CN113979884A - Preparation method of high-conversion-rate and high-purity N-vinyl acetamide without catalyst - Google Patents
Preparation method of high-conversion-rate and high-purity N-vinyl acetamide without catalyst Download PDFInfo
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Abstract
The invention relates to the technical field of chemical synthesis, in particular to a preparation method of N-vinyl acetamide with high conversion rate and high purity without a catalyst. The invention provides a preparation method of high-purity N-vinyl acetamide without a catalyst, with high conversion rate, in order to solve the problems that a catalyst is needed in the existing preparation process of N-vinyl acetamide, acid-base neutralization is needed, and the thermal cracking temperature is too high. The method adopts physical means, realizes the preparation of N-vinyl acetamide by a one-pot method through a high-temperature high-pressure method, and can realize the conversion rate of raw materials and the purity of N-vinyl acetamide without a catalyst. When the pipeline reactor is selected as a reaction container, the thermal cracking temperature can be obviously reduced, the thermal cracking reaction can be completed at the temperature of 200-250 ℃, the energy consumption is low, the reaction time is short, the generation of more byproducts can be avoided, and the conversion rate is relatively high.
Description
Technical Field
The invention relates to the technical field of chemical synthesis, in particular to a preparation method of N-vinyl acetamide with high conversion rate and high purity without a catalyst.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
Currently, there are two major synthetic routes to N-vinyl acetamide (NVA):
(1) n- (a-alkoxyethyl) -carboxylic acid amide cleavage:
first-step hydroxyethylation: taking acetaldehyde and acetamide as raw materials, adding a solvent (methanol, cyclohexane and the like), and generating an intermediate under the action of an alkaline catalyst;
and (2) etherification in a second step: adding ethanol and certain concentrated sulfuric acid into the materials to react to generate an intermediate again;
third step cracking: and (3) cracking the intermediate obtained twice at a high temperature (400-450 ℃).
The inventor finds that the method is a batch manual operation and is carried out in three steps (hydroxyethylation-etherification-thermal cracking) and the experimental operation steps are complicated. And the cracking temperature is too high in the later period, so that the byproducts are increased, and the yield is greatly reduced.
(2) N-ethylene bis-acetamide cleavage:
the first step of ethylization: taking acetaldehyde and acetamide as raw materials, and generating an intermediate product N- (alkoxy ethyl) acetamide under the action of an acid catalyst;
second step thermal cracking: and carrying out thermal cracking on the material N- (alkoxy ethyl) acetamide, wherein the cracking temperature is 180-220 ℃.
The inventor finds that compared with the N- (a-alkoxyethyl) -carboxylic acid amide cracking method, the method has low cracking temperature and less side reaction, but the low cracking temperature causes the conversion rate of acetamide to be only 10 percent; the use of the catalyst also increases the generation of 'three wastes'. In addition, the synthesis reaction of the N- (alkoxy ethyl) acetamide is an equilibrium reaction, more reaction raw materials are left, the reaction is incomplete, and the subsequent separation is complicated; acid is used as a catalyst in the reaction, and alkali is needed to neutralize the acid before thermal cracking, so that the process is complicated, and salt solid waste is not generated in the neutralization process; the thermal cracking temperature needs to reach more than 400 ℃, and the energy consumption is higher.
Disclosure of Invention
The invention provides a preparation method of high-purity N-vinyl acetamide without a catalyst, with high conversion rate, in order to solve the problems that a catalyst is needed in the existing preparation process of N-vinyl acetamide, acid-base neutralization is needed, and the thermal cracking temperature is too high. The method adopts physical means, realizes the preparation of N-vinyl acetamide by a one-pot method through a high-temperature high-pressure method, and can improve the conversion rate of raw materials and the purity of N-vinyl acetamide products without using a catalyst.
When the pipeline reactor is selected as a reaction container, the thermal cracking temperature can be obviously reduced, the thermal cracking reaction can be completed at the temperature of 200-250 ℃, the energy consumption is low, the reaction time is short, the generation of more byproducts can be avoided, the reaction is close to one-step synthesis, the process steps are not so complicated, the product purification adopts a conventional atmospheric and vacuum distillation mode, and the conversion rate is relatively high. In addition, the reaction raw materials are in a closed container, so that the problem of evaporation of the high-temperature raw materials is solved, the raw materials can be in full contact reaction, the reaction time is short, and the conversion rate is high.
Specifically, the invention is realized by the following technical scheme:
in a first aspect of the present invention, there is provided a process for preparing high conversion and high purity N-vinylacetamide without a catalyst, comprising at least one of the following two processes:
adopting a high-temperature high-pressure method: taking acetaldehyde, acetamide and ethanol as raw materials, preheating at low temperature and then heating at high temperature under a closed condition, and reacting to obtain N-vinyl acetamide;
or a pipeline reactor is adopted: acetaldehyde, acetamide and ethanol are used as raw materials, and after reaction in a pipeline reactor, N-vinyl acetamide is obtained through atmospheric distillation and reduced pressure distillation.
