Method and system for recovering methanol in sucralose production

Abstract

The invention discloses a method and a system for recovering methanol in sucralose production, and relates to the technical field of methanol recovery. Comprising the following steps that (1) gas-phase methanol produced in a rectifying tower and hot water enter a first-stage heat exchanger at the same time, and gas-phase methanol obtained after heat exchange enters a second-stage condenser; (2) circulating water and liquid methanol obtained after heat exchange of the first-stage heat exchanger and the second-stage condenser enter a third-stage condenser; and (3) outputting and collecting methanol condensed by the third-stage condenser. The method is simple, the purposes of recycling waste heat and saving steam consumption are achieved, and the situation that a large amount of waste heat remains on the top of the rectifying tower and influences the finished product quality is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of methanol recovery, and in particular to a method and system for recovering methanol in sucralose production. Background Art

[0002] In the production process of sucralose, the crude product of sucralose-6-ethyl ester is recrystallized with ethyl acetate and then recrystallized with water to obtain sucralose-6-ethyl ester water crystals, which contain trace amounts of ethyl acetate that can be removed by vacuum without affecting the alcoholysis reaction. The sucralose-6-ethyl ester water crystals are dissolved in methanol and reacted with sodium methoxide to produce sucralose and methyl acetate. After the reaction is completed, most of the methanol is concentrated and removed to obtain sucralose syrup, which is then concentrated with purified water to reduce the methanol content as much as possible. Waste methanol is generated during the above-mentioned concentration and demethanolation process and needs to be recycled.

[0003] In the process of recycling waste methanol, the waste methanol is mainly treated by extraction and distillation to remove the water in it for reuse. This process causes a large amount of residual heat to remain at the top of the distillation tower, resulting in poor cooling effect of the finished product. In addition, the evaporation capacity (reflux + extraction) of the methanol distillation tower is about 7.5-8.5m 3 / h, the huge evaporation capacity is not effectively utilized.

[0004] Chinese patent CN113698275A discloses a device and method for recovering methanol from dimethyl carbonate, methyl acetate, and methanol system in the production process of sucralose. The method comprises the following steps in sequence: S1 acid preparation: mixing waste methanol and concentrated sulfuric acid to obtain an alcohol-acid mixture; S2 acidolysis: the alcohol-acid mixture is successively subjected to acidolysis reaction and heated gasification to form liquid vapor II; S3 distillation: the liquid vapor II is distilled to obtain liquid vapor III; the liquid vapor III is condensed to obtain a distillation section condensate; when the methanol content of the distillation section condensate is greater than the threshold value I, the distillation section condensate is collected; the method can solve the technical problems of unsatisfactory recovery rate, purity, and efficiency of methanol recovery from sucralose production tail gas, and can be applied in the production practice of sucralose to recycle materials such as methanol to reduce production costs and improve efficiency. The method requires sulfuric acid, has high requirements for equipment, and does not consider the effects of heat saving and heat recovery.

[0005] Chinese patent CN212395918U discloses a waste heat utilization system of a methanol recovery tower or a methanol distillation tower, including an absorption heat pump connected to a methanol recovery tower or a methanol distillation tower, the top steam of the methanol recovery tower or the methanol distillation tower is connected to the absorption heat pump through a low-temperature waste heat pipeline and heat exchanged with the absorption heat pump, the absorption heat pump is provided with a heated medium circulation pipeline, the methanol recovery tower or the methanol distillation tower is provided with a methanol heating circulation pipeline for high-temperature heating of the bottom liquid of the methanol recovery tower or the methanol distillation tower, and the methanol heating circulation pipeline is connected to the heated medium circulation pipeline. The system can reduce the consumption of steam and cooling circulating water, and reduce operating costs. The system adopts a low-temperature waste heat pipeline, a heating medium circulation pipeline, and a heating circulation pipeline, and the device is relatively complex, and it is also not suitable for the production system of sucralose.

[0006] Currently, there is still a lack of a methanol recovery method with simple process and significant energy saving for the production process of sucralose. Summary of the invention

[0007] The purpose of the present invention is to provide a method for recovering methanol in the production of sucralose. The method is simple, and the purpose of waste heat recovery and steam consumption saving is achieved, and a large amount of waste heat remaining at the top of the distillation tower is avoided, which affects the quality of the finished product.

[0008] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0009] In one aspect, the present invention provides a method for recovering methanol in the production of sucralose, comprising the following steps:

[0010] (1) The gaseous methanol produced in the distillation tower and the hot water enter the primary heat exchanger at the same time, and the gaseous methanol obtained after heat exchange enters the secondary condenser;

[0011] (2) Liquid methanol obtained after heat exchange between circulating water and the primary heat exchanger and the secondary condenser enters the tertiary condenser;

[0012] (3) The methanol condensed by the tertiary condenser is output and collected.

