A double-effect azeotropic distillation device system for recovering acetic acid

Abstract

The utility model provides a kind of for recovering acetic acid double-effect azeotropic distillation device system, the device system includes one-effect rectification unit and two-effect rectification unit;The two-effect rectification unit includes two-effect rectification device and vacuumizing unit, and the bottom of two-effect rectification device is connected with second two-effect reboiler and first two-effect reboiler;The top outlet of two-effect rectification device is connected with two-effect gas phase product separation unit;The one-effect rectification unit includes one-effect rectification device, and the top outlet of one-effect rectification device is connected with one-effect gas phase product separation unit by first two-effect reboiler.The utility model reduces energy consumption and simplifies recovery process by simultaneously adding high concentration acetic acid, low concentration acetic acid and ester into rectification device for azeotropic distillation;Meanwhile, in order to further reduce energy consumption, it is designed into double-effect azeotropic distillation device, by steam of one-effect as heat source of two-effect, so as to realize the saving of energy.

Description

Technical Field

[0001] This utility model belongs to the field of acetic acid recovery technology, specifically relating to a double-effect azeotropic distillation device system for recovering acetic acid. Background Technology

[0002] Biomass refining, as a highly promising green chemical process, is receiving increasing attention. Biomass refining aims to transform biomass resources into high-value-added chemicals, materials, and energy products through a series of physical, chemical, and biological methods, which is of great significance for alleviating the energy crisis, reducing environmental pollution, and achieving carbon cycling.

[0003] Among numerous biomass refining processes, using acetic acid as a solvent exhibits unique advantages. Acetic acid possesses excellent dissolving properties, effectively processing various biomass feedstocks and promoting the decomposition and conversion of biomass. However, this process inevitably generates two streams of acetic acid solutions with different concentrations, posing challenges to subsequent acetic acid recovery and reuse.

[0004] One component is high-concentration acetic acid, with an acetic acid content ranging from 65% to 85% wt%. Currently, the general processing method for this high-concentration acetic acid is direct distillation to concentrate it to the desired concentration. However, this method has significant drawbacks. Because the distillation process requires a large amount of heat energy to vaporize and separate the acetic acid, it results in extremely high steam loss. This not only significantly increases production costs but also wastes energy from an energy utilization perspective.

[0005] The other component is low-concentration acetic acid, with a concentration between 5% and 30 wt%. Current methods for handling this low-concentration acetic acid are more complex. Typically, an extraction step is required to enrich the acetic acid from the low-concentration mixture. However, the resulting solution requires further processing, usually through azeotropic distillation using water as an azeotropic agent to concentrate it to the desired concentration. This entire process involves multiple operating units, requires significant equipment investment, and has a complex operational procedure. Each step requires strict control of conditions; even slight errors can affect the recovery efficiency and purity of the acetic acid, while also increasing labor and time costs during operation.

[0006] In summary, existing acetic acid recovery processes in biomass refining have significant shortcomings when handling both high-concentration and low-concentration acetic acid. There is an urgent need to develop an innovative, efficient, energy-saving, and easy-to-operate acetic acid recovery device and process to meet the needs of sustainable development in the biomass refining industry. Utility Model Content

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a double-effect azeotropic distillation system for recovering acetic acid. This invention reduces energy consumption and simplifies the recovery process by simultaneously adding high-concentration acetic acid, low-concentration acetic acid, and esters to the distillation unit for azeotropic distillation. Furthermore, to further reduce energy consumption, it is designed as a double-effect azeotropic distillation unit, using the steam from the first effect as the heat source for the second effect, thus achieving energy savings.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a double-effect azeotropic distillation system for recovering acetic acid, the system comprising a first-effect distillation unit and a second-effect distillation unit;

[0010] The double-effect distillation unit includes a double-effect distillation apparatus and a vacuum unit. A first double-effect reboiler and a second double-effect reboiler are connected in parallel at the bottom of the double-effect distillation apparatus. The top outlet of the double-effect distillation apparatus is connected to the double-effect gas phase product separation unit.

