A separation and recovery system and process for ester-alcohol mixed solvents

Abstract

This invention discloses a separation and recovery system and process for mixed ester and alcohol solvents, relating to the field of mixed solvent recovery technology. The recovery system includes an extraction unit, a first adsorption unit, a multi-stage distillation unit, a second adsorption unit, a cryogenic crystallization unit, a filtration unit, and a DCS control unit connected in sequence. The extraction unit is used to remove free water from the mixed solvent; the first adsorption unit is a 3Å molecular sieve column used to adsorb and remove dissolved water; the multi-stage distillation unit is used to separate the organic phase into single components; the second adsorption unit is a 4Å molecular sieve column used to adsorb and remove impurities; the cryogenic crystallization unit is used to cool and crystallize dissolved water; the filtration unit is used to filter out ice crystals; and the DCS control unit is used to solidify process parameters and achieve fully automated control of the entire process. This invention can efficiently separate and recover mixed ester and alcohol solvents, with a recovered solvent purity ≥99.9%, which can be directly reused in the production line.

Description

Technical Field

[0001] This invention relates to the field of mixed solvent recovery technology, and in particular to a separation and recovery system and process for ester-alcohol mixed solvents. Background Technology

[0002] In industrial sectors that easily generate volatile organic compounds (VOCs), such as spraying, printing, electronic cleaning, and pharmaceutical synthesis, companies commonly employ technologies like adsorption, absorption, and condensation to treat waste gases in response to increasingly stringent environmental regulations controlling VOC emissions. One of the core objectives of these treatment technologies is to recover the organic solvent components carried in the waste gases, achieving resource recycling and reducing environmental pollution.

[0003] However, the solvents recovered by VOCs waste gas treatment systems are usually multi-component mixtures of esters (such as ethyl acetate, propyl acetate, butyl acetate, etc.) and alcohols (such as isopropanol, ethanol, n-butanol, etc.). Due to the easy introduction of impurities such as moisture, particulate matter, and reaction byproducts during waste gas treatment, the recovered mixed solvents generally suffer from the following problems: First, high water content, often accompanied by water vapor entrainment or condensate during waste gas treatment, resulting in a large amount of free and dissolved water in the recovered solvent; second, complex composition, with large fluctuations in the proportion of esters and alcohols in waste gas emitted from different production processes, making it difficult to separate components with similar boiling points; and third, high impurity content, containing small amounts of by-reaction products and mechanical impurities in addition to the target solvent.

[0004] The aforementioned issues prevent the recycled solvent from being directly reused in production lines with stringent requirements for solvent purity and stability. If reused directly without effective treatment, residual moisture can easily trigger hydrolysis, affecting product quality or causing production process malfunctions; the mixing of ester and alcohol components can cause the solvent's solubility to deviate from process requirements; and trace impurities may gradually accumulate during recycling, ultimately affecting product quality.

[0005] Existing technologies for treating this type of recovered mixed solvent have significant shortcomings: First, the dehydration process is relatively simple, mostly relying on simple adsorption or atmospheric distillation, which makes it difficult to reduce the water content to an acceptable low level for the production line (usually requiring ≤100ppm), and the processing efficiency is low and energy consumption is high; Second, component separation mostly adopts a single-tower distillation mode, which makes it difficult to achieve accurate separation for esters and alcohols with small boiling point differences, and the purity of the finished product is usually below 99%, which cannot meet the needs of high-end manufacturing; Third, the entire process lacks systematic automated control, and the adsorbent failure warning, distillation parameter adjustment and product quality detection are disconnected, which easily leads to fluctuations in the purity of the treated solvent and makes it difficult to achieve stable production line reuse. Summary of the Invention

[0006] The purpose of this invention is to provide a separation and recovery system and process for ester-alcohol mixed solvents, in order to solve the problems existing in the prior art and achieve efficient separation and high-purity recovery of the main components of complex mixed solvent systems containing multiple esters, alcohols and a small amount of water.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a separation and recovery system for ester-alcohol mixed solvents, comprising: an extraction unit, a first adsorption unit, a distillation unit, a second adsorption unit, a cryogenic crystallization unit, a filtration unit, and a DCS control unit. The extraction unit has a light liquid outlet and a heavy liquid outlet, used to remove free water from the ester-alcohol mixed solvent, forming an organic phase (with free water removed) and an aqueous extract phase. The inlet of the first adsorption unit is connected to the light liquid outlet of the extraction unit, used to adsorb and remove dissolved water and remaining free water from the organic phase. The distillation unit includes multiple distillation columns connected in sequence, the inlet of the first distillation column being connected to the... The outlet of the first adsorption unit is connected to multiple distillation columns for separating the organic phase after removing dissolved water into single components; the inlet of the second adsorption unit is connected to the outlet of each component of the distillation unit for adsorbing and removing impurities in the single components; the inlet of the cryogenic crystallization unit is connected to the outlet of the second adsorption unit for cooling the adsorbed single components to allow dissolved water to crystallize and precipitate; the inlet of the filtration unit is connected to the outlet of the cryogenic crystallization unit for filtering out the precipitated ice crystals; and the DCS control unit is connected to the signals of each of the aforementioned units for solidifying process parameters and realizing fully automated control of the entire process.

[0008] Preferably, the extraction unit includes a mixed solvent feed tank, an extraction tower, an oil-water separator, and an extract water storage tank; the heavy liquid outlet of the extraction tower is connected to the oil-water separator, the light phase outlet of the oil-water separator is connected to the mixed solvent feed tank, the heavy phase outlet of the oil-water separator is connected to the extract water storage tank, and the outlet of the extract water storage tank is connected to the light liquid inlet of the extraction tower.

[0009] Preferably, the extraction tower has a heavy liquid inlet at the top and a light liquid inlet at the bottom. A rotary table and a fixed table are coaxially installed inside the tower, and the rotary table is connected to a variable frequency motor. An electromagnetic flow meter and a pneumatic regulating valve are connected in series on the pipes of the light liquid inlet and the heavy liquid inlet, respectively. A differential pressure level gauge is installed in the middle of the extraction tower to detect the stratification interface. The electromagnetic flow meter, differential pressure level gauge, variable frequency motor, and pneumatic regulating valve are all connected to the DCS control unit for signal transmission.

[0010] Preferably, the first adsorption unit includes multiple 3Å molecular sieve adsorption towers connected in parallel, and the second adsorption unit includes multiple 4Å molecular sieve adsorption towers connected in parallel; the feed inlet of each 3Å molecular sieve adsorption tower is connected to the light liquid outlet of the extraction unit through a switching valve, and the feed inlet of each 4Å molecular sieve adsorption tower is connected to the component outlets of the distillation unit through a switching valve, for switching to another adsorption tower when one adsorption tower reaches saturation; each adsorption tower is provided with a support grid, a molecular sieve adsorption bed and a feed distributor in sequence from bottom to top; multiple temperature sensors are provided in the bed area of ​​each adsorption tower, a pressure sensor is provided in the gas phase space at the top of the tower, a regulating valve is provided on the feed pipe, and a shut-off valve is provided on the feed pipe and the discharge pipe; each switching valve, regulating valve, shut-off valve and sensor is connected to the DCS control unit for signal transmission.

