CN112675811B - High-efficiency separation N2O/CO2Silver exchange molecular sieve adsorbent and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of separation materials, and discloses a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ and a preparation method thereof. Taking 13X and 5A molecular sieves as basic framework materials, and adjusting the composition of balanced cations, prepared AgX and AgA molecular sieves with a certain Ag ⁺ exchange degree. In the present invention, since the balance cation is changed from alkali metal or alkaline earth metal to Ag ⁺ , it exhibits excellent N ₂ O preferential adsorption capacity, and has high selectivity and adsorption capacity for N ₂ O/CO ₂ . The invention can be applied to the separation and recovery of N ₂ O in the tail gas produced in the industrial production processes such as nitric acid and adipic acid, and has good application prospect and very important practical value.

Description

A kind of silver-exchange molecular sieve adsorbent for efficiently separating N2O/CO2 and preparation method thereof

technical field

The invention belongs to the technical field of separation materials, and relates to a preparation method of _N2O and _CO2 separation materials, in particular to a silver-exchange molecular sieve adsorbent for efficiently separating _N2O / _CO2 and a preparation method thereof.

Background technique

Nitrous oxide (N ₂ O, laughing gas) is the third largest greenhouse gas after carbon dioxide (CO ₂ ) and methane (CH ₄ ) among the six gases restricted by the Kyoto Protocol. Its greenhouse effect is 298 times that of carbon dioxide and its damage to ozone in the stratosphere. In addition, N ₂ O has important applications in the fields of medicine, food, and aerospace. Therefore, the recycling of N ₂ O has a double meaning. 40% of N ₂ O emissions are caused by human activities, mainly agriculture, transportation and industry. Industrially, N ₂ O is often emitted as a by-product during the production of adipic acid and nitric acid. At present, there are three main methods for the treatment of N ₂ O in industry, one of which is to combust with CH ₄ gas as an oxidant, but it will produce CO ₂ gas and cause secondary pollution; ₂ O, N ₂ O can be directly catalytically decomposed into N ₂ and O ₂ which are non-polluting to the environment, but the decomposition of N ₂ O requires high temperature, high energy consumption and N ₂ O cannot be used as a valuable intermediate after decomposition. It is used to produce other fine chemical products; thirdly, for high concentration of N ₂ O, N ₂ O can be used as an oxidant. In industry, benzene is oxidized to produce phenol in one step, but the concentration of N ₂ O in the tail gas is usually as high as If not required, further enrichment is required. Therefore, it is very necessary to find a cost-effective method to separate or enrich N ₂ O for other industrial production. In addition to N ₂ O, there is also CO ₂ with very similar properties in the production tail gas of adipic acid and nitric acid. Although CO ₂ and N ₂ O are composed of different elements, they have the same relative molecular mass and kinetic diameter, similar liquefaction temperature and polarizability, etc. Therefore, the separation of N ₂ O/CO ₂ has a great effect. challenge. Pressure swing adsorption (PSA) has received more and more attention in recent years due to its advantages of low energy consumption and simple operation. The most important thing in pressure swing adsorption separation is the choice of adsorbent, and the commonly used adsorbents in the adsorption separation process are carbon materials (activated carbon and carbon molecular sieve), molecular sieves, silica sol, and metal organic frameworks (MOFs) and other materials . Comparing these types of adsorbents, it is found that carbon materials do not have a uniform pore structure, and MOFs have poor stability. In contrast, molecular sieves have uniform pore structure and pore size, good thermal stability, and adjustable specific surface area and pore size. Therefore, there are more studies and applications of molecular sieve adsorbents. As an important factor affecting the properties of molecular sieves, the type of equilibrium cations also has a great influence on the adsorption and separation of gases. Type X and Type A molecular sieves have low silica-alumina ratios (1.15 and 1.00, respectively) and have more equilibrium cations in the pores. Therefore, these two molecular sieves are selected for silver ion exchange to achieve the adsorption and separation of N ₂ O/CO ₂ .