In a second aspect of the present invention, there is provided an apparatus for realizing a catalyst-free, high-conversion, high-purity process for producing N-vinylacetamide, the apparatus for producing N-vinylacetamide using a pipe reactor comprising: mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment, mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment connect gradually.
In a third aspect, the invention provides the application of the device for realizing the preparation method of the N-vinyl acetamide without a catalyst, with high conversion rate and high purity in the preparation of the N-vinyl acetamide.
One or more of the technical schemes have the following beneficial effects:
1) the method adopts a physical means, realizes the preparation of N-vinyl acetamide by a one-pot method through a high-temperature high-pressure method, and can improve the conversion rate of raw materials and the purity of an N-vinyl acetamide product without using a catalyst;
2) experiments show that in the process of producing the N-vinyl acetamide by thermal cracking by using acetamide, acetaldehyde and ethanol as raw materials, the thermal cracking temperature can be obviously reduced by using a pipeline reactor, and the reaction can be completed only at 200-250 ℃.
3) The process of producing N-vinyl acetamide by using a pipeline reactor does not need to use a catalyst, avoids the problem of acid-base neutralization treatment caused by the use of the catalyst, is energy-saving and environment-friendly, does not generate three wastes, and is a green synthesis method.
4) The present commonly used method for producing N-vinyl acetamide can not increase the degree of reaction to the right, but can continuously provide power for the equilibrium reaction to proceed to the right under the high pressure condition of a closed pipeline reactor, and reactants continuously generate products, so the acetamide conversion rate participating in the reaction can reach more than 97 percent, and the yield is greatly improved.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The invention provides a preparation method of high-purity N-vinyl acetamide without a catalyst, with high conversion rate, in order to solve the problems that a catalyst is needed in the existing preparation process of N-vinyl acetamide, acid-base neutralization is needed, and the thermal cracking temperature is too high. The method adopts physical means, realizes the preparation of N-vinyl acetamide by a one-pot method through a high-temperature high-pressure method, and can improve the conversion rate of raw materials and the purity of N-vinyl acetamide products without using a catalyst.
When the pipeline reactor is selected as a reaction container, the thermal cracking temperature can be obviously reduced, the thermal cracking reaction can be completed at the temperature of 200-250 ℃, the energy consumption is low, the reaction time is short, the generation of more byproducts can be avoided, the reaction is close to one-step synthesis, the process steps are not so complicated, the product purification adopts a conventional atmospheric and vacuum distillation mode, and the conversion rate is relatively high. In addition, the reaction raw materials are in a closed container, so that the problem of evaporation of the high-temperature raw materials is solved, the raw materials can be in full contact reaction, the reaction time is short, and the conversion rate is high.
Specifically, the invention is realized by the following technical scheme:
in a first aspect of the present invention, there is provided a process for preparing high conversion and high purity N-vinylacetamide without a catalyst, comprising at least one of the following two processes:
adopting a high-temperature high-pressure method: taking acetaldehyde, acetamide and ethanol as raw materials, preheating at low temperature and then heating at high temperature under a closed condition, and reacting to obtain N-vinyl acetamide;
or a pipeline reactor is adopted: acetaldehyde, acetamide and ethanol are used as raw materials, and after reaction in a pipeline reactor, N-vinyl acetamide is obtained through atmospheric distillation and reduced pressure distillation.
The two methods belong to the same technical concept, and both improve the conversion rate and the purity of the N-vinyl acetamide by controlling physical parameters.
In the high-temperature high-pressure method:
the method is carried out in a high-temperature high-pressure closed environment, for example, the reaction is completed in one step in an autoclave by detecting the reaction progress in real time, and the reaction principle is as follows:
in one or more embodiments of the invention, in the high-temperature and high-pressure method, the low-temperature is 55-75 ℃, and the low-temperature preheating time is 0.5-1.5 h;
in one or more embodiments of the invention, in the high-temperature and high-pressure method, the high-temperature is 170-230 ℃, and the high-temperature heating time is 0.5-1.0 h;
the inventor finds that the reaction is basically non-reactive at normal temperature by taking acetaldehyde, acetamide and ethanol as raw materials, and the reaction is carried out in a high-temperature and high-pressure mode to achieve higher conversion rate, which indicates that the high-pressure condition provides considerable promotion and power effects.
The reaction is also relatively affected by temperature, and the reactions occurring at lower and higher temperatures are different, and the temperature is controlled so that the reactions between the raw materials proceed in stages. Currently, there are devices in the industry for real-time monitoring of the reaction progress, so that the reaction temperature can be gradually adjusted by real-time monitoring of the reaction progress. Thereby achieving the effect that the reactions are not mutually influenced.
