A device and method for continuous production of DOTP by recovering waste heat at the top of a tower and refining alcohol in a closed loop

Abstract

The application discloses a kind of tower top waste heat recovery and alcohol closed loop refining DOTP continuous production device and method, device includes slurry preparation-esterification-distillation unit, neutralization-washing stratification unit and two-stage stripping-decoloring filtration unit in sequence.The steam outlet of first, second esterification kettle is respectively connected with the shell side of first condenser via process column, and the tube side of first condenser is connected with fresh isooctanol pipe and slurry preparation tank, and fresh isooctanol is preheated to 120~150 DEG C by using 170~230 DEG C azeotropic steam waste heat;The outlet of condensate liquid in distillation column top is connected with slurry preparation tank via reused isooctanol pipe, to realize the closed loop recovery of alcohol.The application also provides a production method using the above device, including continuous esterification, rectification recovery, neutralization-washing, two-stage stripping and decoloring filtration steps, and adapts specific catalyst, neutralizing liquid, decoloring aid and polymerization inhibitor formula.The application significantly reduces steam consumption and raw material loss, and less wastewater discharge, and can stably produce food contact grade and medical grade DOTP products.

Description

Technical Field

[0001] This invention belongs to the technical field of continuous synthesis equipment for plasticizers, specifically relating to a fully continuous DOTP production device and method suitable for the liquid-phase continuous esterification process of terephthalic acid and isooctanol. It integrates the functions of top heat recovery and alcohol closed-loop purification, and can be extended to the continuous production of phthalate and isophthalic ester plasticizers. Background Technology

[0002] Diisooctyl terephthalate (DOTP) is a terephthalate plasticizer widely used in PVC products due to its excellent plasticizing properties. Compared with the commonly used diisooctyl phthalate (DOP), DOTP has advantages such as heat resistance, cold resistance, low volatility, pull-out resistance, flexibility, and good electrical insulation properties. In finished products, it exhibits excellent durability, soap water resistance, and low-temperature flexibility.

[0003] Traditional production of diisooctyl terephthalate (DITB) employs a batch pulping and single-reactor batch esterification method, which has the following technical drawbacks: First, the raw material pretreatment is an intermittent operation, resulting in low production efficiency. Terephthalic acid and isooctanol are manually mixed in batches, resulting in sedimentation and uneven mixing. Each batch of mixing takes one to two hours. The esterification cycle is six to ten hours per reactor, with heating, cooling, discharging, and cleaning taking up a lot of time, resulting in low capacity and high labor costs.

[0004] Secondly, the thermal energy utilization rate is extremely low. The high-temperature isooctanol-water azeotropic steam at the top of the esterification tower is directly fed into the cooling water for condensation, resulting in a complete waste of latent heat of vaporization; fresh isooctanol and washing water are both heated by independent steam heat exchangers, resulting in high steam consumption and high operating costs for the entire plant.

[0005] Third, the isooctanol recovery methods are crude. Relying solely on simple gravity stratification in a condenser, a large amount of isooctanol dissolved in the aqueous phase and entrained during emulsification is directly discharged with the wastewater, resulting in high raw material losses and excessive COD in the wastewater. At the same time, due to the lack of a rectification and purification process, the organic acids and catalyst residues enriched in the recycled crude isooctanol continuously worsen the esterification reaction rate.

[0006] Fourth, there is a lack of continuous post-processing refining units. The crude ester is discharged directly, and free acids, titanium-based catalysts, residual isooctanol, and colored impurities cannot be removed. Only low-end industrial-grade diisooctyl terephthalate can be produced, which cannot meet the standards for food, medical, and high-end cable products.

[0007] Fifth, water consumption is high. The washing process continuously adds fresh desalinated water, and the high-temperature wastewater generated from de-alcoholization and esterification lacks a recycling channel, resulting in a large wastewater discharge and a high wastewater treatment load.

[0008] Sixth, the decolorization and filtration processes are intermittent. A transfer tank is required to buffer the crude ester, disrupting the production line's continuity. During transfer, the product's color and acid value fluctuate significantly, and solid impurities easily clog conveying instruments and pipelines.

[0009] In the prior art, patent CN222606353U discloses a continuous production apparatus for diisooctyl terephthalate, which includes a slurry preparation tank, a slurry intermediate tank, a slurry transfer pump, a monoesterification reactor, a monoesterification process tower, a monoesterification condenser, a monoesterification condensate collection tank, a diester reactor, a diester process tower, a diester condenser, and a diester condensate collection tank. The monoesterification reactor is equipped with multiple reaction chambers to achieve segmented continuous reaction, and the output from the diester reactor is directly sent to the finished product storage system via a finished product conveying pipeline. This apparatus achieves continuous production of slurry preparation and two-stage esterification reaction units, and can shorten reaction time and achieve stable and controllable finished product quality. However, this apparatus still has the following shortcomings: Firstly, the lack of a waste heat exchange unit for the steam at the top of the towers results in complete waste of thermal energy. At the top of the primary and secondary esterification process towers in this patent, the high-temperature isooctanol-water azeotropic steam at temperatures of 170℃~230℃ is directly cooled by the condenser, without any waste heat exchange branch. The fresh isooctanol required for slurry preparation lacks a preheating heat source and requires a separate steam heat exchanger for heating. The entire unit consumes a large amount of live steam and lacks energy-saving design.

[0010] Secondly, the patented method relies solely on simple stratification for isooctanol recovery, lacking a distillation and de-alcoholization system, resulting in significant raw material losses and the accumulation of impurities. This method uses only a primary esterification condensate collection tank and a secondary esterification condensate collection tank for gravity stratification. The upper isooctanol is directly returned to the process tower via a reflux pipe. The crude isooctanol, being recycled without distillation purification, accumulates organic acids and hydrolysis catalyst impurities over time, reducing esterification conversion and deepening product color. Simultaneously, the isooctanol dissolved in the esterification wastewater lacks a recovery channel and is directly discharged through the esterification water pipe, causing raw material losses.

[0011] Third, the esterification process lacks a continuous refining system for neutralization and water washing, making it impossible to remove acidic substances and salt impurities from the crude ester. The patented two-stage esterification reactor discharges the product directly through a finished product conveying pipeline for storage, completely lacking a complete set of neutralization and water washing equipment. Specifically, residual free monoester acids and titanium-based acidic catalysts in the crude ester cause the finished product's acid value to exceed the standard; the lack of an alkali neutralization reaction unit leads to continuous acid backflow of acidic impurities during storage; and the absence of a countercurrent water washing desalination process results in sodium and titanium salts generated during neutralization remaining suspended in the oil phase, causing a decrease in the transparency of the finished product.

[0012] Fourth, the lack of a two-stage negative pressure stripping and de-alcoholization unit and hot water recycling unit results in excessive residual isooctanol in the finished product and waste of water resources. This patent does not include a stripping and de-alcoholization tower, preventing the removal of a large amount of free isooctanol dissolved in the crude ester, leading to excessive volatile matter in the finished product and the release of odors during high-temperature processing. Furthermore, it lacks a top oil-water separation structure for the stripping tower and a channel for recycling the high-temperature hot water from the de-alcoholization process.

[0013] Fifth, the lack of a continuous filtration, decolorization, and refining system means that colored impurities and solid particles in the finished product cannot be removed. This patent lacks decolorization mixing and precision filtration equipment, allowing pigments, salt residue, and catalyst particles generated during esterification to directly enter the finished product storage tank, resulting in a yellowish product with poor light transmittance.

[0014] Sixth, the process units are fragmented and lack a continuous series design throughout the entire process. This patent only achieves single-stage continuous processing from slurry preparation to the two-stage esterification reaction. The neutralization, washing, de-alcoholization, distillation, and decolorization processes after esterification are all missing. If qualified high-end diisooctyl terephthalate products are required, intermittent transfer tanks must be added to transfer materials, resulting in a break in the automation continuity of the production line. Summary of the Invention

[0015] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the invention.

[0016] The purpose of this invention is to provide a continuous DOTP production apparatus and method for top waste heat recovery and closed-loop purification of alcohols, which aims to fully recover and utilize the waste heat of high-temperature azeotropic steam at the top of the esterification column to preheat fresh isooctanol and supply the heat source for subsequent distillation and stripping processes, thereby significantly reducing the overall live steam consumption of the apparatus.

[0017] First, this invention provides a continuous DOTP production apparatus for top heat recovery and closed-loop purification of alcohol, the technical solution of which is as follows: A continuous DOTP production unit for top heat recovery and closed-loop purification of alcohol includes a slurry preparation-esterification-distillation unit, a neutralization-water washing and stratification unit, and a two-stage stripping-decolorization and filtration unit connected in series. The slurry preparation-esterification-distillation unit includes a slurry preparation tank, a first esterification kettle, a second esterification kettle, a first esterification process tower, a second esterification process tower, a first esterification primary condenser, and a second esterification primary condenser. The outlet of the slurry preparation tank is sequentially connected to the first esterification reactor and the second esterification reactor; the steam outlet of the first esterification reactor is connected to the shell side of the first esterification primary condenser via the first esterification process tower, the steam outlet of the second esterification reactor is connected to the shell side of the second esterification primary condenser via the second esterification process tower, and the fresh isooctanol tube is connected to the slurry preparation tank via the tube side of the first esterification primary condenser and the second esterification primary condenser. The outlet of the second esterification reactor is connected to the inlet of the distillation column. The condensate outlet at the top of the distillation column is connected to the slurry preparation tank via a recycled isooctanol pipe. The outlet at the bottom of the distillation column is connected to the neutralization-washing stratification unit. The outlet of the neutralization-washing stratification unit is connected to the two-stage stripping-decolorization filtration unit.

