CN109433200B

CN109433200B - Low-load noble metal catalyst for reducing dilute nitric acid, preparation and application

Info

Publication number: CN109433200B
Application number: CN201811383700.8A
Authority: CN
Inventors: 李文龙; 宋元江; 李扬; 王科; 王雪峰; 董玲玉; 刘亚华
Original assignee: Southwest Research and Desigin Institute of Chemical Industry
Current assignee: Southwest Research and Desigin Institute of Chemical Industry
Priority date: 2018-11-20
Filing date: 2018-11-20
Publication date: 2020-05-26
Anticipated expiration: 2038-11-20
Also published as: CN109433200A

Abstract

The invention provides a low-load noble metal catalyst for reducing dilute nitric acid, belonging to the technical field of dilute nitric acid catalysis. The catalyst comprises the following components in percentage by mass based on the total mass of the catalyst: 0.02 to 0.25 percent of active component, 0.5 to 5 percent of auxiliary agent and the balance of carrier; the active component is one or more of noble metals Pd, Pt and Rh, the auxiliary agent is alkali metal element K or Na, and the carrier is activated carbon. The invention also provides a preparation method of the catalyst, which comprises the following steps: 1) preparing an assistant salt solution and an active component salt solution according to the proportion; 2) loading the prepared auxiliary agent salt solution on an activated carbon carrier, and drying and roasting to obtain a standby sample after loading; 3) and loading the prepared active component salt solution on a standby sample, and drying and roasting to obtain the catalyst after loading. The loading amount of the noble metal in the catalyst is only 0.02-0.25%, the cost is reduced, and the catalyst can effectively catalyze the reduction of dilute nitric acid to generate nitrite, the nitric acid conversion rate reaches over 90%, and the selectivity of the nitrite reaches 100%.

Description

Low-load noble metal catalyst for reducing dilute nitric acid, preparation and application

Technical Field

The invention belongs to the technical field of dilute nitric acid catalysis, and particularly relates to a low-load noble metal catalyst for reducing dilute nitric acid, and preparation and application thereof.

Background

Ethylene glycol belongs to a large amount of chemical products and is an important organic chemical raw material. China has abundant coal resources, and the route of preparing the ethylene glycol by using the coal to prepare the synthetic gas through the oxalate is rapidly developed in China. By 3 months in 2018, 17 coal (syngas) to ethylene glycol (CTMEG) projects which have been put into operation and successfully run in china result in a total ethylene glycol capacity of 300 million tons per year. It is expected that a total of about 1350 million tons/year CTMEG capacity will be produced in 2022, along with 17 projects that have been commissioned and commissioned successfully. In the technical route of preparing ethylene glycol from coal, a large amount of nitric acid as a byproduct is generated in the regeneration reaction process of nitrite, the concentration of the nitric acid is about 2 wt%, the current main treatment method in the industry is to add stoichiometric NaOH for neutralization, then directly discharge waste liquid containing a large amount of sodium nitrate, and the environmental protection cost is high. Therefore, the treatment of the acid-containing wastewater is always a great problem in the normal operation of the coal-to-ethylene glycol project.

The patent (EP 1346976A1) proposes the combination of NO and HNO₃Reacting with the mixed solution of alcohol to prepare the nitrite (see the formula 1). NO can react with dilute nitric acid and alkyl alcohol to generate nitrous acid ester, and the nitrous acid ester is an intermediate substance in the process of preparing ethylene glycol from coal, which is an effective way. However, the concentration of nitric acid is too low, and the reaction is difficult to occur. In the process of preparing the glycol from the coal, 2 wt% of dilute nitric acid is generated in the kettle liquid of the regeneration reaction, the concentration of the nitric acid is low, and the conversion of the nitric acid is limited. In a literature report, a noble metal catalyst such as 3.5 wt% Pd or Pt is adopted, so that the reduction reaction of dilute nitric acid can be effectively catalyzed to generate nitrite, but the loading of the noble metal is too high, and the cost of the catalyst is higher; in the patent (CN106565494A), 0.2-2% of palladium is used as an active component, 0-10% of iron or titanium is used as an auxiliary agent, the prepared catalyst can effectively catalyze the reduction of dilute nitric acid, and the loading amount of noble metal is reduced.

