A low-carbon alcohol propionate synthesis device and synthesis process

Abstract

The present invention relates to a low-carbon alcohol propionate synthesis device and synthesis process. Using low-carbon alcohol and propionic acid as raw materials, the propionate is produced using a reaction-separation-reaction process. The low-carbon alcohol and propionic acid undergo an esterification reaction in a fixed-bed main reactor filled with a strongly acidic cation exchange resin, and the reaction liquid is purified by distillation to obtain the propionate. Compared with traditional reactive distillation processes, this invention features a simple process and equipment structure, achieving high alcohol conversion rates. It addresses the problems of existing propionate ester synthesis processes, such as the complex reactive distillation device structure, the need for special catalytic packing in the reaction section, and the occurrence of alcohol etherification side reactions within the reactive distillation tower.

Description

Technical field:

[0002] The invention belongs to the technical field of low-carbon alcohol propionate synthesis, and in particular relates to a low-carbon alcohol propionate synthesis device and a synthesis process thereof. Background technology:

[0004] Propionate esters are important basic chemical raw materials, widely used in perfumes, water-based cosmetics, and food flavorings. Propionate esters have low melting points and viscosities, high boiling points, and excellent thermal stability at high temperatures. They can balance the high and low temperature performance of lithium-ion batteries. Therefore, electrolytes formulated with them exhibit high conductivity and can operate at very low temperatures. The lithium-ion battery market has grown rapidly in recent years, and demand for propionate esters in lithium-ion battery electrolytes has been increasing. The market prospects for propionate esters are promising.

[0005] Propionic esters are a type of organic compound. Common propionic esters of low-carbon alcohols include methyl propionate, ethyl propionate, and propyl propionate. Propionic esters are generally obtained by the esterification reaction of propionic acid with alcohols. The esterification reaction of propionic acid with alcohols is slightly exothermic, and the equilibrium conversion rate decreases slightly with increasing reaction temperature. Simultaneously, the equilibrium constant of the esterification reaction is large. Liang Shu (Petrochemical Engineering, Issue 1, 2022) showed that the equilibrium constant for the esterification reaction of propionic acid with ethanol is 4.71. Because the esterification reaction of propionic acid with alcohols is reversible, using reactive distillation to promptly remove the product water or propionic ester from the system can improve the single-pass conversion rate of the esterification reaction. In his master's thesis (Hebei University of Technology, 2017), Wang Fengzhu reported that the equilibrium constant Keq = 9.40 for the reaction of propionic acid with methanol at 60°C using C100FLH resin catalyst was used. Experimental results and simulation data for the preparation of methyl propionate by reactive distillation were also presented. To avoid acid in the overhead stream of the reactive distillation column, which could result in substandard methyl propionate, the acid content in the reactor bottom of the reactive distillation column is controlled at 30-65%. Under these conditions, the methanol conversion rate is approximately 97%. Du Huili, in her master's thesis (Hebei University of Technology, 2018), also reported using Amberlyst 45 resin catalyst to synthesize ethyl propionate via esterification with an equilibrium constant, Keq, of 7.18 (at 75°C). Under optimal reactive distillation conditions for ethyl propionate production, the ethanol conversion rate can reach over 93%. Patent CN201910304020 discloses a method for producing propionate esters via reactive distillation using sodium bisulfate as a catalyst. Patent CN207944042 U discloses a process for producing propionate esters via reactive distillation using a strongly acidic cation exchange resin as a catalyst. Reactive distillation, as a process intensification technology for the synthesis of propionate esters, can improve reaction conversion rates, but it still has some shortcomings. Compared with ordinary distillation, the reactive distillation device has a complex structure and requires the preparation of corresponding catalyst bundles for loading. At the same time, due to the high temperature of the reaction section in the reactive distillation tower, alcohol is prone to etherification reaction under the catalysis of acidic resin, which reduces the selectivity of the esterification reaction and increases the difficulty of subsequent separation. Summary of the invention:

[0007] The present invention aims to improve the problems existing in the above-mentioned prior art. That is, the technical problem to be solved by the present invention is to provide a low-carbon alcohol propionate synthesis device and a synthesis process thereof. The device has a reasonable design and solves the problems of complex structure of the reaction distillation device in the existing propionate synthesis process, the need to prepare special catalytic fillers in the reaction section, and the existence of alcohol etherification side reactions in the reaction distillation tower.