[0018] Optionally, the slurry preparation-esterification-distillation unit further includes a PTA silo, a PTA discharge rotary valve, a vibrating screen, and a PTA metering scale. The discharge port of the PTA silo is connected in sequence to the inlet of the slurry preparation tank via the PTA discharge rotary valve, the vibrating screen, and the PTA metering scale.

[0019] Optionally, the slurry preparation-esterification-distillation unit further includes a first esterification secondary condenser and a second esterification secondary condenser, wherein the shell-side outlet of the first esterification primary condenser is connected to the shell-side inlet of the first esterification secondary condenser; and the shell-side outlet of the second esterification primary condenser is connected to the shell-side inlet of the second esterification secondary condenser.

[0020] Optionally, the slurry preparation-esterification-distillation unit further includes a separation tank and a hot water tank. The aqueous phase outlets of the overhead condensate from the first esterification process tower and the second esterification process tower are respectively connected to the separation tank. The outlet of the separation tank is connected to the hot water tank, and the outlet of the hot water tank is connected to the hot water inlet of the neutralization-washing stratification unit.

[0021] Optionally, the neutralization-washing stratification unit includes a pipeline mixer, a neutralization tank, a primary stratification tank, a washing vessel, and a secondary stratification tank. The bottom outlet of the distillation column and the alkali pipe are respectively connected to the feed end of the pipeline mixer. The outlet of the pipeline mixer is sequentially connected to the neutralization tank, the primary stratification tank, the washing vessel, and the secondary stratification tank. The oil phase outlet of the secondary stratification tank is connected to the two-stage stripping-decolorization filtration unit.

[0022] Optionally, the neutralization tank is equipped with an online pH meter, the signal output of which is connected to a DCS automatic control system, and the control output of the DCS automatic control system is connected to an alkali metering pump on the alkali pipe.

[0023] Optionally, the two-stage stripping-decolorizing filtration unit includes a primary stripping tower, a secondary stripping tower, and a primary stripping heat exchanger. The outlet of the neutralization-washing stratification unit is connected to the cold-side inlet of the primary stripping heat exchanger, and the cold-side outlet of the primary stripping heat exchanger is connected to the feed inlet of the primary stripping tower. The bottom liquid phase outlet of the primary stripping tower is connected to the hot-side inlet of the primary stripping heat exchanger via a primary stripping material conveying pump, and the hot-side outlet of the primary stripping heat exchanger is connected to the feed inlet of the secondary stripping tower. The bottom liquid phase outlet of the secondary stripping tower is connected to the decolorizing filtration unit.

[0024] Optionally, the condensate outlets at the top of the primary stripping tower and the secondary stripping tower are respectively connected to the isooctanol recycling pipe, the aqueous phase outlets of the condensate at the top of the primary stripping tower and the secondary stripping tower are respectively connected to the hot water recycling pipeline, and the hot water recycling pipeline is connected to the hot water inlet of the neutralization-washing stratification unit.

[0025] Optionally, the decolorization filtration unit includes a decolorization tank, a primary filter, and a fine filter. The bottom liquid phase outlet of the secondary stripping tower is connected to the feed inlet of the decolorization tank, and the outlet of the decolorization tank is sequentially connected to the primary filter and the fine filter.

[0026] Optionally, the two-stage stripping-decolorization filtration unit further includes a diatomaceous earth silo and a diatomaceous earth discharge rotary valve, wherein the discharge port of the diatomaceous earth silo is connected to the solid feed port of the decolorization tank via the diatomaceous earth discharge rotary valve.

[0027] Optionally, the two-stage stripping-decolorization filtration unit further includes a product cooler and a product intermediate tank, with the outlet of the fine filter connected to the hot-side inlet of the product cooler and the hot-side outlet of the product cooler connected to the inlet of the product intermediate tank.

[0028] Secondly, the present invention also provides a continuous DOTP production method using the apparatus described in any one of claims 1 to 11 for top heat recovery and alcohol closed-loop purification, the technical solution of which is as follows: A continuous DOTP production method involving waste heat recovery from the top of the column and closed-loop purification of alcohol includes the following steps: Slurry preparation steps: Terephthalic acid (PTA) powder is metered and fed into the slurry preparation tank. Fresh isooctanol is preheated to 120℃~150℃ using residual heat from the azeotropic steam at the top of the esterification tower and then fed into the slurry preparation tank. High-purity isooctanol recovered by distillation is also fed into the slurry preparation tank. A titanium-based composite catalyst solution is continuously added to the slurry preparation tank in a specific ratio, and the mixture is stirred until homogeneous to prepare the reaction slurry. The molar ratio of terephthalic acid to isooctanol is 1:2.30~2.60, and the solid content of the slurry is 32wt%~38wt%. Continuous esterification step: The reaction slurry is sequentially fed into a first esterification reactor and a second esterification reactor for continuous esterification reaction; the reaction temperature of the first esterification reactor is 180℃~210℃, the gauge pressure is 0.10MPa~0.25MPa, and the material residence time is 2.0 hours~3.0 hours; the reaction temperature of the second esterification reactor is 210℃~235℃, the gauge pressure is 0.05MPa~0.20MPa, and the material residence time is 2.5 hours~3.5 hours; Waste heat recovery step: The isooctanol-water azeotropic vapor generated by the first esterification reactor and the second esterification reactor at 170℃~230℃ is fed into the shell side of the first-stage condenser after passing through the first esterification process tower and the second esterification process tower respectively, and exchanges heat with the fresh isooctanol flowing through the tube side of the first-stage condenser. The latent heat of vaporization of the azeotropic vapor is used to preheat the fresh isooctanol to 120℃~150℃. Distillation recovery step: The effluent from the second esterification reactor is fed into a distillation column for distillation. The top temperature of the distillation column is 155℃~175℃, the bottom temperature is 220℃~245℃, and the absolute pressure at the top is 0.07MPa~0.09MPa. A portion of the high-purity isooctanol obtained by condensation at the top of the column is refluxed back to the distillation column, and the other portion is returned to the slurry preparation tank for recycling. The bottom effluent from the distillation column is the crude ester material after most of the isooctanol has been removed. Neutralization-washing step: The crude ester material and alkaline solution are premixed in a pipeline mixer and then sent to a neutralization tank for neutralization reaction. The neutralized material is separated into layers in a primary layering tank. The oil phase is sent to a washing kettle and washed countercurrently with recycled hot water from the stripping step. The washed material is separated into layers in a secondary layering tank to obtain desalted crude ester. Two-stage negative pressure stripping process: The desalted crude ester is sequentially fed into a primary stripping tower and a secondary stripping tower for negative pressure stripping to remove residual isooctanol; the temperature of the primary stripping tower is 170℃~195℃, and the absolute pressure at the top of the tower is 0.080MPa~0.092MPa; the temperature of the secondary stripping tower is 180℃~205℃, and the absolute pressure at the top of the tower is 0.085MPa~0.095MPa; the vapor at the top of the stripping tower is condensed and separated into layers, the upper layer of crude isooctanol is sent to the distillation tower for recovery, and the lower layer of high-temperature hot water is reused in the washing kettle; Decolorization and filtration steps: The stripped semi-finished product is sent to a decolorization tank, a decolorization aid is added for adsorption and decolorization, and then it is filtered through primary filtration and precision filtration to obtain the DOTP finished product.

[0029] Preferably, the titanium-based composite catalyst solution is formulated as follows: based on the total mass of PTA feed, the amount of tetraisopropyl titanate as the main catalyst is 0.025%~0.045%, and the amount of ethylene glycol diacetate as the synergistic stabilizer is 30% of the amount of tetraisopropyl titanate; a 10wt% homogeneous catalytic mother liquor is prepared by circulating and refining isooctyl alcohol, and continuously metered and injected into the first esterification reactor.

[0030] Preferably, the alkaline solution is a weak alkaline composite solution with the following mass formula: 94wt% deionized water, 3wt% sodium carbonate, and 3wt% sodium bicarbonate, prepared at a temperature of 50℃~60℃; the molar amount of alkaline solution added is 1.05~1.10 times the total amount of free acid in the crude ester.

[0031] Preferably, the decolorizing agent is formulated as follows: based on the mass of crude ester, 0.12%~0.20% food-grade diatomaceous earth and 0.04%~0.08% activated clay.

[0032] Preferably, a polymerization inhibitor, p-tert-butylcatechol (TBC), is added to the feed of the distillation column, and is continuously added at 0.008% to 0.015% of the mass of crude isooctanol in the total distillation feed.

[0033] Compared with the prior art, the present invention has achieved the following beneficial effects: First, it achieves uninterrupted, continuous, and automated operation throughout the entire process, significantly enhancing production stability. The newly added neutralization pH interlock control module, stripping vacuum automatic control module, distillation purity online monitoring module, and waste heat exchange temperature automatic adjustment module are fully integrated with the existing esterification unit's liquid level, flow rate, and pressure automatic control system. The entire unit, from terephthalic acid powder feeding to DOTP finished product discharge, requires no intermediate storage tanks or manual material handling. The material flows continuously within closed pipelines and equipment, resulting in minimal fluctuations in product indicators. Compared to intermittent production modes and existing semi-continuous units, the degree of automation and capacity utilization are significantly improved.

