Preparation method of modified molecular sieve applied to olefin cracking

Abstract

The invention provides a preparation method of a modified molecular sieve applied to olefin cracking, which comprises the following steps: S1, respectively weighing potassium silicate, aluminum chloride, sodium hydroxide and deionized water, and stirring and mixing to obtain aluminosilicate gel; s2, adding amorphous silicon dioxide and ethidene diamine into the mixture obtained in the step S1, and carrying out constant-temperature crystallization; s3, modified resin, N, N-methylene bisacrylamide and ammonium persulfate are added into the mixture obtained in the step S2, and the mixture continues to be stirred for a reaction; and S4, filtering and roasting the product obtained in the step S3 to obtain the modified molecular sieve. By improving the water absorption performance, crushing resistance and the like of the modified molecular sieve drying agent, the long-period operation requirement of an olefin device is met.

Description

Technical Field

[0001] The invention belongs to the technical field of desiccants, and specifically relates to a method for preparing a modified molecular sieve used for olefin cracking. Background Art

[0002] Olefin Cracking is an important chemical process widely used in the field of petrochemicals. This process decomposes large molecular olefins or other hydrocarbon compounds into smaller molecular olefins and alkanes through thermal cracking or catalytic cracking. Olefin cracking is a key step in the production of important basic chemicals such as ethylene and propylene, which are raw materials for the manufacture of plastics, synthetic rubber, solvents and many other products. The following is detailed information about olefin cracking, including its principles, process types, reaction conditions, catalyst selection and application areas.

[0003] The basic principle of olefin cracking is to break large molecular olefins or alkanes through high temperature or catalyst to generate smaller molecular olefins and alkanes. During the cracking process, CC bonds break to form free radical intermediates, which then react further to generate target products. The cracking reaction is usually an endothermic reaction, which requires sufficient heat to drive the reaction.

[0004] In the current petrochemical industry, the demand for olefin units is growing, and the long-term operation has higher and higher requirements for desiccants. Although the molecular sieves currently on the market have good adsorption performance, they often have problems with insufficient crushing strength and bulk density, which is not conducive to the long-term safe operation of olefin units. Summary of the invention

[0005] The purpose of the present invention is to provide a novel desiccant-modified 3A molecular sieve to meet the long-term operation requirements of olefin units. By adding amorphous silica, ethylenediamine, modified resin, N,N-methylenebisacrylamide and ammonium persulfate and other ingredients during the 3A preparation process, the water absorption performance and crushing resistance of the 3A desiccant are improved.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for preparing a modified molecular sieve for olefin cracking comprises the following steps: S1: Weigh potassium silicate, aluminum chloride, sodium hydroxide and deionized water respectively, and stir and mix to obtain aluminosilicate gel; S2: adding amorphous silicon dioxide and ethylenediamine to step S1 for constant temperature crystallization; S3: Add modified resin, N,N-methylenebisacrylamide and ammonium persulfate to step S2, and continue stirring to react; S4: The product obtained in step S3 is filtered and calcined to obtain a modified molecular sieve.

[0007] Furthermore, in step S1, the weight ratio of potassium silicate, aluminum chloride, sodium hydroxide and deionized water is 10-15:8-12:2-5:90-130.

[0008] Furthermore, in step S1, the reaction is stirred at a temperature of 75-85° C. and a rate of 500-800 r / min for 40-60 min.

[0009] Furthermore, step S2 also includes carboxymethyl cellulose.

[0010] Furthermore, in step S2, the weight ratio of amorphous silicon dioxide, carboxymethyl cellulose and ethylenediamine is 2-4:1-3:0.5-1.5; the constant temperature crystallization temperature is 140-160° C., and the crystallization reaction time is 1-2 hours.

[0011] Furthermore, the specific surface area of ​​the amorphous silicon dioxide is 500-800 m² / g.

[0012] Furthermore, in step S3, the weight ratio of the modified resin, N,N-methylenebisacrylamide and ammonium persulfate is 15-25:1-3:0.5-1.5; the reaction is stirred at a temperature of 160-180° C. for 35-55 minutes.

[0013] Furthermore, the preparation process of the modified resin in step S3 is: 15-25 parts of acrylic acid-maleic anhydride copolymer resin, 2-4 parts of sodium alginate and 1-3 parts of chitosan are stirred and mixed at a temperature of 120-130° C. for 35-55 minutes.

[0014] Furthermore, in step S4, the calcination temperature is 200-300° C., and the calcination time is 10-20 min.

