CN113042025B - A kind of non-metallic porous carbon material catalyst prepared with sugar as raw material, and preparation method and application thereof - Google Patents

Abstract

The invention discloses a non-metal porous carbon material catalyst which is directly used for catalyzing propane dehydrogenation to prepare propylene without loading any metal. Firstly, the invention adopts cheap saccharides as carbon sources, and then changes the roasting temperature and the alkali treatment strength to prepare the high-performance propane dehydrogenation non-metallic porous carbon material catalyst, and has the advantages of cheap and easily-obtained raw materials, no metal pollution, no toxicity and simple and easy manufacturing process. And secondly, the porous structure of the catalyst improves the mass transfer and heat transfer efficiency and increases the contact area of propane and active groups, and the catalyst has the advantages of high catalytic activity and high catalytic stability when applied to the propane dehydrogenation catalytic reaction.

Description

A kind of non-metallic porous carbon material catalyst prepared with carbohydrates as raw material and its preparation method and application

technical field

The invention relates to a non-metallic porous carbon material catalyst and a method for preparing the catalyst using saccharides as raw materials, and applying the catalyst to catalyzing propane dehydrogenation to produce propylene, belonging to the field of low-carbon alkane dehydrogenation catalyst preparation.

Background technique

Cr-based catalysts and Pt-based catalysts are the two most commonly used catalysts in the industry to catalyze the dehydrogenation of propane to propylene. Dehydrogenation of propane to propylene is a highly endothermic reaction with increasing number of molecules. The reaction conditions of high temperature and low pressure are favorable for the dehydrogenation of propane to propylene. At present, traditional Cr-based catalysts have been gradually eliminated due to the serious environmental pollution problem. Although Pt-based catalysts have little environmental pollution, they are expensive and prone to irreversible agglomeration of metal particles at high reaction temperatures, resulting in a significant reduction in the activity of propane dehydrogenation. This disadvantage is usually improved by adding some metal promoters. The most commonly used carriers in the industry are alumina and molecular sieves, but due to the strong acidity of the carriers, by-products will be generated from the deep cracking of propane, which will further generate carbon deposits to cover the active center and reduce the catalyst activity.

In recent years, carbon materials such as carbon black, activated carbon, carbon nanotubes, nanodiamonds, and ordered mesoporous carbon have gradually been used as a new type of support or catalyst for propane dehydrogenation. Due to their unique physical and chemical properties, these carbon materials change the electron density and geometric structure of the supported active metals, which greatly improves their catalytic performance. Secondly, these carbon materials contain a large number of active groups on the surface, so they can be directly used as catalysts for propane. For dehydrogenation reactions, such as Liu et al. (L. Liu, Q.F. Deng, B. Agula, X. Zhao, T.Z. Ren, Z.Y. Yuan, Orderedmesoporous carbon catalyst for dehydrogenation of propane to propylene, ChemCommun (Camb), 47 (2011) 8334-8336.) Using resorcinol, F127 triblock polymer and formaldehyde solution as raw materials, phenolic resin was synthesized by low temperature hydrothermal method, and then calcined at high temperature to synthesize an ordered mesoporous carbon containing a large number of active groups, and The ordered mesoporous carbon was successfully applied to the catalytic reaction of propane dehydrogenation. However, the cost of the raw materials of the carbon material catalyst obtained by this method is relatively high, the raw materials and the reagents used in the preparation process have certain pollution and toxicity, and the preparation process is also complicated.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention has synthesized a non-metallic porous carbon material catalyst with low price, non-metal, no metal pollution, non-toxicity and simple manufacturing process, and used it to catalyze the dehydrogenation of propane to produce propylene. The catalyst does not need to be loaded with any metal, and can be directly applied to the catalytic reaction, which overcomes the disadvantages of the traditional supported metal catalyst, such as high price, easy metal pollution, and easy sintering at high temperature to cause deactivation. Has high activity and high stability.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for preparing a non-metallic porous carbon material catalyst by using carbohydrates as a raw material, comprising the following steps:

