Preparation method of high-activity low-load palladium-carbon catalyst for disproportionated rosin

Abstract

The invention discloses a preparation method of a high-activity low-load palladium-carbon catalyst for disproportionated rosin. The preparation method comprises the following steps: 1) preparing a carbon carrier; 2) preparing a palladium precursor solution; 3) preparing a reducing agent solution; 4) reduction treatment; and 5) vacuum drying. According to the invention, palladium nitrate is used as a precursor of an active component palladium, activated carbon is used as a carrier, water is used as a solvent, and the catalyst is prepared by combining a deposition-precipitation method and wet reduction. The activity of the prepared catalyst is improved by 1.27 times, meanwhile, the palladium consumption is reduced by 50%, and the consumption of precious metal resources is remarkably reduced. The palladium-carbon catalyst prepared by the method has the characteristics of high dispersity, small particle size and low precious metal palladium consumption, shows remarkable catalytic activity, can be continuously and repeatedly used for more than five times, and has good application prospect and practical value.

Description

Technical Field

[0001] The present invention relates to the field of deep processing of rosin, and particularly to a preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin. Background Art

[0002] Disproportionated rosin is widely used in industry due to its low production cost and large consumption. Potassium salt of disproportionated rosin is an important auxiliary raw material in the production of synthetic rubber and is used as an emulsifier for emulsion polymerization in the production of synthetic rubbers such as styrene-butadiene rubber, chloroprene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene-styrene copolymer, etc. In recent years, it has been found that dehydroabietic acid, the main component of disproportionated rosin, can be used as a raw material for producing physiologically active materials and also has optical activity. Therefore, disproportionated rosin also has wide application value in the fields of medicine, pesticides, and photochemistry.

[0003] The main component of rosin is abietic acid type resin acid. Due to the presence of relatively high-energy conjugated double bonds in abietic acid, rosin has extremely unstable properties and is easily oxidized by oxygen in the air to form dark-colored oxidized rosin, accompanied by polymerization in this process. In order to change the unstable structure of the conjugated double bond, abietic acid has a tendency to dehydrogenate to form a benzene ring or add hydrogen to remove the double bond to transform into a relatively stable form. The rosin disproportionation reaction is a process in which hydrogenation and dehydrogenation reactions occur simultaneously. Under the action of a catalyst, two hydrogen atoms are lost from the conjugated double bonds in some abietic acid molecules to form a stable benzene ring structure, generating dehydroabietic acid (DAA); at the same time, some other abietic acid molecules obtain two or four hydrogen atoms to generate dihydroabietic acid (DDAA) or tetrahydroabietic acid (TAA). This process not only changes the chemical structure of rosin but also significantly improves its thermal stability and chemical stability, making the disproportionated rosin have a wider application prospect and higher commercial value in the fields of rubber, coatings, adhesives, etc.

[0004] Currently, the types of catalysts for rosin disproportionation reaction are mainly divided into non-noble metal catalysts and noble metal catalysts. Non-noble metal catalysts mainly include transition metal single-element catalysts (mainly using Fe, Co, Ni, Cu, etc. as active components, TiO2 or activated carbon as carriers), iodine catalysts, and sulfide catalysts. Although such non-noble metal catalysts have achieved certain effects in the laboratory research stage, there are still problems such as low activity, large consumption of transition metals, long reaction time, high reaction temperature, corrosion of equipment, and environmental pollution, which limit their application and development in the production process of disproportionated rosin.

[0005] At present, palladium-carbon noble metal catalysts are mainly used in the preparation of disproportionated rosin at home and abroad. Due to its advantages in the rosin disproportionation catalytic reaction, such as high activity, good selectivity, short reaction time, low temperature, and small dosage, it is widely used in industrial production. However, the methods for preparing palladium-carbon catalysts are different. For example, the dispersibility of activated carbon is different, and its activity is also different. In addition, the activated carbon in the existing palladium-carbon catalysts still has the following problems:

[0006] (1) Palladium loaded on activated carbon has poor dispersion and is easy to agglomerate, resulting in larger particle size, which reduces the number of active centers per unit surface area of activated carbon and reduces the catalytic activity of activated carbon;

[0007] (2) The amount of precious metal palladium used is large, and it is necessary to reduce the amount of precious metal to reduce production costs;

[0008] (3) It is easy to lose activation, has poor stability, and can be reused only a few times.

