CN1323753C - Catalyst used for preparing phenylethylene and its application - Google Patents

Abstract

The invention discloses a catalyst for preparing styrene and its application. Its components and mass percentage content include: 79-90% of nano-carbon fiber, 9-20% of iron or vanadium oxide, and 1%-10% of additives. The catalyst of the invention can prepare styrene by using carbon dioxide and ethylbenzene as raw materials, and the selectivity of the obtained styrene and the stability of the catalyst are higher than those of other supports.

Description

A kind of catalyst for preparing styrene and its application

technical field

The invention relates to a catalyst for the preparation of styrene, in particular to a catalyst for the preparation of styrene, which uses nano-carbon fiber as a carrier, iron or vanadium oxide as an active component, and adds transition metals and alkaline earth or alkali metals as auxiliary agents. and its preparation method.

Background technique

Styrene is a very important chemical raw material. It is usually obtained by high-temperature dehydrogenation of ethylbenzene in the presence of excess water vapor, using potassium as an auxiliary agent, and Fe oxides. The process consumes high energy and is affected by thermodynamics. Equilibrium limitation, the catalyst is easy to coke, and the use of carbon dioxide instead of superheated steam is expected to reduce energy loss, increase conversion and selectivity, but the key to using carbon dioxide to replace superheated steam to prepare styrene is to synthesize a stable and high selectivity Sexual catalysts have not been reported yet.

Contents of the invention

The technical problem to be solved in the present invention is to disclose a catalyst for preparing styrene and its application, so as to meet the needs of relevant departments.

Technical concept of the present invention is such:

Tubular carbon nanofibers show good prospects in the fields of composite material reinforcement, battery electrode material, new hydrogen storage material and catalyst carrier. As far as carbon nanofibers are used as catalyst supports, many applied results have been obtained through research, such as: (M.S.Hoogenraad, R.A.G.M.van Leeuwarden, G.J.B.van Breda Vriesman, A.Broersma, A.J.van dillen and J.W.Geus, Studies Surf .Sci.Catal., 1994, 91:263;

A. Chambers T. Nemes, N.M. Rodriguez and R.T.K. Baker, J. Phys. Chem. B, 102: 12 (1998), 2251; C. Park and R. T. K. Baker, J. Phys. Chem. B, 102: 26 (1998), 5168 ; A. Chambers and R.T.K. Baker, J. Phys. Chem. B, 103:13 (1999), 2454; R. Gao, C.D. Tan and R.T.K. Baker, Catal. Today 65 (2001) 19). Therefore, due to the superior physical and chemical properties of carbon nanofibers, it is expected to replace conventional supports to improve the conversion rate and selectivity of catalysts.

The catalyst for the preparation of styrene of the present invention uses carbon nanofibers as a carrier, iron or vanadium oxides as active components, and the components and mass percentages include:

Nano carbon fiber 79-90%

Oxides of iron or vanadium 9-20%

Auxiliary 1%-10%

Auxiliaries are selected from alkali metals, alkaline earth metals or transition metals;

The alkali metal is preferably K, Na, or Li;

Alkaline earth metals are preferably Ca, Mg or Ba;

The transition metal is preferably Mn, Cr, Ce, La or Zn;

The so-called carbon nanofiber is a porous carbon material with a certain hardness, which has a large specific surface area and pore volume, a small density, a small number of micropores, a relatively uniform fibrous structure, and a controllable surface affinity. And, high mechanical strength and other physical and chemical properties.

Heterogeneous catalytic reactions widely exist in the fields of petroleum, petrochemical and chemical industries. The characteristic of the reaction system is the presence of a solid catalyst and fluid state reactants and products. In a heterogeneously catalyzed reaction, the reaction takes place at the interphase surfaces, ie the fluid and the inner surface of the catalyst. Therefore, the performance of the catalyst support largely affects the performance of the catalyst. In particular, the surface area of the catalyst support and its interaction with the active metal will affect the outcome of the catalytic reaction. In addition, the purity of the catalyst support and the purity of the active metal also affect the selectivity of the reaction. Generally speaking, the catalytic performance is usually proportional to the surface area of the catalyst, therefore, the catalyst pursues a higher specific surface area. The adsorption and desorption rates of reactants on the catalyst surface during the reaction are often related to the pore structure of the catalyst support.

Specifically, the nano-carbon fiber carrier involved in this patent has few micropores, most of which are mesopores and macropores, and the atomic arrangement on the surface of the nano-carbon fiber is conducive to the formation of a special interaction between the active metal and the carrier. Carbon nanofibers with three different arrangements of graphite sheets can be obtained by catalytic chemical vapor deposition, which are called fishbone, tubular and flat carbon nanofibers. The different structures depend on the corresponding catalyst, reaction temperature and type of carbon-containing precursor.

Terminology: "fishbone type, tube type and plate type" carbon nanofibers already exist in the literature of Catal.Rev.-Sci.Eng., 2000, 42:481-510 or J.Mater.Res.1993, 8:3233-50 The published report and its preparation method are also described in detail in the above-mentioned documents, which will not be repeated in the present invention.

The preparation method of the catalyst for obtaining styrene of the present invention can adopt conventional impregnation method or deposition precipitation method.

The catalyst of the present invention can be used to prepare styrene with carbon dioxide as a raw material. The gas-phase ethylbenzene is introduced at a reaction pressure of 0.05-0.15 MPa, the reaction temperature is 530-620°C, and the space velocity is 0.2-1.2h ^-1 . During the reaction, CO The molar ratio of ₂ to ethylbenzene is 5-15, and inert gas such as Ar can be added. The conversion rate can reach 55-80%, and the selectivity can reach 95-98%.