[0008] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: a low-carbon alcohol propionate synthesis device, comprising a fixed-bed main reactor, a fixed-bed secondary reactor, an acid recovery tower, a dehydration tower, a product tower, a propionic acid tank and a stratification tank, the discharge port of the fixed-bed main reactor is connected to the feed port of the acid recovery tower, the top extraction pipeline of the acid recovery tower is connected to the feed port of the stratification tank, the upper oil phase liquid outlet of the stratification tank is connected to the feed port of the product tower, the top extraction pipeline of the product tower is connected to the feed port of the stratification tank, the lower water phase liquid of the stratification tank is connected to the feed port of the dehydration tower, the top extraction pipeline of the dehydration tower is connected to the feed port of the fixed-bed secondary reactor, the discharge port of the fixed-bed secondary reactor is connected to the feed port of the acid recovery tower, the bottom discharge pipeline of the acid recovery tower is connected to the feed port of the propionic acid tank, and the discharge port of the propionic acid tank is respectively connected to the feed ports of the fixed-bed main reactor and the fixed-bed secondary reactor.

[0009] Furthermore, the acid recovery tower is a plate separation tower or a packed separation tower, the number of theoretical plates of the distillation section of the acid recovery tower is 15 to 30, and the number of theoretical plates of the stripping section is 10 to 40.

[0010] Furthermore, the dehydration tower is a plate separation tower or a packed separation tower, the number of theoretical plates of the rectification section of the dehydration tower is 5 to 15, and the number of theoretical plates of the stripping section is 10 to 20.

[0011] Furthermore, the product tower is a plate separation tower or a packed separation tower, the number of theoretical plates in the rectification section of the product tower is 10 to 20, and the number of theoretical plates in the stripping section is 10 to 30.

[0012] Another technical solution adopted by the present invention is: a process for synthesizing low-carbon alcohol propionate, the process flow of which is as follows:

[0013] Step A, Pre-reaction: Propionic acid and lower alcohol raw materials from the propionic acid tank are mixed in proportion and fed into a fixed-bed main reactor. Propionic acid and lower alcohol undergo an esterification reaction in the fixed-bed main reactor under the catalysis of a strongly acidic cation exchange resin to produce propionic ester and water;

[0014] Step B, propionic acid recovery: The esterification reaction liquid from the fixed-bed main reactor is sent to an acid recovery tower. Under the heating effect of the reboiler in the acid recovery tower, vapor-liquid mass transfer is carried out in the distillation section of the acid recovery tower. Lower carbon alcohol, propionate, and water are extracted from the gas phase extraction port at the top of the acid recovery tower. The gas phase material is condensed in a condenser to form a liquid phase mixture of alcohol-propionate-water. Part of it is returned to the acid recovery tower as reflux, and part of it is extracted and sent to a separation tank. The oil phase extracted from the upper layer of the separation tank is sent to the product tower, and the water phase from the lower layer of the separation tank is sent to a dehydration tower for further separation. The propionic acid extracted from the bottom of the acid recovery tower is returned to the propionic acid tank for further recycling.

[0015] Step C, Dehydration: The aqueous phase material in the lower layer of the dehydration tank is fed into a dehydration tower. Under the heating effect of the reboiler of the dehydration tower, vapor-liquid mass transfer occurs in the dehydration tower, and water forms an azeotrope with a small amount of alcohol and propionate and is extracted from the top of the dehydration tower. The vapor phase material extracted from the top of the dehydration tower is condensed in a condenser to form a liquid phase, part of which is returned to the dehydration tower as reflux, and part is extracted and sent to the fixed-bed secondary reactor; the water extracted from the bottom of the dehydration tower is directly discharged as wastewater;

[0016] Step D, secondary reaction: a portion of the propionic acid from the propionic acid tank is sent to a fixed-bed secondary reactor, where the propionic acid continues to undergo esterification reaction with the lower alcohol in the propionate-alcohol-water azeotrope. The reacted materials are sent to an acid recovery tower for separation;

[0017] Step E, product separation: The oil phase material in the upper layer of the stratification tank is sent to the product tower. Under the heating action of the reboiler in the product tower, vapor-liquid mass transfer is carried out in the distillation section of the product tower. The propionate forms an azeotropic reaction with a small amount of alcohol and water and is extracted from the gas phase at the top of the tower. The gas phase material is condensed in the condenser to form a liquid phase, part of which is returned to the product tower as reflux, and part is extracted and sent to the feed port of the stratification tank; the propionate product is extracted from the bottom of the product tower.

