CN111346669B - Method for preparing low-carbon olefin by catalyzing synthesis gas through heteroatom-doped molecular sieve - Google Patents
Method for preparing low-carbon olefin by catalyzing synthesis gas through heteroatom-doped molecular sieve Download PDFInfo
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Abstract
The invention relates to a catalyst containing a heteroatom-doped molecular sieve and a method for preparing low-carbon olefin by directly converting synthesis gas, wherein the catalyst is a composite catalyst, a component I and a component II are compounded together in a mechanical mixing mode, the active ingredient of the component I is a metal oxide, the component II is the heteroatom-doped molecular sieve, the topological structure of the molecular sieve is CHA or AEI, framework atoms comprise Al, P and O, and the heteroatoms can be one or more of divalent metals Mg, ca, cr, mn, fe, co, ni, cu, zn, sr, zr, mo, cd, ba and Ce, trivalent Ti, ga and tetravalent Ge; the weight ratio of the active component I to the component II in the component I is in the range of 0.1-20 times. The reaction process has high selectivity of low-carbon olefin, the sum of the selectivity of the low-carbon olefin including ethylene, propylene and butylene can reach 50-90%, and the selectivity of the byproduct methane is lower than 7%, so that the method has a good application prospect.
Description
Technical Field
The invention belongs to the field of low-carbon olefin preparation by using synthesis gas, and particularly relates to a method for preparing low-carbon olefin by catalyzing synthesis gas through a heteroatom-doped molecular sieve.
Background
The lower olefin is an olefin having 4 or less carbon atoms. The low-carbon olefin represented by ethylene and propylene is a very important basic organic chemical raw material, and the market of the low-carbon olefin is short in supply and demand for a long time along with the rapid growth of the economy of China. At present, the production of low-carbon olefin mainly adopts a petrochemical route of light hydrocarbon (ethane, naphtha and light diesel oil) cracking, and due to the gradual shortage of global petroleum resources and the long-term high-order running of the price of crude oil, the development of the tubular cracking furnace process which only depends on the light hydrocarbon as the raw material in the low-carbon olefin industry encounters larger and larger raw material problems, and the production process and the raw material of the low-carbon olefin need to be diversified. The process for preparing olefin by selecting synthesis gas can broaden the source of raw materials, and provides an alternative scheme for the steam cracking technology based on high-cost raw materials such as naphtha by using crude oil, natural gas, coal and renewable materials as raw materials to produce synthesis gas. The process for directly preparing the low-carbon olefin by the synthesis gas one-step method is a process for directly preparing the low-carbon olefin with the carbon number less than or equal to 4 through the Fischer-Tropsch synthesis reaction under the action of the catalyst by using the carbon monoxide and the hydrogen, and the process does not need to further prepare the olefin from the synthesis gas through methanol or dimethyl ether like an indirect process, thereby simplifying the process flow and greatly reducing the investment.
The direct preparation of low-carbon olefin from synthesis gas through Fischer-Tropsch synthesis becomes one of the research hotspots for developing Fischer-Tropsch synthesis catalysts. In patent CN1083415A published by the institute of chemical and physical sciences of the Chinese academy of sciences, an iron-manganese catalyst system carried by alkali metal oxides of group IIA such as MgO or high-silicon zeolite molecular sieves (or phosphorus-aluminum zeolite) is used, strong base K or Cs ions are used as an auxiliary agent, and higher activity (90% of CO conversion rate) and selectivity (66% of low-carbon olefin selectivity) can be obtained under the reaction pressure of 1.0-5.0 MPa and the reaction temperature of 300-400 ℃ for preparing low-carbon olefin from synthesis gas. In patent ZL03109585.2 filed by Beijing university of chemical industry, a vacuum impregnation method is adopted to prepare a Fe/activated carbon catalyst with manganese, copper, zinc, silicon, potassium and the like as auxiliaries, the Fe/activated carbon catalyst is used for reaction for preparing low-carbon olefin from synthesis gas, and under the condition of no circulation of feed gas, the CO conversion rate is 96%, and the selectivity of the low-carbon olefin in hydrocarbon is 68%. Recently, a Netherlands university of Utrecht de Jong teaches a team that Fe supported by inert carriers such as SiC, carbon nanofibers and the like and Fe catalysts modified by auxiliaries such as Na, S and the like are adopted to achieve good progress and obtain 61% of low-carbon olefin selectivity, but when the conversion rate is increased, the selectivity is reduced. In the process of directly preparing olefin from synthesis gas, because raw materials CO and H2 are gaseous, and the boiling point of ethylene in a target product is low, cryogenic separation is generally required, if olefin containing three carbon atoms and four carbon atoms, namely propylene and a C3-C4 olefin product of butylene, can be obtained with high selectivity, cryogenic separation is not required, the energy consumption and cost of separation are greatly reduced, and the method has great application value. In the above reports, the catalyst adopts metallic iron or iron carbide as an active component, the reaction follows a chain growth reaction mechanism on the metal surface, the selectivity of the product low-carbon olefin is low, and the selectivity of C3-C4 olefin is lower.
