TWI508782B - Oxidative dehydrogenation catalyst and preparation method thereof - Google Patents

Description

Oxidative dehydrogenation catalyst and preparation method thereof

The present disclosure relates to an oxidative dehydrogenation catalyst, and more particularly to an oxidative dehydrogenation catalyst for the preparation of butadiene.

The demand for butadiene in the petrochemical market is increasing, and the production methods of butadiene include petroleum brain cracking and oxidative dehydrogenation of 1-butene. Petroleum brain lysis is not a process for the production of butadiene, so it is difficult to optimize the investment and management of petroleum brain cracking equipment. At present, shale gas has been successfully introduced into the market, but since the products produced by shale gas are mainly ethylene, increasing the feed ratio of shale gas has led to a decline in butadiene production. In order to increase the source of butadiene production, oxidative dehydrogenation can be carried out by 1-butene or butane to produce butadiene. The thermodynamically exothermic reaction is beneficial to reduce energy loss, and the reaction can additionally produce stable water. Vapor, in terms of thermodynamic reaction analysis, is of commercial economic value.

However, oxidative dehydrogenation of butane or 1-butene to produce butadiene, the main core technology from catalyst design and preparation. Transition metal oxides (Mg _x V _y O _z ) are most commonly used as catalysts in industry or literature. In addition, there are also literatures on the oxidative dehydrogenation of butane by surface-functionalized carbon nanotubes. In general, the surface of the carbon material is composed, for example, of a graphite structure, which has relatively stable chemical properties, requires violent reaction conditions such as high acid high temperature reaction, and introduces different kinds of oxygen-containing functional groups under severe reaction conditions, and the catalytic activity of the carbon material is So it is affected.

The present disclosure provides an oxidative dehydrogenation catalyst that catalyzes the dehydrogenation of n-butane or 1-butene at a lower oxygen ratio and at a lower temperature to produce butadiene.

A method for preparing an oxidative dehydrogenation catalyst according to the present disclosure comprises the following steps. A phosphorus-containing polymer is grafted onto the nano carbon material. A sintering process is performed such that a surface of the nanocarbon material is mainly formed with a C=O structure and doped with phosphorus.

An oxidative dehydrogenation catalyst according to the present disclosure, which comprises a nano carbon material. Most of the surface of the nano carbon material forms a C=O structure and is doped with a phosphorus element. The ratio of the C=O structure to the C-O structure is greater than or equal to 3, and the content of the phosphorus element is 1 wt% to 3 wt%.

The above described features and advantages of the present invention will be more apparent from the following description.

S110, S120‧‧‧ steps

FIG. 1 is a schematic view showing the preparation process of an oxidative dehydrogenation catalyst according to an embodiment of the present disclosure.

2 is a schematic view showing the preparation process of the oxidative dehydrogenation catalyst of Example 1.

3 is a schematic view showing the preparation process of the oxidative dehydrogenation catalyst of Example 2.

4 is an XPS spectrum chart of the oxidative dehydrogenation catalyst of Example 1.

Fig. 5 is an XPS spectrum chart of the oxidative dehydrogenation catalyst of Example 2.

Fig. 6 is an XPS spectrum chart of the oxidative dehydrogenation catalyst of Comparative Example 1.

Fig. 7 is an XPS spectrum chart of the oxidative dehydrogenation catalyst of Comparative Example 2.

Figure 8 is a comparison of butane conversion and butadiene selectivity of Examples 1-2 and Comparative Examples 1-3 at different mixed gas flow rates.

FIG. 1 is a schematic view showing the preparation process of an oxidative dehydrogenation catalyst according to an embodiment of the present disclosure. Referring to FIG. 1, step S110 is performed to graft a phosphorus-containing polymer onto a nano carbon material. First, a nano carbon material is provided, which is, for example, a carbon nanotube, a nanodiamond, graphene, graphite, or a combination thereof. Next, a phosphorus-containing polymer is grafted onto the nano carbon material.