[0034] Secondly, the invention significantly reduces the overall live steam consumption of the unit, resulting in outstanding energy-saving effects. By adding a first-stage esterification condenser and a second-stage esterification condenser at the top of the primary and secondary esterification process towers respectively as waste heat exchange units, the high-temperature azeotropic steam (170℃~230℃) directly exchanges heat with the fresh isooctanol in the tubes. The latent heat of vaporization of the azeotropic steam preheats the fresh isooctanol to 120℃~150℃ before sending it to the slurry preparation tank. Simultaneously, the cooled steam continues to enter the original secondary esterification condenser for condensation. This waste heat recovery method completely replaces the independent steam preheating equipment for fresh isooctanol, and the heat source required by the distillation tower and the two-stage stripping tower can also partially reuse the esterification waste heat, thereby reducing the overall live steam consumption of the unit by more than 30%. This overcomes the shortcomings of existing technologies, such as complete waste of latent heat of vaporization at the top of the towers and high heating costs.

[0035] Third, this invention achieves closed-loop recovery of isooctanol throughout the entire process, significantly reducing raw material loss. The invention centrally feeds alcohol-containing wastewater generated in each process into a distillation column for purification. Specifically, this includes three streams of alcohol-containing materials: esterification condensate drainage, water washing layered wastewater, and crude isooctanol obtained from two-stage stripping. After distillation in the column, high-purity isooctanol is produced at the top and returned to the slurry preparation tank via a recycled isooctanol pipe for further slurry preparation. Compared to traditional processes, this closed-loop recovery system reduces isooctanol raw material loss by 95%. Simultaneously, the distillation purification process effectively removes impurities such as organic acids and catalyst residues accumulated in the crude isooctanol, thereby stabilizing the esterification reaction rate, improving product color, and significantly reducing wastewater COD and hazardous waste treatment costs.

[0036] Fourth, the high-temperature hot water recycling significantly reduces wastewater discharge. In this invention, the top steam from the primary and secondary stripping towers is condensed and enters a reflux tank to achieve oil-water two-phase stratification. The lower layer of high-temperature hot water is entirely recycled to the washing kettle as washing water through a hot water supply pipe. The device only needs a small amount of demineralized water lost in the process and does not require continuous addition of fresh demineralized water. This hot water recycling structure reduces the total amount of wastewater discharged by 80%, significantly reducing the operating load of wastewater treatment facilities and overcoming the shortcomings of existing technologies, such as the continuous consumption of fresh water in the washing process and the direct discharge of esterification wastewater and stripping wastewater.

[0037] Fifth, the process removes various impurities from the crude ester in stages, resulting in a comprehensive upgrade in product quality. This invention integrates neutralization, counter-current washing, and two-stage negative pressure stripping processes after esterification. The neutralization system uses an online pH meter to interlock and control the amount of alkali added, precisely removing free acids from the crude ester and deactivating the titanium-based catalyst. The counter-current washing system uses high-temperature hot water to contact the crude ester in reverse, fully separating the sodium and titanium salts generated during neutralization. The two-stage negative pressure stripping tower uses low-pressure steam for counter-current stripping under negative pressure conditions, deeply removing residual free isooctanol. After the above continuous refining process, the core indicators of the finished product, such as acid value, volatile matter, and transmittance, meet the national standards for DOTP used in food contact, medical, and high-end cable materials, overcoming the limitations of existing technologies that directly discharge crude ester and can only produce low-end industrial-grade products.

[0038] Sixth, the raw material formulation is precise and continuous, resulting in good product consistency. The molar ratio of the main raw material PTA to isooctanol, the titanium-based composite catalyst formulation, the neutralizing weak alkali solution formulation, and the decolorizing agent formulation used in this invention are all automatically metered and controlled online. This eliminates the problems of fluctuations caused by manual, rough feeding in intermittent processes. The esterification conversion rate is stably maintained above 99.5%, and the acid value of the finished product is consistently ≤0.03mgKOH / g, significantly improving the consistency of batch product indicators.

[0039] Seventh, the environmentally friendly and low-loss formulation system achieves a high level of green production. The titanium-based heavy metal-free catalytic formulation, the weak-base composite neutralization formulation, and the stripping hot water circulation washing formulation work synergistically to reduce the output of hazardous catalyst waste and salt-containing solid waste by more than 35%; the distillation polymerization inhibition formulation solves the problem of octanol high-temperature polymerization loss, and the purity of recycled octanol is stable at ≥99.8%.

[0040] Eighth, the graded additive formula is suitable for high-end products, resulting in excellent product quality. The diatomaceous earth and activated clay composite decolorizing formula used in this invention can completely remove organic pigments. Combined with a low-temperature negative pressure stripping process, the produced DOTP meets the GB / T30822 standards for food contact and medical PVC plasticizers, solving the defects of incomplete decolorization and yellowing of finished products caused by traditional single decolorizing agents.

[0041] Ninth, it improves the appearance and storage stability of the finished product and reduces the frequency of equipment maintenance. The two-stage stripping of this invention operates under negative pressure, with the stripping temperature significantly lower than the atmospheric boiling point, effectively preventing DOTP materials from oxidizing and turning yellow at high temperatures. Subsequently, diatomaceous earth is continuously and quantitatively added in the decolorization tank to fully adsorb organic pigments. After two stages of precision filtration—a primary filter and a fine filter—diatomaceous earth, salt residue, and catalyst solid particles are completely removed, resulting in a product with high light transmittance and no precipitation during long-term storage. Simultaneously, the effective interception of solid impurities by the filtration unit significantly improves the clogging problems of downstream pipelines, conveying instruments, and regulating valves, reducing the frequency of equipment maintenance by 60%. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of 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. The drawings are provided for reference and illustration only and are not intended to limit the present invention. Wherein: Figure 1 This is a flowchart of the slurry preparation-esterification-distillation unit in this invention; Figure 2 This is a flowchart of the neutralization-washing stratification unit in this invention; Figure 3 This is a flowchart of the two-stage stripping-decolorizing filtration unit in this invention; Explanation of reference numerals in the attached figures: B1. Slurry conveying pump; B2. Esterification circulating pump; B3. Esterification conveying pump; B4. Tower top circulating pump; B5. Crude ester material conveying pump; B6. Neutralization material conveying pump; B7. Intermediate material conveying pump; B8. Layered material conveying pump; B9. Primary stripping material conveying pump; B10. Secondary stripping material conveying pump; B11. Decolorizing material conveying pump; B12. Product conveying pump; B13. Hot water conveying pump; C1. First esterification process tower; C2. Second esterification process tower; C3. Distillation tower; C4. First-stage stripping tower; C5. Second-stage stripping tower; E1. First esterification stage condenser; E2. First esterification stage condenser; E3. Second esterification stage condenser; E4. Second esterification stage condenser; E5. Distillation column top condenser; E6. First-stage stripping heat exchanger; E7. First-stage stripping column top condenser; E8. Second-stage stripping column top condenser; E9. Decolorized material cooler; E10. Product cooler; G1. Fresh isooctanol pipe; G2. Recycled isooctanol pipe; G3. High-pressure steam pipe; G4. Condensate collection pipe; G5. Cooling water supply pipe; G6. Cooling water return pipe; G7. Hot water collection pipe; G8. Alkali solution pipe; G9. Pure water pipe; G10. Hot water supply pipe; G11. Low-pressure steam pipe; H1. Esterified heater; L1. Primary filter; L2. Fine filter; M1. Vibrating screen; M2. Pipeline mixer; W1. PTA weighing scale; PH1. Online pH meter; Q1. PTA discharge rotary valve; Q2. Diatomaceous earth discharge rotary valve; R1. First esterification reactor; R2. Second esterification reactor; R3. Water washing reactor; S1. PTA silo; S2. Diatomaceous earth silo; T1. Slurry preparation tank; T2. First esterification tower top reflux tank; T3. Separation tank; T4. Second esterification tower top reflux tank; T5. Intermediate tank; T6. Collection tank; T7. Neutralization tank; T8. Primary stratification tank; T9. Secondary stratification tank; T10. Stripping transfer tank; T11. Primary stripping tower top reflux tank; T12. Secondary stripping tower top reflux tank; T13. Decolorization tank; T14. Product intermediate tank; T15. Hot water tank; X1. Exhaust gas treatment system; X2. Wastewater treatment plant; X3. Packaging system; ZG1. Esterification liquid ring vacuum pump set; ZG2. Stripping liquid ring vacuum pump set. Detailed Implementation

[0043] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0044] like Figure 1 , Figure 2 and Figure 3As shown, a continuous DOTP production unit for top heat recovery and closed-loop purification of alcohol is described. The complete unit consists of a slurry preparation-esterification-distillation unit, a neutralization-water washing and stratification unit, and a two-stage stripping-decolorization and filtration unit, and is equipped with a catalyst preparation unit, an alkali preparation unit, utility pipelines, and a DCS automatic control system.

[0045] I. Slurry Preparation-Esterification-Distillation Unit The slurry preparation-esterification-distillation unit includes a PTA silo S1, a PTA discharge rotary valve Q1, a vibrating screen M1, a PTA weighing scale W1, a slurry preparation tank T1, a slurry transfer pump B1, an esterification circulation pump B2, an esterification transfer pump B3, a tower top circulation pump B4, a crude ester material transfer pump B5, a first esterification kettle R1, a second esterification kettle R2, a first esterification process tower C1, a second esterification process tower C2, a first esterification primary condenser E1, a first esterification secondary condenser E2, a second esterification primary condenser E3, a second esterification secondary condenser E4, a distillation tower top condenser E5, a first esterification tower top reflux tank T2, a separation tank T3, a second esterification tower top reflux tank T4, an intermediate tank T5, a collection tank T6, a hot water tank T15, a hot water transfer pump B13, a distillation tower C3, and an esterification liquid ring vacuum pump group ZG1.

