Catalyst for hydrofining crude terephthalic acid and preparation method thereof

文档序号:1806826 发布日期:2021-11-09 浏览:38次 中文

阅读说明:本技术 粗对苯二甲酸加氢精制催化剂及其制备方法 (Catalyst for hydrofining crude terephthalic acid and preparation method thereof ) 是由 肖忠斌 朱小丽 于 2020-05-08 设计创作,主要内容包括:本发明涉及粗对苯二甲酸加氢精制催化剂及其制备方法,主要解决现有技术中存在的催化剂初活性高导致加氢精制产品中对甲基苯甲酸偏高的问题,本发明通过采用粗对苯二甲酸加氢精制催化剂,所述催化剂包括载体和活性组分,所述的载体为活性炭,所述活性组分为钯元素,所述钯元素包括Pd~(0)和Pd~(+2),且Pd~(+2)与Pd~(0)的重量比为0.3~3的技术方案,较好地解决了该技术问题,可用于粗对苯二甲酸加氢精制生产中。(The invention relates to a crude terephthalic acid hydrofining catalyst and a preparation method thereof, mainly solving the problem that the initial activity of the catalyst in the prior art is high, which causes the p-toluic acid in a hydrofining product to be higherThe acid hydrorefining catalyst comprises a carrier and an active component, wherein the carrier is activated carbon, the active component is palladium element, and the palladium element comprises Pd 0 And Pd +2 And Pd +2 And Pd 0 The weight ratio of the component (a) to the component (b) is 0.3-3, so that the technical problem is well solved, and the method can be used in the hydrofining production of crude terephthalic acid.)

1. The catalyst comprises a carrier and an active component, wherein the carrier is activated carbon, the active component is palladium element, and the palladium element comprises Pd0And Pd+2And Pd+2And Pd0The weight ratio of (A) to (B) is 0.3 to 3. More preferably 0.4 to 0.7.

2. The catalyst of claim 1, wherein the palladium content in the catalyst is 0.2 to 1.0 wt%. More preferably 0.3 to 0.6 wt%.

3. The catalyst of claim 1, wherein the activated carbon is coal, wood or shell carbon. The shell carbon is preferably coconut shell carbon.

4. The catalyst according to claim 1, wherein the specific surface area of the carrier is 800 to 1600m2/g。

5. The catalyst according to claim 1, wherein the carrier preferably has a pore volume of 0.35 to 0.80 ml/g.

6. A method of preparing the catalyst of claim 1, comprising the steps of:

(1) adjusting the pH value of the palladium-containing compound aqueous solution to 1-10 by using an alkaline compound to obtain a catalyst precursor;

(2) mixing a carrier and a catalyst precursor to obtain a catalyst precursor i;

(3) aging the catalyst precursor i in the step (2) to obtain a catalyst precursor ii;

(4) carrying out heat treatment on the catalyst precursor ii in the step (3) under an inert atmosphere to enable palladium element to exist in a PdO form, so as to obtain a catalyst precursor iii; the temperature of the heat treatment is preferably 300-600 ℃; the time of heat treatment is preferably 1-8 h;

(5) reducing part of the combined palladium in the catalyst precursor iii in the step (4) into Pd by using a reducing agent0To obtain a catalyst precursor iv;

(6) washing with water removes impurities from the catalyst precursor iv to obtain the catalyst.

7. The process according to claim 6, wherein the basic compound in the step (1) is at least one of an alkali metal hydroxide, an alkali metal carbonate or ammonia.

8. The method according to claim 6, wherein the palladium-containing compound in the step (1) is at least one selected from the group consisting of palladium nitrate, palladium acetate, chloropalladic acid and salts thereof, and tetraamminepalladium dichloride.

9. Use of the catalyst according to any one of claims 1 to 5 or the catalyst obtained by the preparation method according to any one of claims 6 to 9 for hydrorefining hydrogenation of crude terephthalic acid.

