to the mixed solution obtained in step (1) to obtain a green sol; (3) Aging the green sol obtained in step (2), then adding liquid paraffin, and finally performing a heat treatment to obtain a lower alcohol catalyst. The present invention prepares a CuZnM catalyst by adopting a complete liquid phase method, and adds Al(NO3 ) 3 ·9H 2 O or Ga(NO 3 ) 3 ·xH 2 O can act as a structural promoter, increasing the content of oxygen vacancies in the CuZn catalyst, thereby improving the selectivity of the catalyst for lower alcohols, and further achieving a good catalytic effect for synthesizing lower alcohols from syngas, realizing the highly selective synthesis of lower alcohols. In the process of preparing the CuZnM catalyst in liquid phase in the present invention, liquid paraffin is added and then heat treatment is carried out to obtain a slurry catalyst. In the present invention, liquid paraffin serves as a medium, which helps to form the catalyst in liquid phase. This preparation method realizes the direct conversion from solution to slurry, avoiding the problem of catalyst deactivation existing when a solid powder catalyst is dispersed in an inert reaction medium for slurry bed reaction. The Cu particles in the lower alcohol catalyst obtained in the present invention are all relatively smooth spherical and the Cu crystal grain size reaches the nanoscale. This catalyst has the characteristics of large specific surface area, large pore volume and large pore diameter, making the lower alcohol catalyst have high catalytic activity. The results of the examples show that the catalyst prepared by the preparation method provided in the present invention shows a high CO conversion rate of 17.22%, and at the same time, the proportions of ethanol and lower alcohols reach 60.22% and 71.90% respectively, which are significantly higher than those of the CuZn catalyst, indicating that the preparation method of the present invention improves the catalytic activity of the catalyst and the selectivity for lower alcohols. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 TEM diagram of the catalyst provided in Example 1 of the present invention;

[0022] Figure 2 TEM diagram of the catalyst provided in Example 2 of the present invention;

[0023] Figure 3 TEM diagram of the catalyst provided in Comparative Example 1 of the present invention;

[0024] Figure 4 TEM diagram of the catalyst provided in Comparative Example 2 of the present invention;

[0025] Figure 5 XRD diagrams of the catalysts obtained in Examples 1-2 and Comparative Examples 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention provides a preparation method for a lower alcohol catalyst, comprising the following steps:

[0027] (1) Mix citric acid, a structural promoter and water and carry out heat treatment to obtain a mixed solution; the structural promoter is Al(NO 3 ) 3 ·9H2 O or Ga(NO 3 ) 3 ·xH 2 O;

[0028] (2) Add a glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O to the mixed solution obtained in the above step (1) to obtain a green sol;

[0029] (3) Age the green sol obtained in the above step (2), then add liquid paraffin, and finally perform heat treatment to obtain a lower alcohol catalyst.

[0030] In the present invention, there is no special limitation on the specific source of the raw materials, and commercially available products well-known to those skilled in the art can be used.

[0031] In the present invention, citric acid, a structure promoter, and water are mixed and subjected to heat treatment to obtain a mixed solution.

[0032] In the present invention, the structure promoter is Al(NO 3 ) 3 ·9H 2 O or Ga(NO 3 ) 3 ·xH 2 O. By adding the structure promoter in the present invention, the oxygen defect structure of ZnO can be modified, so that the catalyst has high selectivity for lower alcohols, and further increases the proportion of lower alcohols in the total alcohols.

[0033] In the present invention, the water is preferably deionized water. Using deionized water in the present invention can reduce the content of impurities.

[0034] In the present invention, the mass ratio of citric acid, the mass of the structure promoter, and the volume of water is preferably (5 - 8) g:(4 - 10) g:(80 - 100) mL, more preferably (6 - 7) g:(5.5 - 9.5) g:(90 - 100) mL.