[0046] The material outlet of the PTA silo S1 is connected to the PTA discharge rotary valve Q1. The discharge port of the PTA discharge rotary valve Q1 is connected to the feed port of the vibrating screen M1. The discharge end of the vibrating screen M1 is connected to the feed port of the PTA metering scale W1. The discharge port of the PTA metering scale W1 is connected to the slurry preparation tank T1. The outlets of the fresh isooctanol pipe G1 and the recycled isooctanol pipe G2 are respectively connected to the feed interface of the slurry preparation tank T1. The bottom discharge port of the slurry preparation tank T1 is connected to the inlet of the slurry conveying pump B1. The outlet of the slurry conveying pump B1 is connected to the bottom feed port of the first esterification reactor R1. The first esterification reactor R1 is a vertical esterification reactor.

[0047] The bottom circulation outlet of the first esterification reactor R1 is connected to the inlet of the esterification circulation pump B2. The outlet of the esterification circulation pump B2 is connected to the lower inlet of the tube side of the esterification heater H1. The upper outlet of the tube side of the esterification heater H1 is connected to the upper circulation inlet of the side wall of the first esterification reactor R1. The shell-side steam inlet of the esterification heater H1 is connected to the outlet of the high-pressure steam pipe G3. The shell-side condensate outlet of the esterification heater H1 is connected to the condensate collection pipe G4. The material outlet in the middle of the side wall of the first esterification reactor R1 is connected to the bottom feed port at the inlet end of the second esterification reactor R2.

[0048] The top steam outlet of the first esterification reactor R1 is connected to the lower side wall inlet of the first esterification process tower C1. The top gas phase outlet of the first esterification process tower C1 is connected to the shell inlet of the first esterification primary condenser E1. The tube inlet of the first esterification primary condenser E1 is connected to the outlet of the fresh isooctanol tube G1. The tube outlet of the first esterification primary condenser E1 is connected to the isooctanol feed port of the slurry preparation tank T1. The shell-side outlet of the first esterification stage condenser E1 is connected to the shell-side inlet of the first esterification stage condenser E2. The tube-side inlet of the first esterification stage condenser E2 is connected to the cooling water supply pipe G5. The tube-side outlet of the first esterification stage condenser E2 is connected to the cooling water return pipe G6. The shell-side outlet of the first esterification stage condenser E2 is connected to the exhaust gas treatment system X1.

[0049] The condensate outlets of the first-stage condenser E1 and the second-stage condenser E2 of the first esterification process are respectively connected to the inlet of the first esterification tower top reflux tank T2. The first esterification tower top reflux tank T2 is equipped with a baffle extending from the bottom upwards. The lighter oil phase overflows from the top of the baffle into the oil phase space, which is equipped with an oil phase outlet. The oil phase outlet of the first esterification tower top reflux tank T2 is connected to the top reflux port of the first esterification process tower C1, and the aqueous phase outlet of the first esterification tower top reflux tank T2 is connected to the inlet of the separator T3.

[0050] The second esterification reactor R2 is a horizontal esterification reactor. The top gas phase outlet of the second esterification reactor R2 is connected to the lower side wall inlet of the second esterification process tower C2. The top gas phase outlet of the second esterification process tower C2 is connected to the shell-side inlet of the first-stage condenser E3 of the second esterification process. The tube-side inlet of the first-stage condenser E3 of the second esterification process is connected to the outlet of the fresh isooctanol tube G1. The tube-side outlet of the first-stage condenser E3 of the second esterification process is connected to the isooctanol feed port of the slurry preparation tank T1.

[0051] The shell-side outlet of the second esterification stage condenser E3 is connected to the shell-side inlet of the second esterification stage condenser E4. The tube-side inlet of the second esterification stage condenser E4 is connected to the cooling water supply pipe G5. The tube-side outlet of the second esterification stage condenser E4 is connected to the cooling water return pipe G6. The shell-side outlet of the second esterification stage condenser E4 is connected to the exhaust gas treatment system X1.

[0052] The condensate outlets of the first-stage condenser E3 and the second-stage condenser E4 of the second esterification process are respectively connected to the inlet of the top reflux tank T4 of the second esterification tower. The top reflux tank T4 of the second esterification tower is equipped with a baffle extending from the bottom upwards. The lighter oil phase overflows from the top of the baffle into the oil phase space, which is equipped with an oil phase outlet. The oil phase outlet of the top reflux tank T4 of the second esterification tower is connected to the top reflux port of the second esterification process tower C2. The water phase outlet of the top reflux tank T4 of the second esterification tower is connected to the inlet of the separator T3. The bottom outlet of the separator T3 is connected to the inlet of the hot water tank T15 through the hot water collection pipe G7. The bottom outlet of the hot water tank T15 is connected to the inlet of the hot water transfer pump B13. The outlet of the hot water transfer pump B13 is connected to the hot water supply pipe G10.

[0053] The liquid discharge port on the side wall of the discharge end of the second esterification reactor R2 is connected to the upper feed port of the intermediate tank T5. The intermediate tank T5 is equipped with a heating coil, and a heat tracing pipe is coiled around its outer wall. The inlets of both the heating coil and the heat tracing pipe are connected to the high-pressure steam pipe G3, and the outlets of both are connected to the condensate collection pipe G4. The top exhaust port of the intermediate tank T5 is connected to the tail gas treatment system X1. The bottom discharge port of the intermediate tank T5 is connected to the inlet of the esterification transfer pump B3, and the outlet of the esterification transfer pump B3 is connected to the lower side wall inlet of the distillation column C3.

[0054] The vapor outlet at the top of distillation column C3 is connected to the shell-side inlet of distillation column top condenser E5. The tube-side inlet of distillation column top condenser E5 is connected to cooling water supply pipe G5. The tube-side outlet of distillation column top condenser E5 is connected to cooling water return pipe G6. The shell-side outlet of distillation column top condenser E5 is connected to the inlet of esterification liquid ring vacuum pump group ZG1. The outlet of esterification liquid ring vacuum pump group ZG1 is connected to tail gas treatment system X1.

[0055] The shell-side condensate outlet of the top condenser E5 of the distillation column is connected to the top inlet of the collection tank T6. The bottom outlet of the collection tank T6 is connected to the inlet of the top circulation pump B4. One outlet of the top circulation pump B4 is connected to the upper reflux port of the distillation column C3, and the other outlet is connected to the inlet of the slurry preparation tank T1 through the isooctanol recycling pipe G2.

[0056] A distillation column heater is installed at the bottom of the inner cavity of distillation column C3. The inlet of the distillation column heater is connected to the high-pressure steam pipe G3, and the outlet of the distillation column heater is connected to the condensate collection pipe G4. The bottom outlet of distillation column C3 is connected to the inlet of crude ester material transfer pump B5, and the outlet of crude ester material transfer pump B5 is connected to the material inlet of pipeline mixer M2.

[0057] II. Neutralization-Washing Layered Unit like Figure 2As shown, the neutralization-washing stratification unit includes a pipeline mixer M2, a neutralization tank T7, a neutralization material transfer pump B6, a primary stratification tank T8, a washing kettle R3, an intermediate material transfer pump B7, a secondary stratification tank T9, a stripping transfer tank T10, and a stratification material transfer pump B8. An online pH meter PH1 is installed on the side wall of the neutralization tank T7. The signal output terminal of the online pH meter PH1 is connected to the signal input terminal of the DCS automatic control system. The control output terminal of the DCS automatic control system is connected to the alkali metering pump on the alkali pipe G8 to automatically adjust the amount of alkali added according to the pH signal.

[0058] The outlet pipe of the crude ester material conveying pump B5, along with the outlet pipes of the alkali solution pipe G8 and the pure water pipe G9, are connected to the feed end of the pipeline mixer M2. The discharge port of the pipeline mixer M2 is connected to the feed port of the neutralization tank T7, which is equipped with a stirring mechanism. The bottom discharge port of the neutralization tank T7 is connected to the inlet of the neutralizing material conveying pump B6, and the outlet of the neutralizing material conveying pump B6 is connected to the feed port of the primary stratification tank T8. The primary stratification tank T8 has a baffle extending from the bottom upwards. The lighter oil phase overflows from the top of the baffle into the oil phase space, and the outlet of the oil phase space is connected to the upper oil phase discharge pipe. The upper oil phase discharge pipe of the primary stratification tank T8 is connected to the feed port of the washing kettle R3. The bottom wastewater outlet of the primary stratification tank T8 is connected to the wastewater treatment plant X2.

[0059] The outlet of the hot water supply pipe G10 is connected to the hot water inlet of the washing vessel R3. The outlet of the washing vessel R3 is connected to the top inlet of the secondary stratification tank T9 via the intermediate material conveying pump B7. The secondary stratification tank T9 is equipped with a baffle extending from the bottom upwards. The lighter desalted crude ester overflows from the top of the baffle into the desalted crude ester space, which has an upper desalted crude ester outlet. The upper desalted crude ester outlet of the secondary stratification tank T9 is connected to the top inlet of the stripping transfer tank T10. The bottom wastewater outlet of the secondary stratification tank T9 is connected to the sewage treatment plant X2. The bottom outlet of the stripping transfer tank T10 is connected to the inlet of the stratification material conveying pump B8, and the outlet of the stratification material conveying pump B8 is connected to the two-stage stripping-decolorization filtration unit.