10. A process for hydrorefining crude terephthalic acid, which comprises subjecting crude terephthalic acid to a hydrorefining reaction with hydrogen in the presence of the catalyst according to any one of claims 1 to 5 or the catalyst obtained by the production process according to any one of claims 6 to 9, using water as a solvent, to obtain refined terephthalic acid. Preferably, the reaction temperature of hydrofining is 265-295 ℃. Preferably, the reaction pressure for hydrorefining is 7.0 to 10.0 MPa.

Technical Field

The invention relates to a crude terephthalic acid hydrofining catalyst and a preparation method thereof.

Background

Purified terephthalic acid, commonly known as PTA, is a basic raw material for the synthesis of polyethylene terephthalate (PET). The supported palladium/carbon catalyst is suitable for refining crude terephthalic acid, wherein impurities such as p-carboxybenzaldehyde (4-CBA for short) in the crude terephthalic acid are hydrogenated and converted into other compounds, and then separated and purified by adopting a crystallization method. Because the palladium/carbon catalyst adopts a single active component, the distribution condition of metal palladium on the carrier has great influence on the performance of the catalyst.

The reaction pressure of the terephthalic acid hydrofining is 6.5-8.5 MPa, the reaction temperature is 250-290 ℃, the reaction process of the terephthalic acid hydrofining is a first-stage reaction, the reaction speed is high, reactants are difficult to penetrate into catalyst particles to react in the reaction process, and therefore active metals in the particles cannot contact with molecular components of the reactants with large diameters to play a role due to steric effect. At this time, the active metal of the outer surface exhibits high catalytic activity. In order to fully utilize the noble metal, the palladium/carbon catalyst is usually made into an eggshell type, that is, the active component palladium is mainly loaded on the surface of the carrier. The greater the surface area of the palladium in contact with the reactants, the better the activity. The catalyst with the distributed eggshell type active components has higher hydrogenation catalytic capability than the catalyst with wider distribution range. However, in the initial stage of the reaction, due to the overhigh palladium reaction activity, the terephthalic acid is over-hydrogenated to generate p-toluic acid (p-TA), and the solubility of the p-TA in water is much smaller than that of the methyl hydroxybenzoic acid (HMBA) and the Benzoic Acid (BA), so that the excessive p-TA in the reaction product is difficult to remove, and the p-TA in the PTA product exceeds the standard. U.S. Pat. No. 4,892,972(Purification of particulate terephthalic acid) reduces the p-toluic acid (p-TA) content of the PTA product by employing a Pd/C and Rh/C double layer catalyst, with a Pd to Rh ratio of 10:1, for the hydrofinishing of crude terephthalic acid, but Rh is ten times more expensive than Pd and therefore not practical.

Disclosure of Invention

One of the technical problems to be solved by the invention is the problem that the initial activity of the catalyst in the prior art is high, which results in higher p-toluic acid in a hydrofining product, and provides a novel catalyst for hydrofining crude terephthalic acid, which is used for the hydrofining reaction of the crude terephthalic acid and has the characteristic of low p-toluic acid.

The second technical problem to be solved by the present invention is a method for preparing a catalyst corresponding to the first technical problem.

The third problem to be solved by the present invention is the application of the above catalyst.

The fourth problem to be solved by the present invention is a process for hydrorefining crude terephthalic acid.

In order to solve one of the above technical problems, the technical scheme adopted by the invention is as follows:

the catalyst comprises a carrier and an active component, wherein the carrier is activated carbon, the active component is palladium element, and the palladium element comprises Pd0And Pd+2And Pd+2And Pd0The weight ratio of (A) to (B) is 0.3 to 3.

We have surprisingly found that when the palladium element in the catalyst comprises Pd0And Pd+2And Pd+2And Pd0When the weight ratio of (a) to (b) is 0.3-3, the catalyst is used for hydrofining reaction of crude terephthalic acid, and has the advantage of low residue of p-toluic acid.

In the above technical solution, by way of non-limiting example, Pd+2And Pd0The weight ratio of (A) to (B) may be 0.35, 0.4, 0.45, 0.5, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.9, 0.95, 1.0, etc., more preferably 0.4 to 0.7.

