Device and process for preparing propionate

Abstract

The present application discloses a device I, which comprises: a first distillation tower; a propionic acid inlet is provided at the top of the first distillation tower; an alcohol compound inlet is provided at the bottom of the first distillation tower; and an intermediate product gas outlet is provided at the top of the first distillation tower. In the present application, liquid propionic acid moves from the top of the distillation tower to the bottom of the distillation tower, and the alcohol raw material flows from the bottom of the distillation tower to the top of the distillation tower in a gas phase state. The two are in countercurrent contact and react. The closer to the top of the tower, the higher the propionic acid content and the lower the alcohol content, and the reaction eliminates the influence of multi-element azeotropy.

Description

Technical Field

[0001] The present application relates to a device and a process for preparing propionate, belonging to the technical field of propionate. Background Art

[0002] Propionate esters are low in toxicity and can be used as solvents for natural or synthetic resins. As a fragrance, they can be used to blend apple, banana, plum, and pineapple flavors, as well as as butter, western wine, and many other edible flavors. They can also be used as flavors for high-end daily cosmetics. Ethyl propionate and propyl propionate can promote the low-temperature performance of lithium-ion batteries, improve the compatibility of electrolytes with positive electrode materials and negative electrode graphite materials, reduce the viscosity and eutectic point of the electrolyte system, and facilitate the migration of lithium ions.

[0003] Taking the synthesis of ethyl propionate as an example, the traditional process adopts an esterification method, concentrated sulfuric acid, p-toluenesulfonic acid or sulfonic acid resin as a catalyst, and benzene, toluene or cyclohexane as an intermittent reaction process of water-carrying agent. Among them, the water generated after the esterification of propionic acid and ethanol is separated from the reaction system by the water-carrying agent, but because the azeotropic point of ethanol and the water-carrying agent is lower, the mass composition of ethanol, water and water-carrying agent at the top of the tower is generally 30% ethanol + 10% water + 60% water-carrying agent, resulting in a large amount of ethanol being carried out of the reaction system, and a large amount of ethanol and water-carrying agent are wasted in the distillation process, resulting in high energy consumption; the reaction raw material ethanol is in excess, and the conversion rate of propionic acid is as high as possible to be higher than 90%, while the ethanol separated from the top of the tower can only be recovered as an azeotropic composition of 95% ethanol + 5% water; the tower bottom product has about 2% propionic acid, 5% ethanol, 2% water and about 91% ethyl propionate, which needs to be alkali washed to remove the unreacted propionic acid and catalyst before distillation separation, resulting in a low propionic acid yield of only about 95%, causing a waste of raw materials. Summary of the invention

[0004] According to one aspect of the present application, a device I is provided, in which liquid propionic acid moves from the top of a distillation tower to the bottom of the distillation tower, and an alcohol raw material flows in a gaseous state from the bottom of the distillation tower to the top of the distillation tower. The two are in countercurrent contact and react. The closer to the top of the tower, the higher the propionic acid content and the lower the alcohol content, thereby eliminating the influence of multi-electrode azeotropy by reaction.

[0005] According to a first aspect of the present application, a device I is provided, comprising: a first distillation tower; a propionic acid inlet is provided at the top of the first distillation tower; an alcohol compound inlet is provided at the bottom of the first distillation tower;

[0006] An intermediate product gas outlet is provided at the top of the first distillation tower.

[0007] Optionally, a propionic acid outlet is also provided at the bottom of the first distillation tower;

[0008] The propionic acid outlet is connected to the propionic acid inlet at the top of the first distillation tower.

[0009] Optionally, the height between the propionic acid inlet and the top of the first distillation tower is 1 / 6 to 1 / 2 of the full tower height;

[0010] The height between the alcohol compound inlet and the bottom of the first distillation tower is 0 to 1 / 2 of the full tower height;

[0011] The propionic acid inlet is higher than the alcohol compound inlet.

[0012] Optionally, the height between the propionic acid inlet and the top of the first distillation tower is 1 / 5 to 1 / 3 of the total tower height;

[0013] The height between the alcohol compound inlet and the bottom of the first distillation tower is 1 / 10 to 1 / 4 of the total tower height.

[0014] Optionally, the first distillation tower has 40 to 60 plates.

[0015] Optionally, the device I further comprises a water separation tank and a second distillation tower;

[0016] The inlet end of the water separation tank is connected to the top of the first distillation tower, and the outlet end of the water separation tank is connected to the top of the second distillation tower;

[0017] Preferably, the second distillation tower has 30-80 plates.

[0018] Preferably, the water separation tank comprises at least one of molecular sieve and anhydrous calcium chloride.

[0019] Optionally, the water separation tank functions as follows: anhydrous calcium chloride chemically absorbs water in the propionate-alcohol-water system, and then a 4A or 5A molecular sieve is used to absorb a small amount of residual water, so that the water content of the system is controlled below 500 ppm, preferably below 100 ppm.

[0020] Optionally, the water separation tank contains a molecular sieve inorganic membrane, which can control the water content of the system below 500 ppm, preferably below 100 ppm.

[0021] Optionally, the top of the second distillation tower is connected to the bottom of the first distillation tower, so that the overhead stream of the second distillation tower passes into the bottom of the first distillation tower;

[0022] The second distillation tower kettle is provided with a propionate outlet.

[0023] Optionally, the device I further comprises a third distillation tower; the first distillation tower kettle is connected to the top of the third distillation tower so that the third distillation tower kettle logistics passes into the third distillation tower;

[0024] The third distillation tower kettle is connected to the top of the first distillation tower, so that the third distillation tower kettle logistics is passed into the first distillation tower;

[0025] Preferably, the third distillation tower has 30-60 plates.

[0026] According to the second aspect of the present application, a process method I for preparing propionate is provided, which is carried out using the above-mentioned device I.

[0027] Optionally, the following process steps are included:

[0028] (1) introducing a raw material I containing propionic acid from the top of a first distillation tower, and introducing a raw material II containing alcohol compounds from the bottom of the first distillation tower, and reacting to obtain the intermediate product gas containing propionic ester at the top of the first distillation tower;

[0029] The first distillation tower is filled with a catalyst I or the raw material I containing propionic acid contains the catalyst I;

[0030] The molar ratio of the propionic acid to the alcohol compound is 2:1 to 10:1.