The reaction is mainly a main reaction, the occurrence of side reactions is influenced by many factors, such as temperature, reaction time, catalyst addition amount, pressure and the like, the reaction time is too long, the main reaction has reached a stable state, if the reaction is continuously heated, the degree of the side reactions is increased, acetaldehyde and ethanol exist in raw materials, the etherification reaction of alcohol is likely to occur to generate ether substances, the addition reaction between aldehyde and aldehyde, the exchange between reactive groups and the like.
In the reaction, the reaction time is reduced by heating at a high temperature for too long to increase by-products, so that the reaction time is reduced mainly to reduce the occurrence of side reactions, and the reaction degree of the main reaction cannot be reached in a short time under the same temperature condition, so that the reaction is increased by properly increasing the temperature, thereby achieving a better effect.
Preferably, in the high-temperature high-pressure method, the ratio of acetamide: acetaldehyde: the molar ratio of ethanol is 0.5-1: 1-2: 1 to 2.
In one or more embodiments of the present invention, the method using high temperature and high pressure further includes a step of mixing and stirring before low temperature preheating, and the temperature of mixing and stirring is lower than the temperature of low temperature preheating.
The scheme of using the channel reactor is a one-step reaction, one-step synthesis without cracking, the required product is synthesized in one step by controlling the high heat transfer efficiency of the pipeline reactor and the conditions of back pressure, flow rate and temperature, and the subsequent normal-pressure and reduced-pressure distillation aims at only recovering unreacted substances and purifying the product and does not involve cracking.
The pipeline reactor specification that generally uses in the laboratory is less, and pipeline inside is convoluted, says from the aspect of circle, and pipeline reactor's specification is big more, and the radian that same arc length corresponds can be big more, and the mobility of material can be more smooth relatively like this, more difficult jam, and the input speed of material is unanimous, and the reaction can be steady relatively. The space effect is an important factor influencing the organic reaction, and in a pipeline reactor, compared with a large reaction kettle, the reaction space is relatively small, so that the side reaction is not facilitated, and the occurrence of the side reaction is reduced.
The diameter of the pipeline reactor is generally selected to be 8-20 mm, the larger the diameter is, the faster the controlled flow rate is, and the smaller-diameter pipeline can enable the materials to be heated and react more quickly and completely.
Generally speaking, the higher the flow rate, the higher the back pressure, and the two are in a proportional relationship, and the flow rate is generally controlled to be 10-20 kg of material per hour according to the density of the material and the reaction time, and the larger the diameter is, the more material per hour is fed, because the reaction time is basically consistent, the material passes through a certain length of pipeline reaction tube in a certain time.
In one or more embodiments of the present invention, in the method using the pipe reactor, the pipe diameter of the pipe reactor is 8 to 20mm, preferably 8 to 10 mm.
Preferably, the temperature of the pipeline reactor is 200-250 ℃, and the reaction time is 3-4 h.
In the method for generating NVA by thermally cracking ethylene bis-acetamide, acetamide and acetaldehyde are used as raw materials, acid is used as a catalyst, white solid can be generated in the reaction temperature rise process, the generation process is rapid, the reaction of the unreacted raw materials is hindered, the white solid can be continuously reacted only by raising the temperature to dissolve, a large amount of acetaldehyde can be evaporated due to the high temperature, even if the acetaldehyde is condensed and refluxed, the refluxed acetaldehyde can be evaporated in a large amount due to heat, the reaction time is long, polymerization is likely to occur inside along with the overlong heating time, the reaction conversion rate is less than 30%, and the conversion rate is low.
In the present invention, the pipeline reactor is used as the reaction vessel, which has at least two advantages:
firstly, the conventional thermal cracking temperature needs to reach more than 400 ℃, the energy consumption is higher, the pipeline reactor can obviously reduce the thermal cracking temperature required by the reaction as a reaction container, the thermal cracking temperature in some embodiments of the invention is 200-250 ℃, the reaction can be completed, the energy consumption is low, the reaction time is shorter, the generation of more byproducts can be avoided, the reaction is close to one-step synthesis, the process steps are not so complicated, the product purification adopts the conventional atmospheric and vacuum distillation mode, the conversion rate is relatively higher, and the occurrence of more problems is avoided.
Compared with a pipeline reactor, the heat transfer efficiency of the pipeline reactor is far higher than that of a conventional reaction kettle or a conventional cracking kettle, and certain pressure given by the scheme of the invention also plays a certain promoting role, so that the effect of reducing the thermal cracking temperature is achieved.
And secondly, the pipeline reactor is selected as a reaction container, the reaction raw materials are in the closed container, the problem of high-temperature raw material evaporation is avoided, the raw materials can be in full contact reaction, the reaction time is short, and the conversion rate is high.
