CN106673977A - Catalyst for preparing acetaldehyde through direct dehydrogenation of ethyl alcohol as well as preparation method and application thereof - Google Patents

Abstract

The invention provides a catalyst for preparing acetaldehyde by direct dehydrogenation of ethanol, a preparation method and an application thereof, belonging to the technical field of chemical catalysis. The active component of the catalyst is Cu, and the carrier of the catalyst is a composite of carbon-coated oxides; the components contained in the catalyst are calculated by mass percentage, with Cu as the active component, and the active component is 0.1-30wt of the mass of the catalyst %; the composite of carbon-coated oxide is used as the carrier, and the carrier is 70-99.9 wt% of the mass of the catalyst; wherein, the carbon is 0.5-50 wt% of the mass of the carrier, and the rest is oxide. The catalyst provided by the invention has very high acetaldehyde selectivity, the acetaldehyde selectivity is higher than 92.1%; at the same time, the catalyst has excellent stability and basically no deactivation within 40 hours of testing.

Description

Catalyst for preparing acetaldehyde by direct dehydrogenation of ethanol, preparation method and application thereof

technical field

The invention relates to a catalyst for preparing acetaldehyde by direct dehydrogenation of ethanol, a preparation method and an application thereof, belonging to the technical field of chemical catalysis. In particular, it refers to the catalyst for preparing acetaldehyde by dehydrogenating ethanol under the condition of gas phase and normal pressure.

Background technique

Acetaldehyde is an important aliphatic compound, widely used in agriculture, industry and daily life, etc. Alcohol, ethyl acetate, chloral and other important chemical raw materials, with high application value.

At present, the synthesis routes of acetaldehyde mainly include ethylene oxidation, acetylene hydration, acetic acid reduction, ethane oxidation, _CH4 and CO synthesis and ethanol oxidative dehydrogenation. The above-mentioned acetaldehyde production method has a series of problems such as equipment corrosion, environmental pollution and low atom economy. The production of bioethanol in my country is increasing year by year, and the price is low. The direct dehydrogenation of ethanol is used to prepare acetaldehyde, and the route of by-product hydrogen meets the requirements of sustainable energy development. Moreover, this method has the advantages of mild reaction conditions, high atom economy, environmental friendliness, and easy separation of gas and liquid, and is an important route for the production of acetaldehyde in the future.

At present, the Cu/SiO ₂ catalyst used in the direct dehydrogenation of ethanol to acetaldehyde has the problem of low product selectivity. Zhang Yue [Master's Thesis, Tianjin University, China, 2007] prepared a 5wt% Cu/ _SiO2 catalyst by impregnation method to catalyze the dehydrogenation of ethanol at 280 °C with a conversion rate of 48.6% and acetaldehyde selectivity of 68.7%. Shin-ichiro Fujita et al [React.Kinet.Catal.Lett.2001, 73:367] prepared a 30wt% Cu/ _SiO2 catalyst by impregnation method, which catalyzed the dehydrogenation of ethanol at 220°C with a conversion rate of 76% and acetaldehyde selectivity Sex is only 21.6%. Chinese patent CN103880661A reported a Cu-based catalyst with mesoporous SBA-15 molecular sieve (SiO ₂ ) as a carrier for ethanol conversion. At 260°C, the conversion rate of ethanol was 45%, the selectivity of acetaldehyde was 21%, and the selectivity of ethyl acetate was Sex is 66%. Chinese patent CN103880660A reports that Cu is supported on microporous MCM-41 molecular sieves (SiO ₂ ) for ethanol conversion. The ethanol conversion rate at 260° C. is 40.6%, and the acetaldehyde selectivity is only 18.6%.

The reason for the low selectivity of acetaldehyde is that the abundant silanol (Si-OH) on the surface of the silica carrier can catalyze secondary reactions such as aldol condensation of the target product acetaldehyde, or catalyze the dehydration of ethanol to form ethylene or ether, which reduces the selectivity of acetaldehyde. sex.