[0031] Optionally, the raw materials are propionic acid (with a purity greater than 99%) and a plurality of alcohols (with a purity greater than 99.5%), and the feed molar ratio thereof is 2:1 to 10:1, preferably 4:1 to 6:1.

[0032] Optionally, the alcohol compound is selected from the group consisting of isomers and isomers of alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol.

[0033] Optionally, the process method I provided in the present application includes a first distillation tower, a water separation tank and a second distillation tower.

[0034] Optionally, the step (1) comprises: the raw material I and the raw material II react in the first distillation tower to generate a gas-phase azeotrope containing propionate, the gas-phase azeotrope flows toward the top of the first distillation tower, and continues to react with the raw material I introduced from the top of the first distillation tower to generate an intermediate product gas containing propionate.

[0035] In the process method I provided in the present application, the propionate-alcohol system after water separation in the water separation tank is separated by a second distillation tower, the light components at the top of the second distillation tower are recycled back to the alcohol raw material, and the propionate product is extracted from the bottom of the second distillation tower, and the purity reaches more than 99%.

[0036] Optionally, the intermediate product gas also contains water and alcohol compounds;

[0037] The content of the alcohol compound in the intermediate product gas is 0-3wt%.

[0038] Optionally, in the raw material I containing propionic acid, the mass content of the catalyst I is 0.5-3%.

[0039] Optionally, the alcohol compound is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol.

[0040] Optionally, the catalyst I is selected from any one of a homogeneous catalyst and a heterogeneous catalyst.

[0041] Optionally, the homogeneous catalyst is selected from any one of concentrated sulfuric acid and p-toluenesulfonic acid;

[0042] The heterogeneous catalyst is selected from sulfonic acid resins.

[0043] Optionally, the process operating conditions of the first distillation tower are: tower top temperature is 55-110°C; tower bottom temperature is 135-150°C; and tower top reflux ratio is 1:1-2:1.

[0044] Optionally, the propionic acid obtained in the bottom of the first distillation tower is recycled to the top of the first distillation tower for use.

[0045] Optionally, the following process steps are also included:

[0046] (2) passing the propionate-containing stream obtained at the top of the first distillation tower into a water separation tank;

[0047] (3) passing the stream obtained after dehydration in the water separation tank into the top of the second distillation tower, and circulating the stream taken out from the top of the second distillation tower to the bottom of the first distillation tower, so that the propionic ester can be obtained in the bottom of the second distillation tower;

[0048] The water separation tank contains at least one of anhydrous calcium chloride and molecular sieve.

[0049] Optionally, the process operating conditions of the second distillation tower are: tower top temperature is 50-80°C; tower bottom temperature is 80-120°C; and tower top reflux ratio is 1:1-2:1.

[0050] Optionally, the water content of the logistics obtained after dehydration in the water separation tank is less than or equal to 500 ppm.

[0051] Optionally, the following process steps are also included:

[0052] (4) passing the stream obtained from the bottom of the first distillation tower into the top of the third distillation tower, passing the stream from the bottom of the third distillation tower into the top of the first distillation tower, and returning the stream from the top of the third distillation tower to the top of the third distillation tower;

[0053] The third distillation tower is filled with a water-carrying agent;

[0054] Preferably, the water-carrying agent is selected from any one of toluene, benzene, toluene and cyclohexane.

[0055] Optionally, the process operating conditions of the third distillation tower are: the tower top temperature is 80-100°C; the tower bottom temperature is 90-130°C; and the tower top reflux ratio is 1:1-2:1. Optionally, the process method I for preparing propionic ester comprises the following process steps:

[0056] (1) The raw material propionic acid carries a homogeneous catalyst and is fed from the top of the first distillation tower, and the raw material containing alcohol compounds is fed from the bottom of the first distillation tower; or a sulfonic acid resin catalyst is used and directly loaded into the first distillation tower, and the propionic acid raw material does not need to carry an additional homogeneous catalyst;

[0057] (2) the propionic acid flows in the first distillation tower in a liquid phase from the top of the first distillation tower to the bottom of the first distillation tower; the various alcohol compounds flow in a gas phase from the bottom of the first distillation tower to the top of the first distillation tower; the gas-liquid two phases contact in the first distillation tower;

[0058] (3) the generated propionate and water form a binary or ternary azeotrope with the unreacted alcohol and continue to move toward the top of the first distillation tower in the gas phase;

[0059] (4) The closer to the top of the first distillation tower, the higher the propionic acid content is, and it continues to react with various alcohols; the top product of the first distillation tower is propionic ester and water, and the alcohol content is less than 3%. The alcohol raw material is consumed by means of reactive distillation and a large amount of excess propionic acid;

[0060] (5) the overhead product of the first distillation tower is dehydrated by calcium chloride and then dehydrated by 4A or 5A molecular sieve; or dehydrated by an inorganic molecular sieve membrane;

[0061] (6) The propionic acid in the bottom of the first distillation tower is recycled as a reaction raw material;

[0062] (7) the dehydrated material (propionate product with a content of more than 95% and a small amount of corresponding alcohol) enters the second distillation tower for product separation;

[0063] (9) Qualified propionate products are extracted from the bottom of the second distillation tower; and the propionate and alcohol at the top of the second distillation tower are recycled back to the reaction raw materials.

[0064] In the process method I provided in the present application, the raw material propionic acid is fed from the lower part of the top of the first distillation tower, and various alcohol raw materials are fed from the bottom of the first distillation tower. The two are reversely contacted in the first distillation tower and react under the action of the catalyst. The excess propionic acid at the top of the first distillation tower continuously consumes the alcohol raw material, breaking the binary or ternary azeotropic system of propionate-alcohol-water; the top of the first distillation tower is composed of about more than 80% propionate, less than 3% alcohol and about 15% water, which enters the second distillation tower for separation after dehydration; the propionic acid in the bottom of the first distillation tower is circulated to the feed port close to the top of the first distillation tower; the azeotrope of alcohol and propionate produced from the top of the second distillation tower is circulated back to the bottom of the first distillation tower, and qualified propionate products are produced from the bottom of the second distillation tower.

