124results about "Ethylene production" patented technology

Disclosed are a fluidized bed separation method and device for methanol-to-olefins quenched water. The method may subject quenched water to liquid-solid separation via a micro-cyclone separator. The method may also subject clear liquid from the micro-cyclone separator to a secondary separation via a fluidized bed separator, then sending the same to an olefin separation device, then recovering some waste heat of the quenched water, and then returning the same to a quenching tower after performing heat exchange. The method may also regenerate a separation medium by reversely feeding stripping tower purified water or quenched water, so as to release catalyst particles absorbed by the separation medium. The method may also send a catalyst slurry concentrated by the micro-cyclone separator and the fluidized bed separator to a filter-press unit for filter-press dehydration, so as to recover a catalyst.

The present invention relates to a zeolitic material having an AEI-type framework structure comprising SiO2, Al2O3 and B2O3, wherein the Al:B molar ratio of the zeolitic material, is comprised in the range of from 3 to 500, and wherein the zeolitic material displays an Si:(Al+B) molar ratio of the zeolitic material, which is comprised in the range of from 2 to 11. The present invention also relates to a process for the preparation of the zeolitic material according to the present invention, to a process for the treatment of NOx by selective catalytic reduction and to an apparatus for the treatment of a gas stream containing NOx, as well as to the use of a zeolitic material according to the present invention.

The present application relates to the technical field of molecular sieve preparation, and particularly relates to a mesoporous pore size adjustable SAPO-34 / pure silicon molecular sieve and a preparation method thereof, which comprises the following steps: uniformly stirring an aluminum source, a silicon source, a phosphorus source, a structure directing agent and distilled water to obtain an initial gel; placing the initial gel in a reaction kettle and performing hydrothermal crystallization in a static oven; sequentially performing filtration, washing, drying and calcination on the obtained product to obtain a SAPO-34 molecular sieve; adding the SAPO-34 molecular sieve into a functional solution of a cationic surfactant, performing water bath heating, and sequentially performing filtration, washing, drying and calcination on the obtained product to obtain a mesoporous pore size adjustable SAPO-34 / pure silicon molecular sieve; wherein the functional solution of the cationic surfactant comprises a cationic surfactant, an organic alcohol, a silicon source, an organic base and distilled water. The preparation method of the present application significantly improves the service life of the SAPO-34 / pure silicon molecular sieve as a catalyst in MTO reaction and the selectivity of the SAPO-34 / pure silicon molecular sieve to low carbon olefins.

A fluidized catalytic cracking unit system includes: a fluidized catalytic cracking unit assembly including a first catalyst regenerator and a cracking unit, the cracking unit configured to output spent catalyst to the first catalyst regenerator; and a reformer-electrolyzer-purifier assembly comprising a reformer-electrolyzer-purifier cell, the reformer-electrolyzer-purifier cell comprising an anode section and a cathode section.

Provided are (1) a method for converting ethanol, comprising contacting a raw material mixture containing ethylene and ethanol with a catalyst in an adiabatic reactor to obtain a reaction gas containing an olefin having 3 or more carbon atoms, (2) a method for converting ethanol, comprising contacting a raw material mixture containing methanol and ethanol with a catalyst in an adiabatic reactor to obtain a reaction gas containing an olefin having 3 or more carbon atoms, and (3) a method for converting ethanol, comprising: contacting a raw material mixture containing ethanol and ethylene with a catalyst in an adiabatic reactor to obtain a reaction gas containing an olefin having 3 or more carbon atoms; separating the reaction gas into fraction A mainly containing a hydrocarbon having 2 to 3 carbon atoms and fraction B mainly containing a hydrocarbon having 4 to 6 carbon atoms by a first distillation column; and recycling at least a portion of the fraction A as a portion of the raw material mixture to the reaction step.

The application discloses a preparation method of MTO catalyst. The method comprises the following steps: a) treating a phosphosilicate aluminosilicate molecular sieve in a titanium acid ester-containing alcohol solution, and drying to obtain a modified molecular sieve; b) mixing the modified molecular sieve obtained in the step a), a liquid medium, a matrix material, a structure reinforcing material and a binder to form a suspension; the structure reinforcing material is ceramic fiber with a diameter of 2-6 microns and a length-diameter ratio of 1-15; c) high-speed shearing the suspension obtained in the step b), and spray drying to obtain a microsphere catalyst; and d) calcining the microsphere catalyst obtained in the step c) to obtain a finished catalyst. The catalyst solves the problems of poor catalytic performance and high abrasion index of the fluidized bed catalyst in the prior art.

