阅读说明：本技术 一种对低碳烯烃具有较高的选择性的催化剂及其制备方法 (Catalyst with high selectivity on low-carbon olefin and preparation method thereof ) 是由 代成义 杜康 *** 陈星月 时一鸣 刘丹 马晓迅 于 2019-08-23 设计创作，主要内容包括：本发明公开了一种对低碳烯烃具有较高的选择性的催化剂及其制备方法,其中,制备方法包括以下步骤：(1)以硅源、去离子水、模板剂、碱源、硼源和晶种溶液为原料经过晶化和焙烧制备得到B-ZSM-5分子筛母体-1；(2)将NaOH、Al(NO<Sub>3</Sub>)<Sub>3</Sub>和水混合制成处理液,并加入B-ZSM-5分子筛母体-1,经搅拌和焙烧制备得到B-ZSM-5分子筛母体-2；(3)经过铵交换制备得到B-ZSM-5分子筛母体-3；(4)经过压片和过筛制备得到最终的ZSM-5分子筛。本发明的有益之处在于：(1)制得的ZSM-5分子筛既可用在MTO工艺中,也可用在MTP工艺中；(2)无论是在MTO工艺中还是在MTP工艺中,制得的ZSM-5分子筛对C2-C4烯烃都具有较高的总选择性；(2)制得的ZSM-5分子筛催化稳定性得到了提高。(The invention discloses a catalyst with high selectivity on low-carbon olefin and a preparation method thereof, wherein the preparation method comprises the following steps: (1) the B-ZSM-5 molecular sieve matrix-1 is prepared by taking a silicon source, deionized water, a template agent, an alkali source, a boron source and a seed crystal solution as raw materials through crystallization and roasting; (2) adding NaOH and Al (NO) 3 ) 3 Mixing with water to obtain a treatment solution, adding B-ZSM-5 molecular sieve matrix-1, stirring and roasting to obtain B-ZSM-5 molecular sieve matrix-2; (3) preparing a B-ZSM-5 molecular sieve parent body-3 by ammonium exchange; (4) and tabletting and sieving to obtain the final ZSM-5 molecular sieve. The invention has the advantages that: (1) the prepared ZSM-5 molecular sieve can be used in an MTO process and an MTP process; (2) the prepared ZSM-5 molecular sieve has higher total selectivity to C2-C4 olefin in MTO process or MTP process; (2) the catalytic stability of the prepared ZSM-5 molecular sieve is improved.)

1. A preparation method of a catalyst with high selectivity on low-carbon olefin is characterized by comprising the following steps:

step 1: preparation of B-ZSM-5 molecular Sieve precursor-1

Sequentially adding a silicon source, deionized water, a template agent, an alkali source, a boron source and a seed crystal solution into a polytetrafluoroethylene reaction kettle, uniformly stirring, crystallizing at 170 ℃ for 3d in the air atmosphere, centrifuging, washing, drying, grinding, and roasting at 550 ℃ for 6h in the air atmosphere to obtain a B-ZSM-5 molecular sieve matrix-1;

step 2: alkali treatment

Adding NaOH and Al (NO)₃)₃Mixing with water to obtain a treatment solution, placing a beaker containing the treatment solution in a 65 ℃ water bath kettle, adding the B-ZSM-5 molecular sieve matrix-1 after keeping the temperature constant, stirring for 30min, taking out, centrifuging, washing, drying, grinding, and roasting at 500 ℃ for 4h in an air atmosphere to obtain a B-ZSM-5 molecular sieve matrix-2;

step 3: ammonium exchange

Will contain NH₄Placing a beaker of the Cl solution in a water bath kettle at 60 ℃, adding the B-ZSM-5 molecular sieve matrix-2 after keeping the temperature constant, stirring for 2 hours, taking out, centrifuging and washing to finish 1 time of ammonium exchange operation, repeating the ammonium exchange operation for 2 times, drying and grinding the product, and roasting for 4 hours at 500 ℃ in the air atmosphere to obtain the B-ZSM-5 molecular sieve matrix-3;

step 4: shaping of

Tabletting and molding the B-ZSM-5 molecular sieve matrix-3, and then sieving the molded product into particles of 20-40 meshes by using a sieve to obtain the final ZSM-5 molecular sieve.