[0065] According to a third aspect of the present application, there is provided an apparatus II, the apparatus II comprising: a first distillation tower and a second distillation tower;

[0066] The top of the first distillation tower is provided with an inlet for propionic acid and alcohol compounds;

[0067] The top of the first distillation tower is connected to the top of the second distillation tower, so that the logistics at the top of the first distillation tower is passed into the top of the second distillation tower;

[0068] The top of the second distillation tower is provided with an azeotropic agent inlet; or,

[0069] The top of the first distillation tower and the top of the second distillation tower are connected by a pipeline; an azeotropic agent inlet is arranged on the pipeline.

[0070] Optionally, the device II further comprises a water separator;

[0071] The water separator inlet is connected to the top of the second distillation tower, so that the top stream of the second distillation tower passes into the water separator;

[0072] The outlet of the water separator is connected to the propionic acid inlet at the top of the second distillation tower and the top of the first distillation tower respectively;

[0073] Preferably, the number of plates of the first distillation tower and the number of plates of the second distillation tower are both 40 to 60.

[0074] Optionally, the device II further comprises a distillation tower III;

[0075] The kettle of the second distillation tower is connected to the top of the third distillation tower, so that the logistics of the kettle of the second distillation tower is passed into the top of the third distillation tower;

[0076] The bottom of the III distillation tower is connected to the azeotropic agent inlet at the top of the II distillation tower, so that the bottom flow of the III distillation tower is passed into the top of the II distillation tower;

[0077] Preferably, the number of plates of the third distillation tower is 40 to 60.

[0078] Optionally, the device II further comprises a distillation tower IV;

[0079] The tower kettle of the first distillation tower is connected to the top of the fourth distillation tower, so that the logistics of the tower kettle of the first distillation tower is passed into the top of the fourth distillation tower;

[0080] The top of the IV distillation tower is connected to the propionic acid inlet at the top of the I distillation tower, so that the top stream of the IV distillation tower passes into the top of the I distillation tower;

[0081] Preferably, the number of plates of the IV distillation tower is 40-60.

[0082] Optionally, the device II further comprises a pre-reactor;

[0083] One end of the pre-reactor is provided with an inlet for propionic acid and alcohol compounds; the other end of the pre-reactor is connected to the top of the first distillation tower.

[0084] According to the fourth aspect of the present application, a process method II for preparing propionate is also provided, characterized in that the process is carried out using the above-mentioned device II.

[0085] Optionally, the following process steps are included:

[0086] (a) introducing a raw material containing propionic acid and an alcohol compound into the top of a first distillation tower, reacting in the first distillation tower, mixing the stream obtained at the top of the first distillation tower with the stream containing an azeotropic agent, and then introducing the stream into the top of a second distillation tower, and obtaining the propionic ester in the bottom of the second distillation tower;

[0087] The catalyst II is filled in the first distillation tower or the raw material containing propionic acid and alcohol compounds contains the catalyst II.

[0088] Optionally, the catalyst II is selected from any one of a homogeneous catalyst and a heterogeneous catalyst.

[0089] Preferably, the homogeneous catalyst is selected from any one of concentrated sulfuric acid and p-toluenesulfonic acid;

[0090] The heterogeneous catalyst is selected from sulfonic acid resins.

[0091] Optionally, the molar ratio of the propionic acid to the alcohol compound is 1:1 to 1:10;

[0092] Preferably, in the raw material containing propionic acid and alcohol compounds, the mass content of the catalyst II is 1-2%.

[0093] Optionally, the process operating conditions of the first distillation tower are: the tower top temperature is 55-110° C.; the tower bottom temperature is 135-150° C.; and the tower top reflux ratio is 1:1-2:1;

[0094] The process operating conditions of the second distillation tower are: the tower top temperature is 60-80°C; the tower bottom temperature is 80-100°C; and the tower top reflux ratio is 1:1-2.

[0095] Optionally, in the step (a), the mass ratio of the logistics obtained at the top of the first distillation tower to the azeotropic agent is 1:0.5-2.

[0096] Optionally, the logistics obtained from the top of the second distillation tower is separated into layers after standing, and the alcohol compounds obtained after separation are recycled back to the reaction raw materials, and the obtained n-heptane is recycled back to the top of the second distillation tower.

[0097] Optionally, in the step (a), the raw material containing propionic acid and alcohol compounds is pre-reacted in a pre-reactor and then introduced into the top of the first distillation tower;

[0098] The pre-reactor is filled with the catalyst II or the raw material containing propionic acid and alcohol compounds contains the catalyst II.

[0099] Optionally, the following process steps are also included:

[0100] (b) passing the stream obtained in the kettle of the second distillation tower into the top of the third distillation tower, and obtaining the propionic ester at the top of the third distillation tower, and passing the stream obtained in the kettle of the third distillation tower into the top of the second distillation tower;

[0101] Preferably, the process operating conditions of the third distillation tower are: the tower top temperature is 70-90°C; the tower bottom temperature is 90-110°C; and the tower top reflux ratio is 1:1-2:1.

[0102] Optionally, the following process steps are also included:

[0103] (c) passing the stream obtained in the kettle of the first distillation tower into the fourth distillation tower, and circulating the stream obtained at the top of the fourth distillation tower to the top of the first distillation tower for recycling;

[0104] Preferably, the process operating conditions of the IV distillation tower are:

[0105] The tower top temperature is 60-70°C; the tower bottom temperature is 99-105°C; the tower top reflux ratio is 1:1-2:1.

[0106] The beneficial effects of this application include:

[0107] 1. The excessive alcohol content in the ternary azeotropic system of propionate, water and alcohol is eliminated by using a large amount of excess propionic acid at the top of the distillation tower and reaction-distillation technology. The propionate content can be controlled to more than 80% and the alcohol content to less than 3% in a single tower;

[0108] 2. No need to carry water agent and the content of alcohol and propionate returned from the second distillation tower is significantly reduced, which significantly reduces energy consumption;

[0109] 3. Use chemical adsorbent or inorganic membrane to separate water, the process is simple;

[0110] 4. Continuous process, stable product quality and high propionate yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Figure 1 This is a schematic diagram of an embodiment of the process flow of the present invention;

[0112] Figure 2 This is a schematic diagram of an embodiment of the process flow of the present invention;

[0113] Figure 3 This is a schematic diagram of an embodiment of the process flow of the present invention;

[0114] The reference numerals in the figures are described as follows:

[0115] 1 first distillation tower, 2 water separation tank, 3 second distillation tower;

[0116] 4 the third distillation tower, 5 the first distillation tower, 6 the second distillation tower;

[0117] 7 water separator, 8 third distillation tower, 9 fourth distillation tower. DETAILED DESCRIPTION

[0118] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0119] The invention uses propionic acid and various alcohols as raw materials, concentrated sulfuric acid, p-toluenesulfonic acid and sulfonic acid resin as catalysts, and obtains products methyl propionate, ethyl propionate, propyl propionate and butyl propionate, including isomers, through processes such as reaction distillation and reaction separation.

