Nickel tungsten carbide catalyst for catalytic synthesis of ethylene glycol, preparation method and application

Abstract

The application discloses a nickel tungsten carbide catalyst for catalytically synthesizing ethylene glycol, a preparation method and application. The catalyst is prepared by using blueberry wine lees carbon pretreated by acid and alkali as a carrier and using nickel tungsten carbide as an active component. The loading amount of tungsten carbide is 10% to 40% and the loading amount of nickel is 0.5% to 5% based on the total mass of the catalyst. The active component is dispersed on the surface and in the pores of the carrier to form a nanoscale active phase. The catalyst can realize efficient and high-selectivity conversion of cellulose under mild to moderate reaction conditions, directly generate ethylene glycol, and exhibit significantly better cycle stability and sintering resistance than existing non-noble metal catalyst systems.

Description

Technical Field

[0001] This invention relates to a nickel-tungsten carbide catalyst for the catalytic synthesis of ethylene glycol, its preparation method, and its application, belonging to the field of chemical engineering. Background Technology

[0002] Ethylene glycol, commonly known as glycol, is the simplest diol. Since its discovery in the mid-19th century, it has gradually developed from a common chemical reagent into an indispensable bulk basic organic chemical raw material in modern chemical industry, and is known as one of the "chemical masterbatches". The most important use of ethylene glycol is in the polycondensation reaction with purified terephthalic acid (PTA) to produce polyester (PET). Polyester materials are widely used in fibers, bottle chips, films and other fields, and are an important source of synthetic materials in daily life. In addition, due to the significantly lower freezing point and higher boiling point of aqueous ethylene glycol solutions—for example, the freezing point of a 60% aqueous ethylene glycol solution can drop to -48°C—it is a key component in the formulation of engine coolants (antifreeze) for automobiles, ships and other vehicles, accounting for about 50% of the antifreeze composition. This property effectively ensures the normal starting and operation of vehicles in extremely cold environments.

[0003] Several key defects exist in existing biomass catalytic conversion technologies and their catalyst systems: First, insufficient catalytic efficiency and selectivity: Cellulose molecules have high crystallinity and a dense hydrogen bond network, making efficient activation and directional bond breaking difficult, resulting in low conversion rates. Furthermore, the reaction pathway is complex, easily generating various byproducts such as lactic acid, acetic acid, and polyols, and the selectivity for the target product, ethylene glycol, is unsatisfactory. Second, poor catalyst stability: Under the relatively harsh reaction conditions required for the hydrothermal conversion of cellulose (medium-high temperature, high-pressure water environment), the active components of traditional catalysts are prone to sintering, loss, or phase transformation, leading to rapid degradation of catalytic performance and poor recyclability. Third, high catalyst cost and poor support compatibility: High-performance catalysts often rely on noble metals (such as Ru and Pt) or use conventional commercial carbon materials (such as activated carbon) whose structure and surface chemistry have not been optimized as supports. These supports lack ideal compatibility with cellulose macromolecules and reaction media: their pore structure may be unfavorable for the diffusion and mass transfer of cellulose-derived intermediates, and their surface properties make it difficult to achieve efficient anchoring and stable dispersion of non-noble metal active centers, thus restricting further improvement in the overall performance and cost-effectiveness of the catalyst. Summary of the Invention

[0004] As a first aspect of the present invention, a nickel-tungsten carbide catalyst for the catalytic synthesis of ethylene glycol is provided, which uses blueberry lees char pretreated with acid and alkali as a support and nickel-tungsten carbide as an active component; wherein, based on the total mass of the catalyst, the loading of tungsten carbide is 10%-40% and the loading of nickel is 0.5%-5%, and the active component is dispersed on the surface and in the pores of the support to form a nanoscale active phase.

[0005] The loading of tungsten carbide is 25%-35%, and the loading of nickel is 1%-3%.