2. The method according to claim 1, wherein in Step1, the silicon source is selected from silica sol, ethyl orthosilicate or white carbon black.

3. The method of claim 1, wherein in Step1, the template is selected from the group consisting of tetrapropylammonium bromide, tetrapropylammonium hydroxide, and n-butylamine.

4. The method of claim 1, wherein in Step1, the alkali source is selected from ethylamine, sodium hydroxide or sodium metaaluminate.

5. The method of claim 1, wherein in Step1, said boron source is selected from boric acid or boron oxide.

6. The method of claim 1, wherein in Step1, the seed crystal solution is prepared by mixing tetraethoxysilane, tetrapropylammonium hydroxide and deionized water at a mass ratio of 5:7:3 and aging at 80 ℃ for 72h, and the particle size distribution of the seed crystal is in the range of 10-100 nm.

7. The method according to claim 1, wherein in Step2, the concentration of NaOH in the treatment solution is 0.2mol/L and Al (NO) is₃)₃The concentration of (2) was 26.6. mu. mol/L.

8. The method of claim 1, wherein said NH is performed in Step3₄The concentration of the Cl solution was 0.4 mol/L.

9. The method of claim 1, wherein in each of Step1, Step2 and Step3, said drying is performed at 80 ℃ in an air atmosphere.

10. A catalyst having high selectivity for low carbon olefins, which is prepared by the method of any one of claims 1 to 9, and has a mesoporous structure and weak acid sites.

Technical Field

The invention relates to a catalyst and a preparation method thereof, in particular to a catalyst with high selectivity on low-carbon olefin and a preparation method thereof, belonging to the technical field of catalysts.

Background

The low-carbon olefins such as ethylene, propylene and the like are important basic chemical raw materials, and with the development of national economy of China, particularly the development of modern chemical industry, the demand of China for the low-carbon olefins is gradually increased, and the contradiction between supply and demand is increasingly prominent.

The MTO process for preparing low-carbon olefins such as ethylene and propylene from methanol and the MTP process for preparing propylene from methanol are currently important chemical technologies. The technology takes methanol synthesized by coal or natural gas as a raw material to produce low-carbon olefin, and is a core technology for developing non-petroleum resources to produce products such as ethylene, propylene and the like.

At present, in an MTO process for preparing low-carbon olefins such as ethylene, propylene and the like from methanol, a ZSM-5 molecular sieve is generally used as a catalyst, most of the existing ZSM-5 molecular sieves are granular, and the following problems are found in practical use:

1. the catalytic stability is poor;

2. the overall selectivity of the lower olefins is lower.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a catalyst which has better catalytic stability and higher total selectivity of low-carbon olefin and a preparation method thereof.

In order to achieve the above object, the present invention adopts the following technical solutions:

a preparation method of a catalyst with high selectivity on low-carbon olefin is characterized by comprising the following steps:

step 1: preparation of B-ZSM-5 molecular Sieve precursor-1

Sequentially adding a silicon source, deionized water, a template agent, an alkali source, a boron source and a seed crystal solution into a polytetrafluoroethylene reaction kettle, uniformly stirring, crystallizing at 170 ℃ for 3d in the air atmosphere, centrifuging, washing, drying, grinding, and roasting at 550 ℃ for 6h in the air atmosphere to obtain a B-ZSM-5 molecular sieve matrix-1;

step 2: alkali treatment

Adding NaOH and Al (NO)₃)₃Mixing with water to obtain a treatment solution, placing a beaker containing the treatment solution in a 65 ℃ water bath kettle, adding the B-ZSM-5 molecular sieve matrix-1 after keeping the temperature constant, stirring for 30min, taking out, centrifuging, washing, drying, grinding, and roasting at 500 ℃ for 4h in an air atmosphere to obtain a B-ZSM-5 molecular sieve matrix-2;

