An acetic acid dehydration purification system and process with a closed heat pump coupled with double towers in series

Abstract

The present application relates to a kind of closed heat pump coupling double-tower series' s acetic acid dehydration purification system and process, belong to chemical separation technical field;The purification system includes distillation section dehydration tower and rectification section dehydration tower, the bottom of the rectification section dehydration tower is communicated with the upper portion of the distillation section dehydration tower by pipeline, the top of the rectification section dehydration tower is connected with trap and reflux tank after condenser, the lower portion of the trap is communicated with the top of the reflux tank by pipeline, the bottom of the reflux tank is communicated with the upper portion of the rectification section dehydration tower by reflux pump, the top of the distillation section dehydration tower is communicated with the lower portion of the rectification section dehydration tower by pipeline.The purification system of the present application not only can reduce separation energy consumption, while effectively inhibiting equipment corrosion, from energy saving, reliability, economy three dimensions synchronous promotion, overcome the technical bottleneck that energy saving and anticorrosion is difficult to take into account in traditional process.

Description

Technical Field

[0001] This invention relates to a closed-loop heat pump coupled with two towers connected in series for acetic acid dehydration and purification, and to a process that belongs to the field of chemical separation technology. Background Technology

[0002] Acetic acid is an important basic organic chemical raw material, widely used in the production processes of terephthalic acid, vinyl acetate, acetate esters, pharmaceutical intermediates, and high-performance materials. These production processes often generate acetic acid-containing wastewater or dilute acetic acid solutions, which require dehydration and purification for recycling or to obtain high-purity acetic acid products. Acetic acid and water form a non-ideal binary system with a minimum azeotropic point under normal pressure; their relative volatility is low, making separation significantly more difficult than with ordinary organic-water systems. With increasingly stringent limits on acetic acid purity, moisture content, and residual metal ions in downstream high-end applications, coupled with rising requirements for energy conservation, emission reduction, and long-term stable equipment operation, existing acetic acid dehydration and purification technologies are showing increasingly prominent contradictions in terms of overall efficiency.

[0003] Currently, the widely used acetic acid dehydration technologies in industry mainly include conventional vacuum distillation, azeotropic distillation, and a small number of improved distillation forms supplemented by heat pumps. Conventional vacuum distillation reduces the operating pressure to decrease the reboiler temperature and alleviate high-temperature corrosion, but it still relies on external steam heating and circulating water cooling to achieve phase change separation, resulting in low energy utilization efficiency, huge consumption of steam and cooling water, and high operating costs. Azeotropic distillation requires the introduction of entrainers such as benzene and acetate esters into the system to change the relative volatility. Although this can reduce the theoretical plate number requirement, the addition of entrainers not only increases material loss and recovery processes, but also easily introduces new impurities, complicating the process and requiring high control precision. It is difficult to stably produce acetic acid products that meet high-quality requirements, and the risk of entrainer residue limits its application in the production of pharmaceutical and electronic grade acetic acid.

[0004] To reduce energy consumption, some technical solutions attempt to introduce heat pump distillation. In one approach, an open-loop heat pump directly extracts the vapor from the top of the distillation column, pressurizes and heats it using a compressor, and then uses it as a heat source for the bottom of the column. However, acetic acid vapor is highly corrosive to compressor impellers, seals, and bearings during high-temperature compression. This is especially true when the feedstock contains reactive corrosive impurities such as fluoride ions, leading to a sharp increase in compressor failure rates and frequent seal failures. This prevents the unit from achieving long-term continuous operation, severely hindering the industrial-scale adoption of this technology.

[0005] In terms of equipment corrosion prevention and product purity control, acetic acid systems exhibit significant corrosive effects on ordinary stainless steel at high temperatures, while the presence of impurities such as fluoride ions further exacerbates the risks of pitting corrosion, crevice corrosion, and stress corrosion cracking. Existing technologies often employ methods such as upgrading material grades (e.g., titanium, Hastelloy) or surface lining. However, even high-grade metal materials cannot completely avoid the dissolution of trace metal ions under long-term exposure to corrosive media. This not only shortens equipment lifespan and increases maintenance costs but also directly affects the metal ion content of acetic acid products, making them unable to meet the stringent requirements of high-end applications for trace metal impurities. Furthermore, a single corrosion prevention method cannot resolve the coupling contradiction between corrosion and mass transfer efficiency.

