CN105582957B - Cobalt-based Fischer-Tropsch synthesis catalyst loaded on spherical carrier and preparation method thereof - Google Patents
Cobalt-based Fischer-Tropsch synthesis catalyst loaded on spherical carrier and preparation method thereof Download PDFInfo
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Abstract
A cobalt based fischer-tropsch synthesis catalyst supported on a spherical carrier, the catalyst comprising 1 to 50 wt% cobalt oxide, 50 to 99 wt% mixed oxide spherical carrier particles having a particle size of 10 to 100 microns, and less than 0.1 wt% of a noble metal selected from Pd, Pt, Au, Ag, Rh, Ru or a combination thereof; the mixed oxide spherical carrier particles are composed of microspheres and an auxiliary agent, wherein the microspheres are composed of the following materials: silica, alumina, zirconia, or mixtures thereof; the auxiliary is an oxide of an element selected from the group consisting of: ni, Ca, Mg, La, Zr, Ce, Ti, Mn, V, Nb, or combinations thereof. The invention also provides a method for preparing the catalyst.
Description
Technical Field
The invention relates to the field of catalytic synthesis, and particularly provides a supported cobalt-based catalyst suitable for Fischer-Tropsch synthesis reaction and a preparation method thereof.
Background
Fischer-Tropsch (F-T) Synthesis of Synthesis gas (CO + H)2) The hydrocarbon products including gasoline, diesel oil, wax, naphtha and low-carbon olefin, and the byproducts of carbon dioxide, water and oxygen-containing organic compounds are mainly generated in the process of generating the hydrocarbon under the action of the catalyst. Fischer-tropsch synthesis is widely used to convert coal, natural gas or biomass first into synthesis gas and then into liquid fuels. The catalysts mainly used for the Fischer-Tropsch synthesis include iron-based catalysts and cobalt-based catalysts. Compared with iron-based catalysts, cobalt-based catalysts are one of the most industrially applicable catalysts due to their characteristics of high activity, low water gas shift reaction, long service life, suitability for natural gas-based synthesis gas with high hydrogen-carbon ratio, and the like. The slurry bed reactor is also the most promising process for replacing the traditional F-T synthesis technology due to the advantages of good heat conductivity, smaller pressure drop, high target hydrocarbon selectivity, capability of replacing the catalyst on line, easiness in realizing large-scale production and the like, and is also the development direction for synthesizing liquid fuel. The slurry bed reactor is a gas-liquid-solid three-phase reactorIn the process, the catalyst particles are subjected to reaction environments such as fluctuation in reaction temperature, severe collision between catalyst particles, and between the catalyst and the reactor wall. The cobalt-based catalyst used for the slurry bed system not only needs to have high specific surface area, uniform particle size distribution and regular spherical morphology, but also needs to have proper density and strong wear resistance so as to adapt to a harsher operating environment in the slurry bed reactor, so that the catalyst keeps ideal catalytic activity and product selectivity to produce high value-added chemicals and reduce subsequent processing cost. Meanwhile, the catalyst also needs to keep a relatively stable particle shape, and the mechanical strength and the abrasion resistance of the cobalt-based catalyst particles are improved, so that the cobalt-based catalyst particles can be effectively separated from heavy wax generated in the F-T synthesis process, and the service life of the cobalt-based catalyst is prolonged. With the development and popularization of the application of the cobalt-based slurry bed F-T synthesis process, people put higher requirements on the research and development of a cobalt-based catalyst.
Co/ZrO2The catalyst is a catalyst which is widely and deeply researched at present. Although Co/ZrO2The catalyst shows high activity and low CH in the fixed bed F-T synthesis4Selectivity and long run life, but for the preparation of Co/ZrO for slurry beds using precipitation and spray drying processes2In the case of the catalyst, the catalyst prepared by the method has poor formability, the obtained particles have rough surfaces, uneven particle sizes and low yield, and are easy to pulverize in the F-T synthesis process of a slurry bed with high temperature, high pressure and water vapor, which can cause difficulty in subsequent oil-wax separation. In addition, the pulverized fine particles are easy to block a gas distributor to cause uneven diffusion of the synthesis gas, and the loss rate of the catalyst is high. In order to improve the abrasion resistance of the cobalt-based catalyst in a slurry bed, some structural auxiliary agents, such as Al, are often added into the cobalt-based catalyst in the preparation process of the catalyst2O3And (3) a carrier. However, since Co-Al2O3Has strong interaction, and easily forms CoAl which is difficult to reduce and has no catalytic activity in the reaction process2O4The substances, in turn, reduce the catalytic activity to some extent, increase the methane selectivity and shorten the operating life of the catalyst, which are all phenomena known to researchers in the fieldWhich is undesirable.
