CN102516009B - Method for preparing isoprene through liquid phase method - Google Patents

Abstract

The invention relates to a method for preparing isoprene by a liquid phase method. By isobutylene and/or tert-butanol, with paraformaldehyde and/or formaldehyde aqueous solution, react under the action of acid catalyst to obtain the reaction solution containing intermediate product 4,4-dimethyl-1,3-dioxane, and then The reaction solution containing the intermediate product is continuously passed into the falling film reactor after purification and/or without purification to carry out the thermal cracking reaction, while spraying water mist from the top of the falling film reactor to control the temperature of the inner wall of the reactor to be 150 ～300℃, the reaction pressure is stable at 0.5～2.0MPa. The isoprene produced by the cracking is evaporated from the top of the reactor together with part of the solvent, and the formaldehyde is taken out from the bottom of the reactor along with the water mist and the liquid flow on the wall of the reactor, so that the yield of isoprene is >80%.

Description

A kind of method for preparing isoprene by liquid phase method

Technical field:

The invention relates to a method for producing isoprene by reacting isobutene and/or tert-butanol with paraformaldehyde and/or formaldehyde aqueous solution.

Background technique

Isoprene is an important raw material for the production of isoprene rubber. Isoprene rubber is used more and more widely because its structure and properties are close to natural rubber. The current production methods of isoprene include cracking C5 fraction extractive distillation, dehydrogenation, chemical synthesis and so on. Among them, chemical synthesis methods include isobutylene-formaldehyde method, acetylene-acetone method, propylene dimerization method, etc. The synthesis of isoprene by the alkenal method has been industrialized in Russia and Japan, and the chemical reactions that occur are as follows:

The reaction process is usually realized by a liquid-phase two-step method. The first step isobutene and formaldehyde are condensed under the action of an acidic catalyst to generate 4,4-dimethyl-1,3-dioxane (DMD), and the second step is The two-step DMD is cracked under the catalytic action of acidic solution to generate isoprene, formaldehyde and water. Regarding these two processes, Russian patent RU2085552, Russian patent RU2098398, Russian patent RU2099318, Russian patent RU2203878, Russian patent RU2280022, US patent US4511751, and European patent EP0106323 are all introduced.

A method for preparing isoprene is described in Japanese Patent CN200480008845.X. Isobutylene and formaldehyde are passed into a stirred reactor with multi-layer baffles, and the intermediate product DMD produced is further cracked to generate isoprene. The process adopts a kettle-type reaction. Even if baffles are installed vertically in the kettle, the back-mixing is still relatively large, and the generated isoprene is easy to react with the formaldehyde produced by cracking to form methyldihydropyran, and there are as many as 10 in the reaction system. % of high boilers, the presence of high boilers aggravates the occurrence of by-products.

In Russian patent RU2280022C1, after adding a large amount of tert-butanol or isobutene to the intermediate product DMD generated in the first step, it is passed into a tubular reactor for catalytic cracking to generate isoprene. Although adding isobutene or tert-butanol can neutralize the formaldehyde produced by the reaction, excessive isobutene and formaldehyde will inevitably bring about higher energy consumption, and in the tubular reaction, the generated isoprene goes through a long period of time before leaving the system. A large number of by-products are generated.

The existing method for preparing isoprene is difficult to overcome the problem that the by-product formaldehyde reacts with the product isoprene to generate a large number of by-products, or causes a large amount of energy consumption to overcome this problem, so there is no effective preparation The isoprene approach overcomes the above problems.

Contents of the invention

The object of the present invention is to provide a method for preparing isoprene by a liquid phase method, which can effectively reduce the reaction between by-product formaldehyde and product isoprene, increase the yield of isoprene, reduce by-products, and reduce energy consumption.

