CN102372288B - Method for preparing SAPO-34 molecular sieve - Google Patents

Abstract

The invention relates to a preparation method of SAPO-34 molecular sieve, which mainly solves the problems of low crystallinity of SAPO-34 molecular sieve prepared by gas phase method, poor reactivity and fast coking rate when used for methanol to light olefins. In the present invention, the dry glue prepared from the precursor compounds of aluminum, silicon and phosphorus, fluoride and organic template is placed on the upper part of the reactor, and the mixed solution of water and organic amine is placed on the lower part of the reactor, and the crystallization temperature is 140 The technical scheme of preparing SAPO-34 molecular sieve catalyst under the reaction condition of ~220°C solves this problem well, and can be used in the industrial production of methanol to light olefins.

Description

The preparation method of SAPO-34 molecular sieve

technical field

The present invention relates to a kind of preparation method of SAPO-34 molecular sieve, specifically, the present invention relates to the method for preparing SAPO-34 molecular sieve by gas phase method. the

Background technique

In 1984, the United States Union Carbide Corporation developed a series of silicoaluminophosphate molecular sieves, among which SAPO-34 molecular sieve has a structure similar to phosphozeolite and belongs to small-pore zeolite, which can be used as adsorbent, catalyst and catalyst carrier. It shows very good catalytic activity in the reaction of methane to low carbon olefins (MTO), the selectivity of low carbon olefins is as high as 90%, and the selectivity of ethylene can reach more than 50%, and the amount of products above C ₅ is very small. The classic method of preparing SAPO-34 is hydrothermal synthesis (USP4440871, CN 1037334C, CN 1038125C, CN 1048428C), which is obtained by crystallization in a high-temperature hydrothermal system. The process of preparing molecular sieves by hydrothermal method is relatively complicated, requiring the use of a large amount of organic templates, and finally the molecular sieve product needs to be separated from the mother liquor.

As a method of preparing molecular sieves, the gas phase method has been deeply studied on zeolite molecular sieves, especially ZSM-5 molecular sieves, but there are few reports on the synthesis of aluminum phosphorus molecular sieves. The so-called gas phase method means that in the synthesis process, the molecular sieve synthesis precursor is first prepared into dry glue under certain conditions, and then the dry glue is placed in the upper part of the reaction kettle, and at the same time, a certain amount of organic amine and water are added to the bottom of the reaction kettle. The solution is used as a template, and the dry glue is not in contact with the liquid phase. Compared with the traditional hydrothermal synthesis, the gas phase method can greatly reduce the use of organic templates, eliminating the complicated steps of separating the product from the mother liquor, and the organic templates are easy to recycle and reuse. It is a simple and economical method for preparing molecular sieves. Environmentally friendly approach. the

At present, there is also CN1363519A that uses gas phase method to prepare SAPO-34 molecular sieve, but it only uses organic template agent in the liquid phase part, and the crystallinity is poor. CN1693202 puts template agent in the dry glue preparation process, but it is verified by experiments that the SAPO-34 molecular sieve prepared by this method has no obvious improvement in crystallinity, and its activity is poor when it is used in the reaction of methanol to olefins, and the coking rate is relatively fast. the

Contents of the invention

The technical problem to be solved by the present invention is to overcome the relatively low crystallinity of SAPO-34 molecular sieve prepared by gas phase method reported in previous documents, low activity and fast coking rate when used for methanol conversion to light olefins, and to provide a Preparation of new SAPO-34 molecular sieves. The method has the characteristics that the prepared SAPO-34 molecular sieve has high relative crystallinity, high activity and slow coking rate when used for methanol conversion to produce light olefins. the

In order to solve the problems of the technologies described above, the technical scheme adopted in the present invention is as follows: a preparation method of SAPO-34 molecular sieve comprises the steps successively:

(a) Dissolving the precursor compounds of phosphorus, aluminum and silicon in water to obtain solution I, adding organic amine and fluoride to obtain solution II, so that the molar ratio of each substance in solution II is composed of: Al ₂ O ₃ : a SiO ₂ : bP ₂ O ₅ : cH ₂ O : d organic amine : e fluoride, wherein a ranges from 0.05 to 2, b ranges from 0.05 to 2, and c ranges from 10~200, the value range of d is 0~10, and the value range of e is 0.03~0.6;

(b) Raise the temperature of solution II to 70-90°C to obtain a colloid, and then raise the temperature of the colloid to 100-160°C to obtain a dry glue;

(c) Place the dry glue in the gas phase position on the upper part of the reaction kettle, place the mixture of water and organic amine with a mass ratio of 0.1 to 4:1 in the liquid phase position in the lower part of the reaction kettle, and organically React amine vapor with dry glue for 12-72 hours to obtain SAPO-34 molecular sieve. the