[0011] Preferably, the distillation unit includes a short column, a main distillation column, and a long column connected in sequence; each column is connected to a condenser and a reflux condenser at the top, and the reflux condenser has a reflux branch and a product branch at the bottom. A reflux pump is installed on the reflux branch, and the product branch is connected to a buffer tank; a side product outlet is provided in the upper middle section of the main distillation column; a reboiler is provided at the bottom of each column; a temperature sensor is installed at the top and bottom of each column, a pressure sensor is installed at the top of the column, and flow sensors are installed on the product branch, reflux branch, and side product branch. All sensors, reboilers, and reflux pumps are connected to the DCS control unit.

[0012] Preferably, the outlet of the filtration unit is connected to a post-refining buffer tank, and the discharge pipe of the post-refining buffer tank is equipped with an online moisture analyzer and an online chromatograph connected to the DCS control unit. The discharge pipe is connected to a reflux branch and multiple product branches. The reflux branch is connected to the inlet of the second adsorption unit, and the multiple product branches are connected to multiple solvent storage tanks. The reflux branch is equipped with a shut-off valve connected to the DCS control unit, and each of the product branches is equipped with a shut-off valve connected to the DCS control unit.

[0013] Preferably, the cryogenic crystallization unit is a deep condenser, and the filtration unit is a membrane separation filtration assembly with a filtration accuracy of 0.1~0.3μm.

[0014] The present invention also provides a process for separating and recovering mixed ester and alcohol solvents based on the system described above, comprising the following steps: (1) Extraction and water separation: The ester alcohol mixed solvent containing free water and the extractant are introduced into the extraction unit. The feed ratio of the extractant and the mixed solvent is fixed by the DCS control unit to control the layer interface height in the extraction unit, remove the free water in the mixed solvent, and obtain the organic phase and the aqueous extract phase after the free water is removed. (2) Oil-water separation and circulation: The aqueous extract phase obtained in step (1) is passed into an oil-water separator for static separation. The separated trace organic phase is returned to the mixed solvent raw material tank. The separated extract phase is circulated back to the extraction unit after being mixed with water in the extract liquid storage tank. (3) Deep dehydration: The organic phase obtained in step (1) after removing free water is introduced into the first adsorption unit. The feed flow rate is controlled by the DCS control unit so that the organic phase stays in the first adsorption unit for a sufficient time to adsorb and remove the dissolved water therein, and an organic phase with a water content ≤500ppm is obtained. (4) Multi-stage distillation separation: The organic phase obtained in step (3) is sequentially fed into multiple distillation columns of the distillation unit, and the reflux ratio of each column is fixed by the DCS control unit to separate different single components; (5) Refining and purification: Each single component obtained in step (4) is passed into the second adsorption unit to adsorb and remove trace impurities, then passed into the cryogenic crystallization unit to cool to -5°C to crystallize and precipitate dissolved water, and finally passed into the filtration unit to filter out ice crystals to obtain the refined single component. The process parameters in each of the above steps are monitored and automatically adjusted in real time by the DCS control unit, realizing full-process automated control.

[0015] Preferably, it also includes: (6) detection and reuse: the purified single component obtained in step (5) is detected by an online moisture analyzer and an online chromatograph. The qualified product is stored in the solvent storage tank for reuse, and the unqualified product is returned to the inlet of the second adsorption unit through the reflux branch for re-refinement. The extractant in step (1) is methanol or ethanol, the feed volume ratio of extractant to mixed solvent is 1:3 to 1:5, the layer interface height is controlled at 40% to 60% of the height of the extraction unit tower, the water separation efficiency is ≥95%, and more than 80% of free water is separated.

[0016] Preferably, the distillation unit in step (4) includes a short column, a main distillation column and a long column connected in sequence; The short column has a reflux ratio of 1:1.5 to 1:2.5 and the feed inlet is 4 to 6 meters from the bottom of the column. It is used to separate alcohol components with the lowest boiling point. The main distillation column has a reflux ratio of 1:4 to 1:6, the feed inlet is 7 to 9 m from the bottom of the column, and a side stream outlet is provided in the upper middle section of the column, 6 to 8 m from the top of the column, for separating low-boiling-point esters from the top of the column and medium-boiling-point esters from the side stream. The long column has a reflux ratio of 1:7 to 1:9 and the feed inlet is 9 to 11 m from the bottom of the column. It is used to purify high-boiling-point components. The cooling temperature of the cryogenic crystallization unit in step (5) is -5℃, and the filtration accuracy of the filtration unit is 0.1~0.3μm; The qualified standards for step (6) are: purity ≥ 99.9%, impurity content ≤ 1 ppm, and water content ≤ 10 ppm.

[0017] The present invention achieves the following technical effects compared to the prior art: This embodiment divides the system into modular structures such as extraction, adsorption, distillation, cryogenic crystallization, and filtration units, and establishes an orderly interconnection between these units, forming a complete processing chain of "extraction for water separation → adsorption for dehydration → distillation for separation → adsorption for purification → cryogenic crystallization → filtration for de-icing." Because each unit has a clear division of labor and processes materials sequentially, it can remove different forms of water (free water and dissolved water) and impurities of different properties from ester-alcohol mixed solvents using the most suitable methods, avoiding the limitations of single-treatment methods. Simultaneously, the DCS control unit is connected to each unit's signals, enabling real-time acquisition of process parameters and automatic adjustment of actuators, achieving fully automated and coordinated control of the entire process. This ensures long-term stable operation of the entire system, ultimately achieving a high-purity standard for direct reuse of the recovered solvent. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the separation and recovery system for ester-alcohol mixed solvents provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the extraction tower provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a distillation unit provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the molecular sieve adsorption tower provided in an embodiment of the present invention; Figure 5 This is a block diagram of the control logic of the DCS control unit provided in an embodiment of the present invention; Figure 6 The logic control diagram of PLC substation 2 (adsorption unit) and DCS master station provided in the embodiment of the present invention.

[0020] In the diagram: 1-Mixed solvent feed tank; 2-Extraction tower; 3-Oil-water separator; 4-Extractant water storage tank; 5-3Å molecular sieve adsorption tower; 6-Short tower; 7-Main distillation tower; 8-Long tower; 9-4Å molecular sieve adsorption tower; 10-Cryogenic crystallization unit; 11-Filtration unit; 12-Online chromatograph; 13-Online moisture analyzer; 14-DCS control unit; 15-First buffer tank; 16-Second buffer tank; 17-Third buffer tank; 18-Fourth buffer tank; 19-Pre-refining buffer tank; 20-Post-refining buffer tank; 21-First solvent storage tank; 22-Second solvent storage tank; 23-Third solvent storage tank; 24-Fourth solvent storage tank; 25-Heavy liquid inlet; 26-Light liquid inlet; 27-Heavy liquid outlet; 28-Light liquid outlet; 29-Drain port; 30-Variable frequency drive Machine; 31-Pressure transmitter; 32-Grid plate; 33-Fixed disc; 34-Rotary disc; 35-Manhole; 36-First electromagnetic flowmeter; 37-Second electromagnetic flowmeter; 38-First pneumatic regulating valve; 39-Second pneumatic regulating valve; 40-Third pneumatic regulating valve; 41-Pneumatic shut-off valve; 42-Differential pressure level gauge; 43-Molecular sieve inlet; 44-Feed distributor; 45-Molecular sieve adsorption bed; 46-Support grid; 47-Outlet; 48-First temperature sensor; 49-Second temperature sensor; 50-Third temperature sensor; 51-First condenser; 52-Second condenser; 53-Third condenser; 54-First reboiler; 55-Second reboiler; 56-Third reboiler; 57-First reflux condenser; 58-Second reflux condenser; 59-Third reflux condenser. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The purpose of this invention is to provide a separation and recovery system and process for ester-alcohol mixed solvents, in order to solve the problems existing in the prior art and achieve efficient separation and high-purity recovery of the main components of complex mixed solvent systems containing multiple esters, alcohols and a small amount of water.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] The following is combined with Figures 1 to 6 The following describes embodiments of the present invention.