In the technical scheme, the content of the palladium element in the catalyst is preferably 0.2-1.0 wt%. Such as, but not limited to, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.60 wt%, 0.65 wt%, 0.70 wt%, and the like.

In the above technical solution, Pd is preferred as the catalyst+2In the form of PdO.

In the above technical scheme, the activated carbon is preferably coal, wood or shell carbon.

In the above technical scheme, the shell carbon is preferably coconut shell carbon.

In the technical scheme, the specific surface of the carrier is preferably 800-1600 m2(ii) in terms of/g. Such as but not limited to 850m2/g、900m2/g、950m2/g、1000m2/g、1500m2/g、2000m2G,/etc.

In the technical scheme, the pore volume of the carrier is preferably 0.35-0.80 ml/g. Such as, but not limited to, 0.40ml/g, 0.45ml/g, 0.50ml/g, 0.55ml/g, 0.60ml/g, 0.65ml/g, 0.70ml/g, 0.75ml/g, and the like.

To solve the second technical problem, the invention adopts the following technical scheme:

the preparation method of the catalyst in the technical scheme of one of the technical problems comprises the following steps:

(1) adjusting the pH value of the palladium-containing compound aqueous solution to 1-10 by using an alkaline compound to obtain a catalyst precursor;

(2) mixing a carrier and a catalyst precursor to obtain a catalyst precursor i;

(3) aging the catalyst precursor i in the step (2) to obtain a catalyst precursor ii;

(4) carrying out heat treatment on the catalyst precursor ii in the step (3) under an inert atmosphere to enable palladium element to exist in a PdO form, so as to obtain a catalyst precursor iii;

(5) reducing part of the combined palladium in the catalyst precursor iii in the step (4) into Pd by using a reducing agent0To obtain a catalyst precursor iv;

(6) washing with water removes impurities from the catalyst precursor iv to obtain the catalyst.

In the above technical solution, the catalyst carrier in step (2) may be directly prepared from commercially available activated carbon, or may be added before step (1):

(i) washing and drying the commercially available activated carbon; and/or

(ii) The commercially available activated carbon is treated in an aqueous solution containing an oxidant, and then drained and dried.

In the above technical solution, the temperature of the heat treatment in the step (4) is preferably 300 to 600 ℃, for example, but not limited to 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, and the like.

In the above technical scheme, the time for the heat treatment in the step (4) is preferably 1 to 8 hours, such as but not limited to 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours and the like;

in the above technical solution, the alkaline compound in step (1) is preferably at least one of alkali metal hydroxide, alkali metal carbonate or ammonia, most preferably alkali metal carbonate, and sodium carbonate is most common and most inexpensive, and therefore sodium carbonate is most preferred, and the concentration of the aqueous solution of sodium carbonate is preferably 5 to 15 wt% (for example, but not limited to, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%).

In the above technical solution, the palladium-containing compound in step (1) is at least one selected from palladium nitrate, palladium acetate, chloropalladic acid and salts thereof, and tetraamminepalladium dichloride, and is preferably chloropalladic acid.

In the above technical solution, the pH value in step (1) is more preferably 3 to 7, for example, but not limited to, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5.

In the above technical solution, the mixing manner of the catalyst carrier and the catalyst precursor in the step (2) may be dipping or spraying, and preferably dipping. The volume of the impregnation liquid is preferably 0.3 to 2.0 times, for example, but not limited to, 0.35 times, 0.4 times, 0.45 times, 0.5 times, 0.55 times, 0.6 times, 0.65 times, 0.7 times, 0.75 times, 0.8 times, 0.9 times, 1.0 times, 1.5 times, etc., more preferably 0.3 to 0.8 times, most preferably 0.52 times, the volume of the catalyst support.

In the above technical solution, the aging time in the step (3) is preferably 8 to 48 hours, such as but not limited to 9 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, and the like, and more preferably 10 to 30 hours.