[0006] As a second aspect of the present invention, a method for preparing the nickel-tungsten carbide catalyst for the catalytic synthesis of ethylene glycol as described above is provided, comprising the following steps:

[0007] (1) Preparation of carrier: Blueberry lees were dried at 105℃ and normal pressure for 24h to obtain dried blueberry lees. The dried blueberry lees were placed in a tube furnace and heated to 500-600℃ at 3-5℃ / min under a nitrogen / air mixed atmosphere (nitrogen: air = 20:1) and held for 80-100min. After the reaction was completed, the reactants were taken out while hot and sprayed with water to cool down quickly. After cooling, they were washed with water and dried at 80℃ to obtain blueberry lees char.

[0008] (2) Carrier pretreatment:

[0009] Alkali washing: Place the blueberry lees charcoal in a 3%-10% sodium hydroxide aqueous solution and reflux at 70-90℃ for 2-6 hours. After the reaction is complete, filter while hot, wash with deionized water until the filtrate is neutral, and dry at 80-110℃.

[0010] Acid washing: Place the alkaline-washed blueberry lees charcoal in a 3%-10% nitric acid (HNO3) aqueous solution and reflux at 60-80℃ for 2-6 hours. After the reaction is complete, filter, wash with deionized water until the filtrate is neutral, and dry at 80-110℃.

[0011] Objective: To remove impurities from the surface of blueberry lees charcoal and introduce oxygen-containing functional groups to enhance the anchoring ability of metal precursors;

[0012] (3) Equal volume impregnation load:

[0013] According to the above-designed loading, weigh out the tungsten source precursor (such as ammonium metatungstate, AMT) and the nickel source precursor (such as nickel nitrate, Ni(NO3)2·6H2O), dissolve them together in deionized water, and prepare a metal salt mixed solution; the volume of the solution is equal to the pore volume of the blueberry lees char obtained in step (1) (i.e., equal volume impregnation method); add the above mixed solution dropwise to the pretreated blueberry lees char, sonicate at room temperature for 20-40 minutes to mix it evenly, and then stir and impregnate at room temperature for 12-36 hours; finally, dry the impregnated sample in an oven at 100-120℃ for 6-12 hours to obtain the catalyst precursor;

[0014] (4) Programmed temperature reduction carbonization:

[0015] The dried catalyst precursor was placed in a tube furnace for programmed temperature reduction carbonization treatment, the specific steps of which are as follows:

[0016] ① Inert gas purging: Inert gas (such as N2 or Ar) is introduced into the tubular furnace at a flow rate of 50-200 mL / min for 20-40 minutes to completely remove air from the furnace.

[0017] ② Switch to reducing gas: Switch the gas to a reducing gas (such as H2), with a gas flow rate of 50-200 mL / min, and purge for 10-20 minutes;

[0018] ③Programmed temperature rise: Increase the temperature from room temperature to 400-500℃ at a first heating rate of 5-15℃ / min; then, slowly increase the temperature to 700-800℃ at a second heating rate of 0.5-2℃ / min (this slow heating stage is key to the formation of uniform carbides).

[0019] ④Heat preservation: Maintain a constant temperature at the final temperature for 0.5-4 hours to allow the metal oxides to be fully reduced and carbonized, forming nickel-tungsten carbides (Ni-W). x C) Active phase;

[0020] ⑤ Cooling and passivation: After the reaction is completed, stop heating and allow the catalyst to cool naturally to below 200°C under a reducing atmosphere. Then switch to an inert gas (such as N2) to protect it and cool it to room temperature. Subsequently, passivate the catalyst by introducing an inert gas mixture containing 0.5%-2% O2 (such as 1% O2 / N2) for 6-12 hours to form a dense oxide film on its surface, which allows it to be stably stored in air.

[0021] As a third aspect of the present invention, a method for synthesizing ethylene glycol using the above-mentioned nickel-tungsten carbide catalyst is provided. Biomass raw materials and the above-mentioned catalyst are added to a high-pressure reactor at a mass ratio of 1:(0.075-0.5). Deionized water is added as a solvent, and the reactor is sealed. The air inside the reactor is first replaced with inert gas 3-5 times, and then replaced with hydrogen gas 3-5 times. Hydrogen gas with an initial pressure of 2-10 MPa is introduced into the reactor. The reaction system is heated to 220-260°C at a rate of 2-10°C / min and reacted at this temperature for 0.5-6 hours. After the reaction is completed, the mixture is rapidly cooled to room temperature. The reaction product is removed, and after filtering to separate the catalyst, the liquid product is subjected to chromatographic analysis.