s1. Mix the carbohydrate raw material with water, place it in a hydrothermal kettle, and perform hydrothermal carbonization at 120 to 200° C. to obtain a carbonized material, and filter and wash the carbonized material;

s2, roasting the carbonized material at a low temperature of 300-600 °C;

s3, put the carbonized material after low-temperature roasting into a strong alkaline aqueous solution and stir to remove the amorphous carbon therein, then roast at a high temperature at 600-1100 °C, and then wash the carbonized material after high-temperature roasting to neutrality;

s4. The carbonized material obtained in s3 is subjected to reduction treatment using a reducing agent or a hydrogen reducing atmosphere to obtain a non-metal porous carbon material catalyst.

In the present invention, sugars are used as raw materials, and the basic carbonized material is first obtained by hydrothermal treatment of the sugars, and then the carbonized material is calcined at a relatively low temperature, so that the uncarbonized part is further carbonized to complete the carbonized material obtained at this time. It is a mixture of porous carbon and free carbon, and then the amorphous free carbon in it is removed by lye, and the porous carbon is eroded by lye, so that more pores and active sites are generated on the porous carbon, and the mass transfer is improved. Thermal efficiency and increase the contact area between propane and active groups, and finally the porous carbon is shaped by high-temperature calcination, and is subjected to reduction treatment to obtain a catalyst product. The invention increases the pores of the porous carbon through the two-step roasting and lye treatment process, enhances the catalytic activity, and at the same time enhances the stability, and is not easy to be deactivated at high temperature.

Further, the sugars are selected from one or more of starch, sucrose, fructose, glucose, maltose, cellulose or lactose.

Further, the reducing agent described in s4 is selected from one or more of ethylene glycol, C1～C3 carboxylic acid or C1～C3 sodium carboxylate.

Further, the strong alkali aqueous solution is a NaOH solution, a KOH solution or a mixed solution of NaOH and KOH, and the quality of the alkali in the strong alkali aqueous solution is 1 to 10 times the quality of the carbonized material after low-temperature roasting in s2. Preferably, the mass of the strong base is 2-4 times the mass of the carbonized material.

Preferably, the temperature of the high-temperature roasting process is 650-750°C.

Further, the low-temperature calcination process is carried out under a protective atmosphere of inert gas or nitrogen.

Further, the high temperature calcination process is carried out under the protective atmosphere of inert gas or nitrogen.

Since the carbon material is used as the catalyst in the present invention, oxygen needs to be isolated during the high-temperature treatment, so the calcination needs to be carried out under the protection of inert gas or nitrogen.

As another object of the present invention, the present invention also uses the above catalyst to catalyze the dehydrogenation of propane to prepare propylene. Preferably, the catalytic reaction is carried out at a temperature of 550-750° C. and a pressure of 0-0.3 MPa.

In summary, the application of the present invention has the following advantages:

1. The invention adopts non-metal porous carbon material as catalyst, can achieve high catalytic activity without metal loading, avoids the problem of rising cost and metal pollution caused by metal loading, and also avoids the reaction of conventional metal-loaded catalysts in the reaction The problem of activity decline due to metal loss during the process.

2. The present invention adopts saccharides as the raw material for preparing the non-metal porous carbon material, the raw material is renewable material, the source is wide and the cost is low, the cost of the catalyst can be greatly reduced, and the use of some toxic chemical raw materials can be avoided at the same time.

3. The non-metal porous carbon material catalyst prepared by the invention has strong stability and can maintain high selectivity for a long time under high temperature conditions.

Description of drawings

Figure 1 is a scanning electron microscope image (SEM, the scale bar in the figure is 8 μm) of the catalyst F of the comparative example;

Figure 2 is a scanning electron microscope image (SEM, the scale bar in the figure is 8 μm) of the catalyst C of the present invention.

