Method for recycling urotropine in glycine synthetic liquid by using supercritical extraction technology

Abstract

The invention provides a method for recovering urotropin from glycine synthetic liquid by using a supercritical extraction technology, which is characterized in that after carbon dioxide is pumped into the glycine synthetic liquid, supercritical carbon dioxide extraction is performed under a high-pressure condition, so that glycine is separated from the glycine synthetic liquid, and meanwhile, urotropin is recovered. According to the method, the glycine synthesis liquid produced by a chloroacetic acid ammonolysis method is treated by adopting a supercritical CO2 extraction technology, the urotropin catalyst in the glycine synthesis liquid can be efficiently recovered, the recovery rate is high, the loss of the urotropin catalyst is reduced, and the resource utilization rate is improved.

Description

Technical Field

[0001] The technical solution mainly relates to the technical field of supercritical fluid extraction, and specifically to a method for recovering urotropine from glycine synthesis liquid in the technical field of glycine synthesis. Background Art

[0002] Glycine is an important organic chemical raw material, widely used in medicine, pesticides, food additives and other fields. At present, the main production method of glycine is the chloroacetic acid ammonolysis method, which uses chloroacetic acid and ammonia as raw materials, and urotropine aqueous solution as catalyst, and reacts under high temperature and high pressure conditions to produce glycine and by-product ammonium chloride. However, the urotropine catalyst will partially decompose in the subsequent recovery process due to the acidity and high temperature state of the solution system, generating ammonia and carbon monoxide, which not only reduces the utilization rate of the urotropine catalyst, but also makes it difficult to recycle the urotropine catalyst. As a new separation technology, supercritical fluid extraction technology has the advantages of high efficiency, environmental protection, and no solvent residue. It has been widely used in chemical, pharmaceutical, environmental protection and other fields. Among them, CO2 is widely used as a supercritical extraction fluid because of its non-toxic, odorless, moderate critical temperature (31.1℃), moderate critical pressure (7.38MPa), cheap and easy to obtain.

[0003] Solutions of the prior art: The existing recovery scheme of urotropine catalyst is mainly to recover the urotropine catalyst in the glycine synthesis solution by physical or chemical methods, and then recycle it. For example, Chinese patent CN102807497A mentions a method for recovering urotropine by evaporating and concentrating the filtrate of glycine and ammonium chloride crystals, in which the filtrate of glycine and ammonium chloride crystals is evaporated and concentrated, and then a filter aid is added for hot filtration to obtain urotropine containing the filter aid, which is configured into a 14%-35% urotropine aqueous solution, the filter aid in the solution is recovered, and activated carbon is used for decolorization. At this time, the urotropine solution can be returned to the glycine production for recycling. Chinese patent CN101648114A describes a method for separating and recovering urotropine and glycine in glycine synthesis liquid using nanofiltration membrane. The cut-off molecular weight of the nanofiltration membrane used in this method is 50-300 Daltons. Under the conditions of operating pressure of 1.8-4.0Mpa and operating temperature of 20-50°C, most of the ammonium chloride passes through the nanofiltration membrane and enters the permeate through the nanofiltration membrane. The urotropine and most of the glycine are retained in the retained liquid. The urotropine and glycine in the retained liquid can be recycled. Chinese patent CN116022982B describes a method for recovering urotropine by adsorbing modified diatomaceous earth. This method first distills the wastewater produced by glycine, mixes the obtained distillation synthesis liquid with modified diatomaceous earth, and then filters after sufficient mixing to obtain filtrate and filter residue. The filter residue contains the recovered urotropine, and the filtrate can recover the ammonium chloride after double-effect evaporation. The distillation, nanofiltration, adsorption and other methods recorded in the above patents can all recover the urotropine catalyst. However, these methods often require high energy consumption and complex equipment, and may cause certain losses to the hexamethylenetetramine catalyst.

[0004] Problems with the prior art: Although the distillation, nanofiltration, adsorption and other technologies described in the above patents have been able to achieve the recovery and recycling of the urotropine catalyst, there are still some problems and shortcomings. First, these methods often require high energy consumption and complex equipment, which is not conducive to energy conservation and emission reduction. Secondly, the existing recovery method may cause certain losses to the urotropine catalyst, affecting its catalytic activity and service life. In addition, the existing recovery method may introduce new impurities, thereby affecting the purity of glycine. Finally, the existing recovery method is complicated to operate and is not conducive to large-scale industrial production. Summary of the invention

[0005] Compared with the prior art, the technical solution mainly solves the following problems: 1. How to achieve efficient recovery of hexamethylenetetramine catalyst with low energy consumption; 2. How to avoid loss of hexamethylenetetramine catalyst during the recovery process to ensure its catalytic activity and service life; 3. How to prevent the introduction of new impurities during the recovery process to affect the purity of the target product glycine; 4. How to simplify the recovery operation to adapt to large-scale industrial production technology problems.