[0022] The beneficial effects that this invention can produce include:

[0023] (1) Development of a special carrier suitable for cellulose conversion reaction: The pore size distribution and surface chemical properties of conventional carbon carriers (such as activated carbon) are difficult to perfectly match with cellulose macromolecules and their hydrolysis and hydrogenation cracking reaction pathways; This invention innovatively uses blueberry lees char (BRC) as a carrier to solve this compatibility problem: its unique interconnected hierarchical porous structure (coexistence of micro-meso-macropores) provides superior diffusion channels and abundant accessible active sites for cellulose-derived macromolecular intermediates, effectively alleviating mass transfer limitations, which is not available in many commercial carbon materials; its natural surface properties and elemental composition can be precisely controlled after specific acid and alkali pretreatment, which is more conducive to the anchoring and dispersion of active components;

[0024] (2) Establishing a precise carrier surface pretreatment process to optimize the construction of active sites: In order to solve the problem of possible impurity interference on the surface of BRC carrier and the weak interaction between it and active components, this invention adopts a set of precise acid and alkali pretreatment processes: Alkali washing: not only removes some ash impurities, but more importantly, it regulates the acidity and alkalinity of the carrier surface and the distribution of functional groups, creating an environment more conducive to the adsorption and interaction of nickel and tungsten precursors; Acid washing: further purifies the pores, removes soluble inorganic salts, and may introduce an appropriate amount of oxygen-containing functional groups to enhance the bonding strength between the carrier and metal species, laying the foundation for the subsequent formation of highly dispersed and stable nickel-tungsten carbide nano-active phases;

[0025] (3) During the process of impregnating and loading nickel and tungsten active components in equal volume, ultrasonic treatment and long-term stirring are combined. The ultrasonic action promotes the penetration and dispersion of the metal salt solution in the pores of the carrier, while the subsequent continuous stirring ensures the uniformity and consistency of the loading process, laying an important foundation for the formation of a highly dispersed active phase.

[0026] (4) Constructing a non-precious metal active center with high activity, high selectivity and excellent stability: Through the successful application and fine pretreatment of the above BRC support, combined with the optimized impregnation and programmed temperature reduction carbonization process, the aim is to prepare a novel catalyst with highly dispersed Ni-WxC nanoparticles and strong interaction with the support; the catalyst needs to be able to achieve efficient and highly selective conversion of cellulose under mild to moderate intensity reaction conditions, directly generate ethylene glycol, and exhibit significantly better cycle stability and anti-sintering ability than existing non-precious metal catalyst systems. Attached Figure Description

[0027] Figure 1 This is a gas chromatogram of the product according to Example 1 of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these embodiments.

[0029] Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased through commercial channels.

[0030] In the embodiments of the present invention, the ethylene glycol yield is calculated according to the formula: Yield (%) = (mass of ethylene glycol in the product) / (mass of cellulose added to the reactor) × 100%.

[0031] Example 1

[0032] 20g of blueberry lees was dried at 105℃ under normal pressure for 24h to obtain 7.4g of dried blueberry lees. The dried blueberry lees was placed in a tube furnace and heated to 500℃ at 3℃ / min under a nitrogen / air mixed atmosphere (nitrogen:air = 20:1) and held for 100min. After the reaction was completed, the reactants were removed while hot and sprayed with water to cool them down quickly. The cooled carbon was washed with water and dried at 80℃ to obtain blueberry lees char. Organic element analysis of blueberry lees char: 1.59% N, 86.85% C, 2.15% H, 0.14% S, 5.98% O; Industrial analysis: fixed carbon 83.67%, ash 2.58%, moisture 6.54%, volatile matter 7.21%.