The present application relates to the technical field of adsorbent preparation, in particular to a preparation method and application of an adsorbent for purifying oxygen-containing compounds in an olefin stream. The preparation method comprises the following steps: (1) first, adding alumina to an alkali metal solution to modify it, filtering and drying the modified alumina to obtain modified alumina balls; (2) adding molecular sieves to a solution containing transition metal ions to perform ion exchange modification, filtering, washing, and drying the modified molecular sieves; (3) adding the modified alumina balls into a sugar bowl, then adding the obtained modified molecular sieves, adding a binder and water, and performing ball forming; (4) drying and activating the formed adsorbent to obtain a finished product. Compared with existing adsorbents, the adsorbent has the advantages of simple preparation, high adsorption precision, low adsorption heat, simple regeneration operation, low energy consumption, and the like.

This invention discloses a method for preparing zeolite molecular sieves with precisely adjustable particle size, comprising the following steps: (1) adding aluminum source and other raw materials to deionized water and stirring evenly at room temperature; (2) adding silicon source, stirring at room temperature, and then adding template agent to obtain precursor slurry; (3) adding zeolite molecular sieve, the amount of zeolite molecular sieve being 1-15 mg / g of precursor slurry, transferring the precursor slurry to a high-pressure reactor, fixing it on a homogeneous reactor, heating to 0-150℃, maintaining for 1-200 h, and then heating to 160-230℃ for 3 hours to crystallize for 6-96 h; (4) obtaining zeolite molecular sieve after centrifugal washing, drying, and calcination. The innovation of the preparation method of this invention lies in the first use of a two-stage synthesis method, which can gradually reduce the particle size of the zeolite molecular sieve product while increasing the yield of zeolite molecular sieves. This method successfully synthesized SAPO-34 zeolite molecular sieve with a particle size deviation of less than 0.4 μm and ZSM-5 zeolite molecular sieve with a particle size deviation of less than 0.2 μm.

A processing facility is provided that includes a feedstock separation system configured to separate a feed stream into a light stream and a heavy stream, a hydrogen production system configured to produce hydrogen and carbon dioxide from the light stream, and a carbon dioxide conversion system configured to produce synthetic hydrocarbons or carbon dioxide. The processing facility also includes a hydrotreating system configured to process the heavy stream, and a hydrotreater separation system configured to separate the hydrotreating system effluent into a separator tops stream and a separator bottoms stream, the separator bottoms stream being fed to the hydrogen production system.

According to the nano SAPO-34 molecular sieve and the normal-pressure synthesis method and application thereof, the method for synthesizing the nano SAPO-34 molecular sieve under the normal pressure adopts a dry gel conversion method and combines seed crystal induction to synthesize the nano SAPO-34 molecular sieve under the normal pressure, so that potential safety hazards and high equipment cost of a traditional high-pressure process are avoided; integration of molecular sieve synthesis and performance evaluation can be realized on the same reactor; meanwhile, the particle size and crystallinity of the molecular sieve can be effectively controlled and improved by adjusting the input amount of the seed crystal, and the obtained nano SAPO-34 molecular sieve is small in product particle size, uniform in distribution, high in specific surface area, high in crystallinity and excellent in stability, and shows excellent performance of low carbon deposition rate and long catalytic life when being applied to a methanol-to-olefin reaction. The mild synthesis route can provide a potential way for preparation of other molecular sieves.

The invention provides a preparation method and application of an SAPO-34 molecular sieve. The preparation method of the SAPO-34 molecular sieve provided by the invention comprises the following steps: S1, carrying out first high-speed shear mixing on a used methanol-to-olefin catalyst, an aluminum source, a phosphorus source and an optional silicon source to obtain first gel; s2, performing second high-speed shearing mixing on the first gel and a template agent to obtain second gel; and S3, carrying out crystallization treatment on the second gel. According to the method provided by the invention, resource utilization of the main MTO catalyst after service can be realized, the problem of utilization of the MTO catalyst after service is efficiently and greenly solved, and meanwhile, the prepared SAPO-34 molecular sieve can still keep relatively high catalytic performance when being applied to a methanol-to-olefin reaction.