step 3: ammonium exchange

Will contain NH₄Placing a beaker of Cl solution in a water bath kettle at 60 ℃, adding a B-ZSM-5 molecular sieve matrix-2 after keeping the temperature constant, stirring for 2 hours, taking out, centrifuging and washing to finish 1 time of ammonium exchange operation, repeating the ammonium exchange operation for 2 times, drying and grinding the product, and roasting for 4 hours at 500 ℃ in an air atmosphere to obtain the catalystB-ZSM-5 molecular sieve mother body-3;

step 4: shaping of

Tabletting and molding the B-ZSM-5 molecular sieve matrix-3, and then sieving the molded product into particles of 20-40 meshes by using a sieve to obtain the final ZSM-5 molecular sieve.

The preparation method is characterized in that in Step1, the silicon source is selected from silica sol, ethyl orthosilicate or white carbon black.

The preparation method is characterized in that in Step1, the template is selected from tetrapropylammonium bromide, tetrapropylammonium hydroxide or n-butylamine.

The preparation method is characterized in that in Step1, the alkali source is selected from ethylamine, sodium hydroxide or sodium metaaluminate.

The preparation method is characterized in that in Step1, the boron source is boric acid or boron oxide.

The preparation method is characterized in that in Step1, the seed crystal solution is obtained by mixing tetraethoxysilane, tetrapropylammonium hydroxide and deionized water in a mass ratio of 5:7:3 and aging at 80 ℃ for 72 hours, and the particle size distribution of the seed crystal is within the range of 10-100 nm.

The process according to Step2, wherein the concentration of NaOH in the treatment solution is 0.2mol/L and Al (NO) is added₃)₃The concentration of (2) was 26.6. mu. mol/L.

The process according to Step3, wherein the NH is added₄The concentration of the Cl solution was 0.4 mol/L.

The above-mentioned production method is characterized in that in each of Step1, Step2 and Step3, the above-mentioned drying is carried out at 80 ℃ in an air atmosphere.

The invention has the advantages that:

(1) after alkali treatment and aluminum addition, the strong acid position of the obtained catalyst is reduced, a weak acid center appears, and the generation of low-carbon olefin is facilitated, so that the catalyst has higher total selectivity on C2-C4 olefin no matter in an MTO process for preparing low-carbon olefin such as ethylene, propylene and the like from methanol or an MTP process for preparing propylene from methanol, wherein the total selectivity of the catalyst on the C2-C4 olefin reaches 85.83% in the MTO process for preparing the low-carbon olefin such as ethylene, propylene and the like from methanol;

(2) after alkali treatment, the mesoporous structure is introduced into the catalyst, and the diffusion performance of the carbon deposit precursor in the pore channel of the catalyst is improved, so that the catalytic stability of the catalyst is improved in an MTO process for preparing low-carbon olefins such as ethylene and propylene from methanol and an MTP process for preparing propylene from methanol;

(3) the catalyst can be used in MTO process for preparing low-carbon olefins such as ethylene, propylene and the like from methanol, can also be used in MTP process for preparing propylene from methanol, and has a wide application range.

Drawings

FIG. 1 is a scanning electron micrograph of B-ZSM-5 molecular sieve mother-1 at 15.00K magnification;

FIG. 2 is a scanning electron micrograph of B-ZSM-5 molecular sieve mother-1 at 30.00K magnification;

FIG. 3 is a scanning electron micrograph of B-ZSM-5 molecular sieve precursor-2 at 15.00K magnification;

FIG. 4 is a scanning electron micrograph of B-ZSM-5 molecular sieve precursor-2 at 30.00K magnification;

FIG. 5 is a scanning electron micrograph of B-ZSM-5 molecular sieve mother-3 at 15.00K magnification;

FIG. 6 is a scanning electron micrograph of B-ZSM-5 molecular sieve precursor-3 at 30.00K magnification.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

