Rectification system and method for improving the uv value of ethylene glycol product

Abstract

The present application belongs to the technical field of coal-to-ethylene glycol rectification, and particularly relates to a rectification system and method for improving the UV value of ethylene glycol products, which comprises a methanol recovery tower, a dehydration tower, a dealcoholization tower, a product tower, an ethylene glycol recovery tower, and the like. In the present application, lye and desalted water are added to the dehydration tower kettle, and desalted water is added to the top of the dealcoholization tower. The chemical reaction between the impurities such as aldehydes, ketones, acids, and esters in the dehydration tower kettle liquid and water and lye removes part of the impurities, and the chemical reaction between ketones and esters and water in the dealcoholization tower further removes the impurities, so that the content of impurities such as aldehydes, ketones, acids, and esters in the ethylene glycol products taken from the product tower and the ethylene glycol recovery tower is reduced, the ultraviolet transmittance of ethylene glycol products at 220 nm is increased from 75% to 78% to 80% to 85%, and the ethylene glycol rectification efficiency is improved. A reboiler is arranged in the middle of the methanol recovery tower, low-grade steam generated by the ethylene glycol rectification system is used to heat the methanol recovery tower, the low-grade steam generated by the rectification system is utilized, and the consumption of high-quality steam by the methanol recovery tower is reduced.

Description

Technical Field

[0001] This invention belongs to the field of coal-to-ethylene glycol distillation technology, and in particular to a distillation system and method for improving the UV value of ethylene glycol products. Background Technology

[0002] Ethylene glycol (EG) is a crucial raw material in the organic chemical industry, primarily used in the production of polyester resins and antifreeze. It also finds applications in unsaturated polyester resins, lubricants, plasticizers, and nonionic surfactants. Currently, EG production methods worldwide mainly fall into two categories: petroleum-based and non-petroleum-based. Petroleum-based methods are mature and widely used, but they are highly susceptible to fluctuations in international oil prices, have a high water ratio, high energy consumption, and high production costs. Given my country's resource situation of being "poor in oil, rich in coal, and lacking in gas," non-petroleum-based coal-to-ethylene glycol technology represents the future direction for research and development. However, since 2011, my country has seen a surge in interest in coal-to-ethylene glycol production. Nevertheless, to date, the technology remains immature and incomplete. One major problem is product quality. Ethylene glycol produced through distillation systems can only reach industrial-grade levels, not polyester-grade requirements. To achieve polyester-grade quality, impurity removal via liquid-phase hydrogenation is necessary. Polyester-grade ethylene glycol requires a purity of over 99.9%. The coal-based ethylene glycol route, involving the carbonylation of syngas to dimethyl oxalate and subsequent hydrogenation of dimethyl oxalate, has become the mainstream process. However, the hydrogenation of dimethyl oxalate is a complex chemical synthesis process. As catalyst lifespan increases, side reactions also increase, leading to a greater variety and concentration of impurities. This makes distillation separation difficult, and conventional treatment methods are insufficient for deep removal, significantly impacting product quality and yield. Impurities in crude ethylene glycol include methyl glycolate, dimethyl oxalate, 1,2-butanediol oxalate, acids, aldehydes, ketones, and ethers. The increased levels of these impurities complicate the ethylene glycol distillation system, resulting in low UV transmittance of the product. This leads to increased load on the liquid-phase hydrogenation unit, and the distillation process itself severely impacts the ethylene glycol yield. Summary of the Invention

[0003] Based on the problems existing in the prior art, the purpose of this invention is to provide a distillation system and method for improving the UV value of ethylene glycol products, which has a simple process, good impurity removal effect in the distillation process, high UV transmittance of ethylene glycol products, large yield, and low liquid phase hydrogenation load.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A distillation system for improving the UV value of ethylene glycol products includes a methanol recovery tower, a dehydration tower, a dealcoholization tower, a product tower, an ethylene glycol recovery tower, and a liquid-phase hydrogenation unit. The methanol recovery tower has a central inlet a connected to a crude methanol storage tank of an upstream ethylene glycol synthesis unit via a pipe b. An inlet b is located in the middle or lower part of the methanol recovery tower and connected to the crude ethylene glycol storage tank of the upstream ethylene glycol synthesis unit via a pipe c. A refined methanol side inlet is also provided at the top of the methanol recovery tower. The bottom of the methanol recovery tower is connected to the middle of the dehydration tower via a pipe, the bottom of the dehydration tower is connected to the middle of the dealcoholization tower via a pipe, and the bottom of the dealcoholization tower is connected to the product tower via a pipe. In the middle of the tower, the bottom of the product tower is connected to the middle of the ethylene glycol recovery tower via a pipeline; the top of the deethanolination tower is equipped with a top condenser, a top reflux tank, and a top reflux pump, which are connected in sequence via pipelines. The top reflux tank is also connected to a vacuum device; the bottom of the dehydration tower is also equipped with alkali and demineralized water inlets; the ethylene glycol outlet of the liquid-phase hydrogenation device is divided into two paths, one of which is connected to the middle of the deethanolination tower via a pipeline, and the other is connected to the pipeline connecting the outlet of the top reflux pump of the product tower to the top of the product tower; the deethanolination tower also includes a demineralized water pipeline, allowing demineralized water to be added to the top of the deethanolination tower.

[0006] Furthermore, reboilers are installed at the bottom of the methanol recovery tower, dehydration tower, deethanolating tower, product tower, and ethylene glycol recovery tower.

[0007] Furthermore, the methanol recovery tower, dehydration tower, product tower, and ethylene glycol recovery tower are all equipped with a top condenser, a top reflux tank, and a top reflux pump that are connected in sequence by pipelines at the top of the tower.

[0008] Furthermore, the reflux tanks at the top of the methanol recovery tower, dehydration tower, product tower, and ethylene glycol recovery tower are all connected to a vacuum device via pipelines.

[0009] Furthermore, the demineralized water pipeline is connected to the top of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the top reflux tank of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the outlet of the top reflux pump of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the gas phase inlet of the top condenser of the deethanolating tower.

[0010] Furthermore, a reboiler is also provided in the middle of the methanol recovery tower;

[0011] A distillation method for improving the UV value of ethylene glycol products includes the following steps:

[0012] Step 1: Crude methanol from the ethylene glycol synthesis unit is fed into the middle of the methanol recovery tower via pipe b, and crude ethylene glycol from the ethylene glycol synthesis unit is fed into the middle or lower part of the methanol recovery tower via pipe c. The crude methanol and crude ethylene glycol are heated and distilled in the methanol recovery tower via the reboiler at the bottom of the tower and the reboiler in the middle of the tower. The vapor phase from the top of the methanol recovery tower is condensed by the condenser at the top of the tower and enters the reflux tank at the top of the tower. The condensate in the reflux tank is pressurized by the reflux pump and divided into two parts: one part is refluxed back to the top of the methanol recovery tower, and the other part is collected and sent to the fusel oil storage tank. Qualified refined methanol is collected from the side of the methanol recovery tower and sent to the refined methanol storage tank. The liquid from the bottom of the methanol recovery tower is sent to the dehydration tower.

[0013] Step 2: The methanol recovery tower bottom liquid is pressurized by the dehydration tower feed pump and enters the middle of the dehydration tower. Alkali solution and demineralized water are added to the bottom of the dehydration tower and heated and distilled by the reboiler of the bottom of the dehydration tower. The vapor phase at the top of the dehydration tower is condensed by the top condenser of the dehydration tower and enters the top reflux tank of the dehydration tower. The condensate in the top reflux tank of the dehydration tower is pressurized by the top reflux pump of the dehydration tower and divided into two parts. One part is refluxed to the top of the dehydration tower, and the other part is collected and sent to the fusel oil storage tank. The bottom liquid of the dehydration tower is sent to the dealcoholization tower.

[0014] Step 3: The liquid in the bottom of the dehydration tower is pressurized by the feed pump and sent to the middle of the dehydration tower. There, it is heated and distilled with ethylene glycol from the liquid hydrogenation unit in the reboiler of the dehydration tower. The vapor phase from the top of the dehydration tower is condensed by the top condenser and enters the top reflux tank. The condensate in the top reflux tank is pressurized by the top reflux pump and divided into two parts. One part is refluxed back to the top of the dehydration tower, and the other part is collected and sent to the light fraction storage tank. The liquid in the bottom of the dehydration tower is sent to the product tower. At the same time, demineralized water is added to the top of the dehydration tower through the demineralized water pipeline.