[0006] At the engineering implementation level, the number of theoretical separation plates required for acetic acid dehydration is usually large. Conventional single-tower structural designs result in a significant increase in tower height, which not only places extremely high demands on on-site installation space, hoisting capabilities, and transportation conditions, but also increases the risk of structural stability under wind loads and seismic actions, causing inconvenience for equipment maintenance. Although some existing technologies attempt to reduce tower height through optimization of tower internals or segmented design, this often comes at the cost of sacrificing separation efficiency or increasing operational flexibility, failing to fundamentally solve the problem of matching equipment structural rationality with process performance.

[0007] In summary, existing acetic acid dehydration and purification technologies all exhibit a clear tendency towards single-function optimization. Some prioritize energy saving while neglecting equipment corrosion and product purity, while others emphasize corrosion prevention at the expense of energy consumption and economy, or simplify the structure while reducing separation precision. There is currently no comprehensive technical solution that can simultaneously achieve highly efficient and energy-saving separation, long-life and reliable equipment operation, low metal ion content in the product, and a compact structure for easy engineering under highly corrosive, high-purity, and long-cycle operating conditions. Therefore, developing a new acetic acid dehydration and purification process and supporting equipment that can comprehensively address these multiple objectives has become an urgent technical challenge in this field. Summary of the Invention

[0008] This invention provides a novel acetic acid dehydration and purification system and process that integrates closed-loop heat pump energy saving, a dual-tower series structure, micro-negative pressure operation, and a composite anti-corrosion system. The closed-loop recycling of waste heat from the top of the towers significantly reduces system energy consumption; the dual-tower series structure increases the theoretical plate number of the dehydration towers, optimizing equipment layout and reducing installation difficulty; and the micro-negative pressure operation lowers the system temperature and mitigates corrosion from acetic acid and fluoride ions. Ultimately, this achieves a comprehensive improvement in energy saving, corrosion prevention, product purity, operational stability, and engineering applicability, providing a more advanced, reliable, and economical solution for the efficient purification of acetic acid aqueous solutions.

[0009] The technical solution provided by this invention is as follows: One objective of this invention is to provide a closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification system, comprising a stripping section dehydration tower and a rectifying section dehydration tower. The bottom of the rectifying section dehydration tower is connected to the top of the stripping section dehydration tower via a pipe. The top of the rectifying section dehydration tower is connected to a trap and a reflux tank via a condenser. The lower part of the trap is connected to the top of the reflux tank via a pipe. The bottom of the reflux tank is connected to the top of the rectifying section dehydration tower via a reflux pump. The top of the stripping section dehydration tower is connected to the lower part of the rectifying section dehydration tower via a pipe. The bottom of the stripping section dehydration tower is connected to a reboiler via a pipe. The bottom of the reboiler is connected to the lower part of the stripping section dehydration tower. The lower part of the reboiler is connected to a water circulation tank via a pipe. The top of the water circulation tank is connected to the upper part of the reboiler via a compressor. The bottom of the water circulation tank is connected to the top of the condenser via a circulation pump. The bottom of the condenser is connected to the top of the water circulation tank via a pipe.

[0010] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the upper part of the stripping section dehydration tower is provided with a raw material inlet, and the connecting pipe between the reboiler and the compressor is provided with a steam inlet.

[0011] Furthermore, the connecting pipe between the stripping section dehydration tower and the reboiler is provided with a crude acetic acid outlet, and the outlet pipe of the reflux pump is provided with a wastewater outlet.

[0012] The second objective of this invention is to provide a closed-loop heat pump coupled with two towers in series for acetic acid dehydration and purification, using the purification system described above.

[0013] Furthermore, the proposed process includes the following steps: The acetic acid aqueous solution to be treated enters the stripping section dehydration tower through the raw material inlet. Fresh steam is introduced through the steam inlet as a heat source to heat the bottom of the stripping section dehydration tower through the reboiler. The vapor phase generated at the top of the stripping section dehydration tower enters the lower part of the rectification section dehydration tower. The vapor phase produced at the top of the rectification section dehydration tower is condensed into liquid water through the condenser and the collector and enters the reflux tank. It is refluxed by the reflux pump and the wastewater is collected at the wastewater outlet. The crude acetic acid product is collected from the crude acetic acid product outlet on the bottom pipe of the stripping section dehydration tower. The liquid phase material at the bottom of the rectification section dehydration tower is transferred to the upper part of the stripping section dehydration tower through the pipeline. Mixed water produced at the bottom of the condenser enters the top of the water circulation tank. At the bottom of the water circulation tank, negative pressure low-temperature liquid saturated water is produced. It enters the top of the condenser for heat exchange via a circulation pump. Mixed water is produced at the bottom of the condenser. After gas-liquid separation in the water circulation tank, the gas phase water vapor enters the compressor for compression, temperature and pressure increase, and becomes high-temperature water vapor. It then enters the reboiler as a heat source for heat exchange. After heat exchange, it becomes low-temperature liquid water and returns to the water circulation tank through the lower part of the reboiler. Furthermore, the operating pressure of the stripping section dehydration tower and the rectifying section dehydration tower is 30~40 kPaA, and the operating reflux ratio is 3~5.