[0060] III. Two-stage stripping-decolorization filtration unit like Figure 3 As shown, the two-stage stripping-decolorization filtration unit includes a first-stage stripping tower C4, a first-stage stripping heat exchanger E6, a first-stage stripping tower top condenser E7, a first-stage stripping tower top reflux tank T11, a second-stage stripping tower C5, a second-stage stripping tower top condenser E8, a second-stage stripping tower top reflux tank T12, a stripping liquid ring vacuum pump group ZG2, a diatomaceous earth silo S2, a diatomaceous earth discharge rotary valve Q2, a decolorization tank T13, a primary filter L1, a fine filter L2, a decolorization material cooler E9, a product cooler E10, a product intermediate tank T14, a product transfer pump B12, a first-stage stripping material transfer pump B9, and a second-stage stripping material transfer pump B10.

[0061] The discharge pipeline of the stripping transfer tank T10 is connected to the cold side inlet of the first-stage stripping heat exchanger E6 via the stratified material conveying pump B8. The cold side outlet of the first-stage stripping heat exchanger E6 is connected to the upper feed inlet of the first-stage stripping tower C4. The bottom of the inner cavity of the first-stage stripping tower C4 is equipped with a first-stage stripping heating coil. The inlet of the first-stage stripping heating coil is connected to the high-pressure steam pipe G3, and the outlet of the first-stage stripping heating coil is connected to the condensate collection pipe G4.

[0062] The liquid phase outlet at the bottom of the first-stage stripping tower C4 is connected to the inlet of the first-stage stripping material conveying pump B9. The outlet of the first-stage stripping material conveying pump B9 is connected to the hot-side inlet of the first-stage stripping heat exchanger E6. The hot-side outlet of the first-stage stripping heat exchanger E6 is connected to the upper feed inlet of the second-stage stripping tower C5.

[0063] The bottom of the inner cavity of the secondary stripping tower C5 is equipped with a secondary stripping heating coil. The inlet of the secondary stripping heating coil is connected to the low-pressure steam pipe G11, and the outlet of the secondary stripping heating coil is connected to the condensate collection pipe G4. The bottom liquid phase outlet of the secondary stripping tower C5 is connected to the inlet of the secondary stripping material conveying pump B10. The outlet of the secondary stripping material conveying pump B10 is connected to the hot side inlet of the decolorizing material cooler E9. The hot side outlet of the decolorizing material cooler E9 is connected to the upper feed inlet of the decolorizing tank T13. The cold side inlet of the decolorizing material cooler E9 is connected to the cooling water supply pipe G5, and the cold side outlet of the decolorizing material cooler E9 is connected to the cooling water return pipe G6.

[0064] The vapor outlet at the top of the first-stage stripping tower C4 is connected to the shell-side inlet of the first-stage stripping tower top condenser E7. The tube-side inlet of the first-stage stripping tower top condenser E7 is connected to the cooling water supply pipe G5, and the tube-side outlet of the first-stage stripping tower top condenser E7 is connected to the cooling water return pipe G6. The shell-side outlet of the first-stage stripping tower top condenser E7 is connected to the inlet of the stripping liquid ring vacuum pump unit ZG2, and the exhaust port of the stripping liquid ring vacuum pump unit ZG2 is connected to the tail gas treatment system X1. The shell-side condensate outlet of the first-stage stripping tower top condenser E7 is connected to the inlet of the first-stage stripping tower top reflux tank T11. The upper crude isooctanol outlet of the first-stage stripping tower top reflux tank T11 is connected to the feed interface of the slurry preparation tank T1 through the recycled isooctanol pipe G2. The lower drain outlet of the first-stage stripping tower top reflux tank T11 is connected to the inlet of the hot water tank T15 through the hot water collection pipe G7.

[0065] The vapor outlet at the top of the secondary stripping column C5 is connected to the shell-side inlet of the secondary stripping column overhead condenser E8. The tube-side inlet of the secondary stripping column overhead condenser E8 is connected to the cooling water supply pipe G5, and the tube-side outlet of the secondary stripping column overhead condenser E8 is connected to the cooling water return pipe G6. The shell-side outlet of the secondary stripping column overhead condenser E8 is connected to the inlet of the stripping liquid ring vacuum pump unit ZG2. The shell-side condensate outlet of the secondary stripping column overhead condenser E8 is connected to the inlet of the secondary stripping column overhead reflux tank T12. The upper crude isooctanol outlet of the secondary stripping column overhead reflux tank T12 is connected to the feed interface of the slurry preparation tank T1 through the recycled isooctanol pipe G2. The lower drain outlet of the secondary stripping column overhead reflux tank T12 is connected to the inlet of the hot water tank T15 through the hot water collection pipe G7.

[0066] The discharge port of the diatomaceous earth silo S2 is equipped with a diatomaceous earth discharge rotary valve Q2, which is connected to the solid feed port of the decolorization tank T13. The decolorization tank T13 is equipped with a stirring device. The bottom discharge port of the decolorization tank T13 is connected to the inlet of the decolorization material conveying pump B11. The outlet of the decolorization material conveying pump B11 is connected in series with a primary filter L1 and a fine filter L2. The discharge port of the fine filter L2 is connected to the hot side inlet of the product cooler E10. The cold side inlet of the product cooler E10 is connected to the cooling water supply pipe G5. The cold side outlet of the product cooler E10 is connected to the cooling water return pipe G6. The hot side outlet of the product cooler E10 is connected to the inlet of the intermediate product tank T14. The bottom outlet of the intermediate product tank T14 is connected to the packaging system X3 through the product conveying pump B12.

[0067] IV. Working process of this device The working process of the device of the present invention is as follows: The first step, slurry preparation process: PTA powder is stored in PTA silo S1. The powder is discharged via PTA discharge rotary valve Q1, and after being screened by vibrating screen M1 to remove agglomerated impurities, it enters PTA metering scale W1 for continuous metering. The metered PTA powder is then sent to slurry preparation tank T1. Fresh isooctanol enters the tube side of the first esterification stage condenser E1 and the tube side of the second esterification stage condenser E3 through fresh isooctanol pipe G1, absorbing heat from the azeotropic vapor at the top of the esterification tower for preheating. The preheated fresh isooctanol is then sent to slurry preparation tank T1. High-purity recycled isooctanol obtained from the top of distillation column C3 is sent to slurry preparation tank T1 through recycled isooctanol pipe G2. The catalyst solution prepared by the catalyst preparation unit is continuously added to the slurry preparation tank T1 in proportion. Inside slurry preparation tank T1, PTA powder, preheated fresh isooctanol, recycled isooctanol, and catalyst are thoroughly stirred and mixed to prepare the reaction slurry.

[0068] As a preferred embodiment, in the slurry preparation process, the molar ratio of terephthalic acid to isooctanol is 1:2.30~2.60, and the solid content of the slurry is 32wt%~38wt%. The formulation of the titanium-based composite catalyst solution is as follows: based on the total mass of PTA feed, the amount of tetraisopropyl titanate as the main catalyst is 0.025%~0.045%, and the amount of ethylene glycol diacetate as the synergistic stabilizer is 30% of the amount of tetraisopropyl titanate. A 10wt% homogeneous catalytic mother liquor is prepared by circulating and refining isooctanol and continuously metered into the first esterification reactor R1.

[0069] The second step, continuous esterification process: The prepared slurry is transported by slurry transfer pump B1 to the first esterification reactor R1 for the first esterification reaction. Esterification product circulation pump B2 enables forced circulation and heating of the material in the first esterification reactor R1. The material after the reaction in the first esterification reactor R1 is sent to the second esterification reactor R2 for a deeper esterification reaction. The isooctanol-water azeotropic vapor generated in the first esterification reactor R1 enters the first esterification process tower C1. The high-temperature vapor at the top of the tower enters the shell side of the first esterification primary condenser E1, where it exchanges heat with the fresh isooctanol in the tube side. The vapor after heat exchange and cooling enters the first esterification secondary condenser E2 for condensation. The condensate enters the first esterification tower top reflux tank T2 for oil-water separation.

[0070] The isooctanol-water azeotropic vapor generated in the second esterification reactor R2 enters the second esterification process tower C2. The high-temperature vapor at the top of the tower enters the shell side of the first-stage condenser E3 of the second esterification process to exchange heat with fresh isooctanol. The cooled vapor enters the second-stage condenser E4 of the second esterification process to be condensed. The condensate enters the reflux tank T4 at the top of the second esterification tower.

[0071] Preferably, the operating temperature of the first esterification reactor R1 is 180℃~210℃, the gauge pressure is 0.10MPa~0.25MPa, and the material residence time is 2.0 hours~3.0 hours; the operating temperature of the second esterification reactor R2 is 210℃~235℃, the gauge pressure is 0.05MPa~0.20MPa, and the material residence time is 2.5 hours~3.5 hours; the top temperature of both the first esterification process tower C1 and the second esterification process tower C2 is 170℃~230℃.

[0072] The third step is the waste heat recovery process: the condensate from the top reflux tank T2 of the first esterification tower and the top reflux tank T4 of the second esterification tower undergoes oil-water two-phase separation respectively; the crude isooctanol separated from the top reflux tank T2 of the first esterification tower returns to the top of the first esterification process tower C1, and the crude isooctanol separated from the top reflux tank T4 of the second esterification tower returns to the top of the second esterification process tower C2.

[0073] The aqueous phases separated from the first esterification tower top reflux tank T2 and the second esterification tower top reflux tank T4 enter the separation tank T3 respectively. The drainage from the separation tank T3 enters the hot water tank T15 for collection. The hot water in the hot water tank T15 is sent out by the hot water transfer pump B13 and the hot water supply pipe G10 to provide hot water for washing the washing kettle R3.