In order to improve the selectivity of acetaldehyde, many researchers doped Cu/SiO ₂ catalysts with alkali metals or alkaline earth metals [Zhang Yue, master's dissertation, Tianjin University, China, 2007; Ind.Eng.Chem.Res., 1998, 37:2618], or increase the space velocity of the reaction and reduce the residence time [Appl.Catal.A: General, 2006, 304:30], however, the introduction of alkali (earth) metals will cover the active sites and reduce the utilization of metal Cu and reactivity. Chinese patent CN103127945A introduces at least one of SiO ₂ , ZrO ₂ , Al ₂ O ₃ as a carrier, Cu as an active component, and adding P as an auxiliary agent. The prepared catalyst is used for ethanol dehydrogenation to acetaldehyde, and the ethanol conversion rate is greater than 55%, acetaldehyde selectivity greater than 93%. International patent PCT/EP2007/056940 (Chinese Publication No. CN101489967A) reports that between 270-300°C, ethanol can be dehydrogenated on a Cu catalyst modified by ZnO, Co _x O _y or Cr ₂ O ₃ to generate acetaldehyde, and ethanol conversion The rate is 30-50%, and the acetaldehyde selectivity is 90-95%. However, the above methods cannot essentially solve the problem of low acetaldehyde selectivity in the reaction process.

Contents of the invention

The object of the present invention is to address the deficiencies in the prior art and provide a catalyst for the direct dehydrogenation of ethanol to prepare acetaldehyde, the carrier being carbon-coated oxides (Al ₂ O ₃ , SiO ₂ , ZrO ₂ , ZnO , MgO, etc.), the catalyst is a supported catalyst. The catalyst precursor was firstly prepared by an equal volume impregnation method, and then the catalyst was prepared by treating the precursor under a hydrogen atmosphere. Since copper can catalyze the reaction of carbon and hydrogen to produce methane, the formed copper nanoparticles can "penetrate" the carbon layer, come into contact with the oxide surface and form a chemical force. Among them, catalyst innovation includes two aspects: carrier preparation innovation and catalyst preparation innovation. Compared with traditional catalysts, the prepared catalyst has higher acetaldehyde selectivity, excellent catalytic stability, and has good industrial application prospects.

Technical scheme of the present invention:

A kind of catalyst that directly dehydrogenates ethanol to prepare acetaldehyde, the active component of this catalyst is Cu, and the carrier of catalyst is the composite of carbon-coated oxide; The component contained in the catalyst is by mass percent,

Cu is used as the active component, and the active component is 0.1 to 30 wt% of the mass of the catalyst;

The carbon-coated oxide composite is used as the carrier, and the carrier is 70-99.9 wt% of the mass of the catalyst; wherein, the carbon is 0.5-50 wt% of the carrier mass, and the rest is oxide.

The carbon source can be in any form such as amorphous or graphitized; further, one of ethylene glycol, glucose, sucrose, furfuryl alcohol, ethylene, and acetylene can be selected, but not limited to these carbon sources.

The oxide support can be Al ₂ O ₃ , SiO ₂ , ZrO ₂ , ZnO, MgO, etc., and the preferred solution is SiO ₂ , including SBA-15, amorphous SiO ₂ and other different shapes and pore sizes.

When the carbon-coated oxide composite is a carbon-coated _SiO2 composite, the active component is 5-30 wt% of the catalyst mass, the carbon is 10-40 wt% of the carrier mass, and the rest is oxide.

A method for preparing a catalyst for preparing acetaldehyde by direct dehydrogenation of ethanol, comprising a method for preparing a catalyst carrier and a method for preparing a catalyst, and the specific steps are as follows:

The first step, the method of preparing catalyst carrier includes the method of using liquid carbon source as carbon source to prepare catalyst carrier and the method of using gaseous carbon source as carbon source to prepare catalyst carrier

The first method using liquid carbon source as carbon source to prepare catalyst support

① Prepare a carbon source solution with a volume fraction of 5-80vol%, and add oxalic acid as a catalyst at the same time;

② Impregnate the oxide carrier with equal volume of the carbon source solution prepared in step ① for 1 to 3 times, let stand at room temperature for 0.5 to 10 hours, and dry;

③Stay the dried product in step ② at 600-850° C. for 0.5-10 hours under an inert atmosphere to obtain a carbon-coated oxide composite.

