A kind of refining method of polymethoxy dibutyl ether

Abstract

The present invention provides a method for refining polymethoxy dibutyl ether, belongs to the field of chemical separation technology, and comprises the following steps: step 1: preparing ZSM-5 molecular sieve; step 2: mixing butanol and paraformaldehyde in a molar ratio of 1: (1.8-2.2), the paraformaldehyde is calculated as formaldehyde, the mixture is pumped into a reactor, and under the action of ZSM-5 molecular sieve as a catalyst, react to obtain a reactant; step 3: pumping the reactant into a pressurized distillation tower, separating, separating polymethoxy dibutyl ether from the bottom of the tower, and obtaining a light component from the top of the tower. The present invention solves the problem of low yield and purity of synthesizing polymethoxy dibutyl ether using butanol and paraformaldehyde in the prior art, selects a ZSM-5 molecular sieve with low corrosiveness as a catalyst, and the prepared new ZSM-5 molecular sieve can meet the requirements for the acidity of the system, and has high stability, and can reduce the frequency of catalyst recovery and reprocessing.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation, and in particular relates to a method for refining polymethoxy dibutyl ether. Background Art

[0002] Polymethoxy alkyl ether has high oxygen content and high cetane number. Due to its environmental friendliness and advantages in combustion performance, polymethoxy dimethyl ether is considered to be a high-quality supplementary fuel for traditional diesel, which can help reduce harmful emissions and improve engine efficiency. It is completely miscible with diesel and is a very good diesel quality improver. It is also a hot topic in the field of clean new energy in recent years. Polymethoxy alkyl ether has similar physical properties to diesel. As a diesel quality improver, it does not require any changes to the engine of the vehicle in use when used. It is currently recognized as an environmentally friendly diesel quality improver in the world.

[0003] In order to reduce costs, the existing technology uses butanol and polyformaldehyde to synthesize polyoxymethylene dibutyl ether, which can recover the unreacted raw low-carbon alcohol in the wastewater, greatly reducing production energy consumption and costs. The reaction is carried out under acidic catalyst conditions. Under high temperature and high pressure environment, acidic catalysts will accelerate equipment corrosion, and equipment maintenance costs are also a consideration. Compared with sulfuric acid and hydrochloric acid, ZSM-5 molecular sieves are less corrosive and are the first choice as acid catalysts in actual industrial production. However, the use of ZSM-5 molecular sieves as catalysts also has the following problems: (1) The catalytic activity of ZSM-5 molecular sieves mainly comes from their acid sites. However, these acid sites are not evenly distributed inside the molecular sieve, resulting in fluctuations in reaction selectivity and activity, affecting the target reaction. (2) The relationship between the activity and temperature of the catalyst is complex and usually follows a "volcano-type" curve, which means that there is an optimum temperature. ZSM-5 molecular sieves usually have good thermal stability. However, in the reaction of preparing polyoxymethylene dibutyl ether, the optimal reaction temperature of ZSM-5 molecular sieves is 130-150°C. However, long-term operation in this temperature range may still cause structural changes or loss of acidic sites, resulting in a decrease in catalyst activity. (3) Hydrothermal stability: In a reaction environment containing water, the stability of ZSM-5 molecular sieves will be challenged. Polyformaldehyde can be hydrolyzed to formaldehyde and water in the presence of water, and the presence of water will accelerate the hydrothermal aging of ZSM-5 molecular sieves. The presence of water may cause the destruction of the molecular sieve skeleton structure or the passivation of acidic sites, especially under high temperature conditions. (4) After long-term use of ZSM-5 molecular sieves, the surface may be covered by by-products or coke, resulting in a reduction in active sites. The regeneration process of ZSM-5 molecular sieves is complex and costly, so improving the catalyst stability of ZSM-5 molecular sieves is also an urgent problem to be solved. In addition, the yield using ZSM-5 molecular sieve is also lower than that using cation exchange resin.

