CN108568311B - Catalyst and method for preparing ethylene by directly converting synthesis gas - Google Patents
Catalyst and method for preparing ethylene by directly converting synthesis gas Download PDFInfo
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Abstract
The invention belongs to the field of direct preparation of ethylene by using synthesis gas, and particularly relates to a catalyst and a method for preparing ethylene by direct conversion of synthesis gas, wherein the synthesis gas is used as a reaction raw material, and a conversion reaction is carried out on a fixed bed or a moving bed, the catalyst is a composite catalyst and is prepared by compounding a component A and a component B in a mechanical mixing manner, the active component of the component A is a metal oxide, and the component B is a molecular sieve with an MOR structure; the weight ratio between the active ingredient in the A component and the B component is in the range of 0.1-20, preferably 0.3-8. The reaction process has high product yield and selectivity, the selectivity of the low-carbon olefin can reach 80-90%, wherein the space-time yield of the ethylene is high, the selectivity reaches 75-80%, and meanwhile, the selectivity of the byproduct methane is extremely low (< 15%), so that the method has a good application prospect.
Description
Technical Field
The invention belongs to preparation of low-carbon olefin by using synthesis gas, and particularly relates to a catalyst and a method for preparing ethylene by converting synthesis gas.
Background
Ethylene is a very important basic chemical raw material, is one of the chemical products with the largest yield in the world, and the ethylene industry is the core of the petrochemical industry and plays an important role in national economy. 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 with the rapid growth of the economy of China, the ethylene industry of China develops rapidly and occupies an important position in the ethylene market of the world. For a long time, the market of low-carbon olefins is in short supply. At present, the petrochemical route of naphtha and light diesel oil cracking or the ethane cracking technology are mainly adopted for producing ethylene, and because petroleum in China depends on import for a long time, the energy safety in China has higher risk, and the development of the petroleum-independent ethylene production technology is urgently needed. The route of converting coal, renewable materials and the like into synthesis gas and then producing olefin by taking the synthesis gas as a raw material in one step provides an alternative scheme for producing ethylene by naphtha cracking technology. The one-step method for directly preparing the low-carbon olefin from the synthesis gas is a process for directly preparing the low-carbon olefin with the carbon atom number less than or equal to 4 by the Fischer-Tropsch synthesis reaction of carbon monoxide and hydrogen under the action of the catalyst, 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 synthesis gas is directly used for preparing the low-carbon olefin through Fischer-Tropsch synthesis, and is one of the research hotspots for directly producing the olefin from the synthesis gas. In patent CN1083415A published by institute of chemical and physical sciences in the chinese academy of sciences, an iron-manganese catalyst system supported by an alkali metal oxide of group IIA such as MgO or a high-silicon zeolite molecular sieve (or a phospho-aluminum zeolite) is used, and strong base K or Cs ions are used as an auxiliary agent, so that high activity (90% of CO conversion) and high selectivity (66% of low-carbon olefin selectivity) can be obtained at a reaction temperature of 300-400 ℃ under a reaction pressure of 1.0-5.0 MPa 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 taking manganese, copper, zinc, silicon, potassium and the like as additives for the reaction of preparing low-carbon olefin from synthesis gas, and under the condition of no circulation of raw material gas, the conversion rate of CO is 96 percent, and the selectivity of the low-carbon olefin in hydrocarbon is 68 percent. The catalyst reported above adopts metallic iron or iron carbide as active component, the reaction follows the chain growth reaction mechanism of metal surface, the selectivity of the product low carbon olefin is low, especially the selectivity of single product such as ethylene is lower than 30%. In 2016, Sunrichan researchers and Chongxian researchers at Shanghai high research institute reported a preferential exposure [101 ]]And [020]The manganese-assisted cobalt carbide-based catalyst realizes the selectivity of low-carbon olefin of 60.8 percent and the selectivity of methane of 5 percent under the CO conversion rate of 31.8 percent. But the ethylene single selectivity was less than 20%. Alumina-loaded ZnCr was reported by the institute of encyclopedia of chemico-physical research, the institute of academia and Panxilian, academy of sciences2O4The oxide and multi-stage 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 with 17% of CO conversion rate, but the selectivity of ethylene is lower than 30%. Patent 20161060 filed on them0945.6, the dual-function catalyst containing oxygen holes and MOR molecular sieve is used for the reaction of one-step preparation of olefin from synthesis gas, the selectivity of ethylene is improved to 30-75%, but the number of carbon atoms in the by-product is more than 3, which affects the application of the technology.