[0013] Preferably, in step (1), the temperature of the hot water is 55-70°C, more preferably 60-65°C.

[0014] Preferably, in step (1), the temperature range of the primary heat exchanger is 55-62°C, more preferably 58-60°C.

[0015] Preferably, in step (1), the temperature range of the secondary condenser is 55-62°C, more preferably 58-60°C.

[0016] Preferably, in step (2), the temperature range of the condenser is 45-60°C, more preferably 50-55°C.

[0017] In step (2), the circulating water is input into the three-stage condenser through a pipeline to perform condensation.

[0018] Preferably, in step (3), after the condensed methanol is output, it is sequentially input into a methanol receiving tank and a methanol finished product tank.

[0019] Further preferably, the flow rate of the methanol product tank is 3-10m 3 / h, more preferably 5-8.5m 3 / h.

[0020] Preferably, before step (1), the method further comprises the following steps: steam enters a reboiler to heat the methanol liquid in the reboiler, the heated methanol liquid enters a distillation tower to be distilled into a methanol gas phase, and outputs the methanol liquid; the methanol liquid at the bottom of the distillation tower is input into a reboiler to be heated, and then returns to the distillation tower to be distilled into a methanol gas phase.

[0021] More preferably, the temperature of the steam is 90-120°C, and more preferably 100-112°C.

[0022] More preferably, the temperature range of the reboiler is 55-70°C, and more preferably 60-65°C.

[0023] More preferably, the temperature of the heated methanol liquid is 90-102° C., more preferably 90-102° C. More preferably, the pressure at the top and bottom of the distillation tower is 0.25-0.35 Pa, more preferably 0.3 Pa.

[0024] On the other hand, the present invention provides a system for recovering methanol in the production of sucralose, comprising a distillation tower, a primary heat exchanger, a secondary condenser and a tertiary condenser, wherein the inlet of the primary heat exchanger is connected to the top of the distillation tower, the inlet of the secondary condenser is connected to the outlet of the primary heat exchanger, and the inlet of the tertiary condenser is connected to the outlet of the primary heat exchanger and the outlet of the secondary condenser.

[0025] Preferably, the system further comprises a methanol receiving tank and a methanol finished product tank, wherein the outlet of the tertiary condenser is connected to the inlet of the methanol receiving tank, and the outlet of the methanol receiving tank is connected to the inlet of the methanol finished product tank.

[0026] Preferably, the system further comprises a reboiler, the reboiler comprising a steam inlet, a condensate outlet, a distillation inlet and a distillation outlet, wherein the distillation inlet is connected to the bottom of the distillation tower, and the distillation outlet is connected to the middle or top of the distillation tower.

[0027] The beneficial effects of the present invention are:

[0028] (1) The separation and recycling of methanol is realized, which reduces the loss of methanol and increases the production efficiency;

[0029] (2) By allowing the methanol gas phase to enter the primary heat exchanger, the primary heat exchanger can be preheated, thereby achieving the purpose of recycling waste heat in the methanol recovery process, saving steam consumption and having a significant energy-saving effect;

[0030] (3) The device is simple and the process is not complicated, which avoids too many people being involved in the production of the device, saves manpower, reduces labor costs, and improves the safety of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the system structure of Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of the present application.

[0033] Example 1

[0034] This embodiment Figure 1 The process is carried out in the system shown, which includes a distillation tower, a primary heat exchanger, a secondary condenser and a tertiary condenser, wherein the inlet of the primary heat exchanger is connected to the top of the distillation tower, the inlet of the secondary condenser is connected to the outlet of the primary heat exchanger, and the outlet of the primary heat exchanger and the outlet of the secondary condenser are connected to the inlet of the tertiary condenser.

[0035] The system also includes a methanol receiving tank and a methanol finished product tank, wherein the outlet of the three-stage condenser is connected to the inlet of the methanol receiving tank, and the methanol receiving tank is pumped to a crude methanol tank by a production pump.

[0036] The system also includes a reboiler, which includes a steam inlet, a condensate outlet, a distillation inlet and a distillation outlet, wherein the distillation inlet is connected to the bottom of the distillation tower, and the distillation outlet is connected to the middle or top of the distillation tower.

[0037] (1) Steam (100-112℃) enters the reboiler, and the temperature range of the reboiler is 60-65℃; the steam heats the methanol liquid in the reboiler (heating temperature is 90-102℃), and after heating, the methanol liquid (90-102℃) enters the distillation tower, and the pressure at the top and bottom of the distillation tower is 0.3pa. The methanol liquid at the bottom of the distillation tower is input into the reboiler and heated to 90-102℃, and then returns to the distillation tower again and is distilled into methanol gas phase.