The solvent required to prepare the carbon source solution is one or more mixtures of methanol, ethanol, benzene, and trimethylbenzene, preferably trimethylbenzene;

The second method is to use a gaseous carbon source as a carbon source to prepare a catalyst carrier

①The carbon-coated oxide composite is prepared by chemical vapor deposition, the oxide carrier is placed in a constant temperature zone, and the inert atmosphere is purged;

②Heat the dried product in step ① to 500-900°C in an inert atmosphere and stay there for 0.5-10 hours; then feed the mixed gas of gaseous carbon source and inert gas, wherein the volume fraction of gaseous carbon source in the mixed gas is 0.1- 99.9vol%; stay at 500-900°C for 0.1-5h to obtain a carbon-coated oxide compound; turn off the gas carbon source, replace it with an inert gas, continue purging for 1-10h, and then cool down to room temperature.

The inert gas can be at least one of He, Ar, and _N2 .

The second step, preparation catalyst method

① Prepare copper salt solution and/or copper salt alcohol solution, immerse the carbon-coated oxide composite carrier prepared in the first step in copper salt solution and/or copper salt alcohol solution for 1 to 3 times, and let stand at room temperature for 0.5 ~2h, dry;

② Reducing the dried product in step ① at 350-450° C. for 1-5 hours in a hydrogen atmosphere to obtain the supported composite catalyst.

The concentration of the copper salt aqueous solution is 0.075g/mL-0.75g/mL, and the concentration of the copper salt alcohol solution is 0.075g/mL-0.225g/mL.

The copper salt is selected from at least one of chloride, nitrate or acetate.

The alcohol solvent can be selected from at least one of methanol and ethanol.

The reducing concentration of the hydrogen atmosphere is 5-20vol% one of H ₂ /N ₂ , H ₂ /He, and H ₂ /Ar.

The invention discloses a method for preparing acetaldehyde by dehydrogenating ethanol. Under the condition of reaction temperature of 140-350 DEG C and reaction pressure of 0.1 MPa, ethanol is passed into a reactor loaded with the above-mentioned catalyst, and acetaldehyde is directly dehydrogenated to produce acetaldehyde.

Beneficial effects of the present invention: the catalyst provided by the present invention has very high acetaldehyde selectivity, and the acetaldehyde selectivity is higher than 92.1%; simultaneously this catalyst has excellent stability, does not have deactivation substantially (Cu/10C) in test 40h /SiO ₂ as an example). This is mainly due to the inert surface of the carbon material, which has a small amount of oxygen-containing functional groups, which promotes the desorption of acetaldehyde, thereby inhibiting the secondary reaction of acetaldehyde (as shown in Figure 5); at the same time, Cu and the oxide surface are bonded by chemical bonds. With chemical interaction, it ensures the stability of copper under reaction conditions. Furthermore, the preparation method of the present application is simple and does not require any additives.

Description of drawings

Fig. 1 is the XRD pattern of 10Cu/C/SiO ₂ -furfuryl alcohol in Example 3 after reduction.

Fig. 2 is a graph showing the effect of the residence time of Example 7 on the product selectivity of 10Cu/9C/SiO ₂ -furfuryl alcohol samples.

Fig. 3 is a graph showing the effect of the residence time of Example 7 on the ethanol conversion rate of the 10Cu/9C/SiO ₂ -furfuryl alcohol sample.

Figure 4 is a graph showing the influence of the residence time of Example 7 on the product selectivity of 10Cu/SiO ₂ samples.

Fig. 5 is the graph that the residence time of embodiment 7 affects 10Cu/SiO ₂ sample ethanol conversion rate.

Fig. 6 is a diagram showing the change of conversion rate and selectivity of the 10Cu/9C/SiO ₂ -furfuryl alcohol sample in Example 8 within 40 hours.

detailed description

The present invention is described in detail below through some examples, but the present invention is not limited to these examples.