The method of grafting a phosphorus-containing polymer onto a nano carbon material is explained below. First, a nano carbon material is mixed with a phosphorus-containing monomer, and a phosphorus-containing monomer is polymerized to be polymerized into a phosphorus-containing polymer and simultaneously grafted onto the surface of the nanocarbon material. In detail, the nano carbon material and the phosphorus-containing monomer may be uniformly mixed, and then a polymerization initiator may be added to carry out a polymerization reaction. The phosphorus-containing monomer may be Ethylene Glycol Methacrylate Phosphate (EGMP), Diethyl vinylphosphonate (DVP) or other suitable phosphorus-containing monomer. Gather The kind of the reaction initiator is determined by the kind of the phosphorus-containing monomer. In this embodiment, a radical initiator is used as a polymerization initiator.

In another embodiment, different methods can be used to graft the nano carbon material. Phosphorus containing polymer. First, a nano carbon material is mixed with a non-phosphorus-containing monomer, and a non-phosphorus-containing monomer is polymerized to be polymerized into a non-phosphorus-containing polymer and simultaneously grafted onto the surface of the nanocarbon material. In detail, the nano carbon material and the non-phosphorus-containing monomer may be uniformly mixed, and then a polymerization initiator is added to carry out a polymerization reaction. The non-phosphorus containing monomer may be Hydroxyethylmethacrylate (HEMA). Next, the nanocarbon material to which the non-phosphorus-containing polymer has been grafted is subjected to a phosphorylation reaction to form a non-phosphorus-containing polymer to form a phosphorus-containing polymer.

In other words, at least the phosphorus-containing high score that has been grafted can be obtained by the above method. The nano carbon material in which the content of the phosphorus-containing polymer is 10% by weight (wt%) to 50% by weight. The content of the phosphorus-containing polymer can be determined by a thermogravimetric analyzer (TGA). For example, the phosphorus-containing polymer may be polyethylene glycol methacrylate phosphate, polyvinyl phosphate or phosphorylated polyhydroxyethyl methacrylate. However, the disclosure is not limited thereto, and the phosphorus-containing polymer may be other types of phosphorus-containing polymers.

Referring again to FIG. 1, step S120 is performed. The above has been grafted with high phosphorus content The molecular nanocarbon material is subjected to a sintering process to form a C=O structure on the surface of the nanocarbon material and doped with phosphorus. So far, the production of the oxidative dehydrogenation catalyst is completed. The temperature of the sintering process is 600 ° C ~ 1000 ° C. The sintering process takes 30 minutes to 2 hours. If the sintering temperature is too high or the time is too long, most of the functional groups on the surface of the carbon material The group is easily cleaved and the conversion rate is too high. On the contrary, if the sintering temperature is too low or the time is too short, the carboxyl group is not easily cleaved and the selectivity is too low.

In detail, when a phosphorus-containing polymer is grafted on the surface of the nano-carbon material, the carbon material structure of the graft in the nano-carbon material is destroyed to form a defect, and the defect position is easily oxidized during high-temperature sintering. An oxygen-containing functional group such as a ketone group, a carboxyl group, and an alcohol group are formed, wherein the ketone group contains a C=O structure, and a carboxyl group and an alcohol group form a CO structure when formed on the surface of the carbon material. Taking the reaction of oxidative dehydrogenation of 1-butene as an example, the C=O structure contributes to the improvement of the catalytic selectivity to butadiene. The C-O structure will cleave the C-C bond to form a lower molecular weight alkane or oxidize to carbon monoxide or carbon dioxide, thus reducing the catalytic selectivity to butadiene.

In this embodiment, the surface of the nano carbon material is grafted with a phosphorus-containing polymer, and the phosphorus-containing polymer is thermally cracked while the sintering process is performed to leave a phosphorus-containing group (for example, phosphorus oxide) in the nanometer. The carbon material is such that the surface of the nanocarbon material is doped with phosphorus. When the defect position of the nano carbon material forms an oxygen-containing functional group during sintering, the phosphorus-containing group contributes to suppressing the formation of the CO structure, so that the amount ratio of the C=O structure can be relatively increased to form, for example, a high ketone. An oxidative dehydrogenation catalyst that is phosphorylated and catalyzed by phosphorus. The number ratio of C=O structure to C-O structure can be identified by X-ray Photoelectron Spectroscope (XPS). In the present embodiment, the ratio of the number of C=O structures to C-O structures is greater than or equal to three. In another embodiment, the ratio of the number of C=O structures to C-O structures is 3-5. In other words, since the oxidative dehydrogenation catalyst of the present embodiment has a high ratio of C=O structure to C-O structure, it can effectively increase the catalytic selectivity to butadiene and can be at a lower oxygen/1- Butene is either an effective catalytic oxidative dehydrogenation reaction at a lower oxygen/n-butane ratio and at a low temperature.