[0015] Step 4: The liquid in the bottom of the de-alcoholizing tower is pressurized by the product tower feed pump and enters the middle of the product tower. It is heated and distilled by the reboiler in the bottom of the product tower. The vapor phase at the top of the product tower is condensed by the product tower top condenser and enters the product tower top reflux tank. The condensate in the product tower top reflux tank is pressurized by the product tower top reflux pump and divided into two parts. One part is mixed with ethylene glycol from the liquid phase hydrogenation unit and refluxed to the top of the product tower. The other part is collected as industrial-grade ethylene glycol and sent to the liquid phase hydrogenation unit. The purified ethylene glycol collected from the product tower side is sent to the dealdehyde removal unit. The liquid in the bottom of the product tower is sent to the ethylene glycol recovery tower.

[0016] Step 5: The product column bottom liquid is pressurized by the ethylene glycol recovery column feed pump and enters the middle of the ethylene glycol recovery column, where it is heated and distilled by the reboiler at the bottom of the ethylene glycol recovery column. The vapor phase at the top of the ethylene glycol recovery column is condensed by the top condenser and enters the top reflux tank. The condensate in the top reflux tank is pressurized by the top reflux pump and divided into two parts. One part is refluxed back to the top of the ethylene glycol recovery column, and the other part is mixed with the industrial-grade ethylene glycol from the product column and sent to the liquid phase hydrogenation unit. The bottom liquid of the ethylene glycol recovery column is sent to the heavy fraction storage tank by the bottom liquid discharge pump.

[0017] Furthermore, the methanol recovery tower controls the top temperature at 48℃~52℃, the middle temperature at 52℃~58℃, the bottom temperature at 130℃~150℃, and the top pressure at 48KPaA~53KPaA; the dehydration tower controls the top temperature at 45℃~55℃, the bottom temperature at 149℃~153℃, and the top pressure at 15KPaA~22KPaA; the dealcoholization tower controls the top temperature at 128℃~133℃ and the bottom temperature at 150℃~150℃. The temperature is controlled at 55℃, and the pressure at the top of the column is controlled at 9 kPaA~12 kPaA. The water content in the reflux tank at the top of the deethanolination column is controlled at 0.5%~6%. The product column has a top temperature controlled at 132℃~135℃, a bottom temperature controlled at 140℃~145℃, and a top pressure controlled at 9 kPaA~12 kPaA. The ethylene glycol recovery column has a top temperature controlled at 120℃~130℃, a bottom temperature controlled at 125℃~135℃, and a top pressure controlled at 4 kPaA~9 kPaA.

[0018] Furthermore, the mass content of the water in the bottom of the dehydration tower is controlled at 0.2% to 0.5%; the mass content of the alkalinity at the bottom of the dealcoholization tower is controlled at 0.001% to 0.1%; and the mass content of the water in the bottom of the dealcoholization tower is controlled at 0.01% to 0.05%.

[0019] Furthermore, the alkaline solution is a sodium hydroxide solution and a potassium hydroxide solution.

[0020] The chemical reactions that occur in the dehydration tower and dealcoholization tower during the crude ethylene glycol distillation process of this invention are as follows:

[0021] 1. Aldehydes can react with sodium hydroxide solution, which can be divided into two situations:

[0022] (1) In the absence of α-hydrogen, aldehydes can undergo disproportionation reactions under alkaline conditions to produce acids and alcohols;

[0023] 2RCHO + NaOH ---> RCOONa + RCH2OH, the first carbon closest to the aldehyde group on R has no hydrogen atom. (2) In the presence of α hydrogen, the aldehyde itself undergoes a condensation reaction to form a hydroxyl group;

[0024] 2. Esters undergo hydrolysis with water to produce acids and alcohols: RCOOR′ + H2O ---> RCOOH + R′OH;

[0025] 3. Acid reacts with NaOH to produce carboxylate and water: RCOOH + NaOH ---> RCOONa + H2O;

[0026] 4. The ester reacts with NaOH to produce a carboxylate and an alcohol: RCOOR′ + NaOH ---> RCOONa + R′OH;

[0027] 5. Ketones react with H2O to form diols: RCOR′ + H2O ---> RR′C(OH)2; Beneficial effects

[0028] 1. This invention introduces alkaline solution and demineralized water into the bottom of a dehydration tower, causing some impurities such as aldehydes, ketones, acids, and esters in the bottom liquid to react chemically with water and alkaline solution, transforming them into substances that are easily separated by distillation. Furthermore, by adding demineralized water to the top of the dealcoholization tower, ketones and esters that have not yet reacted with water in the dehydration tower react with water in the dealcoholization tower, further removing ketones and esters. This reduces the content of impurities such as aldehydes, ketones, acids, and esters in the ethylene glycol product obtained from distillation, increasing the 220nm ultraviolet transmittance of the ethylene glycol product from the product tower and ethylene glycol recovery tower from 75%~78% to 80%~85%, significantly improving the distillation efficiency of the ethylene glycol distillation system and also greatly reducing the load on the liquid-phase hydrogenation unit.

[0029] 2. This invention reduces the consumption of high-quality steam by installing a reboiler in the middle of the methanol recovery tower and using low-quality steam to provide a heat source for the methanol recovery tower. At the same time, it makes full use of the low-grade steam generated by the ethylene glycol distillation system, thereby reducing the energy consumption of the distillation system. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention;

[0031] Figure 2 This is the process flow diagram a of the present invention;

[0032] Figure 3 This is schematic diagram b of the present invention;

[0033] Figure 4 This is the process flow diagram b of the present invention;

[0034] Figure 5 This is a structural schematic diagram of the present invention (c);

[0035] Figure 6 This is the process flow diagram c of the present invention;

[0036] In the diagram: 1-Methanol recovery tower; 2-Dehydration tower; 3-De-alcoholization tower; 4-Product tower; 5-Ethylene glycol recovery tower; 6-Reboiler a; 7-Reboiler b; 8-Reboiler c; 9-Reboiler d; 10-Reboiler e; 11-Dehydration tower feed pump; 12-De-alcoholization tower feed pump; 13-Product tower feed pump; 14-Ethylene glycol recovery tower feed pump; 15-Ethylene glycol recovery tower bottom liquid discharge pump; 16-Methanol recovery tower top condenser; 17-Dehydration tower top condenser; 18-De-alcoholization tower top condenser; 19-Product tower top condenser; 20-Ethylene glycol recovery tower top condenser; 21-Methanol recovery tower top reflux tank. 22-Reflux tank at the top of the dehydration tower; 23-Reflux tank at the top of the dealcoholization tower; 24-Reflux tank at the top of the product tower; 25-Reflux tank at the top of the ethylene glycol recovery tower; 26-Reflux pump at the top of the methanol recovery tower; 27-Reflux pump at the top of the dehydration tower; 28-Reflux pump at the top of the dealcoholization tower; 29-Reflux pump at the top of the product tower; 30-Reflux pump at the top of the ethylene glycol recovery tower; 31-Pipeline a; 32-Pipeline b; 33-Pipeline c; 34-Pipeline d; 35-Deionized water pipe; 36-Pipeline e; 37-Pipeline f; 38-Pipeline g; 39-Pipeline h; 40-Pipeline i; 41-Pipeline j; 42-Pipeline k; 43-Reboiler f. Detailed Implementation

[0037] The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation before the implementation of this invention was sampled and analyzed. The analysis results are shown in Table 1. This results in low efficiency of the ethylene glycol distillation system and increased load on the downstream liquid phase hydrogenation unit, thereby leading to low product quality and yield of polyester-grade ethylene glycol.

[0038] Table 1 shows the 220nm ultraviolet transmittance of the ethylene glycol product obtained by distillation before the implementation of this invention.