[0011] The vacuum pumping unit is used to provide a vacuum environment for the double-effect distillation unit;

[0012] The first-effect distillation unit includes a first-effect distillation device, and the top outlet of the first-effect distillation device is connected to the first-effect gas phase product separation unit through the first second-effect reboiler.

[0013] The side walls of the single-effect distillation unit and the double-effect distillation unit are independently provided with nitrogen inlet, acetic acid inlet, ester inlet and aqueous phase inlet, respectively.

[0014] In this invention, the acetic acid inlets on the side walls of the first-effect distillation apparatus and the second-effect distillation apparatus are used to transport a mixture of low-concentration acetic acid and high-concentration acetic acid; the mass ratio of the low-concentration acetic acid to the high-concentration acetic acid is 0.1 to 0.5:1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] More specifically, the concentration of the low-concentration acetic acid is 5 to 30 wt%, for example, it can be 5 wt%, 10 wt%, 20 wt% or 30 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] The concentration of the high-concentration acetic acid is 65-85 wt%, for example, it can be 65 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In addition, the bottom of the double-effect distillation apparatus of this invention is provided with a first double-effect reboiler and a second double-effect reboiler. The first double-effect reboiler can use the steam of the first-effect distillation apparatus for distillation, thereby realizing the reuse of the steam of the first-effect distillation apparatus. The second double-effect reboiler is used to supplement the heat of the double-effect distillation apparatus before the first-effect distillation apparatus is started, so as to realize the preheating of the double-effect distillation apparatus during startup. In summary, this design realizes both independent distillation of the double-effect distillation apparatus and reuse of the steam of the first-effect distillation apparatus.

[0018] This invention reduces energy consumption and simplifies the acetic acid recovery process by simultaneously adding high-concentration acetic acid, low-concentration acetic acid, and esters into a distillation unit (a single-effect distillation unit and a double-effect distillation unit) for azeotropic distillation. Furthermore, the steam from the single-effect distillation unit can be used as a heat source for the double-effect distillation unit, further saving energy. In summary, this invention achieves low-cost recovery of acetic acid (low-concentration and high-concentration acetic acid) obtained from biomass refining through a rationally designed double-effect azeotropic distillation system. The operation is simple and has broad prospects for industrial-scale production.

[0019] As a preferred technical solution of this utility model, the first-effect gas phase product separation unit includes a first-effect gas phase condenser and a first-effect phase separator connected in sequence.

[0020] Preferably, the gas phase outlet of the first double-effect reboiler is connected to the inlet of the first-effect gas phase condenser.

[0021] Preferably, the single-effect phase separator is provided with an azeotropic agent replenishment channel.

[0022] As a preferred embodiment of this utility model, the ester outlet of the first-effect phase separator is connected to the first-effect ester storage tank;

[0023] The outlet of the single-effect ester storage tank is divided into two branches by a single-effect distillation ester replenishment pump. One branch is connected to the ester inlet of the single-effect distillation unit, and the other branch is used for discharge.

[0024] As a preferred technical solution of this utility model, the water phase outlet of the first-effect phase separator is connected to the first-effect water phase storage tank;

[0025] Preferably, the outlet of the first-effect aqueous phase storage tank is divided into two branches by the first-effect aqueous phase transfer pump, one branch is connected to the aqueous phase inlet of the first-effect distillation unit, and the other branch is used for external discharge;

[0026] Preferably, a connecting line is provided between the first-effect phase separator and the first-effect aqueous phase storage tank to stabilize the pressure.

[0027] As a preferred technical solution of this utility model, a single-effect distillation discharge pump is provided at the bottom outlet of the single-effect distillation device.

[0028] Preferably, a reboiler is provided at the bottom of the single-effect distillation apparatus.

[0029] As a preferred embodiment of this utility model, the double-effect gas phase product separation unit includes a double-effect condenser and a double-effect phase separator connected in sequence.

[0030] Preferably, the double-effect phase separator is provided with an azeotropic agent replenishment channel.

[0031] Preferably, according to the gas phase flow direction at the top of the double-effect distillation unit, the double-effect condensation unit includes a first double-effect gas phase condenser and a second double-effect gas phase condenser connected in series.