To achieve the above object, the present invention adopts the following technical solutions:

A method for preparing isoprene by a liquid phase method is provided, comprising the following steps:

a) isobutylene and/or tert-butanol, and paraformaldehyde and/or formaldehyde aqueous solution, react in the presence of an acidic catalyst to obtain a reaction solution containing the intermediate product DMD;

b) The DMD-containing reaction solution obtained in step a) is continuously fed into the mixer at the top of the falling film reactor after purification and/or without purification or optionally adding a low-boiling inert The solvent is diluted, and the obtained solution diluted with a low-boiling inert solvent is continuously passed into the mixer located at the top of the falling film reactor, and an acidic aqueous solution is added to the mixer in the reactor at the same time, and the two pass through After mixing to form a lysate, it is distributed to the reactor wall, and the thermal cracking reaction is carried out during the process of flowing down the reactor wall;

Wherein in step b), the isoprene generated by cracking and a part of the optional low-boiling inert solvent are distilled from the top of the reactor to obtain the crude product of isoprene, wherein the cracking mother liquor containing formaldehyde is obtained from the reaction Extracted from the bottom of the device.

The method step a) of the present invention generates the reaction solution containing intermediate DMD via isobutene and/or tert-butanol and the aqueous solution of paraformaldehyde and/or formaldehyde in the presence of an acidic catalyst, and the temperature in the reaction process is 60-85 ℃, pressure is 0.7～2.0MPa, the weight ratio of the consumption of isobutene and/or tert-butanol and paraformaldehyde and/or formaldehyde in the aqueous solution of paraformaldehyde and/or formaldehyde is 0.15～2:1, preferably 0.3～0.9 : 1; Described acidic catalyst is the aqueous solution of acid or acidic salt or the mixture of cation exchange resin and water, acidic catalyst is preferably common inorganic acid or organic acid, is preferably selected from phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, acetic acid , methanesulfonic acid, ethanesulfonic acid, trifluoromethanesulfonic acid or such various acids in an aqueous solution with a concentration between 60-99 wt%, preferably between 65-95 wt%. The acidic catalyst and the acid in the acidic aqueous solution may be the same or different, preferably the same. In addition, the acid concentration of the acidic aqueous solution is lower than that of the acidic catalyst, and the acid concentration of the acidic aqueous solution is generally between 0.05-20 wt%, more preferably between 0.5-5 wt%. Wherein the consumption of this acidic catalyst is 0.1～6: 1 with respect to the weight ratio of raw material isobutene and/or tert-butanol, preferably 0.5～4:1, and aforementioned isobutene and/or tert-butanol can be isobutene solution And/or tert-butanol solution, also can be made up of the material that contains isobutene or tert-butanol. The reaction is carried out in one-stage or multi-stage reactors, and the isoprene synthesis intermediate DMD or its crude product is obtained through a separation unit or without a separation unit. The reaction process has been described in detail in CN200480008845.X, CN200810013740.3, RU2280022C1 and other patents. In the present invention, the synthesis of the intermediate 4,4-dimethyl-1,3-dioxane or its crude product adopts the reactor and its process adopted in the above-mentioned patent, or a similar reactor and its process.

Method steps b) of the present invention purify and/or do not adopt the falling film reactor (as Fig. 1) to realize that the cracking reaction of the reaction solution containing DMD that does not purify is equipped with a water mist distributor at the top of the reactor; The isoprene escapes from the thinner liquid film into the gas phase system with relatively low temperature, which reduces the chance of the reaction between isoprene and by-products in the liquid phase, and also reduces the isoprene self-sustainability. get together. At the same time, water mist is sprayed from the water mist distributor on the top of the falling film reactor to absorb the formaldehyde generated by the reaction, reducing the chance of formaldehyde combining with isoprene, thereby reducing the occurrence of side reactions.

The method step b) of the present invention is cracked and purified and/or the DMD-containing reaction solution without purification is preheated to 130-200° C. through a preheater using an acidic aqueous solution, and the preheating process is realized under a pressure of 0.5-2.0 MPa. The hot pressure is 1.1 to 1.5 times the saturated vapor pressure of water at this temperature; the preheated acidic aqueous solution is quickly mixed with the DMD solution through a static mixer, and then introduced from the top of the reactor, distributed by the lysate distributor and then along the wall It flows downward in the form of a liquid film and decomposes into isoprene and formaldehyde at the same time. Water enters the falling film reactor through the water mist distributor, and flows out of the reactor together with the cracking mother liquor flowing down the wall after absorbing formaldehyde.

