A method for the production of neopentyl glycol with reduced wastewater

Abstract

The application discloses a method for preparing neopentyl glycol with reduced wastewater, wherein formaldehyde-containing reaction gas is introduced into an absorption tower T1 to obtain a formaldehyde solution; the formaldehyde solution collected from the tower bottom of the absorption tower T1 is transported to a concentrator R1 for vacuum concentration; concentrated formaldehyde solution S3 is obtained at the bottom of the concentrator R1, and dilute formaldehyde solution S2 is obtained at the top of the concentrator R1 and is returned to the absorption tower T1; the concentrated formaldehyde solution S3 is mixed with reused water S4 returned from a dehydration tower T2 and light components S1, and then is sent into a condensation reactor R2 together with isobutyraldehyde and trimethylamine to generate condensation discharge containing hydroxyl-containing tert-pentanal through an aldol condensation reaction; the condensation discharge is sent into the dehydration tower T2 for separation; light components S1 are collected from the top of the dehydration tower T2 and are returned to the condensation reactor R2, and gas-phase reused water S4 is collected from a side line of the dehydration tower T2; and the aqueous solution containing hydroxyl-containing tert-pentanal is collected from the tower bottom of the dehydration tower T2; under the premise of ensuring reaction stability, the consumption of desalination water, the wastewater discharge and the energy consumption of the whole process are reduced.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing neopentyl glycol that reduces wastewater volume. Background Technology

[0002] Neopentyl glycol (chemical name: 2,2-dimethyl-1,3-propanediol) is a high-quality aliphatic diol with heat resistance, hydrolysis resistance, and light stability. It is widely used in fine chemical fields such as unsaturated polyester resins, powder coatings, high-grade polyurethanes, synthetic plasticizers, and lubricants, and is an indispensable basic organic raw material in the chemical industry.

[0003] Currently, the main industrial production of neopentyl glycol employs the isobutyraldehyde-formaldehyde condensation-catalytic hydrogenation process. This process consists of two steps: the first step involves the aldol condensation reaction of isobutyraldehyde and formaldehyde aqueous solution under the action of an alkaline catalyst to generate the intermediate hydroxypentylaldehyde; the second step involves the catalytic hydrogenation reduction of the hydroxypentylaldehyde aqueous solution to obtain the neopentyl glycol product. Compared with the traditional disproportionation method, this process has advantages such as high product yield, low waste, and high product purity, and has become the mainstream process for neopentyl glycol production worldwide.

[0004] Currently, both domestic and international industrial neopentyl glycol plants use 37wt% industrial formaldehyde aqueous solution as the core raw material. Although this concentration of formaldehyde has the advantages of stable storage, convenient transportation, and low procurement cost, the raw material has an excessively high water content. The 37wt% formaldehyde aqueous solution has a water content of over 63%, and a large amount of water enters the reaction system. It needs to be removed through multiple steps of evaporation and distillation, resulting in high steam energy consumption and circulating water consumption of the plant. In addition, a large amount of wastewater needs to be incinerated, which significantly increases the production cost.