[0120] The specific process of the present invention is:

[0121] The raw material propionic acid carries a certain amount of homogeneous catalyst and is fed from 1 / 4 of the top of the first distillation tower 1, and various alcohol raw materials are fed from the bottom of the first distillation tower 1. The top temperature of the first distillation tower 1 is controlled between 55-110°C, and the bottom temperature of the first distillation tower 1 is controlled between 135-145°C. Propionic acid flows from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in the first distillation tower 1 in a liquid phase, and various alcohols flow from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase. The gas-liquid two phases contact and react in the first distillation tower 1. The generated propionic ester and water form a binary or ternary azeotrope with the unreacted alcohols and continue to move to the top of the first distillation tower 1 in the gas phase. The closer to the top of the first distillation tower 1, the higher the propionic acid content, and it continues to react with various alcohols. The top product of the first distillation tower 1 is propionic ester and water, and the alcohol content is less than 3%. The alcohol raw material is consumed by means of reactive distillation and a large amount of excess propionic acid. The bottom of the first distillation tower 1 is the excess propionic acid, which is directly circulated to the top of the first distillation tower 1. The light components taken from the top of the first distillation tower 1 are dehydrated with calcium chloride and then with 4A or 5A molecular sieves, or dehydrated with inorganic molecular sieve membranes before entering the second distillation tower 3 (product separation tower). The propionic ester and alcohol azeotrope taken from the top of the second distillation tower 3 are circulated to the bottom of the first distillation tower 1, and the product is separated from the bottom of the second distillation tower 3. If the sulfonic acid resin is a heterogeneous catalyst, it is directly loaded into the distillation tower, and the propionic acid raw material does not need to carry a homogeneous catalyst.

[0122] In the present application, the process I for preparing propionate comprises the following process steps:

[0123] (1) The raw material propionic acid is fed from the lower part of the top of the first distillation tower 1, and various alcohol raw materials are fed from the bottom of the first distillation tower 1. The two are reversely contacted in the first distillation tower 1 and react under the action of the catalyst. The excess propionic acid at the top of the tower continuously consumes the alcohol raw material, breaking the binary or ternary azeotropic system of propionate-alcohol-water;

[0124] (2) The top of the first distillation tower 1 contains about 80% or more propionate, less than 3% alcohol and about 15% water, which are then dehydrated and enter the second distillation tower 3 for separation.

[0125] (3) The propionic acid in the bottom of the first distillation tower 1 is circulated to the feed inlet at the top of the first distillation tower 1;

[0126] (4) The azeotrope of alcohol and propionate is taken out from the top of the second distillation tower 3 and recycled to the bottom of the first distillation tower 1, and qualified propionate products are taken out from the bottom of the second distillation tower 3.

[0127] The model of the gas chromatograph used in the examples of the present application is Shimadzu GC-2014C.

[0128] Example 1

[0129] like Figure 1As shown, ethyl propionate is prepared from propionic acid and ethanol as raw materials, the feed molar ratio of the raw materials propionic acid and ethanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, the catalyst is p-toluenesulfonic acid, the catalyst content is 1% of the mass fraction of propionic acid, and the catalyst is completely dissolved in the propionic acid, and the propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. Ethanol is fed from the bottom of the first distillation tower 1, flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The first distillation tower 1 has 60 plates, metal θ ring packing, and a packing height of 2m. The reflux ratio at the top of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 80-85°C, and the bottom temperature of the first distillation tower 1 is between 135-140°C. It is determined that the top composition of the first distillation tower 1 is about 82.4% ethyl propionate, 14.5% water and 3.1% ethanol. After adsorption by anhydrous calcium chloride and 4A molecular sieve, the water content can be reduced to 100ppm. Enter the second distillation tower 3 (the number of plates is 60) for separation, and the metal θ ring packing is still used, the packing height is 2m, the reflux ratio at the top of the second distillation tower 3 is controlled between 1:1-2:1, the top temperature of the second distillation tower 3 is between 78-80°C, and the bottom temperature of the second distillation tower 3 is between 98-100°C. It is determined that the top composition of the second distillation tower 3 is about 55% ethanol and 45% ethyl propionate. The propionic acid in the bottom of the first distillation tower 1 and the additional propionic acid are directly circulated to the top of the first distillation tower 1, the light components at the top of the second distillation tower 3 and the additional ethanol are circulated to the bottom of the first distillation tower 1, and the qualified ethyl propionate product is extracted from the bottom of the second distillation tower 3, and the single ethyl propionate yield can be close to 95%.

[0130] Example 2

[0131] like Figure 1As shown, ethyl propionate is prepared from propionic acid and ethanol as raw materials, the feed molar ratio of raw material propionic acid and ethanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, the catalyst is p-toluenesulfonic acid resin, the catalyst is loaded into the first distillation tower 1, and the loading method of the θ ring filler is one layer of catalyst and one layer of filler, with a height of about 8 cm. Propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. Ethanol is fed from the bottom of the first distillation tower 1, and flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The first distillation tower 1 has 60 plates, metal θ ring packing, and a packing height of 2m. The top reflux ratio of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 80-85°C, and the bottom temperature of the first distillation tower 1 is between 135-140°C. It is determined that the top composition of the first distillation tower 1 is about 82.2% ethyl propionate, 14.3% water and 3.5% ethanol. After adsorption by anhydrous calcium chloride and 4A molecular sieve, the water content can be reduced to 100ppm. Enter the second distillation tower 3 (the number of plates is 60) for separation, and the metal θ ring packing is still used, the packing height is 2m, the top reflux ratio of the second distillation tower 3 is controlled between 1:1-2:1, the top temperature of the second distillation tower 3 is between 78-80°C, and the bottom temperature of the second distillation tower 3 is between 98-100°C. It is determined that the top composition of the second distillation tower 3 is about 55% ethanol and 45% ethyl propionate. The propionic acid in the bottom of the first distillation tower 1 and the additional propionic acid are directly circulated to the top of the first distillation tower 1, the light components at the top of the second distillation tower 3 and the additional ethanol are circulated to the bottom of the first distillation tower 1, and the qualified ethyl propionate product is extracted from the bottom of the second distillation tower 3, and the single ethyl propionate yield can be close to 95%.