Disclosure of Invention
The invention solves the problems: the invention overcomes the defects of the prior art and provides a catalyst and a method for preparing ethylene by directly converting synthesis gas, the catalyst can catalyze the synthesis gas to directly convert the synthesis gas to generate low-carbon olefin, and the selectivity of a single product of ethylene can reach 75-80%.
The technical scheme of the invention is as follows: a catalyst is prepared by compounding a component A and a component B in a mechanical mixing mode, wherein the active component of the component A is a metal oxide, and the component B is a molecular sieve with an MOR topological structure, and is characterized in that: in the component B, the content of B acid in an 8-membered ring cage of the molecular sieve with the MOR topological structure is 0.01mmol/g-0.6 mmol/g.
The content of B acid in the 8-membered ring cage of the molecular sieve with the MOR topological structure is preferably 0.1-0.6mmol/g, and more preferably 0.25-0.6 mmol/g. The B acid is protonic acid in a molecular sieve skeleton, and the characteristics and the content of the B acid can be determined by an infrared spectrum or a nuclear magnetic resonance method. The B acid sites in different channels correspond to different Vibrational wavenumber ranges in the IR spectrum (according to the document N.Cherkasov et al/visual Spectroscopy 83(2016) 170-.
The weight ratio of the active component in the component A to the component B is in the range of 0.1-20 times, and the weight ratio is preferably 0.3-8;
the metal oxide is composed of crystal grains having a size of 5 to 30nm, and a large number of oxygen vacancies are present in the range of a depth of 0.3nm from the crystal grain surface to the crystal grain interior direction, i.e., the molar amount of oxygen atoms is 80% or less of the theoretical stoichiometric oxygen molar content, preferably the molar amount of oxygen atoms is 80 to 10%, more preferably 60 to 10%, most preferably 50 to 10% of the theoretical stoichiometric oxygen molar content; surface oxygen vacancies are defined as (1-molar amount of oxygen atoms to theoretical stoichiometric oxygen molar content), corresponding to an oxygen vacancy concentration of preferably 20-90%, more preferably 40-90%, most preferably 50-90%.
The component A is also added with a dispersant which is Al2O3、SiO2、Cr2O3、ZrO2、TiO2、Ga2O3One or two of the above, the metal oxide is dispersed in the dispersant, the content of the dispersant in the A component is 0.05-90wt%, preferably 0.05-25 wt%, and the rest is the metal oxide.
The MOR topological structure is an orthorhombic system, has a one-dimensional pore channel structure of oval through pore channels which are parallel to each other, and comprises 8 circular ring pockets and 12 circular ring one-dimensional pore channels; [ ATLAS OF ZEOLIE FRAMEWORK TYPES, Ch.Baerlocher et al, 2007, Elsevier ].
The framework element composition of the molecular sieve with MOR topological structure can be one or more than two of Si-Al-O, Ga-Si-O, Ga-Si-Al-O, Ti-Si-O, Ti-Al-Si-O, Ca-Al-O, Ca-Si-Al-O.
The preparation process of the metal oxide comprises the following steps: soaking metal oxide in one or more of etching agents such as oleic acid, urotropine, ethylenediamine, ammonia water, hydrazine hydrate and the like; heating the suspended matter at 100-150 deg.c for 30-90 min, washing and filtering to obtain metal oxide material with great amount of surface oxygen holes; drying and reducing the filtered substance in an atmosphere of inert gas or a mixture of inert gas and reducing atmosphere, wherein the inert gas is N2One or more of He and Ar, and reducing atmosphere is H2And one or more than two of CO, wherein the volume ratio of the inert gas to the reducing gas in the mixed gas is 100/10-0/100, and the treatment is carried out for 0.5-5 hours at the temperature of 20-350 ℃.