[0032] In this invention, two condensers are continuously installed at the top outlet of the double-effect distillation device to achieve sufficient condensation and separation of the ester-water mixture, thereby reducing the water content in the upper layer of esters and the ester content in the lower layer of water in the double-effect phase separator.

[0033] As a preferred embodiment of this utility model, the ester outlet of the double-effect phase separator is connected to the double-effect ester storage tank; the aqueous phase outlet of the double-effect phase separator is connected to the double-effect aqueous phase storage tank.

[0034] Preferably, the double-effect ester storage tank is divided into two branches by a double-effect distillation ester replenishment pump, one branch is connected to the ester inlet of the double-effect distillation device, and the other branch is used for discharge.

[0035] Preferably, the outlet of the double-effect aqueous phase storage tank is divided into two branches by a double-effect aqueous phase transfer pump. One branch is connected to the aqueous phase inlet of the double-effect distillation unit, and the other branch is used for external discharge.

[0036] As a preferred embodiment of this invention, the vacuum pumping unit includes a vacuum buffer tank and a vacuum water ring pump connected in sequence.

[0037] In this invention, a vacuum water ring pump is used to achieve vacuum treatment of the double-effect distillation unit, so that the steam produced by the first-effect distillation unit can guarantee the operation of the double-effect distillation unit.

[0038] Preferably, the gas phase outlet of the second double-effect gas phase condenser is connected to the vacuum buffer tank.

[0039] As a preferred embodiment of this utility model, the double-effect phase separator, the double-effect ester storage tank, and the double-effect aqueous phase storage tank are each independently connected to the vacuum buffer tank via pressure regulating valves.

[0040] As a preferred technical solution of this utility model, a double-effect distillation discharge pump is provided at the bottom outlet of the double-effect distillation device.

[0041] It is worth noting that the single-effect distillation apparatus and the double-effect distillation apparatus of this utility model are each independently equipped with a temperature detection point, a pressure detection device, and a bottom acetic acid concentration detection device.

[0042] In addition, the first-effect gas phase condenser, the first-second-effect gas phase condenser, and the second-second-effect gas phase condenser of this utility model are each independently equipped with a circulating cooling water reuse pipe and a circulating cooling water supply pipe.

[0043] The first-effect reboiler and the second-effect reboiler are each independently equipped with steam delivery pipelines to provide an external heat source for the distillation unit.

[0044] For the double-effect distillation unit, a portion of the esters in the double-effect ester storage tank and a portion of the water in the double-effect aqueous phase storage tank are added to the double-effect distillation unit, while the remainder is discharged as wastewater; when the solute concentration in the vacuum buffer tank reaches a certain concentration, it is discharged into the wastewater.

[0045] The above-mentioned method of using the double-effect azeotropic distillation unit system for recovering acetic acid includes:

[0046] (1) Regarding the single-effect distillation unit:

[0047] Open the nitrogen valve of the first-effect distillation unit and supply nitrogen to the first-effect distillation unit through the nitrogen inlet. Then, automatically adjust the pressure of the first-effect distillation unit to 0.3 MPa. Acetic acid and esters are then simultaneously and continuously supplied to the first-effect distillation unit through the acetic acid inlet and the ester inlet.

[0048] By heating by inputting steam into the first-effect reboiler, after the temperature and pressure of each section of the first-effect distillation unit reach a stable state, esters and water are continuously extracted from the top of the first-effect distillation unit through azeotropic action, while acetic acid remains in the unit.

[0049] The gas phase at the top of the first-effect distillation unit is condensed by the first and second-effect reboilers and the first-effect gas phase condenser, and then separated by the first-effect phase separator to obtain esters and aqueous phases, which are then transported to the first-effect ester storage tank and the first-effect aqueous phase storage tank for storage, respectively.

[0050] By monitoring the changes at different temperature points on the single-effect distillation unit, it can be determined whether the ester or water content in the single-effect azeotropic distillation column is insufficient for azeotropic distillation, and ester or water should be added in a timely manner. As the ester and water are azeotropically distilled out, the acetic acid content at the bottom of the single-effect distillation unit continuously increases. The acetic acid concentration is detected by the acetic acid concentration detector at the bottom, and the bottom acetic acid is collected.