[0132] Example 3

[0133] like Figure 2As shown, methyl propionate is prepared from propionic acid and methanol as raw materials, the feed molar ratio of raw materials propionic acid and methanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, the catalyst is p-toluenesulfonic acid resin, the catalyst is filled in the distillation tower, and the filling method of the θ ring filler is a layer of catalyst and a layer of filler, with a height of about 10 cm. Propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. Methanol is fed from the bottom of the first distillation tower 1, and flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The first distillation tower 1 has 60 plates, metal θ ring packing, and a packing height of 2m. The reflux ratio at the top of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 67-73°C, and the bottom temperature of the first distillation tower 1 is between 110-115°C. It is determined that the top composition of the first distillation tower 1 is about 95.5% methyl propionate, 2.5% water and 2% methanol. After gasification, the water can be separated by an inorganic molecular sieve membrane and reduced to 200ppm. Enter the second distillation tower 3 (with 60 plates) for separation, still using metal θ ring packing, the packing height is 2m, the reflux ratio at the top of the second distillation tower 3 is controlled between 1:1-2:1, the top temperature of the second distillation tower 3 is between 59.5-62.5°C, and the bottom temperature of the second distillation tower 3 is between 79-83°C. It is determined that the top composition of the second distillation tower 3 is about 48% methanol and 52% methyl propionate. The bottom of the kettle of the first distillation tower 1 contains about 2%-3% water, which enters the third distillation tower 4 and is separated by adding toluene with water. The number of plates of the third distillation tower 4 is 60, and the metal θ ring packing is 2m high. The reflux ratio of the top of the third distillation tower 4 is controlled between 1:1-2:1, the top temperature of the third distillation tower 4 is stable between 83-88°C, and the kettle temperature of the third distillation tower 4 is between 115-120°C. The propionic acid in the kettle of the third distillation tower 4 and the additional propionic acid are directly circulated to the top of the first distillation tower 1, the light components at the top of the second distillation tower 3 and the additional methanol are circulated to the bottom of the first distillation tower 1, and the qualified methyl propionate product is extracted from the bottom of the second distillation tower 3, and the yield of methyl propionate in a single time can exceed 95%.

[0134] Example 4

[0135] like Figure 2As shown, methyl propionate is prepared from propionic acid and methanol as raw materials, the feed molar ratio of raw material propionic acid and methanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, concentrated sulfuric acid is used as a catalyst, and the catalyst content is 1% of the mass fraction of propionic acid, which is completely dissolved in propionic acid, and propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. Methanol is fed from the bottom of the first distillation tower 1, and flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The first distillation tower 1 has 60 plates, metal θ ring packing, and a packing height of 2m. The reflux ratio at the top of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 67-73°C, and the bottom temperature of the first distillation tower 1 is between 110-115°C. It is determined that the top composition of the first distillation tower 1 is about 95.6% methyl propionate, 2.2% water and 2.2% methanol. After gasification, the water can be separated by an inorganic molecular sieve membrane and reduced to 200ppm. Enter the second distillation tower 3 (with 55 plates) for separation, still using metal θ ring packing, the packing height is 2m, the reflux ratio at the top of the second distillation tower 3 is controlled between 1:1-2:1, the top temperature of the second distillation tower 3 is between 59.5-62.5°C, and the bottom temperature of the second distillation tower 3 is between 79-83°C. It is determined that the top composition of the second distillation tower 3 is about 48% methanol and 52% methyl propionate. The bottom of the kettle of the first distillation tower 1 contains about 2%-3% water, which enters the third distillation tower 4 and is separated by adding toluene with water. The number of plates of the third distillation tower 4 is 50, and the metal θ ring packing is 2m high. The reflux ratio of the top of the third distillation tower 4 is controlled between 1:1-2:1, the top temperature of the third distillation tower 4 is stable between 83-88°C, and the kettle temperature of the third distillation tower 4 is between 115-120°C. The propionic acid in the kettle of the third distillation tower 4 and the additional propionic acid are directly circulated to the top of the first distillation tower 1, the light components at the top of the second distillation tower 3 and the additional methanol are circulated to the bottom of the first distillation tower 1, and the qualified methyl propionate product is extracted from the bottom of the second distillation tower 3, and the yield of methyl propionate in a single time can exceed 95%.