[0025] Example 1 This invention provides a separation and recovery system for a mixed ester and alcohol solvent, comprising: an extraction unit, a first adsorption unit, a distillation unit, a second adsorption unit, a cryogenic crystallization unit 10, a filtration unit 11, and a DCS control unit 14. The extraction unit has a light liquid outlet 28 and a heavy liquid outlet 27 for removing free water from the mixed ester and alcohol solvent, forming an organic phase (with free water removed) and an aqueous extract phase. The inlet of the first adsorption unit is connected to the light liquid outlet 28 of the extraction unit for adsorbing and removing remaining free water and dissolved water from the organic phase. The distillation unit includes multiple distillation columns connected in sequence, the first of which... The inlet of the distillation column is connected to the outlet of the first adsorption unit. Multiple distillation columns are used to separate the organic phase after removing dissolved water into single components. The inlet of the second adsorption unit is connected to the outlet of each component of the distillation unit and is used to adsorb and remove impurities in the single components. The inlet of the cryogenic crystallization unit 10 is connected to the outlet of the second adsorption unit and is used to cool the adsorbed single components to allow dissolved water to crystallize and precipitate. The inlet of the filtration unit 11 is connected to the outlet of the cryogenic crystallization unit 10 and is used to filter out the precipitated ice crystals. The DCS control unit 14 is connected to the signals of each of the aforementioned units and is used to solidify process parameters and realize full-process automated control.

[0026] This embodiment divides the system into modular structures such as an extraction unit, an adsorption unit, a distillation unit, a cryogenic crystallization unit 10, and a filtration unit 11, and establishes an orderly interconnection between these units, forming a complete processing chain of "extraction for water separation → adsorption for dehydration → distillation for separation → adsorption for purification → cryogenic crystallization → filtration for de-icing". Because each unit has a clear division of labor and processes materials sequentially, it can remove different forms of water (free water, dissolved water) and impurities of different properties from ester-alcohol mixed solvents using the most suitable methods, avoiding the limitations of single-method treatment. Simultaneously, the DCS control unit 14 is connected to the signals of each unit, enabling real-time acquisition of process parameters and automatic adjustment of actuators, achieving fully automated and coordinated control of the entire process. This ensures the long-term stable operation of the entire system, ultimately achieving a high-purity standard for direct reuse of the recovered solvent.

[0027] In some embodiments, the extraction unit includes a mixed solvent feed tank 1, an extraction tower 2, an oil-water separator 3, and an extract water storage tank 4; the heavy liquid outlet 27 of the extraction tower 2 is connected to the oil-water separator 3, the light phase outlet of the oil-water separator 3 is connected to the mixed solvent feed tank 1, the heavy phase outlet of the oil-water separator 3 is connected to the extract water storage tank 4, and the outlet of the extract water storage tank 4 is connected to the light liquid inlet 26 of the extraction tower 2.

[0028] This embodiment constructs a closed-loop circulation system for the extractant by setting up an oil-water separator 3 and an extractant water storage tank 4. The aqueous extractant phase discharged from the bottom of the extraction tower 2 enters the oil-water separator 3, where it is separated into a trace organic phase and an extractant phase. The trace organic phase is recycled back to the mixed solvent feed tank 1 to participate in the extraction again, avoiding the loss of useful solvent. The extractant phase enters the extractant water storage tank 4, and can be adjusted to a suitable concentration and recycled back to the extraction tower 2 as needed. Because the extractant is recycled, the consumption of extractant and operating costs are significantly reduced, while waste liquid discharge is also reduced, meeting green environmental protection requirements. Furthermore, the reflux design of the trace organic phase further improves the overall solvent recovery rate.

[0029] In some examples, the oil-water separator 3 can be other oil-water separation equipment, such as coalescing plate separators, hydrocyclones, or membrane separators; the extract water storage tank 4 can be equipped with an online concentration detector and an automatic water replenishment device to achieve automatic adjustment of the extractant concentration; the reflux path of the trace organic phase can directly enter the feed pipe of the extraction tower 2 without passing through the mixed solvent raw material tank 1; the extractant phase can be directly recycled to the extraction tower 2 without passing through the extract water storage tank 4, which is suitable for operating conditions where the extractant concentration does not change much.

[0030] In some embodiments, such as Figure 2 As shown, the extraction tower 2 has a heavy liquid inlet 25 at the top and a light liquid inlet 26 at the bottom. A rotary table 34 and a fixed table 33 are coaxially mounted inside the tower. The rotary table 34 is connected to a variable frequency motor 30. Electromagnetic flow meters and pneumatic regulating valves are connected in series on the pipes of the light liquid inlet 26 and the heavy liquid inlet 25, respectively. The electromagnetic flow meters are the first electromagnetic flow meter 36 and the second electromagnetic flow meter 37, respectively. The pneumatic regulating valves are the first pneumatic regulating valve 38 and the second pneumatic regulating valve 39, respectively. A third regulating valve and a pneumatic shut-off valve 41 are installed at the heavy liquid outlet 27. A differential pressure level gauge 42 is installed in the middle of the extraction tower 2 to detect the stratification interface. The electromagnetic flow meters, differential pressure level gauge 42, variable frequency motor 30, and pneumatic regulating valves are all connected to the DCS control unit 14. When the differential pressure level gauge 42 detects that the height of the stratification interface exceeds the 40%-60% range, the DCS control unit 14 activates the pneumatic regulating valve to adjust the feed flow rate, ensuring stable water separation efficiency.

[0031] In this embodiment, by setting a rotating disk 34 and a fixed disk 33 inside the extraction tower 2, and driving the rotating disk 34 to rotate under the control of the DCS control unit 14 and the variable frequency motor 30, the light and heavy phase liquids can be dispersed into fine droplets, significantly increasing the phase contact area and forming a forced flow path, thereby significantly improving mass transfer efficiency and extraction speed. An electromagnetic flowmeter monitors the feed flow rates of the light and heavy phases in real time, and a differential pressure level gauge 42 monitors the height of the stratification interface in the tower in real time. The DCS control unit 14 automatically adjusts the opening of the pneumatic regulating valve and the rotation speed of the variable frequency motor 30 based on the monitoring data, achieving precise locking of the feed ratio and stable control of the stratification interface height. Because the interface height is stable, phase entrainment caused by interface fluctuations is avoided, ensuring the stability and reliability of the extraction and water separation effect.