[0051] (2) Regarding the double-effect distillation unit

[0052] Open the nitrogen valve of the double-effect distillation unit and supply nitrogen to the double-effect distillation unit through the nitrogen inlet. Then, turn on the vacuum water ring pump to perform vacuum treatment and adjust the pressure of the double-effect distillation unit to -0.09MPa. Then, supply acetic acid and esters to the double-effect distillation unit simultaneously and continuously through the acetic acid inlet and the ester inlet.

[0053] Steam is introduced into the second reboiler for heating. Once steam is extracted from the first-effect distillation unit as a heat source for the second-effect distillation unit, the steam supply to the second reboiler is stopped. After the temperature and pressure of each section in the second-effect distillation unit reach a stable state, esters and water are continuously extracted from the top of the first-effect distillation unit through azeotropic action, while acetic acid remains in the unit.

[0054] The gas phase at the top of the double-effect distillation unit is condensed by the double-effect condenser and then separated by the double-effect phase separator to obtain esters and aqueous phases, which are then transported to the double-effect ester storage tank and the double-effect aqueous phase storage tank for storage, respectively.

[0055] By monitoring the changes at different temperature points on the double-effect distillation unit, it is determined whether the ester or water content in the double-effect azeotropic distillation column is insufficient for azeotropic distillation, and ester or water is added in a timely manner. As the ester and water are azeotropically distilled out, the acetic acid content at the bottom of the single-effect distillation unit continuously increases, and the acetic acid concentration at the bottom is detected by the acetic acid concentration detector to collect the bottom acetic acid.

[0056] It is worth noting that the top gas phase extracts of the first-effect distillation device and the second-effect distillation device of this utility model include esters and water. The esters include any one of ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert-butyl acetate, ethyl valerate, or glyceryl acetate.

[0057] In addition, esters can be used to recover acetic acid by mixing with low-concentration and high-concentration acetic acid. This is because esters form an azeotrope with water, which allows for distillation at a lower temperature under the same pressure, and acetic acid is not mixed in the ester-water azeotrope.

[0058] The numerical range described in this utility model includes not only the point values ​​listed above, but also any point values ​​within the numerical range not listed above. Due to space limitations and for the sake of brevity, this utility model will not exhaustively list the specific point values ​​included in the range.

[0059] The system refers to an equipment system, device system, or production device.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) The double-effect azeotropic distillation device system for recovering acetic acid provided by this utility model simplifies the recovery process of mixed acetic acid and reduces energy consumption by simultaneously adding high-concentration acetic acid, low-concentration acetic acid and esters into the first-effect distillation unit and the second-effect distillation unit.

[0062] (2) By optimizing the connection method between the first-effect distillation unit and the second-effect distillation unit, this utility model realizes the use of the steam of the first-effect distillation unit as the heat source of the second-effect distillation unit, thereby saving energy consumption and further realizing the efficient and low-cost recovery of mixed acetic acid.

[0063] (3) The concentration of acetic acid recovered by the double-effect azeotropic distillation device system for recovering acetic acid provided by this utility model shall not be less than 95 wt%. Attached Figure Description

[0064] Figure 1 This is a structural diagram of the double-effect azeotropic distillation apparatus system for recovering acetic acid provided in Embodiment 1 of this utility model;

[0065] Among them: 1 is a first-effect distillation feed pump; 2 is a first-effect reboiler; 3 is a first-effect distillation unit; 4 is a first-effect distillation ester replenishment pump; 5 is a first-effect ester storage tank; 6 is a first-effect phase separator; 7 is a first-effect vapor phase condenser; 8 is a second-effect distillation unit; 9 is a first-effect aqueous phase storage tank; 10 is a first-effect aqueous phase transfer pump; 11 is a second-effect distillation feed pump; 12 is a first-second-effect reboiler; 13 is a second-second-effect reboiler; 14 is a first-second-effect vapor phase condenser; 15 is a second-second-effect vapor phase condenser; 16 is a second-effect distillation ester replenishment pump; 17 is a second-effect ester storage tank; 18 is a second-effect phase separator; 19 is a second-effect aqueous phase storage tank; 20 is a second-effect aqueous phase transfer pump; 21 is a vacuum buffer tank; 22 is a vacuum water ring pump. Detailed Implementation

[0066] It should be understood that in the description of this utility model, the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0067] It should be noted that, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0068] The technical solution of this utility model will be further described below with reference to the accompanying drawings and specific embodiments.