The method for obtaining more 8-ring cage B acid comprises the following steps: ammonium nitrate chloride carries out ion exchange on MOR for many times, so that alkali metal ions in the 8-ring cage are completely converted into B acid, in addition, a proper amount of pyridine is used for selectively occupying the position of a 12-ring pore channel, and then aluminum nitrate is used for carrying out aluminum supplement treatment on the 8-ring cage, so that more B acid sites are obtained.
The mechanical mixing can be carried out by one or more than two of mechanical stirring, ball milling, shaking table mixing and mechanical grinding.
A method for preparing ethylene by directly converting synthesis gas relates to a method for performing conversion reaction on the fixed bed or a moving bed by using the synthesis gas as a reaction raw material, wherein the adopted catalyst is the catalyst.
The pressure of the synthesis gas is 0.5-10MPa, preferably 1-8MPa, more preferably 2-8 MPa; the reaction temperature is 300-600 ℃, preferably 300-450 ℃; airspeed of 300-10000h-1Preferably 500--1More preferably 500--1。
The synthesis gas H for the reaction2The molar ratio/CO is between 0.2 and 3.5, preferably between 0.3 and 2.5.
The bifunctional composite catalyst is used for directly converting synthesis gas into ethylene or C2-C4 low-carbon olefin by one-step method, wherein the selectivity of ethylene reaches 75-80%, and meanwhile, the selectivity of byproduct methane is low (< 15%).
The invention has the following advantages:
(1) the invention is different from the traditional technology (MTO for short) for preparing low-carbon olefin by methanol, and realizes the one-step direct conversion of synthesis gas to prepare ethylene.
(2) The single ethylene product in the product has high selectivity which can reach 75-80%, and the method has high space-time yield, easy separation of the product and good application prospect.
(3) The catalyst of the present invention is different from the catalyst of the aforementioned patent application 201610600945.6 in that the content of B acid in the 8-membered ring cage of the component B in the catalyst is 0.01mmol/g-0.6mmol/g, the selectivity of catalyzing the conversion of synthesis gas to obtain single component ethylene is up to 75-80%, while the catalyst of the aforementioned 201610600945.6 can not satisfy the condition, so the catalytic reaction result is wider product, and the selectivity of ethylene is lower than 75%.
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 satisfied for achieving the purpose.
Example 1
Preparation of component A
Synthesizing a ZnO material with a polar surface by an etching method:
(1) 4 parts, 0.446g (1.5mmol) of Zn (NO) are weighed out separately3)2·6H2And O, respectively weighing 0.300g (7.5mmol), 0.480g (12mmol), 0.720g (18mmol) and 1.200g (30mmol) of NaOH in 4 containers, sequentially adding the weighed materials into the 4 containers, respectively weighing 30ml of deionized water, adding the weighed materials into the 4 containers, and stirring for more than 0.5h to uniformly mix the solution. Heating to 160 ℃, reacting for 20h, and decomposing the precipitate into zinc oxide; 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 ZnO oxide;
the product, 0.480g (12mmol) of NaOH used therein, was subjected to the following treatment:
(2) adopting an etching agent such as oleic acid, urotropine, ethylenediamine, ammonia water, hydrazine hydrate and the like, ultrasonically mixing the etching agent with ZnO oxide at normal temperature, soaking the ZnO oxide in the etching agent solution, and allowing the etching agent and zinc oxide to form a complex or direct reduction reaction;
and heating the suspended matter, taking out, washing and filtering to obtain the nano ZnO material with a large number of surface oxygen cavities.