[0032] The extraction tower 2 is equipped with a grid plate 32, and a manhole 35 is provided on the wall. In some embodiments, such as Figure 4 As shown, the first adsorption unit includes multiple parallel 3Å molecular sieve adsorption towers 5, and the second adsorption unit includes multiple parallel 4Å molecular sieve adsorption towers 9. The feed inlet of each 3Å molecular sieve adsorption tower 5 is connected to the light liquid outlet 28 of the extraction unit through a switching valve, and the feed inlet of each 4Å molecular sieve adsorption tower 9 is connected to the component outlets of the distillation unit through a switching valve, which is used to switch to another adsorption tower when one adsorption tower reaches saturation. Each adsorption tower is provided with a support grid 46, a molecular sieve adsorption bed 45 and a feed distributor 44 from bottom to top. Each adsorption tower is provided with multiple temperature sensors in the tower bed area, specifically three, which are set as the first temperature sensor 48, the second temperature sensor 49 and the third temperature sensor 50 from bottom to top. A pressure sensor is provided in the gas phase space at the top of the tower. A regulating valve is provided on the feed pipe, and a shut-off valve is provided on the feed pipe and the discharge pipe. Each switching valve, regulating valve, shut-off valve and sensor are connected to the DCS control unit 14. When the temperature sensor of the molecular sieve adsorption tower monitors the bed temperature in real time and it exceeds 40°C, the DCS control unit 14 immediately issues an early warning and controls the shut-off valve to close the feed.

[0033] In this embodiment, a 3Å molecular sieve is used as the adsorbent in the first adsorption unit. Its pore size is 3 Å, allowing only water molecules with a kinetic diameter of 2.8 Å to enter and be adsorbed. Ester and alcohol molecules, with kinetic diameters greater than 3.5 Å, cannot enter, thus selectively removing dissolved water from the organic phase without losing useful solvent. A 4Å molecular sieve is used as the adsorbent in the second adsorption unit. Its pore size is 4 Å, capable of adsorbing molecules with kinetic diameters less than 4 Å, including water (2.8 Å) and small molecule alcohols such as methanol and ethanol (3.8~4.0 Å). The target product, ester molecules, typically have kinetic diameters greater than 4.5 Å and cannot enter. Therefore, it can further remove residual water while removing trace amounts of small molecule alcohol impurities that may still exist after distillation, increasing product purity from approximately 99.7% to over 99.9%. Multiple temperature sensors are installed in the bed region of the tower to monitor the temperature distribution during adsorption in real time. The feed distributor 44 ensures a uniform distribution of the organic phase in the adsorption bed, avoiding channeling and flow deviation, and guaranteeing consistent adsorption performance. The DCS control unit 14 automatically adjusts the opening of the feed valve based on the monitoring data of each sensor, controls the feed flow rate, and ensures that the organic phase has sufficient residence time in the adsorption bed, thereby achieving deep dehydration to a moisture content of ≤500ppm.

[0034] In alternative embodiments, the first adsorption unit may employ molecular sieves with other pore sizes, such as 4Å molecular sieves, suitable for applications requiring simultaneous removal of small molecule alcohols such as water and methanol; the molecular sieve adsorption tower may employ a horizontal or radial flow structure; the temperature sensor may employ a fiber optic temperature sensor or an infrared thermal imager; the pressure sensor may employ a differential pressure transmitter to determine bed blockage by monitoring the pressure difference before and after the adsorption bed; and the switching valve and shut-off valve may employ electric or hydraulic valves.

[0035] In some embodiments, the adsorption tower is equipped with a regeneration system, which mainly includes a nitrogen source interface, a bypass switching valve, and the original tower's inlet and outlet pipes. When the adsorption tower needs purging, the switching valve group is controlled by the DCS control unit 14 to cut off the process feed, while simultaneously introducing dry hot nitrogen into the adsorption tower bypass branch. The gas passes through the molecular sieve bed from bottom to top, carrying the desorbed impurities and moisture and being discharged through the top pipe. This design eliminates the need for a separate purging pipeline; the switching between "process operation" and "purging regeneration" modes can be achieved simply by switching valves.

[0036] In some embodiments, since the present invention processes each component separately, the equipment after the distillation unit can be equipped with a cleaning / purging procedure, combined with online detection and control, which can effectively avoid cross-contamination.

[0037] In some embodiments, such as Figure 3As shown, the distillation unit includes a short column 6, a main distillation column 7, and a long column 8 connected in sequence. Each column is topped with a condenser and a reflux condenser. The condensers are a first condenser 51, a second condenser 52, and a third condenser 53, respectively. The reflux condensers are a first reflux 57, a second reflux 58, and a third reflux 59, respectively. Each reflux condenser has a reflux branch and a collection branch at its bottom. The collection branch connects to a buffer tank. The number of buffer tanks depends on the number of components; in this embodiment, four are provided: a first buffer tank 15, a second buffer tank 16, a third buffer tank 17, and a fourth buffer tank 18. The four buffer tanks are connected by pipelines and a second suction... The feed pipeline of the auxiliary unit is connected, and a switching valve is installed on the pipeline so that the four buffer tanks can be connected to the second adsorption unit respectively; the upper section of the main distillation column 7 is provided with a side-stream outlet, which is connected to the third buffer tank 17; each column is equipped with a reboiler at the bottom, namely the first reboiler 54, the second reboiler 55 and the third reboiler 56; temperature sensors are installed at the top and bottom of each column, pressure sensors are installed at the top of the column, flow sensors are installed on the outlet branch, reflux branch and side-stream outlet branch, and the valves of each sensor, reboiler and reflux branch are all connected to the DCS control unit 14.

[0038] This embodiment establishes a multi-stage distillation separation system by connecting three distillation columns of different heights and functions in series. The short column 6, with its lower height and smaller reflux ratio, is used for rapid separation of the lowest-boiling-point alcohol components, reducing the processing load on subsequent columns. The main distillation column 7, with a moderate height and reflux ratio, simultaneously separates two ester components with different boiling points through top and side streams, achieving two products from a single column and improving equipment utilization efficiency. The long column 8, with the highest height and largest reflux ratio, is used for fine separation of the highest-boiling-point or most difficult-to-separate components, ensuring all components achieve high purity. The reboilers and reflux branch valves of each column are precisely controlled by the DCS control unit 14, fixing the reflux ratio of each column and maintaining stable temperature and concentration distributions within the column, thereby ensuring repeatability and consistency of the separation effect. The design of the column top condenser and reflux valve allows for sufficient condensation and partial reflux of the gas phase, forming a stable gas-liquid two-phase mass transfer process.

[0039] Of course, the number of distillation columns can be adjusted according to the number of components in the mixed solvent. For example, for a mixed solvent containing more than four components, the number of distillation columns can be increased or multiple side-stream outlets can be set on one column. The reflux ratio of each column can be adjusted according to the difference in boiling points of the components. The smaller the difference in boiling points, the larger the required reflux ratio. Packed columns can be used instead of plate columns to improve separation efficiency. Condensers can be air-cooled or water-cooled. Reboilers can be heated by hot oil or steam.