[0035] In the present invention, the heat treatment is preferably carried out by first heating to 45 - 60°C for 2 - 4 h, and then heating to 90 - 100°C for 0.5 - 1 h. More preferably, it is first heated to 50°C for 3 h, and then heated to 95°C for 0.5 h. The heat treatment is preferably carried out under stirring conditions. The present invention has no special limitation on the heating rate, and any heating method well-known to those skilled in the art can be used to make the temperature meet the requirements. The present invention has no special limitation on the stirring rate, which is determined according to the common technical knowledge of those skilled in the art as long as it can prevent the solution from splashing. By carrying out the heat treatment, the structural aid can undergo a hydrolysis reaction to generate a citric acid gel containing Al or Ga.

[0036] After obtaining the mixed solution, the present invention adds an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O to the mixed solution to obtain a green sol.

[0037] In the present invention, the temperature of the mixed solution is preferably 85 - 95°C, more preferably 95°C. When the temperature of the mixed solution does not meet the above requirements in the present invention, the present invention preferably heats the mixed solution. In the present invention, the heating method is preferably water bath heating. By controlling the temperature of the mixed solution and adding an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O, a reduction reaction can occur along with the decomposition reaction of nitric acid, and at the same time, the higher temperature can evaporate the solvent, thereby concentrating the solution to form a gel.

[0038] In the present invention, the container for holding the mixed solution is preferably a beaker, more preferably a 500 mL beaker. By using a beaker to hold the mixed solution, it is convenient for the evaporation of the solvent during the subsequent reaction.

[0039] In the present invention, the mass of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O in the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2·6H 2 The mass ratio of O to the volume of ethylene glycol is preferably (50 - 80) g : (15 - 30) g : 100 mL, and more preferably (60 - 70) g : (20 - 25) g : 100 mL.

[0040] In the present invention, the volume ratio of the ethylene glycol solution of the water and Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O is preferably (80 - 100) : (90 - 110), and more preferably 90 : 100.

[0041] In the present invention, the addition method of the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O is preferably by dropping. In the present invention, the dropping rate is preferably 2.5 - 3.5 mL / min, and more preferably 3 mL / min. By dropping the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O, it is beneficial to the full progress of the reaction.

[0042] In the present invention, the addition of the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O is preferably carried out under stirring conditions. The present invention has no special limitation on the stirring rate, which is determined according to the common technical knowledge of those skilled in the art and can avoid splashing of the solution. By adding the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O under stirring conditions, it can make each component fully contact, thus being beneficial to the progress of the reaction.

[0043] The present invention preferably adds Cu(NO 3 ) 2 ·3H2 O and Zn(NO 3 ) 2 ·6H 2 O's ethylene glycol solution and then continue stirring. The present invention has no special limitation on the rate of the stirring, which is determined according to the common technical knowledge of those skilled in the art and can avoid splashing of the solution. The present invention has no special limitation on the time of the stirring, which is determined according to the common technical knowledge of those skilled in the art, and the stirring can be stopped when the color of the mixed solution changes from blue to dark green.

[0044] The present invention preferably cools the green sol to room temperature. The present invention has no special limitation on the cooling method, and natural cooling is sufficient.

[0045] After obtaining the green sol, the present invention ages the green sol, then adds liquid paraffin, and finally conducts heat treatment to obtain a lower alcohol catalyst.

[0046] In the present invention, the aging time is preferably 5 to 20 days, more preferably 10 to 15 days. The purpose of the aging treatment in the present invention is to form a stable three-dimensional framework structure through further polymerization, making the three components of Cu, Zn, and the structural assistant evenly mixed.

[0047] In the present invention, the volume ratio of water to liquid paraffin is preferably (80 - 100):(200 - 400). By adding liquid paraffin to the catalyst precursor obtained by aging and conducting heat treatment in the present invention, a slurry catalyst is obtained. In the present invention, liquid paraffin serves as a medium, which helps to form a catalyst in the liquid phase. This preparation method realizes the direct conversion from a solution to a slurry, avoiding the problem of catalyst deactivation existing when a solid powder catalyst is dispersed in an inert reaction medium for a slurry bed reaction.