The invention relates to the technical field of preparation of olefin by methanol conversion, and discloses an SAPO-34 molecular sieve, a preparation method thereof and application of the SAPO-34 molecular sieve in a methanol-to-olefin process. The method comprises the following steps: (1) mixing melamine with water to obtain a mixed solution of melamine and water, and then mixing the mixed solution of melamine and water with an aluminum source, a silicon source, a phosphorus source, a template agent and water to obtain a mixture; and (2) mixing the mixture obtained in the step (1) with polyoxyethylene sorbitan fatty acid ester, carrying out hydrothermal crystallization reaction, and then sequentially separating, drying and roasting the obtained molecular sieve stock solution. The prepared SAPO-34 molecular sieve can improve the catalytic activity and selectivity to low-carbon olefins in a methanol-to-olefin reaction, can accommodate more carbon deposits, can effectively delay the deactivation speed caused by the carbon deposits, and further significantly prolongs the service life of a catalyst, and the method has the advantages of simple process, mild reaction conditions and low cost, and is suitable for industrial production. The method has obvious economic value and wide application prospect.

The present invention relates to the field of chemical technology, and discloses a reactor for preparing light olefins, comprising a cyclone body and a flow guide cylinder, wherein a cyclone chamber is provided in the cyclone body, a cyclone channel for a cyclone of raw gas to enter the cyclone chamber is provided on the circumferential wall of the cyclone body, and the cyclone chamber has a reaction area close to the circumferential wall of the cyclone chamber; the flow guide cylinder comprises an annular wall, which is arranged around the circumferential wall of the cyclone body, and an annular flow guide chamber is formed between the annular wall and the circumferential wall, and a raw gas inlet for the raw gas to enter the annular flow guide chamber is provided on the annular wall, wherein: a first end of the annular wall is provided with a product gas discharge port and a catalyst inlet respectively connected to the cyclone chamber, and a second end of the annular wall is provided with a catalyst outlet connected to the cyclone chamber. The reactor for preparing light olefins can enable the raw gas and the catalyst to react rapidly under cyclone operation, thereby reducing side reactions and improving the selectivity of the target product.

Methods for producing olefins through hydrocarbon steam cracking include passing a hydrocarbon feed that includes one or more hydrocarbons to a hydrocarbon cracking unit and passing one or more sulfur-containing compounds to the hydrocarbon cracking unit. The sulfur-containing compounds include at least hydrogen sulfide gas, and a flow rate of the sulfur-containing compounds to the hydrocarbon cracking unit is sufficient to produce a molar concentration of elemental sulfur in the hydrocarbon cracking unit of from 10 ppm to 200 ppm. The methods include cracking the hydrocarbon feed in the hydrocarbon cracking unit to produce a cracker effluent and contacting the cracker effluent with a quench fluid in a quench unit to produce at least a cracked gas and a first pygas. The first pygas has a concentration of carbon disulfide less than 50 ppmw based on the total mass flow rate of the first pygas.

The present invention relates to a catalyst for preparing a light olefin, a preparation method therefor, and a method for preparing a light olefin by using same, and can provide a catalyst for preparing a light olefin, a preparation method therefor, and a method for preparing a light olefin by using same, the catalyst comprising a porous zeolite, a clay, an inorganic oxide binder, and Ag2O and P2O5 which are supported in the pores and / or on the surface of the porous zeolite.

The invention relates to an integrated method for thermal conversion and indirect combustion of a heavy hydrocarbon feedstock in a redox chemical loop for producing hydrocarbon streams. The heavy hydrocarbon feedstock (1) is brought into contact with inert particles (2) in a thermal conversion zone (100). Thermal conversion in the absence of hydrogen, water vapour and a catalyst produces a first gaseous effluent of hydrocarbon compounds (4) and coke, which effluent is deposited on the inert particles (5). The latter is then burned in a redox chemical loop (200) in the presence of oxygen-carrying solid particles (6). The inert particles thus flow between the thermal conversion zone (100) and a reduction zone (300) of the chemical loop while the oxygen-carrying solid particles flow between the oxidation (400) and reduction zones (300) of the chemical loop.