In the above technical scheme, the preferred solution of fluoride is hydrofluoric acid; the preferred solution of the precursor of phosphorus is orthophosphoric acid, and the more preferred solution is orthophosphoric acid with a mass of 85%; the preferred solution of the precursor of aluminum is selected from activated alumina, pseudo thin water Alite or aluminum isopropoxide; the preferred solution for the precursor of silicon is silica sol, and the more preferred solution is silica sol with a mass of 30-40%; the preferred solution for organic amines is selected from triethylamine, tetraethylammonium hydroxide or morpholine at least one of the The precursor compounds of phosphorus, aluminum and silicon are dissolved in water to obtain solution I, and after stirring at room temperature for 1 to 3 hours, organic amine and fluoride are added to obtain solution II. In step (b), the solution II is stirred at room temperature for 12-24 hours, then the temperature is raised to 80-90°C, and then the stirring is continued for 3-5 hours to obtain a colloid. In step (b), the temperature of solution II is raised to 120-140° C., and dry glue is obtained after 12-24 hours. the

The preferred range of the crystallization temperature of the reactor in the above technical solution is 160-200°C. the

The present invention synthesizes SAPO-34 molecular sieve by introducing fluoride into the gas phase method, which improves the relative crystallinity of the molecular sieve, and when it is used as a catalyst for methanol conversion to produce low-carbon olefins, the activity is improved and the coking rate is also reduced. Nice technical effect. the

The present invention will be further elaborated below by embodiment. the

Detailed ways

【Comparative Example 1】

In the state of stirring, 23g of 85% phosphoric acid and 28.2g of silica sol with a silicon content of 30% were dropped into 94g of deionized water, and after fully mixing, 14.6g of alumina was added. the

After stirring at room temperature for 2 hours, TEAOH was added. At this time, the molar ratio of the components added was Al ₂ O ₃ :P ₂ O ₅ :1.25SiO ₂ :75H _{2 O:} TEAOH.

Continue to stir at room temperature for 24 hours, then gradually increase the temperature to 80°C, and continue to stir for 3-5 hours. With the evaporation of water during the reaction, the viscosity of the system gradually increases and becomes colloidal. Put the colloid into the oven and heat it at 120°C for more than 12 hours. The water will evaporate completely and become dry glue. the

Grind the dry glue into powder, take 6.5g of dry glue and put it in the upper part of the reactor, and the lower part of the reactor is a mixed solution of 7.5g of triethylamine and 15g of water. After the reaction kettle was sealed, it was crystallized at 180°C for 48 hours. After cooling, the obtained product was fully washed, filtered, dried at 120°C for 5 hours, and calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve. The crystallinity was specified as 100%. the

【Comparative Example 2】

According to the various steps and conditions of Comparative Example 1, but the templating agent triethylamine at the bottom of the reactor was replaced with morphine, and finally the crystallinity of SAPO-34 was 125.1%. the

[Example 1]

Put 23g of 85% phosphoric acid and 28.2g of silica sol with 30% silicon content into 94g of deionized water while stirring, and then add 14.6g of alumina after mixing thoroughly. the

After stirring at room temperature for 2 hours, TEAOH and hydrofluoric acid were added. At this time, the molar ratio of each component added was Al ₂ O ₃ :P ₂ O ₅ :1.25SiO ₂ :75H 2 _O: TEAOH:0.06HF.

Continue to stir at room temperature for 24 hours, then gradually increase the temperature to 80°C, and continue to stir for 3-5 hours. With the evaporation of water during the reaction, the viscosity of the system gradually increases and becomes colloidal. Put the colloid into the oven and heat it at 120°C for more than 12 hours. The water will evaporate completely and become dry glue. the

Grind the dry glue into powder, take 6.5g of dry glue and put it in the upper part of the reactor, and the lower part of the reactor is a mixed solution of 7.5g of triethylamine and 15g of water. After the reaction kettle was sealed, it was crystallized at 180°C for 48 hours. After cooling, the obtained product was fully washed, filtered, dried at 120°C for 5 hours, and calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve with a crystallinity of 123.3%. the

【Example 2】

According to the various steps and conditions of Example 1, but raising the reaction temperature to 200° C., the finally obtained SAPO-34 has a crystallinity of 105%. the

[Example 3]

According to the various steps and conditions of Example 1, but the reaction temperature was lowered to 160° C., finally the crystallinity of SAPO-34 was 127.5%. the

【Example 4】

According to the various steps and conditions of Example 1, but the molar ratio of each component is adjusted to Al ₂ O ₃ : P ₂ O ₅ : 1.25SiO ₂ : 75H _{2 O} : TEAOH : 0.04HF, and finally the crystallization of SAPO-34 is obtained The degree is 120.5%.

【Example 5】

Follow the steps and conditions of Example 1, but adjust the molar ratio of each component to Al ₂ O ₃ : P ₂ O ₅ : 1.25SiO ₂ : 75H _{2 O :} TEAOH : 0.08HF, and finally obtain the crystallization of SAPO-34 The degree is 126.3%.