[0048] As an implementation mode of the present invention, the volume ratio of water to liquid paraffin can be 90:200, 90:250, 90:300, 90:350, or 90:400.

[0049] In the present invention, the heat treatment temperature is preferably 300 - 400 °C; the heat treatment time is preferably 6 - 10 h; the heat treatment atmosphere is preferably an inert atmosphere, more preferably a nitrogen atmosphere. In the present invention, the flow rate of the nitrogen atmosphere is preferably 40 - 60 mL / min, more preferably 50 mL / min. By controlling the heat treatment temperature in the present invention, the catalytic activity of the catalyst can be further improved; by conducting heat treatment in a nitrogen atmosphere, the active components in the catalyst can be prevented from reacting with oxygen in the air.

[0050] As an embodiment of the present invention, the temperature of the heat treatment can be 300°C, 320°C, 340°C, 360°C, 380°C or 400°C; the time of the heat treatment can be 6 h, 7 h, 8 h, 9 h or 10 h.

[0051] In the present invention, the Cu crystal grain size in the lower alcohol catalyst is < 35 nm; the specific surface area of the lower alcohol catalyst is preferably 60 - 70 m 2 / g; the pore volume of the lower alcohol catalyst is preferably 0.20 - 0.25 cm 3 / g; the pore diameter of the lower alcohol catalyst is preferably 14 - 16 nm. In the present invention, the Cu particles in the lower alcohol catalyst preferably exhibit relatively smooth spherical shapes. The Cu crystal grain size in the lower alcohol catalyst prepared by the present invention is small, the pore volume and pore diameter of the lower alcohol catalyst are large, and it is a relatively smooth sphere, so that the lower alcohol catalyst has good catalytic activity.

[0052] The present invention prepares the CuZnM catalyst by adopting the complete liquid phase method. During the preparation process, adding Al(NO 3 ) 3 ·9H 2 O or Ga(NO 3 ) 3 ·xH 2 O can play the role of a structure promoter, increase the content of oxygen vacancies in the CuZn catalyst, thereby improving the selectivity of the catalyst for lower alcohols, and further achieving a good catalytic effect for synthesizing lower alcohols from syngas, and realizing the high-selectivity synthesis of lower alcohols. In the process of preparing the CuZnM catalyst in the liquid phase in the present invention, heat treatment is carried out after adding liquid paraffin, thereby obtaining a slurry catalyst. In the present invention, liquid paraffin is used as a medium, which helps to form the catalyst in the liquid phase. This preparation method realizes the direct conversion from solution to slurry, and avoids the problem of catalyst deactivation existing when a solid powder catalyst is dispersed in an inert reaction medium for a slurry bed reaction. The Cu particles in the lower alcohol catalyst obtained by the present invention all exhibit relatively smooth spherical shapes and the Cu crystal grain size reaches the nanometer level. This catalyst has the characteristics of a large specific surface area, a large pore volume and a large pore diameter, making the lower alcohol catalyst have high catalytic activity.

[0053] The present invention also provides a lower alcohol catalyst prepared by the preparation method described in the above technical solution.

[0054] In the present invention, the chemical composition of the lower alcohol catalyst preferably includes Cu, Zn and M; M is preferably Al or Ga.

[0055] In the present invention, based on the total mass of Cu, Zn and M being 100%, the low-carbon alcohol catalyst preferably comprises: Cu: 73.35 - 81.00%, Zn: 14.12 - 21.10% and M: 4.50 - 6.10%.

[0056] Based on the total mass of Cu, Zn and M being 100%, the low-carbon alcohol catalyst provided by the present invention preferably comprises Cu: 73.35 - 81.00%, more preferably 75.00 - 80.00%. In the present invention, Cu is the active component for providing active sites.