[0040] In some embodiments, the outlet of the filtration unit 11 is connected to a post-refining buffer tank 20. The discharge pipe of the post-refining buffer tank 20 is equipped with an online moisture analyzer 13 and an online chromatograph 12, both connected to the DCS control unit 14. The discharge pipe is connected to a reflux branch and multiple product branches. The reflux branch is connected to the inlet of the second adsorption unit (in a preferred example, a pre-refining buffer tank 19 is provided between them). The multiple product branches are connected to multiple solvent storage tanks. In some embodiments, four solvent storage tanks are provided: a first solvent storage tank 21, a second solvent storage tank 22, a third solvent storage tank 23, and a fourth solvent storage tank 24. A shut-off valve connected to the DCS control unit 14 is provided on the reflux branch, and a shut-off valve connected to the DCS control unit 14 is provided on each product branch. When the online moisture analyzer 13 and the online chromatograph 12 detect that the solvent is substandard, the DCS control unit 14 controls the valves to return the substandard solvent to the pre-refining buffer tank 19 for re-refining. This embodiment achieves real-time monitoring of product quality by installing online detection instruments on the discharge pipe of the post-refining buffer tank 20. The online moisture analyzer 13 and online chromatograph 12 continuously detect the water content, purity, and impurity content of the refined solvent, and transmit the detection data to the DCS control unit 14 in real time. When the detection results meet the qualified standards (purity ≥ 99.9%, impurity content ≤ 1 ppm, water content ≤ 10 ppm), the DCS control unit 14 automatically opens the shut-off valve of the corresponding product branch, storing the qualified product in the corresponding solvent storage tank; when the detection results are unqualified, the DCS control unit 14 automatically closes the product branch shut-off valve and opens the reflux branch shut-off valve, returning the unqualified product to the inlet of the second adsorption unit for re-refining. This interlocking control design of online detection and automatic reflux prevents unqualified products from entering the product storage tank, ensuring the consistency of the quality of the outgoing products. It also achieves automatic rework of unqualified products without manual intervention, improving production efficiency and automation levels.

[0041] In some examples, online monitoring instruments can also be installed between the outlet of the filter unit 11 and the purified buffer tank 20, or on each product branch. When only the water content is substandard, the return path of the defective product can be made to return to the cryogenic crystallization unit 10 or the inlet of the filter unit 11 without passing through the second adsorption unit (this requires setting up another branch to achieve this function). The shut-off valve of the product branch can be a manual valve combined with an automatic control system, which is suitable for small-scale production. The solvent storage tank can be equipped with a level gauge and an alarm device to achieve automatic switching when the tank is full.

[0042] In some embodiments, the cryogenic crystallization unit 10 is a deep condenser, and the filtration unit 11 is a membrane separation filtration assembly with a filtration accuracy of 0.1~0.3μm.

[0043] In this embodiment, the deep condenser cools the adsorbed solvent to -5°C, causing the supersaturated dissolved water to crystallize and precipitate. Since the solubility of water decreases sharply with decreasing temperature, this step can reduce the water content from tens of ppm to below 10 ppm. The membrane separation filtration unit filters out the precipitated ice crystals and any possible solid particles with an accuracy of 0.1~0.3 μm, ensuring the final product is clear, transparent, and free of particulate matter. The synergistic effect of these three purification methods enables the product to meet top-level standards for direct reuse in the production line.

[0044] In some examples, the second adsorption unit can be a 5Å molecular sieve or activated carbon, suitable for applications requiring the adsorption of impurities with larger molecular sizes; the cooling temperature of the cryogenic crystallization unit 10 can be adjusted according to the type of solvent and water content requirements, such as -10℃ or -15℃ for some solvents; the filtration unit 11 can be a ceramic membrane or a metal sintered membrane, suitable for high-temperature or corrosive applications; a pre-filtration device can be installed before the membrane separation filtration assembly to extend the service life of the main filtration assembly.

[0045] In some embodiments, when the DCS control unit 14 monitors that the adsorption tower has been running for 20 hours (80% of the preset single adsorption time threshold), it switches to the bypass adsorption tower and replaces the molecular sieve packing or regenerates the molecular sieve packing.

[0046] In some embodiments, the DCS control unit 14 synchronously records all process parameters (feed flow rate, extraction ratio, temperature / reflux ratio of each tower, adsorption time, etc.) to achieve data archiving and traceability.

[0047] In some embodiments, the DCS control unit 14 communicates with each PLC substation via industrial Ethernet to collect data from electromagnetic flowmeters, differential pressure level gauges 42, pressure transmitters 31, temperature sensors, online moisture analyzers 13, chromatographs, and temperature and pressure sensors on the molecular sieve adsorption tower; it outputs commands to control pneumatic regulating valves, pneumatic shut-off valves 41, switching valves, frequency converter motors 30, and the power of each tower reboiler, thereby achieving feed ratio solidification, stratification interface locking, adsorption tower timed switching, distillation parameter stabilization, and end-of-pipe detection interlock control.

[0048] like Figure 5 As shown, the DCS control unit 14 of the present invention adopts a master-slave hierarchical distributed control system architecture, including a DCS master station and several PLC substations.

[0049] The DCS master station, as a monitoring and operation station, integrates a human-machine interface, a data server, and an alarm management system. Its main functions include: real-time display of various process parameters (such as flow rate, temperature, pressure, liquid level, purity, and water content), generation and storage of historical trend curves, sending control commands to each PLC substation, and triggering audible and visual alarms when parameters exceed limits or equipment malfunctions.

[0050] The PLC substation corresponds to the extraction unit, and its monitoring points include the flow rate of the extractant and the flow rate of the mixed solvent. The control points include the opening degree of the extractant feed valve. By monitoring the two-phase feed flow rate in real time and adjusting the valve opening, the precise solidification of the feed ratio of extractant and mixed solvent can be achieved.

[0051] The second PLC substation corresponds to the molecular sieve unit (including the first adsorption unit and the second adsorption unit). Its monitoring points include the outlet moisture content and the molecular sieve saturation (indirectly judged by the bed temperature distribution), and the control points include the reflux flow rate and the outflow flow rate. By monitoring the changes in the outlet moisture content and bed temperature of the adsorption tower, the degree of molecular sieve adsorption saturation is judged, and the switching valve is controlled to realize the operation / regeneration switching of the adsorption tower.

[0052] The PLC substation corresponds to a multi-stage distillation unit. Its monitoring points include the top temperature, bottom temperature, and top pressure of each distillation column, while the control points include the bottom heating power and reflux pump speed. By monitoring the temperature and pressure parameters of each column and adjusting the reboiler heating power and reflux pump speed, the reflux ratio of each column can be accurately fixed, ensuring the stability of component separation.

[0053] The PLC substation corresponds to the refining unit (i.e., cryogenic crystallization unit 10 and filtration unit 11). Its monitoring points include the impurity content of the refined solvent (detected by online chromatograph 12) and the temperature of the cryogenic tank. The control points include the opening degree of the refrigerant valve and the filter switching valve. By monitoring the temperature of the cryogenic tank, the opening degree of the refrigerant valve is controlled to maintain a crystallization temperature of -5℃. Based on the online detection results, the switching valves of the product branch and the reflux branch are controlled to realize the automatic sampling of qualified products and the automatic rework of unqualified products.

[0054] Each PLC substation communicates with the DCS master station in real time via industrial Ethernet, uploading the collected field data to the master station and receiving setpoints and interlocking commands from the master station. This hierarchical distributed control structure ensures both the real-time performance and reliability of field control, while also achieving centralized monitoring and unified scheduling of the entire process, making it the core of the automation control in this invention.