Recently, the institute of chemical and physical research in the university of Chinese academy of sciences reports that a ZnCr2O4 oxide and a hierarchical pore SAPO-34 molecular sieve composite bifunctional catalyst (Jiao et al, science 351 (2016) 1065-1068) realizes the selectivity of 80% of low-carbon olefin when the CO conversion rate is 17%, wherein the selectivity of the low-carbon alkane is 14%, and the ratio of the olefin to the alkane (the alkene-alkane ratio) reaches 5.7. When the conversion increased to 35%, the olefin selectivity was 69% and the alkane selectivity was 20%, the alkene/alkane ratio decreased to 3.5 and the propene/butene selectivity was 40-50%.
Disclosure of Invention
Aiming at the problems, the invention provides a catalyst, a catalyst for preparing low-carbon olefin by directly converting synthesis gas and a method.
The technical scheme of the invention is as follows:
in one aspect, the invention provides a catalyst comprising component i and component ii, the component i and component ii being prepared separately and then mixed; the active component of the component I is metal oxide, and the component II is a molecular sieve doped with heteroatoms;
the metal oxide is MnO x 、MnaCr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、ZnO x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、CeO x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、GaO x 、BiO x 、InO x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x One or more than two of them; the value range of x is 0.7-3.7, and the value range of a is 0-1; the value range of a + b is 0-1;
the molecular sieve is a CHA or AEI topological structure molecular sieve, and the framework atoms comprise Al, P and O; the heteroatom is one or more than two of divalent metals Mg, ca, cr, mn, fe, co, ni, cu, zn, sr, zr, mo, cd, ba and Ce, trivalent Ti, ga and tetravalent Ge; the molecular sieve doped with the heteroatoms is formed by doping the heteroatoms in the molecular sieve framework to replace Al or P in the molecular sieve framework, wherein the divalent metal and the trivalent metal generally replace the position of Al in the framework, and the tetravalent and higher valence metals replace the position of P.
Based on the technical scheme, preferably, the MnO x 、ZnO x 、CeO x 、GaO x 、BiO x 、InO x Has a specific surface area of 1 to 100m 2 (ii)/g; the preferred specific surface area is 50 to 100m 2 /g；
The MnaCr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、ZnO x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x Has a specific surface area of 5 to 150m 2 A preferred specific surface area is from 50 to 150m 2 /g；
Based on the technical scheme, preferably, the ratio of the sum of the molar weights of the heteroatoms in the heteroatom-doped molecular sieve to the molar weight of P is 0.001-0.6.
Based on the technical scheme, the weight ratio of the active ingredients in the component I to the component II is preferably 0.1-20, and preferably 0.3-5.
Based on the technical scheme, preferably, a dispersant is further added into the component I, and the metal oxide is dispersed in the dispersant; the dispersant is Al 2 O 3 、SiO 2 、Cr 2 O 3 、ZrO 2 、TiO 2 、Ga 2 O 3 One or more of activated carbon, graphene and carbon nanotubes; in the component I, the content of the dispersant is 0.05 to 90 weight percent, and the balance is metal oxide.