The invention relates to the field of molecular sieves, in particular to a surface silicon-poor nano SAPO-34 molecular sieve as well as a preparation method and application thereof. The method comprises the following steps: (1) mixing an SAPO-34 molecular sieve seed crystal with a template agent, and then carrying out first pretreatment to obtain a mixture A; (2) mixing an aluminum source, a silicon source, a phosphorus source and water, and then performing second pretreatment to obtain a mixture B; (3) mixing the mixture A with the mixture B to obtain initial gel; and (4) carrying out rapid heating and hydrothermal crystallization on the initial gel, and then washing and roasting the obtained solid product to obtain the surface silicon-poor nano SAPO-34 molecular sieve. According to the preparation method, an expensive template agent or other organic additives do not need to be added, the process is easy to operate, and the SAPO-34 molecular sieve obtained by the method has the characteristics of nanoscale particle size and poor silicon on the surface of a crystal phase; the catalyst has the advantages of long service life, high selectivity of ethylene and propylene and high ratio of ethylene selectivity to propylene selectivity when catalyzing methanol to prepare olefin.

The present disclosure provides a method of preparing olefins from methanol, in which methanol and phenol-like molecules are used as raw material, which is gasified and then passed into a two-stage fixed-bed catalytic reactor. The raw material reacts with a catalyst A (silica-aluminum molecular sieve) and a catalyst B (silica-aluminum or phosphorus-aluminum molecular sieve) in sequence to produce ethylene. The method of the present disclosure has a high selectivity, which using phenol-like molecules as a molecular catalyst, and a catalytic reaction by co-feeding methanol and the phenol-like molecules. After gasification of the raw material, the raw material is brought into the reactor by an inert gas, and after a two-stage catalyst system, the selectivity of ethylene reaches more than 90%, which solves the problem of the products separation in the current process. In addition, the process described in the present disclosure has a good stability. A little coke is formed in catalyst during the reaction, which solves the problem that the catalyst is required to be regenerated repeatedly.

The invention discloses a methanol-to-olefin production safety anomaly detection method based on an LSTM algorithm. The method comprises the following steps: acquiring methanol-to-olefin real-time process parameters and control instruction data; preprocessing the process parameters and the control instruction data to obtain a training set and a test set; constructing a reconstruction model based on the multilayer LSTM network, and carrying out training learning on the reconstruction model by adopting the training set to obtain a joint normal model; inputting the test set into the joint normal model, and calculating and outputting a reconstruction error of the test set and the test set in real time; and establishing a multi-stage abnormal response mechanism. According to the method, by analyzing the joint change mode of the multi-dimensional time sequence data, the complex abnormal condition can be accurately identified, the high-efficiency detection of the potential safety hazard in the olefin production process is realized, and the defect that the traditional method is difficult to fuse the multi-dimensional information and accurately identify the complex abnormal condition is overcome.

The application provides a kind of hollow SAPO-34 molecular sieve prepared by using aluminum phosphate with kanemite structure and its preparation method and application, characterized by using aluminum phosphate with kanemite structure as aluminum source and phosphorus source, and grinding and mixing with silicon source, template agent and a small amount of water, then adding into hydrothermal kettle to synthesize SAPO-34 molecular sieve with hollow structure. The synthesis method of the hollow SAPO-34 molecular sieve of the application can form hollow structure without acid-base post-treatment process or adding mesoporous template agent, the process is simple, which is beneficial to industrial scale production; and the formation of hollow structure is beneficial to diffusion mass transfer and heat conduction in methanol to olefin reaction. The SAPO-34 molecular sieve prepared by the method has a selectivity of ethylene and propylene as high as 85% in methanol to olefin reaction, and the service life reaches more than 400 minutes, which is beneficial to industrial application.

To provide a method for converting ethanol, and a method for producing hydrocarbon.SOLUTION: Provided are (1) a method for converting ethanol including bringing mixed raw material containing ethylene and ethanol in contact with a catalyst in an adiabatic reactor to obtain reaction gas containing olefin having carbon number 3 or more, (2) a method for converting ethanol including bringing mixed raw material containing methanol and ethanol in contact with a catalyst in an adiabatic reactor to obtain reaction gas containing olefin having carbon number 3 or more, and (3) a method for converting ethanol including bringing a mixed raw material containing ethanol and ethylene in contact with a catalyst in an adiabatic reactor to obtain reaction gas containing olefin having carbon number 3 or more, separating the reaction gas into fraction A which mainly contains hydrocarbon having carbon number 2 to 3 and fraction B which mainly contains hydrocarbon having carbon number 4 to 6 by a first distillation tower, and recycling at least a part of fraction A to the reaction step as a part of the mixed raw material.SELECTED DRAWING: Figure 1