[0009] Therefore, how to prepare a palladium-carbon catalyst for disproportionated rosin preparation with good dispersibility, low precious metal loading, high catalytic activity and good repeated stability is a technical problem to be solved urgently in this field. Summary of the invention

[0010] In view of this, the present invention provides a method for preparing a high-activity low-loaded palladium-carbon catalyst for disproportionated rosin.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0012] A method for preparing a high-activity low-load palladium-carbon catalyst for disproportionated rosin comprises the following steps:

[0013] 1) Preparation of carbon carrier: weigh Na2CO3 and dissolve it in deionized water, then add activated carbon, stir, adjust the pH value of the solution, and prepare a uniform carbon slurry solution;

[0014] 2) preparing a palladium precursor solution: measuring a palladium precursor solution, dissolving it in water and stirring it evenly, then adding a dispersant and stirring to prepare a solution A;

[0015] 3) Prepare reducing agent solution: weigh the reducing agent and dissolve it in deionized water, stir and mix well, and record it as solution B;

[0016] 4) Reduction treatment: Solution A and solution B are added dropwise to the activated carbon solution under magnetic stirring, heated in a water bath, and reacted at a constant temperature;

[0017] 5) Vacuum drying: After the reaction is completed, the mixed solution in step 4) is vacuum filtered and washed with anhydrous ethanol and deionized water respectively, and then placed in a vacuum drying oven to dry overnight to obtain the palladium carbon catalyst with the required palladium loading amount.

[0018] Preferably, in the step 1), the addition amount of Na2CO3 is 0.1 - 0.2 g, the addition amount of deionized water is 50 mL, and the addition amount of activated carbon is 1.00 g.

[0019] Preferably, in the step 1), the activated carbon has a specific surface area of more than 1500 m 2 / g, a total pore volume of 1.38 cm 3 / g, more micropores, well-developed mesopores, and an average pore diameter of 3 nm, which is a wood-based activated carbon.

[0020] Preferably, in the step 1), the stirring time is 10 - 30 minutes, and the pH value of the solution is adjusted to 8 - 10.

[0021] Preferably, in the step 2), the palladium precursor solution is palladium nitrate, chloropalladic acid, palladium acetate, or palladium acetylacetonate solution; the palladium loading is 1.00 - 4.00 wt%; and the palladium concentration is 0.4 - 1.6 mg / L.

[0022] Preferably, in the step 2), the dispersant is sodium citrate, citric acid, polyethylene glycol PEG, or polyvinylpyrrolidone PVP. The addition amount is 5 - 10 times the mass of palladium, the concentration of the added dispersant is 2000 - 4000 mg / L, and the stirring time is 3 - 8 hours.

[0023] Preferably, in the step 3), the reducing agent is sodium borohydride, ethylene glycol, hydrazine hydrate, formaldehyde, or ascorbic acid.

[0024] Preferably, in the step 3), the concentration of the added reducing agent is 1000 - 5000 mg / L.

[0025] Preferably, in the step 4), the temperature of the water bath heating is 30 - 70 °C, and the constant temperature reaction time is 3 - 5 hours.

[0026] Preferably, in the step 5), the washing sequence of anhydrous ethanol and deionized water is to wash 3 times with deionized water first, then wash 3 times with anhydrous ethanol, and finally wash 2 times with deionized water; the temperature of the vacuum drying is 60 - 70 °C.

[0027] The present invention has achieved the following technical effects compared with the prior art:

[0028] (1) The highly active palladium-carbon catalyst for disproportionated rosin prepared by the present invention has a high dispersion degree, which can reach 33.13% - 38.17%. The Pd nanoparticles have uniform sizes of 3 - 6 nm and high catalytic activity.

[0029] (2) The preparation method of the present invention greatly reduces the dosage of precious metal palladium, realizes the reduction of precious metals, and compared with the commercial palladium-carbon catalyst used in the market, the palladium-carbon catalyst prepared by the present invention has 1.27 times higher activity, while the palladium dosage is reduced by 50%, significantly reducing the consumption of precious metal resources and effectively reducing the production cost;

[0030] (3) The disproportionated rosin prepared by the present invention has a higher acid value, lighter color, and the highest DAA yield can reach 71.13%;

[0031] (4) The highly active palladium-carbon catalyst for disproportionated rosin prepared by the present invention still has high catalytic activity after multiple cycles of rosin disproportionation experiments, and the dehydroabietic acid content remains at a high level (≥52%), indicating that the prepared palladium-carbon catalyst has good stability and reusability;

[0032] (5) The preparation method of the present invention is simple, mild in conditions, low in cost, easy to industrialize, and will not cause additional environmental hazards, improving the utilization efficiency of biomass resources, solving the problem of recycling of agricultural and forestry waste, and has great social significance and economic value. Description of the Drawings

[0033] Figure 1 It is the transmission electron microscope TEM images of six samples obtained from Examples 1-6 of the present invention;

[0034] Figure 2 It is the nitrogen adsorption-desorption isotherm, pore size distribution and X-ray diffraction powder diffraction XRD images of six samples obtained from Examples 1-6 of the present invention;

[0035] Figure 3 It is the X-ray photoelectron spectroscopy XPS images of six samples obtained from Examples 1-6 of the present invention;

[0036] Figure 4 It is the catalytic performance images of six samples obtained from Examples 1-6 of the present invention for rosin disproportionation reaction under different reaction times, catalyst dosages and palladium loadings;

[0037] Figure 5 It is the catalytic performance images of the sample obtained from Example 3 of the present invention for rosin disproportionation reaction at different temperatures;

[0038] Figure 6 It is the catalytic performance comparison images of the sample obtained from Example 3 of the present invention and the commercial palladium-carbon catalyst (Pd loading 4wt%) used in the market in rosin disproportionation reaction;