Chinese patent applications CN1395992A and CN1583259A disclose preparation methods of iron-based catalysts for fischer-tropsch synthesis reaction, respectively, and the process concept thereof is to prepare suspension slurry of catalyst active components and promoter precursors in advance, then mix the slurry with silica solids or a solution system capable of forming silica, and then spray-dry the mixture, thereby synthesizing spherical iron-based catalysts. However, the catalyst synthesis methods disclosed in these two patents are also prone to strong carrier-active component interactions, and the carrier covers the active sites, which both result in a decrease in the catalytic activity of the catalyst. In addition, since iron-based is used as an active component, making it unsuitable for use in natural gas-based syngas, the reactivity and stability are inferior to those of cobalt-based catalysts. And SiO2The carrier is inferior to Al in mechanical strength and abrasion resistance2O3And (3) a carrier. Therefore, solving the problem of mechanical properties of the catalyst carrier is a key problem in slurry bed reactors, and the key is the catalyst carrier.
The invention aims to solve the problem of developing a supported cobalt-based catalyst suitable for Fischer-Tropsch synthesis reaction, wherein a carrier of the supported cobalt-based catalyst has excellent mechanical strength performance, does not have strong interaction with active catalytic components, does not cover a catalytic active center, is suitable for a slurry bed reactor, and has high activity, high target selectivity, high mechanical strength and wear resistance.
Disclosure of Invention
According to the invention, firstly, an auxiliary agent coating is coated on part or all of the surface of the microsphere to obtain mixed oxide spherical carrier particles, and then cobalt is combined on the mixed oxide spherical carrier particles, so that the cobalt-based catalyst with excellent catalytic performance and mechanical performance is prepared.
In a first aspect the present invention provides a cobalt-based catalyst for use in carrying out a fischer-tropsch synthesis reaction in a slurry bed reactor or stirred reactor, the catalyst comprising from 1 to 50 wt% cobalt oxide, from 50 to 99 wt% of mixed oxide spherical support particles having a particle size in the range 10 to 100 microns, preferably 50 to 100 microns, more preferably 50 to 80 microns, and less than 0.1 wt% of a noble metal selected from Pd, Pt, Au, Ag, Rh, Ru or a combination thereof, based on the total weight of the catalyst;
the mixed oxide spherical carrier particles consist of microspheres and an auxiliary agent, wherein the auxiliary agent accounts for 1-20 wt% of the total weight of the cobalt-based catalyst, and the microspheres are made of materials selected from the following materials: silica, alumina, zirconia, or mixtures thereof; the auxiliary is an oxide of an element selected from the group consisting of: ni, Ca, Mg, La, Zr, Ce, Ti, Mn, V, Nb, or combinations thereof;
with the proviso that when the microspheres comprise zirconia, the adjuvant does not comprise zirconium; the auxiliary agent simultaneously contains no more than 4 kinds of metal elements;
the cobalt-based catalyst optionally further comprises a transition metal oxide other than cobalt oxide supported on the mixed oxide spherical support particles, the species of the promoter transition metal oxide other than cobalt oxide being the same as the species of the oxide of the element contained in the promoter.
In a preferred embodiment of the invention, the auxiliary agent is in the form of a coating covering part or all of the surface of the microspheres, more preferably covering all of the surface of the microspheres.
In another preferred embodiment of the invention, the microspheres consist of alumina and the auxiliary agent is selected from the following materials: zirconia, nickel oxide, manganese oxide, or a combination thereof.
In another preferred embodiment of the present invention, the cobalt oxide is present in an amount of from 1 to 50 wt%, preferably from 15 to 35 wt%, based on the total weight of the catalyst; the content of the microspheres is 50-99 wt%, preferably 65-85 wt%; the content of the auxiliary agent is 1 to 20 weight percent, and preferably 2 to 10 weight percent.
In a second aspect, the present invention provides a process for the preparation of a cobalt-based catalyst according to the invention, said process comprising the steps of:
i) preparing an adjuvant precursor solution comprising the following elements: ni, Ca, Mg, La, Zr, Ce, Ti, Mn, V, Nb, or combinations thereof;
ii) mixing the aid precursor solution with microspheres to obtain coated microspheres under the condition of pH value increase;
iii) curing and roasting the coated microspheres to obtain the mixed oxide spherical carrier particles;
iv) preparing a precursor solution containing cobalt, and mixing the precursor solution containing cobalt with the mixed oxide spherical carrier particles prepared in the step iii) to obtain mixed oxide spherical carrier particles loaded with cobalt, or directly mixing the precursor containing cobalt with the mixed oxide spherical carrier particles prepared in the step iii) in a solid form to obtain mixed oxide spherical carrier particles loaded with cobalt;
v) then roasting, reducing and passivating the cobalt-loaded mixed oxide spherical carrier particles to obtain the cobalt-based catalyst.