[0136] Example 5

[0137] like Figure 3As shown, methyl propionate is prepared from propionic acid and methanol as raw materials, the feed molar ratio of raw propionic acid and methanol is 1:6, propionic acid and methanol and 1% p-toluenesulfonic acid catalyst are uniformly mixed, and enter the middle of the first distillation tower 5 after passing through the pre-reactor (50°C). The number of plates of the first distillation tower 5 is 60, the metal θ ring packing, the packing height is 2m, the reflux ratio of the top of the first distillation tower 5 is controlled between 1:1-2:1, the top temperature of the first distillation tower 5 is stable at 59.5-62.5°C, and the bottom temperature of the first distillation tower 5 is stable at 75-78°C. It is determined that the top composition of the first distillation tower 5 is about 48% methanol and 52% methyl propionate, and the water content is less than 100ppm. The light components extracted from the top of the first distillation tower 5 are mixed with about half of its mass of n-heptane and then enter the middle of the second distillation tower 6. The number of plates of the second distillation tower 6 is 60, and the metal θ ring packing is 2m. The reflux ratio of the top of the second distillation tower 6 is controlled between 1:1-3:1, the top temperature of the second distillation tower 6 is stable at 58-60°C, the bottom temperature of the second distillation tower 6 is 61-63°C, and the top composition of the second distillation tower 6 is about 52% methanol and 48% n-heptane. Methanol and n-heptane can be separated after cooling and standing in the water separator 7. Methanol is circulated as a raw material, and n-heptane is circulated as an azeotropic agent. The bottom composition of the first distillation tower 5 is less than 0.5% propionic acid, about 79.5% methanol and 20% water. Water and methanol are not azeotropic and are directly distilled. Methanol with a purity higher than 99.9% is extracted from the top of the third distillation tower 8 and circulated to the reaction raw material. The propionic acid aqueous solution in the bottom of the III distillation tower 8 is washed with alkali and discharged to the waterless treatment plant after reaching a neutral pH value. The product composition of the bottom of the II distillation tower 6 is about 0.5% methanol, 3% n-heptane and 96.5% methyl propionate. The product of the bottom of the II distillation tower 6 enters the middle of the III distillation tower 8. The number of distillation tower plates of the III distillation tower 8 is 30, and the metal θ ring packing has a packing height of 1m. The reflux ratio of the top of the III distillation tower 8 is controlled between 1:1-2:1, the top temperature of the III distillation tower 8 is 79-81°C, the bottom of the III distillation tower 8 is 98-100°C, and the top of the III distillation tower 8 extracts methyl propionate with a content higher than 99.9%. The bottom of the III distillation tower 8 is n-heptane, which is circulated to the entrainer for recycling. The IV distillation tower 9 (the top temperature of the IV distillation tower 9 is 65°C, the bottom temperature is 100.5°C, and the top operating reflux ratio is 2:1) separates the methanol and water at the bottom of the I distillation tower 5. The two do not azeotropically form, and the methanol at the top of the IV distillation tower 9 is recycled to the reaction raw material.

[0138] Example 6

[0139] like Figure 3As shown, methyl propionate is prepared from propionic acid and methanol as raw materials, the feed molar ratio of raw material propionic acid and methanol is 1:6, propionic acid and methanol are loaded into p-toluenesulfonic acid fixed bed reactor (i.e. pre-reactor), the reaction temperature is 60-100°C, and then enter the middle of the first distillation tower 5 (p-toluenesulfonic acid solid catalyst is loaded in the first distillation tower 5, and the loading mode of catalyst and θ ring filler is one layer of catalyst and one layer of filler, and the height is about 7cm). The number of plates of the first distillation tower 5 is 60, metal θ ring filler, the filler height is 2m, the reflux ratio of the top of the first distillation tower 5 is controlled between 1:1-2:1, the top temperature of the first distillation tower 5 is stabilized at 59.5-62.5°C, and the bottom temperature of the first distillation tower 5 is stabilized at 75-78°C. It is determined that the top composition of the first distillation tower 5 is about 48% methanol and 52% methyl propionate, and the water content is less than 100ppm. The light components extracted from the top of the first distillation tower 5 are mixed with about half of its mass of n-heptane and then enter the middle of the second distillation tower 6. The number of plates of the second distillation tower 6 is 60, and the metal θ ring packing is 2m. The reflux ratio of the top of the second distillation tower 6 is controlled between 1:1-3:1, the top temperature of the second distillation tower 6 is stable at 58-60°C, the bottom temperature of the second distillation tower 6 is 61-63°C, and the top composition of the second distillation tower 6 is about 52% methanol and 48% n-heptane. Methanol and n-heptane can be separated after cooling and standing in the water separator 7. Methanol is circulated as a raw material, and n-heptane is circulated as an azeotropic agent. The bottom composition of the first distillation tower 5 is less than 0.5% propionic acid, about 79.5% methanol and 20% water. Water and methanol are not azeotropic, and are directly distilled in the fourth distillation tower 9. Methanol with a purity higher than 99.9% is extracted from the top of the fourth distillation tower 9 and circulated to the reaction raw material. The propionic acid aqueous solution in the bottom of the IV distillation tower 9 is washed with alkali and discharged to the sewage treatment plant after reaching a neutral pH value. The product composition of the bottom of the II distillation tower 6 is about 0.5% methanol, 3% n-heptane and 96.5% methyl propionate. The product of the bottom of the II distillation tower 6 enters the middle of the III distillation tower 8. The number of plates of the III distillation tower 8 is 20-30, and the metal θ ring packing has a packing height of 1m. The reflux ratio of the top of the III distillation tower 8 is controlled between 1:1-2:1, the top temperature of the III distillation tower 8 is 79-81°C, the bottom of the III distillation tower 8 is 98-100°C, and the top of the III distillation tower 8 extracts methyl propionate with a content higher than 99.9%. The bottom of the bottom of the III distillation tower 8 is n-heptane, which is circulated to the entrainer for recycling. The IV distillation tower 9 (the top temperature of the IV distillation tower 9 is 65°C, the bottom temperature is 100.5°C, and the top operating reflux ratio is 2:1) separates the methanol and water at the bottom of the I distillation tower 5. The two do not azeotropically form, and the top methanol of the IV distillation tower 9 is recycled to the reaction raw material.

[0140] Example 7

[0141] like Figure 1As shown, propyl propionate is prepared from propionic acid and n-propanol as raw materials, the feed molar ratio of the raw materials propionic acid and n-propanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, the catalyst is p-toluenesulfonic acid, the catalyst content is 1% of the mass fraction of propionic acid, and the catalyst is completely dissolved in the propionic acid, and the propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. The n-propanol is fed from the bottom of the first distillation tower 1, flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The number of plates of the first distillation tower 1 is 60, the metal θ ring packing is used, the packing height is 2m, the reflux ratio of the top of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 88-103°C, the bottom temperature of the first distillation tower 1 is between 140-145°C, and the top composition of the first distillation tower 1 is determined to be approximately 83.5% propyl propionate, 13% water and 3.5% n-propanol. After gasification, it is dehydrated by an inorganic molecular sieve membrane, and the water content is reduced to 200ppm. The propionic acid in the bottom of the first distillation tower 1 and the additional propionic acid are directly circulated to the top of the first distillation tower 1. Propyl propionate and n-propanol do not form an azeotrope, and enter the second distillation tower 3 (the number of tower plates is 60) for separation. The n-propanol is produced at the top temperature of the second distillation tower 3 at 97-100° C. and recycled back to the reaction raw material. The bottom temperature of the second distillation tower 3 is 118-123° C., and propyl propionate is produced at the bottom of the second distillation tower 3. The single-time yield of propyl propionate is higher than 96%.