[0057] Based on the total mass of Cu, Zn and M being 100%, the low-carbon alcohol catalyst provided by the present invention preferably comprises Zn: 14.12 - 21.10%, more preferably 15.00 - 20.00%. In the present invention, Zn acts as an active component and can form an oxygen defect structure (i.e., oxygen vacancy) of ZnO. During the preparation of low-carbon alcohols, this structure enables the dissociation of adsorbed water on the oxygen vacancy to form OH*, and then OH* interacts with the activated CO* to form a surface CH x O* intermediate. Finally, at the Zn δ+ defect site, the CH x O* / CO* species couples with the surface CH x * to achieve carbon chain growth; meanwhile, the oxygen vacancy promotes the transfer of electrons from ZnO to the Cu surface, generating more Zn δ+ defects and regulating the Cu 0 / (Cu 0 +Cu + ) ratio. The electron-rich Cu species is beneficial to the dissociation and adsorption of CO, which promotes the formation of the important surface intermediate CH x * required for the production of low-carbon alcohols.

[0058] Based on the total mass of Cu, Zn and M being 100%, the low-carbon alcohol catalyst provided by the present invention preferably comprises M: 4.50 - 6.10%. In the present invention, the M is preferably Al or Ga, more preferably Ga. In the present invention, Al or Ga can act as a structure promoter, increasing the content of oxygen vacancies in the CuZn catalyst, thereby improving the selectivity of the catalyst for low-carbon alcohols and further achieving a good catalytic effect for synthesizing low-carbon alcohols from syngas.

[0059] By introducing Al or Ga into the catalyst in the present invention, it can act as a structure promoter, increasing the content of oxygen vacancies in the CuZn catalyst, thereby improving the selectivity of the catalyst for low-carbon alcohols and further achieving a good catalytic effect for synthesizing low-carbon alcohols from syngas.

[0060] In the present invention, the Cu crystal grain size in the low-carbon alcohol catalyst < 35 nm; the specific surface area of the low-carbon alcohol catalyst is preferably 60 - 70 m2 / g; The pore volume of the lower alcohol catalyst is preferably 0.20 - 0.25 cm 3 / g; The pore diameter of the lower alcohol catalyst is preferably 14 - 16 nm. In the present invention, the Cu particles in the lower alcohol catalyst preferably exhibit relatively smooth spherical shapes. The Cu crystal grains in the lower alcohol catalyst provided by the present invention are small, the pore volume and pore diameter of the lower alcohol catalyst are large, and they are relatively smooth spheres, so that the lower alcohol catalyst has good catalytic activity.

[0061] The present invention also provides the use of the lower alcohol catalyst prepared by the preparation method described in the above technical solution or the lower alcohol catalyst described in the above technical solution in the synthesis of lower alcohols from syngas. The present invention has no special limitation on the specific manner of the use, which is determined according to the common technical knowledge of those skilled in the art, as long as the synthesis of lower alcohols from syngas can be achieved.

[0062] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the examples in the present invention. Obviously, the described examples are only a part of the examples of the present invention, rather than all the examples. All other examples obtained by those of ordinary skill in the art based on the examples in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0063] Example 1

[0064] A preparation method of a lower alcohol catalyst is as follows:

[0065] (1) Dissolve citric acid and a structure assistant in 90 mL of water, and then perform heat treatment to obtain a mixed solution; the structure assistant is Al(NO 3 ) 3 ·9H 2 O, and the water is deionized water; the mass ratio of citric acid, the mass of the structure assistant, and the volume of water is 6.41 g: 8.63 g: 90 mL; the heat treatment is to first heat up to 50 °C and heat for 3 h, and then heat up to 95 °C and heat for 0.5 h, and the heat treatment is carried out under stirring conditions;

[0066] (2) Control the temperature of the mixed solution obtained in step (1) at 95 °C, and then dropwise add 100 mL of an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O at a dropping rate of 3 mL / min, continuously stir until the mixed solution turns dark green and then stop stirring, and stop heating and cool to room temperature after a dark green sol is formed; the Cu(NO 3 ) 2·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O in an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2 ·6H 2 O and the volume of ethylene glycol are in the ratio of 69.58 g: 21.42 g: 100 mL;

[0067] (3) The green sol obtained in step (2) is aged for 10 days, then 300 mL of liquid paraffin is added, and finally heat-treated at 300 °C for 8 h in a nitrogen atmosphere with a flow rate of 50 mL / min to obtain a lower alcohol catalyst, denoted as CZA, where A represents Al.