The support is represented _by nC/MOx-carbon source, where:

n=the mass of the coated carbon layer accounts for the percentage of the total weight of the carrier×100; -the carbon source indicates the use of one of ethylene glycol, glucose, sucrose, furfuryl alcohol, ethylene, and acetylene.

Catalysts are expressed in mCu/support where:

m=the percentage of Cu loading in the total weight of the catalyst×100.

Example 1

The preparation process of _SiO2 coated carbon support:

(1) take trimethylbenzene as solvent, prepare 10 and 40vol% furfuryl alcohol/trimethylbenzene solution, add trace oxalic acid simultaneously as catalyst;

(2) Impregnate the carrier once with an equal volume of the furfuryl alcohol solution prepared in step (1); after the impregnation, let stand at room temperature for 0.5-2 hours;

(3) Place the mixture after step (2) standing in an oven at 60°C and 80°C for 12 hours to dry;

(4) The product dried in step (3) was dried at 150° C. for 3 h under Ar atmosphere, and then stayed at 850° C. for 2 h to obtain the C/SiO ₂ composite with C coated on the SiO ₂ surface.

(5) Using 10 and 40vol% furfuryl alcohol/trimethylbenzene solutions, the thickness of the carbon layer on the surface of _SiO2 is 0.5 and 1.5nm respectively, and the carbon content is respectively 9 and 24wt%. The obtained carriers are respectively recorded as 9C/ _SiO2 -furfuryl alcohol and 24C /SiO ₂ -furfuryl alcohol.

Example 2

The preparation process of Al ₂ O ₃ coated carbon support:

(1) Using acetylene as a carbon source, a C/Al ₂ O ₃ composite carrier with a carbon layer coating surface was prepared by chemical vapor deposition;

②Place the chemical vapor deposition furnace horizontally, place the porcelain boat carrying 1.0g sample in the constant temperature zone of the furnace, and purge with Ar for 30 minutes;

③Dry the Al ₂ O ₃ placed in step ② in an Ar inert atmosphere at 150°C for 2 hours to remove impurities such as water adsorbed on the surface;

④Heat the dried product in step ③ to 600°C for 1h under an Ar inert atmosphere; then pass 100mL/min of 10vol% C ₂ H ₂ /Ar gas, and then stay at 600°C for 0.1h to obtain the C C/Al ₂ O ₃ composite coated on the surface of Al ₂ O ₃ . Then turn off the C ₂ H ₂ /Ar gas, replace it with Ar gas, continue purging for 1 h, and then cool down to room temperature. The tested carbon content is 8.6wt%, and the theoretical carbon layer thickness is ~1.6nm, recorded as 8.6C/Al ₂ O ₃ -C ₂ H ₂ .

Example 3

Preparation process of 9C/SiO ₂ -furfuryl alcohol and 24C/SiO ₂ -furfuryl alcohol supported Cu catalysts:

(1) Take 9C/SiO ₂ -furfuryl alcohol and dry it in an airflow oven at 120°C for 2 hours to remove physically adsorbed water on the surface;

(2) At 25°C, take the Cu(NO ₃ ) ₂ ·3H ₂ O aqueous solution prepared according to No. 3 in Table 1 and impregnate the 9C/SiO ₂ -furfuryl alcohol charcoal obtained by drying in step (1) with an equal volume, and let it stand for 2 hours ;

(3) drying the mixture after step (2) at 50° C. for 10 h to obtain a catalyst precursor;

(4) The catalyst precursor obtained in step (3) was dried at 140°C for 0.5h, followed by hydrogen reduction at 450°C for 2h (10vol%H ₂ /N ₂ ), and 10Cu/9C/SiO ₂ -furfuryl alcohol (Table 1 No. 3) Catalyst.

(5) The process of 24C/SiO ₂ -furfuryl alcohol-supported copper catalyst is the same as the above steps, corresponding to No. 7 in Table 1.

The XRD pattern of the obtained catalyst is shown in Figure 1.

The preparation condition process of other catalysts is identical with embodiment 3. The corresponding relationship between sample number and preparation conditions is shown in Table 1.