SUMMARY OF THE INVENTION

In order to solve the problem of difficult separation of N ₂ O and CO ₂ in the tail gas generated by adipic acid and nitric acid, the invention discloses a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ and a preparation method thereof. The mixed tail gas of ₂ O and CO ₂ preferentially adsorbs N ₂ O and has a good N ₂ O/CO ₂ separation effect.

The present invention is achieved through the following technical solutions:

On the one hand, the present invention discloses a silver-exchanged molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ . The silver-exchanged molecular sieve with Ag ⁺ exchange degree ≥ 66% is obtained by exchanging molecular sieves with a silicon-aluminum ratio of not more than 1.2 through silver exchange.

Further, the molecular sieve is a 13X molecular sieve or a 5A molecular sieve, the silicon-to-aluminum ratio of the 13X molecular sieve is 1.15, and the 13X molecular sieve obtains a silver-exchanged 13X molecular sieve adsorbent with Ag ⁺ exchange degree ≥ 84% through silver exchange; the 5A The silicon-to-aluminum ratio of the molecular sieve is 1, and the 5A molecular sieve obtains a silver-exchanged 5A molecular sieve adsorbent with an Ag ⁺ exchange degree of ≥66% through silver exchange respectively.

On the other hand, the present invention also discloses a preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ , which is achieved by the following steps:

(1) Add molecular sieve with a silicon-to-aluminum ratio of not more than 1.2 into the AgNO ₃ aqueous solution, heat and stir, and perform at least one silver exchange;

(2) Washing, filtering and drying the silver-exchanged molecular sieve in step (1) with deionized water to obtain silver-exchanged molecular sieve with Ag ⁺ exchange degree ≥ 66%;

(3) activating the silver-exchanged molecular sieve obtained in step (2) by vacuuming at 150-200° C. to obtain a silver-exchanged molecular sieve adsorbent that has adsorption and reversal effects on N ₂ O/CO ₂ ;

Wherein, the molecular sieve is 13X molecular sieve or 5A molecular sieve.

As a preferred embodiment, the mass volume ratio _of 13X molecular sieve and AgNO solution is 1g/(50~100) mL, and the mass volume ratio _of 5A molecular sieve and AgNO solution is 1g/(50~100) mL, and the heating temperature is 60-80 ℃, stirring time is 1-3h; further, in step (1), the concentration of AgNO ₃ aqueous solution is 0.05-0.4 mol/L.

As a preferred embodiment, in step (1), the concentration of the AgNO ₃ aqueous solution is 0.05~0.4 mol/L, the temperature of heating and stirring is 60~80°C, and the time is 1~3h.

As a preferred embodiment, in step (2), the drying temperature is 80-120° C. and the drying time is 24 h.

As a preferred embodiment, in step (3), the vacuum activation time of the silver-exchanged 13X and 5A molecular sieves is 5-10 h; further, after the 13X molecular sieves are exchanged with silver, 13X with Ag ⁺ exchange degree ≥ 84% is obtained Molecular sieve adsorbent, 5A molecular sieve adsorbent with Ag ⁺ exchange degree ≥66% is obtained after 5A molecular sieve silver exchange.

In addition, the application of the silver-exchange molecular sieve adsorbent for high-efficiency separation of N ₂ O/CO ₂ prepared by the present invention is to separate the mixture of CO ₂ and N ₂ O in the tail gas of nitric acid or adipic acid.

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

(1) In the present invention, AgA (exchange degree ≥ 66%) and AgX (exchange degree ≥ 84%) molecular sieves obtained by exchanging silver for 13X and 5A molecular sieves and controlling their exchange degrees have realized the adsorption reaction of N ₂ O/CO ₂ . Turn; the introduction of the balance Ag ⁺ ions replaces the original alkaline earth metal (Ca ²⁺ ) or alkali metal (Na ⁺ ) balance cations, and introduces Ag ⁺ , which has a stronger affinity for N ₂ O, thus realizing N ₂ Preferential adsorption of O to achieve N ₂ O/CO ₂ separation;

(2) The present invention has a simple preparation method for preparing AgA and AgX molecular sieve adsorbents by exchanging 13X and 5A molecular sieves with silver, is easy to mass produce, has good stability, can be reused, and has good application prospects, especially for nitric acid and hexane. Separation of N ₂ O/CO ₂ in the tail gas produced in industrial production processes such as diacids, to achieve effective use of N ₂ O.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is a schematic diagram of the adsorption reversal of N ₂ O and CO ₂ achieved by 13X and 5A molecular sieves after silver exchange in the present invention.