First part, preparation of ZSM-5 molecular sieve

Step 1: preparation of B-ZSM-5 molecular Sieve precursor-1

333.3g of silica sol (silicon source) with the silica content of 30 wt%, 225g of deionized water (reaction medium), 66.7g of tetrapropylammonium bromide (template), 111.3g of ethylamine aqueous solution (alkali source) with the concentration of 65 wt%, 8.24g of boric acid (boron source) and 10.4g of seed crystal solution are sequentially added into a polytetrafluoroethylene reaction kettle, uniformly stirred and crystallized at 170 ℃ for 3d under the air atmosphere, then centrifuged, washed with deionized water for 3 times, dried at 80 ℃ under the air atmosphere, ground and transferred into a crucible, and roasted at 550 ℃ for 6h under the air atmosphere to obtain the B-ZSM-5 molecular sieve matrix-1.

The preparation method of the seed crystal solution is as follows: 50g of Tetraethoxysilane (TEOS), 70g of tetrapropylammonium hydroxide (TPAOH) and 30g of deionized water are mixed and stirred to prepare a solution, the solution is aged for 72 hours at the temperature of 80 ℃, a seed crystal solution is obtained, and the particle size of the seed crystal is distributed in the range of 10-100 nm.

Silicon source: besides silica sol, white carbon black or tetraethoxysilane can be selected.

Template agent: in addition to tetrapropylammonium bromide, tetrapropylammonium hydroxide (TPAOH) or n-butylamine may also be used.

Alkali source: in addition to ethylamine, sodium hydroxide or sodium metaaluminate may also be used.

A boron source: boron oxide may be selected in addition to boric acid.

The scanning electron microscope pictures of the B-ZSM-5 molecular sieve parent-1 are respectively shown in figure 1 and figure 2 when the amplification is 15.00K times and 30.00K times.

As can be seen from fig. 1 and 2: the external surface appearance of the B-ZSM-5 molecular sieve parent body-1 is regular.

Step 2: alkali treatment

Preparing a treatment solution: weighing 0.48g NaOH solid in a 100ml beaker, weighing 60ml deionized water in a measuring cylinder, pouring into the beaker, adding 0.02gAl (NO) after stirring uniformly₃)₃·9H₂O, stirring uniformly to prepare a treatment solution, wherein each liter of the treatment solution contains 0.2mol of NaOH and 26.6 mu mol of Al (NO)₃)₃。

Placing a beaker filled with 60ml of treatment solution in a 65 ℃ water bath, adding 2g B-ZSM-5 molecular sieve matrix-1 after keeping the temperature constant, stirring for 30min, taking out and centrifuging, washing for 3 times by deionized water, drying at 80 ℃ in the air atmosphere, taking out and grinding, transferring to a crucible, and roasting at 500 ℃ for 4h in the air atmosphere to obtain the B-ZSM-5 molecular sieve matrix-2.

During the alkaline treatment, the following changes mainly occur:

(1) a large amount of silicon on the B-ZSM-5 molecular sieve parent body-1 is removed by the treatment liquid, and a small amount of aluminum on the B-ZSM-5 molecular sieve parent body-1 is also removed;

(2) the treatment liquid is used for etching silicon, a mesoporous structure is introduced into the B-ZSM-5 molecular sieve matrix-1, the diffusion performance of a carbon deposit precursor in a pore channel of the B-ZSM-5 molecular sieve matrix-1 is improved, and the catalytic stability of the final ZSM-5 molecular sieve in the MTO process for preparing low-carbon olefin from methanol can be improved;

(3) aluminum in the treatment solution is slowly deposited on the surface of the B-ZSM-5 molecular sieve matrix-1, silicon is protected, excessive etching is avoided, and the B-ZSM-5 molecular sieve matrix-2 obtained by treatment has uniform mesoporous distribution (when the treatment solution is prepared, a control group is arranged, so that the treatment solution only contains 0.2mol/LNaOH and does not contain Al (NO)₃)₃Finally, the final ZSM-5 molecular sieve yield was calculated to be 65%, which was 10% lower than the al added experimental group, confirming that: aluminum can avoid over etching).