[0018] Furthermore, in step A, the low-carbon alcohol is one or both of methanol and ethanol, and the propionate is methyl propionate and ethyl propionate.

[0019] Furthermore, in step A, the reaction temperature of the fixed bed main reactor is 50-80° C., the feed molar ratio of propionic acid and low-carbon alcohol is 1:1-10:1, and the material residence time is 30-120 min; in step B, the reaction temperature of the fixed bed secondary reactor is 50-80° C., the material residence time is 30-120 min, and the feed mass ratio of propionic acid to the liquid mixture of alcohol-propionate-water is 4-2:1.

[0020] Furthermore, in step B, the acid recovery tower is operated at normal pressure, the reflux ratio of the acid recovery tower is 0.5-10, and the top temperature of the acid recovery tower is 70-80°C.

[0021] Furthermore, in step C, the dehydration tower is operated at normal pressure, the reflux ratio of the dehydration tower is 1-6, the top temperature of the dehydration tower is 60-80°C, and the bottom temperature of the dehydration tower is 98-100°C.

[0022] Furthermore, in step E, the product tower is operated at normal pressure, the reflux ratio of the product tower is 0.5-10, the top temperature of the product tower is 65-80°C, and the bottom temperature of the product tower is 75-100°C.

[0023] Compared with the existing technology, the present invention has the following effects: the present invention adopts a reaction-separation-re-reaction process, and a low-carbon alcohol and propionic acid undergo an esterification reaction in a fixed-bed reactor equipped with a strong acidic cation exchange resin. The reaction liquid is purified by distillation to obtain propionic ester. Compared with the traditional reaction distillation process, the present invention has the characteristics of simple process and equipment structure, and can achieve a high alcohol conversion rate. Description of the drawings:

[0025] Figure 1 It is a process flow chart of an embodiment of the present invention.

[0026] In the picture:

[0027] 1-Fixed bed main reactor; 2-Acid recovery tower; 3-Layering tank; 4-Propionic acid tank; 5-Dehydration tower; 6-Fixed bed secondary reactor; 7-Product tower. Specific implementation method:

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention.

[0031] like Figure 1 As shown, the present invention provides a low-carbon alcohol propionate synthesis device, comprising a fixed-bed main reactor, a fixed-bed secondary reactor, an acid recovery tower, a dehydration tower, a product tower, a propionic acid tank and a stratification tank, wherein the discharge port of the fixed-bed main reactor is connected to the feed port of the acid recovery tower, the top extraction pipeline of the acid recovery tower is connected to the feed port of the stratification tank, the upper oil phase liquid outlet of the stratification tank is connected to the feed port of the product tower, the top extraction pipeline of the product tower is connected to the feed port of the stratification tank, the lower water phase liquid of the stratification tank is connected to the feed port of the dehydration tower, the top extraction pipeline of the dehydration tower is connected to the feed port of the fixed-bed secondary reactor, the discharge port of the fixed-bed secondary reactor is connected to the feed port of the acid recovery tower, the bottom discharge pipeline of the acid recovery tower is connected to the feed port of the propionic acid tank, and the discharge port of the propionic acid tank is respectively connected to the feed ports of the fixed-bed main reactor and the fixed-bed secondary reactor.

[0032] The process for synthesizing low-carbon alcohol propionate is as follows:

[0033] Step A, Pre-reaction: Propionic acid and lower alcohol raw materials from the propionic acid tank are mixed in proportion and fed into a fixed-bed main reactor. Propionic acid and lower alcohol undergo an esterification reaction in the fixed-bed main reactor under the catalysis of a strongly acidic cation exchange resin to produce propionic ester and water;

[0034] Step B, propionic acid recovery: The esterification reaction liquid from the fixed-bed main reactor is sent to an acid recovery tower. Under the heating effect of the reboiler in the acid recovery tower, vapor-liquid mass transfer is carried out in the acid recovery tower. Lower carbon alcohol, propionate, and water are extracted from the gas phase extraction port at the top of the acid recovery tower. The gas phase material is condensed in a condenser to form a liquid phase mixture of alcohol-propionate-water. Part of it is returned to the acid recovery tower as reflux, and part of it is extracted and sent to a separation tank. The oil phase extracted from the upper layer of the separation tank is sent to the product tower, and the water phase from the lower layer of the separation tank is sent to a dehydration tower for further separation. The propionic acid extracted from the bottom of the acid recovery tower is returned to the propionic acid tank for further recycling.