Figure 2 is the PXRD diffractograms of the A-4 and X-4 molecular sieves obtained in Examples 5 and 6 and the original powders 13X and 5A. It can be seen from Figure 1 that the A-4 and X obtained after the 13X and 5A molecular sieves are exchanged with silver -4 The molecular sieve structure is intact and not damaged.

Figure ₃ is the N adsorption and desorption curves at 77 K of A-4 and X-4 obtained in Examples 5 and 6 and original powders 13X and 5A, indicating that by replacing the original Na ^{+ with larger Ag+ or} After Ca ²⁺ , the specific surface area of the material decreased.

4 shows the adsorption isotherms of CO ₂ and N ₂ O at 298 K for X-4 obtained in Example 5 and the original powder 13X. From the adsorption isotherm, it can be seen that the adsorption amount of _CO2 in the original 13X powder is greater than that of _N2O , which is a selective adsorption material for _CO2 , while the equilibrium cation in 13X is replaced by Ag ⁺ and reaches a certain degree of exchange (84 %), which is a selective adsorbent for N ₂ O, and when the exchange degree is 89%, the difference between the adsorption capacity of N ₂ O and CO ₂ is the largest.

5 shows the adsorption isotherms of CO ₂ and N ₂ O at 298 K for A-4 and original powder 5A obtained in Example 6. FIG. From the adsorption isotherm, it can be seen that the adsorption amount of _CO2 in the original 5A powder is greater than that of _N2O , which is a selective adsorption material for _CO2 , while the equilibrium cation in 5A is replaced by Ag ⁺ and reaches a certain degree of exchange ( 66%), which is a selective adsorbent for N ₂ O, and when the exchange degree is 79%, the difference between the adsorption capacity of N ₂ O and CO ₂ is the largest.

Figure 6 is the ideal solution adsorption theory (IAST) calculation of A-4 and X-4 obtained in Examples 5 and 6 and original powders 13X and 5A. The adsorption selectivity of the material to the binary N ₂ O/CO ₂ mixed gas, Langmuir - The Freundlich isotherm model was fitted to the gas adsorption isotherms of the pure gas components of CO ₂ and N ₂ O of the samples. The selective adsorption of N ₂ O was achieved after ^Ag exchange was further verified from the IAST selectivity.

7 is a graph of breakthrough curves of CO ₂ and N ₂ O mixtures (1:1 v/v) of A-4 and X-4 after Ag exchange in Examples 5 and 6. FIG. It can be seen from the breakthrough curves that on both A-4 and X-4, CO ₂ is preferentially penetrated, which further proves that it is a selective adsorption material for N ₂ O after Ag ⁺ exchange, and realizes N ₂ O/ The adsorption of _CO2 is reversed.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below 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 the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) Add 1 g of 13X molecular sieve to 60 mL of 0.1 mol/mL AgNO ₃ aqueous solution, heat and stir at 80 °C for 1 h to perform a silver exchange, and keep the total amount of the solution unchanged during the heating process;

(2) Wash the silver-exchanged molecular sieve in step (1), wash with deionized water, filter, and dry at 120 °C for 24 h to obtain silver-exchanged 13X molecular sieve;

(3) The silver-exchanged 13X molecular sieve obtained in step (2) was vacuum-activated at 200 ° C for 5 h to obtain an X-2 molecular sieve adsorbent with an Ag ⁺ exchange degree of 84%; then the N ₂ O/ Gas adsorption separation performance of _CO2 .