Based on the technical scheme, preferably, the heteroatom-doped molecular sieve is prepared by an in-situ hydrothermal growth method or a post-treatment method; the in-situ hydrothermal growth method comprises the following steps: (1) sol precursor preparation: dissolving an aluminum source and a phosphorus source in a certain proportion in water, uniformly stirring, adding the solution containing a heteroatom precursor and a template agent, and stirring; (2) hydrothermal crystallization: reacting and crystallizing the sol precursor obtained in the step (1) at 160-200 ℃ for 4-7 days; (3) separating and washing: centrifuging and washing a product after the crystallization reaction; and (4) drying and roasting: roasting the product of the step (3) at 550-600 ℃ for 3-6h; the ratio of the heteroatom precursor heteroatom to the phosphorus source is 0-0.6; the post-treatment method comprises the following steps: (1) Preparing a solution of a heteroatom precursor, soaking an AlPO-18 or AlPO-34 molecular sieve in the solution of the precursor, drying, roasting at 550-600 ℃ for 3-6h, loading by an impregnation method and the like to obtain the heteroatom precursor, and embedding heteroatoms into a framework in a roasting mode; the AlPO-18 or AlPO-34 can be a commercially available sample or a sample synthesized by a method reported in the literature. The doped heteroatom molecular sieves obtained by the two methods are obviously different from ion-exchanged molecular sieves in that the AEI molecular sieve taking Al, P and O as frameworks is electrically neutral, and does not have exchangeable H atoms on O, so that the heteroatoms are difficult to be doped in an ion exchange manner. And the heteroatom of the molecular sieve obtained by ion exchange is positioned outside the molecular sieve framework, while the heteroatom of the heteroatom-doped molecular sieve obtained by the invention is embedded into the molecular sieve framework, so that the catalyst structure and the reaction performance are obviously different from those of an ion exchange sample.
Based on the above technical scheme, preferably, the aluminum source includes, but is not limited to boehmite, aluminum hydroxide, aluminum nitrate, aluminum sulfate or aluminum isopropoxide; the heteroatom precursors include, but are not limited to, metal nitrates, sulfates, acetates, halides or oxides of the corresponding metal atoms.
The invention also provides a method for preparing low-carbon olefin by catalyzing synthesis gas with high selectivity, which takes the synthesis gas as a reaction raw material to carry out conversion reaction on a fixed bed or a moving bed to prepare the low-carbon olefin, wherein the catalyst adopted by the method is the catalyst
Based on the technical scheme, preferably, the pressure of the synthesis gas is 0.5-10MPa, preferably 1-8MPa, and more preferably 2-8MPa; the reaction temperature is 300-600 ℃, preferably 370-450 ℃; the space velocity is 300-10000h -1 Preferably 500 to 9000h -1 More preferably 1000-6000h-1; the synthesis gas is H 2 Mixed gas of/CO, H 2 The molar ratio/CO is between 0.2 and 3.5, preferably between 0.3 and 2.5; the synthesis gas may also contain CO 2 In which CO is 2 The volume concentration in the synthesis gas is 0.1-50%.
Based on the technical scheme, preferably, the method directly converts the synthesis gas into the C by a one-step method 2-4 Olefins, C 2-4 The selectivity of olefin is 50-90%, and the selectivity of byproduct methane<7％。
Advantageous effects
The technology is different from the traditional technology (MTO for short) for preparing the low-carbon olefin by the methanol, and the synthesis gas is directly converted into the low-carbon olefin by one step.
The preparation process of the composite catalyst is simple and has mild conditions; by embedding the hetero atoms into the CHA or AEI structure molecular sieve framework, the activity of the reaction and the selectivity of the product are effectively improved, the conversion rate of the reaction is improved, the selectivity of the low-carbon olefin is improved, the conversion rate of the reaction can reach 10-55%, the selectivity of the propylene butene product in the product can reach 40-75%, and C is 2-4 The selectivity of the low-carbon olefin can reach 50-90%. The product can be separated without deep cooling, thereby greatly reducing the energy consumption and the cost of separation. While the selectivity of the by-product methane is low (<7%) and the catalyst has a long life,>700 hours, has good application prospect.
Detailed Description
The invention is further illustrated by the following examples, but the scope of the claims of the invention is not limited by these examples. Meanwhile, the embodiments only give some conditions for achieving the purpose, but do not mean that the conditions must be met for achieving the purpose.
The specific surface area of the sample can be measured by nitrogen or argon physical adsorption.
