Novel negative pressure steam heating process for sucralose continuous esterification dehydration tower

Abstract

The invention provides a novel negative pressure steam heating process for a sucralose continuous esterification dehydration tower, and belongs to the technical field of chemical engineering. The process method comprises the following steps: opening a valve from a steam outlet of a dehydrating tower heater to a condensate tank, supplementing water to a buffer tank, and starting a circulating pump to form negative pressure in the condensate tank; opening a steam inlet valve of the dehydrating tower, so that a steam inlet of the dehydrating tower generates negative pressure, the temperature of the steam inlet is reduced, and negative-pressure steam heating is realized. The ejector is additionally arranged to generate negative pressure steam, the temperature of heating steam of the dehydrating tower is reduced, decomposition of sugar is reduced, and therefore the conversion rate of sucrose hexaester is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a novel negative pressure steam heating process for a sucralose continuous esterification dehydration tower. Background Art

[0002] As a high-intensity sweetener, sucralose is not absorbed by the human body, has no bioaccumulation, is highly safe, and is gradually replacing sucrose. Currently, the sucralose industry is developing rapidly, and the output of sucralose is also increasing year by year. How to reduce production costs and increase conversion rates is particularly important.

[0003] Sucrose-6-ester is an important intermediate in the synthesis of sucralose. There are two main methods for preparing sucrose-6-ester. One is the dibutyltin oxide method, which uses sucrose as a raw material, an organic tin compound as a catalyst, and acetic anhydride as an acylating agent. The high selectivity of the organic tin compound is used to react with the 6-hydroxyl group of sucrose, and then reacts with the acylating agent to obtain a high yield of sucrose-6-ester; the other is the orthoester method, which was invented by Simpson and Tadley (US Pat. No. 4,889,928) in 1989. It uses p-toluenesulfonic acid as a catalyst and trimethyl orthoacetate as an acylating agent. Sucrose and trimethyl orthoacetate are reacted to generate sucrose-4,6-cyclic ester, which is then ring-opened by adding water, and then the 4-ester migrates to the 6-ester under alkaline conditions to finally obtain sucrose-6-ester.

[0004] The most commonly used method is the dibutyltin oxide method, which mainly has three steps. The first step is to prepare the catalyst organotin ester, which is synthesized by organotin and acetic anhydride in cyclohexane as solvent; the second step is the acylation process, in which the organotin ester and sucrose form an organotin sucrose complex in DMF as solvent and dehydrating agent; the third step is the esterification process, in which acetic anhydride is added to the organotin sucrose complex to react, and phase separation is performed to obtain a DMF solution of sucralose 6-6 ethyl ester and an organotin ester cyclohexane solution. The organotin ester is concentrated and dried to remove cyclohexane and then the second step is continued. In the second step of acylation, the water content in the system is a key factor affecting the formation of the organotin sucrose complex, which is very easy to decompose in the presence of water, thereby affecting the conversion rate of the esterification product sucrose-6-ester in the third step.

[0005] Patent CN104098617A discloses a method for preparing sucrose-6-acetate, (1) adding sucrose to an organic solvent N, N-dimethylformamide, heating to 80-100°C to dissolve, then cooling to 70°C, adding a non-polar organic solvent and an organic tin compound to reflux with water for 5-8 hours, and controlling the reflux temperature at 80-100°C; (2) cooling the above reactants to below 25°C, then dripping acetic anhydride thereto for 2-8 hours; (3) adding an appropriate amount of water to the above reaction solution, extracting the organic tin compound with a non-polar organic solvent, concentrating and recovering it, and then azeotropically extracting the raffinate with a non-polar organic solvent to obtain a sucrose-6-acetate solution. This method uses a non-polar organic solvent for extraction, which requires a large amount of solvent consumption, is relatively costly, and later solvent recovery has always been a problem that plagues this process.

[0006] Patent CN102627675A discloses a method for preparing sucrose-6-ester, comprising the following steps: (1) dissolving sucrose in an organic solvent of 2-6 times its volume, then adding an organic tin compound, stirring the reaction at 70-130°C, and removing the water generated by the reaction by intermittent vacuum dehydration until the reaction is complete; (2) after the reaction is complete, adding an acylating agent under low temperature to generate sucrose-6-ester, adding water to stop the reaction, and finally adding a certain amount of cyclohexane to recover the organic tin compound. This method uses a vacuum dehydration method with high energy consumption.

[0007] In production, dehydration is mainly achieved by low-pressure steam heating method, but the temperature of low-pressure steam is generally around 140°C, which is relatively high and results in high sugar loss. Summary of the invention

[0008] The object of the present invention is to provide a novel negative pressure steam heating process for a sucralose continuous esterification dehydration tower in view of the deficiencies of the prior art, thereby reducing the temperature of the heating steam in the dehydration tower, reducing the decomposition of sugar, improving the conversion rate of sucrose-6-ester, and increasing the output of the esterified liquid.