And thirdly, acid or alkali catalysts are used in the traditional synthesis method, and inevitable salt solid waste is generated after neutralization. Therefore, on the premise of not using a catalyst and reducing the thermal cracking temperature, the NVA product is ensured to have extremely high yield and purity.
In conclusion, the process has the advantages of simple steps, low energy consumption, short reaction time, less byproducts, less waste and high conversion rate, and is a novel synthesis process which accords with the concepts of energy conservation, environmental protection and the like.
Furthermore, the inventors have studied and found that microchannel reactors are not suitable for use in the process for the thermal cracking of ethylene bis-acetamide for the following reasons:
1. the acetamide in the raw material is added in excess, the acetaldehyde used is not enough to completely dissolve the acetamide, and the feeding is difficult.
2. Even if acetamide is melted at high temperature and then enters a pipeline reactor, solid is generated in the reaction process to block the pipeline, and the acetamide melting energy consumption is large.
3. Cracking is more prone to pipe plugging if microchannel reactors are used, and ethylene bis-acetamide, which has a higher melting point than acetamide, is more likely to plug during entry into the reactor, especially during cold winter months. Therefore microchannel reactors cannot be applied in this process.
In the method for generating NVA by cracking ethoxyethyl acetamide, the generation of ethoxyethyl acetamide is carried out in two steps, acetaldehyde and acetamide are used as raw materials, alkali is used as a catalyst to generate hydroxyethyl acetamide, then ethanol is added, acid is used as a catalyst to generate ethoxyethyl acetamide, when the hydroxyethyl acetamide is generated, the acetaldehyde is excessively added, the acetamide cannot be completely reacted even if the acetaldehyde is excessively added, the reaction by-products are more, when etherification is carried out, because the peak position of the generated ethoxyethyl acetamide is difficult to judge in a gas chromatography due to the existence of more by-products and a large amount of acetaldehyde and ethanol, partial light components are required to be distilled off before etherification, but the generated hydroxyethyl acetamide is yellow oily matter and is influenced by the state, whether distillation is carried out by normal reduced pressure distillation or solvent dilution, acetaldehyde can not be completely removed, and by-products are more and more along with the prolonging of heating time, so that the proportion of generated products is reduced, and even though light impurities are completely removed to generate ethoxy ethyl acetamide through etherification, the ethoxy ethyl acetamide generated during cracking is less, and in addition, the cracking temperature is too high, so that not only is the energy consumption higher, but also the by-products are increased rapidly, NVA generated after cracking is very little, and the subsequent purification is very difficult.
In the method, if a microchannel reactor is used, the generated hydroxyethyl acetamide is oily, the reaction is exothermic, and the reaction needs to be carried out in a cooling environment, so that firstly, the feeding is easy to block, and secondly, the hydroxyethyl acetamide is easy to adhere to the inner wall of a pipeline to block, and therefore, the microchannel reactor is not suitable for the method.
Thus in one or more embodiments of the invention, the pipe reactor pipe diameter is from 8 to 10 mm.
In one or more embodiments of the present invention, a pipeline reactor is used, and a microchannel reactor is not recommended, and the smallest pipeline reactor diameter is generally more than 10 times of that of the microchannel reactor, and the size of the microchannel reactor is less than 1mm, so that although the present invention adds excessive acetaldehyde and ethanol to dissolve acetamide, insoluble fine particles are prevented from entering the reactor and blocking the reactor, the pipeline reactor is used instead of the microchannel reactor.
Preferably, the pipeline reactor further comprises a step of adding a polymerization inhibitor after reaction;
preferably, after the reaction of the pipeline reactor, adding a polymerization inhibitor into the system, then carrying out atmospheric distillation, collecting excessive acetaldehyde and ethanol, then carrying out reduced pressure distillation, collecting fractions with the top temperature of 60-65 ℃, and condensing;
preferably, the polymerization inhibitor is selected from at least one of tert-butyl hydroquinone, p-hydroxyanisole, hydroquinone, 2-tert-butyl hydroquinone and methyl hydroquinone;
the N-vinyl acetamide contains carbon-carbon double bonds and is easy to generate polymerization reaction at high temperature, and a certain amount of polymerization inhibitor is added to avoid that the polymer of the product is generated when the generated product is continuously heated in the later atmospheric and vacuum distillation, so that the yield is influenced, and the byproducts are increased. The polymerization inhibitor prevents polymerization reaction, a large amount of polymerization inhibitor is used in the prior art, the amount of polymerization inhibitor can reach 5-10% of the material, only 50-500 ppm is used in the invention, and the consumption of polymerization inhibitor is very small in comparison.
