Process for preparing undecylenic acid through microwave heating enzyme hydrolysis under negative pressure

Abstract

The invention discloses a process for preparing undecylenic acid by microwave heating and enzyme hydrolysis under negative pressure, namely water and methyl undecylenate are subjected to enzyme catalytic hydrolysis under the conditions of microwave heating and negative pressure to generate undecylenic acid and methanol. According to the process, bio-enzyme is used as a catalyst, the process of a traditional saponification and acidification process is shortened, the reaction rate and selectivity are improved, and meanwhile, mild reaction conditions are more friendly to equipment and the environment; the removal of methanol is accelerated under a negative pressure condition, and the reaction rate and the conversion rate of hydrolysis are effectively improved; the reaction rate and the conversion rate are improved by utilizing the thermal effect and the non-thermal effect of microwave heating, the reaction temperature is only 40 DEG C, the reaction time is 2 hours, the conversion rate reaches 95% or above, and meanwhile, the energy consumption in the process is relatively low. A new process is provided for preparing undecylenic acid, the reaction rate and the conversion rate are effectively increased, and the purposes of energy conservation, consumption reduction and environmental protection in the technological process are achieved.

Description

Technical Field

[0001] The invention relates to the field of oil and fat chemical industry, and in particular to a process for preparing undecylenic acid by microwave heating and enzyme hydrolysis under negative pressure. Background Art

[0002] Undecylenic acid is an important chemical intermediate that can be used to prepare nylon 11, medicines, spices, etc. It can be prepared by cracking castor oil or ricinoleic acid, or by saponification and acidification of undecylenic acid methyl ester. The process of preparing undecylenic acid by direct cracking of castor oil or ricinoleic acid as raw materials has technical problems such as high cracking energy consumption, many by-products, easy coking and low yield. The preparation of undecylenic acid from undecylenic acid methyl ester after cracking ricinoleic acid methyl ester generally requires saponification and acidification process (Zhao Xuejing. Chemical Principle and Preparation of Undecylenic Acid, a Castor Oil Derivative Product [J]. Modern Food, 2015 (22): 38-43.), which requires a large amount of alkali solution and acid solution, which will cause corrosion to equipment and also bring about the problem of waste salt and wastewater treatment.

[0003] Undecylenic acid can also be prepared by hydrolysis of undecylenic acid methyl ester. The process described in Chinese patent CN 116063171 A uses pressurized high temperature to produce undecylenic acid. Adding a catalyst can accelerate the chemical reaction rate, but the temperature is high, the energy consumption is large, and there is also a problem of catalyst reprocessing. Chinese patent CN 115784866 A uses a bubble tower as a reactor, which can reduce the energy loss caused by mechanical stirring, and mixes and exchanges heat through the contact of upper and lower liquids, saving energy, but pressurization and high temperature conditions still require large energy consumption.

[0004] In recent years, biological enzymes have been widely used in oil hydrolysis due to their mild reaction conditions and fast reaction rates. Chinese patents CN 101294170A, CN 101100628 A and CN 102417916 B use lipase to hydrolyze oils, which accelerates the reaction process and improves the hydrolysis rate under mild conditions, and also achieves enzyme reuse. However, since the hydrolysis reaction is generally a reversible reaction, the enzymatic hydrolysis process still has the problems of low conversion rate and insufficient reaction rate. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a process for producing fatty acids by hydrolyzing fatty acid methyl esters by microwave heating under negative pressure to enhance the reaction and using biological enzymes as catalysts, which is a new process with low energy consumption, high yield and low pollution. The present invention relates to a new process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure.