[0033] Weigh 4.6 g of blueberry lees activated carbon and place it in a round-bottom flask containing 150 mL of 5 wt% NaOH solution. Reflux at 80 °C for 4 h. After the reaction is complete, filter while hot, wash with deionized water until the filtrate is neutral, and dry at 80 °C. Place the alkali-treated activated carbon in 150 mL of 5 wt% HNO3 solution and reflux at 70 °C for 4 h. Filter and wash with water until neutral, then dry at 80 °C to obtain pretreated blueberry lees activated carbon.

[0034] Accurately weigh 1.188g of ammonium metatungstate ((NH4)2) 10 Dissolve H2(W2O7)6·6H2O in 10 mL of deionized water, then add 0.297 g of Ni(NO3)2·6H2O and stir until completely dissolved. Add 2.0 g of pretreated activated carbon to the solution, sonicate for 30 min, and then stir continuously at room temperature for 24 h. Dry the mixture at 120 °C for 8 h to obtain the catalyst precursor.

[0035] The precursor was placed in a magnetic boat and transferred to a tube furnace. It was first purged with N2 for 20 min, then switched to H2 and purged for 10 min. Subsequently, under H2 atmosphere, the temperature was increased to 450℃ at 10℃ / min, then increased to 750℃ at 1℃ / min and held for 1 h. After the reaction, it was allowed to cool naturally to 200℃ under H2 atmosphere, then switched to N2 protection and cooled to room temperature. Afterwards, a 1% O2 / N2 mixture was introduced for passivation treatment for 9 h. The resulting catalyst was stored in a vacuum desiccator and labeled as 2%Ni-30%W. x C / AC.

[0036] Cellulose was subjected to segmental vacuum drying at 80℃ and 120℃ for a total of 6 hours. 3g of dried cellulose, 0.9g of the above-mentioned catalyst, and 15mL of deionized water were added to a high-pressure reactor. After sealing, the reactor was first purged with N2 four times, then with H2 four times, and H2 was added until the initial pressure reached 8MPa. The temperature was increased to 245℃ at a rate of 5℃ / min, and the reaction was carried out for 0.5 hours. The reactor was then rapidly cooled, filtered, and refrigerated. Gas chromatography analysis was performed, and the gas chromatogram is attached. Figure 1 In the figure, peak 4 represents the target product, ethylene glycol, and the figure shows that few byproducts were generated. Gas chromatography analysis showed that the yield of ethylene glycol was 91%.

[0037] Example 2

[0038] With other conditions remaining unchanged, the processing conditions of the blueberry lees were modified: the dried blueberry lees were placed in a tube furnace, and under a nitrogen / air mixed atmosphere, the temperature was increased to 550°C at a rate of 5°C / min and held for 80 min. After the reaction was completed and the temperature was lowered to room temperature, the next step of alkaline washing was performed. The remaining steps were the same as in Example 1. The calcination program in catalyst preparation was adjusted: the heating rate in the first stage was changed to 8°C / min to 450°C, and in the second stage it was 1.5°C / min to 700°C, with the holding time extended to 3 h and the passivation time changed to 10 h. The remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 75%.

[0039] Example 3

[0040] With other conditions remaining unchanged, the pretreatment conditions for blueberry lees charcoal were modified: the alkaline washing temperature was adjusted to 85℃, the acid washing temperature was adjusted to 75℃, and the remaining steps were the same as in Example 1. The calcination program in catalyst preparation was adjusted: the first stage heating rate was changed to 8℃ / min to 450℃, the second stage to 1.5℃ / min to 700℃, the holding time was extended to 3 hours, and the passivation time was changed to 10 hours; the remaining steps were the same as in Example 1. Gas chromatography analysis showed an ethylene glycol yield of 68%.

[0041] Example 4

[0042] With other conditions remaining unchanged, the pretreatment conditions for blueberry lees charcoal were modified: the alkaline washing temperature was adjusted to 75℃, and the acid washing temperature was adjusted to 65℃; the remaining steps were the same as in Example 1. The calcination program in catalyst preparation was adjusted: the first stage heating rate was changed to 12℃ / min to 450℃, and the second stage heating rate was 0.5℃ / min to 800℃; the holding time was shortened to 0.5h, and the passivation time was changed to 8h; the remaining steps were the same as in Example 1. Gas chromatography analysis showed an ethylene glycol yield of 73%.