[0006] Technical Solutions In order to achieve the above-mentioned purpose, the technical scheme mainly adopts the following technical means: 1. Supercritical CO2 extraction technology is used to treat the glycine synthesis liquid produced by the chloroacetic acid ammonolysis method. Supercritical CO2 has low viscosity, high diffusion coefficient and adjustable solubility, which can effectively extract the urotropine catalyst from the glycine synthesis liquid, while avoiding the environmental pollution and safety problems that other traditional solvents may bring. 2. Optimize the extraction conditions, such as extraction temperature, extraction pressure, CO2 flow rate, extraction time, glycine synthesis liquid and CO2 mass ratio, etc., to improve the recovery efficiency and purity of the urotropine catalyst. At the same time, through experimental optimization, determine the optimal extraction conditions to achieve efficient recovery and recycling of the urotropine catalyst under low energy consumption. No other impurities are introduced during the recovery process to ensure that the urotropine catalyst is minimized during the recovery process, and its catalytic activity and service life are maintained. 3. Develop a highly automated recovery operation process to adapt to large-scale industrial production. The process should be simple and easy to implement. The operator only needs to perform simple operations to achieve efficient recovery and recycling of the hexamethylenetetramine catalyst, which greatly improves production efficiency and reduces production costs.

[0007] The principle of the present invention is: supercritical CO2 refers to CO2 that exceeds the critical point (31.26°C and 8.025Mpa), which has the characteristics of both gaseous and liquid CO2 and exhibits unique solubility properties. In supercritical CO2, the solubility of the solute increases with the increase of the density of the CO2 fluid. By utilizing this characteristic, at the beginning of extraction, under specific temperature and pressure conditions, the CO2 fluid extracts the target substance from the glycine synthetic liquid. After the extraction is completed, by increasing the temperature of the fluid or reducing the pressure of the fluid, the density of the fluid decreases, and the solute will precipitate from the CO2 fluid, and at this time, the purpose of selective extraction and separation of the extraction product can be achieved.

[0008] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0009] After carbon dioxide is pumped into the glycine synthetic liquid, supercritical carbon dioxide extraction is performed under high pressure conditions to separate glycine from the glycine synthetic liquid and recover hexamethylenetetramine at the same time.

[0010] Preferably, the supercritical fluid must be CO2 with a purity greater than 99.9%, purchased from Hubei Heyuan Gas Company.

[0011] Preferably, the glycine synthetic liquid produced by the chloroacetic acid ammonolysis method mainly comprises glycine, ammonium chloride, urotropine and water, wherein the glycine content is 23-30%, the ammonium chloride content is 16-25%, and the urotropine content is 2-6%.

[0012] Preferably, the extraction temperature is 80-120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, etc., but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. Preferably, the glycine synthesis solution is heated to 90-120°C before extraction.

[0013] Preferably, the extraction pressure is 10-45 MPa, for example, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, etc., but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. Preferably, the extraction pressure is 20-40 MPa, and the extraction time is 30-120 min.

[0014] The extraction capacity of supercritical CO2 is mainly affected by the density of the fluid. Under the conditions of low temperature and high pressure, the density is relatively high. At this time, the solubility of the supercritical CO2 fluid is relatively strong. In the subsequent separation stage, the density of the supercritical CO2 fluid needs to be reduced by reducing the pressure, thereby reducing the solubility and achieving the separation of the supercritical CO2 fluid and the extracted product. In addition, this temperature and pressure condition is related to the physical and chemical properties of CO2 and the crystallization temperature of the glycine synthetic liquid. The critical temperature of CO2 gas is 31.1°C and the critical pressure is 7.38Mpa. The glycine synthetic liquid will solidify into a solid when it is lower than 78°C, which will cause the extraction test to be unable to be carried out. Preferably, the CO2 flow rate is 20-45L / h, for example, 20L / h, 25L / h, 30L / h, 35L / h, 40L / h, 45L / h, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, the extraction time is 30-120 min, for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the mass ratio of glycine synthesis liquid to CO2 in the extraction conditions is 5:1-5:2, for example, 5:1, 5:1.2, 5:1.5, 5:1.8, 5:2, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Technical Effects Compared with the existing technology, the beneficial effects of the technical solution are as follows: 1. Efficient recovery: The present invention adopts supercritical CO2 extraction technology to treat the glycine synthesis liquid produced by the chloroacetic acid ammonolysis method, which can efficiently recover the urotropine catalyst in the glycine synthesis liquid, with a high recovery rate, reducing the loss of the urotropine catalyst and improving the resource utilization rate. 2. Environmental protection and pollution-free: Supercritical CO2 extraction technology is a green and environmentally friendly separation technology, with no solvent residue, no pollution to the environment, and meets the current environmental protection requirements. 3. Energy saving: Compared with the existing physical or chemical recovery methods, supercritical CO2 extraction technology has lower energy consumption, is conducive to energy conservation and emission reduction, and is in line with the current green development concept. 4. Simplified operation: The recovery method of the present invention is simple and easy to implement, avoiding the complicated operation steps in the existing recovery method, reducing the production cost, and is conducive to large-scale industrial production. 5. Improve product quality: Since the recovery method of the present invention does not introduce new impurities, the recovered urotropine catalyst has high purity, good activity, and long service life, which is conducive to improving the product quality of glycine. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a process flow chart for recovering urotropine from glycine synthesis solution by supercritical extraction. DETAILED DESCRIPTION