In table 1: the mass ratio of the catalyst to the etchant is 1: 3. The mass ratio of the oleic acid to the urotropine is 1:1, no solvent is used, the mass ratio of the oleic acid to 5 wt% of hydrazine hydrate is 95:5, and no solvent is used; specific process conditions including etchant, temperature, process time and atmosphere type are shown in table 1 below.
(3) Drying or drying and reducing
Centrifuging or filtering the obtained product, washing with deionized water, drying or drying and reducing in an atmosphere of inert gas or a mixture of inert gas and reducing atmosphere, wherein the inert gas is N2One or more of He and Ar, and reducing atmosphere is H2And one or more of CO, wherein the volume ratio of the inert gas to the reducing gas in the drying and reducing mixed gas is 100/10-0/100, the temperature of the drying and reducing treatment is 350 ℃, and the time isAnd 4 h. Thus obtaining the ZnO material with the surface rich in oxygen vacancies. Specific samples and their preparation conditions are shown in table 1 below. Wherein surface oxygen vacancies are defined as (1-molar amount of oxygen atoms to theoretical stoichiometric oxygen molar content).
TABLE 1 preparation of ZnO materials and their parametric properties
The surface oxygen vacancy is the distance range from the surface of the crystal grain to the depth of the inner direction of the crystal grain, and the oxygen atom molar quantity accounts for the percentage of the theoretical stoichiometric oxygen molar content;
as comparative examples, ZnO4 having no oxygen vacancies on the surface, which was not etched in the step (2), and metallic Zn 5 in which Zn was completely reduced;
(II) synthesizing a MnO material with a polar surface by an etching method: the preparation process is the same as that of the product (1) corresponding to the amount of 0.480g (12mmol) of NaOH and the product (3) in the step (A), except that the precursor of Zn is replaced by the corresponding precursor of Mn, which can be one of manganese nitrate, manganese chloride and manganese acetate, and is manganese nitrate.
The etching treatment process is the same as the preparation process of the product ZnO 3 in the step (2) in the step (I), and a catalyst with a large number of surface oxygen vacancies is synthesized; surface oxygen vacancies 67%;
the corresponding product is defined as MnO 1;
(III) Synthesis of CeO with polar surface by etching2Materials: the preparation process is the same as that of the product (1) corresponding to the amount of 0.480g (12mmol) of NaOH and the product (3) in the step (A), except that the precursor of Zn is replaced by the corresponding precursor of Ce, and the precursor of Zn can be one of cerium nitrate, cerium chloride and cerium acetate, and is cerium nitrate.
The etching treatment process is the same as the preparation process of the product ZnO 3 in the step (2) in the step (I), and a catalyst with a large number of surface oxygen vacancies is synthesized; surface oxygen vacancies 56%;
the corresponding product was defined as CeO 1;
(IV) synthesizing the nano-particles with high specific surface area and high surface energyRice ZnCr2O4、ZnAl2O4、MnCr2O4、MnAl2O4,MnZrO4Spinel:
zinc nitrate, aluminum nitrate, chromium nitrate, manganese nitrate and zirconium nitrate are used as precursors and are mixed with urea in water at room temperature; and aging the mixed solution, taking out, washing, filtering and drying, and roasting the obtained solid in an air atmosphere to obtain the spinel oxide growing along the (110) crystal face direction. The sample is also processed by an etching method to synthesize a catalyst with a large number of surface oxygen vacancies; the etching treatment and the post-treatment processes are the same as those in (2) and (3) in the step (a), and the sample has large specific surface area and many surface defects and can be applied to catalytic synthesis gas conversion.
Specific samples and their preparation conditions are shown in table 2 below. Likewise, surface oxygen vacancies are defined as (1-molar amount of oxygen atoms to theoretical stoichiometric oxygen molar content).
TABLE 2 preparation of spinel materials and their Property parameters
(V) synthesizing nano FeAl with high specific surface area and high surface energy2O4、CoAl2O4Spinel: the preparation process is the same as (2) in the fourth step, except that the precursor of Zn is replaced by the corresponding precursor of Fe or Co, which can be one of ferric nitrate, ferric chloride and ferric citrate or one of cobalt nitrate, cobalt chloride and cobalt acetate, here, ferric nitrate and cobalt nitrate.