[0043] Example 5

[0044] With other conditions remaining unchanged, the pretreatment conditions for blueberry lees charcoal were modified: acid-base pretreatment was omitted, and the blueberry lees charcoal was directly used for impregnation of Ni / W; the remaining steps were the same as in Example 1. The calcination program in catalyst preparation was adjusted: the first stage heating rate was changed to 12℃ / min to 450℃, and the second stage was 0.5℃ / min to 800℃, with the holding time shortened to 0.5h and the passivation time changed to 8h; the remaining steps were the same as in Example 1. Gas chromatography analysis showed an ethylene glycol yield of 52%.

[0045] Example 6

[0046] With other conditions unchanged, the loading of the active component was adjusted: 0.9029 g of ammonium metatungstate and 0.9194 g of Ni(NO3)2·6H2O were weighed to prepare the impregnation solution, thus obtaining 0.5% Ni-40% W. x The catalyst was C / AC, and the remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 48%.

[0047] Example 7

[0048] With other conditions unchanged, the loading of the active component was adjusted: 1.9591 g of ammonium metatungstate and 0.0565 g of Ni(NO3)2·6H2O were weighed to prepare the impregnation solution, thus obtaining 5%Ni-10%W. x The catalyst was C / AC, and the remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 45%.

[0049] Example 8

[0050] With other conditions unchanged, the feed ratio was changed, and 3g of dried cellulose, 0.225g of the above catalyst, and 15mL of deionized water were added to the high-pressure reactor. After sealing, the reactor was first purged with N2 four times, then with H2 four times, and H2 was added until the initial pressure reached 2MPa. The temperature was increased to 220℃ at 2℃ / min, and the reaction was carried out for 6 hours. After rapid cooling, the reaction solution was filtered, refrigerated, and analyzed by gas chromatography. The remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 35%.

[0051] Example 9

[0052] With other conditions unchanged, the feed ratio was changed, and 3g of dried cellulose, 0.45g of the above catalyst, and 15mL of deionized water were added to a high-pressure reactor. After sealing, the reactor was first purged with N2 four times, then with H2 four times, and H2 was added until the initial pressure reached 10MPa. The temperature was increased to 260℃ at 10℃ / min, and the reaction was carried out for 0.5h. After rapid cooling, the reaction solution was filtered, refrigerated, and analyzed by gas chromatography. The remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 56%.

[0053] Example 10

[0054] With other conditions unchanged, the raw materials were changed. 3g of dried glucose, 0.9g of the above catalyst and 15mL of deionized water were added to the high-pressure reactor. The remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 82%.

[0055] Example 11

[0056] With other conditions unchanged, the catalyst raw material was changed. Instead of using blueberry lees charcoal, conventional finished activated carbon (≥100 mesh) was used. The remaining steps were the same as in Example 1. Gas chromatography analysis showed that the ethylene glycol yield was 64%.

[0057] The results from the above examples show that, compared with conventional finished activated carbon, using blueberry lees char as a catalyst support increased the ethylene glycol yield by 27 percentage points, indicating that the catalytic effect of blueberry lees char as a catalyst support is significant. Regarding the loading of active components, the ethylene glycol yields in Examples 6 and 7 are both less than 50%, while the loading of active components in Example 1 is 2% Ni - 30% W. x C / AC significantly improves the ethylene glycol yield; as can be seen from Example 10, even when using glucose as a raw material, the ethylene glycol yield can still exceed 75%, reaching 82%, which further verifies the rationality and efficiency of the ethylene glycol synthesis process catalyzed by the catalyst formed by the treatment of blueberry lees char as a carrier in this invention.

Claims

1. The application of a nickel-tungsten carbide catalyst for the catalytic synthesis of ethylene glycol, characterized in that, 3g of biomass feedstock and 0.9g of catalyst were added to a high-pressure reactor at a mass ratio of 1:0.