[0055] Example 2 The present invention also provides a process for separating and recovering mixed ester and alcohol solvents based on the system in Example 1, comprising the following steps: (1) Extraction and water separation: The mixed solvent of esters and alcohols containing free water and the extractant are introduced into the extraction unit. The feed ratio of the extractant and the mixed solvent is fixed by the DCS control unit 14 to control the layering interface height in the extraction unit, remove the free water in the mixed solvent, and obtain the organic phase and the aqueous extract phase after the free water is removed. (2) Oil-water separation and circulation: The aqueous extract phase obtained in step (1) is passed into the oil-water separator 3 for static separation. The separated trace organic phase is returned to the mixed solvent raw material tank 1. The separated extract phase is circulated back to the extraction unit after being mixed with water in the extract liquid storage tank 4. (3) Deep dehydration: The organic phase obtained in step (1) after removing free water is introduced into the first adsorption unit. The feed flow rate is controlled by the DCS control unit 14 so that the organic phase stays in the first adsorption unit for a sufficient time to adsorb and remove the dissolved water therein, and an organic phase with a water content ≤500ppm is obtained. (4) Multi-stage distillation separation: The organic phase obtained in step (3) is sequentially fed into multiple distillation columns of the distillation unit, and the reflux ratio of each column is fixed by the DCS control unit 14 to separate different single components; (5) Refining and purification: Each single component obtained in step (4) is passed into the second adsorption unit to adsorb and remove trace impurities, then passed into the cryogenic crystallization unit 10 to cool down to -5℃ to crystallize the dissolved water, and finally passed into the filtration unit 11 to filter out ice crystals to obtain the refined single component. The process parameters in each of the above steps are monitored and automatically adjusted in real time by the DCS control unit 14, realizing full-process automated control.

[0056] This embodiment divides the entire process into five logically progressive steps, forming a complete process route. Step (1) Extraction and water separation first removes more than 80% of the free water, significantly reducing the load on subsequent steps; Step (2) Oil-water separation and circulation realize the recycling of the extractant, reducing operating costs; Step (3) Deep dehydration uses the selective adsorption of 3Å molecular sieves to reduce the dissolved water to below 500ppm, creating favorable conditions for distillation; Step (4) Multi-stage distillation separation uses three distillation columns with different functions to accurately separate the mixed solvent into single components; Step (5) Refining and purification uses adsorption, cryogenic crystallization and filtration to purify each component to ≥99.9%. Since the material flow between each step is clear, the parameters are precisely controlled, and all are uniformly coordinated by the DCS control unit 14, the entire process has the advantages of high processing efficiency, good separation effect, strong operational stability and high degree of automation. The treated solvent can be directly reused in the production line.

[0057] In some embodiments, it also includes: (6) detection and reuse: the purified single component obtained in step (5) is detected by an online moisture analyzer 13 and an online chromatograph 12. The qualified product is stored in a solvent storage tank for reuse, and the unqualified product is returned to the inlet of the second adsorption unit through the reflux branch for re-purification. In step (1), the extractant is methanol or ethanol, the feed volume ratio of extractant to mixed solvent is 1:3 to 1:5, the layer interface height is controlled at 40% to 60% of the height of the extraction unit tower, the water separation efficiency is ≥95%, and more than 80% of free water is separated.

[0058] Among them, separating more than 80% of free water means separating more than 80% of the free water (i.e., water that does not bind with solvent molecules and exists as an independent liquid phase) contained in the raw material mixed solvent. This is a quantitative requirement for the amount of water removed.

[0059] Water separation efficiency ≥95%: This means that the purity of water in the separated aqueous phase reaches 95% or higher. This is a quantitative requirement for separation effect, that is, to minimize the organic solvents entrained in the aqueous phase, while also ensuring that the residual water content in the organic phase is sufficiently low. Simply put, the former is "how much water is removed", and the latter is "how cleanly it is removed". Both of them together ensure the high efficiency and high quality of the extraction and dehydration unit.

[0060] This embodiment optimizes key parameters for water separation during extraction, ensuring efficient dehydration in the pretreatment stage. Methanol or ethanol is used as the extractant because it is infinitely miscible with water and partially miscible with ester-alcohol solvents, efficiently separating water from the mixed solvent. The feed volume ratio is controlled at 1:3 to 1:5, ensuring sufficient extractant dosage for thorough removal of free water while avoiding excessive extractant leading to increased load on subsequent separation processes. The separation interface height is controlled at 40% to 60% of the column height, preventing the aqueous phase from entering the light liquid outlet 28 due to an excessively high interface, and preventing the extractant phase from entering the heavy liquid outlet 27 due to an excessively low interface, thus ensuring clear separation of the light and heavy phases. With the synergistic effect of these parameters, the water separation efficiency can reach over 95%, meaning that over 95% of the free water in the feed is removed, laying a solid foundation for subsequent deep dehydration.

[0061] In some examples, ketone solvents such as acetone or methyl ethyl ketone can be used as the extractant, which is suitable for certain specific ester-alcohol systems; the feed volume ratio can be adjusted according to the moisture content of the raw material, and the proportion of extractant can be appropriately increased when the moisture content is high; the control range of the layer interface height can be adjusted according to the structure of extraction tower 2, and 30%~50% or 50%~70% can be used for some tower types; the target value of extraction water separation efficiency can be adjusted according to the processing capacity of subsequent processes. For example, when the adsorption capacity of subsequent molecular sieves is large, the extraction water separation efficiency requirement can be appropriately reduced to save the amount of extractant used.

[0062] In some embodiments, the distillation unit in step (4) includes a short column 6, a main distillation column 7, and a long column 8 connected in sequence; the reflux ratio of the short column 6 is 1:1.5~1:2.5, and the feed inlet is 4~6m from the bottom of the column, used to separate the alcohol components with the lowest boiling point; the reflux ratio of the main distillation column 7 is 1:4~1:6, the feed inlet is 7~9m from the bottom of the column, and a side stream outlet is provided in the upper section of the column body 6~8m from the top of the column, used to separate the low-boiling-point esters at the top of the column and the medium-boiling-point esters in the side stream; the reflux ratio of the long column 8 is 1:7~1:9, and the feed inlet is 9~11m from the bottom of the column, used to purify the high-boiling-point components; the cooling temperature of the cryogenic crystallization unit 10 in step (5) is -5℃, and the filtration accuracy of the filtration unit 11 is 0.1~0.3μm; the qualified test standard in step (6) is: purity ≥99.9%, impurity content ≤1ppm, and water content ≤10ppm.

[0063] This embodiment achieves precise separation of components with different boiling points by accurately setting the reflux ratio and feed position of each distillation column. Short column 6 uses a smaller reflux ratio (1:1.5~1:2.5) and a lower feed position, allowing the lowest boiling point alcohol components to be rapidly enriched and collected at the top of the column, while avoiding excessive distillation of low-boiling-point esters. Main distillation column 7 uses a moderate reflux ratio (1:4~1:6), collecting low-boiling-point esters (such as ethyl acetate) at the top and medium-boiling-point esters (such as propyl acetate) from the side stream. Through reflux ratio control and side stream position optimization, both products are ensured to achieve high purity. Long column 8 uses the largest reflux ratio (1:7~1:9), purifying the most difficult-to-separate high-boiling-point components (such as isopropyl acetate) to over 99.6% through more theoretical plates and more sufficient vapor-liquid contact. Step (5) involves -5℃ cryogenic crystallization and 0.1~0.3μm precision filtration, which reduces residual water to below 10ppm while removing all solid impurities. Step (6) involves online detection and reflux interlocking, ensuring that only products with a purity ≥99.9%, impurities ≤1ppm, and water content ≤10ppm can enter the storage tank. The synergistic effect of the entire parameter system enables the final product to meet the top standard for direct reuse in the production line.

[0064] Of course, the reflux ratio of each column can be adjusted according to the difference in boiling points of the components; the smaller the difference in boiling points, the larger the required reflux ratio. The feed inlet position can be adjusted according to the feed composition; when the content of light components is high, the feed inlet position can be appropriately lowered. The side stream outlet position can be optimized according to the boiling point and concentration distribution of the target product, which can be determined through simulation calculation or experiment. The cryogenic crystallization temperature can be adjusted according to the freezing point of the solvent and the target water content. The filtration accuracy can be selected according to the ice crystal size and impurity particle size distribution. The test qualification standard can be adjusted according to the specific requirements of the production line; for example, some production lines can accept recycled solvent with a purity of ≥99.5%.