In the above technical solution, the inert atmosphere in the step (4) is preferably nitrogen and/or an inert gas, and the inert gas is preferably helium and/or argon.The weight space velocity of the inert atmosphere relative to the catalyst precursor ii is preferably 20-100 h-1For example, but not limited to, 25h-1、30h-1、35h-1、40h-1、45h-1、50h-1、55h-1、60h-1、65h-1、70h-1、75h-1、80h-1、85h-1、90h-1、95h-1And so on.

The heat treatment process of the above step (4) is a critical step of the process of the present invention, and if this process is absent, Pd is caused to be present in the conventional water washing step of step (6) even if the combined palladium is not completely reduced in step (5)+2Run off and cannot achieve the purpose of obtaining the catalyst of the invention.

In the above technical solution, the reducing agent in step (5) may be at least one of the group consisting of formic acid, formate and aldehyde with a structural formula of R-CHO, wherein R is phenyl or C1-C6 alkyl.

In the conventional preparation of a hydrorefining catalyst, it is necessary to reduce all of the palladium in a combined state to Pd0For this purpose, the person skilled in the art will generally choose a reducing agent with high reducing activity, such as formic acid or formate from step (5) above, but will generally not choose a reducing agent of the aldehyde of formula R-CHO above (where R is phenyl or C1-C6 alkyl); however, the invention needs to partially reduce the palladium in a combined state, and the aldehyde with the structural formula of R-CHO (wherein R is phenyl or C1-C6 alkyl) enables the reduction reaction to be slowly controlled, and is very convenient for Pd to be carried out+2And Pd0The weight ratio of (A) to (B) is adjusted to a desired ratio. Therefore, the reducing agent in step (5) is preferably an aldehyde of the formula R-CHO (wherein R is phenyl or C1-C6 alkyl).

The reducing agent is preferably acetaldehyde; the mass ratio of acetaldehyde to palladium is 10 to 50, for example, but not limited to, the mass ratio of acetaldehyde to palladium is 15, 20, 25, 30, 35, 40, 45; the reduction time is preferably 1 to 8 hours, for example, but not limited to, the reduction time is preferably 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and 7 hours.

In the above-mentioned embodiment, the step (6) of removing impurities in the catalyst precursor iv by washing with water is preferably carried out by washing with water to washingAgNO for liquid3Detection of Cl-free-Until now.

To solve the third technical problem, the technical scheme of the invention is as follows:

use of a catalyst according to any one of the preceding claims or of a catalyst obtained by a process according to any one of the preceding claims for hydrorefining crude terephthalic acid.

The technical key of the invention is the selection of the catalyst, and the technical conditions for concrete application can be reasonably determined by a person skilled in the art without creative work, and can achieve comparable technical effects.

To solve the fourth technical problem, the technical scheme of the invention is as follows:

a process for hydrorefining crude terephthalic acid, which comprises subjecting crude terephthalic acid to a hydrorefining reaction with hydrogen in the presence of the catalyst according to any one of the above-mentioned technical problems or the catalyst obtained by the production process according to any one of the above-mentioned technical problems.

In the technical scheme, the hydrofining reaction temperature is preferably 265-295 ℃;

in the technical scheme, the hydrofining reaction pressure is preferably 7.0-10.0 MPa.

XPS analysis is carried out by an ESCA-IAB MK II photoelectron spectrometer, a laser source adopts MgKa rays (hv-1486.6eV), the working voltage is 10kV, the X-ray current is 20mA, and polluted carbon C is adopted1s (Eb 284.6eV) was corrected for energy at 335.2eV (Pd3 d)5/2) And 340.6ev (Pd3 d)3/2) Is Pd0Characteristic peak at 337.1ev (Pd3 d)5/2) And 342.2ev (Pd3 d)3/2) Is Pd+2And fitting and peak splitting are carried out on the Pd3d peak by adopting xps peakfit4.1 software, and then calculation is carried out on the corresponding characteristic peak.