Furthermore, when the surface of the nano-carbon material is doped with phosphorus, it helps Maintaining the activity of the catalyst in the catalytic reaction, since the oxidative dehydrogenation reaction is in an aerobic state, the carbon material is easily oxidized to a functional group containing a CO structure, and the doped phosphorus suppresses the formation of these functional groups during the reaction, Ensure catalytic selectivity. The doping content of the phosphorus element can be identified by an Energy Dispersive Spectrometer (EDS) and an Electron Energy Loss Spectrometer (EELS). In the present embodiment, the content of the phosphorus element in the oxidative dehydrogenation catalyst is from 1% by weight to 3% by weight, so that it has good reaction durability and contributes to maintaining the efficiency of the oxidative dehydrogenation reaction. However, although the aforementioned high content of the phosphorus element contributes to an increase in the selectivity, the excessively high content tends to cause a decrease in the conversion ratio.

The oxidative dehydrogenation catalysts of the present disclosure are illustrated by the following examples and comparative examples, but are merely illustrative to enable those skilled in the art to better understand the present disclosure and not to limit the disclosure.

Example 1

2 is a schematic view showing the preparation process of the oxidative dehydrogenation catalyst of Example 1. Referring to Fig. 2, a nanocarbon material and a hydroxyethyl methacrylate monomer are polymerized, followed by a phosphorylation reaction. First, 10 g of a carbon nanotube (CNT) was added to 100 ml (mL) of a methyl hydroxyethyl acrylate (HEMA) monomer and 100 mL of an ethanol solvent to form a mixed solution. Next, the carbon nanotubes were uniformly dispersed in the mixed solution by a wet mill. Then, with Benzoyl peroxide (BPO) As a radical initiator, 3 g (g) of benzene peroxide was dissolved in 20 ml of ethanol in an auto-injector to form a BPO solution, and then the BPO solution was injected into the carbon nanotube at a rate of 20 ml / 1 hour. In the liquid. The carbon nanotube/HEMA/EtOH mixture was subjected to ultrasonic wave shock reaction at 80 ° C for 1.5 hours, and then acetone was added thereto and centrifuged several times to remove the polymer not grafted on the carbon nanotubes to obtain a product. Next, the product was dispersed in a small amount of 20 ml of ethanol, and then added with 300 mL of phosphoric acid to be uniformly stirred, and phosphoric acid was reacted under a refluxing nitrogen atmosphere at 160 ° C for 30 minutes. Next, acetone is slowly added and the product is centrifuged to remove excess unreacted material to obtain the final phosphorylated product. The product is dried by vacuum drying to obtain a grafted polyhydroxyethyl methacrylate (CNT-PHEMA) on a carbon nanotube. Phosphating product.

Then, the phosphating product of CNT-PHEMA is sintered at a high temperature, and the polymer (polyhydroxyethyl methacrylate) is cleaved by a suitable sintering temperature and the region of the polymer grafted on the carbon nanotube is trapped. Position) is easily oxidized to an oxygen-containing functional group. The formation of a C-O structure (for example, a carboxyl group) which causes a decrease in selectivity is suppressed by the residual phosphide of the polymer, and thus the relative proportion of the C=O structure (for example, a ketone group) as a catalytic active center can be increased. Controlling the appropriate sintering time and temperature can greatly increase the ketone grouping ratio of the carbon material and the phosphorus doping ratio. In detail, the dried CNT-PHEMA phosphating product can be placed on a quartz ship and sent to a tubular high-temperature furnace, and sintered under a nitrogen atmosphere at a sintering temperature of 800 °C. The sintering time was 1 hour. The finished product can be subjected to XPS analysis, BET specific surface area analysis, and catalytic performance analysis (as shown in Table 1).