[0065] Example 3 This embodiment provides a highly efficient method for the separation, purification, and recovery of a multi-component mixed solvent. The mixed solvent to be treated consists of: 69.27% ​​propyl acetate, 25.7% ethyl acetate, 3.67% isopropanol, 0.4% isopropyl acetate, and 3.5% water (all by mass). The specific processing steps are as follows: (1) Extraction and water separation: The above mixed solvent is used in a 5m solution. 3 A flow rate of / h is introduced into extraction column 2 (column height 10m, diameter 600mm) through heavy liquid inlet 25; simultaneously, a flow rate of 1.2m... 3 Methanol is introduced into the extraction tower 2 at a flow rate of / h through the light liquid inlet 26 as the extractant. The volume ratio of extractant to mixed solvent is locked at 1:4.2 in real time by the DCS control unit 14, and the variable frequency motor 30 drives the turntable 34 to rotate to enhance liquid-liquid mass transfer. The differential pressure level gauge 42 monitors the height of the stratification interface in the tower and maintains it at 3m from the bottom of the tower (corresponding to 50% of the tower height). The lower aqueous phase in the tower is discharged from the heavy liquid outlet 27 at the bottom of the tower and enters the oil-water separator 3. The upper organic phase is discharged from the light liquid outlet 28 in the upper middle part of the tower. The water separation efficiency of this step is tested to be 96.5%.

[0066] (2) Oil-water separation and circulation: The mixture in the oil-water separator 3 is completely separated by static sedimentation. The trace organic phase recovered in the upper layer is discharged through the light phase outlet at the top of the separator and returned to the mixed solvent raw material tank 1 to be mixed with the new raw material and then re-enter the extraction tower 2. The water + methanol mixed phase in the lower layer is discharged through the heavy phase outlet at the bottom of the separator and enters the extract water storage tank 4. After being adjusted, it is recycled as an extractant to the light liquid inlet 26 of the extraction tower 2.

[0067] (3) Deep dehydration: The organic phase discharged in step (1) is at 4.8m 3 A flow rate of [flow rate] / h is fed into the 3Å molecular sieve adsorption tower 5 (vertical structure, 900mm diameter, 2200mm height, 45 layers of molecular sieve adsorption bed with a height of 1800mm). The flow rate is fixed by the regulating valve of the feed pipeline controlled by DCS to ensure that the residence time of the organic phase in the adsorption bed is 12 minutes. The organic phase is evenly distributed in the adsorption bed through the feed distributor 44 at the top of the tower, and trace amounts of water are removed by utilizing the selective adsorption performance of the 3Å molecular sieve. The organic phase at the outlet of the adsorption tower is sampled offline, and the water content is detected to be 38ppm (≤500ppm). After meeting the standard, it enters the subsequent unit. When the DCS monitors that the adsorption tower has been running for 20 hours (80% of the preset single adsorption time threshold), the feed is stopped and the molecular sieve packing is replaced or regenerated.

[0068] (4) Multistage distillation: ① The dehydrated organic phase is first fed into short column 6 (column height 12m, diameter 600mm, feed inlet 5m from bottom of column). The solidification reflux ratio is 1:2 controlled by DCS, and the power of the reboiler at the bottom of the column is controlled to maintain the top temperature of 82.4℃. Isopropanol component is separated from the top of the column, and the purity is tested to be 99.6%. It is stored in the corresponding buffer tank through the outflow branch; ② The material at the bottom of short column 6 is fed into a 4.6m... 3 A flow rate of / h is fed into the main distillation column 7 (column height 20m, diameter 1000mm, feed inlet 8m from bottom), the DCS solidification reflux ratio is 1:5, the column top temperature is maintained at 77.1℃, ethyl acetate (purity 99.7%) is separated from the top of the column and stored in a buffer tank; propyl acetate (purity 99.85%) is collected from the side stream 7m from the top of the column and directly stored in the corresponding buffer tank; ③ The bottom material of the main distillation column 7 is fed at a flow rate of 0.3m... 3 A flow rate of / h is fed into long column 8 (column height 25m, diameter 700mm, feed inlet 10m from bottom of column), DCS solidification reflux ratio is 1:8, column top temperature is maintained at 88.1℃, isopropyl acetate (purity 99.6%) is purified from the column top and stored in buffer tank.

[0069] (5) Refining and Temperature Control: The solvents of each component in the buffer tank were respectively passed into a 4Å molecular sieve adsorption tower 9 (700 mm in diameter and 2000 mm in height) to adsorb and remove residual trace impurities. After adsorption, the impurity content of each component was tested and found to be ≤0.7 ppm. Then, the adsorbed solvent was passed into a deep condenser (1.5 m³). 3 The temperature inside the tank was maintained at 5°C using refrigerant temperature control. The agitator was turned on (50 r / min) to allow trace amounts of water to precipitate out as ice crystals, and volatile impurities were further condensed. The solvent remained in the tank for 10 minutes. After condensation, the solvent was filtered through a 0.1 μm membrane separation filter to remove ice crystals and solid impurities, and then directly introduced into a purified buffer tank 20 to naturally heat to room temperature. The final purity of each component was tested to be: isopropanol 99.93%, ethyl acetate 99.92%, propyl acetate 99.95%, and isopropyl acetate 99.91%.

[0070] (6) Full-process control and reuse: After purification, each component is re-tested by the centralized detection module (online moisture analyzer 13 + online chromatograph 12) to confirm that the water content is ≤10ppm, the purity is ≥99.9% and the impurity content is ≤1ppm, and then the sample is retained; among them, isopropanol, ethyl acetate and propyl acetate are mixed according to the production line requirements and stored in the reuse storage tank for reuse in the production line; isopropyl acetate is stored separately in the spare storage tank; the DCS control cabinet synchronously records the process parameters of the whole process (feed flow rate, extraction ratio, temperature / reflux ratio of each tower, adsorption time, etc.) to realize data archiving and traceability.

[0071] Safety and Interlock Control: ① The temperature sensor of the 3Å / 4Å molecular sieve adsorption tower 9 monitors the bed temperature in real time. When the temperature exceeds 40℃, the DCS immediately issues an early warning and controls the shut-off valve to close the feed. ② When the differential pressure level gauge 42 of the extraction tower 2 detects that the height of the stratification interface exceeds the range of 40%-60%, the DCS links with the pneumatic regulating valve to adjust the feed flow rate to ensure stable water separation efficiency. ③ When the centralized detection module detects that the solvent is unqualified, the DCS controls the pneumatic shut-off valve 41 to switch to the reflux branch, returning the unqualified solvent to the pre-refining buffer tank 19 for re-refining.