[0006] The technical solution adopted by the present invention is as follows: A process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure, comprising the following steps: Step 1: adding water, methyl undecylenate and biological enzyme into a microwave hydrolysis reactor and continuously stirring; the biological enzyme is lipase, which refers to an enzyme that can catalyze the hydrolysis of ester bonds of oils and fats, and is in the form of solid or liquid enzyme; Step 2: After evacuating the microwave hydrolysis reactor to place the reaction system under negative pressure, microwave heating is started, and the reaction system is placed at a desired reaction temperature by adjusting the microwave heating power and the evacuation pressure, and the temperature is maintained constant to allow the hydrolysis reaction to proceed under microwave radiation and stirring; Step 3: During the reaction, water and the generated methanol vapor are continuously evaporated and condensed and collected, and water is added to the reaction system in a timely manner to maintain the liquid level of the reaction system at the initial level; Step 4: After the reaction is completed, the biological enzyme is separated and recovered from the reaction solution to obtain a feed solution containing the undecylenic acid product, and the separated biological enzyme is repeatedly used for the next batch of reactions.

[0007] Further, the microwave heating power is 5-10 kW / kg methyl undecylenate. That is, the microwave heating power is determined according to the mass of methyl undecylenate, for example, when the amount of methyl undecylenate used in the hydrolysis reaction is 1 kg, the microwave heating power is 5-10 kW, if the amount of methyl undecylenate used is 2 kg, the microwave heating power is 10-20 kW, and so on.

[0008] Furthermore, the negative pressure condition in the reaction system is an absolute pressure of 5-20 kPa.

[0009] Furthermore, in step 1, the mass ratio of the reaction raw materials water and methyl undecylenate is 3:1-6:1.

[0010] Furthermore, in the hydrolysis reaction of step 2, the reaction temperature is 40-60°C.

[0011] Furthermore, the reaction time of the hydrolysis reaction is 1-3 hours.

[0012] Furthermore, the stirring speed of the hydrolysis reaction in step 2 is 400-700 rpm.

[0013] Furthermore, the mass concentration of the biological enzyme in the reaction system is 0.5-20%.

[0014] Furthermore, the biological enzyme is immobilized lipase Novozym 435, and the mass concentration of the biological enzyme in the reaction system is 0.5-3%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Using biological enzymes as catalysts greatly improves the reaction rate and selectivity of the hydrolysis of methyl undecenoate, and the mild reaction conditions are more friendly to the equipment and environment. Under negative pressure conditions, the removal of methanol is accelerated, which effectively improves the reaction rate and conversion rate of the hydrolysis. The thermal and non-thermal effects of microwave heating are used to increase the reaction rate. At a relatively low temperature (reaction temperature of 40°C) and a reaction time of 2 hours, a conversion rate of more than 96% can be achieved, reducing the energy consumption of the process. The process has mild reaction conditions and a simple process flow, and achieves the goals of high reaction rate, high conversion rate, and high yield of the hydrolysis of methyl undecenoate under low energy consumption and environmentally friendly conditions. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0017] Immobilized lipase Novozym 435 was obtained from Novozymes of Denmark.

[0018] Example 1: Immobilized lipase Novozym 435 was added to a hydrolysis reactor, and water and methyl undecylenate were added to the hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed solution was 1%. The mass of methyl undecylenate in the hydrolysis reactor was 30 g, and stirring was started at a speed of 500 rpm. At the same time, water bath heating was turned on, and the water bath temperature was set to 40°C. The reaction temperature was stabilized at 40°C and the reaction was started. After 4 hours of reaction, the conversion rate of methyl undecylenate was 54.93%, and the yield of undecylenic acid was 54.93%.

[0019] Example 2: Immobilized lipase Novozym 435 was added to a microwave hydrolysis reactor, and water and methyl undecenoate were added to the microwave hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed solution was 1%. The mass of methyl undecenoate in the microwave hydrolysis reactor was 30 g, and stirring was started at a speed of 500 rpm. At the same time, microwave heating was turned on, and the microwave power was 189 W. The reaction solution was heated at a microwave heating power of 6.3 kW / kg methyl undecenoate, and the temperature was maintained at 40°C to start the reaction. After 4 hours of reaction, the conversion rate of methyl undecenoate was 59.54%, and the yield of undecenoic acid was 59.54%.