[0039] Monitoring Samples 220nm UV transmittance (%) Monitoring Samples 220nm UV transmittance (%) Sample 1 75.0 Sample 6 77.9 Sample 2 76.8 Sample 7 76.3 Sample 3 77.4 Sample 8 77.2 Sample 4 76.1 Sampling 9 78.0 Sample 5 75.4 Sample 10 75.3 Example 1

[0040] Combination Figure 1 and Figure 2To improve the UV value of ethylene glycol products and thus enhance their quality, this invention utilizes a distillation system to maximize the removal of impurities from crude ethylene glycol, thereby increasing the efficiency of the ethylene glycol distillation system, reducing the load on the downstream liquid-phase hydrogenation unit, and simultaneously improving the product quality and yield of polyester-grade ethylene glycol. This invention provides a distillation system for improving the UV value of ethylene glycol products, comprising a methanol recovery tower 1, a dehydration tower 2, a dealcoholization tower 3, a product tower 4, an ethylene glycol recovery tower 5, and a liquid-phase hydrogenation unit. The methanol recovery tower 1 has a central inlet a connected to the crude methanol storage tank of the upstream ethylene glycol synthesis unit via pipe b32. The methanol recovery tower 1 also has a central inlet b connected to the crude ethylene glycol storage tank of the upstream ethylene glycol synthesis unit via pipe c33. The central inlet a of the methanol recovery tower 1 is higher than inlet b. A refined methanol side sampling port is also provided at the top of the methanol recovery tower 1, and the collected refined methanol is sent to the refined methanol storage tank via pipe a31. The bottom of the methanol recovery tower 1 is connected to the dehydration tower via a pipe. Feed pump 11 is connected to the middle of dehydration tower 2. The bottom of dehydration tower 2 is connected to the middle of dehydration tower 3 via a pipeline and feed pump 12 of dehydration tower 3. The bottom of dehydration tower 3 is connected to the middle of product tower 4 via a pipeline and feed pump 13 of product tower 4. The bottom of product tower 4 is connected to the middle of ethylene glycol recovery tower 5 via a pipeline and feed pump 14 of ethylene glycol recovery tower 5. The bottom of ethylene glycol recovery tower 5 is connected to the heavy fraction storage tank via a pipeline and bottom liquid discharge pump 15 of ethylene glycol recovery tower 5. The dehydration tower 3 is located at the top of the dehydration tower 3. The top condenser 18, the top reflux tank 23 of the dehydrogenation tower, and the top reflux pump 28 of the dehydrogenation tower are connected in sequence by pipelines. The top reflux tank 23 of the dehydrogenation tower is also connected to a vacuum device. The bottom of the dehydration tower 2 is also equipped with an alkali and demineralized water inlet connected to pipeline d34. The ethylene glycol outlet of the liquid phase hydrogenation device is divided into two paths. One path is connected to the middle of the dehydrogenation tower 3 by a pipeline, and the other path is connected to the pipeline connecting the outlet of the product tower top reflux pump 29 and the top of the product tower 4 by pipeline e36.

[0041] The methanol recovery tower 1, dehydration tower 2, deethanolating tower 3, product tower 4, and ethylene glycol recovery tower 5 are all equipped with reboilers at their bottoms, namely reboiler a6, reboiler b7, reboiler c8, reboiler d9, and reboiler e10, respectively; a reboiler f43 is also provided in the middle of the methanol recovery tower 1, through which the low-grade steam generated by the ethylene glycol distillation system is used to heat the distillate in the methanol recovery tower.

[0042] The methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all equipped with a top condenser, a top reflux tank, and a top reflux pump connected sequentially by pipelines at their tops. The top of the methanol recovery tower 1 is connected to the gas phase inlet of the top condenser 16 via a pipeline. The condensate outlet of the top condenser 16 is connected to the top reflux tank 21 via a pipeline. The top reflux tank 21 is connected to the top of the methanol recovery tower 1 via a pipeline and a top reflux pump 26. The outlet of the top reflux pump 26 is also connected to a fusel oil storage tank via a pipeline f37 for extracting the condensate from the top reflux tank 21. The top of the dehydration tower 2 is connected to the top of the dehydration tower via a pipeline. The vapor inlet of condenser 17 and the condensate outlet of condenser 17 at the top of the dehydration tower are connected to the top reflux tank 22 of the dehydration tower via a pipeline. The top reflux tank 22 is connected to the top of the dehydration tower 2 via a pipeline and a top reflux pump 27. The outlet of the top reflux pump 27 is also connected to a fusel oil storage tank via a pipeline g for extracting the condensate from the top reflux tank 22. The top of the dealcoholization tower 3 is connected to the vapor inlet of condenser 18 at the top of the dealcoholization tower via a pipeline. The condensate outlet of condenser 18 is connected to the top reflux tank 23 at the top of the dealcoholization tower via a pipeline and a top reflux pump 28 at the top of the dealcoholization tower 3. The outlet of the top reflux pump 28 is also connected to a light alcohol storage tank via a pipeline h39. A distillate storage tank is connected to the product column reflux tank 23 for collecting condensate from the top of the dealcoholization column. The dealcoholization column 3 also includes a demineralized water pipeline 35, which is connected to the top of the dealcoholization column reflux tank 23 via a pipeline, allowing demineralized water to be added to the top of the dealcoholization column 3. The top condenser 18 of the dealcoholization column is also connected to the top waste heat boiler of the dealcoholization column. The top of the product column 4 is connected to the gas phase inlet of the top condenser 19 of the product column via a pipeline. The condensate outlet of the top condenser 19 of the product column is connected to the top reflux tank 24 of the product column via a pipeline. The top reflux tank 24 of the product column is connected to the top of the product column 4 via a pipeline and a top reflux pump 29 of the product column. The outlet of the top reflux pump 29 of the product column is also connected to a liquid phase hydrogenation unit via a pipeline i40, which collects the top of the product column. The condensate in reflux tank 24 is sent to the liquid phase hydrogenation device; the top condenser 19 of the product tower is also connected to the top waste boiler of the product tower; the product tower 4 is also provided with a side intake port connected to the formaldehyde removal device through pipe j41; the top of the ethylene glycol recovery tower 5 is connected to the gas phase inlet of the top condenser 20 of the ethylene glycol recovery tower through a pipe, and the condensate outlet of the top condenser 20 of the ethylene glycol recovery tower is connected to the top reflux tank 25 of the ethylene glycol recovery tower through a pipe, the top reflux tank 25 of the ethylene glycol recovery tower is connected to the top of the ethylene glycol recovery tower 5 through a pipe and the top reflux pump 30 of the ethylene glycol recovery tower, and the outlet of the top reflux pump 30 of the ethylene glycol recovery tower is also connected to the liquid phase hydrogenation device through pipe k42, so that the condensate in the top reflux tank 24 of the product tower is sent to the liquid phase hydrogenation device.

[0043] The reflux tanks at the top of the methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all connected to the vacuum device via pipelines. Specifically, the reflux tanks at the top of the methanol recovery tower 21, dehydration tower 22, deethanolating tower 23, product tower 24, and ethylene glycol recovery tower 25 are all connected to the vacuum device via pipelines.

[0044] A reboiler is also installed in the middle of the methanol recovery tower 1.

[0045] A distillation method for improving the UV value of ethylene glycol products includes the following steps:

[0046] Step 1: Crude methanol from the ethylene glycol synthesis unit is fed into the middle section of methanol recovery tower 1 via pipeline b32, and crude ethylene glycol from the ethylene glycol synthesis unit is fed into the middle section of methanol recovery tower 1 via pipeline c33. The crude methanol and crude ethylene glycol are heated and distilled in methanol recovery tower 1 by reboiler a6 in the bottom of tower 1 and reboiler f43 in the middle section of tower 1. The reboiler f43 in the middle section of methanol recovery tower 1 is heated by low-grade steam generated from the waste heat at the top of the deethanolination tower and the waste heat at the top of the product tower in the ethylene glycol distillation system. The pressure of the low-grade steam is 10 kPa to 100 kPa, and the temperature is 100°C to 120°C. The temperature at the top of methanol recovery tower 1 is controlled at 48℃, the temperature in the middle of the tower at 52℃, the temperature at the bottom of the tower at 130℃, and the pressure at the top of the tower at 53 kPa. The vapor phase at the top of methanol recovery tower 1 is condensed by the top condenser 16 and then enters the top reflux tank 21. The condensate in the top reflux tank 21 is pressurized by the top reflux pump 26 and divided into two parts. One part is returned to the top of methanol recovery tower 1, and the other part is collected and sent to the fusel oil storage tank. Qualified refined methanol is collected from the side of pipeline a31 and sent to the refined methanol storage tank. The bottom liquid of methanol recovery tower 1 is sent to dehydration tower 2.