In one or more embodiments of the present invention, the atmospheric distillation temperature is 85 to 95 ℃;
preferably, the reduced pressure distillation temperature is 110-120 ℃, and the vacuum degree is 100-150 Pa;
preferably, the condensation temperature is-10 to-15 ℃;
preferably, the acetamide: acetaldehyde: the molar ratio of ethanol is 2: 2-3: 2-4;
when acetamide, acetaldehyde and ethanol react to generate ethylene bis-acetamide, the addition amount of acetamide is excessive, and because the boiling point of NVA generated after cracking is very close to that of acetamide, the NVA is difficult to separate through atmospheric distillation and reduced pressure distillation, so that the purification work is difficult. In the invention, the acetaldehyde and the ethanol in the raw materials are excessive, the acetamide can be almost completely reacted, even a small amount of residues exist, the influence on the purity of the product is not too great, the boiling points of the acetaldehyde and the ethanol are low, the acetaldehyde and the ethanol can be removed by using conventional distillation and can be recycled, and the problem of separating the acetamide from the product is not worried.
Acetamide is in a solid form at normal temperature, the acetamide is pumped into a pipeline reactor and needs to enter in a liquid form, ethanol and acetaldehyde are both liquid, and the acetamide is firstly dissolved by the ethanol because the acetamide is dissolved and then is subjected to a physical exothermic and re-cooling process if acetaldehyde is directly mixed, so that the acetamide is re-precipitated and becomes a solid, and the acetamide cannot be fed by using a metering pump. If three simultaneous feeds are required, one of ethanol or acetaldehyde must be in large excess, so that the acetamide dilution is greater, the reaction proceeds more slowly, more raw materials are used, and the post-treatment amount is greater, so that three simultaneous feeds are not recommended. Thus, in some embodiments, ethanol is first mixed with a portion of the acetamide, and then acetaldehyde is mixed with the remaining acetamide, separately passed into the pipeline reactor;
preferably, the portion of acetamide mixed with ethanol comprises 50% of the total amount of acetamide.
In a second aspect of the present invention, there is provided an apparatus for realizing a catalyst-free, high-conversion, high-purity process for producing N-vinylacetamide, the apparatus for producing N-vinylacetamide using a pipe reactor comprising: mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment, mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment connect gradually.
In one or more embodiments of the invention, the mixing device is used to mix acetamide, acetaldehyde, ethanol;
preferably, a metering pump is arranged between the mixing device and the pipeline reactor.
In one or more embodiments of the invention, the atmospheric distillation device is provided with at least one feeding port and a discharge port, the feeding port is a polymerization inhibitor feeding port, and the discharge port is an acetaldehyde and ethanol collecting port.
In one or more embodiments of the invention, a receiving tank is arranged between the reduced pressure distillation device and the condensing device, the reduced pressure distillation device and the receiving tank are connected through a receiving pipe, and a heat tracing band is arranged outside the receiving pipe.
In a third aspect, the invention provides the application of the device for realizing the preparation method of the N-vinyl acetamide without a catalyst, with high conversion rate and high purity in the preparation of the N-vinyl acetamide.
The present invention is described in further detail below with reference to specific examples, which are intended to be illustrative of the invention and not limiting.
Firstly, preparing N-vinyl acetamide by adopting high-temperature high-pressure method
Experimental example 1
The low-temperature normal-pressure method comprises the following steps: 41.8g of acetaldehyde, 28g of acetamide, 25g of ethanol and 0.5g of concentrated sulfuric acid (catalyst) were added to a 250mL three-necked flask, and the mixture was placed in a water bath at 6 ℃ and stirred for 12 hours, and GC analysis showed that the reaction did not proceed and that no reaction occurred between the substances.
Experimental example 2
The high-temperature normal-pressure method comprises the following steps: 42g of acetaldehyde, 28.3g of acetamide, 25.1g of ethanol and 0.5g of concentrated sulfuric acid (catalyst) were charged into a 250mL three-necked flask, and the mixture was put into an oil bath at 200 ℃ and stirred for 12 hours, and GC analysis showed that although the reaction occurred between the substances, the conversion of acetamide was only 11.3%, and the reaction was an equilibrium reaction, and therefore the reaction could not be continued rightward under these conditions.
Experimental example 3
The high-temperature high-pressure method comprises the following steps: 80g of acetamide and 100.5g of ethanol were added to a 500mL beaker, and the acetamide was dissolved by magnetic stirring, followed by addition of 98.3g of acetaldehyde and 1g of concentrated sulfuric acid. Feeding into a high-pressure kettle, starting stirring and condensed water circulation, and stirring for 0.5 h; setting the temperature at 60 ℃, and continuing to react for 3 hours; the temperature is increased to 180 ℃, the reaction is carried out for 2 hours, the ratio of the acetamide conversion rate to the substances generated is monitored on line, and the result shows that the acetamide conversion rate under the condition can reach 96 percent, but the reaction time is too long, so that the generated byproducts are increased.