Example 2

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) Add 1 g of 5A molecular sieve to 60 mL of 0.1 mol/mL AgNO ₃ aqueous solution, and heat and stir at 80 °C for 1 h to perform a silver exchange, and keep the total amount of the solution unchanged during the heating process;

(2) washing the silver-exchanged molecular sieve in step (1), washing with deionized water, filtering, and drying at 120 °C for 24 h to obtain silver-exchanged 5A molecular sieve;

(3) The 5A molecular sieve obtained in step (2) was vacuum activated at 200 ° C for 5 hours to obtain A-2 molecular sieve adsorbent with Ag ⁺ exchange degree of 73%; then the N ₂ O/CO ₂ of A-2 molecular sieve was tested gas adsorption separation performance.

Example 3

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) Add 1 g of 13X molecular sieve to 70 mL of 0.3 mol/mL AgNO ₃ solution respectively, and then heat and stir at 60 °C for 2 h to perform a silver exchange, keeping the total amount of the solution unchanged during the heating process;

(2) The silver-exchanged molecular sieve in step (1) was washed with deionized water, filtered, and dried at 100 °C for 24 h to obtain silver-exchanged 13X molecular sieve;

(3) The silver-exchanged 13X molecular sieve obtained in step (2) was vacuum-activated at 180 ° C for 10 h to obtain an X-3 molecular sieve adsorbent with an Ag ⁺ exchange degree of 88%; then the N ₂ O/ Gas adsorption separation performance of _CO2 .

Example 4

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) Add 1 g of 5A molecular sieve to 70 mL of 0.3 mol/mL AgNO ₃ solution respectively, then heat and stir at 60 °C for 2 h to perform a silver exchange, and keep the total amount of the solution unchanged during the heating process;

(2) The silver-exchanged molecular sieve in step (1) was washed with deionized water, filtered, and dried at 100 °C for 24 h to obtain silver-exchanged 5A molecular sieve;

(3) The silver-exchanged 5A molecular sieve obtained in step (2) was vacuum-activated at 180 ° C for 10 h to obtain A-3 molecular sieve with Ag ⁺ exchange degree of 78%; then the N ₂ O/CO ₂ of the A-3 molecular sieve was tested gas adsorption separation performance.

Example 5

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) 1g of 13X molecular sieves were added to 50mL of 0.4mol/mL AgNO ₃ solution respectively, and then heated and stirred at 80 °C for 1 h to perform a silver exchange, keeping the total amount of the solution unchanged during the heating process;

(2) The silver-exchanged 13X molecular sieve in step (1) was washed with deionized water, filtered, and dried at 100 °C for 24 h to obtain silver-exchanged 13X molecular sieve;

(3) The silver-exchanged 13X molecular sieve obtained in step (2) was vacuum-activated at 200 °C for 10 h to obtain an X-4 molecular sieve adsorbent with an Ag ⁺ exchange degree of 89%; then the N ₂ O of the X-4 molecular sieve was tested /CO ₂ gas adsorption separation performance.

Example 6

A preparation method of a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ is realized by the following steps:

(1) 1 g of 5A molecular sieve was added to 50 mL of 0.4 mol/mL AgNO ₃ solution, and then heated and stirred at 80 °C for 1 h to perform a silver exchange, and the total amount of the solution was kept unchanged during the heating process;

(2) The silver-exchanged 5A molecular sieve in step (1) was washed with deionized water, filtered, and dried at 100 °C for 24 h to obtain silver-exchanged 5A molecular sieve;

(3) The silver-exchanged 5A molecular sieve obtained in step (2) was vacuum-activated at 200 °C for 10 h to obtain an A-4 molecular sieve adsorbent with an Ag ⁺ exchange degree of 79%; then the N ₂ O of the A-4 molecular sieve was tested /CO ₂ gas adsorption separation performance.

(1) The 13X and 5A powders purchased from Aladdin are used as the basic framework materials.

(2) 1 g of 13X and 5A molecular sieves from step (1) were added to 0.4 M AgNO ₃ aqueous solution, respectively, and then heated and stirred at 80 °C for 1 h, and the total amount of the solution was kept unchanged during the heating process.