[0068] Example 2

[0069] A method for preparing a lower alcohol catalyst is as follows:

[0070] (1) Citric acid and a structural promoter are dissolved in 90 mL of water, and then heat-treated to obtain a mixed solution; the structural promoter is Ga(NO 3 ) 3 ·xH 2 O, and the water is deionized water; the mass of citric acid, the mass of the structural promoter and the volume of water are in the ratio of 6.41 g: 5.88 g: 90 mL; the heat treatment is to first heat to 50 °C for 3 h, and then heat to 95 °C for 0.5 h, and the heat treatment is carried out under stirring conditions;

[0071] (2) The temperature of the mixed solution obtained in step (1) is controlled at 95 °C, and then an ethylene glycol solution of 100 mL of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O is added dropwise at a rate of 3 mL / min, and stirring is continued until the mixed solution turns dark green, then stirring is stopped. After a dark green sol is formed, heating is stopped and cooled to room temperature; the Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O in the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2The mass of O, Zn(NO 3 ) 2 ·6H 2 O, the mass of ethylene glycol and the volume ratio is 69.58 g: 21.42 g: 100 mL;

[0072] (3) Aging the green sol obtained in step (2) for 10 days, then adding 300 mL of liquid paraffin, and finally heat-treating at 300 °C for 8 h in a nitrogen atmosphere with a flow rate of 50 mL / min to obtain a lower alcohol catalyst, denoted as CZG, where G represents Ga.

[0073] Comparative Example 1

[0074] The preparation method of the lower alcohol catalyst is as follows:

[0075] (1) Dissolve citric acid in 90 mL of deionized water, and then perform heat treatment to obtain a mixed solution; the mass ratio of citric acid to the volume of deionized water is 6.41 g: 90 mL; the heat treatment is to first heat to 50 °C for 3 h, and then heat to 95 °C for 0.5 h, and the heat treatment is carried out under stirring conditions;

[0076] (2) Control the temperature of the mixed solution obtained in step (1) at 95 °C, and then add 100 mL of an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O dropwise at a rate of 3 mL / min, and continue stirring until the mixed solution turns dark green, then stop stirring. After the dark green sol is formed, stop heating and cool to room temperature; the mass of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2 ·6H 2 O in the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2 ·6H 2 O and the volume ratio of ethylene glycol is 69.58 g: 21.42 g: 100 mL;

[0077] (3) Aging the green sol obtained in step (2) for 10 days, then adding 300 mL of liquid paraffin, and finally heat-treating at 300 °C for 8 h in a nitrogen atmosphere with a flow rate of 50 mL / min to obtain a lower alcohol catalyst, denoted as CZ (i.e., CuZn).

[0078] Comparative Example 2

[0079] The preparation method of the lower alcohol catalyst is as follows:

[0080] (1) Dissolve citric acid and Cr(NO 3 ) 3 ·9H 2 O in 90 mL of deionized water, and then perform heat treatment to obtain a mixed solution; the mass ratio of citric acid, Cr(NO 3 ) 3 ·9H 2 O and the volume ratio of water is 6.41 g: 9.20 g: 90 mL; the heat treatment is to first raise the temperature to 50 °C and heat for 3 h, then raise the temperature to 95 °C and heat for 0.5 h, and the heat treatment is carried out under stirring conditions;

[0081] (2) Control the temperature of the mixed solution obtained in step (1) at 95 °C, and then dropwise add 100 mL of an ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O and Zn(NO 3 ) 2 ·6H 2 O at a dropping rate of 3 mL / min, and continuously stir until the mixed solution turns dark green and then stop stirring. Stop heating and cool to room temperature after the dark green sol is formed; the mass of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2 ·6H 2 O in the ethylene glycol solution of Cu(NO 3 ) 2 ·3H 2 O, the mass of Zn(NO 3 ) 2 ·6H 2 O and the volume ratio of ethylene glycol is 69.58 g: 21.42 g: 100 mL;