[0035] Step C, Dehydration: The aqueous phase material in the lower layer of the dehydration tank is fed into a dehydration tower. Under the heating effect of the reboiler of the dehydration tower, vapor-liquid mass transfer occurs in the dehydration tower, and water forms an azeotrope with a small amount of alcohol and propionate and is extracted from the top of the dehydration tower. The vapor phase material extracted from the top of the dehydration tower is condensed in a condenser to form a liquid phase, part of which is returned to the dehydration tower as reflux, and part is extracted and sent to the fixed-bed secondary reactor; the water extracted from the bottom of the dehydration tower is directly discharged as wastewater;

[0036] Step D, secondary reaction: a portion of the propionic acid from the propionic acid tank is sent to a fixed-bed secondary reactor, where the propionic acid continues to undergo esterification reaction with the lower alcohol in the propionate-alcohol-water azeotrope. The reacted materials are sent to an acid recovery tower for separation;

[0037] Step E, product separation: The oil phase material in the upper layer of the stratification tank is sent to the product tower. Under the heating action of the reboiler in the product tower, vapor-liquid mass transfer is carried out in the product tower, and the propionate forms an azeotropic reaction with a small amount of alcohol and water and is extracted from the gas phase at the top of the tower. The gas phase material is condensed in the condenser to form a liquid phase, part of which is returned to the product tower as reflux, and part is extracted and sent to the feed port of the stratification tank; the propionate product is extracted from the bottom of the product tower.

[0038] In this embodiment, the acid recovery tower is a plate separation tower or a packed separation tower, the number of theoretical plates of the rectifying section of the acid recovery tower is 15 to 30, and the number of theoretical plates of the stripping section is 10 to 40.

[0039] In this embodiment, the dehydration tower is a plate separation tower or a packed separation tower, the number of theoretical plates of the rectification section of the dehydration tower is 5 to 15, and the number of theoretical plates of the stripping section is 10 to 20.

[0040] In this embodiment, the product tower is a plate separation tower or a packed separation tower, the number of theoretical plates of the rectifying section of the product tower is 10 to 20, and the number of theoretical plates of the stripping section is 10 to 30.

[0041] In this embodiment, in step A, the low-carbon alcohol is one or both of methanol and ethanol, and the propionate is methyl propionate and ethyl propionate.

[0042] In this embodiment, in step A, the reaction temperature of the fixed-bed main reactor is 50-80°C, and the material residence time is 30-120 minutes. The lower reaction temperature ensures that the alcohol does not undergo etherification side reactions in the fixed bed, thereby improving the selectivity of the esterification reaction.

[0043] In this embodiment, in step A, the feed molar ratio of propionic acid to lower carbon alcohols is 1:1 to 10:1. Preferably, the fixed bed main reactor adopts a propionic acid excess feed mode, and the feed molar ratio of propionic acid to lower carbon alcohols is 2 to 10:1. Since the equilibrium constant of the esterification reaction of propionic acid and lower carbon alcohols is large, the larger the feed molar ratio of propionic acid to lower carbon alcohols, the more conducive it is to improving the conversion rate of alcohols. However, due to the equilibrium constant limit, after the feed molar ratio exceeds 3, the conversion rate of lower carbon alcohols is not significantly improved, and excessive propionic acid circulation will also increase the energy consumption of the entire system. Therefore, the feed molar ratio of propionic acid to lower carbon alcohols is preferably 2 to 3:1. In addition, under the condition of excess propionic acid, acid molecules are distributed around the alcohol molecules, reducing the possibility of intermolecular dehydration between alcohols and improving the selectivity of the esterification reaction.