Example 2

3 is a schematic view showing the preparation process of the oxidative dehydrogenation catalyst of Example 2. please Referring to Figure 3, a phosphorus-containing monomer, ethylene glycol methacrylate phosphate (EGMP), is polymerized and grafted onto the surface of the nanocarbon material without the need for a phosphorylation step. Specifically, 10 g of a carbon nanotube was added to 100 mL of an ethylene glycol methacrylate phosphate monomer and 100 mL of a dimethyl sulfoxide (DMSO) solvent to form a mixed solution. Next, the carbon nanotubes were dispersed in a wet mill to be uniformly dispersed in the mixed solution. Thereafter, benzoyl peroxide was used as a radical initiator, and 3 g of benzene peroxide was dissolved in 20 ml of tetrahydrofuran solvent in an auto-injector to form a BPO solvent. Then, the BPO solution was injected into the nano carbon mixture at a rate of 20 ml/1 hour, and the nanocarbon tube/EGMP mixture was subjected to ultrasonic wave shock reaction at 80 ° C for 1.5 hours, then acetone was added and centrifugation was performed several times to remove the solution. The polymer is grafted onto the carbon tube to give the product. Then, the product is dried by vacuum drying to obtain a phosphating product of grafted polyethylene glycol methacrylate phosphate (CNT-PEGMP) on a carbon nanotube.

Then, the phosphating product of CNT-PEGMP is sintered at a high temperature and will be baked. The dried CNT-PEGMP product was placed on a quartz vessel and sent to a tubular high temperature furnace and sintered under a nitrogen atmosphere at a sintering temperature of 800 °C. The sintering time was 1 hour. The sintered product was subjected to XPS analysis, BET specific surface area analysis, and catalytic performance analysis (as shown in Table 1).

Comparative example 1

Comparative Example 1 is directed to the carbon nanotubes in the case of general strong acid oxidation. The same sintering process. In detail, take 2g of unmodified carbon nanotubes in a round bottom reaction flask, and add 50mL of concentrated nitric acid and 150ml of concentrated sulfuric acid, then heat and reflux. The heating temperature was 130 ° C and the reflux time was 2 hours. Then, the refluxed product was washed by centrifugation, filtration and deionized water to remove excess strong acid, and the acidified and oxidized CNT sample was dried at 80 ° C, and the dried solid was placed on a quartz dish and placed in a tube. In a high temperature furnace, sintering was carried out under a nitrogen atmosphere at a sintering temperature of 800 °C. The sintering time was 1 hour. The sintered product was subjected to XPS analysis, BET specific surface area analysis, and catalytic performance analysis (as shown in Table 1).

Comparative example 2

First, 2 g of unmodified carbon nanotubes were placed in a round bottom reaction flask and 200 mL of concentrated nitric acid was added, and refluxed for 2 hours. The refluxed product was washed by centrifugation, filtration and deionized water to remove excess nitric acid. The acidified CNT sample was dried at 80 ° C, and the dried solid was placed on a quartz dish and placed in a tubular high temperature furnace, purged with argon (Ar) for 30 minutes and controlled by argon gas. The flow rate was 100 sccm, and the temperature increase rate was set to 5 ° C / min from room temperature to 450 ° C, and maintained at a temperature of 450 ° C for 30 minutes for sintering. After sintering, oxidized CNT products (oCNTs) were obtained, and the oCNTs were immersed in (NH ₄ ) ₃ PO ₄ and then dried, and held at 450 ° C for 30 minutes to be sintered, thereby obtaining Comparative Example 2. Phosphated CNTs (P-oCNTs). For a detailed preparation method of Comparative Example 2, reference may be made to J. Zhang, X. Liu, R. Blume, A. Zhang, R. Schlögl, DS Su, Science Vol. 322, p. 73 (2008).