After alkali treatment and aluminum addition, the strong acid position of the obtained B-ZSM-5 molecular sieve parent body-2 is reduced, and a weak acid center appears, which is very beneficial to the generation of low-carbon olefin.

The scanning electron microscope pictures of the B-ZSM-5 molecular sieve parent-2 are respectively shown in figure 3 and figure 4 when the magnification is 15.00K times and 30.00K times.

As can be seen from fig. 3 and 4: the B-ZSM-5 molecular sieve parent body-2 has better dispersibility and embodies a certain depolymerization effect.

Step 3: ammonium exchange

Weighing 0.3209g NH₄Placing Cl solid in a 25ml beaker, measuring 15ml of deionized water by a measuring cylinder, pouring into the beaker, uniformly stirring, and preparing into NH with the concentration of 0.4mol/L₄And (4) Cl solution.

Will contain 15ml of NH₄And (3) placing the beaker of the Cl solution in a water bath kettle at 60 ℃, adding 1.5g B-ZSM-5 molecular sieve matrix-2 after the temperature is constant, stirring for 2 hours, taking out, centrifuging, washing for 3 times by using deionized water, and finishing the ammonium exchange operation for 1 time. The aforementioned ammonium exchange operation was repeated 2 times. And finally, drying the product at 80 ℃ in the air atmosphere, taking out, grinding, transferring to a crucible, and roasting at 500 ℃ for 4h in the air atmosphere to obtain the B-ZSM-5 molecular sieve matrix-3.

The ammonium exchange is carried out by dissolving Na in B-ZSM-5 molecular sieve precursor-2 (sodium type molecular sieve)⁺Replacement by NH₄ ⁺Reducing the introduction of impurity ions, and finally roasting to obtain NH₄ ⁺And (4) removing.

The scanning electron microscope pictures of the B-ZSM-5 molecular sieve parent-3 are respectively shown in FIG. 5 and FIG. 6 when the magnification is 15.00K times and 30.00K times.

As can be seen from fig. 5 and 6: the surface of the B-ZSM-5 molecular sieve parent body-3 is regular and has good dispersibility.

Step 4: shaping of

Taking a certain amount of B-ZSM-5 molecular sieve parent-3, tabletting and forming, and then sieving into 20-40 mesh particles by a sieve to obtain the final ZSM-5 molecular sieve.

The calculated yield of the ZSM-5 molecular sieve was 75%.

And in the second part, evaluating the selectivity and the catalytic stability of the ZSM-5 molecular sieve, weighing 1g of the ZSM-5 molecular sieve, filling the ZSM-5 molecular sieve into a quartz tube, and evaluating the selectivity and the catalytic stability of the ZSM-5 molecular sieve on a fixed bed catalyst evaluation device.

Evaluation conditions were as follows: MTO process, bed temperature 472 deg.C, WHSV 1.5h^-1。

And (3) measuring results:

from the above table, it can be seen that:

(1) when the MTO process is adopted, the selectivity of the ZSM-5 molecular sieve to ethylene and butylene is increased along with the increase of time, the maximum selectivity to ethylene reaches 24.61%, the maximum selectivity to butylene reaches 11.16%, the selectivity to propylene is reduced along with the increase of time, although the selectivity is reduced, the selectivity is still over 43%, the total selectivity to low-carbon olefin (C2-C4) is over 79%, and the maximum selectivity to low-carbon olefin (C2-C4) reaches 85.83%;

(2) when the MTO process is adopted, the total selectivity of the low-carbon olefin (C2-C4) is reduced (by 7 percent) after the reaction is carried out for 5 hours at the bed temperature of 472 ℃, but the reduction is not much.

Therefore, in the MTO process for preparing low-carbon olefins such as ethylene, propylene and the like from methanol, the ZSM-5 molecular sieve provided by the invention has higher selectivity on the low-carbon olefins and also has better catalytic stability.

It should be noted that the above-mentioned embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the protection scope of the present invention.