[0044] In this embodiment, in step B, the reaction temperature of the fixed-bed secondary reactor is 50-80°C, the material residence time is 30-120 minutes, and the feed mass ratio of propionic acid to the alcohol-propionate-water liquid mixture is 4-2:1. By feeding a large excess of propionic acid, unreacted alcohol in the alcohol-propionate-water ternary azeotropic mixture is further reacted and consumed in the fixed-bed secondary reactor. This not only improves the alcohol conversion rate but also breaks the ternary azeotropic composition, simplifying the subsequent distillation separation process.

[0045] In this embodiment, in step B, the acid recovery tower is operated at normal pressure, the reflux ratio R of the acid recovery tower is 0.5-10, the top temperature of the acid recovery tower is 70-80°C, and the bottom temperature of the acid recovery tower is 138-142°C.

[0046] In this embodiment, in step C, the dehydration tower is operated at normal pressure, the reflux ratio R of the dehydration tower is 1-6, the top temperature of the dehydration tower is 60-80°C, and the bottom temperature of the dehydration tower is 98-100°C.

[0047] In this embodiment, in step E, the product tower is operated at normal pressure, the reflux ratio of the product tower is 0.5-10, the top temperature of the product tower is 65-80°C, and the bottom temperature of the product tower is 75-100°C.

[0048] It should be noted that the above-mentioned distillation section is equipped with a reboiler and a condenser, which are all existing technologies and the specific structure of this part will not be repeated here.

[0049] Example 1, taking methyl propionate as an example:

[0050] Fixed-bed main reactor 1 was loaded with A35 strong acid resin catalyst, with a reaction temperature of 70°C and a material residence time of 60 minutes. Propionic acid S1 from propionic acid tank 4 was fed into fixed-bed main reactor 1 at a rate of 148 kg / hr, and methanol feed S2 was fed into fixed-bed main reactor 1 at a rate of 32 kg / hr. The feed molar ratio of propionic acid to methanol was 2. The flow rate of S3 extracted from fixed-bed main reactor 1 was 180 kg / hr.

[0051] Acid recovery tower 2 is packed with Sulzer Mellapak structured packing with a total of 30 theoretical plates, 15 theoretical plates in the rectification section, and 15 theoretical plates in the stripping section. It operates at atmospheric pressure, with a reflux ratio of 1.5, a top temperature of 70.9°C, and a bottom temperature of 140.7°C. The flow rate of S6 produced from the top of acid recovery tower 2 is 115.00 kg / hr, and the flow rate of S8 produced from the bottom is 96.22 kg / hr. Material S6 is fed to layer separation tank 3. The flow rate of aqueous phase S9 produced from layer separation tank 3 is 27.00 kg / hr, and the flow rate of oil phase S10 produced is 158.00 kg / hr. The aqueous phase S9 is fed to dehydration tower 5.

[0052] Dehydration tower 5 was packed with Sulzer Mellapak structured packing, with a total of 28 theoretical plates, including 12 in the rectifying section and 16 in the stripping section. It operated at atmospheric pressure, with a reflux ratio of 3, a top temperature of 62.7°C, and a bottom temperature of 99.7°C. The flow rate of overhead draw S13 was 9.00 kg / hr, and the flow rate of bottom draw S17 was 18.00 kg / hr. Material S13 was fed to fixed-bed secondary reactor 6. Fixed-bed secondary reactor 6 was charged with A35 strong acid resin catalyst. The reaction temperature was 70°C, and the material residence time was 60 minutes. Propionic acid S14 from propionic acid tank 4 was fed to fixed-bed secondary reactor 6 at a flow rate of 22.22 kg / hr, and material S13 was fed to fixed-bed secondary reactor 6 at a flow rate of 9.00 kg / h. The feed mass ratio of propionic acid to overhead draw was 2.47:1. The flow rate of S15 produced from the fixed bed auxiliary reactor 6 is 31.22 kg / hr, and the material S15 is sent back to the acid recovery tower 2;

[0053] The oil phase S10 produced from the stratification tank 3 is sent to the product tower 7. The product tower 7 is filled with Sulzer Mellapak structured packing with a total theoretical plate number of 36, 16 theoretical plates in the distillation section, and 20 theoretical plates in the stripping section. It is operated at normal pressure, with a reflux ratio of 2.8, a top temperature of 67.9°C, a bottom temperature of 79.1°C, and a flow rate of S20 produced from the top of the tower of 70.00 kg / hr. The material S20 is sent back to the stratification tank 3, and the flow rate of S22 produced from the bottom of the tower is 88.00 kg / hr.