The metal oxide of the present invention can be obtained by purchasing commercially available metal oxides with a high specific surface area, or can be obtained by the following methods:
1. preparation of catalyst component I
Synthesizing a ZnO material with a high specific surface by a precipitation method:
(1) 3 parts, 0.446g (1.5 mmol) of Zn (NO) are weighed out separately 3 ) 2 ·6H 2 And putting O into 3 containers, then respectively weighing 0.300g (7.5 mmol), 0.480g (12 mmol) and 0.720g (18 mmol) of NaOH, sequentially adding into the 3 containers, respectively weighing 30ml of deionized water, adding into the 3 containers, stirring at 70 ℃ for more than 0.5h to uniformly mix the solution, and naturally cooling to room temperature. Centrifugally separating the reaction liquid, collecting the precipitate after centrifugal separation, and washing the precipitate for 2 times by using deionized water to obtain a ZnO metal oxide precursor;
(2) Roasting: and drying the obtained product in air, and roasting in the atmosphere to obtain the ZnO material with high specific surface. The atmosphere is inert gas, reducing gas or oxidizing gas; inert gas being N 2 One or more of He and Ar; the reducing gas being H 2 One or two of CO and the reducing gas can also contain inert gas; the oxidizing gas being O 2 、O 3 、NO 2 And the oxidizing gas may contain an inert gas. The roasting temperature is 300-700 ℃ and the time is 0.5-12 h.
The purpose of calcination is to decompose the precipitated metal oxide precursor into oxide nanoparticles with high specific surface area at high temperature, and the decomposed oxide surface adsorbed species can be treated cleanly by the high-temperature treatment of calcination.
Specific samples and their preparation conditions are shown in Table 1 below, in which ZnO #4 is a commercially available ZnO single crystal of low specific surface area as a comparative example.
TABLE 1 preparation of ZnO materials and their Parametric Properties
(II) synthesizing a MnO material with high specific surface area by a coprecipitation method:
the preparation process is the same as that of ZnO #2, except that a precursor of Zn is replaced by a corresponding precursor of Mn, which can be one of manganese nitrate, manganese chloride and manganese acetate, wherein the precursor is manganese nitrate, and a corresponding product is defined as MnO; the specific surface area is: 23m 2 /g。
(III) coprecipitation method for synthesizing CeO with high specific surface area 2 Materials:
the preparation process is the same as that of ZnO #2, except that the precursor of Zn is replaced by the corresponding precursor of Ce, which can be one of cerium nitrate, cerium chloride and cerium acetate, wherein the corresponding product is defined as CeO 2 (ii) a The specific surface area is: 92m 2 /g。
Synthesis of Ga having high specific surface area by coprecipitation method 2 O 3 Materials:
the preparation process is the same as that of ZnO #2, except that the precursor of Zn is replaced by the corresponding precursor of Ga, which can be one of gallium nitrate, gallium chloride and gallium acetate, and the corresponding product is defined as Ga 2 O 3 (ii) a The specific surface area is: 55m 2 /g。
(V) coprecipitation method for synthesizing Bi with high specific surface area 2 O 3 Materials:
the preparation process is the same as the ZnO #2, except that the precursor of Zn is replaced by the corresponding precursor of Bi, and the precursor can be one of bismuth nitrate, bismuth chloride and bismuth acetate, and is bismuth nitrate. The corresponding product is defined as Bi 2 O 3 (ii) a The specific surface areas are: 87m 2 /g。
(VI) coprecipitation method for synthesizing In with high specific surface area 2 O 3 Materials:
the preparation process is the same as that of ZnO #2, except that Zn precursor is replaced by corresponding precursor of In, which can be one of indium nitrate, indium chloride and indium acetate, in this case, the corresponding product is defined as In 2 O 3 (ii) a The specific surface area is: 52m 2 /g
(VII) Synthesis of Mn with high specific surface area by precipitation a Cr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x ：
Zinc nitrate, aluminum nitrate, chromium nitrate, manganese nitrate, zirconium nitrate, indium nitrate, cobalt nitrate and ferric nitrate are used as precursors and mixed with ammonium carbonate in water at room temperature (wherein the ammonium carbonate is used as a precipitant, and the feeding proportion is that the ammonium carbonate is excessive or the proportion of ammonium ions and metal ions is preferably 1); and aging the mixed solution, taking out, washing, filtering and drying, and roasting the obtained solid in an air atmosphere to obtain the metal oxide with the high specific surface, wherein specific samples and preparation conditions thereof are shown in the following table 2.