With respect to the above process, in a preferred embodiment, the promoter precursor solution in step i) is a solution of a salt of the following elements in water, an alcohol or an organic acid: ni, Ca, Mg, La, Zr, Ce, Ti, Mn, V, Nb, or combinations thereof; the salts are preferably nitrates, hydrochlorides, sulfates, phosphates, carboxylates; more preferably, the salt is a nitrate, a hydrochloride, an acetate, or any mixture thereof.
In another preferred embodiment of the present invention, in said step ii), said condition of raising the pH value means raising the pH value to 8 to 11 by adding a base; in step iii), the coated microspheres are aged in water at 50-100 ℃ for 8-24 hours; the calcination is carried out at a temperature of 300-700 ℃ for 2-10 hours in an air atmosphere. Preferably, said steps ii) and iii) may be repeated from 1 to 4 times, thereby applying from 1 to 4 auxiliary layers on the microspheres.
In another preferred embodiment of the present invention, the precursor solution comprising cobalt of step iv) is a solution of a soluble salt of cobalt in water or alcohol; the soluble salt of cobalt is preferably cobalt acetate, cobalt nitrate, or a mixture thereof.
In another preferred embodiment of the present invention, said steps iv) and v) are carried out by: mixing the precursor solution containing cobalt or the precursor containing cobalt in a solid form with the mixed oxide spherical carrier particles prepared in step iii), and then drying in air, nitrogen or vacuum at a temperature of normal temperature to 200 ℃ to obtain mixed oxide spherical carrier particles loaded with cobalt; then roasting the mixed oxide spherical carrier particles loaded with cobalt in an air atmosphere at the temperature of 200-400 ℃; then reducing the mixture for 3 to 5 hours in a hydrogen atmosphere at the temperature of 200 ℃ to 500 ℃, wherein the pressure of the hydrogen is 0.1 to 2MPa, and the concentration of the hydrogen in the hydrogen atmosphere is 1 to 100 percent by volume; and then passivated at a temperature ranging from room temperature to 40 c for 10 minutes to 5 hours in nitrogen containing 1 vol% of oxygen, thereby preparing the cobalt-based catalyst.
In a third aspect the present invention provides a process for carrying out the fischer-tropsch reaction in a slurry bed reactor or stirred reactor, the process comprising the steps of: reacting carbon monoxide and hydrogen in the presence of a cobalt-based catalyst as claimed in any one of claims 1 to 5 to produce a hydrocarbon product, the reaction being carried out under the following reaction conditions: the reaction temperature is 180-270 ℃, the preferable temperature is 180-250 ℃, the reaction pressure is 0.5-5MPa, and the total gas space velocity is 1000-10000 h-1500-8000 hours-1The volume ratio of the carbon monoxide to the hydrogen is 1:1 to 1: 3.
In one embodiment of the invention, the catalyst is subjected to a reductive pre-treatment before the start of the fischer-tropsch reaction under the following conditions: the temperature is 200 ℃ and 500 ℃ and pure hydrogen or hydrogen containing 1% by volume of CO is used at a pressure of 0.1 to 2 MPa.
Drawings
FIG. 1 is an SEM photograph of a catalyst after undergoing a catalytic reaction according to an embodiment of the present invention;
fig. 2 is an SEM photograph of a catalyst of the prior art as a comparative example after a catalytic reaction was performed.
Detailed Description
The "ranges" disclosed herein are in the form of lower and upper limits. There may be one or more lower limits, and one or more upper limits, respectively. The given range is defined by the selection of a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this manner are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for particular parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.
In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers.
The term "two" as used herein means "at least two" if not otherwise specified.
In the present invention, all embodiments and preferred embodiments mentioned herein may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the steps mentioned herein may be performed sequentially or randomly, if not specifically stated, but preferably sequentially. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.
In the present invention, the term "comprising" as used herein means either an open type or a closed type unless otherwise specified. For example, the term "comprising" may mean that other components not listed may also be included, or that only listed components may be included.
The cobalt-based catalyst of the present invention comprises cobalt oxide supported on mixed oxide spherical support particles and may optionally further comprise less than 0.1 wt% of a noble metal selected from Pd, Pt, Au, Ag, Rh, Ru or combinations thereof. The cobalt oxide is present in an amount of 1 to 50 wt%, preferably 15 to 35 wt%, more preferably 20 to 30 wt%, based on the total weight of the cobalt-based catalyst. The content of the mixed oxide spherical support particles as a support is 50 to 99% by weight, preferably 65 to 85% by weight, more preferably 70 to 80% by weight, based on the total weight of the cobalt-based catalyst. The mixed oxide spherical carrier particles consist of an inner microsphere and an outer auxiliary agent layer, and the auxiliary agent layer covers part or all of the surface of the microsphere. The material used to construct the microspheres may be selected from silica, alumina, zirconia, or mixtures thereof. The auxiliary is an oxide of an element selected from the group consisting of: ni, Ca, Mg, La, Zr, Ce, Ti, Mn, V, Nb, or combinations thereof. The number of the metal elements contained in the auxiliary agent can be 1-4. In addition, it is clear that when the microspheres comprise zirconium oxide, the adjuvant should be free of zirconium. In a preferred embodiment of the invention, the cobalt-based catalyst is free of noble metals.