【Example 6】

According to the various steps and conditions of Example 1, but prolonging the reaction time to 72h, the final crystallinity of SAPO-34 was 116.4%. the

【Example 7】

According to the various steps and conditions of Example 1, but the templating agent triethylamine at the bottom of the reactor was replaced with morphineline, and finally the crystallinity of SAPO-34 obtained was 146.7%. the

【Example 8】

According to the various steps and conditions of Example 7, but raising the reaction temperature to 200° C., the finally obtained SAPO-34 has a crystallinity of 129.4%. the

【Example 9】

According to the various steps and conditions of Example 7, but raising the reaction temperature to 160° C., the final crystallinity of SAPO-34 was 151.2%. the

【Example 10】

Follow the steps and conditions of Example 7, but adjust the molar ratio of each component to Al ₂ O ₃ : P ₂ O ₅ : 1.25SiO ₂ : 75H _{2 O :} TEAOH : 0.04HF, and finally obtain the crystallization of SAPO-34 The degree is 141.3%.

[Example 11]

Follow the steps and conditions of Example 7, but adjust the molar ratio of each component to Al ₂ O ₃ : P ₂ O ₅ : 1.25SiO ₂ : 75H _{2 O :} TEAOH : 0.08HF, and finally obtain the crystallization of SAPO-34 The degree is 150.5%.

【Example 12】

According to the various steps and conditions of Example 7, but prolonging the reaction time to 72h, the final crystallinity of SAPO-34 was 129.5%. the

【Example 13】

Molecular sieve catalyst evaluation

Using a fixed-bed catalytic reaction device, respectively adopting triethylamine, morphineline as the liquid phase template and comparative example 1 and comparative example 2 without adding fluoride, and respectively adopting triethylamine and morphine as the liquid phase template and adding The SAPO-34 molecular sieves obtained in Example 1 and Example 7 of fluoride were respectively subjected to catalytic evaluation experiments. The experimental conditions are as follows: the loading amount of the catalyst is 2.0 g, the reaction temperature is 460° C., the reaction pressure is normal pressure, the raw material is pure methanol, and the space velocity is 6 g methanol/g catalyst·hour. See Table 1 and Table 2 for the results. the

Under the condition that the methanol conversion rate of the four catalysts is close to 100%, it can be seen from Table 1 and Table 2 that after the fluoride is introduced into the gas phase synthesis SAPO-34 reaction system, the SAPO-34 molecular sieve is applied to methanol to light olefins The catalytic performance of the reaction system is enhanced. When triethylamine is used as a template, the selectivity of ethylene and propylene is increased from 79.2 to 81.0. When morphine is used as a template, the selectivity of ethylene and propylene is increased from 79.6 to 81.9. , the anti-coking properties of the two catalysts were enhanced. the

Table 1

Table 2

Claims (6)

1. the preparation method of a SAPO-34 molecular sieve in turn includes the following steps:

(a) with the precursor compound of phosphorus, aluminium, the silicon solution I that gets soluble in water, add organic amine and fluorochemical to get solution II in solution I, the mol ratio of each material in solution II is consisted of: Al ₂O ₃: a SiO ₂: bP ₂O ₅: cH ₂O: d organic amine: the e fluorochemical, wherein the span of a is that the span of 0.05～2, b is that the span of 0.05～2, c is that the span of 10～200, d is that the span of 0～10, e is 0.03～0.6;

(b) solution II is raise temperature to 70～90 ℃ colloid, then colloid is warming up to 100～160 ℃ and obtains dried glue;

(c) dried glue is placed in reactor upper gaseous phase position, with mass ratio 0.1～4: 1 water and the mixture of organic amine are placed in liquid phase position, reactor bottom, crystallization temperature be under 140～220 ℃ of conditions organic amine steam and the reaction of dried glue 12～72 hours the SAPO-34 molecular sieve;

Described fluorochemical is hydrofluoric acid.

2. the preparation method of SAPO-34 molecular sieve according to claim 1, the presoma that it is characterized in that phosphorus is ortho-phosphoric acid; The presoma of aluminium is selected from activated alumina, pseudo-boehmite or aluminum isopropylate; The presoma of silicon is silicon sol; Organic amine is selected from least a in triethylamine, tetraethyl-oxyammonia or morpholine.

3. the preparation method of SAPO-34 molecular sieve according to claim 1, it is characterized in that the precursor compound of phosphorus, aluminium, silicon soluble in water solution I, at room temperature stir after 1～3 hour and add organic amine, fluorochemical to get solution II.

4. the preparation method of SAPO-34 molecular sieve according to claim 1, after 12～24 hours rising temperature to 80～90 ℃ in stirring at room to it is characterized in that in step (b) solution II, then continue to stir 3～5 hours to get colloid.

5. the preparation method of SAPO-34 molecular sieve according to claim 1 is characterized in that in step (b) temperature of solution II is risen to 120～140 ℃, obtains dried glue after 12～24 hours.

6. the preparation method of SAPO-34 molecular sieve according to claim 1, is characterized in that crystallization temperature is 160～200 ℃.