[0039] Figure 7 It is the catalytic performance stability cycle test images of the sample obtained from Example 3 of the present invention under the experimental conditions of 270 °C, 0.04wt% addition amount, 180 minutes and nitrogen. Detailed implementation mode

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] A preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin includes the following steps:

[0042] 1) Prepare the carbon support: Weigh 0.12 g of Na2CO3 and dissolve it in 50 mL of deionized water, then add 1.00 g of activated carbon. The activated carbon is wood-based activated carbon with a specific surface area greater than 1500 m 2 / g, a total pore volume of 1.38 cm 3 / g, more micropores, well-developed mesopores, and an average pore diameter of 3 nm. Stir for 10 - 30 minutes, adjust the pH value of the solution to 8 - 10, and make a uniform carbon slurry solution;

[0043] 2) Prepare the palladium precursor solution: Measure a certain amount of palladium precursor solution according to a palladium loading of 1.00 - 4.00 wt% (weight ratio of palladium / activated carbon), dissolve it in water and stir evenly, then add a dispersant. The dispersant is sodium citrate, citric acid, polyethylene glycol PEG, polyvinylpyrrolidone PVP, and the addition amount is 5 - 10 times the mass of palladium; Stir for 3 - 8 hours to prepare solution A;

[0044] 3) Prepare the reducing agent solution: Weigh the reducing agent and dissolve it in deionized water. The reducing agent is sodium borohydride, ethylene glycol, hydrazine hydrate, formaldehyde, and ascorbic acid, with an addition concentration of 1000 - 5000 mg / L, stir and mix evenly, and record it as solution B;

[0045] 4) Reduction treatment: Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring respectively, heat with a water bath, and the temperature of the water bath heating is 30 - 70 °C, and the constant temperature reaction time is 3 - 5 hours;

[0046] 5) Vacuum drying: After the reaction is completed, vacuum filter the mixed solution in step 4) and wash it with absolute ethanol and deionized water respectively. The washing order of absolute ethanol and deionized water is to wash 3 times with deionized water first, then wash 3 times with absolute ethanol, and finally wash 2 times with deionized water; Then place it in a vacuum drying oven for overnight drying, and the temperature of the vacuum drying is 60 - 70 °C, and the palladium-carbon catalyst with the required palladium loading is obtained.

[0047] Example 1:

[0048] 1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon, add it to the above solution, stir for 10 min, and adjust the solution pH = 10;

[0049] 2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate, add it, and stir for 6 h to prepare solution A;

[0050] 3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, and record it as solution B;

[0051] 4) Add solution A and solution B drop by drop to the activated carbon solution under magnetic stirring, and then carry out a constant temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0052] 5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 1-Pd / C.

[0053] Example 2:

[0054] 1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon, add it to the above solution, stir for 10 min, and adjust the solution pH = 10;

[0055] 2) Measure 0.0324 g (0.324 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate, add it, and stir for 6 h to prepare solution A;

[0056] 3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, and record it as solution B;

[0057] 4) Add solution A and solution B drop by drop to the activated carbon solution under magnetic stirring, and then carry out a constant temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0058] 5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 1.5-Pd / C.

[0059] Example 3:

[0060] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon, add it to the above solution, stir for 10 min, and adjust the solution pH = 10;

[0061] (2) Measure 0.0433 g (0.433 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate and add it, stir for 6 h to prepare solution A;

[0062] (3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, denoted as solution B;

[0063] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then carry out a constant temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0064] (5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 2-Pd / C.

[0065] Example 4:

[0066] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 min, and adjust the solution pH = 10;

[0067] (2) Measure 0.054 g (0.540 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate and add it, stir for 6 h to prepare solution A;

[0068] (3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, denoted as solution B;

[0069] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then carry out a constant temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0070] (5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 2.5-Pd / C.

[0071] Example 5:

[0072] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH = 10;

[0073] (2) Measure 0.0649 g (0.649 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate and add it, stir for 6 h to prepare solution A;

[0074] (3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, and record it as solution B;

[0075] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then carry out a constant-temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0076] (5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 3-Pd / C.

[0077] Example 6:

[0078] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH = 10;

[0079] (2) Measure 0.0866 g (0.866 mL, 100 g / L stock solution) of palladium nitrate solution and 20 mL of deionized water, stir evenly, add 0.1 g of sodium citrate, and stir for 6 h to prepare solution A;

[0080] (3) Weigh a certain amount of NaBH4 and dissolve it in 20 mL of deionized water, stir and mix evenly, and record it as solution B;

[0081] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then carry out a constant-temperature reaction at 60 °C with a rotation speed of 500 RPM for 4 h;

[0082] (5) After the reaction is completed, filter and wash with deionized water 5 times, and carry out vacuum drying at 60 °C for 8 h to obtain the palladium-carbon catalyst, denoted as 4-Pd / C.

