Resourceful treatment method for mother liquor in glycine production process

Abstract

The invention discloses a resourceful treatment method for mother liquor in a glycine production process. The method comprises the following steps: introducing hydrogen chloride gas into mother liquor in a glycine production process to obtain hydrolysate; centrifugally separating the hydrolysate to obtain an ammonium chloride product, and treating the primary centrifugal filtrate in the next process; adding urea into the centrifugal filtrate for reaction, and after the reaction is completed, carrying out centrifugal separation to obtain a solid product urea-formaldehyde resin and a secondary centrifugal filtrate; the secondary centrifugal filtrate is heated, methyl alcohol in the filtrate is removed, methyl chloride is recycled, then heating continues, water in the filtrate is removed, evaporation condensate water is obtained, methyl chloride can be collected to serve as a by-product to be sold, the evaporation condensate water is reused for glycine production, and evaporation residual liquid serves as organic matter fertilizer to be treated. Under the condition of low energy consumption, impurities such as urotropin, ammonium chloride and methanol ammonia in the glycine mother liquor are separated, and resources such as urotropin, ammonium chloride and methanol in the mother liquor are recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of glycine synthesis and environmental protection engineering technology, and relates to a method for resource processing of mother liquor in the process of glycine production. Background Art

[0002] The mainstream process for glycine production is the chloroacetic acid ammonolysis process, in which the glycine synthesis liquid is subjected to methanol precipitation and centrifugal separation to obtain glycine, while the mother liquor separated by centrifugation contains complex components such as ammonium chloride, glycine, urotropine, water, methanol, etc. The mother liquor contains 20-25% ammonium chloride, 2-3% methanol, 3-6% urotropine, and 50-60% water.

[0003] At present, evaporation concentration, membrane treatment and other processes are generally used for processing to obtain ammonium chloride products, which are sold as fertilizers. The product added value is not high, the energy consumption is high, and the valuable substances such as methanol and urotropine in the mother liquor are not effectively utilized, and the resource utilization rate is not high. Therefore, it is of great practical significance to develop a method for resource-based treatment of mother liquor in the production process of glycine to reduce the cost of glycine mother liquor treatment. For example, Chinese patent CN108658374B mentions a method for cleaning glycine production wastewater, which uses two-effect evaporation and flash evaporation for evaporation concentration, and then centrifugal separation to obtain ammonium chloride products. The obtained evaporation condensed water is subjected to biochemical treatment after low-temperature evaporation and membrane treatment. The method evaporation crystallization and membrane system remove impurities such as ammonium chloride in the glycine mother liquor, and the treated wastewater is subjected to back-end biochemical treatment. Chinese patent CN 115215394A records a treatment process for ammonium chloride wastewater in glycine production, which obtains ammonium chloride and organic solution through concentration, solvent extraction, distillation and other processes. However, these methods often require high energy consumption and complex equipment, and cannot achieve the effective recovery and utilization of resources such as methanol and hexamethylenetetramine in wastewater.

[0004] Although the distillation, membrane separation and other technologies described in the above patents have been able to achieve the treatment of the mother liquor in the glycine production process, 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 cannot make resource utilization of high value-added substances such as methanol and hexamethylenetetramine in the glycine mother liquor, and the ammonium chloride obtained by evaporation, concentration and separation has a high impurity content and can only be treated as a fertilizer. Summary of the invention

[0005] The invention provides a method for recycling mother liquor in a glycine production process. The principle of the invention is as follows: hydrogen chloride gas is introduced into the glycine mother liquor. On the one hand, ammonium chloride in the mother liquor is crystallized and precipitated through the common ion effect. On the other hand, the incorporation of hydrogen chloride gas promotes the hydrolysis of urotropine in the mother liquor. Ammonia and formaldehyde obtained by hydrolysis are combined with hydrogen chloride to generate ammonium chloride. By centrifugal separation, a high-purity ammonium chloride product can be obtained, which meets the national standard for industrial ammonium chloride. Urea is then added to the filtrate to polymerize with formaldehyde in the filtrate to generate urea-formaldehyde resin. The urea-formaldehyde resin product is obtained through solid-liquid separation. The secondary centrifugal filtrate is heated, and the residual hydrogen chloride in the filtrate reacts with methanol to generate methyl chloride. The methyl chloride can be recovered and sold as a by-product. Finally, it is evaporated and concentrated to obtain evaporation condensate, which is reused in glycine production, thereby achieving effective treatment of glycine mother liquor and obtaining ammonium chloride, urea-formaldehyde resin, methyl chloride and other products. Compared with the traditional glycine mother liquor treatment process, the economic benefit is outstanding, the treatment is more thorough, the resource utilization rate is higher, and the obtained ammonium chloride is of higher quality, meeting the national standard requirements for industrial ammonium chloride.