[0015] The modified molecular sieve prepared as above is used as a desiccant in olefin cracking.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are: The present invention obtains aluminosilicate gel with silicon source, aluminum source, alkali source and the like, and then adds amorphous silicon dioxide, ethylenediamine and carboxymethyl cellulose thereto, so that the prepared 3A molecular sieve is interspersed with cellulose, thereby improving the adsorption performance and crush resistance of the molecular sieve; at the same time, sodium alginate and chitosan-modified acrylic acid-maleic anhydride copolymer resin are grafted on the surface of the 3A molecular sieve, so that more hydrophilic groups such as hydroxyl and carboxyl groups are fully utilized to improve the water absorption performance, and at the same time, grafting and cross-linking are performed to form a network structure, so that the crush resistance is further improved, the long-term operation requirements of the olefin device are met, the operation efficiency of the olefin device is improved, and the operation cost is reduced. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The raw materials used in the present invention are as follows: Amorphous silica (Yumu New Materials Co., Ltd., FEFG006); carboxymethyl cellulose (Shanghai Yuanye Biotechnology Co., Ltd., S14019); acrylic acid-maleic anhydride copolymer resin (Shanghai Yuanye Biotechnology Co., Ltd., T25291); sodium alginate (Jiangsu Weizhirun Biotechnology Co., Ltd., 3346); chitosan (Shandong Haiyihua Biotechnology Co., Ltd., 51); N,N-methylenebisacrylamide (Shanghai Yuanye Biotechnology Co., Ltd., S14002).

[0019] Example 1 This embodiment provides a method for preparing a modified molecular sieve for olefin cracking, comprising the following steps: S1: Weigh 10 g potassium silicate, 8 g aluminum chloride, 2 g sodium hydroxide and 90 g deionized water respectively, stir at 75°C and 500 r / min for 40 min to obtain aluminosilicate gel; S2: Add 2 g of amorphous silicon dioxide, 1 g of carboxymethyl cellulose and 0.5 g of ethylenediamine to step S1, and perform crystallization reaction at 140°C for 1.5 h; S3: 15 g of acrylic acid-maleic anhydride copolymer resin, 2 g of sodium alginate and 1 g of chitosan were mixed, and stirred at 120° C. and 500 r / min for 35 min to obtain a modified resin; Then, 15 g of modified resin, 1 g of N,N-methylenebisacrylamide and 0.5 g of ammonium persulfate were added to step S2, and the mixture was stirred at 160° C. and 600 r / min for 35 min; S4: filtering the product obtained in step S3, and calcining at 200° C. for 10 min to obtain a modified molecular sieve.

[0020] Example 2 This embodiment provides a method for preparing a modified molecular sieve for olefin cracking, comprising the following steps: S1: Weigh 15g potassium silicate, 12g aluminum chloride, 5g sodium hydroxide and 130g deionized water respectively, stir at 85°C and 800r / min for 60min to obtain aluminosilicate gel; S2: Add 4 g of amorphous silicon dioxide, 3 g of carboxymethyl cellulose and 1.5 g of ethylenediamine to step S1, and perform crystallization reaction at 160° C. for 4 h; S3: 25 g of acrylic acid-maleic anhydride copolymer resin, 4 g of sodium alginate and 3 g of chitosan were mixed, and the mixture was stirred at 130° C. and 600 r / min for 55 min to obtain a modified resin; Then, 25 g of modified resin, 3 g of N,N-methylenebisacrylamide and 1.5 g of ammonium persulfate were added to step S2, and the mixture was stirred at a temperature of 180° C. and a speed of 500 r / min for 55 min; S4: filtering the product obtained in step S3, and calcining at 300° C. for 20 min to obtain a modified molecular sieve.

[0021] Example 3 This embodiment provides a method for preparing a modified molecular sieve for olefin cracking, comprising the following steps: S1: Weigh 13g potassium silicate, 10g aluminum chloride, 4g sodium hydroxide and 115g deionized water respectively, stir at 82°C and 600r / min for 55min to obtain aluminosilicate gel; S2: Add 3 g of amorphous silicon dioxide, 2 g of carboxymethyl cellulose and 1 g of ethylenediamine to step S1, and perform crystallization reaction at 150°C for 2.5 h; S3: 20 g of acrylic acid-maleic anhydride copolymer resin, 3 g of sodium alginate and 2 g of chitosan were mixed, and the mixture was stirred at 125° C. and 600 r / min for 50 min to obtain a modified resin; Then, 20 g of modified resin, 2 g of N,N-methylenebisacrylamide and 1.3 g of ammonium persulfate were added to step S2, and the mixture was stirred at a temperature of 175° C. and a speed of 500 r / min for 50 min; S4: Filter the product obtained in step S3, and calcine at 260° C. for 15 min to obtain a modified molecular sieve.