TABLE 2 preparation of high specific surface area metal oxides and their performance parameters
(VIII) dispersant Cr 2 O 3 、Al 2 O 3 Or ZrO 2 Dispersed metal oxide
With dispersant Cr 2 O 3 、Al 2 O 3 Or ZrO 2 As carrier, preparing Cr by precipitation deposition 2 O 3 、Al 2 O 3 Or ZrO 2 A dispersed metal oxide. Taking the preparation of dispersed ZnO as an example, commercial Cr is used 2 O 3 (specific surface area about 5 m) 2 /g)、Al 2 O 3 (specific surface area about 20 m) 2 /g) or ZrO 2 (specific surface area about 10 m) 2 /g) as carrier, dispersing in water in advance, then taking zinc nitrate as raw material, mixing with sodium hydroxide precipitant at room temperature for precipitation, zn 2+ In a molar concentration of 0.067M 2+ The mol part ratio of the organic silicon compound to the precipitant is 1:8; then aging at 160 ℃ for 24 hours to obtain Cr 2 O 3 、Al 2 O 3 Or ZrO 2 ZnO dispersed as a carrier (the content of the dispersant in the component I is 0.1wt%, 20wt%, 85wt% in sequence). The obtained sample is roasted for 1h at 500 ℃ under the air, the products are sequentially defined as dispersed oxides 1-3, and the specific surface areas are sequentially as follows: 148m 2 /g，115m 2 /g，127m 2 /g。
In the same manner, siO can be obtained 2 (specific surface area about 2 m) 2 /g)、Ga 2 O 3 (specific surface area about 10 m) 2 Per g) or TiO 2 (specific surface area about 15 m) 2 /g) as the supported dispersed MnO oxide (5 wt%, 30wt%, 60wt% of dispersant in component I) and the product is defined as dispersed oxide 4-6. The specific surface area is as follows: 97m 2 /g，64m 2 /g，56m 2 /g。
In the same manner, activated carbon (specific surface area about 1000 m) was obtained 2 Per gram), graphene (specific surface area about 500 m) 2 Per g) or carbon nanotubes (specific surface area about 300 m) 2 The ZnO oxide dispersed as a carrier (the content of the dispersant in component I is 5wt%, 30wt%, 60wt% in this order), and the product is defined as a dispersed oxide 7 to 9 in this order. The specific surface area is as follows: 177m 2 /g，245m 2 /g，307m 2 /g。
2. Preparation of component II
The CHA and AEI topologies have eight-membered ring apertures, three-dimensional channels.
Molecular sieve prepared by hydrothermal synthesis method
The preparation process comprises the following steps:
taking MgAPO as an example, according to the oxide MgO: al 2 O 3 :P 2 O 5 :R:H 2 O =0.3: magnesium nitrate; aluminum hydroxide; phosphoric acid; diisopropylethylamine (DIPEA); deionized water, stirring and aging at 30 deg.C for 2h, transferring into hydrothermal kettle, and crystallizing at 180 deg.C for 120h. And cooling to room temperature, repeatedly centrifuging and washing until the pH value of the supernatant is 7 at the end of washing, drying the precipitate at 110 ℃ for 17h, and roasting at 600 ℃ for 3h to obtain the Mg atom-doped molecular sieve.
TABLE 3 preparation of doped heteroatomic molecular sieves with CHA or AEI topology and their performance parameters
(II) impregnation method for synthesizing Zr-AlPO, ba-AlPO and Ce-AlPO molecular sieves
Adding a zirconium nitrate solution with a proper concentration into a 100mL beaker, adding a proper amount of AlPO-18 molecular sieve while stirring, stirring at room temperature until the mixture is stirred to be dry, drying, and roasting at 600 ℃ for 3 hours to obtain Zr-AlPO; ba-AlPO, ce-AlPO molecular sieve method is the same as above, the precursor is changed to barium nitrate, cerium nitrate.
3. Preparation of the catalyst
The component I and the component II in required proportion are added into a container, the purposes of separation, crushing, uniform mixing and the like are realized by utilizing one or more than two of extrusion force, impact force, shearing force, friction force and the like generated by the high-speed movement of the materials and/or the container, the conversion of mechanical energy, heat energy and chemical energy is realized by regulating the temperature and the carrier gas atmosphere, and the interaction among different components is further regulated.