[0072] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A separation and recovery system for mixed ester and alcohol solvents, characterized in that, include: The extraction unit has a light liquid outlet and a heavy liquid outlet, which is used to remove free water from the mixed solvent of esters and alcohols to form an organic phase with free water removed and an aqueous extract phase. The first adsorption unit has its inlet connected to the light liquid outlet of the extraction unit, and is used to adsorb and remove dissolved water and remaining free water from the organic phase. A distillation unit includes a plurality of distillation columns connected in sequence, the inlet of the first distillation column being connected to the outlet of the first adsorption unit, and the plurality of distillation columns being used to separate the organic phase from which dissolved water has been removed into a single component. The second adsorption unit has its inlet connected to the outlet of each component of the distillation unit, and is used to adsorb and remove impurities from the single component. The cryogenic crystallization unit has its inlet connected to the outlet of the second adsorption unit, and is used to cool the adsorbed single component so that the remaining dissolved water crystallizes out. A filtration unit, the inlet of which is connected to the outlet of the cryogenic crystallization unit, is used to filter out the precipitated ice crystals; The DCS control unit is connected to the signals of each of the aforementioned units to solidify process parameters and achieve full-process automated control.

2. The system according to claim 1, characterized in that, The extraction unit includes a mixed solvent feed tank, an extraction tower, an oil-water separator, and an extract water storage tank; the heavy liquid outlet of the extraction tower is connected to the oil-water separator, the light phase outlet of the oil-water separator is connected to the mixed solvent feed tank, the heavy phase outlet of the oil-water separator is connected to the extract water storage tank, and the outlet of the extract water storage tank is connected to the light liquid inlet of the extraction tower.

3. The system according to claim 2, characterized in that, The extraction tower is equipped with a heavy liquid inlet at the top and a light liquid inlet at the bottom. A rotary table and a fixed table are coaxially installed inside the tower, and the rotary table is connected to a variable frequency motor. An electromagnetic flow meter and a pneumatic regulating valve are connected in series on the pipes of the light liquid inlet and the heavy liquid inlet, respectively. A differential pressure level gauge is installed in the middle of the extraction tower to detect the stratification interface. The electromagnetic flow meter, differential pressure level gauge, variable frequency motor, and pneumatic regulating valve are all connected to the DCS control unit for signal transmission.

4. The system according to claim 1, characterized in that, The first adsorption unit includes multiple 3Å molecular sieve adsorption towers connected in parallel, and the second adsorption unit includes multiple 4Å molecular sieve adsorption towers connected in parallel. The feed inlet of each 3Å molecular sieve adsorption tower is connected to the light liquid outlet of the extraction unit through a switching valve, and the feed inlet of each 4Å molecular sieve adsorption tower is connected to the component outlets of the distillation unit through a switching valve, for switching to another adsorption tower when one adsorption tower reaches saturation. Each adsorption tower is provided with a support grid, a molecular sieve adsorption bed, and a feed distributor in sequence from bottom to top. Multiple temperature sensors are installed in the bed area of ​​each adsorption tower, a pressure sensor is installed in the gas phase space at the top of the tower, a regulating valve is installed on the feed pipe, and a shut-off valve is installed on the feed pipe and the discharge pipe. Each switching valve, regulating valve, shut-off valve, and sensor is connected to the DCS control unit for signal transmission.

5. The system according to claim 1, characterized in that, The distillation unit comprises a short column, a main distillation column, and a long column connected in sequence. Each column is connected to a condenser and a reflux condenser at the top. The reflux condenser has a reflux branch and a product branch at the bottom. A reflux pump is installed on the reflux branch, and the product branch is connected to a buffer tank. A side product outlet is provided in the upper section of the main distillation column. A reboiler is provided at the bottom of each column. Temperature sensors are installed at the top and bottom of each column, and a pressure sensor is installed at the top of the column. Flow sensors are installed on the product branch, the reflux branch, and the side product branch. All sensors, the reboiler, and the reflux pump are connected to the DCS control unit.

6. The system according to claim 1, characterized in that, The outlet of the filtration unit is connected to a post-refining buffer tank. The discharge pipe of the post-refining buffer tank is equipped with an online moisture analyzer and an online chromatograph connected to the DCS control unit. The discharge pipe is connected to a reflux branch and multiple product branches. The reflux branch is connected to the inlet of the second adsorption unit, and the multiple product branches are connected to multiple solvent storage tanks. The reflux branch is equipped with a shut-off valve connected to the DCS control unit, and each of the product branches is equipped with a shut-off valve connected to the DCS control unit.

7. The system according to claim 1, characterized in that, The cryogenic crystallization unit is a deep condenser, and the filtration unit is a membrane separation filtration assembly with a filtration accuracy of 0.1~0.3μm.

8. A process for separating and recovering mixed ester and alcohol solvents based on the system described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Extraction and water separation: The ester alcohol mixed solvent containing free water and the extractant are introduced into the extraction unit. The feed ratio of the extractant and the mixed solvent is fixed by the DCS control unit to control the layer interface height in the extraction unit, remove the free water in the mixed solvent, and obtain the organic phase and the aqueous extract phase after the free water is removed. (2) Oil-water separation and circulation: The aqueous extract phase obtained in step (1) is passed into an oil-water separator for static separation. The separated trace organic phase is returned to the mixed solvent raw material tank. The separated extract phase is circulated back to the extraction unit after being mixed with water in the extract liquid storage tank. (3) Deep dehydration: The organic phase obtained in step (1) after removing free water is introduced into the first adsorption unit. The feed flow rate is controlled by the DCS control unit so that the organic phase stays in the first adsorption unit for a sufficient time to adsorb and remove the dissolved water therein, and an organic phase with a water content ≤500ppm is obtained. (4) Multi-stage distillation separation: The organic phase obtained in step (3) is sequentially fed into multiple distillation columns of the distillation unit, and the reflux ratio of each column is fixed by the DCS control unit to separate different single components; (5) Refining and purification: Each single component obtained in step (4) is passed into the second adsorption unit to adsorb and remove trace impurities, then passed into the cryogenic crystallization unit to cool to -5°C to crystallize and precipitate dissolved water, and finally passed into the filtration unit to filter out ice crystals to obtain the refined single component. The process parameters in each of the above steps are monitored and automatically adjusted in real time by the DCS control unit, realizing full-process automated control.

9. The process according to claim 8, characterized in that, Also includes: (6) Detection and reuse: The purified single component obtained in step (5) is detected by an online moisture analyzer and an online chromatograph. The qualified product is stored in the solvent storage tank for reuse, and the unqualified product is returned to the inlet of the second adsorption unit through the reflux branch for re-purification. The extractant in step (1) is methanol or ethanol, the feed volume ratio of extractant to mixed solvent is 1:3 to 1:5, the layer interface height is controlled at 40% to 60% of the height of the extraction unit tower, the water separation efficiency is ≥95%, and more than 80% of free water is separated.

10. The process according to claim 9, characterized in that, The distillation unit in step (4) includes a short column, a main distillation column, and a long column connected in sequence; The short column has a reflux ratio of 1:1.5 to 1:2.5 and the feed inlet is 4 to 6 meters from the bottom of the column. It is used to separate alcohol components with the lowest boiling point. The main distillation column has a reflux ratio of 1:4 to 1:6, the feed inlet is 7 to 9 m from the bottom of the column, and a side stream outlet is provided in the upper middle section of the column, 6 to 8 m from the top of the column, for separating low-boiling-point esters from the top of the column and medium-boiling-point esters from the side stream. The long column has a reflux ratio of 1:7 to 1:9 and the feed inlet is 9 to 11 m from the bottom of the column. It is used to purify high-boiling-point components. The cooling temperature of the cryogenic crystallization unit in step (5) is -5℃, and the filtration accuracy of the filtration unit is 0.1~0.3μm; The qualified standards for step (6) are: purity ≥ 99.9%, impurity content ≤ 1 ppm, and water content ≤ 10 ppm.

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