[0019] Embodiment 1: The present embodiment provides a method for recovering urotropine from glycine synthetic liquid by supercritical extraction, the method comprising the following steps: the glycine synthetic liquid produced by the glycine workshop of Hubei Taisheng Company is synthesized by chloroacetic acid ammonolysis, wherein the glycine content is 29.2%, the ammonium chloride content is 20.09%, and the mass fraction of the catalyst urotropine is 5.37%. While hot, 500g of the above-mentioned glycine synthetic liquid is added to an extraction kettle heated to 90°C in advance, 200g of CO2 gas with a purity greater than 99.99% is added to the extraction kettle, so that the mass ratio of glycine synthetic liquid to CO2 is 5:2, and then the supercritical extraction device is turned on to raise the pressure of the extraction kettle to 40Mpa, and the CO2 flow rate is 20-26.7L / h. Under this condition, the extraction is continued for 90min, and after the extraction is completed, the extraction product is collected in the separation kettle.

[0020] Example 2 This embodiment provides a method for recovering urotropine in glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the extraction temperature is 90° C. and the extraction time is 45 min.

[0021] Example 3 This embodiment provides a method for recovering urotropine in glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the extraction temperature is 90° C. and the extraction time is 120 min.

[0022] Example 4 This embodiment provides a method for recovering urotropine in glycine synthesis liquid by supercritical extraction. The method is similar to the method in Example 1, except that the extraction pressure is 20 MPa and the CO2 flow rate is 30.6-34.0 L / h.

[0023] Example 5 This embodiment provides a method for recovering urotropine in glycine synthesis liquid by supercritical extraction. The method is similar to the method in Example 1, except that the extraction pressure is 30 MPa and the CO2 flow rate is 26.3-30.2 L / h.

[0024] Example 6 This embodiment provides a method for recovering urotropine in glycine synthetic liquid by supercritical extraction. The method refers to the method in Example 1, except that 150 g of CO2 gas with a purity greater than 99.99% is added to the extraction kettle so that the mass ratio of glycine synthetic liquid to CO2 is 5:1.5.

[0025] Comparative Example 1 This embodiment provides a method for recovering urotropine in glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the extraction temperature is 75°C.

[0026] Comparative Example 2 This embodiment provides a method for recovering urotropine in glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the extraction temperature is 130°C.

[0027] Comparative Example 3 This embodiment provides a method for recovering urotropine in glycine synthesis liquid by supercritical extraction. The method is similar to the method in Example 1, except that the extraction pressure is 8 MPa and the CO2 flow rate is 39.7-44.0 L / h.

[0028] Comparative Example 4 This embodiment provides a method for recovering urotropine in glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the extraction time is 20 minutes.

[0029] Comparative Example 5 This embodiment provides a method for recovering urotropine in glycine synthetic liquid by supercritical extraction. The method refers to the method in Example 1, except that 80 g of CO2 gas with a purity greater than 99.99% is added to the extraction kettle so that the mass ratio of glycine synthetic liquid to CO2 is 5:0.8.

[0030] Comparative Example 6 This embodiment provides a method for recovering urotropine in glycine synthesis liquid by supercritical extraction. The method is similar to the method in Example 1, except that the purity of CO2 gas added to the extraction kettle is 99.0%.