[0014] Furthermore, the theoretical number of plates in the stripping section dehydration tower is 20 to 40, and the theoretical number of plates in the rectifying section dehydration tower is 40 to 60.

[0015] Furthermore, the operating temperature at the top of the distillation section dehydration tower is 70~75℃, and the operating temperature at the bottom of the distillation section dehydration tower is approximately 70~80℃.

[0016] Furthermore, the operating temperature at the top of the stripping section dehydration tower is 70~80℃, and the operating temperature at the bottom of the stripping section dehydration tower is 75~85℃.

[0017] Furthermore, the compressor has an inlet pressure of 15~25 kPaA, an outlet pressure of atmospheric pressure, and a compression ratio of 4~6.

[0018] The technical solution provided by this invention has the following advantages compared with the prior art: 1. This invention systematically integrates closed-loop heat pump circulation, dual-tower series distillation, micro-negative pressure operation and full-process composite anti-corrosion system to form a complete dehydration and purification process with synergistic effect. It can not only reduce separation energy consumption, but also effectively inhibit equipment corrosion. It simultaneously improves energy saving, reliability and economy, and overcomes the technical bottleneck of traditional processes where energy saving and corrosion prevention are difficult to balance.

[0019] 2. This invention employs a micro-negative pressure condition in the acetic acid dehydration operation. On the one hand, it reduces the corrosion rate of acetic acid on metal materials, meeting the operational requirements of closed-loop heat pump systems for the stability of low-temperature heat sources. On the other hand, it utilizes the characteristic that the relative volatility of the acetic acid-water system increases with the increase of vacuum under negative pressure conditions, avoiding increased separation difficulty due to decompression operation, thus achieving synergistic optimization of corrosion prevention requirements and separation efficiency.

[0020] 3. This invention divides the dehydration tower into a rectification section tower and a stripping section tower, and adopts a series operation mode. Under the premise of ensuring that the theoretical plate number and separation effect remain unchanged, it effectively reduces the height of a single tower, which facilitates manufacturing, transportation and installation, improves the engineering feasibility and site adaptability of large-scale industrial equipment, and provides more flexible space for the arrangement of composite anti-corrosion structure inside the tower.

[0021] 4. This invention adopts a closed-loop heat pump system, using saturated water vapor under negative pressure as the circulating working fluid. The heat is circulated in a closed loop through heat exchange between the walls. The heat pump working fluid does not come into direct contact with corrosive media such as acetic acid throughout the process. This not only significantly reduces steam consumption and achieves energy-saving effects, but also avoids the problem of contact corrosion between the compressor impeller and corrosive materials. It solves the problem of easy damage and short life of open-loop heat pump compressors and ensures long-term reliable operation of the core power equipment.

[0022] 5. This invention addresses the multiple corrosion factors in the acetic acid dehydration system, including acetic acid, trace amounts of fluoride ions, and vacuum operation. It selects corrosion-resistant materials that match the corrosive environment in different equipment parts (such as the liquid phase zone and gas phase zone of the tower, the tube side and shell side of the heat exchanger, and the condenser). Without excessively increasing the overall cost, it forms a differentiated anti-corrosion protection covering the entire process, meeting the long-term stable production requirements under strong corrosive media and vacuum conditions. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the closed-loop heat pump coupled with two towers connected in series for acetic acid dehydration and purification according to the present invention.