[0005] To address this issue, those skilled in the art have attempted to use high-concentration formaldehyde (55 wt%) or higher as a raw material. However, concentrated formaldehyde leads to excessively vigorous exothermic condensation reactions, significantly increasing the difficulty of temperature control. It also easily triggers side reactions that generate paraformaldehyde, resulting in decreased reaction selectivity, equipment and pipeline blockages, and an inability to achieve long-term stable operation. Furthermore, in traditional processes, the recovery rate of light components at the top of the dehydration tower is only 60-75%, with large amounts of unreacted methanol, formaldehyde, isobutyraldehyde, and catalyst discharged with the wastewater, further increasing raw material consumption and end-of-pipe treatment load. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a new method for preparing pentylene glycol that reduces wastewater volume, while also reducing energy consumption and investment costs throughout the process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing neopentyl glycol with reduced wastewater volume includes the following steps: Formaldehyde-containing reaction gas is passed into absorption tower T1 for washing and absorption to obtain formaldehyde solution; after washing with deionized water at the top of absorption tower T1, formaldehyde solution is collected from the bottom of absorption tower T1. The formaldehyde solution collected from the bottom of the absorption tower T1 is sent to the concentrator R1 for vacuum concentration. The bottom of the concentrator R1 yields concentrated formaldehyde solution S3, and the top of the concentrator R1 yields dilute formaldehyde solution S2, which is then returned to the absorption tower T1. If concentrated formaldehyde is directly fed into the condensation reactor, it will cause violent exothermic reactions and side reactions due to excessively high local concentration. The concentrated formaldehyde solution S3 is mixed with the recycled water S4 returned from the dehydration tower T2 and the light component S1 to adjust the formaldehyde solution concentration to a safe range of 37~55wt%. Then, it is fed into the condensation reactor R2 together with isobutyraldehyde and trimethylamine to undergo an aldol condensation reaction, generating a condensation effluent containing hydroxypentylaldehyde. The water content of the condensation effluent is 20~34wt%, which not only ensures the stability of the reaction system, but also reserves a reasonable load space for the subsequent dehydration process. The condensate is fed into dehydration tower T2 for separation. The light component S1 is collected from the top of dehydration tower T2 and refluxed to condensation reactor R2. The side stream is collected as gaseous recycled water S4. The bottom of dehydration tower T2 is collected as an aqueous solution containing hydroxypentanal. The recycled water S4 is heated and enters the formaldehyde solution in concentrator R1, and then combined with the concentrated formaldehyde solution S3 and sent back to condensation reactor R2. The aqueous solution containing hydroxypentyl aldehyde collected from the bottom of the T2 dehydration tower is sequentially sent to the hydrogenation unit and the distillation unit to obtain neopentyl glycol product. The by-product waste liquid and wastewater are sent for incineration treatment.

[0008] Furthermore, the absorption tower T1 is divided into N sections, where N is a positive integer ≥ 3. Sections 1 to N-1 are packed sections to improve gas-liquid contact efficiency, and the Nth section is equipped with a bubble cap tray to enhance mass transfer. The dilute formaldehyde solution S2 is returned to the packed sections 1 to N-1 to replace part of the fresh demineralized water for absorption. The concentration of the formaldehyde solution collected from the bottom of the absorption tower T1 is 37~55wt%. On the one hand, the amount of fresh demineralized water added is reduced by the dilute formaldehyde reflux; on the other hand, the impact of fluctuations in the formaldehyde concentration at the absorption tower outlet on subsequent processes is avoided.

[0009] Furthermore, the operating pressure of the concentrator R1 is 10~26 kPaA. The concentration of the concentrated formaldehyde solution S3 at the bottom of the concentrator R1 is 55~75 wt%, and the concentration of the dilute formaldehyde solution S2 at the top of the concentrator R1 is 10~20 wt%.

[0010] Furthermore, the operating pressure of the dehydration tower T2 is 40~90 kPaA; the light component S1 collected from the top of the dehydration tower T2 contains 40~95 wt% light component, with the remainder being water; the gas phase recycled water S4 collected from the side stream contains 80~99 wt% water, with the remainder being unreacted methanol, formaldehyde, isobutyraldehyde, and trimethylamine; the temperature of the recycled water S4 is 60~98℃; the recycled water S4 is first used as a heat source to heat the formaldehyde solution entering the concentrator, and after recovering the heat, it is combined with concentrated formaldehyde and the light component from the top of the tower and refluxed to the condensation reactor, thus realizing both energy cascade utilization and concentration dilution of concentrated formaldehyde; Furthermore, the light component recovery rate of the dehydration tower T2 is ≥99%, and the water content of the aqueous solution containing hydroxypentylaldehyde collected from the bottom of the tower is 9~20wt%. After the recycled water is collected from the side stream of the dehydration tower, the water content of the aqueous solution containing hydroxypentylaldehyde in the bottom of the tower can be reduced to 9~20wt%, which reduces the water carryover by nearly 50% compared with the traditional process, significantly reducing the evaporation load and wastewater discharge of subsequent hydrogenation and distillation processes.