Detailed ways

In the present invention, one or more mixtures in different proportions of sugars are fully mixed with water and then put into a hydrothermal kettle for hydrothermal treatment. The original carbon material is mixed with a strong alkali aqueous solution, stirred, and dried, and the dried product is calcined at high temperature under an inert gas atmosphere; the product after high temperature calcination is washed to neutrality, dried, and finally subjected to reduction treatment to obtain the final catalyst.

The present invention will be further described in detail below by means of examples. The following examples are only preferred embodiments of the present invention, and the present invention is not limited thereto.

Example 1

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the raw carbon material after low temperature calcination with an aqueous solution containing 1.1 g NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and after drying was completed, it was calcined at a high temperature of 700 °C for 2 h under a nitrogen atmosphere, and deionized The high-temperature calcined product was filtered and washed with water for several times until it was neutral. The washed product was dried at 110 °C for 12 h, and finally reduced at 580 °C under a hydrogen atmosphere for 1 h to obtain catalyst A.

Take 0.2gA catalyst and load it into a fixed-bed micro-reaction device, use a mixture of propane and nitrogen with a volume fraction of 5% as the reaction raw material, and react at 600 ℃, normal pressure and propane mass space velocity of 0.6h ^-1 under the reaction conditions, After continuously feeding the reaction raw materials for 5min, the mixed gas at the outlet was subjected to composition measurement, the content of propane and propylene was detected, and the conversion rate of propane and the selectivity of propylene were calculated in the following manner (the same below):

Denote the content of propane in the product as x (volume fraction) and the content of propylene as y (volume fraction), there are:

Propane conversion = (5%-x)/5%, propylene selectivity = y/(5%-x).

The results of this example are reported in Table 1.

Example 2

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the original carbon material after low-temperature calcination with an aqueous solution containing 2.2 g of NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and then dried at a high temperature of 700 °C under a nitrogen atmosphere for 2 h. Deionized water was used to calcine the product at high temperature Carry out several times of suction filtration and washing until neutrality, drying at 110 °C for 12 h, and finally reduction at 580 °C for 1 h under a hydrogen atmosphere to obtain catalyst B.

Take 0.2gB catalyst and load it into a fixed-bed micro-reaction device, take 5% propane and nitrogen mixed gas as the reaction raw material, and react under the reaction conditions of 600℃, normal pressure and propane mass space velocity of 0.6h ^-1 , After continuously feeding the reaction raw materials for 5 minutes, the mixed gas at the outlet was subjected to composition measurement, the contents of propane and propylene were detected, and the conversion rate of propane and the selectivity of propylene were calculated. The results of this example are reported in Table 1.

Example 3

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the original carbon material after low-temperature calcination with an aqueous solution containing 3.3 g of NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and then dried at a high temperature of 700 °C under a nitrogen atmosphere for 2 h. Deionized water was used to calcine the product at high temperature Carry out several times of suction filtration and washing until neutrality, drying at 110 °C for 12 h, and finally reduction at 580 °C for 1 h under a hydrogen atmosphere to obtain catalyst C.

Take 0.2gC catalyst and load it into a fixed-bed micro-reaction device, use a mixture of propane and nitrogen with a volume fraction of 5% as the reaction raw material, and react at 600 ℃, normal pressure and propane mass space velocity of 0.6h ^-1 under the reaction conditions, After continuously feeding the reaction raw materials for 5 minutes, the mixed gas at the outlet was subjected to composition measurement, the contents of propane and propylene were detected, and the conversion rate of propane and the selectivity of propylene were calculated. The results of this example are reported in Table 1.

Example 4

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the original carbon material after low-temperature calcination with an aqueous solution containing 2.2 g of NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and then dried at a high temperature of 600 °C under a nitrogen atmosphere for 2 h. Deionized water was used to calcine the product at high temperature Carry out several times of suction filtration and washing until neutrality, drying at 110 °C for 12 h, and finally reducing under hydrogen atmosphere at 580 °C for 1 h to obtain catalyst D.