[0047] Step 2: The methanol recovery tower 1 bottom liquid is pressurized by the dehydration tower feed pump 11 and enters the middle of the dehydration tower 2. Alkali solution and demineralized water are added to the bottom of the dehydration tower 2 through pipe d34. The water is heated and distilled by the reboiler b7 of the bottom of the dehydration tower 2. The top temperature of the dehydration tower 2 is controlled at 55℃, the bottom temperature at 149℃, and the top pressure at 22 kPaA. The mass content of water in the bottom of the dehydration tower 2 is controlled at 0.5%. The vapor phase at the top of the dehydration tower 2 is condensed by the top condenser 17 and enters the top reflux tank 22. The condensate in the top reflux tank 22 is pressurized by the top reflux pump 27 and divided into two parts. One part is refluxed back to the top of the dehydration tower 2, and the other part is collected and sent to the fusel oil storage tank. The bottom liquid of the dehydration tower 2 is sent to the dealcoholization tower 3.

[0048] Step 3: The liquid from the bottom of dehydration tower 2 is pressurized by the feed pump 12 and sent to the middle of dehydration tower 3. There, it is heated and distilled with ethylene glycol from the liquid-phase hydrogenation unit in the reboiler C8 of dehydration tower 3. The top temperature of dehydration tower 3 is controlled at 128℃, the bottom temperature at 150℃, and the top pressure at 12 kPa. The water content in the reflux tank 23 at the top of dehydration tower is controlled at 0.5%. The alkalinity at the bottom of dehydration tower 3 is controlled at 0.001%, and the water content in the bottom of dehydration tower 3 is controlled at... At 0.05%; the vapor phase from the top of the alcoholysher 3 is condensed by the alcoholysher condenser 18 and enters the alcoholysher reflux tank 23. The condensate in the alcoholysher reflux tank 23 is pressurized by the alcoholysher reflux pump 28 and divided into two parts. One part is refluxed back to the top of the alcoholysher 3, and the other part is collected and sent to the light fraction storage tank. The bottom liquid of the alcoholysher 3 is sent to the product tower 4. At the same time, demineralized water is added to the alcoholysher reflux tank 23 through the demineralized water pipeline 35, and then the demineralized water is added to the top of the alcoholysher 3 through the alcoholysher reflux pump 28.

[0049] Step 4: The liquid from the bottom of the de-alcoholizing tower 3 is pressurized by the product tower feed pump 13 and enters the middle of the product tower 4. It is heated and distilled by the reboiler d9 in the bottom of the product tower 4. The top temperature of the product tower 4 is controlled at 132°C, the bottom temperature at 140°C, and the top pressure at 9 kPaA. The vapor phase from the top of the product tower 4 is condensed by the top condenser 19 and enters the top reflux tank 24. The condensate in the top reflux tank 24 is pressurized by the top reflux pump 29 and divided into two parts. One part is mixed with ethylene glycol from the liquid phase hydrogenation unit and refluxed back to the top of the product tower 4. The other part is collected as industrial-grade ethylene glycol and sent to the liquid phase hydrogenation unit. The purified ethylene glycol collected from the side of the product tower 4 is sent to the dealdehyde removal unit. The liquid from the bottom of the product tower 4 is sent to the ethylene glycol recovery tower 5.

[0050] Step 5: The liquid from the bottom of product tower 4 is pressurized by the feed pump 14 and enters the middle of ethylene glycol recovery tower 5. It is heated and distilled by the reboiler e10 in the bottom of ethylene glycol recovery tower 5. The top temperature of ethylene glycol recovery tower 5 is controlled at 120°C, the bottom temperature at 125°C, and the top pressure at 4 kPaA. The vapor phase from the top of ethylene glycol recovery tower 5 is condensed by the top condenser 20 and enters the top reflux tank 25. The condensate in the top reflux tank 25 is pressurized by the top reflux pump 30 and divided into two parts. One part is refluxed to the top of ethylene glycol recovery tower 5, and the other part is mixed with the industrial-grade ethylene glycol from product tower 4 and sent to the liquid phase hydrogenation unit. The liquid from the bottom of ethylene glycol recovery tower 5 is sent to the heavy fraction storage tank by the bottom liquid discharge pump 15.

[0051] The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation before the implementation of this invention was sampled and analyzed, and the analysis results are shown in Table 1. The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation through the technical solution of this invention was sampled and analyzed, and the analysis results are shown in Table 2. Compared with Table 1, Table 2 shows that the 220nm ultraviolet transmittance of ethylene glycol has been improved to a certain extent.

[0052] Table 2 shows the 220nm ultraviolet transmittance of the ethylene glycol product obtained by distillation in Example 1 of the present invention.

[0053] Monitoring Samples 220nm UV transmittance (%) Monitoring Samples 220nm UV transmittance (%) Sample 1 80.0 Sample 6 81.9 Sample 2 80.2 Sample 7 82.6 Sample 3 81.1 Sample 8 82.3 Sample 4 81.6 Sampling 9 81.7 Sample 5 83.4 Sample 10 80.8 Example 2

[0054] Combination Figure 3 and Figure 4 To improve the UV value of ethylene glycol products and thus enhance their quality, this invention utilizes a distillation system to maximize the removal of impurities from crude ethylene glycol, thereby increasing the efficiency of the ethylene glycol distillation system, reducing the load on the downstream liquid-phase hydrogenation unit, and simultaneously improving the product quality and yield of polyester-grade ethylene glycol. This invention provides a distillation system for improving the UV value of ethylene glycol products, comprising a methanol recovery tower 1, a dehydration tower 2, a dealcoholization tower 3, a product tower 4, an ethylene glycol recovery tower 5, and a liquid-phase hydrogenation unit. The methanol recovery tower 1 has a central inlet a connected to the crude methanol storage tank of the upstream ethylene glycol synthesis unit via pipe b32. The lower part of the methanol recovery tower 1 has an inlet b connected to the crude ethylene glycol storage tank of the upstream ethylene glycol synthesis unit via pipe c33. The upper part of the methanol recovery tower 1 also has a refined methanol side sampling port, and the collected refined methanol is sent to the refined methanol storage tank via pipe a31. The bottom of the methanol recovery tower 1 is connected to the dehydration tower feed pump 11 via a pipe. The bottom of dehydration tower 2 is connected to the middle of dehydration tower 3 via a pipeline and dehydration tower feed pump 12. The bottom of dehydration tower 3 is connected to the middle of product tower 4 via a pipeline and product tower feed pump 13. The bottom of product tower 4 is connected to the middle of ethylene glycol recovery tower 5 via a pipeline and ethylene glycol recovery tower feed pump 14. The bottom of ethylene glycol recovery tower 5 is connected to the heavy fraction storage tank via a pipeline and ethylene glycol recovery tower bottom liquid discharge pump 15. The top of dehydration tower 3 is equipped with a dehydration tower top condenser 18, a dehydration tower top reflux tank 23, and a dehydration tower top reflux pump 28, which are connected in sequence via pipelines. The dehydration tower top reflux tank 23 is also connected to a vacuum device. The bottom of dehydration tower 2 is also equipped with an alkali and demineralized water inlet connected to pipeline d34. The ethylene glycol outlet of the liquid phase hydrogenation device is divided into two paths: one path is connected to the middle of dehydration tower 3 via a pipeline, and the other path is connected to the pipeline connecting the outlet of product tower top reflux pump 29 and the top of product tower 4 via pipeline e36.

[0055] The methanol recovery tower 1, dehydration tower 2, deethanolating tower 3, product tower 4, and ethylene glycol recovery tower 5 are all equipped with reboilers at their bottoms, namely reboiler a6, reboiler b7, reboiler c8, reboiler d9, and reboiler e10, respectively; a reboiler f43 is also provided in the middle of the methanol recovery tower 1, through which the low-grade steam generated by the ethylene glycol distillation system is used to heat the distillate in the methanol recovery tower.