[0082] (3) Age the green sol obtained in step (2) for 10 days, then add 300 mL of liquid paraffin, and finally perform heat treatment at 300 °C for 8 h in a nitrogen atmosphere with a flow rate of 50 mL / min to obtain a lower alcohol catalyst, denoted as CZC, where C represents Cr.

[0083] Use a transmission electron microscope to characterize the catalysts obtained in Examples 1-2 and Comparative Examples 1-2 in sequence, and the obtained TEM images are as shown in Figures 1 to 4 shown. From Figures 1 to 4It can be seen that the Cu particles in the catalyst prepared by the preparation method provided by the present invention all exhibit relatively smooth spherical shapes.

[0084] The catalysts obtained in Examples 1-2 and Comparative Examples 1-2 were successively tested using an X-ray diffractometer, and the obtained XRD patterns are as Figure 5 shown. From Figure 5 it can be seen that all the catalysts contain Cu species and free carbon species.

[0085] The physical and chemical properties of the catalysts obtained in Examples 1-2 and Comparative Examples 1-2 were analyzed. The Cu crystal grain size was calculated using the Scherrer formula, and the specific surface area, pore volume, and average pore diameter of the catalysts were measured using a QDS-30 physical adsorption analyzer manufactured by Quantachrome Corporation of the United States. The obtained results are shown in Table 1:

[0086] Table 1 Physical and chemical properties of the catalysts obtained in Examples 1-2 and Comparative Examples 1-2

[0087] catalyst <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore diameter (nm) Cu crystal grain size (nm) Comparative Example 1 45.74 0.18 11.32 30.5 Comparative Example 2 62.38 0.22 14.00 29.8 Example 1 64.21 0.21 14.53 32.6 Example 2 64.35 0.24 15.16 26.5

[0088] As can be seen from Table 1, for the catalysts prepared in Examples 1-2 of the present invention, after adding the structural promoter, compared with Comparative Examples 1-2, the specific surface area and average pore diameter of the catalysts have both increased. Among them, when the structural promoter is Ga(NO 3 ) 3 ·xH 2 O, the improvement amplitude is the largest, and the Cu crystal grain size has also decreased significantly.

[0089] Application Example

[0090] A slurry bed reactor was used to evaluate the catalysts prepared in Examples 1-2 and Comparative Examples 1-2. The specific operation was as follows: The catalyst was placed in the reaction kettle of the slurry bed reactor, and then the reaction kettle was slowly pressurized to 4.0 MPa using a mixed gas of H 2 and CO. In the mixed gas, the molar ratio of H 2 and CO was 2, and the total gas flow was controlled at 150 mL / min by a mass flowmeter. Subsequently, the reaction temperature was raised to 280 °C under stirring conditions for reaction. After steady-state operation for 24 h, data was collected. The generated tail gas was divided into gas phase and liquid phase by a condenser. Among them, the gas-phase product was analyzed online by GC-950 and then discharged into a wet gas flowmeter, and the liquid-phase product was collected every 24 h and analyzed by off-line manual injection. The CO conversion rate, product selectivity, and alcohol distribution of the catalyst are shown in Table 2:

[0091] Table 2 CO conversion rate, product selectivity, and alcohol distribution of the catalysts in Examples 1-2 and Comparative Examples 1-2

[0092]

[0093] In the selectivity of Table 2, S(DME) is the selectivity of the catalyst to dimethyl ether; S(CO 2 ) is the selectivity of the catalyst to carbon dioxide; S(CH x ) is the selectivity of the catalyst to hydrocarbons; S(ROH) is the selectivity of the catalyst to total alcohols (i.e., the alcohol mixture of C 1 ~C 5 );