[0006] The following is the technical solution of the present invention: A method for recycling mother liquor in a glycine production process, the method comprising the following steps: S1. In the mother liquor of glycine production process, hydrogen chloride gas is introduced. According to the common ion effect, ammonium chloride in the mother liquor is crystallized and precipitated. At the same time, hexamethylenetetramine in the mother liquor is hydrolyzed to generate formaldehyde and ammonia. Ammonia and hydrogen chloride are combined to generate ammonium chloride to obtain a hydrolyzate. S2, centrifuging the hydrolyzate to obtain an ammonium chloride product, and the centrifugal filtrate enters the next step for treatment; S3, adding urea to the centrifugal filtrate for reaction, and after the reaction is completed, a white precipitate is generated, and then centrifugation is performed to obtain a solid product urea-formaldehyde resin and a secondary centrifugal filtrate; S4. The secondary centrifugal filtrate is heated to remove methanol from the filtrate and recover methyl chloride. The temperature is then continued to be raised to remove water from the filtrate to obtain evaporated condensed water. The methyl chloride can be collected and sold as a by-product. The evaporated condensed water is reused in glycine production or enters a biochemical system. The evaporated residual liquid is treated as an organic fertilizer. Preferably, the amount of hydrogen chloride gas introduced in step S1 is controlled to be 10%-20% of the amount of the glycine mother liquor, for example, 10%, 15%, 20%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0007] Preferably, the reaction temperature in step S3 is 40-60°C, and the reaction time is 1-3 hours. For example, the reaction temperature is 40°C, 50°C, 60°C, etc., and the reaction time is 1h, 1.5h, 2h, 2.5h, 3h, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0008] Preferably, in step S3, the amount of urea added is 10%-12% of the mass of the mother liquor.

[0009] Preferably, in step S4, the temperature of the filtrate for removing methanol to generate methyl chloride is controlled at 60-90°C, for example, 60°C, 70°C, 80°C, 90°C, etc. The temperature of the filtrate for removing water is controlled at 95-105°C, for example, 95°C, 100°C, 105°C, etc., but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0010] The beneficial effects of the present invention are: 1. The present invention achieves separation of impurities such as urotropine, ammonium chloride, methanol ammonia, etc. in glycine mother liquor under low energy consumption, recycles resources such as urotropine, ammonium chloride, methanol, etc. in the mother liquor, and converts them into products such as ammonium chloride, urea-formaldehyde resin and methyl chloride, thereby improving the resource utilization rate of the glycine mother liquor; the present invention further evaporates and concentrates the treated filtrate, and the impurity content in the obtained evaporated condensed water is greatly reduced, which can reduce the impact on the biochemical system.

[0011] 2. The technical treatment method adopted by the present invention can realize the effective separation and recycling of nitrogen and carbon resources in glycine mother liquor, and the separation and recycling rate is high. The present invention can realize the effective treatment of glycine mother liquor, and convert the ammonium chloride, urotropine, methanol and other substances in the glycine mother liquor into product urea-formaldehyde resin, ammonium chloride and methyl chloride by introducing hydrogen chloride gas and adding urea, which can be sold as products, realizing the recycling of resources in wastewater, improving the resource utilization rate, and the impurity content of the separated ammonium chloride is greatly reduced, and the main content is higher than that of the traditional process, meeting the national standard requirements for industrial-grade ammonium chloride. DETAILED DESCRIPTION The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0012] The mother liquor in the glycine production process used in the examples of the present invention and the comparative examples has an ammonium chloride content of 23%, a methanol content of 2.5%, a urotropine content of 5%, and the balance being water.