In a preferred embodiment of the invention, the microspheres consist of alumina and the auxiliary agent is zirconia. In another preferred embodiment of the present invention, the microspheres are composed of silica and the auxiliary agent is nickel oxide. In another preferred embodiment of the present invention, the microsphere is composed of alumina, the coating layer formed by the zirconia assistant completely covers the surface of the microsphere, and the oxides of Co and Mn are supported on the assistant coating layer.
In the process for preparing the cobalt-based catalyst of the present invention, the promoter precursor solution and the precursor solution comprising cobalt may be solutions of soluble salts of the corresponding metal elements in a suitable solvent. The salt may be a sulfate, nitrate, phosphate, hydrohalide, carboxylate, which may be, for example, a formate, acetate, propionate, acetylacetonate, benzoate, and the like. The solvent may be water, methanol, ethanol, diethyl ether, acetone, or a mixture thereof, as long as the corresponding salt has suitable solubility therein. The solutions can be prepared by dissolving the corresponding metal salts in a solvent, to facilitate the dissolution, the corresponding acids can be added. Alternatively, the solution of the metal salt may be prepared by dissolving the oxide of the corresponding metal in a solution of an acid. In a preferred embodiment of the invention, the total concentration of the one or more metal salts in the promoter precursor solution and the cobalt-comprising precursor solution is in the range of from 0.1 to 20% by weight.
The microspheres used in the present invention may be directly commercially available, for example, silica microspheres may be a product of Q10 available from FUJI, Japan, and alumina microspheres may be a product of SCCa available from SASOL, south Africa.
In the method, before or after the auxiliary agent precursor solution is mixed with the microspheres, alkaline substances capable of generating hydroxide radicals are gradually dripped into the mixture, so that the pH value is increased to 8-11, the metal in the precursor solution forms hydroxide, and a hydroxide coating is formed on the outer surfaces of the microspheres. The operation is carried out at a temperature of from room temperature to 100 ℃. The basic substance used in this step may be those commonly used in the art, such as ammonia, alkali metal hydroxide, alkali metal alkoxide, urea, and the like.
The coated microspheres obtained from the precipitation reaction are filtered, washed and then transferred to water at 50-100 ℃ for maturation for 7-24 hours, or 8-24 hours. Filtering, drying and roasting the cured solid to obtain the spherical carrier particles of the mixed oxides, wherein the shape of the spherical carrier particles is spherical, and the particle size of the spherical carrier particles is 10-100 microns.
The above-described series of operations of depositing the assistant, aging and firing may be repeated more than once in order to obtain a desired coating effect or thickness of the assistant coating layer. For example, it may be repeated 1 to 4 times, preferably not more than four times.
The loading of the cobalt oxide can be carried out by impregnating the spherical support particles of the oxide with a solution of a cobalt-containing precursor, or by mixing a solid cobalt oxide precursor with the spherical support particles of the mixed oxide. When the spherical support particles of the oxide are impregnated with a solution of a cobalt-containing precursor, the concentration of the cobalt-containing precursor in the solution can be adjusted as needed. In a preferred embodiment of the invention, cobalt is supported on spherical support particles by means of an equal volume impregnation. Specifically, by "isovolumetric impregnation" is meant that the concentration and amount of the solution is controlled so that the amount of solvent in the solution is exactly equal to the maximum amount of solvent that can be absorbed by the mixed oxide spherical support particles employed. The amount of solution of any one cobalt-containing precursor can be determined by one of ordinary skill in the art through his experience and simple measurement and experimentation to ensure that it achieves an "equivalent volume impregnation" in a particular type of spherical support particle of oxide.
Examples
Preferred embodiments of the present invention are specifically exemplified in the following examples, but it should be understood that the scope of the present invention is not limited thereto.
The alumina microspheres used in the following examples were purchased from FUJI corporation and had a particle size of 150-; silica microspheres were purchased from SASOL corporation and had a particle size of 100-200 microns. The water used is deionized water; the metal salt reagents used were all commercially available analytical grade reagents and were used without further treatment.