[0004] Therefore, there is an urgent need for a method for preparing polymethoxy dibutyl ether using ZSM-5 molecular sieve as a catalyst to improve the purity and yield of the product. Summary of the invention

[0005] The object of the present invention is to provide a method for refining polymethoxy dibutyl ether.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for refining polymethoxy dibutyl ether, the method comprising the following steps:

[0008] Step 1: Prepare ZSM-5 molecular sieve as follows:

[0009] (1) dissolving 0.3-0.9 parts by mass of Al2(SO4)3·18H2O and 0.2-0.5 parts by mass of NaOH in 2.6-2.9 parts by mass of tetraethylammonium chloride, stirring for 10-20 minutes, and then dropping 4-4.5 parts by mass of silica sol while stirring to obtain a sol;

[0010] (2) adding 0.6-0.8 parts by weight of butanol to the sol, stirring at 25-30° C. for 55-60 hours, adding an auxiliary agent, stirring for 40-50 minutes, and heat treating at 43-48° C. for 0.6-0.8 hours in a saturated hydrothermal atmosphere of sodium hydrogen phosphate to obtain a concentrated sol;

[0011] (3) The concentrated sol is placed in a hydrothermal reactor for crystallization. The obtained product is stirred for 10-15 minutes, centrifuged, and dried to obtain a solid powder;

[0012] (4) calcining the solid powder in a muffle furnace at 560-570°C in an air atmosphere for 4-5 hours to obtain NaZSM-5;

[0013] (5) mixing NaZSM-5 with an aqueous solution of ammonium chloride for ammonium exchange treatment, repeating 3-4 times, centrifuging, washing, drying, and calcining to obtain a ZSM-5 molecular sieve;

[0014] Step 2: mixing butanol and paraformaldehyde in a molar ratio of 1: (1.8-2.2), where the paraformaldehyde is calculated as formaldehyde, pumping the mixture into a reaction kettle, reacting at 130-150° C. and 1.2-1.5 MPa under the action of the ZSM-5 molecular sieve prepared in step 1 as a catalyst to obtain a reactant;

[0015] Step 3: Pump the reactants into a pressurized distillation tower, and separate them under the conditions of a top pressure of 0.2-0.5 MPa, a temperature of 150-170°C, a bottom pressure of 0.5-0.7 MPa, and a temperature of 200-230°C, to separate polymethoxy dibutyl ether from the bottom of the tower and obtain light components from the top of the tower.

[0016] In order to solve the problem that the commercially available ZSM-5 molecular sieve has low reaction yield and purity in catalyzing butanol and polyformaldehyde to synthesize polymethoxy dibutyl ether. The present invention provides a new type of ZSM-5 molecular sieve. In the method of the present invention, when the mass ratio of aluminum source, organic template, alkali source and silicon source is 0.3-0.9: 2.6-2.9: 0.2-0.5: 4-4.5, the obtained ZSM-5 molecular sieve can be used as a catalyst to improve the yield and purity of the product. Analysis shows that under the ratio conditions of the present invention, the amount of aluminum source determines the silicon-aluminum ratio of the molecular sieve, which can make the molecular sieve have strong acidity, meet the strong acid catalytic reaction required by the present invention, and ensure thermal stability at the same time; the amount of organic template added in the present invention can guide the formation of aluminosilicate skeleton, and can also affect the pore size and morphology of the molecular sieve. The shape and size of the pore not only affect whether the reactants can enter, but also affect their ability to reach the catalytic active center. Some active sites may only be accessible through specific directions or paths, which will affect the reaction rate and selectivity, and promote the formation of molecular sieves with higher crystallinity and ideal pore structure. The amount of alkali source added affects the pH value of the system, helps to form a stable gel system, and promotes the crystallization of molecular sieves; the amount of silicon source added in the present invention helps the molecular sieve to form a stable skeleton structure. Through the synergistic compounding of various components, the ZSM-5 type molecular sieve formed is suitable for the reaction system of the present invention, which improves the purity and yield of the product.

[0017] Furthermore, the concentration of the sodium hydrogen phosphate saturated water is 0.012-0.015 mol / L.

[0018] Furthermore, the crystallization conditions are 123-125° C. for 50-55 hours.

[0019] Furthermore, the centrifugal condition is: centrifugation at 7000-8000r / min.