[0069] In one specific embodiment, this utility model provides a double-effect azeotropic distillation system for recovering acetic acid, such as... Figure 1 As shown, the device system includes a first-effect distillation unit and a second-effect distillation unit;

[0070] The double-effect distillation unit includes a double-effect distillation device 8 and a vacuum unit. A first double-effect reboiler 12 and a second double-effect reboiler 13 are connected in parallel at the bottom of the double-effect distillation device 8. The top outlet of the double-effect distillation device 8 is connected to the double-effect gas phase product separation unit.

[0071] The vacuum pumping unit is used to provide a vacuum environment for the double-effect distillation unit;

[0072] The first-effect distillation unit includes a first-effect distillation device 3, and the top outlet of the first-effect distillation device 3 is connected to the first-effect gas phase product separation unit through the first second-effect reboiler 12.

[0073] The side walls of the single-effect distillation unit 3 and the double-effect distillation unit 8 are independently provided with nitrogen inlet, acetic acid inlet, ester inlet and aqueous phase inlet, respectively.

[0074] The first-effect gas phase product separation unit includes a first-effect gas phase condenser 7 and a first-effect phase separator 6 connected in sequence; the gas phase outlet of the first second-effect reboiler 12 is connected to the inlet of the first-effect gas phase condenser 7; the first-effect phase separator 6 is provided with an azeotropic agent replenishment channel.

[0075] The ester outlet of the first-effect phase separator 6 is connected to the first-effect ester storage tank 5; the outlet of the first-effect ester storage tank 5 is divided into two branches by the first-effect distillation ester replenishment pump 4, one branch is connected to the ester inlet of the first-effect distillation device 3, and the other branch is used for discharge.

[0076] The water phase outlet of the first-effect phase separator 6 is connected to the first-effect water phase storage tank 9; the outlet of the first-effect water phase storage tank 9 is divided into two branches by the first-effect water phase transfer pump 10, one branch is connected to the water phase inlet of the first-effect distillation unit 3, and the other branch is used for external discharge.

[0077] A connecting line is provided between the first-effect phase separator 6 and the first-effect aqueous phase storage tank 9 to stabilize the pressure; a first-effect distillation discharge pump 1 is provided at the bottom outlet of the first-effect distillation device 3; a first-effect reboiler 2 is provided at the bottom of the first-effect distillation device 3.

[0078] The double-effect gas phase product separation unit includes a double-effect condenser unit and a double-effect phase separator 18 connected in sequence; according to the gas phase flow direction at the top of the double-effect distillation unit 8, the double-effect condenser unit includes a first double-effect gas phase condenser 14 and a second double-effect gas phase condenser 15 connected in series; the liquid outlet of the double-effect condenser unit is connected to the double-effect phase separator 18.

[0079] The ester outlet of the double-effect phase separator 18 is connected to the double-effect ester storage tank 17; the aqueous phase outlet of the double-effect phase separator 18 is connected to the double-effect aqueous phase storage tank 19; the double-effect ester storage tank 17 is divided into two branches by the double-effect distillation ester replenishment pump 16, one branch is connected to the ester inlet of the double-effect distillation device 8, and the other branch is used for discharge; the outlet of the double-effect aqueous phase storage tank 19 is divided into two branches by the double-effect aqueous phase transfer pump 20, one branch is connected to the aqueous phase inlet of the double-effect distillation device 8, and the other branch is used for external discharge;

[0080] The vacuum pumping unit includes a vacuum buffer tank 21 and a vacuum water ring pump 22 connected in sequence; the double-effect phase separator 18, the double-effect ester storage tank 17, and the double-effect aqueous phase storage tank 19 are independently connected to the vacuum buffer tank 21 through pressure regulating valves; the bottom outlet of the double-effect distillation device 8 is equipped with a double-effect distillation discharge pump 11.