[0094] S(ROH) = S(C 1 ) + S(C 2 ) + S(C 3 ) + S(C 4 ) + S(C 5 );

[0095] S(C 1 ) is the selectivity of the catalyst to methanol, S(C 2 ) is the selectivity of the catalyst to ethanol, S(C 3 ) is the selectivity of the catalyst to propanol, S(C 4 ) is the selectivity of the catalyst to butanol, S(C 5 ) is the selectivity of the catalyst to pentanol;

[0096] S(C 1 ) = (the concentration of methanol in the normalized gas-phase product × the total amount of substances in the tail gas under standard conditions + the amount of substance of methanol in the liquid-phase product) / the total amount of carbon elements in the product;

[0097] S(C 2 ) = (the concentration of ethanol in the normalized gas-phase product × the total amount of substances in the tail gas under standard conditions × 2 + 2 × the amount of substance of ethanol in the liquid-phase product) / the total amount of carbon elements in the product;

[0098] S(C 3 ) = (3 × the amount of substance of propanol in the liquid-phase product) / the total amount of carbon elements in the product;

[0099] S(C 4 ) = (4 × the amount of substance of butanol in the liquid-phase product) / the total amount of carbon elements in the product;

[0100] S(C 5 ) = (5 × the amount of substance of pentanol in the liquid-phase product) / the total amount of carbon elements in the product;

[0101] In the alcohol distribution of Table 2, C 1 is the proportion of methanol in the total alcohols; C 2 is the proportion of ethanol in the total alcohols; C 3is the proportion of propanol in the total alcohol; C 4 is the proportion of butanol in the total alcohol; C 5 is the proportion of pentanol in the total alcohol; C 2+ OH / ROH is the proportion of the alcohol mixture of C 2 ~C 5 in the total alcohol, C 2+ OH is the alcohol mixture of C 2 ~C 5 ;

[0102] C 1 = the amount of carbon element in methanol / the amount of carbon element in the liquid-phase product;

[0103] The amount of carbon element in methanol = the liquid-phase mass × the mass percentage of methanol / the relative molecular mass of methanol;

[0104] C 2 = the amount of carbon element in ethanol / the amount of carbon element in the liquid-phase product;

[0105] The amount of carbon element in ethanol = the liquid-phase mass × the mass percentage of ethanol × 2 / the relative molecular mass of ethanol;

[0106] C 3 = the amount of carbon element in propanol / the amount of carbon element in the liquid-phase product;

[0107] The amount of carbon element in propanol = the liquid-phase mass × the mass percentage of propanol × 3 / the relative molecular mass of propanol;

[0108] C 4 = the amount of carbon element in butanol / the amount of carbon element in the liquid-phase product;

[0109] The amount of carbon element in butanol = the liquid-phase mass × the mass percentage of butanol × 4 / the relative molecular mass of butanol;

[0110] C 5 = the amount of carbon element in pentanol / the amount of carbon element in the liquid-phase product;

[0111] The amount of carbon element in pentanol = the liquid-phase mass × the mass percentage of pentanol × 5 / the relative molecular mass of pentanol;

[0112] The amount of carbon element in the liquid-phase product = the amount of carbon element in methanol + the amount of carbon element in ethanol + the amount of carbon element in propanol + the amount of carbon element in butanol + the amount of carbon element in pentanol;

[0113] C 2+ OH / ROH = (S(C 2 ) + S(C3 ) + S(C 4 ) + S(C 5 )) / S(ROH).