[0054] Some logistics information is shown in Tables 1 and 2.

[0055] Table 1 Partial logistics information of Example 1

[0056]

[0057] Table 2 Partial logistics information of Example 1

[0058]

[0059] Example 2, taking ethyl propionate as an example:

[0060] Fixed-bed main reactor 1 was loaded with A35 strong acid resin catalyst, with a reaction temperature of 75°C and a material residence time of 60 minutes. Propionic acid S1 from propionic acid tank 4 was fed into fixed-bed main reactor 1 at a rate of 148 kg / hr, and ethanol feedstock S2 was fed into fixed-bed main reactor 1 at a rate of 46 kg / hr. The feed molar ratio of propionic acid to ethanol was 2. The flow rate of S3 drawn from fixed-bed main reactor 1 was 194 kg / hr.

[0061] Acid recovery tower 2 was packed with Sulzer Mellapak structured packing, with a total of 35 theoretical plates, 20 theoretical plates in the rectification section, and 15 theoretical plates in the stripping section. It was operated at atmospheric pressure, with a reflux ratio of 1.8, a top temperature of 77.7°C, and a bottom temperature of 140.5°C. The flow rate of S6 produced from the top of the tower was 131.50 kg / hr, and the flow rate of S8 produced from the bottom of the tower was 101.17 kg / hr. Material S6 was fed to layering tank 3. The flow rate of aqueous phase S9 produced from layering tank 3 was 29.99 kg / hr, and the flow rate of oil phase S10 produced from layering tank 3 was 170.51 kg / hr. The aqueous phase S9 was fed to dehydration tower 5.

[0062] Dehydration tower 5 was packed with Sulzer Mellapak structured packing, with a total of 28 theoretical plates, including 16 in the rectifying section and 12 in the stripping section. It operated at atmospheric pressure, with a reflux ratio of 2.5, a top temperature of 77.2°C, and a bottom temperature of 99.6°C. The flow rate of overhead draw S13 was 12.00 kg / hr, and the flow rate of bottom draw S17 was 17.99 kg / hr. Material S13 was fed to fixed-bed secondary reactor 6. Fixed-bed secondary reactor 6 was loaded with A35 strong acid resin catalyst. The reaction temperature was 75°C, and the material residence time was 60 minutes. Propionic acid S14 from propionic acid tank 4 was fed to fixed-bed secondary reactor 6 at a flow rate of 26.67 kg / hr, and material S13 was fed to fixed-bed secondary reactor 6 at a flow rate of 12.00 kg / h. The feed mass ratio of propionic acid to overhead draw was 2.22:1. The flow rate of S15 produced from the fixed bed auxiliary reactor 6 is 38.67 kg / hr, and the material S15 is sent back to the acid recovery tower 2;

[0063] The oil phase S10 extracted from layer separation tank 3 was sent to product tower 7. Product tower 7 was packed with Sulzer Mellapak structured packing with a total of 32 theoretical plates, 14 theoretical plates in the rectification section, and 18 theoretical plates in the stripping section. It was operated at atmospheric pressure, with a reflux ratio of 1.8, a tower top temperature of 76.3°C, a tower bottom temperature of 98.9°C, and a flow rate of 69.00 kg / hr for the overhead extraction of S20. Material S20 was returned to layer separation tank 3, and the flow rate of 101.51 kg / hr for the bottom extraction of S22.

[0064] Some logistics information is shown in Tables 3 and 4.

[0065] Table 3 Partial logistics information of Example 2

[0066]

[0067] Table 4 Partial logistics information of Example 2

[0068]

[0069] The advantages of the present invention are:

[0070] 1) The reaction-separation-re-reaction process is simple and can achieve a high alcohol conversion rate (>99%);

[0071] 2) Leveraging the high equilibrium conversion rate of the esterification reaction between propionic acid and lower alcohols, a fixed-bed main reactor with excess acid feed is employed, achieving a single-pass alcohol conversion rate exceeding 80%. Furthermore, the fixed-bed main reactor has a simple structure, and operating and equipment costs are significantly lower than those of a reactive distillation tower.