Example 1
The method for shortening the reaction time and properly increasing the reaction temperature under the conditions of high temperature and high pressure comprises the following steps: 80.1g of acetamide and 100.3g of ethanol were added to a 500mL beaker, and the acetamide was dissolved by magnetic stirring, followed by addition of 98.5g of acetaldehyde. Feeding into a high-pressure kettle, starting stirring and condensed water circulation, and stirring for 0.5 h; setting the temperature at 60 ℃, and continuing to react for 1 h; the temperature is raised to 200 ℃, the reaction is carried out for 0.5h, the ratio of the acetamide conversion rate to the substances generated is monitored on line, and the result shows that the acetamide conversion rate under the condition can reach 96.5 percent, the purity of the N-vinyl acetamide is 98.5 percent, and the yield is 97 percent.
And discharging the materials after the temperature is reduced to 70 ℃ to obtain a qualified product.
Secondly, preparing N-vinyl acetamide by adopting pipeline reactor
Experimental example 4
Conventional method, N-alpha-alkoxyethyl carboxamide decomposition by heating
A500 mL glass flask equipped with a serpentine condenser was charged with 52.57g of acetamide, 181.65g of toluene (solvent), 47.1g of acetaldehyde, and 0.3g of sodium hydrogencarbonate (catalyst), and then cooled water at-10 ℃ was flowed through the serpentine condenser and heated and stirred at 40 ℃ for 6 hours under a nitrogen atmosphere. The lower layer of the reaction solution separated into two layers was concentrated by an evaporator, and unreacted acetamide was crystallized and precipitated, followed by filtration to give 63g of a crude product as a pale yellow oil containing 42% of hydroxyethylacetamide and 58% of acetamide. The obtained product was purified, and hydroxyethylacetamide was dissolved out with ethyl acetate and concentrated under reduced pressure to obtain white hydroxyethylacetamide as a solid.
Adding 72g ethanol and 1.2g concentrated sulfuric acid into hydroxyethyl acetamide, condensing at-10 deg.C, stirring at 50 deg.C for 4 hr to obtain ethoxy ethyl acetamide crude product containing 39% ethoxy ethyl acetamide,
and thermally cracking the obtained ethoxy ethyl acetamide crude product at 405 ℃, heating for 3 hours to obtain an N-vinyl acetamide crude product, wherein the cracking rate is 55%, carrying out reduced pressure distillation, removing ethanol and hydroxyethyl acetamide in the mixture, and purifying the product to obtain the product with the purity of 97.6%.
Experimental example 5
A500 mL glass flask equipped with a serpentine condenser was charged with 62.4g of acetamide, 150.95g of cyclohexane (solvent), 52.4g of acetaldehyde, and 0.69g of sodium carbonate (catalyst), and then cooled water at-10 ℃ was flowed through the serpentine condenser and heated and stirred at 45 ℃ for 6 hours under a nitrogen atmosphere. The reaction mixture was rotary-distilled to separate unreacted acetamide crystals, which were then filtered to give 71g of a pale yellow oil containing 45% hydroxyethyl acetamide and 55% acetamide. The obtained product was purified, and hydroxyethylacetamide was dissolved out with ethyl acetate and concentrated under reduced pressure to obtain white hydroxyethylacetamide as a solid.
Adding 66g ethanol and 2.5g concentrated hydrochloric acid into hydroxyethyl acetamide, condensing at-10 deg.C, stirring at 50 deg.C for 4 hr to obtain crude product of ethoxyethyl acetamide containing 35% of ethoxyethyl acetamide,
thermally cracking the obtained ethoxy ethyl acetamide crude product at 425 ℃, heating for 3 hours to obtain an N-vinyl acetamide crude product, wherein the cracking rate is 60%, rectifying at 195 ℃ and 25Pa, strictly controlling the reflux ratio, removing ethanol and hydroxyethyl acetamide in the mixture, and purifying the product to obtain the product with the purity of 97.3%.
The method has the advantages of more complicated reaction steps, addition of both a catalyst and a solvent, higher cracking temperature and longer reaction time.
Experimental example 6
The traditional method, ethylene bis-acetamide thermal cracking:
a500 mL glass flask with a serpentine condenser pipe is added with 90.5g of acetamide, 27g of acetaldehyde and 3.62g of 6M sulfuric acid aqueous solution, cooling water at the temperature of-15 ℃ flows in the serpentine condenser pipe, the temperature is gradually increased to 130 ℃ under stirring, white solid is immediately generated when the internal temperature reaches 90 ℃, the white solid is gradually dissolved along with the gradual increase of the temperature, the obtained solution contains 20% of product and is continuously heated for cracking, the heating temperature is gradually increased to 220 ℃, the heating temperature is continuously heated for 2 hours, the obtained mixture only contains 10% of product, and the mixture contains a large amount of acetamide, the difference between the boiling points of the acetamide and the N-vinyl acetamide is extremely small, the separation is difficult to realize, and no industrial report about the success of the method exists, so the method is difficult to realize.