Take 0.2 gD of catalyst and load it into a fixed-bed micro-reaction device, take 5% propane and nitrogen mixed gas as reaction raw materials, and react at 600 °C, normal pressure and propane mass space velocity of 0.6 h ^-1 under the reaction conditions, After continuously feeding the reaction raw materials for 5 minutes, the mixed gas at the outlet was subjected to composition measurement, the contents of propane and propylene were detected, and the conversion rate of propane and the selectivity of propylene were calculated. The results of this example are reported in Table 1.

Example 5

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the original carbon material after low-temperature calcination with an aqueous solution containing 2.2 g of NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and then dried at a high temperature of 800 °C under a nitrogen atmosphere for 2 h. Deionized water was used to calcine the product at high temperature Carry out several times of suction filtration and washing until neutrality, drying at 110 °C for 12 h, and finally reducing under a hydrogen atmosphere at 580 °C for 1 h to obtain catalyst E.

Take 0.2gE catalyst and load it into a fixed-bed micro-reaction device, take 5% propane and nitrogen mixed gas as reaction raw materials, and react at 600℃, normal pressure and propane mass space velocity of 0.6h ^-1 reaction conditions, After continuously feeding the reaction raw materials for 5 minutes, the mixed gas at the outlet was subjected to composition measurement, the contents of propane and propylene were detected, and the conversion rate of propane and the selectivity of propylene were calculated. The results of this example are reported in Table 1.

Comparative ratio

Take 4.0g of anhydrous glucose and mix it with 40mL of deionized water evenly, transfer it to 80mL of PTFE Uchimura stainless steel autoclave, heat it with water at 180℃ for 12h, and after cooling, use deionized water to filter and wash the product several times. Until the filtrate was colorless, the filtered product was dried at 110 °C for 12 h, and after drying, it was calcined at a low temperature of 400 °C for 2 h under a nitrogen atmosphere. Mix 1.1 g of the original carbon material after low-temperature calcination with an aqueous solution without NaOH, and stir for 12 h; the stirred product was dried at 110 °C for 12 h, and then dried at 700 °C under a nitrogen atmosphere for 2 h at high temperature. It was washed with suction for several times until neutral, dried at 110 °C for 12 h, and finally reduced under a hydrogen atmosphere at 580 °C for 1 h to obtain catalyst F.

Take 0.2gF catalyst and load it into a fixed-bed micro-reaction device, take 5% propane and nitrogen mixed gas as reaction raw materials, and react at 600 ℃, normal pressure and propane mass space velocity of 0.6h ^-1 under the reaction conditions, After continuously feeding the reaction raw materials for 5 minutes, the mixed gas at the outlet was subjected to composition measurement, the contents of propane and propylene were detected, and the conversion rate of propane and the selectivity of propylene were calculated. The results of this comparative example are reported in Table 1.

Table 1

When the reaction was carried out for 5 min, since the activity of the catalyst did not substantially decrease due to the progress of the reaction, the activity at this time can be regarded as the initial activity of the catalyst. It can be seen from Table 1 that the propane of Examples 1 to 5 Compared with the comparative example, the conversion rate has different degrees of improvement, while the propane selectivity is different, indicating that the treatment of carbon materials with strong alkali solution can improve its adsorption and processing capacity for propane, while the selectivity should be selected. A suitable ratio of strong alkali solution can achieve the effect of improving the selectivity of propylene, as shown in Example 3. Comparing the scanning electron microscope images of the catalyst F of the comparative example and the catalyst C of the present invention (FIG. 1 and FIG. 2), it can be found that the catalyst C after the strong alkali treatment has a honeycomb-like porous structure, while the catalyst F of the comparative example does not have this structure, indicating that the strong Alkali treatment can remove unstable impurity carbon on the original carbon material and can create a large number of pores; this honeycomb-like porous structure can increase the contact area between propane and active groups, and secondly, it can quickly desorb the product propylene and prevent further deep cracking This leads to a decrease in the selectivity of the target product propylene.