The cracking of the DMD-containing reaction solution of the present invention's method step b) purifying and/or not purifying is to carry out at high temperature, because the isoprene and formaldehyde that pyrolysis produces have very high reactivity, isoprene is easy It reacts with formaldehyde to produce methyl dihydropyran and high-boiling point by-products. In addition, isoprene itself is easy to self-polymerize, so effective measures must be taken to suppress the occurrence of side reactions. In the present invention, the DMD is optionally diluted with a low-boiling point inert solvent, which can reduce the concentration of the generated isoprene, and at the same time, the volatilization of the low-boiling point inert solvent can accelerate the escape of isoprene. The sprayed mist water droplets on the top of the falling film reactor can quickly absorb the formaldehyde generated by the reaction, reducing the chance of contact between formaldehyde and isoprene, thereby reducing the occurrence of side reactions.

The low boiling point inert solvent used for the reaction solution cracking reaction of the present invention's method step b) purifying and/or not purifying containing DMD means that DMD can be dissolved well under reaction conditions, and does not mix with DMD, isoprene, water , any low-boiling inert solvent for the acidic catalyst reaction, the reaction raw material isobutene and/or tert-butanol can also play the role of a low-boiling inert solvent, and the by-product C4 alkane generated during the preparation of the DMD-containing reaction solution can also be used as a low-boiling inert Solvent used.

In order to reduce the technical difficulty of separating the inert solvent from the isoprene product, it is necessary to maximize the boiling point difference between the solvent and the product isoprene while meeting the reaction conditions; If the solvent is too high, the solvent with a lower boiling point is easier to vaporize under the reaction conditions, and can be used as a carrier gas to take away the isoprene generated in the reaction.

The inert solvents that can be used in step b) of the method of the present invention include saturated alkanes, preferably one, two or more of C4-C6 saturated alkanes and/or C4-C6 saturated naphthenes, more preferably selected from cyclohexane , cyclopentane, n-pentane, n-butane, isobutane, two or more. Wherein the weight ratio of the low-boiling inert solvent to the DMD in the purified and/or non-purified DMD-containing reaction solution is 0-5:1, preferably 0-2:1.

In the process step b) of the present invention, purification and/or in the cracking reaction of the reaction solution containing DMD without purification, the low-boiling inert solvent used does not participate in the reaction, and becomes gas phase in the system and the isoprene, isobutylene and light produced by cracking Boiling point by-products evaporate out of the reaction system together with a small amount of water. The inert solvent evaporated out of the reaction system can be separated from other components and reused in the production method of the present invention.

The present invention method step b) purification and/or the used acidic aqueous solution that does not contain the reaction solution cracking of purification DMD, can be mineral acid, organic acid, heteropolyacid or their acid salt, this acid salt can be understood as broad sense acid. Materials with low or no volatility under the reaction conditions are preferred. For example, it can be inorganic acid, preferably phosphoric acid, sulfuric acid, boric acid, nitric acid, methanesulfonic acid; heteropolyacid, preferably silicotungstic acid, phosphotungstic acid; organic acid, preferably p-toluenesulfonic acid, benzoic acid, trifluoromethanesulfonic acid ; Acid salt, preferably sodium bisulfate, sodium dihydrogen phosphate and other aqueous solutions.

The acidic aqueous solution concentration that is used for the purification of the present invention and/or the cracking of the reaction solution containing DMD without purification is too low, and the residence time of reaction will prolong; The acidic aqueous solution concentration is too high, and equipment corrosion is serious, and the selectivity of product isoprene Also lower.

The concentration of the acidic aqueous solution in step b) of the method of the present invention is generally preferably in the range of 0.05-20 wt%, more preferably in the range of 0.5-5 wt%. The weight ratio of the acidic aqueous solution to the DMD in the purified and/or non-purified DMD-containing reaction solution is preferably not less than 0.1, 0.1 to 1.5:1, more preferably 0.25 to 1:1. Addition of more acidic aqueous solution does not improve isoprene selectivity much and is economically unfavorable.