The invention provides a method for preparing low-carbon olefin from C4 hydrocarbon, which comprises the following step: carrying out catalytic cracking reaction on a raw material system containing C4 hydrocarbon and methanol at 240-430 DEG C to obtain the low-carbon olefin. According to the method for preparing the low-carbon olefin from the C4 hydrocarbon, provided by the invention, the C4 hydrocarbon and the methanol are taken as raw materials, the temperature of the catalytic cracking reaction can be reduced, the energy consumption is relatively low, and the yield of the low-carbon olefin is relatively high.

An integrated process for producing light olefins is disclosed. The integrated process comprises passing a syngas stream and a hydrogen stream to a methanol synthesis section to provide a reactor effluent comprising methanol. The reactor effluent is separated into a vapor stream and a liquid stream comprising methanol. The liquid stream comprising methanol is passed to a methanol purification section comprising at least two distillation columns, a first distillation column and a second distillation column to provide a methanol product stream. At least a portion of the methanol product stream is passed to an oxygenate conversion unit to provide an effluent comprising olefins. The reboiling heat to said the first distillation column and the second distillation column is provided from the separation section of the oxygenate conversion unit.

The present invention provides a method for reducing the impact of a polyethylene unit shutdown on the production of an olefin separation unit. The method and system provided by the present invention can significantly reduce the impact of a polyethylene unit shutdown on the production of an olefin separation unit. The method comprises: when the polyethylene unit is in operation, passing liquid ethylene from the ethylene tank area through an ethylene vaporization unit to exchange heat with the propylene flow from a propylene refrigeration compressor to obtain gaseous ethylene; heating and vaporizing unqualified ethylene from the ethylene tank area through an ethylene emergency vaporizer and then feeding it to an ethylene recycling unit for recycling; passing the purge gas from the polyethylene unit to a refining stripping tower of the olefin separation unit for use as stripping gas; and when the polyethylene unit is in operation, passing the gaseous ethylene from the top of the ethylene tank area to an ethylene vaporization unit to exchange heat with the propylene flow from the propylene refrigeration compressor, and then feeding it to the ethylene recycling unit for recycling and / or feeding it to a refining stripping tower for use as stripping gas.

The present application relates to the industrial MTO reaction depth and catalyst activity intelligent control method and device. Among them, the control method is to obtain the operation data of MTO production device, set the optimization target of MTO production, take the reaction residue content as the variable reflecting the reaction depth, calculate the reaction residue content optimization value and the reaction coke rate optimization value to realize the optimization target, adopt the automatic control algorithm or the automatic control model, calculate the regeneration air flow regulating valve valve position optimization value and the regeneration slide valve valve position optimization value to realize the reaction residue content optimization value and the reaction coke rate optimization value respectively, and control the regeneration air flow regulating valve valve position and the regeneration slide valve valve position. The device is provided with an intelligent optimization controller, the operation data is obtained through the DCS of MTO production device, the regeneration air flow regulating valve valve position optimization value and the regeneration slide valve valve position optimization value under the optimization target are calculated according to the intelligent control model, and the corresponding optimization control is realized through the DCS.

An integrated process for producing light olefins is disclosed. The integrated process includes passing a syngas stream and a hydrogen stream to a methanol synthesis section to provide a reactor effluent comprising methanol. The reactor effluent is separated into a vapor stream and a liquid stream comprising methanol. A liquid stream comprising methanol is passed to a methanol purification section comprising at least two distillation columns, a first distillation column and a second distillation column, to provide a methanol product stream. At least a portion of the methanol product stream is passed to an oxygenate conversion unit to provide an effluent comprising olefins. Reboiling heat is provided to the first and second distillation columns from a separation section of the oxygenate conversion unit.