Example 1:
the amounts of the respective raw materials were determined in the weight ratios listed in the following table 1. Dissolving 50 g of zirconium nitrate in water, stirring for 2 hours, soaking in alumina microspheres in equal volume, specifically, adding weighed alumina microspheres to form suspension, keeping stirring for 2 hours, and gradually stirring the suspensionAdding 0.1 mol/L sodium hydroxide aqueous solution, controlling the pH value of the suspension to be not more than 12, filtering the suspension, washing the solid by deionized water, monitoring Na ions in the washing water by an ICP (inductively coupled plasma) element analysis technology in the washing process until the washing water is neutral and the Na ion content is zero, transferring the washed solid into water at the temperature of 70 ℃ for curing for 24 hours, filtering and washing the cured solid, roasting in a muffle furnace at the roasting temperature of 600 ℃ and the heating rate of 5 ℃/min, and keeping for 5 hours to obtain the mixed oxide spherical carrier particles serving as the carrier. The average particle size was 130 microns as determined by malvern particle sizer and it was found by SEM that a zirconia layer was formed on the entire outer surface of the alumina microspheres. Weighing 8.0g of the mixed oxide spherical carrier particles prepared by the above process, placing the particles in a mortar, placing the mortar in a vacuum oven at 60 ℃ for 2 hours, quickly adding cobalt nitrate according to the amount determined in the proportion in Table 1 after removing the particles, carrying out impregnation while stirring with a pestle from time to time, wherein the impregnation lasts for 6 hours, placing the particles at normal temperature overnight, and placing the particles in a tubular reactor with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-1.
Example 2:
the procedure of example 1 above was repeated except that the calcination temperature used in the preparation of the mixed oxide spherical carrier particles was 800 ℃ for 5 hours. The catalyst prepared above was named Cat-2.
Example 3:
the amounts of the respective raw materials were determined in the weight ratios listed in the following table 1.50 g of zirconium nitrate was dissolved in water, stirred for 2 hours, and the alumina microspheres were impregnated with the same volume of the solution, specifically,adding weighed alumina microspheres to form a suspension, keeping stirring for 2 hours, gradually adding ammonia water with the concentration of 0.1 mol/L into the suspension under the stirring condition, controlling the molar ratio of ammonia to zirconium nitrate to be 6:1, finishing the addition within 2 hours, controlling the pH value of the suspension to be not more than 12 in the whole process, filtering the suspension, washing the solid by deionized water until the washing water is neutral, transferring the washed solid into water with the temperature of 50 ℃ for curing for 12 hours, filtering and washing the cured solid, roasting in a muffle furnace, keeping the roasting temperature at 500 ℃, the heating rate at 5 ℃/min, and keeping for 5 hours to obtain the mixed oxide spherical carrier particles serving as the carrier. The average particle size was 160 microns as determined by malvern particle size and a zirconia layer was found to form on the entire outer surface of the alumina microspheres as determined by SEM. Weighing 8.0g of the mixed oxide spherical carrier particles prepared by the above process, placing the particles in a mortar, placing the mortar in a vacuum oven at 60 ℃ for 2 hours, quickly adding cobalt nitrate according to the amount determined in the proportion in Table 1 after removing the particles, carrying out impregnation while stirring with a pestle from time to time, wherein the impregnation lasts for 8 hours, placing the particles at normal temperature overnight, and placing the particles in a tubular reaction furnace with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-3.
Example 4:
the amounts of the respective raw materials were determined in the weight ratios listed in the following table 1.Dissolving 50 g of zirconium nitrate in water, stirring for 2 hours, impregnating alumina microspheres with the solution in equal volume, specifically, adding weighed alumina microspheres to form a suspension, keeping stirring for 2 hours, gradually adding urea with the concentration of 0.1 mol/L into the suspension under the stirring condition, wherein the molar ratio of the urea to the zirconium nitrate is 6:1, the adding is completed within 2 hours, the temperature of the suspension is kept at 90 ℃ in the whole process, and the temperature of the suspension is controlled to be the same as that of the suspensionAnd (2) filtering the suspension liquid until the pH value is not more than 12, washing the solid by using deionized water until the washing water is neutral, transferring the washed solid into water with the temperature of 70 ℃ for curing for 36 hours, filtering and washing the cured solid, roasting in a muffle furnace at the roasting temperature of 500 ℃ and the heating rate of 5 ℃/min for 5 hours, and obtaining the mixed oxide spherical carrier particles serving as the carrier. The average particle size was 90 microns as determined by malvern particle sizer and the zirconia layer was found to be formed on the entire outer surface of the alumina microspheres as determined by SEM. Weighing 8.0g of the mixed oxide spherical carrier particles prepared by the above process, placing the particles in a mortar, placing the mortar in a vacuum oven at 60 ℃ for 2 hours, quickly adding cobalt nitrate according to the amount determined in the proportion in Table 1 after removing the particles, carrying out impregnation while stirring with a pestle from time to time, wherein the impregnation lasts for 10 hours, placing the particles at normal temperature overnight, and placing the particles in a tubular reaction furnace with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-4.