[0072] 3) Compared with the reactive distillation process, the esterification reaction of the present invention is carried out in a fixed bed reactor, the reaction temperature is low and controllable, and the etherification reaction of low-carbon alcohols is avoided;

[0073] 4) Using a large excess of propionic acid as feed, the unreacted alcohol in the alcohol-propionate-water ternary azeotrope is esterified with propionic acid in the fixed-bed secondary reactor. This reaction converts the lower alcohol into propionate, breaking the ternary azeotropic composition and reducing the difficulty of distillation separation.

[0074] 5) In the reaction-distillation separation process, propionic acid has the highest boiling point in the propionic ester esterification system and is not vaporized in the distillation section but is withdrawn from the bottom of the tower in liquid form. Therefore, increasing the excess ratio of propionic acid helps to improve the conversion rate of alcohol without significantly increasing the energy consumption of distillation separation.

[0075] 6) Taking full advantage of the binary or ternary azeotropic properties of alcohol, propionate, and water, water is used as an entrainer in the dehydration tower to completely recover the organic matter (alcohol and ester) in the aqueous phase through azeotropic distillation. In the product tower, ester is used as an entrainer to remove trace amounts of water and alcohol from the crude ester (oil phase of the separator) through azeotropic distillation to obtain qualified propionate product.

[0076] If the present invention discloses or involves components or structural parts that are fixedly connected to each other, then, unless otherwise stated, the fixed connection can be understood as: a detachable fixed connection (for example, connection using bolts or screws), and can also be understood as: a non-detachable fixed connection (for example, riveting, welding). Of course, the mutual fixed connection can also be replaced by an integrated structure (for example, manufactured by integral molding using a casting process) (except where it is obviously not possible to use an integrated molding process).

[0077] In addition, unless otherwise stated, the terms used in any technical solution disclosed in the present invention to express positional relationships or shapes include states or shapes that are approximate, similar, or close thereto.

[0078] Any component provided by the present invention may be assembled from multiple separate components, or may be a separate component manufactured by an integral molding process.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solutions of the present invention. They should all be included in the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A low-carbon alcohol propionate synthesis device, characterized in that: The invention comprises a fixed-bed main reactor, a fixed-bed secondary reactor, an acid recovery tower, a dehydration tower, a product tower, a propionic acid tank and a stratification tank, wherein the discharge port of the fixed-bed main reactor is connected to the feed port of the acid recovery tower, the top extraction pipeline of the acid recovery tower is connected to the feed port of the stratification tank, the upper oil phase liquid outlet of the stratification tank is connected to the feed port of the product tower, the top extraction pipeline of the product tower is connected to the feed port of the stratification tank, the lower aqueous phase liquid of the stratification tank is connected to the feed port of the dehydration tower, the top extraction pipeline of the dehydration tower is connected to the feed port of the fixed-bed secondary reactor, the discharge port of the fixed-bed secondary reactor is connected to the feed port of the acid recovery tower, the bottom discharge pipeline of the acid recovery tower is connected to the feed port of the propionic acid tank, and the discharge port of the propionic acid tank is respectively connected to the feed ports of the fixed-bed main reactor and the fixed-bed secondary reactor; the fixed-bed main reactor adopts a propionic acid excess feeding mode, and the feed molar ratio of propionic acid to low-carbon alcohol is 2-10:

1.

2. A low-carbon alcohol propionate synthesis device according to claim 1, characterized in that: The acid recovery tower is a plate-type separation tower or a packed separation tower. The theoretical number of plates in the rectification section of the acid recovery tower is 15 to 30, and the theoretical number of plates in the stripping section is 10 to 40.

3. The low-carbon alcohol propionate synthesis device according to claim 1, characterized in that: The dehydration tower is a plate separation tower or a packed separation tower. The number of theoretical plates in the rectification section of the dehydration tower is 5 to 15, and the number of theoretical plates in the stripping section is 10 to 20.

4. The low-carbon alcohol propionate synthesis device according to claim 1, characterized in that: The product tower is a plate separation tower or a packed separation tower. The theoretical number of plates in the rectification section of the product tower is 10 to 20, and the theoretical number of plates in the stripping section is 10 to 30.