[0083] Example 7:

[0084] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH = 10;

[0085] (2) Measure 0.0216 g (0.2165 mL, 100 g / L stock solution) of palladium nitrate solution and 20 mL of deionized water, stir evenly, add 0.1 g of sodium citrate, and stir for 10 min to prepare solution A;

[0086] (3) Weigh a certain amount of ethylene glycol and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0087] (4) Add solution A and solution B drop by drop into the activated carbon solution under magnetic stirring, and then carry out a constant temperature reaction at 70 °C with a rotation speed of 600 RPM for 4 h;

[0088] (5) After the reaction is completed, filter and wash 5 times with deionized water, and vacuum dry at 60 °C for 8 h to obtain the palladium-carbon catalyst.

[0089] Example 8:

[0090] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH = 10;

[0091] (2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate and add it, stir for 10 min to prepare solution A;

[0092] (3) Weigh a certain amount of hydrazine hydrate and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0093] (4) Add solution A and solution B drop by drop into the activated carbon solution under magnetic stirring, and then react at 70 °C with a rotation speed of 600 RPM for 4 h;

[0094] (5) After the reaction is completed, filter and wash 5 times with deionized water, and vacuum dry at 60 °C for 8 h to obtain the palladium-carbon catalyst.

[0095] Example 9:

[0096] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of Up water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH = 10;

[0097] (2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of sodium citrate (10 times the mass of palladium) and add it, stir for 10 min to prepare solution A;

[0098] (3) Weigh a certain amount of sodium borohydride and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0099] (4) Add solution A and solution B drop by drop into the activated carbon solution under magnetic stirring, and then react at 70 °C under stirring for 4 h;

[0100] (5) After the reaction is completed, filter and wash 5 times with deionized water, and vacuum dry at 60 °C for 8 h to obtain the palladium-carbon catalyst.

[0101] Example 10

[0102] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of ultrapure water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH to 10;

[0103] (2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of polyethylene glycol (PEG) and add it, stir for 10 min to prepare solution A;

[0104] (3) Weigh a certain amount of sodium borohydride and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0105] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then react for 4 h under stirring at 70 °C;

[0106] (5) After the reaction is completed, filter and wash 5 times with deionized water, and vacuum dry at 60 °C for 8 h to obtain the palladium-carbon catalyst.

[0107] Example 11:

[0108] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of ultrapure water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH to 10;

[0109] (2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir evenly, weigh 0.1 g of (PVP) and add it, stir for 10 min to prepare solution A;

[0110] (3) Weigh a certain amount of sodium borohydride and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0111] (4) Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring, and then react for 4 h under stirring at 70 °C;

[0112] (5) After the reaction is completed, filter and wash 5 times with deionized water, and vacuum dry at 60 °C for 8 h to obtain the palladium-carbon catalyst.

[0113] Example 12:

[0114] (1) Dissolve 0.12 g of Na2CO3 in 50 mL of ultrapure water, weigh 1.00 g of activated carbon and add it to the above solution, stir for 10 minutes, and adjust the solution pH to 10;

[0115] (2) Measure 0.0216 g (0.2165 mL, stock solution of 100 g / L) of palladium nitrate solution and 20 mL of deionized water, stir well, weigh 0.1 g of polyvinylpyrrolidone (PVP) and add it, stir for 10 min to prepare solution A;

[0116] (3) Weigh a certain amount of sodium borohydride and dissolve it in 25 mL of deionized water, stir and mix evenly, and record it as solution B;

[0117] (4) Add solution A and solution B drop by drop into the activated carbon solution under magnetic stirring respectively, and then react under stirring at 70 °C for 4 h;

[0118] (5) After the reaction is completed, filter and wash with deionized water 5 times, and vacuum dry at 60 °C for 8 h to obtain the Pd / C catalyst.

[0119] Performance evaluation method of Pd / C catalyst for disproportionation of rosin:

[0120] Accurately weigh 200 g of raw rosin, crush it and put it into a three-necked flask under nitrogen protection, put in a magnetic rotor, install a thermometer, turn on the switch of the constant temperature heating magnetic stirrer for heating, and turn on the constant temperature heating magnetic stirrer switch when the rosin becomes liquid, and adjust the stirring scale to between 1 and 2; observe the thermometer, when the temperature reaches 230 °C, add 0.06 g (addition amount of three ten-thousandths) of Pd / C catalyst with a dry weight that has been weighed into the three-necked flask and mix it evenly with the rosin. When the temperature reaches 270 °C, start timing, keep the temperature at 270 - 280 °C, keep warm for 1 h, take a small amount of the product with a pipette for analysis, continue to keep warm for 1 h, and then take a sample.

[0121] The contents of abietic acid and dehydroabietic acid in the reaction product are determined with reference to GB / T 14020-2006 of China; weigh about 0.025 g (accurate to 0.0001 g) of the disproportionated rosin product after removing the outer surface into a clean and dry 10 mL small beaker, add a small amount of absolute ethanol to completely dissolve the sample, and then transfer it into a 50 mL volumetric flask, and add absolute ethanol to the mark, shake well and set aside.