[0056] The methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all equipped with a top condenser, a top reflux tank, and a top reflux pump connected sequentially by pipelines at their tops. The top of the methanol recovery tower 1 is connected to the gas phase inlet of the top condenser 16 via a pipeline. The condensate outlet of the top condenser 16 is connected to the top reflux tank 21 via a pipeline. The top reflux tank 21 is connected to the top of the methanol recovery tower 1 via a pipeline and a top reflux pump 26. The outlet of the top reflux pump 26 is also connected to a fusel oil storage tank via a pipeline f37 for extracting the condensate from the top reflux tank 21. The top of the dehydration tower 2 is connected to the top of the dehydration tower via a pipeline. The vapor inlet of condenser 17 and the condensate outlet of condenser 17 at the top of the dehydration tower are connected via pipeline to the top reflux tank 22 of the dehydration tower. The top reflux tank 22 is connected to the top of dehydration tower 2 via pipeline and top reflux pump 27. The outlet of top reflux pump 27 is also connected to a fusel oil storage tank via pipeline g for extracting condensate from the top reflux tank 22. The top of the dealcoholization tower 3 is connected via pipeline to the vapor inlet of condenser 18 at the top of the dealcoholization tower. The condensate outlet of condenser 18 is connected via pipeline to the top reflux tank 23 at the top of the dealcoholization tower. The top reflux tank 23 is connected to the top of dealcoholization tower 3 via pipeline and top reflux pump 28 at the top of the dealcoholization tower. The outlet of top reflux pump 28 is also connected via pipeline h39 to... A light fraction storage tank is connected to the product column reflux tank 23 for collecting condensate from the top of the dealcoholization column. The dealcoholization column 3 also includes a demineralized water pipeline 35, which is connected to the top of the dealcoholization column 3 via a pipeline, allowing demineralized water to be added to the top of the dealcoholization column 3. The top condenser 18 of the dealcoholization column is also connected to the top waste heat boiler of the dealcoholization column. The top of the product column 4 is connected to the gas phase inlet of the top condenser 19 of the product column via a pipeline. The condensate outlet of the top condenser 19 of the product column is connected to the top reflux tank 24 of the product column via a pipeline. The top reflux tank 24 of the product column is connected to the top of the product column 4 via a pipeline and a top reflux pump 29 of the product column. The outlet of the top reflux pump 29 of the product column is also connected to a liquid phase hydrogenation unit via a pipeline i40 to return the product column top reflux water to the product column. The condensate in the reflux tank 24 is sent to the liquid phase hydrogenation device; the product tower 4 is also provided with a side sampling port connected to the formaldehyde removal device via pipe j41; the top condenser 19 of the product tower is also connected to the top waste boiler of the product tower; the top of the ethylene glycol recovery tower 5 is connected to the gas phase inlet of the top condenser 20 of the ethylene glycol recovery tower via a pipe, and the condensate outlet of the top condenser 20 of the ethylene glycol recovery tower is connected to the top reflux tank 25 of the ethylene glycol recovery tower via a pipe, the top reflux tank 25 of the ethylene glycol recovery tower is connected to the top of the ethylene glycol recovery tower 5 via a pipe and the top reflux pump 30 of the ethylene glycol recovery tower, and the outlet of the top reflux pump 30 of the ethylene glycol recovery tower is also connected to the liquid phase hydrogenation device via pipe k42, so that the condensate in the top reflux tank 24 of the product tower is sent to the liquid phase hydrogenation device.

[0057] The reflux tanks at the top of the methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all connected to the vacuum device via pipelines. Specifically, the reflux tanks at the top of the methanol recovery tower 21, dehydration tower 22, deethanolating tower 23, product tower 24, and ethylene glycol recovery tower 25 are all connected to the vacuum device via pipelines.

[0058] A distillation method for improving the UV value of ethylene glycol products includes the following steps:

[0059] Step 1: Crude methanol from the ethylene glycol synthesis unit is fed into the middle of methanol recovery tower 1 via pipe b32, and crude ethylene glycol from the ethylene glycol synthesis unit is fed into the lower part of methanol recovery tower 1 via pipe c33. The crude methanol and crude ethylene glycol are heated and distilled in methanol recovery tower 1 by reboiler a6 in the bottom of tower 1 and reboiler f43 in the middle of tower 1. The reboiler f43 in the middle of methanol recovery tower 1 is heated by low-grade steam generated from the waste heat at the top of the deethanolination tower and the waste heat at the top of the product tower in the ethylene glycol distillation system. The pressure of the low-grade steam is 10 kPa to 100 kPa, and the temperature is 100°C to 120°C. The methanol recovery tower 1 controls the top temperature at 50℃, the middle temperature at 54℃, the bottom temperature at 140℃, and the top pressure at 50.5 kPa. The vapor phase at the top of the methanol recovery tower 1 is condensed by the top condenser 16 and enters the top reflux tank 21. The condensate in the top reflux tank 21 is pressurized by the top reflux pump 26 and divided into two parts: one part is refluxed back to the top of the methanol recovery tower 1, and the other part is collected and sent to the fusel oil storage tank. Qualified refined methanol from the methanol recovery tower 1 is collected from the side of pipeline a31 and sent to the refined methanol storage tank. The bottom liquid from the methanol recovery tower 1 is sent to the dehydration tower 2.

[0060] Step 2: The methanol recovery tower 1 bottom liquid is pressurized by the dehydration tower feed pump 11 and enters the middle of the dehydration tower 2. Alkali solution and demineralized water are added to the bottom of the dehydration tower 2 through pipe d34 and heated and distilled by the reboiler b7 of the bottom of the dehydration tower 2. The top temperature of the dehydration tower 2 is controlled at 50°C, the bottom temperature at 151°C, and the top pressure at 19 kPaA. The mass content of water in the bottom of the dehydration tower 2 is controlled at 0.35%. The vapor phase at the top of the dehydration tower 2 is condensed by the top condenser 17 and enters the top reflux tank 22. The condensate in the top reflux tank 22 is pressurized by the top reflux pump 27 and divided into two parts. One part is refluxed back to the top of the dehydration tower 2, and the other part is collected and sent to the fusel oil storage tank. The bottom liquid of the dehydration tower 2 is sent to the dealcoholization tower 3.

[0061] Step 3: The liquid from the bottom of dehydration tower 2 is pressurized by the feed pump 12 and sent to the middle of dehydration tower 3. There, it is heated and distilled with ethylene glycol from the liquid-phase hydrogenation unit in the reboiler C8 of dehydration tower 3. The top temperature of dehydration tower 3 is controlled at 131℃, the bottom temperature at 152℃, and the top pressure at 10.5 kPa. The water content in the reflux tank 23 at the top of dehydration tower is controlled at 3.0%, and the alkalinity at the bottom of dehydration tower 3 is controlled at 0.01%. The mass content of the bottom water in the dealcoholization tower 3 is controlled at 0.03%. The vapor phase from the top of the dealcoholization tower 3 is condensed by the top condenser 18 and enters the top reflux tank 23. The condensate in the top reflux tank 23 is pressurized by the top reflux pump 28 and divided into two parts. One part is refluxed back to the top of the dealcoholization tower 3, and the other part is collected and sent to the light fraction storage tank. The bottom liquid of the dealcoholization tower 3 is sent to the product tower 4. At the same time, demineralized water is added to the top of the dealcoholization tower 3 through the demineralized water pipeline 35.

[0062] Step 4: The liquid from the bottom of the de-alcoholizing tower 3 is pressurized by the product tower feed pump 13 and enters the middle of the product tower 4. It is heated and distilled by the reboiler d9 in the bottom of the product tower 4. The top temperature of the product tower 4 is controlled at 134℃, the bottom temperature at 142℃, and the top pressure at 11 kPa. The vapor phase from the top of the product tower 4 is condensed by the top condenser 19 and enters the top reflux tank 24. The condensate in the top reflux tank 24 is pressurized by the top reflux pump 29 and divided into two parts. One part is mixed with ethylene glycol from the liquid phase hydrogenation unit and refluxed back to the top of the product tower 4. The other part is collected as industrial-grade ethylene glycol and sent to the liquid phase hydrogenation unit. The purified ethylene glycol collected from the side of the product tower 4 is sent to the dealdehyde removal unit. The liquid from the bottom of the product tower 4 is sent to the ethylene glycol recovery tower 5.

[0063] Step 5: The liquid from the bottom of product tower 4 is pressurized by the feed pump 14 and enters the middle of ethylene glycol recovery tower 5. It is heated and distilled by the reboiler e10 in the bottom of ethylene glycol recovery tower 5. The top temperature of ethylene glycol recovery tower 5 is controlled at 125°C, the bottom temperature at 130°C, and the top pressure at 7 kPaA. The vapor phase from the top of ethylene glycol recovery tower 5 is condensed by the top condenser 20 and enters the top reflux tank 25. The condensate in the top reflux tank 25 is pressurized by the top reflux pump 30 and divided into two parts. One part is refluxed to the top of ethylene glycol recovery tower 5, and the other part is mixed with the industrial-grade ethylene glycol from product tower 4 and sent to the liquid phase hydrogenation unit. The liquid from the bottom of ethylene glycol recovery tower 5 is sent to the heavy fraction storage tank by the bottom liquid discharge pump 15.