5. A process for synthesizing low-carbon alcohol propionate, characterized in that: The method comprises using the low-carbon alcohol propionate synthesis device according to any one of claims 1 to 4, and the process flow is as follows: Step A, Pre-reaction: Propionic acid and lower alcohol raw materials from the propionic acid tank are mixed in proportion and fed into a fixed-bed main reactor. Propionic acid and lower alcohol undergo an esterification reaction in the fixed-bed main reactor under the catalytic action of a strongly acidic cation exchange resin to produce propionic ester and water. The fixed-bed main reactor adopts a propionic acid excess feed method, and the feed molar ratio of propionic acid to lower alcohol is 2-10:

1. Step B, propionic acid recovery: The esterification reaction liquid from the fixed-bed main reactor is sent to an acid recovery tower. Under the heating effect of the reboiler in the acid recovery tower, vapor-liquid mass transfer is carried out in the acid recovery tower. Lower carbon alcohol, propionate, and water are extracted from the gas phase extraction port at the top of the acid recovery tower. The gas phase material is condensed in a condenser to form a liquid phase mixture of alcohol-propionate-water. Part of it is returned to the acid recovery tower as reflux, and part of it is extracted and sent to a separation tank. The oil phase extracted from the upper layer of the separation tank is sent to the product tower, and the water phase from the lower layer of the separation tank is sent to a dehydration tower for further separation. The propionic acid extracted from the bottom of the acid recovery tower is returned to the propionic acid tank for further recycling. Step C, dehydration: The aqueous phase material in the lower layer of the dehydration tank is fed into a dehydration tower. Under the heating effect of the reboiler of the dehydration tower, vapor-liquid mass transfer is carried out in the dehydration tower. Water forms an azeotrope with a small amount of alcohol and propionate and is extracted from the top of the dehydration tower. The vapor phase material extracted from the top of the dehydration tower is condensed in a condenser to form a liquid phase. Part of it is returned to the dehydration tower as reflux, and part of it is extracted and fed to the fixed-bed secondary reactor. The produced water from the dehydration tower kettle is directly discharged as wastewater; Step D, secondary reaction: a portion of the propionic acid from the propionic acid tank is sent to a fixed-bed secondary reactor, where the propionic acid continues to undergo esterification reaction with the lower alcohol in the propionate-alcohol-water azeotrope. The reacted materials are sent to an acid recovery tower for separation; Step E, product separation: The oil phase material in the upper layer of the stratification tank is sent to the product tower. Under the heating action of the reboiler in the product tower, vapor-liquid mass transfer is carried out in the product tower, and the propionate forms an azeotropic reaction with a small amount of alcohol and water and is extracted from the gas phase at the top of the tower. The gas phase material is condensed in the condenser to form a liquid phase, part of which is returned to the product tower as reflux, and part is extracted and sent to the feed port of the stratification tank; the propionate product is extracted from the bottom of the product tower.

6. A process for synthesizing low-carbon alcohol propionate according to claim 5, characterized in that: In step A, the low-carbon alcohol is one or both of methanol and ethanol, and the propionate is methyl propionate and ethyl propionate.

7. The process for synthesizing low-carbon alcohol propionate according to claim 5, wherein: In step A, the reaction temperature of the fixed-bed main reactor is 50-80° C., and the material residence time is 30-120 min. In step B, the reaction temperature of the fixed-bed secondary reactor is 50-80° C., and the material residence time is 30-120 min. The feed mass ratio of propionic acid to the liquid mixture of alcohol-propionate-water is 4-2:

1.

8. The process for synthesizing low-carbon alcohol propionate according to claim 5, wherein: In step B, the acid recovery tower is operated at normal pressure, the reflux ratio of the acid recovery tower is 0.5-10, and the top temperature of the acid recovery tower is 70-80°C.

9. The process for synthesizing low-carbon alcohol propionate according to claim 5, wherein: In step C, the dehydration tower is operated at normal pressure, the reflux ratio of the dehydration tower is 1-6, the top temperature of the dehydration tower is 60-80°C, and the bottom temperature of the dehydration tower is 98-100°C.

10. The process for synthesizing low-carbon alcohol propionate according to claim 5, wherein: In step E, the product tower is operated at normal pressure, the reflux ratio of the product tower is 0.5-10, the top temperature of the product tower is 65-80°C, and the bottom temperature of the product tower is 75-100°C.

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