Experimental example 7
Mixing acetamide solid and ethanol according to a molar ratio of 1: 3, stirring and dissolving acetamide according to a molar ratio of acetamide to acetaldehyde of 1: the raw material ratio of 2.5 and the dissolved mixed solution are respectively pumped into a pipeline reactor with the inner diameter of 8mm through a metering pump, the flow rate is controlled at 10kg/h, the material system is kept in the pipeline reactor for 1.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 150 ℃, the backpressure is adjusted to 2MPa, the acetamide conversion rate after the reaction is 37.5 percent, the conversion rate is lower, and the purity of the purified product is 66.3 percent.
Experimental example 8
Mixing acetamide solid and ethanol according to a molar ratio of 1: 3, stirring and dissolving acetamide according to a molar ratio of acetamide to acetaldehyde of 1: the raw material ratio of 2.5 and the dissolved mixed solution are respectively pumped into a pipeline reactor with the inner diameter of 8mm through a metering pump, the flow rate is controlled at 10kg/h, the material system stays in the pipeline reactor for 2.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 180 ℃, the backpressure is adjusted to be 2.5MPa, the acetamide conversion rate after the reaction is 49.5 percent, the conversion rate is lower, and the purity of the purified product is 60 percent.
Experimental example 9
Mixing acetamide solid and ethanol according to a molar ratio of 1: 3, stirring and dissolving acetamide according to a molar ratio of acetamide to acetaldehyde of 1: the raw material ratio of 2.5 and the dissolved mixed solution are respectively pumped into a pipeline reactor with the inner diameter of 8mm through a metering pump, the flow rate is controlled at 10kg/h, the material system stays in the pipeline reactor for 3 hours by controlling the flow rate of the pump, the operation is carried out at the temperature of 205 ℃, the back pressure is adjusted to 3MPa, the acetamide conversion rate after the reaction is 72.9 percent, the conversion rate is lower, and the purity of the purified product is 79.9 percent.
Experimental example 10
Mixing acetamide solid and ethanol according to a molar ratio of 1: 3, stirring and dissolving acetamide according to a molar ratio of acetamide to acetaldehyde of 1: the raw material ratio of 2.5 and the dissolved mixed solution are respectively pumped into a pipeline reactor with the inner diameter of 12mm through a metering pump, the flow rate is controlled at 12kg/h, the material system stays in the pipeline reactor for 3.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 210 ℃, the backpressure is adjusted to be 3MPa, and the acetamide conversion rate after the reaction is 75.1 percent. The conversion rate is low, and the purity of the purified product is 80.7 percent.
Example 2
The material ratio is the same as that of the experimental example 10, the mixture is pumped into a pipeline reactor with the inner diameter of 12mm through a metering pump, the flow rate is controlled to be 12kg/h, the material system stays in the pipeline reactor for 3.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 230 ℃, the backpressure is adjusted to be 4MPa, and the acetamide conversion rate after the reaction is 96.2 percent. Before distillation, 200ppm of polymerization inhibitor tert-butylhydroquinone is added into the obtained material, then normal pressure distillation is carried out to collect acetaldehyde and ethanol, reduced pressure distillation is carried out to obtain the product, and the purity of the purified product is 97.5%.
The effect of temperature and pressure on the reaction was greater and example 2 increased the pressure by 20 ℃ and 1MPA, respectively, compared to example 10, resulting in a greater increase in conversion and purity. Mainly affected by temperature and pressure.
Example 3
The material ratio is the same as that of the experimental example 10, the mixture is pumped into a pipeline reactor with the inner diameter of 16mm through a metering pump, the flow rate is controlled to be 15kg/h, the material system stays in the pipeline reactor for 3.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 240 ℃, the backpressure is adjusted to be 4MPa, and the acetamide conversion rate after the reaction is 97.1 percent. Before distillation, 100ppm of polymerization inhibitor p-hydroxyanisole and 100ppm of hydroquinone are added into the obtained material, then normal pressure distillation is carried out to collect acetaldehyde and ethanol, reduced pressure distillation is carried out to obtain the product, and the purity of the purified product is 97.9%.
Example 4
The material ratio is the same as that of the experimental example 10, the mixture is pumped into a pipeline reactor with the inner diameter of 16mm through a metering pump, the flow rate is controlled to be 15kg/h, the material system stays in the pipeline reactor for 3.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 240 ℃, the backpressure is adjusted to be 4.5MPa, and the acetamide conversion rate after the reaction is 98.4 percent. The conversion rate is high, before distillation, 100ppm polymerization inhibitor 2-tert-butylhydroquinone and 100ppm methylhydroquinone are added into the obtained material, then normal pressure distillation is carried out to collect acetaldehyde and ethanol, reduced pressure distillation is carried out to obtain the product, and the purity of the purified product is 98.5%.