In the mechanical mixing process, the mixing temperature can be set to be 20-100 ℃, and the mixing can be carried out in an atmosphere or directly in air, wherein the atmosphere is selected from any of the following gases:
a) Nitrogen and/or inert gas;
b) The mixed gas of hydrogen and nitrogen and/or inert gas, wherein the volume of the hydrogen in the mixed gas is 5-50%;
c) The mixed gas of CO and nitrogen and/or inert gas, wherein the volume of CO in the mixed gas is 5-20%;
d)O 2 mixed with nitrogen and/or inert gases, in which O 2 The volume of the inert gas in the mixed gas is 5-20%, and the inert gas is one or more than two of helium, argon and neon.
The mechanical mixing can be one or more of mechanical stirring, ball milling, table mixing and mechanical grinding, and specifically comprises the following steps:
mechanical stirring: in the stirring tank, the component I and the component II are mixed by a stirring rod, and the mixing degree of the component I and the component II can be adjusted by controlling the stirring time (5 min-120 min) and the stirring speed (30-300 r/min).
Ball milling: the grinding material and the catalyst are rolled in a grinding tank at a high speed to generate strong impact and rolling on the catalyst, so that the effects of dispersing and mixing the component I and the component II are achieved. By controlling the abrasive (the material can be stainless steel, agate and quartz, the size range is 5mm-15 mm). Ratio to catalyst (mass ratio range: 20-100.
A shaking table mixing method: premixing the component I and the component II, and filling the mixture into a container; mixing the component I and the component II by controlling the reciprocating oscillation or the circumferential oscillation of the shaking table; the uniform mixing is realized by adjusting the oscillation speed (range: 1-70 r/min) and the time (range: 5min-120 min).
Mechanical grinding method: premixing the component I and the component II, and filling into a container; under a certain pressure (range: 5 kg-20 kg), the catalyst is mixed by a grinder and the mixed catalyst is moved relatively (speed range: 30-300 r/min) to realize uniform mixing.
Specific catalyst preparations and their parametric characteristics are shown in table 6.
TABLE 6 preparation of the catalysts and their parametric characterization
Examples of catalytic reactions
Fixed bed reactions are exemplified, but the catalyst is also suitable for use in moving bed reactors. The device is provided with a gas mass flow meter and an on-line product analysis chromatograph (tail gas of a reactor is directly connected with a proportional valve of the chromatograph to carry out periodic real-time sampling analysis).
2g of the catalyst of the present invention was placed in a fixed bed reactor, and the air in the reactor was replaced with Ar, followed by H 2 Raising the temperature to 300 ℃ in the atmosphere, and switching the synthesis gas (H) 2 The mol ratio of/CO = 0.2-3.5), the pressure of the synthetic gas is 0.5-10MPa, the temperature is raised to 300-600 ℃, and the space velocity of the reaction raw material gas is adjusted to 300-12000ml/g/h. The product was analyzed by on-line chromatographic detection.
Changing temperature, pressure and space velocity and H in syngas 2 The molar ratio of/CO can vary the reaction properties. The selectivity sum of propylene and butylene reaches 30-75%, the selectivity sum of low-carbon olefin (ethylene, propylene and butylene can reach 50-90%, the generation of a large amount of methane is avoided due to low surface hydrogenation activity of the catalyst metal compound, and the methane selectivity is low, and specific application and effect data of the catalyst are listed in Table 7.
TABLE 7 specific use of the catalyst and Effect data thereof
Comparative example 1 catalyst component I was ZnO #4 and component II was GeAPO.
Comparative example 4 the molecular sieve in the catalyst used was a commercial SAPO-34, NH, from southern Kai university catalyst works 3 The temperature corresponding to the desorption peak of the medium strong acid on TPD is 390 ℃ and the amount of medium strong acid sites is 0.6mol/kg.
The molecular sieve in the catalyst used in comparative example 5 was commercial ZSM-5 available from southern university catalyst plant, full microporous structure, si/Al =30.
The reaction results of comparative examples 4 and 5 show that the topology of CHA or AEI and its acid strength are critical for modulation of product selectivity.
The catalyst adopted in comparative example 6 is a sample containing only component I ZnO #1 without molecular sieve, the reaction conversion rate is very low, and the product is mainly composed of dimethyl ether, methane and other by-products, and almost no ethylene is generated.