[0081] Example 1

[0082] This embodiment provides a double-effect azeotropic distillation system for recovering acetic acid, such as... Figure 1 As shown, the device system includes a first-effect distillation unit and a second-effect distillation unit;

[0083] The double-effect distillation unit includes a double-effect distillation device 8 and a vacuum unit. A first double-effect reboiler 12 and a second double-effect reboiler 13 are connected in parallel at the bottom of the double-effect distillation device 8. The top outlet of the double-effect distillation device 8 is connected to the double-effect gas phase product separation unit.

[0084] The vacuum pumping unit is used to provide a vacuum environment for the double-effect distillation unit;

[0085] The first-effect distillation unit includes a first-effect distillation device 3, and the top outlet of the first-effect distillation device 3 is connected to the first-effect gas phase product separation unit through the first second-effect reboiler 12.

[0086] The side walls of the single-effect distillation unit 3 and the double-effect distillation unit 8 are independently provided with nitrogen inlet, acetic acid inlet, ester inlet and aqueous phase inlet, respectively.

[0087] The first-effect gas phase product separation unit includes a first-effect gas phase condenser 7 and a first-effect phase separator 6 connected in sequence; the gas phase outlet of the first second-effect reboiler 12 is connected to the inlet of the first-effect gas phase condenser 7; the first-effect phase separator 6 is provided with an azeotropic agent replenishment channel.

[0088] The ester outlet of the first-effect phase separator 6 is connected to the first-effect ester storage tank 5; the outlet of the first-effect ester storage tank 5 is divided into two branches by the first-effect distillation ester replenishment pump 4, one branch is connected to the ester inlet of the first-effect distillation device 3, and the other branch is used for discharge.

[0089] The water phase outlet of the first-effect phase separator 6 is connected to the first-effect water phase storage tank 9; the outlet of the first-effect water phase storage tank 9 is divided into two branches by the first-effect water phase transfer pump 10, one branch is connected to the water phase inlet of the first-effect distillation unit 3, and the other branch is used for external discharge.

[0090] A connecting line is provided between the first-effect phase separator 6 and the first-effect aqueous phase storage tank 9 to stabilize the pressure; a first-effect distillation discharge pump 1 is provided at the bottom outlet of the first-effect distillation device 3; a first-effect reboiler 2 is provided at the bottom of the first-effect distillation device 3.

[0091] The double-effect gas phase product separation unit includes a double-effect condenser unit and a double-effect phase separator 18 connected in sequence; according to the gas phase flow direction at the top of the double-effect distillation unit 8, the double-effect condenser unit includes a first double-effect gas phase condenser 14 and a second double-effect gas phase condenser 15 connected in series; the liquid outlet of the double-effect condenser unit is connected to the double-effect phase separator 18.

[0092] The ester outlet of the double-effect phase separator 18 is connected to the double-effect ester storage tank 17; the aqueous phase outlet of the double-effect phase separator 18 is connected to the double-effect aqueous phase storage tank 19; the double-effect ester storage tank 17 is divided into two branches by the double-effect distillation ester replenishment pump 16, one branch is connected to the ester inlet of the double-effect distillation device 8, and the other branch is used for discharge; the outlet of the double-effect aqueous phase storage tank 19 is divided into two branches by the double-effect aqueous phase transfer pump 20, one branch is connected to the aqueous phase inlet of the double-effect distillation device 8, and the other branch is used for external discharge;

[0093] The vacuum unit includes a vacuum buffer tank 21 and a vacuum water ring pump 22 connected in sequence; the double-effect phase separator 18, the double-effect ester storage tank 17, and the double-effect aqueous phase storage tank 19 are independently connected to the vacuum buffer tank 21 through pressure regulating valves; the bottom outlet of the double-effect distillation device 8 is equipped with a double-effect distillation discharge pump 11.

[0094] Example 2

[0095] This embodiment provides a double-effect azeotropic distillation system for recovering acetic acid. The only difference between this double-effect azeotropic distillation system and that of Embodiment 1 is:

[0096] This embodiment omits the inclusion of the second double-effect gas phase condenser.

[0097] Example 3

[0098] This embodiment provides a double-effect azeotropic distillation system for recovering acetic acid. The only difference between this double-effect azeotropic distillation system and that of Embodiment 1 is:

[0099] This embodiment omits the branch line between the single-effect ester storage tank and the single-effect distillation unit.