[0122] Transfer absolute ethanol into two clean quartz cuvettes with a thickness of 1 cm respectively, and then transfer the test solution into the same cuvette, wipe the outer wall of the cuvette clean with lens paper; put it into the cuvette rack of the ultraviolet spectrophotometer, adjust the slit width of the instrument to 0.2 nm, and measure at ultraviolet light with wavelengths of 241 nm and 250 nm, 273 nm and 276 nm and nearby respectively, and calculate by canceling the values at the peak and valley of the extinction value. The abietic acid content is calculated according to formula (1), and the dehydroabietic acid content is calculated according to formula (2):

[0123] Abietic acid:

[0124] Dehydroabietic acid:

[0125] Where: E 241 , E 250 , E 273 , E 276 are the values at the peak and valley of the extinction value of ultraviolet light near wavelengths of 241 nm, 250 nm, 273 nm, and 276 nm, respectively;

[0126] c—the concentration of the sample, unit (g / L);

[0127] l—the thickness of the cuvette, unit centimeter (cm);

[0128] k—the specific absorption coefficient of pure abietic acid (k = 28);

[0129] f—the specific absorption coefficient of pure dehydroabietic acid (f = 1.06);

[0130] Table 1 is a summary of the results of rosin disproportionation evaluation (the experimental conditions for the rosin disproportionation reaction are: reaction temperature 270 °C, reaction time 2 h, catalyst addition amount 0.03%, under nitrogen atmosphere).

[0131] Table 1:

[0132]

[0133]

[0134] Among them, the analysis methods of the transmission electron microscope (TEM) images, nitrogen adsorption-desorption isotherms and pore size distribution diagrams, X-ray powder diffraction (XRD) diagrams, and X-ray photoelectron spectroscopy (XPS) diagrams of the six Pd / C catalyst samples prepared in Examples 1-6 are as follows.

[0135] I. High-resolution transmission electron microscope test method:

[0136] The transmission electron microscope (TEM) uses an electron wave to penetrate a thin sample and forms an image by focusing with a magnetic lens to observe the internal structure and interfacial characteristics of the sample. The TEM used in this experiment is the FEI Talos F200X G2 transmission electron microscope from the United States, equipped with a high-resolution field emission gun, with a device resolution of 0.16 nm and a scanning speed as high as 105 spectra / second. During the sample preparation process, the powder sample is dispersed in an ethanol solution and ultrasonically treated for 20 min to ensure sufficient dispersion. Subsequently, a glass capillary is used to suck the mixed solution and drop it onto a copper grid with a carbon film to form a thin layer. After the ethanol evaporates, the sample film is formed, and then it can be installed on the sample stage and inserted into the electron microscope for TEM observation.

[0137] II. Specific surface area determination:

[0138] Experimental method: The specific surface area of all phosphoric acid modified biochars was measured using a specific surface area analyzer. A laboratory specific surface area analyzer (JW-BK132F) was used to characterize the samples. Mainly through the BET method, with N2 as the interaction medium, when the specified relative pressure is reached, under the low-temperature liquid nitrogen environment, N2 will have a physical interaction with the surface of the solid sample. By calculating the pressure difference before and after the interaction, the specific surface area, pore size, pore volume distribution, and nitrogen interaction desorption curve are calculated according to the BET formula, so as to obtain the specific surface area of each sample.

[0139] The specific steps are as follows: Weigh about 100 mg of the dried biochar powder sample and load it into the carrier tube, and a mandrel must be added to the carrier tube. Then place it at the instrument pretreatment station and heat it under negative pressure at 120 °C for 3 h to ensure that the sample is completely dried of water vapor. After heating, move the sample carrier tube to the sample workstation and turn on the vacuum pump (and check for air leakage). Create a new workstation and start pre-pumping, then start the experiment, select the micropore integrated analysis module, and set the parameters. After the pressure is less than 0.2 KPa, raise the liquid nitrogen cup. Make sure the carrier tube is completely inside the liquid nitrogen cup before leaving. After the micropore integrated measurement is completed, create a new workstation to measure the cold free space coefficient. After the measurement is completed, recheck the mass: Take out the liquid nitrogen cup from the workstation, start pre-pumping and heating for 15 min. After completion, stop pre-pumping and fill with nitrogen. After the pressure returns to 80 KPa, take out the carrier tube and reweigh the mass. Calculate the average value of the Q value and input it into the micropore integrated module to obtain the specific surface area and micropore data.

[0140] III. XRD measurement:

[0141] Experimental method: X-ray diffraction analysis (XRD) obtains information on its composition or molecular structure by analyzing the diffraction pattern generated by the sample. In this experiment, a Rigaku Ultima IV rotating anode X-ray diffractometer was used. After pressing the dried sample into a tablet and putting it into the X-ray generator for testing. The radiation source is a Cu-Kα target (wavelength λ = 0.15406 nm), and the tube voltage is set at 40 kV and the tube current is 40 mA. The test conditions include a scanning speed of 10 ° / min, a scanning range of 5 - 90 °, using the θ - 2θ step scanning method, a step size of 0.01 °, and a fixed counting time of 3 seconds for each step. X-ray diffraction method (X-Ray Diffraction, XRD) is mainly used to determine the composition, relative content, and grain size of nanomaterials. A research method that analyzes the diffraction pattern of a substance using X-ray diffraction technology to obtain information such as the composition of the substance, the structure or morphology of atoms or molecules inside the substance.