[0020] Furthermore, in step (4), the heating rate of the muffle furnace is 3-5°C / min.

[0021] Furthermore, the concentration of the aqueous ammonium chloride solution is 1.2-1.5 mol / L.

[0022] Further, NaZSM-5 is mixed with an aqueous solution of ammonium chloride at a solid-liquid ratio of 1 g:22-25 mL.

[0023] Furthermore, the calcination conditions in step (5) are: calcination at 570-580° C. for 7-8 hours.

[0024] Furthermore, the auxiliary agent is a mixture of N-vinyl pyrrolidone and threonine in a mass ratio of (1.5-2):1.

[0025] Furthermore, the mass ratio of the auxiliary agent to the sol is (0.03-0.07):1.

[0026] In addition to considering the purity and yield of the product, the high stability of the ZSM-5 molecular sieve is of great significance for reducing costs. On the basis of the system of the present invention, the inventor added an auxiliary agent to improve the stability of the ZSM-5 molecular sieve. The analysis is that N-vinyl pyrrolidone and threonine can help form a specific pore structure during the synthesis of the molecular sieve, occupy a certain spatial position during the growth of the molecular sieve crystal, guide the crystal growth, and thus obtain the desired pore size and morphology. After the molecular sieve is synthesized, the template can be removed by appropriate heat treatment steps, leaving an ordered pore structure. At the same time, it can affect the growth rate of the molecular sieve grains and slow down the growth of the grains, thereby obtaining a more uniform small grain size. Small grains usually have a larger specific surface area and more active sites, which can improve the catalytic activity and stability of the molecular sieve. It can also reduce the excessive concentration of acidic sites: acidic sites in molecular sieves are essential for many catalytic reactions, but over-concentrated acidic sites may cause side reactions, such as excessive dehydration, cracking and coking. N-vinylpyrrolidone and threonine can adjust the distribution of acid sites in the molecular sieve to avoid excessive density of acid sites, thereby reducing the possibility of side reactions and improving catalytic efficiency and selectivity. They can also promote the orderly arrangement of Si-O-Si and Al-O-Al bonds in the molecular sieve framework, enhance the structural strength of the molecular sieve, and make it less likely to break or deactivate during long-term use and regeneration.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0028] 1. The present invention provides a method for refining polymethoxy dibutyl ether, which solves the problem of low yield and purity of polymethoxy dibutyl ether synthesized from butanol and paraformaldehyde in the prior art. The ZSM-5 molecular sieve with low corrosivity is selected as a catalyst. The prepared new ZSM-5 molecular sieve can meet the requirements of system acidity and has high stability, which can reduce the frequency of catalyst recovery and reprocessing and reduce production costs.

[0029] 2. When preparing ZSM-5 molecular sieve, when the mass ratio of aluminum source, organic template, alkali source and silicon source is 0.3-0.9:2.6-2.9:0.2-0.5:4-4.5, the prepared ZSM-5 molecular sieve can be used as a catalyst to improve the yield and purity of the product.

[0030] 3. On the basis of the system of the present invention, additives are added to the preparation of ZSM-5 molecular sieves to improve the stability of the ZSM-5 molecular sieves. DETAILED DESCRIPTION

[0031] 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.

[0032] Example 1

[0033] This embodiment provides a method for refining polymethoxy dibutyl ether, which comprises the following steps:

[0034] Step 1: Prepare ZSM-5 molecular sieve as follows:

[0035] (1) 0.6 parts by mass of Al2(SO4)3·18H2O and 0.4 parts by mass of NaOH were dissolved in 2.8 parts by mass of tetraethylammonium chloride, stirred for 15 min, and then 4.2 parts by mass of silica sol was added dropwise while stirring to obtain a sol; the silica sol was purchased from Zhejiang Delixin Micro-Nano Technology Co., Ltd., model JN4-15 / 1;

[0036] (2) adding 0.7 parts by mass of butanol to the sol, stirring at 27°C for 58 hours, adding an auxiliary agent, wherein the auxiliary agent is a mixture of N-vinyl pyrrolidone and threonine in a mass ratio of 1.7:1, and the mass ratio of the auxiliary agent to the sol is 0.05:1, stirring for 45 minutes, and heat-treating at 45°C for 0.7 hours in a saturated hydrothermal atmosphere of 0.014 mol / L sodium hydrogen phosphate to obtain a concentrated sol;

[0037] (3) The concentrated sol was placed in a hydrothermal reactor for crystallization at 124° C. for 52 h. The obtained product was stirred for 12 min and then centrifuged at 7500 r / min. The product was dried to obtain a solid powder.