[0100] Example 4

[0101] This embodiment provides a double-effect azeotropic distillation system for recovering acetic acid. The only difference between this double-effect azeotropic distillation system and that of Embodiment 1 is:

[0102] This embodiment omits the branch line between the two-effect ester storage tank and the two-effect distillation unit.

[0103] Comparative Example 1

[0104] This comparative example provides a double-effect azeotropic distillation apparatus system for recovering acetic acid. The only difference between this double-effect azeotropic distillation apparatus system and Example 1 is that:

[0105] This comparative example omits the setting of the second double-effect reboiler.

[0106] Comparative Example 2

[0107] This comparative example provides a double-effect azeotropic distillation apparatus system for recovering acetic acid. The only difference between this double-effect azeotropic distillation apparatus system and Example 1 is that:

[0108] This comparative example omits the setup of the first and second reboilers.

[0109] Comparative Example 3

[0110] This comparative example provides a double-effect azeotropic distillation apparatus system for recovering acetic acid. The only difference between this double-effect azeotropic distillation apparatus system and Example 1 is that:

[0111] This comparative example omits the vacuum pumping unit.

[0112] Application examples

[0113] The double-effect azeotropic distillation apparatus system for recovering acetic acid provided in the above embodiments and comparative examples is used to recover acetic acid, wherein the mass ratio of low-concentration acetic acid to high-concentration acetic acid during the recovery process is:

[0114] The concentration of the low-concentration acetic acid is 5-30 wt%, and the concentration of the high-concentration acetic acid is 65-85 wt%.

[0115] Analysis of the recycling results reveals the following:

[0116] (1) Analysis of Example 1 shows that the device system provided by this utility model can achieve efficient and low-energy recovery of mixed acetic acid, and the concentration of the recovered acetic acid is not less than 95 wt%, and the recovery rate is not less than 99.8%.

[0117] (2) Comprehensive analysis of Examples 1 and 2 shows that omitting one of the two-effect gas phase condensers in the two-effect condensation unit will result in a higher water content in the esters, affecting the efficiency of ester recycling; a higher ester content in the water will result in a larger loss of esters.

[0118] (3) Comprehensive analysis of Examples 1 and 3-4 shows that the device system provided in Examples 3-4 cannot provide ester feedstock for the distillation device, which leads to the inability to effectively form azeotropic distillation in the distillation device, resulting in acetic acid being drawn off at the top of the column, reducing the recovery rate, and consuming more energy.

[0119] (4) According to the comprehensive analysis of Example 1 and Comparative Example 1, omitting the second double-effect reboiler will cause the double-effect distillation unit to fail to operate when the heat source cannot be provided by the first-effect distillation unit; when the heat source is effectively provided by the first-effect distillation unit, the double-effect distillation unit will fail to reach a stable state in the early stage of startup, which will greatly reduce the system output.

[0120] (5) A comprehensive analysis of Example 1 and Comparative Example 2 shows that omitting the first double-effect reboiler will cause the entire operation of the double-effect distillation unit to be powered by the second double-effect reboiler, which will not achieve the energy-saving effect.

[0121] (6) According to the comprehensive analysis of Example 1 and Comparative Example 3, omitting the vacuum unit will prevent the second-effect distillation unit from achieving a vacuum state during operation, which will result in the steam of the first-effect distillation column not being able to ensure the effective operation of the second-effect distillation column. The second second-effect reboiler is required to supplement the steam, which increases energy consumption.

[0122] In summary, this invention reduces energy consumption and simplifies the recovery process by simultaneously adding high-concentration acetic acid, low-concentration acetic acid, and esters to a distillation apparatus for azeotropic distillation. Furthermore, to further reduce energy consumption, a double-effect azeotropic distillation apparatus is designed, using the steam from the first effect as the heat source for the second effect, thereby achieving energy savings.

[0123] The applicant declares that the above description is only a specific embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present utility model fall within the protection and disclosure scope of the present utility model.