[0038] (2) The gaseous methanol and hot water (60-65°C) in the distillation tower enter the primary heat exchanger at the same time, and the gaseous methanol obtained after heat exchange enters the secondary condenser; the temperature range of the secondary condenser during the heat exchange reaction is: 58-60°C.

[0039] (3) The liquid methanol obtained from the primary heat exchanger and the secondary condenser enters the tertiary condenser. The circulating water pipeline is connected to the tertiary condenser. The circulating water is input into the tertiary condenser through the pipeline to achieve condensation. The temperature range of the condenser is 50-55°C.

[0040] (4) The liquid methanol (50-55°C) obtained from the tertiary condenser is fed into the methanol receiving tank and then 3 / h flow rate into the methanol finished product tank.

[0041] Comparative Example 1

[0042] The difference from Example 1 is that Comparative Example 1 does not have a primary heat exchanger and a third-stage condenser.

[0043] The methanol gas phase temperature at the top of the distillation tower in Comparative Example 1 is 65-70°C, and the methanol gas phase temperature at the top of the distillation tower in Example 1 is 60-65°C. When the temperature of the methanol gas phase is lower, the volatilization amount is less, and the methanol consumption is less.

[0044] In the comparative example 1, the temperature of the methanol receiving tank is 50-53°C, and in the example 1, the temperature of the methanol receiving tank is 40-45°C. The decrease in the temperature of the methanol receiving tank can reduce the volatilization of methanol.

[0045] The steam usage of Example 1 and Comparative Example 1 is compared as follows:

[0046] Example 1 Comparative Example 1 Steam consumption 30 tons / day 50 tons / day

[0047] The results show that, compared with the comparative example 1, the improved embodiment 1 significantly reduces the steam consumption. Calculated based on the average market price of steam of 200 yuan / ton, the cost can be saved by 4,000 yuan / day.

Claims

1. A method for recovering methanol in sucralose production, characterized in that: The following steps are involved: (1) The gaseous methanol produced in the distillation tower and the hot water enter the primary heat exchanger at the same time, and the gaseous methanol obtained after heat exchange enters the secondary condenser; (2) Liquid methanol obtained after heat exchange between circulating water and the primary heat exchanger and the secondary condenser enters the tertiary condenser; (3) The methanol condensed by the tertiary condenser is output and collected.

2. The method according to claim 1, characterized in that In step (1), the temperature of the hot water is 55-70°C, preferably 60-65°C.

3. The method according to claim 1, characterized in that In step (1), the temperature range of the primary heat exchanger is 55-62°C, preferably 58-60°C.

4. The method according to claim 1, characterized in that: In step (1), the temperature range of the secondary condenser is 55-62°C, preferably 58-60°C.

5. The method according to claim 1, characterized in that In step (2), the temperature range of the condenser is 45-60°C, preferably 50-55°C.

6. The method according to claim 1, characterized in that In step (3), the condensed methanol is output and then sequentially input into a methanol receiving tank and a methanol finished product tank.

7. The method according to claim 1, characterized in that Prior to step (1), the method further includes the following steps: steam enters a reboiler to heat the methanol liquid in the reboiler, the heated methanol liquid enters a distillation tower to be distilled into a methanol gas phase, and outputs the methanol liquid; the methanol liquid at the bottom of the distillation tower is input into a reboiler to be heated, and then returns to the distillation tower to be distilled into a methanol gas phase.

8. The method according to claim 7, characterized in that The temperature of the steam is 90-120°C, preferably 100-112°C.

9. The method according to claim 7, characterized in that: The temperature range of the reboiler is 55-70°C, preferably 60-65°C.

10. The method according to claim 7, characterized in that The temperature of the heated methanol liquid is 85-110°C, preferably 90-102°C.

11. The method according to claim 7, characterized in that The pressure at the top and bottom of the distillation tower is 0.25-0.35 Pa, preferably 0.3 Pa.

12. A system for recovering methanol in sucralose production, characterized in that: It includes a distillation tower, a primary heat exchanger, a secondary condenser and a tertiary condenser, wherein the inlet of the primary heat exchanger is connected to the top of the distillation tower, the inlet of the secondary condenser is connected to the outlet of the primary heat exchanger, and the inlet of the tertiary condenser is connected to the outlet of the primary heat exchanger and the outlet of the secondary condenser.

13. The system according to claim 12, characterized in that It also includes a methanol receiving tank and a methanol finished product tank, wherein the outlet of the three-stage condenser is connected to the inlet of the methanol receiving tank, and the outlet of the methanol receiving tank is connected to the inlet of the methanol finished product tank.

14. The system according to any one of claims 12-13, characterized in that: The system further comprises a reboiler, which comprises a steam inlet, a condensate outlet, a distillation inlet and a distillation outlet, wherein the distillation inlet is connected to the bottom of the distillation tower, and the distillation outlet is connected to the middle or top of the distillation tower.

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