[0038] (4) calcining the solid powder in a muffle furnace at 565°C in an air atmosphere for 4.5 h at a heating rate of 4°C / min to obtain NaZSM-5;

[0039] (5) NaZSM-5 was mixed with an aqueous solution of ammonium chloride having a concentration of 1.4 mol / L at a solid-liquid ratio of 1 g:24 mL to perform an ammonium exchange treatment. The mixture was repeated 4 times, and then centrifuged, washed, dried, and calcined. The calcination conditions were as follows: calcination at 575°C for 7.5 h to obtain a ZSM-5 molecular sieve.

[0040] Step 2: Butanol and paraformaldehyde (purchased from Shanghai MacLean Biochemical Technology Co., Ltd., product number P804536) in a molar ratio of 1:2 are mixed, and the paraformaldehyde is calculated as formaldehyde. The mixture is pumped into a reaction kettle, and the ZSM-5 molecular sieve prepared in step 1 is used as a catalyst, and the mass of the ZSM-5 molecular sieve accounts for 5% of the total mass of butanol and paraformaldehyde. The reaction is carried out at 140°C and 1.4 MPa to obtain a reactant;

[0041] Step 3: Pump the reactants into a pressurized distillation tower and separate them under the conditions of a top pressure of 0.3 MPa, a temperature of 160°C, a bottom pressure of 0.6 MPa, and a temperature of 220°C. Polymethoxydibutyl ether is separated from the bottom of the tower, and light components are obtained from the top of the tower.

[0042] Example 2

[0043] This embodiment provides a method for refining polymethoxy dibutyl ether, which comprises the following steps:

[0044] Step 1: Prepare ZSM-5 molecular sieve as follows:

[0045] (1) 0.3 parts by mass of Al2(SO4)3·18H2O and 0.5 parts by mass of NaOH were dissolved in 2.9 parts by mass of tetraethylammonium chloride, stirred for 10 min, and then 4.5 parts by mass of silica sol was added dropwise while stirring to obtain a sol; the silica sol was purchased from Zhejiang Delixin Micro-Nano Technology Co., Ltd., model JN4-15 / 1;

[0046] (2) adding 0.6 parts by mass of butanol to the sol, stirring at 30°C for 60 hours, adding an auxiliary agent, wherein the auxiliary agent is a mixture of N-vinyl pyrrolidone and threonine in a mass ratio of 1.5:1, and the mass ratio of the auxiliary agent to the sol is 0.03:1, stirring for 40 minutes, and heat-treating at 43°C for 0.8 hours in a saturated hydrothermal atmosphere of 0.015 mol / L sodium hydrogen phosphate to obtain a concentrated sol;

[0047] (3) The concentrated sol was placed in a hydrothermal reactor for crystallization at 123° C. for 55 h. The obtained product was stirred for 10 min and then centrifuged at 8000 r / min. The product was dried to obtain a solid powder.

[0048] (4) calcining the solid powder in a muffle furnace at 570°C in an air atmosphere for 4 h at a heating rate of 3°C / min to obtain NaZSM-5;

[0049] (5) NaZSM-5 was mixed with an aqueous solution of ammonium chloride having a concentration of 1.5 mol / L at a solid-liquid ratio of 1 g:25 mL to perform an ammonium exchange treatment. The mixture was repeated three times, and then centrifuged, washed, dried, and calcined. The calcination conditions were as follows: calcination at 570 °C for 8 h to obtain a ZSM-5 molecular sieve.