The method step b) of the present invention adopts spraying water mist in the falling film reactor to absorb cracking purification and/or the formaldehyde that does not contain the DMD-purified reaction solution that purifies produces, the water mist that enters reaction system and purification and/or do not purify The weight ratio of DMD in the DMD-containing reaction solution is preferably not less than 0.2. When the weight ratio is less than 0.2, the trapping effect of formaldehyde is poor, and the yield of isoprene tends to decrease. Although there is no strict upper limit to the weight ratio, adding too much water has little effect on the isoprene yield. On the contrary, it is economically unfavorable to increase the energy consumption of heat and separation due to the increase of the amount of water used. Usually, the weight ratio of the water mist sprayed into step b) and the DMD in the DMD-containing reaction solution without purification is 0.2～10:1, preferably 0.25～5:1, more preferably 0.3～2:1 .

The remaining reaction mother liquor after purification in step b) of the method of the present invention and the liquid phase obtained at the bottom of the reactor in step b) are treated and concentrated to recover formaldehyde and then used in step a).

The mixer mentioned in step b) of the method according to the invention is preferably a static mixer.

Purification in step b) of the process according to the invention is preferably rectification.

The reactor wall temperature suitable for step b) of the method of the present invention is 150-300°C, preferably 180-250°C. The reaction pressure is 0.5-2.0 MPa, preferably 0.7-1.5 MPa. In the present invention, the average residence time of materials in the reactor varies with the reaction temperature and the concentration of reactants, and the average residence time is 3 to 30 minutes, preferably 5 to 15 minutes.

The yield of isoprene produced by the invention is more than 80%, and the yield of one step of DMD cracking is more than 90%.

"Optionally" in this application means with or without.

Description of drawings:

Figure 1 is a schematic diagram of the structure of the falling film reactor.

Figure 2 is a schematic diagram of the entire process flow of the present invention.

Detailed ways

The present invention will be described in detail below through specific implementation examples. The scope of the invention is not limited to this particular embodiment.

As shown in Figure 2, the device proceeds in the following manner:

In the DMD synthesis unit, raw material A isobutene and/or tert-butanol react with raw material B paraformaldehyde and/or formaldehyde aqueous solution to prepare DMD. The synthesis of DMD can be implemented using multiple tower reactors or stirred tank reactors.

The DMD crude product obtained in the DMD synthesis unit enters the DMD purification unit, unreacted isobutene and/or tert-butanol returns to the DMD synthesis unit, and the isobutene obtained by cracking the organic phase treatment unit also returns to the DMD synthesis unit. The purified DMD enters the DMD cleavage unit, or the DMD crude product obtained from the DMD synthesis unit directly enters the DMD cleavage unit without separation.

The reaction mother liquor from the DMD synthesis unit and the water phase from the DMD cracking unit enter the cracking water phase treatment unit, and part of the material flow after the cracking water phase treatment unit enters the formaldehyde concentration unit, and the concentrated formaldehyde returns to the DMD synthesis unit. At the same time, new formaldehyde is supplemented at the entrance of the DMD synthesis unit.

In the DMD cracking unit, while feeding DMD, the acidic aqueous solution is fed as a catalyst. After preheating separately, the static mixer quickly mixes, and then enters the falling film reactor DMD cracking unit to prepare isoprene. Spray preheated water mist to absorb the formaldehyde produced by cracking.

Part of the stream from the cracked organic phase treatment unit and part of the stream from the crackable light component treatment unit enter the isoprene purification unit, and the isoprene product is obtained after purification.

Example 1

The formaldehyde aqueous solution 307Kg/h of 37wt%, the isobutene 60.9Kg/h of 99.5wt%, the phosphoric acid 94.5Kg/h of 85wt% are passed continuously in the overflow stirred tank of 125 liters as reactor, and reaction temperature is 75 ± 5 ℃, the reaction pressure is 1.2Mpa, the obtained DMD crude product is separated by rectification, the output is 113.4Kg/h, and the DMD content is 99.6%; the DMD obtained by rectification is continuously passed into the falling film reactor as shown in Figure 1 In the static mixer, the heating equipment of the reactor is an oil bath jacket, and the feed pipelines are equipped with preheaters respectively. The reaction materials are preheated to 160°C, the pressure inside the reactor is 0.75-0.8MPa, and the temperature of the inner wall of the reactor is It is 190°C; the concentration of phosphoric acid in the acidic aqueous solution is 0.5%, and the feed rate is 39.7Kg/h; the feed rate of liquid water entering the water mist distributor is 37.4Kg/h, and the average residence time of the reaction liquid in the falling film reactor The time is 7 minutes. After continuous operation for 48 hours, the crude product was separated and rectified to obtain 60.7Kg/h of isoprene; calculated as isobutene, the yield was 82.5%.