[0064] The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation before the implementation of this invention was sampled and analyzed, and the analysis results are shown in Table 1. The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation through the technical solution of this invention was sampled and analyzed, and the analysis results are shown in Table 3. Compared with Table 1, Table 3 shows that the 220nm ultraviolet transmittance of ethylene glycol has been improved to a certain extent.

[0065] Table 3 shows the 220nm ultraviolet transmittance of the ethylene glycol product obtained by distillation in Example 2 of the present invention.

[0066] Monitoring Samples 220nm UV transmittance (%) Monitoring Samples 220nm UV transmittance (%) Sample 1 81.5 Sample 6 82.7 Sample 2 81.9 Sample 7 83.9 Sample 3 83.5 Sample 8 82.9 Sample 4 82.4 Sampling 9 83.1 Sample 5 83.6 Sample 10 84.1 Example 3

[0067] Combination Figure 5 and Figure 6 To improve the UV value of ethylene glycol products and thus enhance their quality, this invention utilizes a distillation system to maximize the removal of impurities from crude ethylene glycol, thereby increasing the efficiency of the ethylene glycol distillation system, reducing the load on the downstream liquid-phase hydrogenation unit, and simultaneously improving the product quality and yield of polyester-grade ethylene glycol. This invention provides a distillation system for improving the UV value of ethylene glycol products, comprising a methanol recovery tower 1, a dehydration tower 2, a dealcoholization tower 3, a product tower 4, an ethylene glycol recovery tower 5, and a liquid-phase hydrogenation unit. The methanol recovery tower 1 has a central inlet a connected to the crude methanol storage tank of the upstream ethylene glycol synthesis unit via pipe b32. The methanol recovery tower 1 also has a central inlet b connected to the crude ethylene glycol storage tank of the upstream ethylene glycol synthesis unit via pipe c33. The central inlet a of the methanol recovery tower 1 is higher than inlet b. A refined methanol side sampling port is also provided at the top of the methanol recovery tower 1, and the collected refined methanol is sent to the refined methanol storage tank via pipe a31. The bottom of the methanol recovery tower 1 is connected to the dehydration tower via a pipe. Feed pump 11 is connected to the middle of dehydration tower 2. The bottom of dehydration tower 2 is connected to the middle of dehydration tower 3 via a pipeline and dehydration tower feed pump 12. The bottom of dehydration tower 3 is connected to the middle of product tower 4 via a pipeline and product tower feed pump 13. The bottom of product tower 4 is connected to the middle of ethylene glycol recovery tower 5 via a pipeline and ethylene glycol recovery tower feed pump 14. The bottom of ethylene glycol recovery tower 5 is connected to the heavy fraction storage tank via a pipeline and ethylene glycol recovery tower bottom liquid discharge pump 15. The dehydration tower 3 is located at the top of the dehydration tower. The top condenser 18, the top reflux tank 23 of the dehydrogenation tower, and the top reflux pump 28 of the dehydrogenation tower are connected in sequence by pipelines. The top reflux tank 23 of the dehydrogenation tower is also connected to a vacuum device. The bottom of the dehydration tower 2 is also equipped with an alkali and demineralized water inlet connected to pipeline d34. The ethylene glycol outlet of the liquid phase hydrogenation device is divided into two paths. One path is connected to the middle of the dehydrogenation tower 3 by a pipeline, and the other path is connected to the pipeline connecting the outlet of the product tower top reflux pump 29 and the top of the product tower 4 by pipeline e36.

[0068] The methanol recovery tower 1, dehydration tower 2, deethanolating tower 3, product tower 4, and ethylene glycol recovery tower 5 are all equipped with reboilers at their bottoms, namely reboiler a6, reboiler b7, reboiler c8, reboiler d9, and reboiler e10, respectively; a reboiler f43 is also provided in the middle of the methanol recovery tower 1, through which the low-grade steam generated by the ethylene glycol distillation system is used to heat the distillate in the methanol recovery tower.

[0069] The methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all equipped with a top condenser, a top reflux tank, and a top reflux pump, which are connected sequentially by pipelines at the top. The top of the methanol recovery tower 1 is connected to the gas phase inlet of the top condenser 16 via a pipeline. The condensate outlet of the top condenser 16 is connected to the top reflux tank 21 via a pipeline. The top reflux tank 21 is connected to the top of the methanol recovery tower 1 via a pipeline and the top reflux pump 26. The outlet of the top reflux pump 26 is also connected to a fusel oil storage tank via pipeline f37 for recovering extracted methanol. The condensate in the top reflux tank 21 of the dehydration tower 2 is connected to the gas phase inlet of the top condenser 17 of the dehydration tower 2 via a pipeline. The condensate outlet of the top condenser 17 of the dehydration tower 2 is connected to the top reflux tank 22 of the dehydration tower 2 via a pipeline and the top reflux pump 27 of the dehydration tower 2. The outlet of the top reflux pump 27 of the dehydration tower 2 is also connected to the fusel oil storage tank via a pipeline g for extracting the condensate in the top reflux tank 22 of the dehydration tower 2. The top of the dealcoholization tower 3 is connected to the gas phase inlet of the top condenser 18 of the dealcoholization tower via a pipeline. The condensate outlet of the top condenser 18 of the dealcoholization tower 3 is connected to the gas phase inlet of the top condenser 18 of the dealcoholization tower via a pipeline g. The reflux tank 23 at the top of the dealcoholization column is connected to the top of the dealcoholization column 3 via a pipeline and a dealcoholization column top reflux pump 28. The outlet of the dealcoholization column top reflux pump 28 is also connected to a light fraction storage tank via a pipeline h39 for collecting the condensate from the dealcoholization column top reflux tank 23. The dealcoholization column 3 also includes a demineralized water pipeline 35, which is connected to the gas phase inlet of the dealcoholization column top condenser 18, allowing the demineralized water to enter the dealcoholization column top reflux tank 23 from the dealcoholization column top condenser 18, and then be added to the top of the dealcoholization column 3 via the dealcoholization column top reflux pump 28. The dealcoholization column top condenser 18 is also connected to the top of the dealcoholization column 3. The product tower 4 is connected to the top waste heat boiler via a pipeline; the top of the product tower 4 is connected to the gas phase inlet of the top condenser 19 via a pipeline, and the condensate outlet of the top condenser 19 is connected to the top reflux tank 24 via a pipeline. The top reflux tank 24 is connected to the top of the product tower 4 via a pipeline and a top reflux pump 29. The outlet of the top reflux pump 29 is also connected to a liquid phase hydrogenation device via a pipeline i40 to send the condensate in the top reflux tank 24 to the liquid phase hydrogenation device; the product tower 4 is also provided with a side sampling port connected to the formaldehyde removal device via a pipeline j41; the top condenser 19 is also connected to the top waste heat boiler of the product tower.The top of the ethylene glycol recovery tower 5 is connected via a pipeline to the gas phase inlet of the condenser 20 at the top of the ethylene glycol recovery tower. The condensate outlet of the condenser 20 is connected via a pipeline to the reflux tank 25 at the top of the ethylene glycol recovery tower. The reflux tank 25 is connected to the top of the ethylene glycol recovery tower 5 via a pipeline and a reflux pump 30 at the top of the ethylene glycol recovery tower. The outlet of the reflux pump 30 is also connected via pipeline k42 to a liquid-phase hydrogenation unit, sending the condensate in the reflux tank 24 at the top of the product tower to the liquid-phase hydrogenation unit.

[0070] The reflux tanks at the top of the methanol recovery tower 1, dehydration tower 2, product tower 4, and ethylene glycol recovery tower 5 are all connected to the vacuum device via pipelines. Specifically, the reflux tanks at the top of the methanol recovery tower 21, dehydration tower 22, deethanolating tower 23, product tower 24, and ethylene glycol recovery tower 25 are all connected to the vacuum device via pipelines.