The etching treatment process is the same as the preparation process of the product ZnO 3 in the step (2) in the step (I), and a catalyst with a large number of surface oxygen vacancies is synthesized; 77% and 51% of surface oxygen vacancies;
the corresponding products are defined as spinel 6, spinel 7;
(VI) Cr2O3、Al2O3Or ZrO2Dispersed metal oxide
With Cr2O3、Al2O3Or ZrO2As carrier, preparing Cr by precipitation deposition2O3、Al2O3Or ZrO2A dispersed metal oxide. Taking the preparation of dispersed ZnO oxide as an example, commercial Cr is used2O3、Al2O3Or ZrO2The carrier is pre-dispersed in the base solution, and then zinc nitrate is adopted as the raw material to be mixed with sodium hydroxide precipitator for precipitation at room temperature, Zn2+In a molar concentration of 0.1M, Zn2+The mol part ratio of the organic silicon compound to the precipitant is 1: 6; then aging at 120 deg.C for 24 hr to obtain Cr2O3、Al2O3Or ZrO2ZnO oxide dispersed as a carrier.
The etching process is the same as the preparation process of the product ZnO 3 in the step (2) in the step (I), and a catalyst with a large number of surface oxygen vacancies is synthesized (the content of the dispersant in the component A is 0.2 wt%, 10 wt% and 90wt% in sequence); 25%, 30% and 65% of surface oxygen vacancies; the post-treatment process is the same as that of the step (3) in the step (a);
the corresponding product is defined as dispersed oxide 1-3 from top to bottom;
cr can be obtained in the same manner as described above2O3、Al2O3Or ZrO2MnO oxide dispersed as a carrier (the content of the dispersant in the catalyst A is 7 wt%, 30 wt% and 60 wt% in this order), surface oxygen vacancies 22%, 47% and 68%; the corresponding product is defined as dispersed oxide 4-6 from top to bottom.
Preparation of component II and component B (molecular sieve with MOR topological structure)
The MOR topological structure is an orthorhombic system, has a one-dimensional through hole structure with oval through holes which are parallel to each other, and comprises 8 circular rings and 12 circular rings which are parallel to each other, wherein 8 circular ring pockets are arranged on the side edge of a main hole of each 12 circular ring and communicated with each other.
The preparation process comprises the following steps:
according to n (SiO)2)/n(Al2O3)＝15,n(Na2O)/n(SiO2)＝0.2,n(H2O)/n(SiO2)＝26.
Mixing aluminum sulfate and sodium hydroxide solution, adding silica sol, stirring for 1h to obtain homogeneous initial gel, transferring the initial gel into a high-pressure synthesis kettle, statically crystallizing at 180 ℃ for 24h, quenching, washing and drying to obtain a mordenite sample, wherein the label of the mordenite sample is Na-MOR.
Mixing Na-MOR with 1mol/L ammonium chloride solution, stirring at 90 ℃ for 3h, washing, drying, continuously roasting at 450 ℃ for 6h for 4 times to obtain hydrogen-type mordenite.
Adsorbing the prepared molecular sieve with pyridine at 100Torr for 2h, treating in inert gas at 100 deg.C for 1h, stirring with aluminum nitrate solution (concentration: 1M) at room temperature for 8h, stirring at 60 deg.C for 2h, centrifuging for 1 time, oven drying at 140 deg.C, and air roasting at 380 deg.C for 1 h. Then using 1M ammonium nitrate solution and stirring for 3h at 80 ℃. And (4) centrifugal washing. And then drying at 140 ℃. In the above process, titanium sulfate or gallium nitrate may be used instead of aluminum nitrate.