[0114] As can be seen from Table 2, for the catalyst prepared in Comparative Example 1, the CH x selectivity was 14.25%, the CO 2 selectivity was 74.56%, the ROH selectivity was 10.56%, and the C 2+ OH / ROH was 59.95%; after adding Cr, the catalytic activity of the catalyst prepared in Comparative Example 2 was inhibited, and the CH x selectivity decreased to 8.45%, the CO 2 selectivity increased to 76.75%, the ROH selectivity was 11.60%, and the C 2+ OH / ROH decreased to 49.55%; after adding Al, the catalytic performance of the catalyst prepared in Example 1 was significantly enhanced, manifested as higher selectivities of CH x and ROH and lower selectivity of CO 2 , which were 14.59% (CH x ), 20.06% (ROH), and 60.45% (CO 2 ) in sequence. At the same time, the C 2+ OH / ROH increased to 65.43%; after adding Ga, the catalytic performance of the catalyst prepared in Example 2 was also significantly enhanced, manifested as the CO conversion reaching the maximum (17.22%), which was related to the surface area of Cu, while the CH x selectivity was 14.92%, the ROH selectivity was 8.37%, the CO 2 selectivity was 76.70%, and the C 2+ OH / ROH increased significantly to 71.90%, indicating that doping with Ga was helpful for the formation of lower alcohols; through the comparison of Examples 1 - 2 and Comparative Example 2, it shows that not any metal element can improve the selectivity of the catalyst for lower alcohols, and a suitable structural promoter needs to be selected.

[0115] From the perspective of the alcohol distribution of the catalyst, compared with the catalyst in Comparative Example 1, the proportion of methanol in the catalyst of Comparative Example 2 increased, reaching 41.73%, and the C 2+ OH / ROH decreased, only being 49.55%. While for the catalysts in Examples 1 and 2, the C 2+ OH / ROH was significantly increased. Among them, the catalyst in Example 2 showed the best catalytic performance, and the ethanol and C 2+ OH / ROH reached 60.22% and 71.90% respectively, indicating that the catalyst provided by the present invention has better application prospects in the catalytic synthesis of syngas to lower alcohols.

[0116] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a low-carbon alcohol catalyst comprises the following steps: (1) mixing citric acid, a structural aid and water and heating them to obtain a mixed solution; the structural aid is Al(NO3)3·9H2O or Ga(NO3)3·xH2O; (2) adding ethylene glycol solutions of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O to the mixed solution obtained in step (1) to obtain a green sol; (3) The green sol obtained in step (2) is aged, liquid paraffin is added, and finally heat-treated to obtain a low-carbon alcohol catalyst.

2. The preparation method according to claim 1, characterized in that: In the step (1), the ratio of the mass of citric acid, the mass of the structural auxiliary agent and the volume of water is (5-8) g: (4-10) g: (80-100) mL.

3. The preparation method according to claim 1, characterized in that: The heating treatment in step (1) is firstly heating to 45-60°C for 2-4h, and then heating to 90-100°C for 0.5-1h.

4. The preparation method according to claim 1, characterized in that: In the step (2), the ratio of the mass of Cu(NO3)2·3H2O, the mass of Zn(NO3)2·6H2O and the volume of ethylene glycol in the ethylene glycol solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O is (50-80) g: (15-30) g: 100 mL.

5. The preparation method according to claim 1, characterized in that: The aging time in step (3) is 5 to 20 days.

6. The preparation method according to claim 1, characterized in that: The volume ratio of water in step (1) to liquid paraffin in step (3) is (80-100):(200-400).

7. The preparation method according to claim 1, characterized in that: The heat treatment temperature in step (3) is 300-400° C., the heat treatment time is 6-10 hours, and the heat treatment atmosphere is an inert atmosphere.

8. The low-carbon alcohol catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The low-carbon alcohol catalyst according to claim 8, characterized in that The Cu crystal size in the low-carbon alcohol catalyst is less than 35 nm, and the specific surface area of ​​the low-carbon alcohol catalyst is 60 to 70 m 2 / g, the pore volume of the low-carbon alcohol catalyst is 0.20~0.25cm 3 / g, the pore size of the low-carbon alcohol catalyst is 14-16nm.

10. Use of the low-carbon alcohol catalyst prepared by the preparation method according to any one of claims 1 to 7 or the low-carbon alcohol catalyst according to any one of claims 8 to 9 in synthesizing low-carbon alcohols from synthesis gas.

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