Example 5:
the amounts of the respective raw materials were determined in the weight ratios listed in the following table 1. This example was carried out on alumina microspheres in duplicate And twice, thus half the amount of zirconium salt used per coating.Dissolving 25 g of zirconium nitrate in water, stirring for 2 hours, impregnating alumina microspheres with the solution in equal volume, specifically, adding weighed alumina microspheres to form a suspension, keeping stirring for 2 hours, gradually adding urea with the concentration of 0.1 mol/L into the suspension under the stirring condition, wherein the mol ratio of the urea to the zirconium nitrate is 6:1, adding the urea and the zirconium nitrate is completed within 2 hours, keeping the temperature of the suspension at 90 ℃ in the whole process, controlling the pH value of the suspension to be not more than 12, filtering the suspension, washing the solid with deionized water until the washing water is neutral, transferring the washed solid to water, and transferring the washed solid to waterAging in water at 60 deg.C for 20 hr, filtering and washing the aged solid, calcining in muffle furnace at 600 deg.C and 5 deg.C/min for 5 hr to obtain mixed oxide A.
Then 25 g of zirconium nitrate is weighed, the above steps are repeated, and the mixed oxide A is coated for the second time to prepare the mixed oxide spherical carrier particles as the carrier. The average particle size was 150 microns as determined by malvern particle sizer and it was found by SEM that a zirconia layer was formed on the entire outer surface of the alumina microspheres.
6.0g of the spherical support particles of mixed oxide prepared in the above-described manner were weighed out in a mortar, placed in a vacuum oven at 60 ℃ for 2 hours, removed and impregnated with cobalt nitrate in the amount determined according to the proportions in Table 1, with occasional stirring with a pestle, the impregnation continued for 5 hours, placed overnight at room temperature, and then placed in a tube reactor with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-5.
Example 6:
dissolving 20g of nickel nitrate in water to prepare an aqueous solution, adding a 0.1 mol/L aqueous solution of urea into the solution, wherein the molar ratio of urea to nickel nitrate is 6:1, stirring for 2 hours, then impregnating silica microspheres with the solution, specifically, adding silica microspheres weighed according to the proportion shown in Table 1 to form a suspension, maintaining the mixture under the conditions of vigorous stirring and 90 ℃ for 16 hours, then cooling to room temperature, filtering the cooled suspension to collect a solid, washing the solid with deionized water until the washing water is neutral, roasting the obtained solid in a muffle furnace, wherein the roasting temperature is 700 ℃, the heating rate is 5 ℃/min, and maintaining for 5 hours to prepare the mixed oxide spherical carrier particles serving as a carrier. The average particle size was 110 microns as determined by malvern particle sizer and it was found by SEM that a zirconia layer was formed on the entire outer surface of the alumina microspheres.
6.0g of the spherical support particles of mixed oxide prepared by the above-described process were weighed into a mortar, placed in a vacuum oven at 60 ℃ for 2 hours, removed and then quickly impregnated with cobalt nitrate hexahydrate in the amount determined according to the proportions shown in Table 1, with occasional stirring with a pestle, the impregnation continued for 7 hours, placed overnight at ambient temperature, and then placed in a tubular reactor with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-6.
Example 7:
the procedure described in example 5 was repeated for the catalyst synthesis except that an aqueous solution containing cobalt nitrate Co and manganese nitrate was used at the time of equal volume impregnation of the mixed oxide spherical support particles, the molar ratio of Co to Mn being 96: 4. After impregnation of the solution, the mixture was dried naturally, evaporated to dryness using a rotary evaporator and the dried solid was subjected to reduction and passivation using the conditions described above in example 5. The catalyst prepared above was named Cat-7.
Example 8:
dissolving 20g of cerium nitrate in water to prepare an aqueous solution, adding 0.1 mol/L aqueous solution of urea into the solution, wherein the molar ratio of the urea to the cerium nitrate is 6:1, stirring for 6 hours, adding silica microspheres weighed according to the proportion shown in Table 1 to form a suspension, maintaining for 16 hours under the conditions of vigorous stirring and 90 ℃, cooling to room temperature, filtering the cooled suspension to collect a solid, washing the solid with deionized water until the washing water is neutral, roasting the obtained solid in a muffle furnace at the roasting temperature of 700 ℃, at the heating rate of 5 ℃/min, and keeping for 5 hours to prepare the mixed oxide spherical carrier particles serving as the carrier. The average particle size was 110 microns as determined by malvern particle sizer and it was found by SEM that a zirconia layer was formed on the entire outer surface of the alumina microspheres.
11.0g of the spherical support particles of mixed oxide prepared by the above-described process were weighed into a mortar, placed in a vacuum oven at 75 ℃ for 4.5 hours, removed and quickly impregnated with cobalt nitrate hexahydrate in the amount determined according to the proportions shown in Table 1, with occasional stirring with a pestle, the impregnation continued for 10 hours, placed overnight at ambient temperature, and then placed in a tubular reactor with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-8.