[0022] Comparative Example 1 The difference from Example 1 is that carboxymethyl cellulose and ethylenediamine are not added in step S2, and the other steps remain unchanged.

[0023] Comparative Example 2 The difference from Example 1 is that no modified resin is added in step S3, and the other steps remain unchanged.

[0024] Comparative Example 3 The difference from Example 1 is that sodium alginate and chitosan are not added in step S3, and the other steps remain unchanged.

[0025] Comparative Example 4 The difference from Example 1 is that the crystallization temperature in step S2 is 200° C., and the other steps remain unchanged.

[0026] Comparative Example 5 The difference from Example 1 is that the crystallization time in step S2 is 5 hours, and the other steps remain unchanged.

[0027] Performance Test: Determination of water absorption: Accurately weigh the molecular sieve desiccant samples prepared in each embodiment and comparative example and put them into a 250ml beaker, add 100ml deionized water at 20°C, immerse them in water for 24 hours, filter out the free water in the sample with a 100-mesh sieve and pour it back into the beaker, and let it stand on the sieve for 15 minutes, then use a measuring cylinder to measure the volume V of the remaining water in the beaker, and the water absorption Q (ml / g) is calculated according to the following formula: Q=(100-V) / 0.1, take 4 parallel samples, and take the average value of the data as the experimental result.

[0028] Compressive strength test: 0.8 g of the 3A molecular sieve adsorbent of each embodiment and comparative example after constant temperature and humidity (constant temperature and humidity conditions: temperature is 25°C, humidity is 75% by weight, and time is 18h) is weighed and loaded into a stainless steel cylinder with a closed bottom end. The cross-sectional area of ​​the stainless steel cylinder is 25.34 cm. A cylindrical ejector matched with the stainless steel cylinder is placed above the 4A molecular sieve adsorbent, and then placed on a particle strength tester to pressurize the ejector to 250N. After unloading the pressure, the 4A molecular sieve adsorbent is taken out and sieved with a 0.3mm mesh screen. The small balls that have not passed through the screen are weighed, and the percentage of the reduced mass and the mass of the sample before pressurization is the crushing rate of the tested sample under 250N; the results are shown in the following table.

[0029] Table 1

[0030] It can be seen from the above performance test results that the modified molecular sieves prepared in Examples 1-3 have excellent water absorption and crush resistance. In particular, the comprehensive performance of Example 3 is the most outstanding. However, since Comparative Examples 1-5 do not adopt the necessary technical solutions, their corresponding performance tests are significantly worse than those of the Examples. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0031] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a modified molecular sieve for olefin cracking, characterized in that: The steps include: S1: Weigh potassium silicate, aluminum chloride, sodium hydroxide and deionized water respectively, and stir and mix to obtain aluminosilicate gel; S2: adding amorphous silicon dioxide and ethylenediamine to step S1 for constant temperature crystallization; S3: Add modified resin, N,N-methylenebisacrylamide and ammonium persulfate to step S2, and continue stirring to react; S4: The product obtained in step S3 is filtered and calcined to obtain a modified molecular sieve.

2. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: The weight ratio of potassium silicate, aluminum chloride, sodium hydroxide and deionized water in step S1 is 10-15:8-12:2-5:90-130.

3. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: In step S1, the reaction is stirred at a temperature of 75-85° C. and a speed of 500-800 r / min for 40-60 min.

4. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: Step S2 also includes carboxymethyl cellulose.

5. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: In step S2, the weight ratio of amorphous silicon dioxide, carboxymethyl cellulose and ethylenediamine is 2-4:1-3:0.5-1.5; the constant temperature crystallization temperature is 140-160° C., and the crystallization reaction takes 1-2 hours.

6. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: The specific surface area of ​​the amorphous silicon dioxide is 500-800 m² / g.

7. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: In step S3, the weight ratio of the modified resin, N,N-methylenebisacrylamide and ammonium persulfate is 15-25:1-3:0.5-1.5; the reaction is stirred at a temperature of 160-180° C. for 35-55 minutes.

8. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: The preparation process of the modified resin in step S3 is: 15-25 parts of acrylic acid-maleic anhydride copolymer resin, 2-4 parts of sodium alginate and 1-3 parts of chitosan are stirred and mixed at a temperature of 120-130° C. for 35-55 minutes.

9. The method for preparing a modified molecular sieve for olefin cracking according to claim 1, characterized in that: In step S4, the calcination temperature is 200-300° C. and the calcination time is 10-20 min.

10. Use of the modified molecular sieve prepared according to any one of claims 1 to 9 as a desiccant in olefin cracking.

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