[0142] Example 8

[0143] like Figure 1As shown, propyl propionate is prepared from propionic acid and n-propanol as raw materials, the feed molar ratio of the raw materials propionic acid and n-propanol is 4:1, propionic acid is fed from the lower 1 / 4 of the top of the first distillation tower 1, the catalyst is p-toluenesulfonic acid, the catalyst content is 1% of the mass fraction of propionic acid, and the catalyst is completely dissolved in the propionic acid, and the propionic acid moves from the top of the first distillation tower 1 to the bottom of the first distillation tower 1 in a liquid phase. The n-propanol is fed from the bottom of the first distillation tower 1, flows from the bottom of the first distillation tower 1 to the top of the first distillation tower 1 in a gas phase, and the gas-liquid two phases contact and react in the first distillation tower 1. The number of plates of the distillation tower is 60, the metal θ ring packing is used, the packing height is 2m, the reflux ratio of the top of the first distillation tower 1 is controlled between 1:1-2:1, the top temperature of the first distillation tower 1 is stable between 88-103°C, the bottom temperature of the first distillation tower 1 is between 140-145°C, and the top composition of the first distillation tower 1 is determined to be about 83.5% propyl propionate, 13% water and 3.5% n-propanol. After gasification, it is dehydrated by an inorganic molecular sieve membrane, and the water content is reduced to 200ppm. The propionic acid in the bottom of the first distillation tower 1 and the additional propionic acid are directly circulated to the top of the first distillation tower 1. Propyl propionate and n-propanol do not form an azeotrope, and enter the second distillation tower 3 (the number of tower plates is 60) for separation. The n-propanol is produced at the top temperature of the second distillation tower 3 at 97-100°C and recycled to the reaction raw material. The bottom temperature of the second distillation tower 3 is 118-123°C, and propyl propionate is produced at the bottom of the second distillation tower 3.

[0144] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A process for preparing propionic esters I, characterized in that: The process steps include: (1) introducing a raw material I containing propionic acid from the top of a first distillation tower, and introducing a raw material II containing alcohol compounds from the bottom of the first distillation tower, and reacting to obtain the intermediate product gas containing propionic ester at the top of the first distillation tower; The first distillation tower is filled with a catalyst I or the raw material I containing propionic acid contains the catalyst I; The molar ratio of the propionic acid to the alcohol compound is 2:1 to 10:1; The catalyst I is selected from any one of a homogeneous catalyst and a heterogeneous catalyst; The homogeneous catalyst is selected from any one of concentrated sulfuric acid and p-toluenesulfonic acid; The heterogeneous catalyst is selected from sulfonic acid resins; (2) passing the propionate-containing stream obtained from the top of the first distillation tower into a water separation tank; (3) The stream obtained after dehydration in the water separation tank is introduced into the top of the second distillation tower, and the stream taken out from the top of the second distillation tower is circulated to the bottom of the first distillation tower, and the propionate ester can be obtained in the bottom of the second distillation tower.

2. The process method I according to claim 1, characterized in that: The steps also include: (4) passing the stream obtained in the bottom of the first distillation tower into the top of the third distillation tower, passing the stream in the bottom of the third distillation tower into the top of the first distillation tower, and returning the stream at the top of the third distillation tower to the top of the third distillation tower; The third distillation tower is filled with a water-carrying agent.

3. The process method I according to claim 1, characterized in that: The process method I is carried out using an apparatus I, which comprises: a first distillation tower; a propionic acid inlet is provided at the top of the first distillation tower; an alcohol compound inlet is provided at the bottom of the first distillation tower; An intermediate product gas outlet is provided at the top of the first distillation tower.

4. The process method I according to claim 3, characterized in that: A propionic acid outlet is also provided at the bottom of the first distillation tower; The propionic acid outlet is connected to the propionic acid inlet at the top of the first distillation tower.

5. The process method I according to claim 4, characterized in that: The height of the propionic acid inlet from the top of the first distillation tower is 1 / 6 to 1 / 2 of the full tower height; The height between the alcohol compound inlet and the bottom of the first distillation tower is 0 to 1 / 2 of the full tower height; The propionic acid inlet is higher than the alcohol compound inlet.

6. The process method I according to claim 3, characterized in that: The number of plates of the first distillation tower is 40 to 60.

7. The process method I according to claim 3, characterized in that: The device I also includes a water separation tank and a second distillation tower; The inlet end of the water separation tank is connected to the top of the first distillation tower, and the outlet end of the water separation tank is connected to the top of the second distillation tower.

8. The process method I according to claim 7, characterized in that: The second distillation tower has 30-80 plates.

9. The process method I according to claim 7, characterized in that: The water separation tank includes at least one of molecular sieve and anhydrous calcium chloride.

10. The process method I according to claim 7, characterized in that: The top of the second distillation tower is connected to the bottom of the first distillation tower, so that the overhead stream of the second distillation tower passes into the bottom of the first distillation tower; The second distillation tower kettle is provided with a propionate outlet.

11. The process method I according to claim 3, characterized in that: The device I also includes a third distillation tower; the first distillation tower kettle is connected to the top of the third distillation tower so that the third distillation tower kettle logistics passes into the third distillation tower; The bottom of the third distillation tower is connected to the top of the first distillation tower so that the logistics of the bottom of the third distillation tower can be passed into the first distillation tower.

12. The process method I according to claim 3, characterized in that: The third distillation tower has 30-60 plates.

13. The process method I according to claim 1, characterized in that: The reaction takes place in the first distillation tower to generate a gaseous azeotrope containing propionate, which flows toward the top of the first distillation tower and continues to react with the raw material I introduced from the top of the first distillation tower to generate an intermediate product gas containing propionate.

14. The process method I according to claim 1, characterized in that: The intermediate product gas also contains water and alcohol compounds; The content of the alcohol compound in the intermediate product gas is 0-3wt%.

15. The process method I according to claim 1, characterized in that: In the raw material I containing propionic acid, the mass content of the catalyst I is 0.5-3%.

16. The process method I according to claim 1, characterized in that: The alcohol compound is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol.

17. The process method I according to claim 1, characterized in that: The process operating conditions of the first distillation tower are: tower top temperature is 55-110°C; tower bottom temperature is 135-150°C; and tower top reflux ratio is 1:1-2:

1.