The catalyst used in comparative example 7 was a component II only, component 1 molecular sieve, and the sample containing no component I, and the catalytic reaction was almost inactive.
Comparative examples 6 and 7 had only component I or component II on the surface, and were extremely poor in reaction effect, and did not have the excellent reaction properties described in the present invention at all.
The catalyst used in comparative example 8 had a molecular sieve of self-synthesized AlPO-18, and the remaining parameters and mixing were the same as for catalyst A. The conversion rate and selectivity of the reaction of comparative example 8 are very poor and are much lower than the reaction performance of catalyst a under the same conditions, indicating that the molecular sieve doped with hetero atoms can effectively improve the activity and selectivity of the reaction.
Comparative example 9 uses a catalyst in which the molecular sieve is Mg (NO) 3 ) 2 The ion-exchanged AlPO-18, the rest parameters and the mixing process are the same as those of the catalyst A.
Comparative example 10 useThe molecular sieve in the catalyst is Ca (NO) 3)2 The ion-exchanged AlPO-34, the remaining parameters and the mixing procedure were the same as for catalyst B.
The reaction results of comparative examples 9 and 10 show that the reaction performance of the ion-exchanged AlPO-18 and AlPO-34 samples as catalyst component B is significantly different from that of the heteroatom-doped molecular sieve of the present invention, and the incorporation of heteroatoms into the AlPO molecular sieve framework is critical to the modulation of the reaction activity and selectivity.
In the literature (Jiano et al, science 351 (2016) 1065-1068) comparison technique, the amount of molecular SAPO-34 sieve acid used was large, reaching a medium acid content of 0.32mol/kg according to the NH3-TPD test, so that when the conversion increased to 35%, the olefin selectivity was 69%, while the alkane selectivity was 20%, the alkene ratio decreased to 3.5, and the propene-butene selectivity was 40-50%.
From the above table, it can be seen that the structure of the molecular sieve, including the topology of CHA & AEI and its acid strength and acid content, the amount of heteroatom incorporation and whether it is incorporated into the framework, and the matching between the metal oxide and the molecular sieve are critical and directly affect the conversion of carbon monoxide and the selectivity of propene to butene.
Claims (13)
1. A catalyst, characterized by: the catalyst comprises a component I and a component II, wherein the active component of the component I is a metal oxide, and the component II is a molecular sieve doped with heteroatoms;
the metal oxide is MnO x 、Mn a Cr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、ZnO x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、CeO x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、GaO x 、BiO x 、InO x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x One or more than two of them; the value range of x is 0.7-3.7, and the value range of a is 0-1; the value range of a + b is 0 to 1;
the molecular sieve is a CHA or AEI topological structure molecular sieve, and the framework atoms are Al, P and O; the heteroatom is one or more than two of divalent metals of Mg, ca, cr, mn, fe, co, ni, cu, zn, sr, zr, mo, cd, ba and Ce, trivalent Ti, ga and tetravalent Ge; the molecular sieve doped with the heteroatoms is formed by doping the heteroatoms in the molecular sieve framework to replace Al or P in the molecular sieve framework;
the MnO x 、ZnO x 、CeO x 、GaO x 、BiO x 、InO x Has a specific surface area of 1 to 100m 2 /g；
The MnaCr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、ZnO x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x Has a specific surface area of 5 to 150m 2 /g；
The molecular sieve doped with the heteroatom is prepared by an in-situ hydrothermal growth method or a post-treatment method; the in-situ hydrothermal growth method comprises the following steps: (1) sol precursor preparation: dissolving an aluminum source and a phosphorus source in a certain proportion in water, uniformly stirring, then adding a precursor containing heteroatoms and a template agent, and stirring for 0.5-12 h; (2) hydrothermal crystallization: putting the sol precursor obtained in the step (1) in 160-200 o C, crystallizing for 4-7 days; (3) separating and washing: centrifuging, washing and drying a product after the crystallization reaction; and (4) drying and roasting: will go to stepThe product of step (3) is dissolved in 550-600 o C, roasting for 3-6h; the molar ratio of the heteroatom in the heteroatom precursor to the phosphorus source is 0-0.6; the post-treatment method comprises the following steps: preparing solution of heteroatom precursor, soaking AlPO-18 or AlPO-34 molecular sieve in the solution of the precursor, stoving, and final 550-600 deg.c o C, roasting for 3-6 h.