[0009] To achieve the above-mentioned purpose, the technical solution of the present invention is as follows.

[0010] A novel negative pressure steam heating method for a sucralose continuous esterification dehydration tower comprises the following steps:

[0011] (1) Open the valve from the steam outlet of the dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank;

[0012] (2) Open the steam inlet valve of the dehydration tower to generate negative pressure at the steam inlet of the dehydration tower, reduce the steam inlet temperature, and realize negative pressure steam heating.

[0013] Furthermore, in the method of heating the sucralose continuous esterification dehydration tower with a novel negative pressure steam, the steam is the steam generated during the sucrose esterification process to produce sucrose-6-ester.

[0014] Furthermore, in the method of heating the sucralose continuous esterification dehydration tower with a novel negative pressure steam, in step (1), the negative pressure is generated by circulating a jet circulation pump and an ejector.

[0015] Furthermore, in the method of heating the sucralose continuous esterification dehydration tower with a novel negative pressure steam, the steam outlet of the dehydration tower heater is directly connected to the condensate tank through a pipeline, and the gas phase of the condensate tank is led to the ejector.

[0016] Furthermore, in the method of heating the sucralose continuous esterification dehydration tower with a novel negative pressure steam, the negative pressure is -30 to -80 KPa, preferably the negative pressure is -45 to -80 KPa.

[0017] Furthermore, in the method of heating the sucralose continuous esterification dehydration tower with a novel negative pressure steam, the steam inlet temperature is reduced to 60-90°C, preferably the steam inlet temperature is reduced to 60-85°C.

[0018] The above-mentioned sucralose continuous esterification dehydration tower adopts a novel negative pressure steam heating method, and includes the following equipment:

[0019] Condensate tanks, buffer tanks, ejectors, ejector circulation pumps and condensate pumps;

[0020] The condensate tank is connected to the steam outlet of the esterification dehydration tower in the front section, the gas phase of the condensate tank is connected to the ejector, and the ejector is connected to the outlet of the jet circulation pump and the upper opening of the buffer tank through a pipeline; the condensate in the condensate tank is pumped away by the condensate pump.

[0021] Furthermore, in the method of using a novel negative pressure steam heating method in the continuous esterification and dehydration tower of sucralose, the conversion rate of the obtained sucrose-6-ester is increased by 3-7%, and the output of the obtained esterified liquid is increased by 3-7%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention adopts a negative pressure steam heating method, which has a lower heat source temperature than the traditional low-pressure steam heating method (the low-pressure steam temperature is generally around 140°C, and the negative pressure steam temperature is 70-100°C), is more conducive to esterification, reduces sucrose loss, and increases the conversion rate of sucrose to sucrose-6-ester. The lower heat source temperature can also reduce energy consumption and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a flow chart of the novel negative pressure steam heating method of the sucralose continuous esterification dehydration tower in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] 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 invention.

[0026] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0027] In the present invention, the process of producing sucrose-6-ester using sucrose specifically comprises the following steps:

[0028] The reaction liquid (sucrose solution: organic tin acetate mass ratio of 1:2) is pumped into a dehydration tower, and dehydration is achieved through the novel negative pressure steam heating process of the sucralose continuous esterification dehydration tower of the present invention. When the material in the dehydration tower is sampled and analyzed to be qualified, the extraction pump of the dehydration tower is turned on to send the material in the dehydration tower to the desolventizing gas-liquid separator, and the pressure in the gas-liquid separator is controlled to be -0.098MPa and the temperature is 50°C. The separated gas phase enters the desolventizing buffer tank after two-stage condensation, and the first-stage condensation temperature is controlled to be 25°C and the second-stage condensation temperature is controlled to be 18°C. The first-stage condensate and the second-stage condensate both enter the desolventizing DMF storage tank, and the non-condensable gas in the dehydration buffer tank and the desolventizing buffer tank enters the tail gas recovery system; when the material density in the gas-liquid separator reaches 1095Kg / m 3 When the extraction pump is turned on, the material enters the acylation kettle for acylation and extraction to obtain the esterified liquid.

[0029] The sucralose continuous esterification dehydration tower adopts a novel negative pressure steam heating process and uses the following equipment:

[0030] Condensate tanks, buffer tanks, ejectors, ejector circulation pumps and condensate pumps;

[0031] The condensate tank is connected to the steam outlet of the esterification dehydration tower in the front section, the gas phase of the condensate tank is connected to the ejector, and the ejector is connected to the outlet of the jet circulation pump and the upper opening of the buffer tank through a pipeline; the condensate in the condensate tank is pumped away by the condensate pump.

[0032] The novel negative pressure steam heating process of the sucralose continuous esterification dehydration tower (flow chart as shown in FIG. Figure 1 The specific implementation steps are as follows:

[0033] Example 1

[0034] (1) Open the valve from the steam outlet of the esterification dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank;

[0035] (2) Open the steam inlet valve of the esterification dehydration tower to generate negative pressure at the steam inlet. The steam inlet temperature drops from the original steam temperature of about 1 kg and 120 °C to -45 KPa and 85 °C, thus achieving negative pressure steam heating and dehydration in the dehydration tower.