[0050] Step 2: Butanol and paraformaldehyde (purchased from Shanghai MacLean Biochemical Technology Co., Ltd., product number P804536) in a molar ratio of 1:1.8 are mixed, and the paraformaldehyde is calculated as formaldehyde. The mixture is pumped into a reaction kettle, and the ZSM-5 molecular sieve prepared in step 1 is used as a catalyst, and the mass of the ZSM-5 molecular sieve accounts for 5% of the total mass of butanol and paraformaldehyde. The reaction is carried out at 150°C and 1.2MPa to obtain a reactant;

[0051] Step 3: Pump the reactants into a pressurized distillation tower, and separate them under the conditions of a top pressure of 0.5 MPa, a temperature of 150°C, a bottom pressure of 0.7 MPa, and a temperature of 200°C, to separate polymethoxy dibutyl ether from the bottom of the tower and obtain light components from the top of the tower.

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 1 is that 0.6 parts by mass of Al2(SO4)3·18H2O is replaced by 0.1 parts by mass of Al2(SO4)3·18H2O.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 1 is that 0.6 parts by mass of Al2(SO4)3·18H2O is replaced by 1.5 parts by mass of Al2(SO4)3·18H2O.

[0056] Comparative Example 3

[0057] The difference between this comparative example and Example 1 is that 0.4 parts by mass of NaOH is replaced by 0.1 parts by mass of NaOH.

[0058] Comparative Example 4

[0059] The difference between this comparative example and Example 1 is that 0.4 parts by mass of NaOH is replaced by 0.9 parts by mass of NaOH.

[0060] Comparative Example 5

[0061] The difference between this comparative example and Example 1 is that 2.8 parts by mass of tetraethylammonium chloride is replaced by 2.2 parts by mass of tetraethylammonium chloride.

[0062] Comparative Example 6

[0063] The difference between this comparative example and Example 1 is that 2.8 parts by mass of tetraethylammonium chloride is replaced by 3.4 parts by mass of tetraethylammonium chloride.

[0064] Comparative Example 7

[0065] The difference between this comparative example and Example 1 is that 4.2 parts by mass of silica sol is replaced by 3.5 parts by mass of silica sol.

[0066] Comparative Example 8

[0067] The difference between this comparative example and Example 1 is that 4.2 parts by mass of silica sol is replaced by 5.0 parts by mass of silica sol.

[0068] Comparative Example 9

[0069] The difference between this comparative example and Example 1 is that the auxiliary agent is a mixture of N-vinyl pyrrolidone and threonine in a mass ratio of 0.7:1.

[0070] Comparative Example 10

[0071] The difference between this comparative example and Example 1 is that the mass ratio of the auxiliary agent to the sol is 0.15:1.

[0072] Comparative Example 11

[0073] The difference between this comparative example and Example 1 is that the mass ratio of the auxiliary agent to the sol is 0.01:1.

[0074] Performance Testing

[0075] The products of Examples 1-2 and Comparative Examples 1-11 were subjected to performance tests.

[0076] 1. Purity and yield test of polymethoxy dibutyl ether

[0077] The purity and yield of polymethoxy dibutyl ether were determined. The purity calculation formula was: the mass of pure polymethoxy dibutyl ether / the mass of polymethoxy dibutyl ether separated from the bottom of the tower × 100%; the yield calculation formula was: the mass of polymethoxy dibutyl ether actually generated / the mass of polymethoxy dibutyl ether theoretically generated × 100%. The control group used commercially available ZSM-5 molecular sieves, Shanghai MacLean Biochemical Technology Co., Ltd., item number: Z875520. The test results of the purity and yield of polymethoxy dibutyl ether are shown in Table 1.

[0078] Table 1: Purity and yield of polyoxymethylene dibutyl ether

[0079]

[0080] 2. ZSM-5 molecular sieve stability test

[0081] The stability of ZSM-5 molecular sieve was determined based on 90% raw material conversion rate (conversion rate = total mass of butanol and paraformaldehyde consumed in the reaction / total mass of butanol and paraformaldehyde under initial conditions × 100%). This means that under continuous operation, the catalyst can maintain its activity and selectivity for a period of time that the raw material conversion rate reaches 90%. During this time, the catalyst can effectively promote the reaction, ensuring that most of the raw materials can be converted into the target product, and the conversion rate will not be less than 90%. Among them, the control group used commercially available ZSM-5 molecular sieve, Shanghai McLean Biochemical Technology Co., Ltd., item number: Z875520. The stability test results are shown in Table 2.