Comparative example 3

Take 10g of Mg(NO ₃ ) ₂ and 3.04g of NH ₄ VO ₃ salt and dissolve them in 500mL of water with magnetic stirring. After adding 20 drops of concentrated nitric acid, the dispersibility of the mixed salt can be improved and the dispersibility is better. Dispersions. Next, the dispersion was dried at 80 ° C to obtain a reddish-brown dried product, and the dried product was sintered in an argon atmosphere at 560 ° C for 6 hours to obtain a vanadium magnesium metal catalyst (V/MgO Catalyst The main chemical formula is Mg ₂ V ₂ O ₇ ).

Next, X-ray photoelectrons were performed on Examples 1 to 2 and Comparative Examples 1 and 2. The energy spectrum spectrometer (XPS) is used to analyze the ratio of the C=O structure and the CO structure on the surface of the carbon nanotube. It can be judged as the characteristic peak of the C=O structure by the position of 531.2±0.2eV. It is characterized by a position of 533.1 ± 0.2 eV as a characteristic peak of the CO structure. The integrated area ratio of the C=O structure and the C-O structure can be identified by oxygen signal analysis of XPS. The XPS identification results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. 4 to 7. The proportions of oxygen elements on the surface of the carbon nanotubes of Examples 1 to 2 and Comparative Examples 1 and 2 are shown in Table 1. In addition, Table 1 also shows the phosphorus element ratios of Examples 1 to 2 and Comparative Examples 1 and 2.

Since the C-O structure in the carboxyl group causes the 1-butene or butane to undergo carbon-carbon bond cleavage to form smaller molecules, the existence of the C-O structure leads to a decrease in the catalytic selectivity. Low main cause, therefore, reducing the number of carboxyl groups can increase the catalytic selectivity. In addition, the higher the proportion of the phosphorus element, the catalyst can be catalyzed to have better reaction stability. As can be seen from Table 1, in comparison with Comparative Examples 1 and 2, Examples 1 and 2 have a higher ratio of the C=O structure to the C-O structure and a higher phosphorus doping ratio. In other words, the oxidative dehydrogenation catalysts of Examples 1 to 2 will have good catalytic performance conversion rates and selectivity. Hereinafter, 1-butene was catalyzed by using the oxidative dehydrogenation catalysts of Examples 1 to 2 and Comparative Examples 1 to 3 to prepare butadiene, and the conversion ratio and selectivity were evaluated.

The conversion rate and selectivity of the catalytic performance of the oxidative dehydrogenation catalyst are evaluated and conditions are as follows. An oxidative dehydrogenation catalyst (about 0.2 g to 0.55 g) was packed in the reaction column. When the reactor is filled, the reactor is sealed with glass wool at the front and rear ends to prevent the catalyst from flowing out and destroying the valve member to affect the reactivity. After the filling is completed, nitrogen is supplied to the external piping of the system to remove the air remaining in the pipe and check the pipeline for leaks. After the inspection is completed, the reactor is returned to the high temperature furnace. Thereafter, the start temperature controller starts to heat up and is heated at an ascending temperature of 2 ° C per minute until the temperature reaches 450 ° C before starting the catalytic reaction. The catalytic temperature was maintained at 450 ° C, and a mixed gas of oxygen/1-butene (with a molar ratio of 0.5) was introduced, and the flow rate of the mixed gas of oxygen/1-butene was controlled by a mass flow meter to be 20 ml/min, 10 ml/ Min and 5 ml/min were measured under the above conditions. The column is a 10' x 1/8" stainless steel tube. The carrier gas is helium and the flow rate is 35 ml/min. The detector temperature is 150 ° C and the separation column is VZ-10 60/80. Wait for two hours before each catalytic reaction to bring the system to a steady state, and let the whole system be balanced to prepare for sampling. When sampling, the gas phase product uses an eight-hole valve to pass a 1 ml sampling loop and then enter the gas chromatograph (factory). Brand: Shimadzu, model: GC- Analytical measurements were performed in 2014 ATF/SPL). The linear regression curve obtained by sampling the standard gas 1-butene was used to calculate the conversion of 1-butene and the selectivity of butadiene. Each experiment was eight hours, and samples were analyzed once per hour to calculate eight average conversion rates and selection rates.