Below the catalyst C that embodiment 3 obtains is carried out long-time reaction activity test:

Take 0.2gC catalyst and load it into a fixed-bed micro-reaction device, use a mixture of propane and nitrogen with a volume fraction of 5% as the reaction raw material, and react at 600 ℃, normal pressure and propane mass space velocity of 0.6h-1 under the reaction conditions, And every 30min, the mixed gas at the outlet is measured for composition, the content of propane and propylene is detected, and the conversion rate of propane and the selectivity of propylene are calculated. The reaction lasted for a total of 10 h, and the test results were recorded in Table 2.

Table 2

It can be seen from Table 2 that the catalyst prepared by the present invention can maintain high reactivity under long-term reaction conditions, and produces less by-products during the reaction. Due to the problem of carbon deposition in the reaction process, the catalytic activity of the catalyst is gradually reduced, but because the catalyst prepared by the present invention is low in cost, environmentally friendly and simple in preparation, it can be replaced when the reaction activity is low without causing production costs. greater impact.

Claims (9)

1. a method for preparing non-metallic porous carbon material catalyst with saccharide as raw material, is characterized in that: comprise the following steps: s1. Mix the carbohydrate raw material with water, place it in a hydrothermal kettle, and perform hydrothermal carbonization at 120 to 200° C. to obtain a carbonized material, and filter and wash the carbonized material; s2, roasting the carbonized material at a low temperature of 300-600 °C; s3, put the carbonized material after low-temperature roasting into a strong alkaline aqueous solution and stir to remove the amorphous carbon therein, then roast at a high temperature at 600-1100 °C, and then wash the carbonized material after high-temperature roasting to neutrality; s4, performing reduction treatment on the carbonized material obtained in s3 using a reducing agent or a hydrogen reducing atmosphere to obtain a non-metallic porous carbon material catalyst; The strong alkali aqueous solution is a NaOH solution, a KOH solution or a mixed solution of NaOH and KOH, and the quality of the alkali in the strong alkali aqueous solution is 1 to 10 times the quality of the carbonized material after low-temperature roasting in s2. 2. a kind of method for preparing non-metallic porous carbon material catalyst with saccharide as raw material according to claim 1, is characterized in that: described saccharide is selected from starch, sucrose, fructose, glucose, maltose, cellulose or one or more of lactose. 3. a kind of method for preparing non-metallic porous carbon material catalyst with saccharide as raw material according to claim 1, is characterized in that: the reducing agent described in s4 is selected from ethylene glycol, C1～C3 carboxylic acid or One or more of C1~C3 sodium carboxylates. 4. a kind of method for preparing non-metallic porous carbon material catalyst with saccharide as raw material according to claim 1, is characterized in that: in the described strong alkali aqueous solution, the quality of strong alkali is the carbonized material after low-temperature roasting in s2 2 to 4 times the mass. 5 . The method for preparing a non-metallic porous carbon material catalyst by using sugars as a raw material according to claim 1 , wherein the temperature of the high-temperature roasting process is 650-750° C. 6 . 6 . The method for preparing a non-metallic porous carbon material catalyst with saccharides as a raw material according to claim 1 , wherein the low-temperature roasting process is carried out under a protective atmosphere of inert gas or nitrogen. 7 . 7 . The method for preparing a non-metallic porous carbon material catalyst with saccharides as a raw material according to claim 1 , wherein the high-temperature roasting process is carried out under a protective atmosphere of inert gas or nitrogen. 8 . 8. A non-metallic porous carbon material catalyst, characterized in that: prepared by the method according to any one of claims 1 to 7. 9. Application of the non-metallic porous carbon material catalyst of claim 8 in catalyzing propane dehydrogenation to propylene.

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