2NO+HNO₃+3ROH＝3RONO+2H₂O (1)

Disclosure of Invention

The invention aims to provide a low-load noble metal catalyst for reducing dilute nitric acid, and preparation and application thereof. The catalyst has low noble metal loading capacity, can effectively reduce the cost of the catalyst, can effectively catalyze the reduction reaction of dilute nitric acid to generate nitrite, does not generate other byproducts, and has excellent conversion rate and selectivity. The purpose of the invention is realized by the following technical scheme:

a dilute nitric acid reduction low-load noble metal catalyst comprises the following components in percentage by mass based on the total mass of the catalyst: 0.02 to 0.25 percent of active component, 0.5 to 5 percent of auxiliary agent and the balance of carrier; the active component is one or more of noble metals Pd, Pt and Rh, the auxiliary agent is alkali metal element K or Na, and the carrier is activated carbon.

In the catalyst of the invention, the content of the active component noble metal has important influence on the activity and the production cost of the catalyst, when the content of the noble metal is too low, the active sites which can be provided are not sufficient, the cost is increased when the content is higher, therefore, the loading capacity is reduced, and the activity of the catalyst is not attenuated. Due to the fact that the functional groups on the surface of the activated carbon carrier are complex, the amount of basic functions can be increased by adding alkali metal K or Na, the adsorption amount of the catalyst to NO gas can be increased, mass transfer reaction of NO is facilitated, and therefore high activity of the catalyst is guaranteed while the content of noble metal of an active component is reduced.

Further, the active component accounts for 0.05-0.2% of the total mass of the catalyst, and preferably 0.1-0.15%; the auxiliary agent is 1% -4%, preferably 2% -3%.

Further, the active carbon is active carbon particles with 14-20 meshes.

A preparation method of a low-load noble metal catalyst for reducing dilute nitric acid comprises the following steps:

1) preparing an assistant salt solution and an active component salt solution according to the proportion;

2) loading the prepared auxiliary agent salt solution on an activated carbon carrier, and drying and roasting to obtain a standby sample after loading;

3) and loading the prepared active component salt solution on a standby sample, and drying and roasting to obtain the catalyst after loading.

Further, in the step 2) and the step 3), the drying temperature is 50-150 ℃, and the drying time is 4-24 hours; the roasting temperature is 150-500 ℃, and the roasting time is 1-4 h.

Further, when the impregnation method is adopted to load the auxiliary agent and the active component, the auxiliary agent and the active component may be impregnated separately, or the auxiliary agent and the active component may be impregnated together. Further, when the adjuvant and the active component are separately impregnated, the adjuvant should be impregnated first and then the active component should be impregnated.

Furthermore, when the impregnation method is adopted to load the active components, the impregnation can be carried out step by step or can be carried out in one step aiming at different types of active components.

Further, the roasting needs to be protected by inert gas, and the inert gas is one or more of helium, nitrogen and argon. The activated carbon reacts with oxygen at high temperature to generate carbon dioxide, so that inert gas is required for protection during roasting.

An application of a catalyst for reducing low-load noble metal by dilute nitric acid, which is applied to catalyzing the reduction reaction of dilute nitric acid to generate nitrite.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a low-load noble metal catalyst for reducing dilute nitric acid, wherein the load of noble metal in the catalyst only accounts for 0.02-0.25% of the total mass of the catalyst, and the production cost of the catalyst is effectively reduced. Meanwhile, the catalyst can effectively catalyze the reduction reaction of dilute nitric acid to generate nitrite, the conversion rate of the nitric acid reaches over 90 percent, and the selectivity of the nitrite reaches 100 percent. The catalyst has good adaptability in reaction systems of different alcohols, good stability, simple preparation method and easy popularization.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

Taking 0.259g of potassium nitrate solid, and adding 5.5g of deionized water to prepare an auxiliary agent impregnation liquid; then 5g of activated carbon particles with 14 meshes to 20 meshes are taken, soaked for 4h in equal volume and then dried for 12h at 100 ℃, and N is added₂Calcining at 200 ℃ for 3h under protection to obtain a 2 wt% K/AC standby sample.

Adding 1.6mL palladium nitrate solution (Pd content 4.688mg/mL) into deionized water until the total mass of the mixed solution is 5.5g to prepare active component impregnation solution, taking the prepared K/AC, and performing equal-volume impregnation4h, then drying at 100 ℃ for 12h, N₂The catalyst is calcined for 3 hours at 300 ℃ under the protection to obtain the Pd-K/AC catalyst, the load of Pd is 0.15 percent, the load of K is 2 percent, and the catalyst A is recorded.

Example 2

Using the procedure of example 1, a Pd-Na/AC catalyst was obtained by replacing 0.259 of potassium nitrate with 0.370 of sodium nitrate, the Na content being 2% by mass and the remainder being kept constant, the Pd loading being 0.15% and the Na loading being 2%, and this catalyst being designated as catalyst B.