[0074] The fourth step is the distillation and recovery process: The esterified material discharged from the second esterification reactor R2 is sent to the intermediate tank T5 for buffering. The material in the intermediate tank T5 is then transported to the distillation column C3 by the esterification transfer pump B3 for distillation. The vaporous material at the top of the distillation column C3 is condensed by the distillation column top condenser E5 to obtain high-purity isooctanol, which is then discharged into the collection tank T6 for collection. The discharge from the collection tank T6 is sent out by the column top circulation pump B4, with part of it returning to the top of the distillation column C3 and the other part returning to the slurry preparation tank T1 through the isooctanol recycling pipe G2 for circulation and slurry preparation.

[0075] Preferably, the top temperature of distillation column C3 is 155℃~175℃, the bottom temperature is 220℃~245℃, the absolute pressure at the top is 0.07MPa~0.09MPa, and the total residence time of the material is controlled at 1.5 hours~2.5 hours; the polymerization inhibitor p-tert-butylcatechol (TBC) is added to the feed of the distillation column, and is continuously added at 0.008%~0.015% of the mass of crude isooctanol in the total feed of the distillation column.

[0076] The bottom liquid output of distillation column C3 is crude ester material after most of the isooctanol has been removed, which is then transported to the neutralization-washing stratification unit via crude ester material transfer pump B5.

[0077] Step 5, Neutralization-Washing Process: The crude ester material from the bottom of distillation column C3, along with dilute alkali solution from alkali solution pipe G8 and pure water from pure water pipe G9, enters the pipeline mixer M2 for premixing. The premixed material then enters the neutralization tank T7. Stirring is activated in neutralization tank T7, and the pH value of the material inside the tank is monitored in real time by the online pH meter PH1. The instrument signal interlocks with the alkali solution metering pump to automatically adjust the amount of alkali solution added, completing the neutralization of the free acid in the crude ester and the destruction of the titanium-based catalyst. After neutralization, the material is sent by the neutralized material transfer pump B6 to the primary stratification tank T8 for static stratification of the oil and water phases. The upper oil phase material from the primary stratification tank T8 overflows into the washing kettle R3; the lower wastewater from the primary stratification tank T8 is sent to the wastewater treatment plant X2 for treatment. The washing vessel R3 receives high-temperature recycled hot water from the two-stage stripping unit via the hot water supply pipe G10. The washing vessel R3 is equipped with a stirring mechanism, which performs countercurrent washing on the crude ester under stirring conditions to remove salt impurities. The washed material is sent to the secondary stratification tank T9 for further stratification via the intermediate material transfer pump B7. The wastewater in the lower layer of the secondary stratification tank T9 is sent to the sewage treatment plant X2 for treatment. The overflow of the desalted crude ester in the upper layer of the secondary stratification tank T9 enters the stripping transfer tank T10.

[0078] Preferably, the neutralization tank T7 operates at a temperature of 110℃~140℃ under normal pressure, with an online pH control range of 6.5~8.0 and a material residence time of 0.4 hours~0.8 hours; the primary stratification tank T8 and the secondary stratification tank T9 both operate at a temperature of 100℃~130℃ under normal pressure, with a single tank stratification residence time of 0.6 hours~1.2 hours; the washing kettle R3 operates at a temperature of 95℃~125℃ under normal pressure, with a material residence time of 0.5 hours~1.0 hours; the washing hot water comes from the recycled hot water of the stripping unit. The alkali solution is a weak alkali composite solution with the following mass formula: 94wt% deionized water, 3wt% sodium carbonate, and 3wt% sodium bicarbonate, prepared at a temperature of 50℃~60℃; the molar amount of alkali solution added is 1.05~1.10 times the total amount of free acid in the crude ester.

[0079] Step 6, Two-stage negative pressure stripping process: The crude ester material inside the stripping transfer tank T10 is transported by the stratified material conveying pump B8, and after being heated by the cold side heat exchanger E6, it is sent to the upper part of the first-stage stripping tower C4. High-pressure steam from the high-pressure steam pipe G3 enters the first-stage stripping heating coil to heat the bottom material of the first-stage stripping tower C4. The stripping liquid ring vacuum pump group ZG2 evacuates the first-stage stripping tower C4 to maintain the negative pressure condition inside the tower. Most of the free isooctanol inside the crude ester is stripped and separated by steam. The bottom material of the first-stage stripping tower C4 is sent to the hot side heat exchanger E6 by the first-stage stripping material conveying pump B9, and then enters the upper feed inlet of the second-stage stripping tower C5.

[0080] Low-pressure steam from the low-pressure steam pipe G11 enters the secondary stripping heating coil to heat the bottom material of the secondary stripping tower C5. The stripping liquid ring vacuum pump group ZG2 maintains the negative pressure in the secondary stripping tower C5 to further strip the material to remove residual isooctyl alcohol.

[0081] The stripping steam from the top of the first-stage stripping tower C4 enters the shell side of the first-stage stripping tower top condenser E7 for condensation, and the condensed material enters the first-stage stripping tower top reflux tank T11; the stripping steam from the top of the second-stage stripping tower C5 enters the shell side of the second-stage stripping tower top condenser E8 for condensation, and the condensed material enters the second-stage stripping tower top reflux tank T12; the material inside the first-stage stripping tower top reflux tank T11 and the second-stage stripping tower top reflux tank T12 stratifies, the upper layer of isooctanol enters the slurry preparation tank T1 through the isooctanol recycling pipe G2, and the lower layer of high-temperature hot water enters the hot water tank T15, and is then transported to the washing kettle R3 as washing water through the hot water transfer pump B13 and the hot water supply pipe G10.

[0082] As a preferred embodiment, the temperature of the primary stripping tower C4 is 170℃~195℃, the absolute pressure at the top of the tower is 0.080MPa~0.092MPa, and the material residence time is controlled at 0.8 hours~1.2 hours; the temperature of the secondary stripping tower C5 is 180℃~205℃, the absolute pressure at the top of the tower is 0.085MPa~0.095MPa, and the material residence time is controlled at 1.0 hour~1.5 hours; the operating temperature of the primary stripping tower top reflux tank T11 and the secondary stripping tower top reflux tank T12 is 80℃~110℃.

[0083] Step 7, Decolorization and Filtration Process: The semi-finished material from the bottom of the secondary stripping tower C5, after isooctanol removal, is cooled on the hot side by the decolorizing material cooler E9 and then sent to the decolorization tank T13. Diatomaceous earth stored in the diatomaceous earth silo S2 is continuously and quantitatively added to the decolorization tank T13 through the diatomaceous earth discharge rotary valve Q2. The decolorization tank T13 is stirred to ensure that the diatomaceous earth is fully mixed with the material to adsorb colored impurities. The decolorized material is sequentially conveyed by the decolorizing material transfer pump B11 to the primary filter L1 and the fine filter L2 to filter out diatomaceous earth, salt residue, and catalyst solid particles. The qualified DOTP material after filtration is sequentially cooled on the hot side by the product cooler E10 and then enters the intermediate product tank T14 for buffering. The finished product in the intermediate product tank T14 is conveyed to the packaging system X3 by the product transfer pump B12 for storage and packaging.

[0084] Preferably, the decolorizing tank T13 operates at a temperature of 150℃~175℃ under normal pressure, with diatomaceous earth added at 0.1%~0.5% of the crude ester mass, and the stirring residence time controlled at 0.3 hours~0.6 hours. The decolorizing agent formula is: food-grade diatomaceous earth 0.12%~0.20% and activated clay 0.04%~0.08% by mass of crude ester. The feed temperature of both the primary filter L1 and the fine filter L2 is 145℃~170℃. The discharge temperature of the product after cooling is less than or equal to 60℃.

[0085] V. Public Works and Automatic Control All exhaust gases generated by the equipment are collected and sent to the exhaust gas treatment system X1. Utility pipelines include a high-pressure steam pipe G3, a low-pressure steam pipe G11, a condensate collection pipe G4, a cooling water supply pipe G5, a cooling water return pipe G6, a hot water collection pipe G7, a hot water supply pipe G10, a nitrogen pipeline, and a compressed air pipeline. The catalyst preparation unit outputs a catalyst solution, which is continuously and quantitatively delivered to the slurry preparation tank T1 using a metering pump. The alkali preparation unit prepares a qualified dilute alkali solution, which is then delivered to the pipeline mixer M2 at the neutralization front end via a metering pump.

[0086] All temperature, liquid level, pressure, pH, vacuum, and flow rate sensors in the entire unit are connected to the DCS automatic control system. The neutralization pH interlock control module, the stripping vacuum automatic control module, the distillation purity online monitoring module, and the waste heat exchange temperature automatic adjustment module work together to achieve automatic closed-loop regulation of each process. From PTA powder feeding to DOTP finished product discharge, the material runs continuously throughout the entire process without the need for intermediate storage tanks to buffer the material.

[0087] In this embodiment, the azeotropic vapor temperature range at the top of the first and second esterification process towers is 170℃~230℃, and this part of the steam heat is used to preheat fresh isooctanol; the total steam consumption of the entire unit is reduced by more than 30%; isooctanol produced in all processes is uniformly sent to the distillation tower to complete closed-loop recovery, reducing isooctanol raw material loss by 95%; the high-temperature hot water generated by stripping is all recycled for the water washing process, and the unit only needs to supplement a small amount of demineralized water lost in the process, reducing the total amount of wastewater discharged by 80%; negative pressure low-temperature stripping can avoid the yellowing of DOTP material due to high-temperature oxidation; after neutralization water washing, two-stage negative pressure stripping, diatomaceous earth adsorption decolorization, and two-stage precision filtration, the acid value, volatile matter, and light transmittance of the finished product meet the national standards for food contact grade and medical grade DOTP; after solid impurities are intercepted by the filtration unit, pipeline and instrument blockage failures are reduced, and the frequency of equipment maintenance is reduced by 60%.