The present application relates to a kind of synthetic gas olefin starting system and starting method, synthetic gas olefin starting system includes fluidized bed reactor, also includes: water pipe, steam drum, control system, control system is linked with the control valve on each water pipe, for making steam and boiler water with cascade flow regulation mode control bed temperature after the domestication of synthetic gas olefin late stage.The present application is suitable for the starting stage of synthetic gas olefin technical device, mainly for the adjustment of reactor bed temperature;The present application uses the cascade process of steam and boiler water combination, utilizes the characteristics of steam temperature sensible heat small, heat absorption little, can realize the reasonable transition of heat removal means in the domestication stage, finally realizes gradually input water pipe;The present application can meet the requirement of bed temperature in domestication stage, avoid bed layer sudden drop, energy saving while can avoid the alternate condition of equipment, simultaneously, the present application can avoid catalyst bed layer when bed temperature rises too fast, fly temperature.

The application provides a system for producing low-carbon olefins from methanol and a preparation method thereof, and belongs to the technical field of petroleum chemical industry, and solves the problems of small processing capacity, small operation flexibility and high energy consumption of the existing fluidized dense bed layer methanol low-carbon olefin device. It comprises a riser reactor, the riser reactor is connected with a reaction settler, the reaction settler is communicated with a regenerator, the bottom of the regenerator is connected with a regeneration inclined pipe communicated with the riser reactor, the reaction settler is communicated with a first external heat exchanger, and the first external heat exchanger is communicated with the riser reactor. The mixed gas generated by the reaction enters the reaction settler for separation of products and catalysts, the regenerator performs decoking treatment on the catalyst, and finally the catalyst is introduced into the riser reactor again to continue the reaction; the first external heat exchanger is arranged to introduce part of the cooled catalyst into the riser reactor to reduce the temperature, and the reaction time and the requirement of reaction depth can be flexibly adjusted according to the change of the methanol processing capacity.

The invention belongs to the field of catalysts, and particularly relates to a fluorinion-assisted SAPO-34 catalyst as well as a preparation method and application thereof. In the invention, pseudo-boehmite or aluminum isopropoxide is used as an aluminum source, phosphoric acid is used as a phosphorus source, white carbon black or silica sol is used as a silicon source, triethylamine or tetraethylammonium hydroxide is used as an organic template agent, and fluorine is hydrofluoric acid or ammonium fluoride. The SAPO-34 molecular sieve is synthesized by adopting a traditional hydrothermal method. The preparation method comprises the following steps: adding the raw materials into a beaker, stirring at room temperature to form uniform gel, transferring the gel into a reaction kettle, and crystallizing at 170-200 DEG C for 24-72 hours; and after the reaction is finished, centrifuging, washing and drying the solid product overnight, and calcining the dried sample in a muffle furnace at 550-600 DEG C for 6 hours to remove the template agent, thereby obtaining the molecular sieve catalyst. On the basis, the catalytic performance of the SAPO-34 catalyst in catalysis of methanol to olefin reaction is improved.

Method for carrying out a reaction I, wherein a raw material comprising methanol and / or dimethyl ether and toluene is contacted in a reactor with a catalyst obtained in an in-situ and in-line process to produce light olefins with a co-product of paroxylol, where reaction I is intended to produce light olefins from methanol and / or dimethyl ether and toluene with the co-product paroxylol, wherein a material stream I is brought into contact with the catalyst in the reaction system to obtain a material stream II, and C4 olefin or C 5+ Chain hydrocarbons are separated from material stream II, and the light olefins and paraxylene separated from material stream II and returned to the reaction system are used as products. the material stream I contains methanol and / or dimethyl ether and toluene, wherein the reaction system comprises: a first reaction zone containing a catalyst A; and a second reaction zone containing a catalyst B; and wherein catalyst A is an HZSM-5 molecular sieve catalyst modified by a phosphorus reagent and a silylation reagent, wherein the specific preparation steps are as follows: (A1) A mixture of the phosphorus reagent, the silylation reagent and toluene is fed into the first reaction zone with the HZSM-5 molecular sieve at a temperature in the range of 130°C to 500°C; (A2) The temperature is increased to over 500°C and the mixture is calcined in an air atmosphere for a period of 1 hour to 6 hours to obtain catalyst A, wherein catalyst B is an HZSM-5 molecular sieve catalyst modified by a silylation reagent, the specific preparation steps being as follows: (B1) A mixture of the silylation reagent and methanol is fed into the second reaction zone with the HZSM-5 molecular sieve at a temperature in the range of 120°C to 250°C; (B2) The temperature is increased to over 500°C and the mixture is calcined in an air atmosphere for a period of time ranging from 1 hour to 6 hours to obtain catalyst B.