Example 3

By the method of example 1, 0.53mL and 2.7mL of palladium nitrate solutions (Pd content of 4.688mg/mL) were taken, respectively, to prepare catalysts having promoter K supporting 2% and noble metal negative Pd supporting 0.05% and 0.25%, respectively, which were designated as catalyst C and catalyst D.

Example 4

Using the procedure of example 1, varying the amount of potassium nitrate, 0.129g and 0.518g of potassium nitrate solids were taken, and the others were held constant, to produce catalysts having a noble metal loading of 0.15% for the negative Pd and 1% and 4% for the promoter K, respectively, and were designated as catalyst E and catalyst F.

Example 5

Using the procedure of example 1, a 2 wt% K/AC ready sample was obtained.

Taking 1.4mL of chloroplatinic acid solution (Pt content of 5.357mg/mL), adding deionized water until the total mass of the mixed solution is 5.5g to prepare a steeping fluid, taking a prepared K/AC sample, steeping for 4h in equal volume, and then drying for 12h at 100 ℃, wherein N is₂And (3) burning for 3h at 300 ℃ under protection to obtain the Pt-K/AC catalyst, wherein the load of Pt is 0.15%, the load of K is 2%, and the catalyst G is recorded.

Example 6

Using the procedure of example 1, a 2 wt% K/AC ready sample was obtained.

Taking 1.1mL rhodium trichloride solution (Rh content 6.818mg/mL), adding deionized water until the total mass of the mixed solution is 5.5g, preparing a steeping fluid, taking a prepared K/AC sample, steeping for 4h in the same volume, and then drying for 12h at 100 ℃, wherein N is₂Burning at 300 deg.C for 3h under protection to obtainThe Pt-K/AC catalyst was obtained with a Pt loading of 0.15% and a K loading of 2%, catalyst H.

Example 7

Taking 1.6mL of palladium nitrate solution (Pd content is 4.688mg/mL), adding deionized water until the total mass of the mixed solution is 5.5g, adding 0.259g of potassium nitrate solid to prepare a mixed solution of an active component and an auxiliary agent, soaking for 4h, and drying at 100 ℃ for 12h, wherein N is₂And (3) burning for 3h at 300 ℃ under protection to obtain the Pd-K/AC catalyst, wherein the load of Pt is 0.15%, the load of K is 2%, and the catalyst I is recorded.

Example 8

Using the procedure of example 1, a 2 wt% K/AC ready sample was obtained.

1.5mL of palladium nitrate solution (Pd content 4.688mg/mL) and 1.3mL of rhodium trichloride solution (Rh content 6.818mg/mL) are put into a beaker, deionized water is added until the total mass of the mixed solution is 5.5g, a steeping fluid is prepared, a prepared K/AC sample is taken, soaked for 4h in equal volume, then dried for 12h at 100 ℃, and N is added₂And (2) burning for 3h at 300 ℃ under protection to obtain the Pt-Rh-K/AC catalyst, wherein the total loading of Pt and Rh is 0.15%, and the molar ratio of Pd to Rh is 10: the loading of 1, K was 2%, catalyst J was noted.

Example 9

Using the procedure of example 1, a 2 wt% K/AC ready sample was obtained.

Taking 0.63mL of palladium nitrate solution (Pd content is 4.688mg/mL), 0.76mL of chloroplatinic acid solution (Pt content is 5.357mg/mL) and 0.73mL of rhodium trichloride solution (Rh content is 0.593mg/mL) in a beaker, adding deionized water until the total mass of the mixed solution is 5.5g to prepare a steeping fluid, taking a prepared K/AC sample, soaking for 4h in an equal volume, drying for 12h at 100 ℃, and burning for 3h at 300 ℃ under the protection of N2 to obtain the Pd-Pt-Rh-K/AC catalyst, wherein the total loading of noble metals is 0.15%, and the molar ratio of Pd, Pt and Rh is 20: 15: the loading of 3, K is 2%, catalyst K is noted.

Comparative example 1

Adding 1.6mL of palladium nitrate solution (Pd content of 4.688mg/mL) into deionized water until the total mass of the mixed solution is 5.5g, preparing active component impregnation liquid, removing activated carbon particles between 14 meshes and 20 meshes, impregnating for 4h in equal volume, and drying for 12h at 100 ℃, wherein N is N₂Protection ofThe catalyst was calcined at 300 ℃ for 3 hours to obtain a Pd/AC catalyst, the supported amount of Pd was 0.15%, and the catalyst L was recorded.