[0020] Comparing Example 1 and Example 2, under the same conditions of hydrolysis raw material ratio, reaction temperature, stirring speed, and enzyme dosage, microwave heating has high heating efficiency and accelerates the reaction rate compared with water bath heating, and the yield of undecylenic acid is increased by 4.61%. The possible reason is that the non-thermal effect of microwave heating changes the reaction path and reduces the activation energy of the reaction.

[0021] Example 3: Immobilized lipase Novozym 435 was added to the hydrolysis reactor, and water and methyl undecenoate were added to the hydrolysis reactor in a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, water bath heating was turned on, the water bath temperature was set to 41 ° C, and vacuum was simultaneously drawn, the reaction liquid was heated to boiling, and the temperature was maintained at 40 ° C. At this time, the pressure in the hydrolysis reactor was maintained at 10 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 4 hours of reaction, the conversion rate of methyl undecenoate was 83.88%, and the yield of undecenoic acid was 83.88%.

[0022] Comparing Example 1 and Example 3, when other conditions remain unchanged, methanol can be removed in time after negative pressure is applied, which is conducive to the forward reaction, the hydrolysis reaction rate is accelerated, and the yield of undecylenic acid is increased by 28.95%, indicating that negative pressure conditions can effectively improve the conversion rate of the reaction.

[0023] Example 4: Immobilized lipase Novozym 435 was added to the hydrolysis reactor, and water and methyl undecenoate were added to the hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, water bath heating was turned on, the water bath temperature was set to 50 ° C, and vacuum was simultaneously drawn, the reaction liquid was heated to boiling, and the temperature was maintained at 40 ° C. At this time, the pressure in the hydrolysis reactor was maintained at 5 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 4 hours of reaction, the conversion rate of methyl undecenoate was 93.75%, and the yield of undecenoic acid was 93.75%.

[0024] Example 5: Immobilized lipase Novozym 435 was added to the hydrolysis reactor, and water and methyl undecenoate were added to the hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, water bath heating was turned on, the water bath temperature was set to 55 ° C, and vacuum was simultaneously drawn, the reaction liquid was heated to boiling, and the temperature was maintained at 40 ° C. At this time, the pressure in the hydrolysis reactor was maintained at 2.5 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 4 hours of reaction, the conversion rate of methyl undecenoate was 95.39%, and the yield of undecenoic acid was 95.39%.

[0025] Example 6: Immobilized lipase Novozym 435 was added to the hydrolysis reactor, and water and methyl undecenoate were added to the hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, water bath heating was turned on, the water bath temperature was set to 60 ° C, and vacuum was simultaneously drawn, the reaction liquid was heated to boiling, and the temperature was maintained at 40 ° C. At this time, the pressure in the hydrolysis reactor was maintained at 1.5 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 4 hours of reaction, the conversion rate of methyl undecenoate was 95.48%, and the yield of undecenoic acid was 95.48%.

[0026] Comparing Example 3, Example 4, Example 5 and Example 6, at the same reaction temperature, by increasing the temperature of the water bath heating and reducing the pressure in the reaction system, the evaporation amount of water and the removal amount of methanol were increased, the mass transfer process was accelerated, the hydrolysis was carried out in the forward direction, the reaction rate was accelerated, and the yield of undecylenic acid was increased.

[0027] Example 7: Immobilized lipase Novozym 435 was added to a microwave hydrolysis reactor, and water and methyl undecenoate were added to the microwave hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, and microwave heating was turned on. The microwave power was 189 W, and heating was started at a power of 6.3 kW / kg methyl undecenoate. At the same time, vacuum was drawn, and the reaction liquid was heated to boiling, and the temperature was stabilized at 40 ° C. At this time, the pressure in the microwave hydrolysis reactor was maintained at 10 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 100 min of reaction, the conversion rate of methyl undecenoate was 94.97%, and the yield of undecenoic acid was 94.97%.