[0142] IV. XPS measurement:

[0143] Experimental method: X-ray photoelectron spectroscopy (XPS) obtains information on the elemental composition and atomic valence states of the sample surface by measuring the energies of photoelectrons emitted after the sample is excited by X-rays. In this experiment, a Thermo Scientific K-Alpha XPS instrument from the United States was used, with monochromatic Al Kα rays (hv = 1486.6 eV) as the radiation source, and charge correction was performed using C1s contaminated carbon (284.80 eV). The sample was fixed on a dedicated sample tray after being pressed into a tablet, and detected under an ultra-low pressure (2.0×10 -7 mbar), with a spot size of 400 μm, an operating voltage of 12 kV, and a filament current of 6 mA. The full-spectrum scanning energy range was 150 eV, and the resolution step was 1 eV; the narrow-spectrum scanning energy range was 50 eV, and the resolution step was 0.1 eV. To improve the signal-to-noise ratio, at least 5 cumulative scans were performed in each elemental region, and the analysis chamber was maintained at a high vacuum (≤5.0×10 -7 mbar).

[0144] Experimental results: Through detection, the TEM images, nitrogen adsorption-desorption isotherms and pore size distribution diagrams, X-ray diffraction powder diffraction XRD diagrams, and X-ray photoelectron spectroscopy XPS diagrams of Examples 1-6 are shown in Figure 1 , Figure 2 and Figure 3 respectively.

[0145] The palladium loadings, specific surface areas, pore size distributions, and sizes of the Pd / C catalysts prepared in Examples 1-6 are shown in Table 2. The palladium content in the prepared palladium / carbon (Pd / C) catalysts was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Table 2 shows that the palladium loadings of the six samples were 1.00 wt%, 1.50 wt%, 2.00 wt%, 2.50 wt%, 3.00 wt%, and 4.00 wt% respectively, which were consistent with the target concentrations. This confirmed the successful synthesis of the Pd / C catalysts. In addition, we measured the specific surface area (SBET), total pore volume (TPV), average pore size (MPS), grain size, and palladium dispersion of the Pd / C catalysts, and the results were summarized in Table 2. As the palladium loading increased, the SBET and TPV of the Pd / C catalysts decreased significantly, from 1605.10 m 2 / g and 1.38 cm 3 / g to 667.23 m 2 / g and 0.65 cm3 / g respectively. This decrease was attributed to the aggregation of palladium nanoparticles on the surface or within the pores of the activated carbon support. It should be noted that the increase in the palladium loading on the activated carbon increased the number of active sites, thus enhancing the activity of the catalyst.

[0146] Table 2:

[0147]

[0148]

[0149] a : Determined by ICP - AES; b : Determined by N2 physical adsorption method; c : Calculated by the Scherrer formula; d : The Pd dispersion value (D) is calculated from the crystallite size.

[0150] Figure 1 are TEM images of the Pd / C catalysts with a Pd loading of 1 - 4% prepared in Examples 1 - 6. Against the lighter - colored AC background, a large number of darker PdNPs are clearly visible, confirming the high - density uniform dispersion of PdNPs on AC. To accurately determine the average particle size of the catalyst, 200 particles were randomly selected for analysis in this study, and the results are as Figure 1 (a - f) shown. Statistical analysis shows that PdNPs are highly dispersed on the AC surface, with an average size ranging from 3.32 to 5.98 nm. As the Pd loading increases, the size of PdNPs increases and the size distribution range broadens. The average Pd size calculated according to the Scherrer formula (see Table 2) is consistent with the TEM observation results. When the Pd loading exceeds 2.00 wt%, significant aggregation of Pd species occurs, resulting in a decrease in its dispersion on AC. The HAADF - STEM image shows that the lattice spacing is 0.222 - 0.226 nm, corresponding to the (111) crystal plane of PdNPs.