[0024] In the diagram, 1. Stripping section dehydration tower; 2. Rectifying section dehydration tower; 3. Condenser; 4. Collector; 5. Reflux tank; 6. Reflux pump; 7. Reboiler; 8. Water circulation tank; 9. Compressor; 10. Circulation pump; 11. Raw material inlet; 12. Steam inlet; 13. Crude acetic acid outlet; 14. Wastewater outlet. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0026] As shown in Figure 1, a closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification system includes a stripping section dehydration tower 1 and a rectification section dehydration tower 2. The stripping section dehydration tower 1 has a raw material inlet 11 at its upper part. The bottom of the rectification section dehydration tower 2 is connected to the upper part of the stripping section dehydration tower 1 via a pipe. The top of the rectification section dehydration tower 2 is connected to a collector 4 and a reflux tank 5 via a condenser 3. The lower part of the collector 4 is connected to the top of the reflux tank 5 via a pipe. The bottom of the reflux tank 5 is connected to the upper part of the rectification section dehydration tower 2 via a reflux pump 6. The outlet pipe of the reflux pump 6 has a wastewater outlet 14. The top of the stripping section dehydration tower 1 is connected to the rectification section dehydration tower 2 via a pipe. The lower part of water tower 2 is connected to the bottom of the stripping section dehydration tower 1, which is connected to a reboiler 7 via a pipe. The pipe connecting the stripping section dehydration tower 1 and the reboiler 7 is provided with a crude acetic acid outlet 13. The bottom of the reboiler 7 is connected to the lower part of the stripping section dehydration tower 1. The lower part of the reboiler 7 is connected to a water circulation tank 8 via a pipe. The top of the water circulation tank 8 is connected to the upper part of the reboiler 7 via a compressor 9. The pipe connecting the reboiler 7 and the compressor 9 is provided with a steam inlet 12. The bottom of the water circulation tank 8 is connected to the top of the condenser 3 via a circulation pump 10. The bottom of the condenser 3 is connected to the top of the water circulation tank 8 via a pipe.

[0027] The purification process of the above-mentioned closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification system includes the following steps: The acetic acid aqueous solution to be treated enters the stripping section dehydration tower 1 through raw material inlet 11. The stripping section dehydration tower 1 has a theoretical plate number of 30. The operating pressure of the stripping section dehydration tower 1 is set to 35 kPaA, the operating reflux ratio is 3~5, the top operating temperature is 75℃, and the bottom operating temperature is 81℃. Fresh steam is introduced through steam inlet 12 as a heat source to heat the bottom of the stripping section dehydration tower 1 through reboiler 7. The vapor generated at the top of the stripping section dehydration tower 1 enters the lower part of the rectification section dehydration tower 2. The rectification section dehydration tower 2 has a theoretical plate number of 50. The operating pressure of the rectification section dehydration tower 2 is set to... The pressure is approximately 35 kPaA, the operating reflux ratio is 3~5, the top operating temperature is 72℃, and the bottom operating temperature is 75℃. The gas phase produced at the top of the distillation section dehydration tower 2 is condensed into liquid water by condenser 3 and collector 4 and enters reflux tank 5. It is refluxed by reflux pump 6 and wastewater is collected at wastewater outlet 14. The crude acetic acid product is collected from the crude acetic acid product outlet 13 on the bottom pipeline of the stripping section dehydration tower 1. The crude acetic acid product goes to the acetic acid refining tower to distill off the acetic acid to obtain acetic acid product. The liquid phase material at the bottom of the distillation section dehydration tower 2 is transferred to the upper part of the stripping section dehydration tower 1 through the pipeline as reflux liquid. The cold source is water under negative pressure. Mixed water is produced at the bottom of condenser 3 and enters the top of water circulation tank 8. At the bottom of water circulation tank 8, negative pressure low temperature liquid saturated water is produced. It enters the top of condenser 3 for heat exchange through circulation pump 10. Mixed water is produced at the bottom of condenser 3. After gas-liquid separation through water circulation tank 8, the gas phase water vapor enters compressor 9 (inlet pressure is about 20 kPaA, outlet pressure is atmospheric pressure, compression ratio is 5). After compression, heating and pressurization, it becomes high temperature water vapor and enters reboiler 7 as a heat source for heat exchange. After heat exchange, it becomes low temperature liquid water and returns to water circulation tank 8 through the lower part of reboiler 7.