Detailed ways

Example 1

Weigh 9.5g of tubular carbon nanofibers and put them into a premeasured theoretical load of iron nitrate (3.6399g) or ammonium vanadate (2.1254g) solution. The amount of the solution can be equal to the total pore volume of the corresponding carbon nanofibers. overnight at 120° C., dry the obtained wet solid at 120° C. for more than 12 hours, and seal it for future use. Add alkaline earth metal or alkali metal salt (0.019g) and transition metal such as Cr nitrate (0.81g) to the dried solid, raise the temperature to 550°C under an inert atmosphere, keep it for 1 hour, cool down, and seal it for use. The weight percentage of carbon nanofiber in the catalyst is 95%, the weight percentage of Fe is 5%, the weight percentage of Cr is 1%, the percentage of potassium is 1%, and the percentage of V is 1.5% .

Take by weighing 2.0g the catalyst that obtains by above method, be placed in reactor, pass into the mixed gas of carbon dioxide, ethylbenzene and argon, wherein ratio can be 10: 1: 30ml/min, and reaction temperature can be 550 ℃, by The conversion rate and selectivity of ethylbenzene in chromatographic analysis were 60.5% and 96.2%, respectively.

Example 2

Weigh 9.5g of herringbone carbon nanofibers, mix with the measured Fe or Cr metal salt solution at room temperature to form a suspension, add 4.059g of urea, and keep it at 90°C for 16 hours under vigorous stirring. Suspensions are filtered. After the filter cake is dried at 120° C. for more than 12 hours, potassium nitrate solution consistent with the pore volume is added to the filter cake, and the percentage of K in the catalyst is controlled to be 1%. After the product was dried at room temperature for 5 hours, it was dried at 120°C for more than 12 hours, and collected for future use.

The Fe metal content is 8%, and the Cr content is 2%.

Take by weighing 2.0g the catalyst that obtains by above method, be placed in reactor, pass into the mixed gas of carbon dioxide, ethylbenzene and argon, wherein ratio can be 10: 1: 30ml/min, and reaction temperature can be 550 ℃, by The conversion and selectivity of ethylbenzene in chromatographic analysis were 61.2% and 96.3%, respectively.

Example 3

For the catalyst obtained in Example 2, the reactants are carbon dioxide and ethylbenzene, the ratio is 10/1, and the activity is investigated. Under the condition of 600° C., the conversion rate of ethylbenzene is 78.1%, and the selectivity is 97.3%.

Example 4

Weigh 9.5g of herringbone carbon nanofibers, mix with the measured Fe or Zn metal nitrate solution at room temperature to form a suspension, add 4.059g of urea, and keep it at 90°C for 16 hours under vigorous stirring. The above suspension was filtered. After the filter cake is dried at 120° C. for more than 12 hours, potassium nitrate solution consistent with the pore volume is added to the filter cake, and the percentage of K in the catalyst is controlled to be 1%. After the product was dried at room temperature for 5 hours, it was dried at 120°C for more than 12 hours, and collected for future use.

The content of Fe metal is 5%, and the content of Zn is 1%.

Example 5

Weigh 9.5g of tubular carbon nanofibers, mix them with the measured Fe or Cr metal nitrate solution at room temperature to form a suspension, add 4.059g of urea, and keep it at 90°C for 16 hours under vigorous stirring. Suspensions are filtered. After the filter cake is dried at 120° C. for more than 12 hours, potassium nitrate solution consistent with the pore volume is added to the filter cake, and the percentage of K in the catalyst is controlled to be 1%. After the product was dried at room temperature for 5 hours, it was dried at 120°C for more than 12 hours, and collected for future use.

The content of Fe metal can be 20%, 2%.

Take by weighing 2.0g the catalyst that obtains by above method, be placed in reactor, pass into the mixed gas of carbon dioxide, ethylbenzene and argon, wherein ratio can be 10: 1: 30ml/min, and reaction temperature can be 550 ℃, by The conversion rate and selectivity of ethylbenzene in chromatographic analysis were 60.1% and 95.3%, respectively.

Claims (7)

1. a catalyst for the preparation of styrene, characterized in that components and mass percent content include: Nano carbon fiber 79-90% Oxides of iron or vanadium 9-20% Auxiliary 1%-10% Auxiliaries are selected from alkali metals, alkaline earth metals or transition metals. 2. The catalyst for preparing styrene according to claim 1, characterized in that the alkali metal is selected from K, Na or Li. 3. The catalyst for preparing styrene according to claim 1, characterized in that the alkaline earth metal is selected from Ca, Mg or Ba. 4. The catalyst for preparing styrene according to claim 1, characterized in that the transition metal is selected from Mn, Cr, Ce, La or Zn. 5. The catalyst for preparing styrene according to claim 1, characterized in that, the carbon nanofibers are selected from herringbone, tubular or flat carbon nanofibers. 6. A method for preparing styrene using the catalyst described in any one of claims 1 to 5, characterized in that, using carbon dioxide as a raw material, the reaction temperature is 530-620° C., and the reaction pressure is 0.05-0.15 MPa. Liquid phase ethylbenzene, the space velocity is 0.2-1.2h ^-1 , the molar ratio of CO ₂ to ethylbenzene in the reaction is 5-15. 7. The method according to claim 6, characterized in that an inert gas is added in the reaction system.