[0028] Comparing Example 3 and Example 7, under the same negative pressure conditions, the reaction rate of microwave heating is fast and the conversion rate is high. Microwave heating reaches a conversion rate of 94.97% within 100 minutes, which is 31.49% higher than the yield of undecylenic acid under water bath heating conditions. The yield results of undecylenic acid under different reaction times of Examples 1-5 and Example 7 are summarized in Table 1.

[0029] Table 1 Yield of undecylenic acid in different embodiments at different reaction times .

[0030] The reaction conditions of Examples 1-7 are compared, and the conversion rates at different times and the total mass of evaporated water and methanol vapor are summarized in Table 2.

[0031] Table 2 Comparison of hydrolysis conditions and conversion rates of undecylenic acid methyl ester .

[0032] In addition, comparing Example 5 with Example 7, from the perspective of the amount of steam of water and methanol evaporated, microwave heating consumes the least energy, and the evaporation rate of water and methanol is only about 64.7 g / h. This indicates that compared with water bath heating, water bath heating requires greater heating power and lower pressure to achieve the same high conversion rate and high yield.

[0033] Example 8: Immobilized lipase Novozym 435 was added to a microwave hydrolysis reactor, and water and methyl undecenoate were added to the microwave hydrolysis reactor at a mass ratio of 4:1, and the mass concentration of the enzyme in the feed liquid was 1%. The mass of methyl undecenoate in the hydrolysis reactor was 30 g, stirring was started at a speed of 500 rpm, and microwave heating was turned on. The microwave power was 240 W, and heating was started at a power of 8 kW / kg methyl undecenoate. At the same time, vacuum was drawn, and the reaction liquid was heated to boiling, and the temperature was stabilized at 40 ° C. At this time, the pressure in the microwave hydrolysis reactor was maintained at 9 kPa, and the reaction was started. Water was replenished in time during the reaction to ensure that the reaction liquid level remained at the starting liquid level. After 1.7 hours of reaction, the conversion rate of methyl undecenoate was 99.02%, and the yield of undecenoic acid was 99.02%.

[0034] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. A process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure, characterized in that The following steps are involved: Step 1: adding water, methyl undecylenate and biological enzyme into a microwave hydrolysis reactor and continuously stirring; the biological enzyme is lipase, which refers to an enzyme that can catalyze the hydrolysis of ester bonds of oils and fats, and is in the form of solid or liquid enzyme; Step 2: After evacuating the microwave hydrolysis reactor to place the reaction system under negative pressure, microwave heating is started, and the reaction system is placed at a desired reaction temperature by adjusting the microwave heating power and the evacuation pressure, and the temperature is maintained constant to allow the hydrolysis reaction to proceed under microwave radiation and stirring; Step 3: During the reaction, water and the generated methanol vapor are continuously evaporated and condensed and collected, and water is added to the reaction system in a timely manner to maintain the liquid level of the reaction system at the initial level; Step 4: After the reaction is completed, the biological enzyme is separated and recovered from the reaction solution to obtain a feed solution containing the undecylenic acid product, and the separated biological enzyme is repeatedly used for the next batch of reactions.

2. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The microwave heating power is 5-10 kW / kg methyl undecylenate.

3. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The negative pressure condition in the reaction system is an absolute pressure of 5-20 kPa.

4. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that In step 1, the mass ratio of the reaction raw materials water and methyl undecylenate is 3:1-6:

1.

5. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that In the hydrolysis reaction of step 2, the reaction temperature is 40-60°C.

6. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The stirring speed of the hydrolysis reaction in step 2 is 400-700 rpm.

7. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The mass concentration of the biological enzyme in the reaction system is 0.5-20%.

8. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The reaction time of the hydrolysis reaction is 1-3 hours.

9. The process for preparing undecylenic acid by microwave heating enzymatic hydrolysis under negative pressure as claimed in claim 1, characterized in that The biological enzyme is immobilized lipase Novozym 435, and the mass concentration of the biological enzyme in the reaction system is 0.5-3%.