[0028] The body of the distillation section dehydration tower 2 is made of 316L steel. The body of the stripping section dehydration tower 1 is made of carbon steel coated with soluble polytetrafluoroethylene (PFA) and the packing material is ceramic packing (when the fluoride ion content is high, the packing material is selected as polytetrafluoroethylene). The material of the trap 4 is polytetrafluoroethylene. The tube side of the reboiler 7 is made of silicon carbide and the shell side is made of carbon steel. The tube side of the condenser 3 is made of carbon steel and the shell side is made of 316L steel. The material of the reflux tank 5 is 316L steel.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A closed-loop heat pump coupled with two towers in series for acetic acid dehydration and purification, characterized in that, The system includes a stripping section dehydration tower (1) and a rectification section dehydration tower (2). The bottom of the rectification section dehydration tower (2) is connected to the top of the stripping section dehydration tower (1) via a pipe. The top of the rectification section dehydration tower (2) is connected to a trap (4) and a reflux tank (5) via a condenser (3). The lower part of the trap (4) is connected to the top of the reflux tank (5) via a pipe. The bottom of the reflux tank (5) is connected to the top of the rectification section dehydration tower (2) via a reflux pump (6). The top of the stripping section dehydration tower (1) is connected to the rectification section dehydration tower (2) via a pipe. The bottom of the stripping section dehydration tower (1) is connected to a reboiler (7) via a pipe. The bottom of the reboiler (7) is connected to the bottom of the stripping section dehydration tower (1). The bottom of the reboiler (7) is connected to a water circulation tank (8) via a pipe. The top of the water circulation tank (8) is connected to the top of the reboiler (7) via a compressor (9). The bottom of the water circulation tank (8) is connected to the top of the condenser (3) via a circulation pump (10). The bottom of the condenser (3) is connected to the top of the water circulation tank (8) via a pipe.

2. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification system according to claim 1, characterized in that, The upper part of the stripping section dehydration tower (1) is provided with a raw material inlet (11), and the connecting pipe between the reboiler (7) and the compressor (9) is provided with a steam inlet (12).

3. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification system according to claim 1, characterized in that, The dehydration tower (1) of the distillation section and the reboiler (7) are connected by a crude acetic acid outlet (13), and the outlet pipe of the reflux pump (6) is connected by a wastewater outlet (14).

4. A closed-loop heat pump coupled with two towers in series for acetic acid dehydration and purification, characterized in that, The purification system described in any one of claims 1 to 3 is used.

5. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 4, characterized in that, Includes the following steps: The acetic acid aqueous solution to be treated enters the stripping section dehydration tower (1) through the raw material inlet (11). Steam is introduced through the steam inlet (12) as a heat source, and then the bottom of the stripping section dehydration tower (1) is heated through the reboiler (7). The vapor phase generated at the top of the stripping section dehydration tower (1) enters the lower part of the rectification section dehydration tower (2). The vapor phase produced at the top of the rectification section dehydration tower (2) passes through the condenser (3) and the collector (4) in sequence and is condensed into liquid water, which enters the reflux tank (5). The reflux is carried out by the reflux pump (6) and the wastewater is collected at the wastewater outlet (14). The crude acetic acid is collected at the crude acetic acid outlet (13) on the bottom pipe of the stripping section dehydration tower (1). The liquid phase material at the bottom of the rectification section dehydration tower (2) is transferred to the upper part of the stripping section dehydration tower (1) through the pipeline. Mixed water produced at the bottom of the condenser (3) enters the top of the water circulation tank (8). At the bottom of the water circulation tank (8), negative pressure low-temperature liquid saturated water is produced. After passing through the circulation pump (10), it enters the top of the condenser (3) for heat exchange. Mixed water is produced at the bottom of the condenser (3). After gas-liquid separation through the water circulation tank (8), the gas phase water vapor enters the compressor (9) for compression, temperature increase and pressure increase, and becomes high-temperature water vapor. It is used as a heat source to enter the reboiler (7) for heat exchange. After heat exchange, it becomes low-temperature liquid water and returns to the water circulation tank (8) through the lower part of the reboiler (7).

6. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 5, characterized in that, The operating pressure of the stripping section dehydration tower (1) and the rectification section dehydration tower (2) is 30~40 kPaA, and the operating reflux ratio is 3~5.

7. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 5, characterized in that, The theoretical number of plates in the stripping section dehydration tower (1) is 20 to 40, and the theoretical number of plates in the rectification section dehydration tower (2) is 40 to 60.

8. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 5, characterized in that, The top operating temperature of the distillation section dehydration tower (2) is 70~75℃, and the bottom operating temperature is about 70~80℃.

9. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 5, characterized in that, The top operating temperature of the stripping section dehydration tower (1) is 70~80℃, and the bottom operating temperature of the stripping section dehydration tower (1) is 75~85℃.

10. The closed-loop heat pump coupled dual-tower series acetic acid dehydration and purification process according to claim 5, characterized in that, The compressor (9) has an inlet pressure of 15~25 kPaA, an outlet pressure of atmospheric pressure, and a compression ratio of 4~6.

Images