The framework element composition of the molecular sieve with MOR topological structure prepared by the process can be one of Si-Al-O, Ga-Si-O, Ga-Si-Al-O, Ti-Si-O, Ti-Al-Si-O, Ca-Al-O, Ca-Si-Al-O;
the O element of partial skeleton is connected with H, and the corresponding products are sequentially defined as MOR 1-8;
TABLE 3 preparation of molecular sieves with MOR topology and their performance parameters
Preparation of catalyst
The component A and the component B 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 the atmosphere or directly in the air, wherein the atmosphere is as follows: a) nitrogen and/or inert gas, b) a mixed gas of hydrogen and nitrogen and/or inert gas, wherein the volume of hydrogen in the mixed gas is 5-50%, c) a mixed gas of CO and nitrogen and/or inert gas, wherein the volume of CO in the mixed gas is 5-20%, d) O2Mixed with nitrogen and/or inert gases, in which O2The 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.
Mechanical stirring: in the stirring tank, the A component and the B component are mixed by a stirring rod, and the mixing degree and the relative distance of the A component and the B component can be adjusted by controlling the stirring time (5min-120min) 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 A component and the B component are dispersed and mixed. The particle size and relative distance of the catalyst can be adjusted by controlling the proportion (mass ratio range: 20-100:1) of the abrasive (material can be stainless steel, agate and quartz, size range: 5mm-15mm) and the catalyst.
A shaking table mixing method: premixing the component A and the component B, and filling the mixture into a container; mixing the component A and the component B by controlling the reciprocating oscillation or the circumferential oscillation of the shaking table; by adjusting the oscillation speed (range: 1-70 rpm) and time (range: 5min-120min), uniform mixing is achieved and the relative distance is adjusted.
Mechanical grinding method: premixing the component A and the component B, and filling the mixture into a container; under a certain pressure (range: 5 kg-20 kg), the mixed catalyst is relatively moved by the grinder (speed range: 30-300 r/min), so as to adjust the particle size and relative distance of the catalyst and realize uniform mixing.
Specific catalyst preparations and their parametric characteristics are shown in table 6.
TABLE 4 preparation of the catalyst and its 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 quantitative 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 H2Raising the temperature to 300 ℃ in the atmosphere, and switching the synthesis gas (H)2The mol ratio of/CO is 0.2-3.5), the pressure of the synthetic gas is 0.5-10MPa, the temperature is raised to the reaction temperature of 300-. The product was analyzed by on-line chromatographic detection.
The reaction performance can be varied by varying the temperature, pressure and space velocity. The selectivity of the low-carbon olefin (one or more than two of ethylene, propylene and butylene) in the product can reach 80-90 percent, and the conversion rate of the raw material is 10-60 percent; because the surface hydrogenation activity of the catalyst metal compound is not high, the generation of a large amount of methane is avoided, the methane selectivity is low, and the selectivity of ethylene reaches 75-80%.
TABLE 5 use of the catalyst and its Effect
The catalyst adopted in the comparative example 3 is component A metal ZnCo + MOR3, the mole ratio of ZnCo is 1:1, ZnCo and 1 are mixed according to the mass ratio of 1:1, the rest parameters and the mixing process are the same as the catalyst C.
Comparative example 4 the catalyst used was surface oxygen-free-cavity TiO2+ MOR3, the remaining parameters and the mixing were equivalent to catalyst C.
Comparative example 5 used a catalyst in which the molecular sieve was a commercial SAPO-34 available from southern kaiki university catalyst plant.
The catalyst used in comparative example 6 was a commercial ZSM-5, full pore structure, with Si/Al of 30, available from catalyst works of south opening university.
The reaction results of comparative examples 5 and 6 show that the topology of MOR is critical to the modulation of product selectivity, the pore structure of SAPO34 mainly produces more C3 products and not high ethylene selectivity, while the pore structure of ZSM5 is suitable for producing C4 hydrocarbons and even longer carbon chain hydrocarbons. In contrast, the 8-membered ring structure of MOR is more suitable for the predominant production of ethylene, and has advantageous properties not possessed by molecular sieves of other structures.