(3) The molecular sieve after silver exchange in step (2) was washed and filtered with deionized water, and the obtained sample was dried at 100 °C for 24 h.

(4) The samples X-4 and A-4 obtained in step (3) were vacuum activated at 200 °C for 10 h to obtain X-4 and A-4 molecular sieves with Ag ⁺ exchange degrees of 89% and 79%, respectively material, and then tested its N ₂ O/CO ₂ gas adsorption separation performance.

The foregoing has shown and described the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above-mentioned embodiments. The above-mentioned embodiments and descriptions describe only the principles of the present invention. Without departing from the spirit and scope of the present invention, there will be various Variations and improvements are intended to fall within the scope of the claimed invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims (8)

_1. a silver-exchanged molecular sieve adsorbent for efficiently separating N ₂ O/CO , is characterized in that: the molecular sieve with a silicon-to-aluminum ratio not exceeding 1.2 is obtained by silver exchange and the silver-exchanged molecular sieve of Ag ⁺ exchange degree≥66%; Wherein, the molecular sieve is 13X molecular sieve or 5A molecular sieve, the silicon-aluminum ratio of the 13X molecular sieve is 1.15, and the 13X molecular sieve obtains a silver-exchanged 13X molecular sieve adsorbent with Ag ⁺ exchange degree ≥ 84% through silver exchange; the 5A molecular sieve The silicon-to-aluminum ratio of 1 is 1, and the 5A molecular sieve is exchanged with silver to obtain a silver-exchanged 5A molecular sieve adsorbent with an Ag ⁺ exchange degree of ≥66%. 2. a kind of preparation method of the silver-exchange molecular sieve adsorbent that separates N ₂ O/CO ₂ efficiently, it is characterised in that it is achieved by the following steps: (1) Add molecular sieve with a silicon-to-aluminum ratio of not more than 1.2 into the AgNO ₃ aqueous solution, heat and stir, and perform at least one silver exchange; (2) Washing, filtering and drying the silver-exchanged molecular sieve in step (1) with deionized water to obtain silver-exchanged molecular sieve with Ag ⁺ exchange degree ≥ 66%; (3) activating the silver-exchanged molecular sieve obtained in step (2) by vacuuming at 150-200° C. to obtain a silver-exchanged molecular sieve adsorbent having adsorption reversal effect on N ₂ O/CO ₂ ; Wherein, the molecular sieve is 13X molecular sieve or 5A molecular sieve. 3. The preparation method of the silver-exchange molecular sieve adsorbent for efficient separation of N ₂ O/CO ₂ as claimed in claim 2, characterized in that: in step (1), the mass volume ratio of 13X molecular sieve and AgNO solution is ₁ g/ (50~100)mL, the mass-volume ratio of 5A molecular sieve and AgNO ₃ solution was 1g/(50~100)mL. 4. The preparation method of the silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ as claimed in claim 2, characterized in that: in step ( ₁ ), the concentration of the AgNO aqueous solution is 0.05-0.4 mol/L, The temperature of heating and stirring is 60~80℃, and the time is 1~3h. 5 . The method for preparing a silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ according to claim 2 , wherein in step (2), the drying temperature is 80-120° C. and the time is 24 h. 6 . 6. The method for preparing a silver-exchanged molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ according to claim 2, wherein in step (3), the vacuum activation time of the silver-exchanged 13X and 5A molecular sieves Both are 5-10 h. 7. The preparation method of the silver-exchanged molecular sieve adsorbent for efficient separation of N ₂ O/CO ₂ as claimed in claim 2, characterized in that: in step (3), after 13X molecular sieve silver exchange, Ag ⁺ exchange degree≥84% is obtained 13X molecular sieve adsorbent, 5A molecular sieve silver exchanged to obtain 5A molecular sieve adsorbent with Ag ⁺ exchange degree ≥ 66%. 8 . The application of the silver-exchange molecular sieve adsorbent for efficiently separating N ₂ O/CO ₂ according to claim 1 in the separation of CO ₂ and N ₂ O mixture in nitric acid or adipic acid tail gas. 9 .

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