[0071] A distillation method for improving the UV value of ethylene glycol products includes the following steps:

[0072] Step 1: Crude methanol from the ethylene glycol synthesis unit is fed into the middle section of methanol recovery tower 1 via pipeline b32, and crude ethylene glycol from the ethylene glycol synthesis unit is fed into the middle section of methanol recovery tower 1 via pipeline c33. The crude methanol and crude ethylene glycol are heated and distilled in methanol recovery tower 1 by reboiler a6 in the bottom of tower 1 and reboiler f43 in the middle section of tower 1. The reboiler f43 in the middle section of methanol recovery tower 1 is heated by low-grade steam generated from the waste heat at the top of the deethanolination tower and the waste heat at the top of the product tower in the ethylene glycol distillation system. The pressure of the low-grade steam is 10 kPa to 100 kPa, and the temperature is 100°C to 120°C. The temperature at the top of methanol recovery tower 1 is controlled at 52℃, the temperature in the middle of the tower at 58℃, the temperature at the bottom of the tower at 150℃, and the pressure at the top of the tower at 48 kPa. The vapor phase at the top of methanol recovery tower 1 is condensed by the top condenser 16 and then enters the top reflux tank 21. The condensate in the top reflux tank 21 is pressurized by the top reflux pump 26 and divided into two parts. One part is returned to the top of methanol recovery tower 1, and the other part is collected and sent to the fusel oil storage tank. Qualified refined methanol is collected from the side of pipeline a31 and sent to the refined methanol storage tank. The bottom liquid of methanol recovery tower 1 is sent to dehydration tower 2.

[0073] Step 2: The methanol recovery tower 1 bottom liquid is pressurized by the dehydration tower feed pump 11 and enters the middle of the dehydration tower 2. Alkali solution and demineralized water are added to the bottom of the dehydration tower 2 through pipe d34 and heated and distilled by the reboiler b7 of the bottom of the dehydration tower 2. The top temperature of the dehydration tower 2 is controlled at 55℃, the bottom temperature at 153℃, and the top pressure at 15KPaA. The mass content of water in the bottom of the dehydration tower 2 is controlled at 0.2%. The vapor phase at the top of the dehydration tower 2 is condensed by the top condenser 17 and enters the top reflux tank 22. The condensate in the top reflux tank 22 is pressurized by the top reflux pump 27 and divided into two parts. One part is refluxed back to the top of the dehydration tower 2, and the other part is collected and sent to the fusel oil storage tank. The bottom liquid of the dehydration tower 2 is sent to the deethanolating tower 3.

[0074] Step 3: The liquid from the bottom of dehydration tower 2 is pressurized by the feed pump 12 and sent to the middle of dehydration tower 3. There, it is heated and distilled with ethylene glycol from the liquid-phase hydrogenation unit in the reboiler C8 of dehydration tower 3. The top temperature of dehydration tower 3 is controlled at 133℃, the bottom temperature at 155℃, and the top pressure at 9 kPa. The water content in the reflux tank 23 at the top of dehydration tower is controlled at 6.0%. The alkalinity at the bottom of dehydration tower 3 is controlled at 0.1%, and the water content in the bottom of dehydration tower 3 is controlled at 0.01%. The vapor phase at the top of dehydration tower 3 is then dehydrated... After condensation in the top condenser 18 of the alcohol column, the condensate enters the top reflux tank 23 of the dealcoholization column. The condensate in the top reflux tank 23 is pressurized by the top reflux pump 28 of the dealcoholization column and divided into two parts. One part is refluxed back to the top of the dealcoholization column 3, and the other part is collected and sent to the light fraction storage tank. The bottom liquid of the dealcoholization column 3 is sent to the product column 4. At the same time, demineralized water is added to the top condenser 18 of the dealcoholization column through the demineralized water pipeline 35, so that the demineralized water enters the top reflux tank 23 of the dealcoholization column through the top condenser 18, and is then added to the top of the dealcoholization column 3 through the top reflux pump 28.

[0075] Step 4: The liquid from the bottom of the de-alcoholizing tower 3 is pressurized by the product tower feed pump 13 and enters the middle of the product tower 4. It is heated and distilled by the reboiler d9 in the bottom of the product tower 4. The top temperature of the product tower 4 is controlled at 135℃, the bottom temperature at 145℃, and the top pressure at 12 kPaA. The vapor phase from the top of the product tower 4 is condensed by the top condenser 19 and enters the top reflux tank 24. The condensate in the top reflux tank 24 is pressurized by the top reflux pump 29 and divided into two parts. One part is mixed with ethylene glycol from the liquid phase hydrogenation unit and refluxed back to the top of the product tower 4. The other part is collected as industrial-grade ethylene glycol and sent to the liquid phase hydrogenation unit. The purified ethylene glycol collected from the side of the product tower 4 is sent to the dealdehyde unit. The liquid from the bottom of the product tower 4 is sent to the ethylene glycol recovery tower 5.

[0076] Step 5: The liquid from the bottom of product tower 4 is pressurized by the ethylene glycol recovery tower feed pump 14 and enters the middle of ethylene glycol recovery tower 5. It is heated and distilled by the reboiler e10 in the bottom of ethylene glycol recovery tower 5. The temperature at the top of ethylene glycol recovery tower 5 is controlled at 130°C, the temperature at the bottom of the tower is controlled at 135°C, and the pressure at the top of the tower is controlled at 9 kPaA. The vapor phase at the top of ethylene glycol recovery tower 5 is condensed by the condenser 20 and enters the reflux tank 25. The condensate in the reflux tank 25 is pressurized by the reflux pump 30 and divided into two parts. One part is refluxed back to the top of ethylene glycol recovery tower 5, and the other part is mixed with the industrial-grade ethylene glycol from product tower 4 and sent to the liquid phase hydrogenation unit. The liquid from the bottom of ethylene glycol recovery tower 5 is sent to the heavy fraction storage tank through the bottom liquid discharge pump 15.

[0077] The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation before the implementation of this invention was sampled and analyzed, and the analysis results are shown in Table 1. The 220nm ultraviolet transmittance of ethylene glycol obtained by distillation through the technical solution of this invention was sampled and analyzed, and the analysis results are shown in Table 4. Compared with Table 1, Table 4 shows that the 220nm ultraviolet transmittance of ethylene glycol has been improved to a certain extent.

[0078] Table 4 shows the 220nm ultraviolet transmittance of the ethylene glycol product obtained by distillation in Example 3 of the present invention.

[0079] Monitoring Samples 220nm UV transmittance (%) Monitoring Samples 220nm UV transmittance (%) Sample 1 82.5 Sample 6 83.2 Sample 2 83.6 Sample 7 82.9 Sample 3 82.4 Sample 8 85.0 Sample 4 84.5 Sampling 9 83.8 Sample 5 84.8 Sample 10 84.1

[0080] Another embodiment differs from Embodiment 1 in that the demineralized water pipeline 35 is connected to the pipeline connected to the outlet of the top reflux pump 28 of the deethanolating tower.

[0081] The working principle of this invention is as follows: By adding alkaline solution and demineralized water to the bottom of the dehydration tower, some impurities such as aldehydes, ketones, acids, and esters in the bottom liquid of the dehydration tower react chemically with water and alkaline solution, transforming them into substances that are easily separated by distillation and then removed by distillation. By adding demineralized water to the top of the dealcoholization tower, ketones and esters that have not reacted chemically with water in the dehydration tower react chemically with water in the dealcoholization tower, further removing ketones and esters. This reduces the content of impurities such as aldehydes, ketones, acids, and esters in the ethylene glycol product obtained by distillation, and increases the 220nm ultraviolet transmittance of the ethylene glycol product from the product tower and the ethylene glycol recovery tower from 75%~78% to 80%~85%, greatly improving the distillation efficiency of the ethylene glycol distillation system and also greatly reducing the load on the liquid phase hydrogenation unit. This invention also uses a reboiler in the middle of the methanol recovery tower to provide a heat source for the methanol recovery tower using low-quality steam, reducing the consumption of high-quality steam in the methanol recovery tower, and making full use of the low-grade steam generated by the ethylene glycol distillation system, thus reducing the energy consumption of the distillation system.

[0082] The chemical reactions that occur in the dehydration tower and dealcoholization tower during the crude ethylene glycol distillation process of this invention are as follows:

[0083] 1. Aldehydes can react with sodium hydroxide solution, which can be divided into two situations:

[0084] (1) In the absence of α-hydrogen, aldehydes can undergo disproportionation reactions under alkaline conditions to produce acids and alcohols;

[0085] 2RCHO + NaOH ---> RCOONa + RCH2OH, the first carbon closest to the aldehyde group on R has no hydrogen atom. (2) In the presence of α hydrogen, the aldehyde itself undergoes a condensation reaction to form a hydroxyl group;

[0086] 2. Esters undergo hydrolysis with water to produce acids and alcohols: RCOOR′ + H2O ---> RCOOH + R′OH;

[0087] 3. The acid reacts with NaOH to produce carboxylate and water: RCOOH + NaOH ---> RCOONa + H2O;

[0088] 4. The ester reacts with NaOH to produce a carboxylate and an alcohol: RCOOR′ + NaOH ---> RCOONa + R′OH;

[0089] 5. Ketones react with H2O to form diols: RCOR′ + H2O ---> RR′C(OH)2.