[0082] Table 2: Stability test of ZSM-5 molecular sieve

[0083]

[0084] It can be seen from the test results in Tables 1-2 above that the method of Example 1-2 has high purity and yield, both of which can reach more than 95%, and the stability of the ZSM-5 molecular sieve of Example 1-2 is better than that of commercially available products.

[0085] 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 refining polymethoxy dibutyl ether, characterized in that: The method comprises the following steps: Step 1: Prepare ZSM-5 molecular sieve as follows: (1) dissolving 0.3-0.9 parts by mass of Al2(SO4)3·18H2O and 0.2-0.5 parts by mass of NaOH in 2.6-2.9 parts by mass of tetraethylammonium chloride, stirring for 10-20 minutes, and then dropping 4-4.5 parts by mass of silica sol while stirring to obtain a sol; (2) adding 0.6-0.8 parts by weight of butanol to the sol, stirring at 25-30° C. for 55-60 hours, adding an auxiliary agent, stirring for 40-50 minutes, and heat treating at 43-48° C. for 0.6-0.8 hours in a saturated hydrothermal atmosphere of sodium hydrogen phosphate to obtain a concentrated sol; (3) The concentrated sol is placed in a hydrothermal reactor for crystallization. The obtained product is stirred for 10-15 minutes, centrifuged, and dried to obtain a solid powder; (4) calcining the solid powder in a muffle furnace at 560-570°C in an air atmosphere for 4-5 hours to obtain NaZSM-5; (5) mixing NaZSM-5 with an aqueous solution of ammonium chloride for ammonium exchange treatment, repeating 3-4 times, centrifuging, washing, drying, and calcining to obtain a ZSM-5 molecular sieve; Step 2: mixing butanol and paraformaldehyde in a molar ratio of 1: (1.8-2.2), where the paraformaldehyde is calculated as formaldehyde, pumping the mixture into a reaction kettle, reacting at 130-150° C. and 1.2-1.5 MPa under the action of the ZSM-5 molecular sieve prepared in step 1 as a catalyst to obtain a reactant; Step 3: Pump the reactants into a pressurized distillation tower, and separate them under the conditions of a tower top pressure of 0.2-0.5 MPa, a temperature of 150-170° C., a tower bottom pressure of 0.5-0.7 MPa, and a temperature of 200-230° C., to separate polymethoxy dibutyl ether from the tower bottom and obtain light components from the tower top; Wherein, the auxiliary agent is a mixture of N-vinyl pyrrolidone and threonine in a mass ratio of (1.5-2):1; The mass ratio of the auxiliary agent to the sol is (0.03-0.07):

1.

2. The method for refining polymethoxy dibutyl ether according to claim 1, characterized in that: The concentration of the sodium hydrogen phosphate saturated water is 0.012-0.015 mol / L.

3. The method for refining polymethoxy dibutyl ether according to claim 1, characterized in that: The crystallization conditions are 123-125° C. for 50-55 hours.

4. The method for refining polymethoxy dibutyl ether according to claim 1, characterized in that: The centrifugal conditions are: centrifugation at 7000-8000r / min.

5. The method for purifying polymethoxy dibutyl ether according to claim 1, characterized in that: In step (4), the heating rate of the muffle furnace is 3-5°C / min.

6. The method for purifying polymethoxy dibutyl ether according to claim 1, characterized in that: The concentration of the ammonium chloride aqueous solution is 1.2-1.5 mol / L.

7. The method for purifying polymethoxy dibutyl ether according to claim 1, characterized in that: NaZSM-5 was mixed with an aqueous solution of ammonium chloride at a solid-liquid ratio of 1 g:22-25 mL.

8. The method for purifying polymethoxy dibutyl ether according to claim 1, characterized in that: The calcination conditions in step (5) are: calcination at 570-580° C. for 7-8 hours.

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