Correspondence between the sample numbers and preparation conditions of Table 1 Example 3

Example 4

8. Preparation process of 6C/Al ₂ O ₃ -C ₂ H ₂ supported Cu catalyst:

(1) Take 8.6C/Al ₂ O ₃ -C ₂ H ₂ and dry it in an airflow oven at 120°C for 2 hours to remove physically adsorbed water on the surface;

(2) At 25°C, take the Cu(NO ₃ ) ₂ ·3H ₂ O ethanol solution prepared according to No. 3 in Table 1 and impregnate the 8.6C/Al ₂ O ₃ -C ₂ H obtained in step (1) and dry with equal volume ₂ on charcoal, let stand for 2h;

(3) drying the mixture after step (2) at 50° C. for 10 h to obtain a catalyst precursor;

(4) The catalyst precursor obtained in step (3) was dried at 140°C for 0.5h, followed by hydrogen reduction at 450°C for 2h (10vol%H ₂ /N ₂ ) to prepare 3Cu/8.6C/Al ₂ O ₃ -C _{2 H2} (No. 13 in Table 1) catalyst.

Example 5

Ethanol dehydrogenation experiments catalyzed by Cu catalysts supported on composite supports of different oxides and carbons.

Using ethanol as raw material, the ethanol dehydrogenation reaction is carried out in a fixed bed reactor. The reaction conditions are as follows: a fixed-bed reactor with an inner diameter of 8 mm is filled with catalyst, under normal pressure, the reaction temperature is 260° C., and the ethanol liquid phase flow rate is 0.3 mL/h. After the reaction was stable, the reaction raw materials and products were analyzed by online chromatography. Table 2 shows the correspondence between sample numbers and ethanol dehydrogenation activity.

The corresponding relationship between the sample number of Table 2 Example 5 and the ethanol dehydrogenation activity

Example 6

10Cu/9C/SiO ₂ -furfuryl alcohol catalyzed the dehydrogenation of ethanol at different temperatures.

Using ethanol as raw material, the ethanol dehydrogenation reaction is carried out in a fixed bed reactor. The reaction conditions are as follows: a fixed-bed reactor with an inner diameter of 8mm is filled with 0.1g catalyst, normal pressure, reaction temperature 160-300°C, ethanol liquid phase flow rate 0.3mL/h, GHSV=26,000h ^-1 . After the reaction was stable, the reaction raw materials and products were analyzed by online chromatography. The reaction results are shown in Table 3.

Table 3 The corresponding relationship between the reaction temperature of Example 6 and the activity of 10Cu/9C/SiO ₂ -furfuryl alcohol catalytic ethanol dehydrogenation

Example 7

Product distribution experiments of 10Cu/9C/SiO ₂ -furfuryl alcohol and 10Cu/SiO ₂ catalyzed dehydrogenation of ethanol at different residence times. Using ethanol as raw material, the ethanol dehydrogenation reaction is carried out in a fixed bed reactor. The reaction conditions are as follows: a fixed-bed reactor with an inner diameter of 8 mm is filled with different amounts of catalysts, under normal pressure, the reaction temperature is 260° C., and the flow rate of the ethanol liquid phase is 0.3 mL/h. After the reaction was stable, the reaction raw materials and products were analyzed by online chromatography. The graphs of the influence of residence time on product selectivity and ethanol conversion are shown in Figures 2, 3, 4, and 5.

Example 8

Stability test experiment of 10Cu/9C/SiO ₂ -furfuryl alcohol catalyzed dehydrogenation of ethanol.

Using ethanol as raw material, the ethanol dehydrogenation reaction is carried out in a fixed bed reactor. The reaction conditions are as follows: a fixed-bed reactor with an inner diameter of 8 mm is filled with different amounts of catalysts, under normal pressure, the reaction temperature is 260° C., and the flow rate of the ethanol liquid phase is 0.3 mL/h. After the reaction was stable, the reaction raw materials and products were analyzed by online chromatography. The change diagram of conversion rate and selectivity in the reaction time of 40h is shown in Fig. 6 .