[0090] Modifications and variations made to this invention by those skilled in the art are all within the scope of this invention's patent, and are not limited to the embodiments described.

Claims

1. A distillation system for improving the UV value of ethylene glycol products, comprising a methanol recovery tower, a dehydration tower, a dealcoholization tower, a product tower, an ethylene glycol recovery tower, and a liquid-phase hydrogenation unit, wherein the middle inlet a of the methanol recovery tower is connected to the crude methanol storage tank of the upstream ethylene glycol synthesis unit via a pipe b; the middle or lower part of the methanol recovery tower is provided with inlet b connected to the crude ethylene glycol storage tank of the upstream ethylene glycol synthesis unit via a pipe c; the upper part of the methanol recovery tower is also provided with a refined methanol side inlet; the bottom of the methanol recovery tower is connected to the middle of the dehydration tower via a pipe; the bottom of the dehydration tower is connected to the middle of the dealcoholization tower via a pipe; the bottom of the dealcoholization tower is connected to the middle of the product tower via a pipe; the bottom of the product tower is connected to the middle of the ethylene glycol recovery tower via a pipe; a dealcoholization tower top condenser, a dealcoholization tower top reflux tank, and a dealcoholization tower top reflux pump are sequentially connected via pipes at the top of the dealcoholization tower; the dealcoholization tower top reflux tank is also connected to a vacuum device, characterized in that: The dehydration tower bottom is also equipped with alkali and demineralized water inlets; the ethylene glycol outlet of the liquid phase hydrogenation unit is divided into two paths, one path is connected to the middle of the dehydration tower through a pipeline, and the other path is connected to the pipeline connecting the product tower top reflux pump outlet to the top of the product tower through a pipeline; the dehydration tower also includes a demineralized water pipeline, so that demineralized water can be added to the top of the dehydration tower.

2. The distillation system for improving the UV value of ethylene glycol products according to claim 1, characterized in that: The methanol recovery tower, dehydration tower, deethanolating tower, product tower, and ethylene glycol recovery tower are all equipped with reboilers at their bottoms.

3. The distillation system for improving the UV value of ethylene glycol products according to claim 1, characterized in that: The methanol recovery tower, dehydration tower, product tower, and ethylene glycol recovery tower are all equipped with a top condenser, a top reflux tank, and a top reflux pump, which are connected in sequence by pipelines.

4. The distillation system for improving the UV value of ethylene glycol products according to claim 3, characterized in that: The methanol recovery tower, dehydration tower, product tower, and ethylene glycol recovery tower's top reflux tank are all connected to a vacuum device via pipelines.

5. The distillation system for improving the UV value of ethylene glycol products according to claim 1, characterized in that: The demineralized water pipeline is connected to the top of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the top reflux tank of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the outlet of the top reflux pump of the deethanolating tower via a pipeline, or the demineralized water pipeline is connected to the gas phase inlet of the top condenser of the deethanolating tower.

6. The distillation system for improving the UV value of ethylene glycol products according to claim 1, characterized in that: A reboiler is also installed in the middle of the methanol recovery tower.

7. A distillation method for improving the UV value of ethylene glycol products, characterized in that: Includes the following steps: Step 1: Crude methanol from the ethylene glycol synthesis unit is fed into the middle of the methanol recovery tower via pipe b, and crude ethylene glycol from the ethylene glycol synthesis unit is fed into the middle or lower part of the methanol recovery tower via pipe c. The crude methanol and crude ethylene glycol are heated and distilled in the methanol recovery tower via the reboiler at the bottom of the tower and the reboiler in the middle of the tower. The vapor phase from the top of the methanol recovery tower is condensed by the condenser at the top of the tower and enters the reflux tank at the top of the tower. The condensate in the reflux tank is pressurized by the reflux pump and divided into two parts: one part is refluxed back to the top of the methanol recovery tower, and the other part is collected and sent to the fusel oil storage tank. Qualified refined methanol is collected from the side of the methanol recovery tower and sent to the refined methanol storage tank. The liquid from the bottom of the methanol recovery tower is sent to the dehydration tower. Step 2: The methanol recovery tower bottom liquid is pressurized by the dehydration tower feed pump and enters the middle of the dehydration tower. Alkali solution and demineralized water are added to the bottom of the dehydration tower and heated and distilled by the reboiler of the bottom of the dehydration tower. The vapor phase at the top of the dehydration tower is condensed by the top condenser of the dehydration tower and enters the top reflux tank of the dehydration tower. The condensate in the top reflux tank of the dehydration tower is pressurized by the top reflux pump of the dehydration tower and divided into two parts. One part is refluxed to the top of the dehydration tower, and the other part is collected and sent to the fusel oil storage tank. The bottom liquid of the dehydration tower is sent to the dealcoholization tower. Step 3: The liquid in the bottom of the dehydration tower is pressurized by the feed pump and sent to the middle of the dehydration tower. There, it is heated and distilled with ethylene glycol from the liquid hydrogenation unit in the reboiler of the dehydration tower. The vapor phase from the top of the dehydration tower is condensed by the top condenser and enters the top reflux tank. The condensate in the top reflux tank is pressurized by the top reflux pump and divided into two parts. One part is refluxed back to the top of the dehydration tower, and the other part is collected and sent to the light fraction storage tank. The liquid in the bottom of the dehydration tower is sent to the product tower. At the same time, demineralized water is added to the top of the dehydration tower through the demineralized water pipeline. Step 4: The liquid in the bottom of the de-alcoholizing tower is pressurized by the product tower feed pump and enters the middle of the product tower. It is heated and distilled by the reboiler in the bottom of the product tower. The vapor phase at the top of the product tower is condensed by the product tower top condenser and enters the product tower top reflux tank. The condensate in the product tower top reflux tank is pressurized by the product tower top reflux pump and divided into two parts. One part is mixed with ethylene glycol from the liquid phase hydrogenation unit and refluxed to the top of the product tower. The other part is collected as industrial-grade ethylene glycol and sent to the liquid phase hydrogenation unit. The purified ethylene glycol collected from the product tower side is sent to the dealdehyde removal unit. The liquid in the bottom of the product tower is sent to the ethylene glycol recovery tower. Step 5: The product column bottom liquid is pressurized by the ethylene glycol recovery column feed pump and enters the middle of the ethylene glycol recovery column, where it is heated and distilled by the reboiler at the bottom of the ethylene glycol recovery column. The vapor phase at the top of the ethylene glycol recovery column is condensed by the top condenser and enters the top reflux tank. The condensate in the top reflux tank is pressurized by the top reflux pump and divided into two parts. One part is refluxed back to the top of the ethylene glycol recovery column, and the other part is mixed with the industrial-grade ethylene glycol from the product column and sent to the liquid phase hydrogenation unit. The bottom liquid of the ethylene glycol recovery column is sent to the heavy fraction storage tank by the bottom liquid discharge pump.

8. The distillation method for improving the UV value of ethylene glycol products according to claim 7, characterized in that: The methanol recovery tower controls the top temperature at 48℃~52℃, the middle temperature at 52℃~58℃, the bottom temperature at 130℃~150℃, and the top pressure at 48KPaA~53KPaA; the dehydration tower controls the top temperature at 45℃~55℃, the bottom temperature at 149℃~153℃, and the top pressure at 15KPaA~22KPaA; the dealcoholization tower controls the top temperature at 128℃~133℃ and the bottom temperature at 150℃~155℃. The temperature of the product column is controlled at 132℃~135℃, the temperature of the bottom column is controlled at 140℃~145℃, and the pressure of the top column is controlled at 9KPaA~12KPaA. The temperature of the ethylene glycol recovery column is controlled at 120℃~130℃, the temperature of the bottom column is controlled at 125℃~135℃, and the pressure of the top column is controlled at 4KPaA~9KPaA.

9. The distillation method for improving the UV value of ethylene glycol products according to claim 7, characterized in that: The mass content of the water in the bottom of the dehydration tower is controlled at 0.2% to 0.5%; the mass content of the alkalinity at the bottom of the dealcoholization tower is controlled at 0.001% to 0.1%; and the mass content of the water in the bottom of the dealcoholization tower is controlled at 0.01% to 0.05%.

10. The distillation method for improving the UV value of ethylene glycol products according to claim 7, characterized in that: The alkaline solution is a sodium hydroxide solution and a potassium hydroxide solution.

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