[0011] The principles of this invention are explained in detail below: 1) The condensation effluent from condensation reactor R2 contains 20-34 wt% water. This effluent is first mixed with the concentrated formaldehyde solution S3 fed into condensation reactor R2 to obtain a 37-55 wt% formaldehyde solution. This effectively solves problems such as intense exothermic reaction, difficulty in temperature control, decreased reaction selectivity, and equipment and pipeline blockage caused by concentrated formaldehyde feed. Simultaneously, the water content of the hydroxypentylaldehyde aqueous solution in the bottom of dehydration tower T2 is significantly reduced, effectively decreasing energy consumption in subsequent hydrogenation and distillation units, as well as wastewater volume. If the concentrated formaldehyde solution concentration is too low, the neopentyl glycol unit will have high energy consumption and wastewater volume; if the concentrated formaldehyde solution concentration is too high, it may lead to blockage in the concentrator R1 and related pipelines. Therefore, the formaldehyde solution concentration is maintained at 37-55 wt%.

[0012] 2) The formaldehyde solution in the bottom of the absorption tower T1 is pressurized by pump P3 and heat-exchanged by heaters E2 and E7 before entering the concentrator R1. Heater E2 is heated by the gas phase recycled water S4 collected from the side stream of the dehydration tower T2 to reduce energy consumption. The temperature of the recycled water is 60~98℃. If the temperature is too high, it may cause formaldehyde to undergo a self-condensation reaction, generating byproducts such as paraformaldehyde. If the temperature is too low, the heat exchanger area of ​​E2 is large, resulting in higher investment.

[0013] 3) The light component S1 is collected from the top of the dehydration tower T2 and the recycled water S4 is collected from the side stream. These are then recycled to the condensation reactor R2, increasing the recovery rate of the light component from the traditional 60-75% to over 99%.

[0014] 4) 10~20wt% dilute formaldehyde S2 collected from the top of the concentrator R1 is returned to the absorption tower T1, which can effectively reduce the consumption of demineralized water at the top of the absorption tower T1.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The consumption of demineralized water is significantly reduced, with the amount of demineralized water and wastewater reduced by 57% compared to traditional processes; 2) The recovery rate of light components has increased from the traditional 60-75% to over 99%, significantly improving the utilization rate of raw materials and reducing the amount of downstream by-products generated; 3) The reduced water content in the bottom of the dehydration tower can reduce the investment in the hydrogenation and distillation units by about 7% and energy consumption by about 14%. 4) No new complex equipment is added throughout the entire process, resulting in low modification costs. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process for preparing neopentyl glycol with reduced wastewater volume according to the present invention. Detailed Implementation

[0017] like Figure 1 The method for preparing neopentyl glycol to reduce wastewater volume, as shown, is as follows: Formaldehyde-containing reaction gas is passed into absorption tower T1 for washing and absorption to obtain a formaldehyde solution. Absorption tower T1 is divided into N sections (e.g., N ≥ 3 positive integers), where sections 1 to N-1 are packed sections, and section N is equipped with a bubble cap tray. Deionized water is passed through the top of absorption tower T1 for washing and absorption. The heat absorbed in section N is carried away by circulating water cooling to improve the absorption efficiency. Dilute formaldehyde solution S2 collected from the top of concentrator R1 between sections of absorption tower T1 is returned to absorption tower T1 to absorb formaldehyde material from the formaldehyde-containing reaction gas. Formaldehyde solution with a concentration of 37-55 wt% is collected from the bottom of absorption tower T1. The formaldehyde-containing reaction gas is obtained by oxidizing methanol in the presence of an iron-molybdenum catalyst, with a formaldehyde content of 8-12 wt%, a temperature of 120-130℃, and a pressure of 140-150 kPa.

[0018] The formaldehyde solution collected from the bottom of absorber T1 is pressurized by pump P3 and heated to 50-75°C by heaters E2 and E7 before entering concentrator R1. After vacuum concentration, a 55-75 wt% concentrated formaldehyde solution S3 is collected from the bottom of concentrator R1, and a 10-20 wt% dilute formaldehyde solution S2 is collected from the top of concentrator R1. After being cooled by cooler E3, it is returned to the inter-section of absorber T1 to reduce the consumption of demineralized water at the top of the tower. To improve the concentration effect, the operating pressure of concentrator R1 is 10-26 kPaA.

[0019] To avoid problems such as exothermic and difficult temperature control during condensation reactions, decreased reaction selectivity, and equipment and pipeline blockage, the concentrated formaldehyde solution S3 at the bottom of the concentrator R1 is mixed with the recycled water S4 returned from the dehydration tower T2 and the light component S1. After adjusting the formaldehyde solution concentration to 37~55wt%, it is then introduced into the condensation reactor R2 along with isobutyraldehyde and trimethylamine to undergo an aldol condensation reaction, producing a condensation discharge containing hydroxypentanal.