18. The process method I according to claim 1, characterized in that: The propionic acid obtained in the bottom of the first distillation tower is circulated back to the top of the first distillation tower for use.

19. The process method I according to claim 1, characterized in that: The process operating conditions of the second distillation tower are: tower top temperature is 50-80°C; tower bottom temperature is 80-120°C; and tower top reflux ratio is 1:1-2:

1.

20. The process method I according to claim 1, characterized in that: The water content of the stream obtained after dehydration in the water separation tank is less than or equal to 500 ppm.

21. The process method I according to claim 2, characterized in that: The water-carrying agent is selected from any one of toluene, benzene, toluene and cyclohexane.

22. The process method I according to claim 2, characterized in that: The process operating conditions of the third distillation tower are: tower top temperature is 80-100°C; tower bottom temperature is 90-130°C; and tower top reflux ratio is 1:1-2:

1.

23. A process II for preparing propionic ester, characterized in that: The process steps include: (a) introducing a raw material containing propionic acid and an alcohol compound into the top of a first distillation tower, reacting in the first distillation tower, mixing the stream obtained at the top of the first distillation tower with the stream containing an azeotropic agent, and then introducing the stream into the top of a second distillation tower, and obtaining the propionic ester in the bottom of the second distillation tower; The azeotropic agent is n-heptane; The catalyst II is filled in the first distillation tower or the raw material containing propionic acid and alcohol compounds contains the catalyst II; The catalyst II is selected from any one of a homogeneous catalyst and a heterogeneous catalyst; The homogeneous catalyst is selected from any one of concentrated sulfuric acid and p-toluenesulfonic acid; The heterogeneous catalyst is selected from sulfonic acid resins; (b) the stream obtained in the bottom of the second distillation tower is introduced into the top of the third distillation tower, and the propionic ester can be obtained at the top of the third distillation tower. The stream obtained in the bottom of the third distillation tower is introduced into the top of the second distillation tower.

24. Process II according to claim 23, characterized in that: The process operating conditions of the third distillation tower are: the tower top temperature is 70-90°C; the tower bottom temperature is 90-110°C; and the tower top reflux ratio is 1:1-2:

1.

25. Process method II according to claim 23, characterized in that: The process II also includes: (c) the stream obtained in the bottom of the first distillation tower is passed into the fourth distillation tower, and the stream obtained at the top of the fourth distillation tower is circulated to the top of the first distillation tower for recycling.

26. Process II according to claim 23, characterized in that: The process operating conditions of the IV distillation tower are: the tower top temperature is 60-70°C; the tower bottom temperature is 99-105°C; and the tower top reflux ratio is 1:1-2:

1.

27. Process method II according to claim 23, characterized in that: The process II is carried out using device II, and the device II comprises: a first distillation tower and a second distillation tower; The top of the first distillation tower is provided with an inlet for propionic acid and alcohol compounds; The top of the first distillation tower is connected to the top of the second distillation tower, so that the logistics at the top of the first distillation tower is passed into the top of the second distillation tower; The top of the second distillation tower is provided with an azeotropic agent inlet; or, The top of the first distillation tower and the top of the second distillation tower are connected by a pipeline; an azeotropic agent inlet is arranged on the pipeline.

28. Process II according to claim 27, characterized in that: The device II also includes a water separator; The water separator inlet is connected to the top of the second distillation tower, so that the top stream of the second distillation tower passes into the water separator; The outlet of the water separator is connected to the propionic acid inlet at the top of the second distillation tower and the top of the first distillation tower respectively.

29. Process II according to claim 27, characterized in that: The number of plates of the first distillation tower and the number of plates of the second distillation tower are both 40 to 60.

30. Process II according to claim 27, characterized in that: The device II also includes a distillation tower III; The kettle of the second distillation tower is connected to the top of the third distillation tower, so that the logistics of the kettle of the second distillation tower is passed into the top of the third distillation tower; The bottom of the III distillation tower is connected to the azeotropic agent inlet at the top of the II distillation tower, so that the logistics of the bottom of the III distillation tower can be passed into the top of the II distillation tower.

31. Process method II according to claim 27, characterized in that: The number of plates of the III distillation tower is 40 to 60.

32. Process method II according to claim 27, characterized in that: The device II also includes a distillation column IV; The tower kettle of the first distillation tower is connected to the top of the fourth distillation tower, so that the logistics of the tower kettle of the first distillation tower is passed into the top of the fourth distillation tower; The top of the IV distillation tower is connected to the propionic acid inlet at the top of the I distillation tower, so that the top flow of the IV distillation tower passes into the top of the I distillation tower.

33. Process method II according to claim 27, characterized in that: The number of plates of the IV distillation tower is 40-60.

34. Process method II according to claim 27, characterized in that: The device II also includes a pre-reactor; One end of the pre-reactor is provided with an inlet for propionic acid and alcohol compounds; the other end of the pre-reactor is connected to the top of the first distillation tower.

35. Process method II according to claim 23, characterized in that: The molar ratio of the propionic acid to the alcohol compound is 1:1-1:

10.

36. Process method II according to claim 23, characterized in that: In the raw material containing propionic acid and alcohol compounds, the mass content of the catalyst II is 1-2%.

37. Process method II according to claim 23, characterized in that: The process operating conditions of the first distillation tower are: the tower top temperature is 55-110°C; the tower bottom temperature is 135-150°C; the tower top reflux ratio is 1:1-2:1; The process operating conditions of the second distillation tower are: the tower top temperature is 60-80°C; the tower bottom temperature is 80-100°C; and the tower top reflux ratio is 1:1~2.

38. Process II according to claim 23, characterized in that: In the step (a), the mass ratio of the stream obtained at the top of the first distillation tower to the azeotropic agent is 1:0.5-2.

39. Process method II according to claim 23, characterized in that: The stream obtained at the top of the II distillation tower is allowed to stand and then separated into layers. The alcohol compounds obtained after separation are recycled back to the reaction raw materials, and the n-heptane obtained is recycled back to the top of the II distillation tower.

40. Process method II according to claim 23, characterized in that In the step (a), the raw materials containing propionic acid and alcohol compounds are pre-reacted in a pre-reactor and then introduced into the top of the first distillation tower; The pre-reactor is filled with the catalyst II or the raw material containing propionic acid and alcohol compounds contains the catalyst II.

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