Claims

1. A double-effect azeotropic distillation system for recovering acetic acid, characterized in that, The device system includes a single-effect distillation unit and a double-effect distillation unit; The double-effect distillation unit includes a double-effect distillation apparatus and a vacuum unit. A first double-effect reboiler and a second double-effect reboiler are connected in parallel at the bottom of the double-effect distillation apparatus. The top outlet of the double-effect distillation apparatus is connected to the double-effect gas phase product separation unit. The vacuum pumping unit is used to provide a vacuum environment for the double-effect distillation unit; The first-effect distillation unit includes a first-effect distillation device, and the top outlet of the first-effect distillation device is connected to the first-effect gas phase product separation unit through the first second-effect reboiler. The side walls of the single-effect distillation unit and the double-effect distillation unit are independently provided with nitrogen inlet, acetic acid inlet, ester inlet and aqueous phase inlet, respectively.

2. The double-effect azeotropic distillation system for recovering acetic acid according to claim 1, characterized in that, The single-effect gas phase product separation unit includes a single-effect gas phase condenser and a single-effect phase separator connected in sequence. The gas phase outlet of the first two-effect reboiler is connected to the inlet of the first-effect gas phase condenser; The single-effect phase separator is equipped with an azeotropic agent replenishment channel.

3. The double-effect azeotropic distillation system for recovering acetic acid according to claim 2, characterized in that, The ester outlet of the first-effect phase separator is connected to the first-effect ester storage tank; The outlet of the single-effect ester storage tank is divided into two branches by a single-effect distillation ester replenishment pump. One branch is connected to the ester inlet of the single-effect distillation unit, and the other branch is used for discharge.

4. The double-effect azeotropic distillation system for recovering acetic acid according to claim 2, characterized in that, The water phase outlet of the first-effect phase separator is connected to the first-effect water phase storage tank; The outlet of the first-effect aqueous phase storage tank is divided into two branches by the first-effect aqueous phase transfer pump. One branch is connected to the aqueous phase inlet of the first-effect distillation unit, and the other branch is used for external discharge. A connecting line is provided between the first-effect phase separator and the first-effect aqueous phase storage tank to stabilize the pressure.

5. The double-effect azeotropic distillation system for recovering acetic acid according to claim 1, characterized in that, A single-effect distillation discharge pump is installed at the bottom outlet of the single-effect distillation unit. The bottom of the single-effect distillation unit is equipped with a single-effect reboiler.

6. The double-effect azeotropic distillation system for recovering acetic acid according to claim 1, characterized in that, The double-effect gas phase product separation unit includes a double-effect condenser and a double-effect phase separator connected in sequence. Based on the gas phase flow direction at the top of the double-effect distillation unit, the double-effect condensation unit includes a first double-effect gas phase condenser and a second double-effect gas phase condenser connected in series.

7. The double-effect azeotropic distillation system for recovering acetic acid according to claim 6, characterized in that, The ester outlet of the double-effect phase separator is connected to the double-effect ester storage tank; the aqueous phase outlet of the double-effect phase separator is connected to the double-effect aqueous phase storage tank. The double-effect ester storage tank is divided into two branches by a double-effect distillation ester replenishment pump. One branch is connected to the ester inlet of the double-effect distillation unit, and the other branch is used for discharge. The outlet of the double-effect aqueous phase storage tank is divided into two branches by the double-effect aqueous phase transfer pump. One branch is connected to the aqueous phase inlet of the double-effect distillation unit, and the other branch is used for external discharge.

8. The double-effect azeotropic distillation system for recovering acetic acid according to claim 7, characterized in that, The vacuum pumping unit includes a vacuum buffer tank and a vacuum water ring pump connected in sequence. The gas phase outlet of the second double-effect gas phase condenser is connected to the vacuum buffer tank.

9. The double-effect azeotropic distillation system for recovering acetic acid according to claim 8, characterized in that, The double-effect phase separator, the double-effect ester storage tank, and the double-effect aqueous phase storage tank are each independently connected to the vacuum buffer tank via pressure regulating valves.

10. The double-effect azeotropic distillation system for recovering acetic acid according to claim 1, characterized in that, The bottom outlet of the double-effect distillation unit is equipped with a double-effect distillation discharge pump.

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