[0020] The condensation effluent from condensation reactor R2 has a water content of 20-34 wt%. The condensation effluent enters dehydration tower T2 for separation. The operating pressure of dehydration tower T2 is 40-90 kPaA. Unreacted light components S1 (such as methanol, formaldehyde, isobutyraldehyde, trimethylamine, etc.) are collected from the top of dehydration tower T2. Light components S1 are combined with concentrated formaldehyde solution S3 and then sent back to condensation reactor R2 to improve the reaction conversion rate of condensation reactor R2. The light component content in light component S1 is 40-95 wt%, and the remainder is water.

[0021] Gas-phase recycled water S4 is collected from the side stream of dehydration tower T2. After being heated by heater E2, recycled water S4 enters the formaldehyde solution in concentrator R1, and is then combined with concentrated formaldehyde solution S3 via pump P9 and returned to condensation reactor R2. The temperature of recycled water S4 is 60~98℃. The flow rate of recycled water S4 is controlled to ensure that the formaldehyde solution concentration is adjusted to 37~55wt% after mixing with light components S1. The water content in recycled water S4 is 80~99wt%, with the remainder being unreacted methanol, formaldehyde, isobutyraldehyde, trimethylamine, and other light components. The recovery rate of light components in dehydration tower T2 is increased from the traditional 60~75% to over 99%, improving the utilization rate of formaldehyde, isobutyraldehyde, and trimethylamine, and reducing the generation of byproducts in subsequent hydrogenation and distillation units.

[0022] The water content in the aqueous solution containing hydroxypentylaldehyde collected from the bottom of dehydration tower T2 is reduced from the traditional 20-34 wt% to 9-20 wt%. This aqueous solution is then sequentially fed into the hydrogenation and distillation units to obtain neopentyl glycol with a purity ≥99.5%. Byproduct waste liquid and wastewater are sent for incineration. Reclaimed water S4 collected from the side stream of dehydration tower T2 is returned to the condensation reactor R2. The significantly reduced water content in the aqueous solution containing hydroxypentylaldehyde collected from the bottom of dehydration tower T2 effectively reduces energy consumption in subsequent hydrogenation and distillation units, as well as the amount of wastewater generated by the unit.

[0023] Unless otherwise specified, the formaldehyde-containing reaction gas used in the following examples is prepared by oxidizing methanol in the presence of an iron-molybdenum catalyst. The formaldehyde content in the reaction gas is 8-12 wt%, the temperature is 120-130°C, and the pressure is 140-150 kPaA.

[0024] Example 1 The production scale of this embodiment is 80,000 tons of neopentyl glycol per year.

[0025] Absorption process: Methanol is used as raw material and undergoes an oxidation reaction with air under the action of an iron-molybdenum catalyst. The resulting formaldehyde-containing reaction gas has a formaldehyde content of 9.35 wt%, at a temperature of 126℃ and a pressure of 147 kPaA. The formaldehyde-containing reaction gas is fed into a three-stage absorption tower T1. The first and second stages are packed sections, and the third stage is a bubble cap tray. Demineralized water is introduced at the top of the tower for washing and absorption. The heat of absorption in the third stage is carried away by circulating water cooling to improve the absorption efficiency. At the same time, the 19 wt% dilute formaldehyde solution generated in the concentration process is returned to the top of the first packed section. The bottom of the tower yields a 50 wt% formaldehyde solution. This process reduces the consumption of demineralized water by 57% compared to the traditional process.

[0026] Concentration process: The formaldehyde solution collected from the bottom of the absorption tower T1 is pressurized by pump P3, and after heat exchange with heaters E2 and E7 to 70°C, it enters the concentrator R1. The operating pressure of the concentrator R1 is 18 kPaA. After vacuum concentration, a 70 wt% concentrated formaldehyde solution S3 is obtained at the bottom of the concentrator R1, and a 19 wt% dilute formaldehyde solution S2 is obtained after vapor phase condensation at the top. After being cooled by cooler E3, it is returned to the absorption tower T1.