Claims (9)

1. a kind of catalyzer that the direct dehydrogenation of ethanol prepares acetaldehyde is characterized in that, the active component of this catalyzer is Cu, the composite of the carbon-loaded coating oxide of catalyzer; Component contained in the catalyzer is by mass percent, Cu is used as the active component, and the active component is 0.1 to 30 wt% of the mass of the catalyst; The carbon-coated oxide composite is used as the carrier, and the carrier is 70-99.9 wt% of the mass of the catalyst; wherein, the carbon is 0.5-50 wt% of the carrier mass, and the rest is oxide. 2. The catalyst according to claim 1, characterized in that the oxide carrier is Al ₂ O ₃ , SiO ₂ , ZrO ₂ , ZnO or MgO. 3. The catalyst according to claim ₂ , characterized in that, when the composite of carbon-coated oxide is a composite of carbon-coated SiO, the active component is 5 to 30 wt% of the catalyst mass, and carbon is the carrier 10 to 40 wt% of the mass, and the rest are oxides. 4. a catalyst preparation method for preparing acetaldehyde by direct dehydrogenation of ethanol, is characterized in that, comprises preparation catalyst carrier method and preparation catalyst method, and concrete steps are as follows: The first step, the method of preparing the catalyst carrier includes the method of using the liquid carbon source as the carbon source to prepare the catalyst carrier and the method of using the gaseous carbon source as the carbon source to prepare the catalyst carrier The first method using liquid carbon source as carbon source to prepare catalyst support ① Prepare a carbon source solution with a volume fraction of 5-80vol%, and add oxalic acid as a catalyst at the same time; ② Impregnate the oxide carrier with equal volume of the carbon source solution prepared in step ① for 1 to 3 times, let stand at room temperature for 0.5 to 10 hours, and dry; ③Stay the dried product in step ② at 600-850°C for 0.5-10h under an inert atmosphere to obtain a composite of carbon-coated oxides; The second method is to use a gaseous carbon source as a carbon source to prepare a catalyst carrier ①The carbon-coated oxide composite is prepared by chemical vapor deposition, the oxide carrier is placed in a constant temperature zone, and the inert atmosphere is purged; ②Heat the dried product in step ① to 500-900°C under an inert atmosphere and stay for 0.5-10 hours; then feed the mixed gas of gaseous carbon source and inert gas, wherein the volume fraction of gaseous carbon source in the mixed gas is 0.1- 99.9vol%; stay at 500-900°C for 0.1-5h to obtain a carbon-coated oxide compound; turn off the gas carbon source, replace it with an inert gas, continue purging for 1-10h, and then cool down to room temperature; The second step, preparation catalyst method ① Prepare copper salt solution and/or copper salt alcohol solution, immerse the carbon-coated oxide composite carrier prepared in the first step in copper salt solution and/or copper salt alcohol solution for 1 to 3 times, and let stand at room temperature for 0.5 ~2h, dry; ② Reducing the dried product in step ① at 350-450° C. for 1-5 hours in a hydrogen atmosphere to obtain the supported composite catalyst. 5. The preparation method according to claim 4, characterized in that, the solvent required for preparing the carbon source solution in the first step is one or a mixture of two or more of methanol, ethanol, benzene, and mesitylene. 6. according to the described preparation method of claim 4 or 5, it is characterized in that, described copper salt is selected from at least one in chloride, nitrate or acetate, and the concentration of copper salt aqueous solution is 0.075g/mL ~0.75g/mL, the concentration of the copper salt alcohol solution is 0.075g/mL~0.225g/mL. 7. The preparation method according to claim 4 or 5, wherein the reducing concentration of the hydrogen atmosphere is one of H ₂ /N ₂ , H ₂ /He and H ₂ /Ar in the range of 5-20 vol%. 8 . The preparation method according to claim 6 , wherein the reducing concentration of the hydrogen atmosphere is one of H ₂ /N ₂ , H ₂ /He, and H ₂ /Ar in the range of 5-20 vol%. 9. A method for preparing acetaldehyde by ethanol dehydrogenation with the catalyst described in claim 1-3, characterized in that, at a reaction temperature of 140 to 350° C. and a reaction pressure of 0.1 MPa, ethanol is fed into the In the catalyst reactor, acetaldehyde is directly dehydrogenated.