The prepared catalyst A-J is used for catalyzing the reaction of dilute nitric acid to generate nitrous acid ester. The nitric acid reduction reaction is carried out in a fixed bed reactor, the inner diameter of a reaction tube is 1.2cm, the loading amount of the catalyst is 3g, and glass beads with the size of 3mm are loaded at the upper section and the lower end of the catalyst for uniform distribution of gas. Before the reaction, H is used₂Reducing gas at 250 ℃ for 4h, then reducing the temperature to 70 ℃, controlling the reaction pressure at 0.3Mpa, controlling the liquid feeding amount to be 0.1ml/min (the reaction liquid is 2 wt% of 74% nitric acid ethanol aqueous solution), controlling the gas flow rate to be 100ml/min (the volume content of NO is 10% and the balance is nitrogen) to react, collecting the reacted liquid after reacting for a period of time, carrying out acid-base titration analysis on the reacted liquid phase, measuring the concentration of nitric acid in the solution, and calculating the conversion rate of the nitric acid; the contents of the gaseous and liquid phases of the tail gas were analyzed by gas chromatography and the selectivity of nitrite was calculated and the results are shown in table 1.

TABLE 1 catalytic reduction of nitric acid in ethanol Experimental results

Numbering	Catalyst and process for preparing same	Conversion rate of nitric acid	Selectivity to ethyl nitrite
				1	A	93.0％	100％
2	B	90.2％	100％
				3	C	89.2％	100％
4	D	93.3％	100％
				5	E	87.8％	100％
6	F	92.7％	100％
				7	G	91.1％	100％
8	H	89.7％	100％
				9	I	90.8％	100％
10	J	91.5％	100％
				11	K	91.8％	100％
12	L	79.4％	100％

The experimental results in table 1 show that the prepared low-loading noble metal catalyst has an excellent effect of catalyzing the reaction of dilute nitric acid to generate nitrite, the conversion rate of nitric acid can reach over 90%, and the selectivity of ethyl nitrite reaches 100%. The catalyst prepared without adding the auxiliary agent K or Na has a general catalytic effect, the conversion rate of nitric acid only reaches 79.4%, and after the alkali metal is added, the conversion rate of nitric acid can be effectively improved and reaches over 90%.

Under the condition of ensuring that other conditions are not changed, the reaction solution is changed into a methanol aqueous solution with the concentration of 2 wt% nitric acid of 74%, the reaction temperature is 75 ℃, and the experimental results of testing part of the catalysts are shown in Table 2.

TABLE 2 catalytic reduction of nitric acid in methanol experimental results

Numbering	Catalyst and process for preparing same	Conversion rate of nitric acid	Selectivity to methyl nitrite
				1	A	90.9％	100％
2	L	60.1％	100％

From the experimental results in table 2, it can be seen that the methyl nitrite is generated by using the methanol system to perform the dilute nitric acid catalytic reduction, and the reaction result is similar to that of the ethanol system. The catalysts B-K can achieve the same effect as the catalyst A in a methanol system.

The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The application of the catalyst is characterized in that the catalyst is applied to catalyzing the reduction reaction of dilute nitric acid to generate nitrite;

the catalyst comprises the following components in percentage by mass based on the total mass of the catalyst: 0.02 to 0.25 percent of active component, 0.5 to 5 percent of auxiliary agent and the balance of carrier; the active component is one or more of noble metals Pd, Pt and Rh, the auxiliary agent is alkali metal element K or Na, and the carrier is activated carbon.

2. The use according to claim 1, wherein the active component is present in an amount of 0.05% to 0.2% by mass based on the total mass of the catalyst; the auxiliary agent accounts for 1-4%.

3. The use of claim 1, wherein the activated carbon is activated carbon granules of between 14 mesh and 20 mesh.

4. Use according to any one of claims 1 to 3, wherein the catalyst is prepared by a process comprising the steps of:

5. The use according to claim 4, wherein in step 2) and step 3), the drying temperature is 50-150 ℃ and the drying time is 4-24 h; the roasting temperature is 150-500 ℃, and the roasting time is 1-4 h.

6. The use according to claim 4, wherein the impregnation process is used to load the adjuvant and the active ingredient, either separately or together.

7. Use according to claim 6, wherein the auxiliary agent and the active component are impregnated separately, the auxiliary agent being impregnated before the active component.

8. The use according to claim 4, wherein when the impregnation method is used for loading the active component, the impregnation can be carried out step by step or in one step for different types of active components.

9. The use of claim 4, wherein the firing is carried out under protection of an inert gas, and the inert gas is one or more of helium and argon.