Example 2

307Kg/h of formaldehyde aqueous solution of 37wt%, 60.9kg/h of isobutylene of 99.5wt%, 94.5Kg/h of phosphoric acid of 85wt% are passed continuously in the 125 liters of overflow stirring tanks as reactor, and reaction temperature is 75 ± 5 ℃, the reaction pressure is 1.2Mpa, the DMD crude product yield obtained is 117.9Kg/h, and the DMD content is 95.8%; The DMD crude product obtained is mixed with 56.5Kg/h n-butane to form a DMD solution, and the DMD solution is continuously introduced as shown in the figure In the static mixer in the falling film reactor shown in 1, the reaction device and operation are the same as in Example 1. The heating equipment of the reactor is an oil bath jacket, and the feed lines are equipped with preheaters respectively, and the reaction materials are preheated. Heat to 160°C, the pressure inside the reactor is 0.85-1.05MPa, the temperature of the inner wall of the reactor is 190°C; the concentration of phosphoric acid in the acidic aqueous solution is 0.5wt%, and the feed rate is 39.7Kg/h; the liquid water entering the water mist distributor The feed rate is 37.4Kg/h, and the average residence time of the reaction solution in the falling film reactor is 7min. Continuous operation for 48 hours; the crude product is separated and rectified to obtain 64.2Kg/h of isoprene; calculated as isobutene, the yield is 87.3%.

Comparative example 1

307Kg/h of formaldehyde aqueous solution of 37wt%, 60.9kg/h of isobutylene of 99.5wt%, 94.5Kg/h of phosphoric acid of 85wt% are passed continuously in the 125 liters of overflow stirring tanks as reactor, and reaction temperature is 75 ± 5 ℃, the reaction pressure is 1.2Mpa, the output of the obtained DMD crude product is 117.9Kg/h, and the DMD content is 95.8%. In the device; the concentration is that 0.5wt% phosphoric acid aqueous solution is passed into the static mixer simultaneously, and the feeding speed is 39.7Kg/h, and the lysate obtained by mixing is continuously passed into the tubular cracking reactor, and the heating equipment of the reactor It is an oil bath jacket, and the feed pipelines are equipped with preheaters respectively. The reaction materials are preheated to 160°C, the pressure inside the reaction tube is 0.85-1.05MPa, and the oil bath temperature is 190°C; the average temperature of the reaction liquid in the tubular reactor The residence time is 7min. Continuous operation for 48 hours; the crude product is separated and rectified to obtain 54.9Kg/h of isoprene; calculated as isobutene, the yield is 74.6%.

Claims (14)