The percentage content of palladium with different valence states is measured by XPS, and the calculation formula is as follows:

x is Pd in analyzed valence state; i: photoelectron peak area; n: the number of different valence states in the Pd under consideration; s: sensitivity factor

The catalyst obtained by the method of the invention is evaluated by adopting an autoclave, and the specific evaluation conditions are as follows:

the dosage of the catalyst is as follows: 2.0 g; crude terephthalic acid amount (CTA): 30.0 g; solvent: 1000g of pure water; reaction pressure: 7.5 Mpa; reaction temperature: 280 ℃; the reaction time was 45 min.

High Performance Liquid Chromatography (HPLC) was used to analyze 4-CBA, p-TA, HMBA (p-methylhydroxybenzoic acid), BA (benzoic acid) in the solution before and after the reaction.

The Pd content was analyzed by ICP.

The invention is further illustrated by the following examples and the description of the figures.

Drawings

FIG. 1 shows Pd in the palladium on carbon catalyst in example 10And Pd+2XPS spectra in the 3d region.

Detailed Description

[ example 1 ]

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking in water solution at 25 deg.C for 1.5h with volume ratio of water solution to active carbon of 5:1, draining, and oven drying to obtain catalyst carrier;

preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2And treating at 350 ℃ for 4h under an atmosphere, and cooling to 25 ℃ to obtain a catalyst precursor ii.

The catalyst precursor ii was reduced by immersing in 20 g of a 10 wt% aqueous solution of acetaldehyde at 25 ℃ for 2 hours to obtain a catalyst precursor iii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

XPS is used to determine the percentage of palladium in different valence states, and the XPS spectrum of the catalyst is shown in figure 1.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

[ example 2 ]

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 4 wt% of HNO3And 4 wt% of H2O2Soaking the catalyst carrier in an aqueous solution at 25 ℃ for 1.5h, wherein the volume ratio of the aqueous solution to the activated carbon is 5:1, and then draining and drying the catalyst carrier to obtain the catalyst carrier.

Preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2Treating at 350 deg.C for 4h under atmosphere, cooling to 25 deg.C to obtain catalystA precursor ii.

The catalyst precursor ii was reduced by immersing in 20 g of a 10 wt% aqueous solution of acetaldehyde at 25 ℃ for 2 hours to obtain a catalyst precursor iii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

And measuring the percentage content of palladium with different valence states by adopting XPS.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

[ example 3 ]

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking the catalyst carrier in an aqueous solution at 25 ℃ for 1.5h, wherein the volume ratio of the aqueous solution to the activated carbon is 5:1, and then draining and drying the catalyst carrier to obtain the catalyst carrier.

Preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2And treating at 450 ℃ for 4h under an atmosphere, and cooling to 25 ℃ to obtain a catalyst precursor ii.

The catalyst precursor ii was reduced by immersing in 20 g of a 10 wt% aqueous solution of acetaldehyde at 25 ℃ for 2 hours to obtain a catalyst precursor iii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

And measuring the percentage content of palladium with different valence states by adopting XPS.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

[ example 4 ]

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking the catalyst carrier in an aqueous solution at 25 ℃ for 1.5h, wherein the volume ratio of the aqueous solution to the activated carbon is 5:1, and then draining and drying the catalyst carrier to obtain the catalyst carrier.

Preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2And treating at 350 ℃ for 4h under an atmosphere, and cooling to 25 ℃ to obtain a catalyst precursor ii.