Example 9:
weighing 6.0g of spherical alumina carrier particles, placing the spherical alumina carrier particles in a mortar, placing the mortar in a vacuum oven at 60 ℃ for 7 hours, quickly adding cobalt nitrate hexahydrate with a determined amount according to the proportion shown in the table 1 after removing the spherical alumina carrier particles, soaking the spherical alumina carrier particles by stirring the cobalt nitrate hexahydrate with a pestle from time to time, keeping the soaking process for 9 hours, placing the spherical alumina carrier particles at normal temperature for one night, placing the spherical alumina carrier particles in a tubular reaction furnace, and using 10% of H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-9.
Example 10:
dissolving 25 g of zirconium nitrate in water, stirring for 4 hours, performing equal-volume impregnation on the alumina microspheres by using the solution, adding weighed alumina microspheres to form suspension, keeping stirring for 3.5 hours, gradually adding urea with the concentration of 0.1 mol/L into the suspension under the stirring condition, wherein the mol ratio of the urea to the zirconium nitrate is 6:1, the addition was completed within 2 hours, the temperature of the suspension was maintained at 90 ℃ throughout the process, and the pH of the suspension was controlled not to exceed 12, filtering the suspension, washing the solid with deionized water until the washing water is neutral, transferring the washed solid into water at 60 deg.C for aging for 48 hr, filtering and washing the aged solid, and (3) roasting in a muffle furnace at the roasting temperature of 600 ℃ and the heating rate of 5 ℃/min, and keeping for 5 hours to obtain the mixed oxide A.
Then 5 g of niobate is weighed again, the above steps are repeated, and the mixed oxide A is coated for the second time to prepare the mixed oxide spherical carrier particles as the carrier. The average particle size was 150 microns as measured by a malvern particle sizer.
9.0g of the spherical support particles of mixed oxide prepared in the above-described manner were weighed out in a mortar, placed in a vacuum oven at 60 ℃ for 7 hours, removed and impregnated with cobalt nitrate in the amount determined according to the proportions in Table 1 by rapid addition, with occasional stirring with a pestle, the impregnation was continued for 5 hours, placed overnight at room temperature, and then placed in a tube reactor with 10% H2/N2Reducing at 1 deg.C/min and 350 deg.C for 24 hr, slowly cooling the reduced catalyst to room temperature, maintaining the above mixed gas during cooling, purging with nitrogen gas for 20 min, and adding 1% O2/N2The mixed gas is passivated for 1 hour and then is stored in a closed manner. The catalyst prepared above was named Cat-10.
Synthetic examples
The cobalt-based catalyst synthesized in each example above was weighed in a volume of 20 mL, mixed into 500mL of liquid paraffin, stirred to form a suspension, and the suspension was poured into a 1L slurry bed reactor, the reactor was sealed, purged with nitrogen at a flow rate of 100mL/min for 1 hour, then switched to hydrogen, the temperature was raised to 200 ℃ at a temperature rise rate of 1 ℃/min, and kept reduced at this temperature for 24 hours, and then switched to syngas, and catalytic reaction was started. The conditions of the catalytic reaction are that the temperature is 230 ℃, the pressure is 2.0MPa, and H2volume/CO ratio 2.0, totalGas hourly space velocity of 3000 hours-1. The tail gas composition was analyzed using on-line gas chromatography and the oil wax composition was analyzed off-line. The results of the catalytic reaction are shown in table 1 below.
TABLE 1 evaluation results of catalytic reaction performance of slurry bed Fischer-Tropsch synthesis cobalt-based catalyst
From the data presented in the table above, it can be seen that the catalyst of the present invention has significantly improved CO conversion compared to catalyst Cat-9 without promoter.
In addition, FIGS. 1 and 2 show SEM electron micrographs of catalysts Cat-1 and Cat-9, respectively, after the above-described catalytic reaction. By comparing the two electron micrographs, it can be seen that the catalyst of the invention is better able to maintain the intact spherical morphology after the reaction, which demonstrates that it has significantly improved mechanical strength properties.
Claims (16)
1. A cobalt-based catalyst for use in conducting a fischer-tropsch synthesis reaction in a slurry bed reactor or stirred reactor, the catalyst consisting of, based on the total weight of the catalyst: 1-50% by weight of cobalt oxide, 50-99% by weight of mixed oxide spherical carrier particles having a particle size of 10-100 microns;
the mixed oxide spherical carrier particles consist of microspheres and an auxiliary agent, wherein the content of the auxiliary agent is 1-20 wt% based on the total weight of the cobalt-based catalyst, and the microspheres consist of alumina; the auxiliary agent is a combination of zirconium oxide and cerium oxide.