[0031] Example 7 This embodiment provides a method for recovering urotropine in a glycine synthesis solution by supercritical extraction. The method is similar to the method in Example 1, except that the composition of the glycine synthesis solution is changed, the glycine content is 17.51%, the ammonium chloride content is 27.28%, and the catalyst urotropine content is 2.93%.

[0032] The mass of the extraction products obtained in the embodiments and comparative examples was accurately weighed, and the content of urotropine therein was determined, and the efficiency of urotropine recovery was calculated. The calculation results are shown in Table 1, wherein the calculation formula is shown in Formula (1):

[0033] Table 1 Test data table

[0034] As can be seen from Table 1, Examples 1-6 adopt the method of the present invention, and after supercritical CO2 extraction treatment, the recovery rate of the catalyst urotropine in the glycine synthesis liquid can reach up to 78.32%, indicating that supercritical CO2 extraction can realize the urotropine recovery process; and by comparing Examples 1, 2, 3 and Comparative Example 4, it is found that the extraction time has a greater impact on the recovery rate of urotropine. Too short extraction time will lead to incomplete extraction and reduced quality of the extracted product. Too long extraction time will lead to increased impurities in the extracted product and decreased content of urotropine; by comparing Examples 1, 4, 5 and Comparative Example 3, it is found that too low extraction pressure will affect the extraction capacity of supercritical CO2, resulting in a reduction in the amount of the extracted product. Increasing the pressure within the scope of the claim is beneficial to improving the extraction efficiency; by comparing Example 1 and Comparative Example 1 2, it is found that too low extraction temperature will cause the glycine synthetic liquid to solidify, and the quality of the obtained extraction product will be reduced. If the extraction temperature is too high, the supercritical fluid extraction capacity will decrease, and the urotropine content in the product will decrease. Moreover, higher temperature will increase energy consumption and have no practical value. By comparing Examples 1, 6 and Comparative Example 5, it is found that the reduction in the amount of CO2 will lead to a reduction in the quality of the extraction product, and at the same time, the urotropine content in the extraction product will decrease. By comparing Example 1 and Comparative Example 6, it is found that the reduction in the purity of CO2 gas will lead to a reduction in the quality of the extraction product, and at the same time, the urotropine content in the extraction product will decrease. By comparing Example 1 and Example 7, it is found that when the composition of the glycine synthetic liquid changes and the urotropine content decreases, the urotropine content in the extraction product will decrease, but the recovery efficiency will not decrease significantly.

[0035] It can be seen from the above embodiments and comparative examples that the method of the present invention utilizes the low viscosity, high diffusion coefficient, adjustable solubility and recyclable excellent properties of supercritical CO2 to recover hexamethylenetetramine in glycine synthesis liquid in an environmentally friendly manner. The entire treatment process is simple to operate, avoiding the introduction of other impurities during the extraction process to cause sample contamination. At the same time, there is no waste gas or wastewater discharge, which is conducive to industrial application.

[0036] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the operation of the present invention, addition of auxiliary operations, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering urotropine from glycine synthesis solution using supercritical extraction technology, characterized in that: After carbon dioxide is pumped into the glycine synthetic liquid, supercritical carbon dioxide extraction is performed under high pressure conditions to separate glycine from the glycine synthetic liquid and recover hexamethylenetetramine at the same time.

2. The method for recovering urotropine from glycine synthesis solution by supercritical extraction technology according to claim 1, characterized in that: The glycine content of the glycine synthetic liquid is 23-30%, the ammonium chloride content is 16-25%, and the hexamethylenetetramine content is 2-6%.

3. The method for recovering hexamethylenetetramine from glycine synthesis solution by supercritical extraction technology according to claim 2, characterized in that: Before extraction, the glycine synthesis solution is heated to 80-120°C and subjected to supercritical carbon dioxide extraction at this temperature.

4. The method for recovering hexamethylenetetramine from glycine synthesis solution by supercritical extraction technology according to claim 2, characterized in that: The glycine synthesis solution is heated to 90-120°C before extraction.

5. The method for recovering urotropine from glycine synthesis solution by supercritical extraction technology according to claim 1, characterized in that: The mass ratio of glycine synthesis solution to CO2 in the extraction conditions is 5:1-5:

2.

6. The method for recovering urotropine from glycine synthesis solution by supercritical extraction technology according to claim 1, characterized in that: The extraction pressure is 10-45Mpa, and the extraction time is 30-120min.

7. The method for recovering hexamethylenetetramine from glycine synthesis solution by supercritical extraction technology according to claim 6, characterized in that: The extraction pressure is 20-40Mpa, and the extraction time is 45-120min.

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