[0027] Condensation process: After mixing concentrated formaldehyde solution S3 with recycled water S4 returned from dehydration tower T2 and light component S1, the formaldehyde concentration is adjusted to 50wt%. Then, it enters the condensation reactor with isobutyraldehyde and trimethylamine. Under alkaline conditions, a hydroxyl condensation reaction occurs to generate a condensation discharge containing hydroxypentanal. The water content of the condensation discharge is 23.3wt%.

[0028] Dehydration process: The condensation discharge is fed into dehydration tower T2, operating at 80 kPaA. Unreacted light components S4 (methanol, formaldehyde, isobutyraldehyde, trimethylamine, etc.) are collected from the top of the tower and directly recycled to condensation reactor R2. The light components contain 90 wt% of these components, with the remainder being water. The light component recovery rate reaches 99.8%, improving the utilization rate of formaldehyde, isobutyraldehyde, and trimethylamine, and reducing the generation of byproducts in subsequent hydrogenation and distillation units. Gas-phase recycled water S4 collected from the side stream of dehydration tower T2 is heated to formaldehyde solution via heater E2, and then combined with concentrated formaldehyde solution S3 and recycled back to condensation reactor R2. The recycled water S4 contains 95 wt% water, with the remainder being unreacted methanol, formaldehyde, isobutyraldehyde, and trimethylamine. The recycled water S4 is collected at 90℃, and the flow rate is controlled to ensure that the formaldehyde concentration is adjusted to 50 wt% after mixing the recycled water S4 and light components S1 with the concentrated formaldehyde solution S3. The bottom of the T2 dehydration tower yielded an aqueous solution containing hydroxypentanal, with the water content reduced to 11.5 wt%.

[0029] Refining process: After the aqueous solution is processed by the subsequent hydrogenation and distillation units, neopentyl glycol product with a purity of ≥99.5% is obtained. The by-product waste liquid and wastewater are sent for incineration treatment.

[0030] Example 2 Absorption process: Formaldehyde-containing reaction gas (formaldehyde content 8wt%, temperature 120℃, pressure 140kPaA) is introduced into absorption tower T1. A formaldehyde solution with a concentration of 37wt% is collected from the bottom of the tower.

[0031] Concentration process: After the formaldehyde solution is heated to 50°C, it enters the concentrator R1. The operating pressure is 10 kPaA. A 55 wt% concentrated formaldehyde solution S3 is collected from the bottom, and a 15 wt% dilute formaldehyde solution S2 is collected from the top.

[0032] Condensation process: Concentrated formaldehyde solution S3 is mixed with 60°C recycled water S4 returned from dehydration tower T2 and light component S1. After adjusting the formaldehyde concentration to 37wt%, it is sent to condensation reactor R2 to generate condensed discharge with a water content of 34wt%.

[0033] Dehydration process: The operating pressure of dehydration tower T2 is 40 kPaA. The light component content in the light component S1 at the top of the tower is 40 wt%; the water content in the side stream recycled water S4 is 80 wt%, and the extraction temperature is 60℃. The recovery rate of the light component in the dehydration tower is 99.1%, and the water content of the hydroxypentyl aldehyde aqueous solution extracted from the bottom of the tower is 20 wt%.

[0034] Refining process: Same as in Example 1. Calculations show that in this example, the consumption of demineralized water and the amount of wastewater discharged are reduced by 52% compared to the traditional process, and the energy consumption of hydrodistillation is reduced by 13%.

[0035] Example 3 Absorption process: Formaldehyde-containing reaction gas (formaldehyde content 12wt%, temperature 130℃, pressure 150kPaA) is introduced into absorption tower T1. A formaldehyde solution with a concentration of 55wt% is collected from the bottom of the tower.

[0036] Concentration process: After the formaldehyde solution is heated to 75°C, it enters the concentrator R1. The operating pressure is 26 kPaA. A concentrated formaldehyde solution S3 with a concentration of 75 wt% is collected from the bottom, and a dilute formaldehyde solution S2 with a concentration of 20 wt% is collected from the top.

[0037] Condensation process: Concentrated formaldehyde solution S3 is mixed with 98°C recycled water S4 returned from dehydration tower T2 and light component S1. After adjusting the formaldehyde concentration to 55wt%, it is sent to condensation reactor R2 to generate condensed discharge with a water content of 20wt%.