Example 5
The material ratio is the same as that of the experimental example 10, the mixture is pumped into a pipeline reactor with the inner diameter of 16mm through a metering pump, the flow rate is controlled to be 15kg/h, the material system stays in the pipeline reactor for 3.5h by controlling the flow rate of the pump, the operation is carried out at the temperature of 245 ℃, the backpressure is adjusted to be 4.5MPa, and the acetamide conversion rate after the reaction is 98.9 percent. The conversion rate is high, before distillation, 200ppm polymerization inhibitor methyl hydroquinone is added into the obtained material, then normal pressure distillation is carried out to collect acetaldehyde and ethanol, reduced pressure distillation is carried out to obtain the product, and the purity of the purified product is 99%.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A process for the preparation of high conversion and purity N-vinyl acetamide without catalyst, characterized by at least one of the following two processes:
adopting a high-temperature high-pressure method: taking acetaldehyde, acetamide and ethanol as raw materials, preheating at low temperature and then heating at high temperature under a closed condition, and reacting to obtain N-vinyl acetamide;
or a pipeline reactor is adopted: acetaldehyde, acetamide and ethanol are used as raw materials, and after reaction in a pipeline reactor, N-vinyl acetamide is obtained through atmospheric distillation and reduced pressure distillation.
2. The method for preparing N-vinyl acetamide with high conversion rate and high purity without catalyst according to claim 1, wherein the low temperature is 55-75 ℃ and the low temperature preheating time is 0.5-1.5 h in the high temperature and high pressure method;
preferably, in the high-temperature and high-pressure method, the high-temperature is 170-230 ℃, and the high-temperature heating time is 0.5-1.0 h;
preferably, in the high-temperature high-pressure method, the ratio of acetamide: acetaldehyde: the molar ratio of ethanol is 0.5-1: 1-2: 1 to 2.
3. The method for preparing N-vinyl acetamide with high conversion rate and high purity without catalyst according to claim 1, wherein the method of high temperature and high pressure comprises a step of mixing and stirring before low temperature preheating, and the temperature of mixing and stirring is lower than that of low temperature preheating.
4. The method for preparing N-vinyl acetamide with high conversion rate and high purity without catalyst according to claim 1, wherein the method using a pipeline reactor is characterized in that the diameter of the pipeline reactor is 8-20 mm;
preferably, the temperature of the pipeline reactor is 200-250 ℃, and the reaction time is 3-4 h;
preferably, the pipeline reactor further comprises a step of adding a polymerization inhibitor after reaction;
preferably, after the reaction of the pipeline reactor, adding a polymerization inhibitor into the system, then carrying out atmospheric distillation, collecting excessive acetaldehyde and ethanol, then carrying out reduced pressure distillation, collecting fractions with the top temperature of 60-65 ℃, and condensing;
preferably, the polymerization inhibitor is selected from at least one of tert-butyl hydroquinone, p-hydroxyanisole, hydroquinone, 2-tert-butyl hydroquinone and methyl hydroquinone;
preferably, the dosage of the polymerization inhibitor is 50-500 ppm.
5. The method for preparing N-vinyl acetamide with high conversion rate and high purity without catalyst according to claim 1, wherein the atmospheric distillation temperature is 85-95 ℃;
preferably, the reduced pressure distillation temperature is 110-120 ℃, and the vacuum degree is 100-150 Pa;
preferably, the condensation temperature is-10 to-15 ℃;
preferably, the acetamide: acetaldehyde: the molar ratio of ethanol is 2: 2-3: 2-4;
preferably, ethanol is mixed with part of acetamide, then acetaldehyde is mixed with the rest acetamide, and the mixture is respectively introduced into the pipeline reactor;
preferably, the portion of acetamide mixed with ethanol comprises 50% of the total amount of acetamide.
6. The apparatus for carrying out the catalyst-free, high-conversion, high-purity process for producing N-vinylacetamide according to claim 1, wherein the apparatus for producing N-vinylacetamide using a pipe reactor comprises: mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment, mixing arrangement, pipeline reactor, atmospheric distillation device, vacuum distillation device, condensing equipment connect gradually.
7. The apparatus of claim 6, wherein the mixing device is used to mix acetamide, acetaldehyde, ethanol;
preferably, a metering pump is arranged between the mixing device and the pipeline reactor.
8. The apparatus of claim 6, wherein the atmospheric distillation apparatus is provided with at least one feeding port for a polymerization inhibitor and a discharging port for acetaldehyde and ethanol collection.
9. The device according to claim 6, characterized in that a receiving tank is arranged between the reduced pressure distillation device and the condensing device, the reduced pressure distillation device and the receiving tank are connected through a receiving pipe, and a heat tracing band is arranged outside the receiving pipe.
10. Use of the device of any one of claims 6 to 9 for the preparation of N-vinylacetamide.
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