2. A cobalt-based catalyst according to claim 1, wherein the mixed oxide spherical support particles have a particle size of 50-100 μm.
3. A cobalt-based catalyst according to claim 1, wherein the mixed oxide spherical support particles have a particle size of 50-80 μm.
4. A cobalt-based catalyst according to claim 1, wherein the promoter is in the form of a coating covering part or all of the surface of the microsphere.
5. A cobalt-based catalyst according to claim 1, wherein the cobalt oxide is present in an amount of 15 to 35 wt%, based on the total weight of the catalyst; the content of the mixed oxide spherical carrier particles is 65-85 wt%; the content of the auxiliary agent is 2-10 wt%.
6. A process for the preparation of a cobalt-based catalyst according to any one of claims 1 to 5, comprising the steps of:
i) preparing an adjuvant precursor solution comprising the following elements: a combination of Zr and Ce;
ii) mixing the aid precursor solution with microspheres to obtain coated microspheres under the condition of pH value increase;
iii) curing and roasting the coated microspheres to obtain the mixed oxide spherical carrier particles;
iv) preparing a precursor solution containing cobalt, and mixing the precursor solution containing cobalt with the mixed oxide spherical carrier particles prepared in the step iii) to obtain mixed oxide spherical carrier particles loaded with cobalt, or directly mixing the precursor containing cobalt with the mixed oxide spherical carrier particles prepared in the step iii) in a solid form to obtain mixed oxide spherical carrier particles loaded with cobalt;
v) then roasting, reducing and passivating the cobalt-loaded mixed oxide spherical carrier particles to obtain the cobalt-based catalyst.
7. The method according to claim 6, wherein the solution of the auxiliary agent precursor in step i) is a solution of a salt of the following elements in water, an alcohol or an organic acid: a combination of Zr and Ce.
8. The method of claim 7, wherein the salt is a nitrate, hydrochloride, sulfate, phosphate, or carboxylate.
9. The method of claim 7, wherein the salt is a nitrate, a hydrochloride, an acetate, or any mixture thereof.
10. The method of claim 6, wherein in step ii), the conditions of increasing the pH value represent increasing the pH value to 8-11 by adding a base; in step iii), the coated microspheres are aged in water at 50-100 ℃ for 8-24 hours; the calcination is carried out at a temperature of 300-700 ℃ for 2-10 hours in an air atmosphere.
11. The method of claim 6 or 10, wherein steps ii) and iii) are repeated 1-4 times.
12. The method of claim 6, wherein the soluble salt of cobalt is cobalt acetate, cobalt nitrate, or a mixture thereof.
13. The method of claim 6, wherein steps iv) and v) are performed by: mixing the precursor solution containing cobalt or the precursor containing cobalt in a solid form with the mixed oxide spherical carrier particles prepared in step iii), and then drying in air, nitrogen or vacuum at a temperature of normal temperature to 200 ℃ to obtain mixed oxide spherical carrier particles loaded with cobalt; then roasting the mixed oxide spherical carrier particles loaded with cobalt in an air atmosphere at the temperature of 200-400 ℃; then reducing the mixture for 3 to 5 hours in a hydrogen atmosphere at the temperature of 200 ℃ to 500 ℃, wherein the pressure of the hydrogen is 0.1 to 2MPa, and the concentration of the hydrogen in the hydrogen atmosphere is 1 to 100 percent by volume; and then passivated at a temperature ranging from room temperature to 40 c for 10 minutes to 5 hours in nitrogen containing 1 vol% of oxygen, thereby preparing the cobalt-based catalyst.
14. A process for carrying out a fischer-tropsch reaction in a slurry bed reactor or stirred reactor, the process comprising the steps of: reacting carbon monoxide and hydrogen in the presence of a cobalt-based catalyst as claimed in any one of claims 1 to 5 to produce a hydrocarbon product, the reaction being carried out under the following reaction conditions: the reaction temperature is 180-270 ℃, the reaction pressure is 0.5-5MPa, and the total gas space velocity is 1000-10000 h-1The volume ratio of the carbon monoxide to the hydrogen is 1:1 to 1: 3.
15. The process of claim 14, wherein the reaction is carried out under the following reaction conditions: the reaction temperature is 180-250 ℃, the reaction pressure is 0.5-5MPa, and the total gas space velocity is 500-8000 h-1The volume ratio of the carbon monoxide to the hydrogen is 1:1 to 1: 3.
16. The process of claim 14, wherein prior to the start of the fischer-tropsch reaction, the catalyst is subjected to a reductive pre-treatment under the following conditions: the temperature is 200 ℃ and 500 ℃ and pure hydrogen or hydrogen containing 1% by volume of CO is used at a pressure of 0.1 to 2 MPa.
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