2. The catalyst of claim 1, wherein: the MnO x 、ZnO x 、CeO x 、GaO x 、BiO x 、InO x Has a specific surface area of 50 to 100m 2 /g；
The MnaCr (1-a) O x 、Mn a Al (1-a) O x 、Mn a Zr (1-a) O x 、Mn a In (1-a) O x 、ZnO x 、Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Ga (1-a) O x 、Zn a In (1-a) O x 、Co a Al (1-a) O x 、Fe a Al (1-a) O x 、In a Al b Mn (1-a-b) O x 、In a Ga b Mn (1-a-b) O x Has a specific surface area of 50 to 150m 2 /g。
3. The catalyst of claim 1, wherein: the ratio of the sum of the molar weight of the heteroatoms in the doped heteroatom molecular sieve to the molar weight of P is 0.001-0.6.
4. The catalyst of claim 3, wherein: the weight ratio of the active ingredients in the component I to the component II is 0.1-20.
5. The catalyst of claim 4, wherein: the weight ratio of the active ingredients in the component I to the component II is 0.3-5.
6. The catalyst of claim 3, wherein: a dispersant is also added into the component I, and the metal oxide is dispersed in the dispersant; the dispersant is Al 2 O 3 、SiO 2 、Cr 2 O 3 、ZrO 2 、TiO 2 、Ga 2 O 3 One or more of activated carbon, graphene and carbon nanotubes; in the component I, the content of the dispersant is 0.05 to 90 weight percent, and the balance is metal oxide.
7. The catalyst of claim 1, wherein: the aluminum source is boehmite, aluminum hydroxide, aluminum nitrate, aluminum sulfate or aluminum isopropoxide; the heteroatom precursor is metal nitrate, sulfate, acetate, halide or oxide of corresponding metal atoms; the template agent is triethylamine and diisopropylethylamine.
8. A method for preparing low-carbon olefin by catalyzing synthesis gas with high selectivity is characterized by comprising the following steps: the synthesis gas is used as a reaction raw material, and the conversion reaction is carried out on a fixed bed or a moving bed to prepare the low-carbon olefin, wherein the catalyst adopted by the method is the catalyst in claim 1.
9. The method of claim 8, wherein: the pressure of the synthesis gas is 0.5-10MPa; the reaction temperature is 300-600 ℃; the space velocity is 300-10000h -1 (ii) a The synthesis gas is H 2 Mixed gas of/CO, H 2 The mol ratio of/CO is 0.2-3.5.
10. The method of claim 9, wherein: the pressure of the synthesis gas is 1-8MPa; the reaction temperature is 370-450 ℃; the space velocity is 500-9000h -1 (ii) a The synthesis gas is H 2 Mixed gas of/CO, H 2 The ratio of/CO is 0.3-2.5.
11. The method of claim 10, wherein: the pressure of the synthesis gas is 2-8MPa; the space velocity is 1000-6000h -1 。
12. The method of claim 8, wherein: the synthesis gas also contains CO 2 ，CO 2 The volume concentration in the synthesis gas is 0.1-50%.
13. The method of claim 8, wherein: the method directly converts the synthesis gas into C by a one-step method 2-4 Olefin, C 2-4 The selectivity of olefin is 50-90%, and the selectivity of byproduct methane is<7%。
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| PCT/CN2019/124234 WO2020125487A1 (en) | 2018-12-21 | 2019-12-10 | Method for the preparation of low-carbon olefin in high selectivity from synthesis gas catalyzed by heteroatom-doped molecular sieve |
| EP19900221.3A EP3900829A4 (en) | 2018-12-21 | 2019-12-10 | Method for the preparation of low-carbon olefin in high selectivity from synthesis gas catalyzed by heteroatom-doped molecular sieve |
| US17/286,903 US20210347711A1 (en) | 2018-12-21 | 2019-12-10 | Method for preparing light olefin through catalytic syngas with high selectivity by heteroatom-doped zeolite |
| ZA2021/02711A ZA202102711B (en) | 2018-12-21 | 2021-04-22 | Method for the preparation of low-carbon olefin in high selectivity from synthesis gas catalyzed by heteroatom-doped molecular sieve |
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