1. A method for preparing isoprene by a liquid phase method, comprising the following steps: a) Isobutene and/or tert-butanol react with paraformaldehyde and/or formaldehyde aqueous solution in the presence of an acidic catalyst to obtain the intermediate product 4,4-dimethyl-1,3-dioxane reaction solution; b) The reaction solution containing 4,4-dimethyl-1,3-dioxane obtained in step a) is continuously fed into the falling film reactor after purification and/or without purification In the mixer at the top of the falling film reactor or optionally add a low-boiling inert solvent for dilution, the resulting reaction solution diluted with the low-boiling inert solvent is continuously passed into the mixer at the top of the falling film reactor, and at the same time Acidic aqueous solution is added to the mixer in the reactor, and the two are mixed to form a lysate and then distributed to the reactor wall, and the thermal cracking reaction is carried out during the process of flowing down the reactor wall; Wherein in step b), the isoprene generated by cracking and a part of the optional low-boiling inert solvent are distilled from the top of the reactor to obtain the crude product of isoprene, wherein the cracking mother liquor containing formaldehyde is obtained from the reaction Extracted from the bottom of the device; The step b) also includes spraying water mist from the top of the falling film reactor, and the water mist sprayed in step b) is mixed with the reaction solution containing 4,4-dimethyl-1,3-dioxane 4, The weight ratio of 4-dimethyl-1,3-dioxane is 0.2-10:1. 2. The method according to claim 1, characterized in that: in step b) the sprayed water mist is mixed with 4,4-Dimethyl-1,3-dioxane in the reaction solution containing 4,4-dimethyl-1,3-dioxane The weight ratio of methyl-1,3-dioxane is 0.25-5:1. 3. The method according to claim 2, characterized in that: step b) sprayed water mist and 4,4-dioxane in the reaction solution containing 4,4-dimethyl-1,3-dioxane The weight ratio of methyl-1,3-dioxane is 0.3-2:1. 4. The method according to any one of claims 1-3, characterized in that: the acidic aqueous solution in step b) is preheated and added to the mixer at the top of the falling film reactor, and the preheated temperature is 130 ~200°C range, the preheated pressure is 1.1 to 1.5 times the saturated vapor pressure of water at this temperature. 5. according to the method described in any one of claim 1-3, it is characterized in that: the low-boiling inert solvent in step b) is selected from the one in C4-C6 saturated paraffin and/or C4-C6 saturated cycloalkane or more. 6. method according to claim 5, it is characterized in that: the low-boiling inert solvent in step b) is selected from a kind of in hexanaphthene, cyclopentane, normal pentane, normal butane, isobutane or Various. 7. The method according to claim 5, characterized in that in step b), the amount of the low-boiling inert solvent makes the low-boiling inert solvent and the purified and/or non-purified 4,4-dimethyl-1,3 - The weight ratio of 4,4-dimethyl-1,3-dioxane in the reaction solution of dioxane is 0˜5:1. 8. The method according to claim 7, characterized in that in step b), the amount of the low-boiling inert solvent is such that the low-boiling inert solvent is mixed with the purified and/or non-purified 4,4-dimethyl-1,3 - The weight ratio of 4,4-dimethyl-1,3-dioxane in the reaction solution of dioxane is 0˜2:1. 9. The method according to any one of claims 1-3, characterized in that: the acidic aqueous solution used for the cracking reaction in step b) is an aqueous solution of acid or acid salt. 10. The method according to claim 9, characterized in that: step b) the acidic aqueous solution used in the cleavage reaction is phosphoric acid, sulfuric acid, hydrogen sulfuric acid, boric acid, nitric acid, methanesulfonic acid, p-toluenesulfonic acid, silicotungstic acid, phosphorus Aqueous solutions of tungstic acid, benzoic acid, trifluoromethanesulfonic acid, oxalic acid, sodium bisulfate or sodium dihydrogen phosphate. 11. The method according to claim 9, characterized in that: step b) the concentration of the acidic aqueous solution is 0.05-20wt%, and the acidic aqueous solution is mixed with purified and/or unpurified 4,4-dimethyl-1,3 - The weight ratio of 4,4-dimethyl-1,3-dioxane in the reaction solution of dioxane is 0.1˜1.5:1. 12. The method according to claim 11, characterized in that in step b) the concentration of the acidic aqueous solution is 0.5-5 wt%, and the acidic aqueous solution is mixed with purified and/or unpurified 4,4-dimethyl-1,3 - The weight ratio of 4,4-dimethyl-1,3-dioxane in the reaction solution of dioxane is 0.25˜1:1. 13. The method according to any one of claims 1-3, characterized in that: step b) the inner wall temperature of the falling film reactor is 150-300°C, the reaction pressure is 0.5-2.0MPa, and the reaction materials are in the falling film reactor The average residence time in the medium is 3 to 30 minutes. 14. according to the method of any one in the claim 1-3, wherein step b) carries out after purifying, remaining reaction mother liquor and step b) in the liquid phase that obtains at the bottom of the reactor in the step b) process and concentrate, to reclaim formaldehyde and use again in step a).

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