[0036] Example 2

[0037] (1) Open the valve from the steam outlet of the esterification dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank;

[0038] (2) Open the steam inlet valve of the esterification dehydration tower to generate negative pressure at the steam inlet. The steam inlet temperature drops from the original steam temperature of about 1 kg and 120°C to -30 KPa and 90°C, thus achieving negative pressure steam heating and dehydration in the dehydration tower.

[0039] Example 3

[0040] (1) Open the valve from the steam outlet of the esterification dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank;

[0041] (2) Open the steam inlet valve of the esterification dehydration tower to generate negative pressure at the steam inlet. The steam inlet temperature drops from the original steam temperature of about 1 kg and 120°C to -80 KPa and 60°C, thus achieving negative pressure steam heating and dehydration in the dehydration tower.

[0042] Comparative Example 1

[0043] (1) Open the valve from the steam outlet of the esterification dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank;

[0044] (2) Open the steam inlet valve of the esterification dehydration tower to generate negative pressure at the steam inlet. The steam inlet temperature drops from the original steam temperature of about 1 kg and 120°C to -20 KPa and 93°C, thus achieving negative pressure steam heating and dehydration in the dehydration tower.

[0045] Comparative Example 2

[0046] Low-pressure steam heating method, specific implementation steps: open the steam inlet valve of the esterification dehydration tower heater, the steam used is 1 kg of 120℃ low-pressure (pressure 0.1MPa) steam, and the generated condensate is directly taken away by the condensate tank through a pump.

[0047] The external standard content of sucrose-6-ester in each batch of esterification liquid was tested and the volume of each batch of esterification liquid was measured. The results are shown in Table 1 below.

[0048] Table 1

[0049] Group Sucrose-6-ester external standard content Esterification liquid volume Example 1 175g / L 5400L Example 2 174.5g / L 5370L Example 3 175.5g / L 5420L Comparative Example 1 174g / L 5350L Comparative Example 2 173g / L 5300L

[0050] By testing the external standard content of sucrose-6-ester in each batch of esterified liquid and measuring the volume of each batch of esterified liquid, when the negative pressure steam of the present invention is used, the temperature is low, the reaction is better, and the energy consumption is reduced. Compared with Comparative Example 2, the external standard content of sucrose-6-ester in Example 1 is significantly higher than that in Comparative Example 2, 2 g / L more per batch on average, and the volume of the esterified liquid produced increases, 100 L more per batch on average, that is, the conversion rate of sucrose to produce sucrose-6-ester is improved. The external standard content of sucrose-6-ester in each batch of esterified liquid obtained in Comparative Example 1 and the volume of esterified liquid in each batch are lower than those in Examples 1-3, but higher than those in Comparative Example 2. It can be seen that controlling the negative pressure steam treatment conditions can further improve the conversion rate of sucrose-6-ester.

[0051] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A novel negative pressure steam heating method for a sucralose continuous esterification dehydration tower, characterized in that: The steps include: (1) Open the valve from the steam outlet of the dehydration tower heater to the condensate tank, add water to the buffer tank, and start the circulation pump to form a negative pressure in the condensate tank; (2) Open the steam inlet valve of the dehydration tower to generate negative pressure at the steam inlet of the dehydration tower, reduce the steam inlet temperature, and realize negative pressure steam heating.

2. The method according to claim 1, characterized in that The steam is the steam generated during the process of esterifying sucrose to produce sucrose-6-ester.

3. The method according to claim 1, characterized in that In step (1), the negative pressure is generated by circulating the jet circulation pump and the ejector.

4. The method according to claim 1, characterized in that: The steam outlet of the dehydration tower heater is directly connected to the condensate tank through a pipeline, and the gas phase of the condensate tank is led to the ejector.

5. The method according to claim 1, characterized in that In step (2), the negative pressure generated by the steam inlet is -30 to -80 KPa.

6. The method according to claim 5, characterized in that In step (2), the negative pressure generated by the steam inlet is -45 to -80 KPa.

7. The method according to claim 1, characterized in that In step (2), the steam inlet temperature is reduced to 60-90°C.

8. The method according to claim 7, characterized in that In step (2), the steam inlet temperature is reduced to 60-85°C.

9. The method according to any one of claims 1 to 8, characterized in that: Includes the following equipment: Condensate tanks, ejectors, ejector circulation pumps, buffer tanks and condensate pumps; The gas phase of the condensate tank is connected to the ejector, and the ejector is connected to the outlet of the ejector circulation pump and the upper opening of the buffer tank through a pipeline; the condensate in the condensate tank is pumped away by the condensate pump.

10. The method according to claim 9, characterized in that The condensate tank is connected to the steam outlet of the esterification dehydration tower in the front section.

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