It can be seen from the above table that the content of LF type B acid centers in the 8-membered ring of the MOR molecular sieve significantly affects the selectivity to ethylene. The corresponding catalyst implementation results C, D, J, K, Q, R, S, T, Z4, Z5, Z7, Z8, Z9 show an advantageous ethylene selectivity and space-time yield, since they satisfy both the optimum oxygen vacancies and the content of acid in the 8-membered ring cage at the same time, and the mass ratio of the two is satisfactory. Other samples cannot simultaneously meet the requirements, so that high space-time yield and selectivity cannot be obtained, and the content and matching relationship of the two components in the bifunctional catalyst are very important to the performance.
The above examples are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications can be made without departing from the spirit and principles of the invention, and are intended to be within the scope of the invention.
Claims (14)
1. A catalyst is composed of a component A and a component B, wherein the component A and the component B are compounded together in a mechanical mixing mode, the active component of the component A is a metal oxide, and the component B is a molecular sieve with an MOR topological structure, and is characterized in that: in the component B, the content of B acid in the molecular sieve eight-membered ring cage with the MOR topological structure is 0.01mmol/g-0.6 mmol/g; in the active components of the component A, the metal oxides are MnO and MnCr2O4、MnAl2O4、MnZrO4、ZnO、ZnCr2O4、ZnAl2O4、CeO2、CoAl2O4、FeAl2O4One or more than two of them;
the framework element composition of the MOR topological structure molecular sieve is one or more than two of Si-Al-O, Ga-Si-O, Ga-Si-Al-O, Ti-Si-O, Ti-Al-Si-O, Ca-Al-O, Ca-Si-Al-O.
2. The catalyst of claim 1, wherein: the content of B acid in the molecular sieve eight-membered ring cage with the MOR topological structure is 0.1-0.6 mmol/g.
3. The catalyst of claim 2, wherein: the content of B acid in the molecular sieve eight-membered ring cage with the MOR topological structure is 0.25-0.6 mmol/g.
4. The catalyst of claim 1, wherein: in the active components of the component A, the metal oxides are MnO and MnCr2O4、MnAl2O4、MnZrO4、ZnAl2O4、CeO2、CoAl2O4、FeAl2O4One or more than two of them.
5. The catalyst of claim 1, wherein: in the active components of the component A, the metal oxides are MnO and MnCr2O4、MnAl2O4, MnZrO4、CeO2、CoAl2O4、FeAl2O4One or more than two of them.
6. The catalyst of claim 1, wherein: the weight ratio of the active component in the component A to the component B is 0.1-20.
7. The catalyst of claim 1, wherein: the weight ratio of the active component in the component A to the component B is 0.3-8.
8. The catalyst according to any one of claims 1 to 4, characterized in that: the depth of the metal oxide in the direction from the surface of the crystal grain to the inside of the crystal grain is 0.3nm, and the surface oxygen vacancy is 20% or more.
9. The catalyst according to any one of claims 1 to 4, characterized in that: the component A is also added with a dispersant, and the dispersant is Al2O3、SiO2、Cr2O3、ZrO2、TiO2、Ga2O3One or more than two of the components, the metal oxide is dispersed in the dispersant, the content of the dispersant in the component A is 0.05 to 90 weight percent, and the rest is the metal oxide.
10. A method for preparing ethylene by directly converting synthesis gas is characterized in that: the synthesis gas is used as reaction raw material, conversion reaction is carried out on a fixed bed or a moving bed, and the adopted catalyst is the catalyst of any one of claims 1 to 9.
11. The method of claim 10, wherein: the pressure of the synthesis gas is 0.5-10 MPa; the reaction temperature is 300-600 ℃; airspeed of 300-10000h-1。
12. The method of claim 11, wherein: the pressure of the synthesis gas is 1-8 MPa; the reaction temperature is 300-450 ℃; the space velocity is 500--1。
13. The method of claim 10, wherein: the synthesis gas is H2Mixed gas of/CO, H2The mol ratio of/CO is 0.2-3.5.
14. The method of claim 13, wherein: h2The mol ratio of/CO is 0.3-2.5.
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