[0088] The present invention will be further described below through specific embodiments.

[0089] Example 1 (Compatible with food / medical grade DOTP production lines) 1) Pulp preparation raw material formula and operating parameters The main raw material molar ratio n(PTA):n(octanol) = 1:2.45; the slurry solid content is 35wt%; the octanol is preheated to 132℃ by the waste heat exchanger at the top of the tower; the closed powder is continuously fed and homogenized by frequency conversion stirring, with no sedimentation or stratification.

[0090] 2) Titanium-based composite catalytic system Based on the total mass of PTA feed, tetraisopropyl titanate is 0.035%, and the synergistic stabilizer ethylene glycol diacetate is 30% of the titanium main agent added; a 10wt% catalytic mother liquor is prepared using recycled octanol and continuously metered into the primary esterification reactor.

[0091] 3) Esterification process The primary esterification is carried out at 185℃, the secondary esterification at 198℃, and the total residence time for both stages is 4.5h. All the azeotropic vapor at the top of the esterification tower at 180~220℃ enters the waste heat exchanger to preheat the fresh octanol.

[0092] 4) Neutralization and washing formula Neutralizing alkaline solution: 94wt% demineralized water, 3wt% sodium carbonate, 3wt% sodium bicarbonate, prepared at 55℃; the molar amount of alkaline solution added is 1.08 times that of the crude ester free acid; the washing medium is two-stage stripping recovery of 80℃ circulating hot water, countercurrent contact washing.

[0093] 5) Two-stage stripping and distillation polymerization inhibitor formulation The first-stage stripping vacuum is -0.085MPa and 155℃; the second-stage stripping vacuum is -0.092MPa and 160℃; all alcohol-containing waste liquid is collected in a distillation column, and 0.010% TBC polymerization inhibitor is added according to the mass of crude octanol feed; the purity of the octanol at the top of the column is 99.85% and recycled, while the heavy components at the bottom of the column are intermittently discharged as hazardous waste.

[0094] 6) Decolorizing Filtration Aid Formulation Based on crude ester quality: 0.15% food-grade diatomaceous earth + 0.06% activated clay; decolorization tank residence time 20 minutes, plate primary filter + precision security two-stage filtration.

[0095] 7) Output indicators and energy and material consumption The finished product has an acid value of 0.022 mg KOH / g, a volatile content of 0.06%, and a light transmittance of 98.3%. The consumption of live steam is reduced by 34% compared with traditional batch units. The loss of octanol is 0.04%. The amount of wastewater discharged is reduced by 82%. The continuous and stable operation cycle is 92 days.

[0096] Example 2 (General Industrial Cable Grade DOTP) 1) Pulp preparation raw material formula and operating parameters The main raw material molar ratio n(PTA):n(octanol) = 1:2.30; the slurry solid content is 32wt%; the octanol is preheated with waste heat at 120℃ to reduce the distillation load.

[0097] 2) Titanium-based composite catalytic system Based on the total mass of PTA feed, tetraisopropyl titanate 0.025% and ethylene glycol diacetate 30% of the titanium main agent are used; a 10wt% octanol mother liquor is prepared for continuous addition.

[0098] 3) Esterification process Primary esterification was carried out at 182℃, secondary esterification at 192℃, with a total residence time of 4.2h; the waste heat exchange branch was fully open, and the auxiliary steam preheating of octanol was eliminated.

[0099] 4) Neutralization and washing formula The neutralization alkali solution ratio remains unchanged (3% sodium carbonate + 3% sodium bicarbonate desalination solution), and the molar amount of alkali solution added is 1.05 times that of free acid; the water washing circulation hot water temperature is 75℃.

[0100] 5) Two-stage stripping and distillation polymerization inhibitor formulation First-stage stripping vacuum: -0.082 MPa, 152℃; Second-stage stripping vacuum: -0.088 MPa, 156℃; TBC polymerization inhibitor addition: 0.008%.

[0101] 6) Decolorizing Filtration Aid Formulation Diatomaceous earth 0.12% + activated clay 0.04%, decolorization and retention time 15 min.

[0102] 7) Output indicators and energy and material consumption The finished product has an acid value of 0.030 mg KOH / g, volatile matter of 0.10%, and light transmittance of 96.1%; steam consumption is reduced by 30%; octanol loss is 0.06%; it is suitable for general industrial PVC cables and pipes, and the overall cost of auxiliary materials is lower.

[0103] Example 3 (High-purity, low-volatile, high-end cable material) 1) Pulp preparation raw material formula and operating parameters The molar ratio of main raw materials n(PTA):n(octanol) = 1:2.60; the solid content of the slurry is 38wt%; the octanol is preheated at 140℃ with residual heat, and the excess octanol enhances the removal of water and improves the esterification depth.

[0104] 2) Titanium-based composite catalytic system The addition of tetraisopropyl titanate was increased to 0.045%, and the addition of ethylene glycol diacetate was simultaneously increased to 30% of the titanium agent. 10wt% octanol mother liquor was continuously added.

[0105] 3) Esterification process The primary esterification temperature is 190℃, the secondary esterification temperature is 200℃, and the total residence time is 5.0h; the waste heat at the top of the column is simultaneously supplied to the octanol preparation and the preheating source of the distillation column.

[0106] 4) Neutralization and washing formula The composite weak alkali solution remains unchanged, and the molar amount added is 1.10 times that of the free acid; the water washing hot water temperature is 85℃ to enhance desalination.

[0107] 5) Two-stage stripping and distillation polymerization inhibitor formulation Two-stage steam boosts vacuum: first stage -0.088MPa, second stage -0.094MPa, temperature 162℃; TBC addition for distillation is increased to 0.015%, suppressing high-temperature coking of high-alcohol feed.

[0108] 6) Decolorizing Filtration Aid Formulation Diatomaceous earth 0.20% + activated clay 0.08%, decolorize and stay for 25 minutes to deeply remove trace amounts of colored byproducts.

[0109] 7) Output indicators and energy and material consumption The finished product has an acid value of 0.015 mg KOH / g, volatile matter of 0.03%, and light transmittance of 99.0%. It has excellent insulation and migration resistance properties. Steam consumption is reduced by 31%, and the closed-loop recovery of octanol offsets the loss from high alcohol ratios, with a total octanol loss of 0.03%. It is suitable for high-voltage cables and high-end PVC products with high migration resistance.

[0110] Comparative example (patent CN222606353U, no waste heat recovery, no distillation, no continuous refining unit). Pulp preparation: intermittent pulp preparation, with manual control of the PTA:octanol molar ratio of 1:2.4. There is no preheating waste heat; octanol is heated separately by a steam heat exchanger. Catalysis: Single tetraisopropyl titanate, without stabilizer, added at 0.045%, easily hydrolyzed and deactivated; No neutralization washing, two-stage stripping, or distillation system; crude ester is discharged directly, and octanol is simply recovered by a separate tank; no continuous decolorization and filtration unit; Operating results: Steam consumption is 45% high, octanol loss is 1.2%, finished product acid value is 0.12mgKOH / g, light transmittance is 86%, wastewater discharge is large, it can only produce low-end industrial DOTP, and cannot be used in the food, medical, and high-voltage cable fields.

[0111] As can be seen from the comparison examples and the three sets of embodiments of the present invention: Steam energy consumption: The steam consumption reduction range of the example is 30%~34%, while the comparative example has no waste heat recovery and the steam consumption is significantly higher; Octyl alcohol loss: In the embodiments of the present invention, the octanol loss is 0.03%~0.06%, while in the comparative example it is as high as 1.2%, and the raw material loss is significantly reduced; Product quality: The comparative example showed excessive crude ester acid value and low light transmittance; the embodiment of this invention has an acid value of 0.015~0.030mgKOH / g and a light transmittance of over 96%, which can cover the entire DOTP market. Environmental indicators: The example shows a reduction of more than 80% in wastewater discharge and a significant reduction in hazardous waste. In contrast, the example shows direct discharge of salt-containing and alcohol-containing wastewater, and high costs for COD and solid waste disposal.

[0112] The above description is merely a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention. The technical features described in the various embodiments of the present invention can be arbitrarily combined and used without contradicting each other. All process parameters, material ratios, and operating conditions are illustrative examples. Any modifications, substitutions, and variations made by those skilled in the art to the various embodiments after reading this specification, without departing from the basic concept of the present invention, should fall within the scope of protection of the claims asserted by the present invention.

Claims

1. A continuous DOTP production apparatus for top heat recovery and closed-loop purification of alcohol, characterized in that, It includes a slurry preparation-esterification-distillation unit, a neutralization-water washing and stratification unit, and a two-stage stripping-decolorization and filtration unit connected in series. The slurry preparation-esterification-distillation unit includes a slurry preparation tank (T1), a first esterification vessel (R1), a second esterification vessel (R2), a first esterification process tower (C1), a second esterification process tower (C2), a first esterification primary condenser (E1), and a second esterification primary condenser (E3). The outlet of the slurry preparation tank (T1) is sequentially connected to the first esterification reactor (R1) and the second esterification reactor (R2); the steam outlet of the first esterification reactor (R1) is connected to the shell side of the first esterification primary condenser (E1) via the first esterification process tower (C1), the steam outlet of the second esterification reactor (R2) is connected to the shell side of the second esterification primary condenser (E3) via the second esterification process tower (C2), and the fresh isooctanol tube (G1) is connected to the slurry preparation tank (T1) via the tube sides of the first esterification primary condenser (E1) and the second esterification primary condenser (E3). The outlet of the second esterification vessel (R2) is connected to the inlet of the distillation column (C3). The condensate outlet at the top of the distillation column (C3) is connected to the slurry preparation tank (T1) via the isooctanol recycling pipe (G2). The outlet at the bottom of the distillation column (C3) is connected to the neutralization-washing stratification unit. The outlet of the neutralization-washing stratification unit is connected to the two-stage stripping-decolorization filtration unit.

2. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol as described in claim 1, characterized in that, The slurry preparation-esterification-distillation unit also includes a PTA silo (S1), a PTA discharge rotary valve (Q1), a vibrating screen (M1), and a PTA metering scale (W1). The discharge port of the PTA silo (S1) is connected to the inlet of the slurry preparation tank (T1) in sequence via the PTA discharge rotary valve (Q1), the vibrating screen (M1), and the PTA metering scale (W1).

3. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol as described in claim 1, characterized in that, The slurry preparation-esterification-distillation unit further includes a first esterification secondary condenser (E2) and a second esterification secondary condenser (E4). The shell-side outlet of the first esterification primary condenser (E1) is connected to the shell-side inlet of the first esterification secondary condenser (E2); the shell-side outlet of the second esterification primary condenser (E3) is connected to the shell-side inlet of the second esterification secondary condenser (E4).

4. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 1, characterized in that, The slurry preparation-esterification-distillation unit further includes a separation tank (T3) and a hot water tank (T15). The aqueous phase outlets of the top condensate of the first esterification process tower (C1) and the second esterification process tower (C2) are respectively connected to the separation tank (T3). The outlet of the separation tank (T3) is connected to the hot water tank (T15). The outlet of the hot water tank (T15) is connected to the hot water inlet of the neutralization-washing stratification unit.

5. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 1, characterized in that, The neutralization-washing stratification unit includes a pipeline mixer (M2), a neutralization tank (T7), a primary stratification tank (T8), a washing vessel (R3), and a secondary stratification tank (T9). The bottom outlet of the distillation column (C3) and the alkali pipe (G8) are respectively connected to the feed end of the pipeline mixer (M2). The outlet of the pipeline mixer (M2) is sequentially connected to the neutralization tank (T7), the primary stratification tank (T8), the washing vessel (R3), and the secondary stratification tank (T9). The oil phase outlet of the secondary stratification tank (T9) is connected to the two-stage stripping-decolorization filtration unit.

6. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 5, characterized in that, The neutralization tank (T7) is equipped with an online pH meter (PH1), the signal output of which is connected to the DCS automatic control system, and the control output of which is connected to the alkali metering pump on the alkali pipe (G8).

7. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 1, characterized in that, The two-stage stripping-decolorizing filtration unit includes a primary stripping tower (C4), a secondary stripping tower (C5), and a primary stripping heat exchanger (E6). The outlet of the neutralization-washing stratification unit is connected to the cold-side inlet of the primary stripping heat exchanger (E6), and the cold-side outlet of the primary stripping heat exchanger (E6) is connected to the feed inlet of the primary stripping tower (C4). The bottom liquid phase outlet of the primary stripping tower (C4) is connected to the hot-side inlet of the primary stripping heat exchanger (E6) via a primary stripping material transfer pump (B9), and the hot-side outlet of the primary stripping heat exchanger (E6) is connected to the feed inlet of the secondary stripping tower (C5). The bottom liquid phase outlet of the secondary stripping tower (C5) is connected to the decolorizing filtration unit.

8. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 7, characterized in that, The condensate outlets at the top of the primary stripping tower (C4) and the secondary stripping tower (C5) are respectively connected to the recycled isooctanol pipe (G2). The aqueous phase outlets of the condensate at the top of the primary stripping tower (C4) and the secondary stripping tower (C5) are respectively connected to the hot water recycling pipeline. The hot water recycling pipeline is connected to the hot water inlet of the neutralization-washing stratification unit.

9. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 7, characterized in that, The decolorization and filtration unit includes a decolorization tank (T13), a primary filter (L1), and a fine filter (L2). The bottom liquid phase outlet of the secondary stripping tower (C5) is connected to the feed inlet of the decolorization tank (T13), and the outlet of the decolorization tank (T13) is connected in sequence to the primary filter (L1) and the fine filter (L2).

10. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 9, characterized in that, The two-stage stripping-decolorization filtration unit also includes a diatomaceous earth silo (S2) and a diatomaceous earth discharge rotary valve (Q2). The discharge port of the diatomaceous earth silo (S2) is connected to the solid feed port of the decolorization tank (T13) via the diatomaceous earth discharge rotary valve (Q2).

11. The DOTP continuous production apparatus for top heat recovery and closed-loop purification of alcohol according to claim 9, characterized in that, The two-stage stripping-decolorization filtration unit also includes a product cooler (E10) and a product intermediate tank (T14). The outlet of the fine filter (L2) is connected to the hot side inlet of the product cooler (E10), and the hot side outlet of the product cooler (E10) is connected to the inlet of the product intermediate tank (T14).

12. A continuous DOTP production method using the apparatus described in any one of claims 1 to 11 for top heat recovery and alcohol closed-loop purification, characterized in that, Includes the following steps: Slurry preparation steps: PTA powder is metered and fed into slurry preparation tank (T1). Fresh isooctanol is preheated to 120℃~150℃ by the residual heat of azeotropic steam at the top of the esterification tower and then fed into slurry preparation tank (T1). High-purity isooctanol recovered by distillation and titanium-based composite catalyst solution are continuously added to slurry preparation tank (T1) in proportion and stirred evenly to prepare reaction slurry; the molar ratio of PTA to isooctanol is 1:2.30~2.60, and the solid content of the slurry is 32wt%~38wt%. Continuous esterification step: The reaction slurry is sequentially fed into the first esterification reactor (R1) and the second esterification reactor (R2) for continuous esterification reaction; the reaction temperature of the first esterification reactor (R1) is 180℃~210℃, the gauge pressure is 0.10MPa~0.25MPa, and the residence time is 2.0h~3.0h; the reaction temperature of the second esterification reactor (R2) is 210℃~235℃, the gauge pressure is 0.05MPa~0.20MPa, and the residence time is 2.5h~3.5h. Waste heat recovery step: The isooctanol-water azeotropic vapor generated by the first esterification vessel (R1) and the second esterification vessel (R2) at 170℃~230℃ is sent to the shell side of the first esterification process tower (C1) and the second esterification process tower (C2) respectively, and exchanged heat with the fresh isooctanol in the tube side, preheating the fresh isooctanol to 120℃~150℃; Distillation recovery step: The output from the second esterification vessel (R2) is fed into the distillation column (C3) for distillation. The top temperature of the column is 155℃~175℃, the bottom temperature is 220℃~245℃, and the absolute pressure at the top of the column is 0.07MPa~0.09MPa. A portion of the high-purity isooctanol obtained by condensation at the top of the column is refluxed, and the other portion is returned to the slurry preparation tank (T1) for recycling. The output from the bottom of the column is crude ester material. Neutralization-washing step: The crude ester material and alkaline solution are premixed in a pipeline mixer (M2) and then sent to a neutralization tank (T7) for neutralization. After neutralization, the material is separated into layers in a primary separation tank (T8). The oil phase is sent to a washing kettle (R3) for countercurrent washing with recycled hot water from the stripping step. The material is then separated into layers in a secondary separation tank (T9) to obtain desalted crude ester. Two-stage negative pressure stripping process: The desalted crude ester is sequentially fed into a primary stripping tower (C4) and a secondary stripping tower (C5) for negative pressure stripping to remove residual isooctanol; the temperature of the primary stripping tower (C4) is 170℃~195℃, and the absolute pressure is 0.080MPa~0.092MPa; the temperature of the secondary stripping tower (C5) is 180℃~205℃, and the absolute pressure is 0.085MPa~0.095MPa; after the steam at the top of the tower is condensed and separated into layers, the upper layer of crude isooctanol is sent to a distillation tower (C3) for recovery, and the lower layer of high-temperature hot water is reused in the washing kettle (R3). Decolorization and filtration steps: The stripped semi-finished product is sent to the decolorization tank (T13), a decolorization aid is added for adsorption and decolorization, and then filtered through the primary filter (L1) and the fine filter (L2) to obtain the DOTP finished product.

13. The DOTP continuous production method according to claim 12, characterized in that, The formulation of the titanium-based composite catalyst solution is as follows: based on the total mass of PTA feed, the amount of tetraisopropyl titanate as the main catalyst is 0.025%~0.045%, and the amount of ethylene glycol diacetate as the synergistic stabilizer is 30% of the amount of tetraisopropyl titanate. A 10wt% homogeneous catalytic mother liquor is prepared by circulating and refining isooctyl alcohol and continuously metered and injected into the first esterification reactor (R1).

14. The DOTP continuous production method according to claim 12, characterized in that, The alkaline solution is a weak alkaline composite solution with the following mass formula: 94 wt% deionized water, 3 wt% sodium carbonate, and 3 wt% sodium bicarbonate, prepared at a temperature of 50℃~60℃; the molar amount of alkaline solution added is 1.05~1.10 times the total amount of free acid in the crude ester.

15. The DOTP continuous production method according to claim 12, characterized in that, The decolorizing agent is formulated as follows: based on the mass of crude ester, 0.12%~0.20% food-grade diatomaceous earth and 0.04%~0.08% activated clay.

16. The DOTP continuous production method according to claim 12, characterized in that, The feed to the distillation column (C3) contains a polymerization inhibitor, namely p-tert-butylcatechol (TBC), which is continuously added at a rate of 0.008% to 0.015% of the crude isooctanol mass in the total distillation feed.

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