[0038] Dehydration process: The operating pressure of dehydration tower T2 is 90 kPaA. The light component content in the light component S1 at the top of the tower is 95 wt%; the water content in the side stream recycled water S4 is 99 wt%, and the extraction temperature is 98℃. The recovery rate of light components in the dehydration tower is 99.5%, and the water content of the hydroxypentyl aldehyde aqueous solution extracted from the bottom of the tower is 9 wt%.

[0039] Refining process: Same as in Example 1. Calculations show that in this example, the consumption of demineralized water and the amount of wastewater discharged are reduced by 59.3% compared to the traditional process, and the energy consumption of hydrodistillation is reduced by 15%. The technical specifications of the traditional process and Examples 1-3 are compared in the table below: As shown in the table above, this invention can stably achieve its objectives of reducing demineralized water consumption, increasing raw material recovery rate, and reducing energy consumption by implementing it over a wide range of parameters.

[0040] The above embodiments are merely preferred embodiments of the present invention. Any conventional parameter adjustments or equivalent process substitutions made based on the technical solutions of the present invention should be considered as falling within the protection scope of the present invention.

Claims

1. A method for preparing neopentyl glycol with reduced wastewater volume, characterized in that: Includes the following steps: Formaldehyde-containing reaction gas is passed into absorption tower T1 for washing and absorption to obtain formaldehyde solution; After washing with deionized water at the top of absorption tower T1, formaldehyde solution is collected from the bottom of absorption tower T1. The formaldehyde solution collected from the bottom of the absorption tower T1 is sent to the concentrator R1 for vacuum concentration. The bottom of the concentrator R1 yields concentrated formaldehyde solution S3, and the top of the concentrator R1 yields dilute formaldehyde solution S2, which is then returned to the absorption tower T1. After mixing concentrated formaldehyde solution S3 with recycled water S4 returned from dehydration tower T2 and light component S1, it is fed together with isobutyraldehyde and trimethylamine into condensation reactor R2 to undergo aldol condensation reaction, generating condensate containing hydroxypentanal. The condensate is fed into dehydration tower T2 for separation. The light component S1 is collected from the top of dehydration tower T2 and refluxed to condensation reactor R2. The side stream is collected as gaseous recycled water S4. The bottom of dehydration tower T2 is collected as an aqueous solution containing hydroxypentanal. The recycled water S4 is heated and enters the formaldehyde solution in concentrator R1, and then combined with the concentrated formaldehyde solution S3 and sent back to condensation reactor R2. The aqueous solution containing hydroxypentyl aldehyde collected from the bottom of the T2 dehydration tower is sequentially sent to the hydrogenation unit and the distillation unit to obtain neopentyl glycol product. The by-product waste liquid and wastewater are sent for incineration treatment.

2. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The absorption tower T1 is divided into N sections, where N is a positive integer ≥3. Sections 1 to N-1 are packed sections, and the Nth section is equipped with a bubble cap tray. The dilute formaldehyde solution S2 is returned to the packed section of section 1 to N-1. The concentration of the formaldehyde solution collected from the bottom of the absorption tower T1 is 37~55wt%.

3. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The operating pressure of the concentrator R1 is 10~26 kPaA; the concentration of the concentrated formaldehyde solution S3 at the bottom of the concentrator R1 is 55~75 wt%, and the concentration of the dilute formaldehyde solution S2 at the top of the concentrator R1 is 10~20 wt%.

4. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The concentrated formaldehyde solution S3 is mixed with the recycled water S4 returned from the dehydration tower T2 and the light component S1, and the formaldehyde solution concentration is adjusted to 37~55wt%.

5. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The water content of the condensate is 20-34 wt%.

6. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The operating pressure of the dehydration tower T2 is 40~90 kPaA; the light component S1 extracted from the top of the dehydration tower T2 contains 40~95 wt% light component, with the remainder being water; the gas phase recycled water S4 extracted from the side stream contains 80~99 wt% water, with the remainder being unreacted methanol, formaldehyde, isobutyraldehyde, and trimethylamine.

7. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The extraction temperature of the recycled water S4 is 60~98℃.

8. The method for preparing neopentyl glycol with reduced wastewater volume according to claim 1, characterized in that: The light component recovery rate of the dehydration tower T2 is ≥99%, and the water content of the aqueous solution containing hydroxypentanal collected from the bottom of the tower is 9~20wt%.

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