3. 15mL of deionized water was added as a solvent. The reactor was sealed, and the air inside was first replaced with nitrogen four times, followed by hydrogen four times. Hydrogen gas with an initial pressure of 8MPa was introduced into the reactor, and the reaction system was heated to 245℃ at a rate of 5℃ / min and reacted at this temperature for 0.5h. After the reaction was completed, it was rapidly cooled to room temperature, and the reaction product was taken out. After filtering to separate the catalyst, the liquid product was subjected to chromatographic analysis. The biomass feedstock used was cellulose or glucose. The catalyst uses blueberry lees char pretreated with acid and alkali as a support and nickel tungsten carbide as the active component. Based on the total mass of the catalyst, the loading of tungsten carbide is 30% and the loading of nickel is 2%. The active component is dispersed on the surface and in the pores of the support to form a nanoscale active phase. The method for preparing the catalyst includes the following steps: (1) Preparation of carrier: 20g of blueberry lees was dried at 105℃ and normal pressure for 24h to obtain 7.4g of dried blueberry lees. The dried blueberry lees was placed in a tube furnace and heated to 500℃ at 3℃ / min under a nitrogen / air mixed atmosphere. The temperature was maintained for 100min. After the reaction was completed, the reactants were taken out while hot and sprayed with water to cool down quickly. After cooling, the reactants were washed with water and dried at 80℃ to obtain blueberry lees char. (2) Carrier pretreatment: Alkali washing: Place 4.6g of blueberry lees charcoal in 150mL of 5wt% sodium hydroxide aqueous solution, reflux at 80℃ for 4h, filter while hot after the reaction is complete, wash with deionized water until the filtrate is neutral, and dry at 80℃. Acid washing: The alkaline-washed blueberry lees charcoal was placed in 150 mL of 5 wt% nitric acid aqueous solution and refluxed at 70 °C for 4 h. After the reaction was completed, it was filtered, washed with deionized water until the filtrate was neutral, and dried at 80 °C. (3) Equal volume impregnation load: According to the above-designed loading, 1.188g of tungsten source precursor and 0.297g of nickel source precursor were weighed and dissolved together in 10mL of deionized water to prepare a metal salt mixed solution; the volume of the solution was equal to the pore volume of the blueberry lees char obtained in step (1); the above mixed solution was added dropwise to 2.0g of pretreated blueberry lees char, and ultrasonically treated at room temperature for 30 minutes to make it uniformly mixed, and then stirred and impregnated at room temperature for 24h; finally, the impregnated sample was dried in an oven at 120℃ for 8h to obtain the catalyst precursor; (4) Programmed temperature reduction carbonization: The dried catalyst precursor was placed in a tube furnace for programmed temperature reduction carbonization treatment, the specific steps of which are as follows: ① Inert gas purging: Inert gas is introduced into the tubular furnace and purged for 20 minutes to completely remove the air from the furnace; ② Switch to reducing gas: Switch the gas to a reducing gas and purge for 10 minutes; ③Programmed temperature rise: The temperature is increased from room temperature to 450℃ at a first heating rate of 10℃ / min; then, it is slowly increased to 750℃ at a second heating rate of 1℃ / min. ④Heat preservation: Maintain a constant temperature at the final temperature for 1 hour to allow the metal oxides to be fully reduced and carbonized, forming a nickel-tungsten carbide active phase; ⑤ Cooling and passivation: After the reaction is completed, heating is stopped and the catalyst is naturally cooled to 200°C under H2 atmosphere. Then, it is cooled to room temperature under inert gas protection. Subsequently, a mixed gas containing 1% O2 / N2 is introduced to passivate the catalyst for 9 hours, so that a dense oxide film is formed on its surface, which can be stably stored in air. In step (1), the carrier is prepared in a nitrogen / air mixed atmosphere with a nitrogen:air ratio of 20:

1. In step (3), the tungsten source precursor in the equal-volume impregnation load is ammonium metatungstate, and the nickel source precursor is nickel nitrate. In step (4) of the programmed temperature rise reduction carbonization, the inert gas is N2; the reducing gas is H2.

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