[0151] Figure 2 (a - f) are the nitrogen adsorption - desorption isotherms, pore size distribution diagrams, and XRD patterns of the Pd / C catalysts with a Pd loading of 1 - 4% prepared in Examples 1 - 6. According to the classification standard of the International Union of Pure and Applied Chemistry (IUPAC), both AC and Pd / C catalysts exhibit typical type - IV adsorption isotherms, indicating the co - existence of micropores and mesopores. The sharp adsorption in the low relative pressure region (P / P0 = 0.00 - 0.05) corresponds to the presence of micropores; the hysteresis loop in the medium pressure region (P / P0 = 0.45 - 1.00) indicates the presence of mesopores. The pore size distribution (PSD) curve calculated by DFT shows a uniform distribution of pore sizes in the range of 0.50 to 10.00 nm. The activated carbon support has significant peaks at 1.1 nm (micropores) and 4.08 nm (mesopores), while the pore sizes of the Pd / C catalysts are mainly concentrated at 1.05, 1.83, and 3.68 nm. Compared with AC, the Pd / C catalyst has zero dv / dD pore volume in the range of 0.50 - 0.65 nm, suggesting that the increase in Pd loading leads to a decrease in micropore and total pore volume. The specific surface areas (SBET,m) of AC and Pd / C catalysts 2 / g) Calculated by the Brunauer-Emmett-Teller (BET) equation, as the Pd loading increases, both SBET and TPV decrease: 1-Pd / C (1568.77 m 2 / g, 1.14 cm 3 / g) > 1.5-Pd / C (1482.63 m 2 / g, 1.02 cm 3 / g) > 2-Pd / C (1229.15 m 2 / g, 0.95 cm 3 / g) > 2.5-Pd / C (1081.50 m 2 / g, 0.85 cm 3 / g) > 3-Pd / C (764.85 m 2 / g, 0.75 cm 3 / g) > 4-Pd / C (667.23 m 2 / g, 0.65 cm 3 / g). This trend indicates that Pd nanoparticles (PdNPs) with sizes similar to mesopores may partially block the pores of the support. Consistent with the TEM observations, it shows that Pd NPs may be anchored by the mesopores in the activated carbon, resulting in a decrease in the BET surface area and pore size. At the same time, a larger BET surface area also indicates that there are numerous active catalytic sites on the surface of the activated carbon support, which play an important role in promoting the adsorption and activation processes.

[0152] The XRD pattern shows that the broad peak at 26.0° corresponds to the characteristics of the carbon support (PDF#75 - 0444). In addition, there are three obvious diffraction peaks, corresponding to the (111), (200), and (220) crystal planes of metallic Pd (PDF#00 - 005 - 0681), respectively. At low Pd loadings, the Pd characteristic peaks are hardly visible, indicating the presence of small and highly dispersed PdNPs on the surface of activated carbon (AC)

[126] . When the Pd loading exceeds 2.00 wt%, an obvious diffraction peak appears at 40.1°, corresponding to the (111) crystal plane of Pd, which plays a key role in the dehydrogenation reaction. As the Pd loading increases, the intensity of this peak increases significantly, indicating the effective deposition of Pd. The XRD data is consistent with the ICP - AES results in Table 2. Based on the full width at half - maximum of the Pd(111) peak at 40.1°, the size order of Pd NPs calculated by the Scherrer equation is: 1 - Pd / C < 1.5 - Pd / C < 2 - Pd / C < 2.5 - Pd / C < 3 - Pd / C < 4 - Pd / C. The Pd dispersions calculated from the grain sizes are 38.17%, 37.67%, 36.81%, 33.73%, 34.55%, and 33.13% for the 1 - Pd / C, 1.5 - Pd / C, 2 - Pd / C, 2.5 - Pd / C, 3 - Pd / C, and 4 - Pd / C catalysts, respectively. Although the overlap of the carbon support peaks may affect the measurement accuracy, the trends of the grain size and Pd dispersion changes are consistent with the TEM results, further verifying the catalyst characterization results.

[0153] Figure 3 (a - f) are the XPS spectra of Pd / C catalysts with Pd loadings of 1 - 4% prepared in Examples 1 - 6. In this study, XPS analysis of the Pd 3d energy level was carried out. The deconvoluted XPS spectra show two pairs of characteristic peaks in the Pd / C catalysts. The peaks located at 335.20 - 336.26 eV and 340.33 - 341.29 eV correspond to Pd 0 's Pd 3d 5 / 2 and Pd 3d 3 / 2 orbitals, while the weaker peaks at 336.21 - 337.56 eV and 341.35 - 342.78 eV are attributed to Pd 2+ species, originating from the same orbitals. Further quantitative analysis shows that from the 1 - Pd / C to 4 - Pd / C catalysts, the Pd 0 signal intensity gradually increases, and the Pd 2+ signal intensity decreases correspondingly. Specifically, the Pd 0The proportions are 41.60%, 56.27%, 65.29%, 65.99%, 69.07% and 75.90% respectively. Higher Pd 0 and Pd 2+ ratios and enhanced peak intensities significantly improved the catalytic activity of the Pd / C catalyst.

[0154] Figure 4 Figure showing the catalytic performance of the six samples obtained in Examples 1 - 6 for the disproportionation reaction of rosin under different experimental conditions (reaction time, catalyst dosage, and palladium loading) (using the DAA and AA contents as indicators, the larger the DAA content and the smaller the AA content, the better the catalytic activity);

[0155] Figure 5 Figure showing the catalytic performance of the sample obtained in Example 3 for the disproportionation reaction of rosin at different temperatures, demonstrating the influence of reaction temperature on the catalytic performance of the Pd / C catalyst in the rosin disproportionation reaction. Under the experimental conditions of 0.03 wt% catalyst dosage, 2 - hour reaction time, 2.0 wt% palladium loading, and nitrogen atmosphere, the DAA content increased with increasing temperature. When the temperature increased from 230 °C to 270 °C, the DAA content increased significantly from 7.92% to 54.52%. The reaction rate increased most significantly between 230 °C and 250 °C, and then the increase rate slowed down. Thus, 270 °C was determined to be the optimal temperature for the rosin disproportionation reaction. Previous studies have shown that the activation energy of AA dehydrogenation is higher than that of the hydrogenation process, which means that at higher temperatures, the dehydrogenation reaction will dominate. Given that the dehydrogenation reaction is reversible and endothermic, and it leads to an increase in the number of molecules, increasing the reaction temperature can enhance the selectivity of the rosin disproportionation dehydrogenation process.