The 1-butene conversion rate is estimated by the following formula: Wherein A is the initial concentration of 1-butene and B is the residual concentration of 1-butene.

The butadiene selectivity is estimated by the following formula: Where C is the butadiene concentration produced after the reaction.

Figure 8 is a comparison of the conversion ratios and selectivity of Examples 1 and 2 and Comparative Examples 1 to 3 at different mixed gas flow rates (20 ml/min, 10 ml/min and 5 ml/min from left to right). As can be seen from Fig. 8, in the case where the conversion ratio of 1-butene was similar, the selectivity of butadiene of Examples 1 and 2 was significantly higher than that of Comparative Examples 1 to 3. In Comparative Example 1, the selectivity was rapidly decreased as the reaction gas flow rate was lower in the case of undoped phosphorus, indicating that the stability was poor. Although Comparative Example 2 was doped with phosphorus, since the ratio of the number of C=O structures was low, the conversion ratio and selectivity were far less than those of Examples 1 and 2. The catalytic activity and selectivity of the metal catalyst of Comparative Example 3 were lower than those of Examples 1 and 2 at a low oxygen ratio. From this, it is understood that the oxidative dehydrogenation catalysts of Examples 1 and 2 have a very good catalytic effect on the oxidative dehydrogenation reaction of 1-butene.

In summary, the surface of the oxidative dehydrogenation catalyst prepared by the preparation method of the present disclosure has a higher ratio of the C=O structure and thus has a better butadiene selectivity. Moreover, the surface of the oxidative dehydrogenation catalyst disclosed herein has a higher phosphorus doping ratio and thus has better catalytic stability.

S110, S120‧‧‧ steps

Claims (11)

A method for preparing an oxidative dehydrogenation catalyst comprises: grafting a phosphorus-containing polymer onto a nano carbon material; and performing a sintering process to form a C=O structure on the surface of the nano carbon material and doped with Phosphorus. The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the method for grafting the phosphorus-containing polymer onto the nano carbon material comprises: mixing the nano carbon material with a phosphorus-containing monomer And performing a polymerization reaction to polymerize the phosphorus-containing monomer into a phosphorus-containing polymer and grafting onto the nanocarbon material. The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the method for grafting the phosphorus-containing polymer onto the nano carbon material comprises: the nano carbon material and the non-phosphorus monomer Mixing; performing a polymerization reaction to polymerize the non-phosphorus-containing monomer into a non-phosphorus-containing polymer and grafting the carbon nanomaterial; and performing a monophosphorylation reaction to form the non-phosphorus-containing polymer to form the phosphorus-containing polymer . The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the phosphorus-containing polymer comprises polyethylene glycol methacrylate phosphate, polyethylene phosphate or phosphorylated polyhydroxyl Methyl acrylate. The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the nano carbon material comprises a carbon nanotube, a nanodiamond, a graphene, a graphite or any combination thereof. The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the total amount of the nanocarbon material grafted with the phosphorus-containing polymer is 100% by weight, and the content of the phosphorus-containing polymer is 10wt%~50wt%. The method for preparing an oxidative dehydrogenation catalyst according to the first aspect of the invention, wherein the sintering process has a temperature of from 600 ° C to 1000 ° C. The method for preparing an oxidative dehydrogenation catalyst according to claim 1, wherein the sintering process has a time of 30 minutes to 2 hours. An oxidative dehydrogenation catalyst comprising: a nano carbon material, wherein a surface of the nano carbon material is formed with a C=O structure, a CO structure and doped with a phosphorus element, and the C=O structure is opposite to the CO structure The ratio of the quantity is greater than or equal to 3, and the content of the phosphorus element is 1 wt% in the nano carbon material and the C=O structure on the surface thereof, the total amount of the CO structure and the phosphorus element is 100 wt%. 3wt%. The oxidative dehydrogenation catalyst according to claim 9, wherein the ratio of the C=O structure to the number of the C-O structures is 3 to 5. The oxidative dehydrogenation catalyst of claim 9, wherein the nanocarbon material comprises a carbon nanotube, a nanodiamond, graphene, graphite or any combination thereof.