The catalyst precursor ii was reduced by immersing it in 80 g of a 10 wt% aqueous solution of acetaldehyde at 25 ℃ for 2 hours to obtain a catalyst precursor iii. Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

And measuring the percentage content of palladium with different valence states by adopting XPS.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

Comparative example 1

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking in water solution at 25 deg.C for 1.5h with volume ratio of water solution to active carbon of 5:1, draining, and oven drying to obtain catalyst carrier;

preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

The catalyst precursor i was reduced by immersing it in 20 g of a 10 wt% aqueous solution of acetaldehyde at 25 ℃ for 2 hours to obtain a catalyst precursor ii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

And measuring the percentage content of palladium with different valence states by adopting XPS.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

Comparison of comparative example 1 with example 1 shows that, due to the absence of a heat treatment step of the catalyst precursor i as in example 1, the combined palladium is not converted to the PbO form, and thus Pd remains even in the reduction step+2In the final product Pd+2Also scarcely exists, resulting in Pd+2The washing loss causes low hydrogenation activity of the catalyst, and the 4-CBA and p-TA contents in the product are high, so that the catalyst of the invention can not be obtained.

Comparative example 2

Weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking in water solution at 25 deg.C for 1.5h with volume ratio of water solution to active carbon of 5:1, draining, and oven drying to obtain catalyst carrier;

preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2And treating at 350 ℃ for 4h under an atmosphere, and cooling to 25 ℃ to obtain a catalyst precursor ii.

The catalyst precursor ii was reduced by immersing it in 7.0 g of a 10 wt% aqueous formaldehyde solution at 25 ℃ for 2 hours to obtain a catalyst precursor iii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

XPS is used to determine the percentage of palladium in different valence states, and the XPS spectrum of the catalyst is shown in figure 1.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

Comparative example 2 and example 1 found that the aqueous formaldehyde solution is more reductive than the aqueous acetaldehyde solution, and Pd is easily reduced+2All reduced to Pd0The p-TA content in the product is high.

Comparative example 3

Sodium formate is used as a reducing agent instead of acetaldehyde in example 1, and the redox equivalent amount of the reducing agent is the same, specifically:

weighing 50 g of commercial 4-8 mesh flaky coconut shell activated carbon (the specific surface area is 1100 m)2Per g, pore volume of 0.52ml/g) was washed with pure water at a volume ratio of pure water to activated carbon of 5:1, and then drained and dried.

Drying the activated carbon to obtain the activated carbon containing 2 wt% of HNO3And 2 wt% H2O2Soaking the catalyst carrier in an aqueous solution at 25 ℃ for 1.5h, wherein the volume ratio of the aqueous solution to the activated carbon is 5:1, and then draining and drying the catalyst carrier to obtain the catalyst carrier.

Preparing a catalyst precursor: weighing 1.25 g of palladium-containing 20 wt% chloropalladite aqueous solution, adding 10 wt% sodium carbonate aqueous solution while stirring to adjust the pH of the chloropalladite aqueous solution to 5.0, adding pure water to a constant volume of 26ml, and uniformly stirring to obtain a catalyst precursor.

And (3) soaking the catalyst carrier in a catalyst precursor, and aging for 24 hours to obtain a catalyst precursor i.

Catalyst precursor i at a weight space velocity of 50h-1N2And treating at 350 ℃ for 4h under an atmosphere, and cooling to 25 ℃ to obtain a catalyst precursor ii.

The catalyst precursor ii was reduced by immersing it in 31 g of a 10 wt% aqueous solution of sodium formate at 25 ℃ for 2 hours to obtain a catalyst precursor iii.

Washing catalyst precursor iii with pure water to washing solution with AgNO3Detection of Cl-free-Until now, drying gave the desired catalyst.

And measuring the percentage content of palladium with different valence states by adopting XPS.

ICP measures the mass percentage of Pd in the catalyst.

The catalyst was evaluated using an autoclave and the impurities in the solution before and after the reaction were analyzed using High Performance Liquid Chromatography (HPLC).

For comparison, analytical data and evaluation result data of the catalysts are shown in tables 1 and 2, respectively.

Comparative example 3, in comparison with example 1, found that the aqueous solution of sodium formate is more reductive than the aqueous solution of acetaldehyde, and Pd is easily reduced+2All reduced to Pd0The p-TA content in the product is high.

TABLE 1

TABLE 2

Remarking: impurity content in starting CTA 4-CBA: 3025 ppmw; p-TA: 768 ppmw; HMBA: 56 ppmw; BA: 38 ppmw.

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