[0156] Figure 6 Figure comparing the catalytic performance of the sample obtained in Example 3 with a commercially available palladium - carbon catalyst (Pd loading 4 wt%) used in the rosin disproportionation reaction. Under standard reaction conditions (270 °C, 180 minutes, 0.04 wt% catalyst dosage, nitrogen atmosphere), the 2 - Pd / C catalyst was superior to the commercial catalyst in terms of reducing the AA content and increasing the DAA selectivity. Notably, when the palladium dosage was halved, the activity of the 2 - Pd / C catalyst increased by 1.27 times, significantly improving the cost - effectiveness and sustainability. Compared with other catalysts reported in the literature, the catalyst in this study has more advantages in terms of cost - performance. Through the analysis of Figure 4 the data, it can be seen that the Pd / C catalysts with different palladium loadings synthesized in this invention all exhibited excellent catalytic activity. The obtained disproportionated rosin products meet the strict requirements of the forestry standard LY / T 1357 - 2008 for super - grade disproportionated rosin, i.e., the dehydroabietic acid content ≥ 52% and the abietic acid content ≤ 0.1%.

[0157] Comprehensive comparative analysis shows that the catalyst of the present invention not only has excellent catalytic performance but also has a relatively low preparation cost, and has great practical application prospects in the industrial rosin disproportionation process.

[0158] Figure 7 It is a graph of the catalytic performance stability cycle test carried out on the sample obtained in Example 3 under the experimental conditions of 270 °C, an addition amount of 0.04 wt%, 180 minutes, and nitrogen. The stability test results show that the catalytic efficiency of the 2-Pd / C catalyst gradually decreases within five operating cycles, and the DAA content in the disproportionated rosin decreases from 71.13% to 56.82%. Nevertheless, the catalyst still maintains a DAA content of 56.82%, meeting the national special-grade rosin standard, indicating its good industrial application prospects.

[0159] As mentioned above, it is only a preferred embodiment of the present invention, and does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin, characterized in that, It includes the following steps: 1) Prepare the carbon support: Weigh Na2CO3 and dissolve it in deionized water, then add activated carbon and stir. Adjust the pH value of the solution to make a uniform carbon paste solution; 2) Prepare the palladium precursor solution: Measure the palladium precursor solution, dissolve it in water and stir evenly, then add a dispersant and stir to prepare solution A; 3) Prepare the reducing agent solution: Weigh the reducing agent and dissolve it in deionized water, stir and mix evenly, and record it as solution B; 4) Reduction treatment: Dropwise add solution A and solution B into the activated carbon solution under magnetic stirring respectively, heat with a water bath, and carry out a constant temperature reaction; 5) Vacuum drying: After the reaction is completed, vacuum filter the mixture in step 4) and wash it with absolute ethanol and deionized water respectively, and then place it in a vacuum drying oven to dry overnight to obtain the palladium-carbon catalyst with the required palladium loading amount.

2. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 1), the addition amount of Na2CO3 is 0.1 - 0.2 g, the addition amount of deionized water is 50 mL, and the addition amount of activated carbon is 1.00 g.

3. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In the said step 1), the activated carbon is a wood-based activated carbon with a specific surface area greater than 1500 m 2 / g, a total pore volume of 1.38 cm 3 / g, more micropores, well-developed mesopores, and an average pore diameter of 3 nm.

4. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 1), the stirring time is 10 - 30 minutes, and the pH value of the solution is adjusted to 8 - 10.

5. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 2), the palladium precursor solution is palladium nitrate, palladium chloroacid, palladium acetate, palladium acetylacetonate solution; the palladium loading amount is 1.00 - 4.00 wt%; the palladium concentration is 0.4 - 1.6 mg / L.

6. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 2), the dispersant is sodium citrate, citric acid, polyethylene glycol PEG, polyvinylpyrrolidone PVP, the addition amount is 5 - 10 times the mass of palladium, the concentration of the added dispersant is 2000 - 4000 mg / L, and the stirring time is 3 - 8 hours.

7. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 3), the reducing agent is sodium borohydride, ethylene glycol, hydrazine hydrate, formaldehyde and ascorbic acid.

8. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 3), the concentration of the added reducing agent is 1000 - 5000 mg / L.

9. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 4), the temperature of the water bath heating is 30 - 70 °C, and the constant temperature reaction time is 3 - 5 hours.

10. The preparation method of a highly active and low-loading palladium-carbon catalyst for disproportionated rosin according to claim 1, characterized in that, In step 5), the washing sequence of absolute ethanol and deionized water is to wash 3 times with deionized water first, then wash 3 times with absolute ethanol, and finally wash 2 times with deionized water; the temperature of vacuum drying is 60 - 70 °C.

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