[0013] Example 1 This embodiment provides a method for treating evaporation condensed water in a glycine production process, the method comprising the following steps: S1: the mother liquor from the glycine production process enters a hydrolysis kettle, and hydrogen chloride gas is introduced therein, the amount of which is 10% of the mass of the glycine mother liquor; S2: Then centrifuge to obtain ammonium chloride product, and transfer the centrifugal filtrate into the reactor. S3: Add urea to the reactor, the amount of urea added is 10% of the mother liquor mass, heat to 40°C, react for 1 hour, after the reaction is completed, transfer the reaction liquid to a centrifuge for solid-liquid separation to obtain the product urea-formaldehyde resin. S4. The obtained secondary centrifugal filtrate enters the light removal kettle, is heated to 60°C, and methyl chloride is removed. Then, it is transferred to the evaporation device and heated to 95°C for evaporation to obtain evaporated condensed water.

[0014] Example 2 This embodiment provides a method for treating evaporation condensed water in a glycine production process, the method comprising the following steps: S1: the mother liquor from the glycine production process enters a hydrolysis kettle, into which hydrogen chloride gas is introduced in an amount of 15% of the mass of the glycine mother liquor; S2: Then centrifuge to obtain ammonium chloride product, and transfer the centrifugal filtrate into the reactor. S3: Add urea to the reactor in an amount of 11% of the mother liquor mass, heat to 50°C, and react for 2 hours. After the reaction is completed, transfer the reaction solution to a centrifuge for solid-liquid separation to obtain the product urea-formaldehyde resin. S4. The obtained secondary centrifugal filtrate enters the light removal kettle and is heated to 70°C to remove methyl chloride, and then is transferred to the evaporation device and heated to 100°C for evaporation to obtain evaporated condensed water.

[0015] Example 3 This embodiment provides a method for treating evaporation condensed water in a glycine production process, the method comprising the following steps: S1: the mother liquor from the glycine production process enters a hydrolysis kettle, into which hydrogen chloride gas is introduced, 20% of the mass of the glycine mother liquor; S2: Then centrifuge to obtain ammonium chloride product, and transfer the centrifugal filtrate into the reactor. S3: Add urea to the reactor in an amount of 12% of the mother liquor mass, heat to 60°C, and react for 3 hours. After the reaction is completed, transfer the reaction liquid to a centrifuge for solid-liquid separation to obtain the product urea-formaldehyde resin. S4. The obtained secondary centrifugal filtrate enters the light removal kettle and is heated to 80°C to remove methyl chloride, and then is transferred to the evaporation device and heated to 105°C for evaporation to obtain evaporated condensed water.

[0016] Comparative Example 1 Based on Example 2, in S1: the mother liquor from the glycine production process enters the hydrolysis kettle, hydrochloric acid is added to the hydrolysis kettle, and the amount added is 15% of the mass of the glycine mother liquor, and then centrifugation is performed to obtain an ammonium chloride product, only a small amount of ammonium chloride can be obtained, and most of the ammonium chloride is still dissolved in the centrifugal filtrate, and the centrifugal filtrate is transferred to the reactor. Others are the same as in Example 2.

[0017] Comparative Example 2 Based on Example 2, S3: thiourea is added to the reactor, and the rest is the same as Example 2. After the reaction in S3 is completed, the reaction liquid is transferred to a centrifuge for solid-liquid separation, which makes crystallization separation difficult and introduces sulfur into the system, which is not conducive to subsequent treatment. Comparative Example 3 Based on Example 2, S1: the mother liquor from the glycine production process is directly evaporated and concentrated, and the rest is the same as Example 2. S3: after the reaction is completed, no precipitate is generated. S4: after the reaction is completed, no methyl chloride is generated. Table 1

[0018] As can be seen from the data in Table 1, Example 1-3 adopts the method described in the present invention, and the glycine mother liquor can be effectively treated, and the impurities such as ammonium chloride, urotropine, methanol, etc. therein are converted into subchlorinated ammonium, methyl urea and methyl chloride products, and the nitrogen resources and carbon resources in the wastewater are recycled and utilized, and high-quality products are obtained, which can be sold externally, thereby achieving a thorough treatment of the glycine mother liquor, improving the resource utilization rate, and having a great driving effect on improving the clean production and resource utilization level of the glycine industry. By comparing Example 2 with Comparative Example 1, it can be seen that adding hydrochloric acid solution will introduce a large amount of water, greatly improving the processing capacity of the mother liquor, and it is impossible to completely crystallize the ammonium chloride in the mother liquor, causing the mother liquor to be impure and not thoroughly removed, affecting the treatment effect of the subsequent steps. By comparing Example 2 with Comparative Example 2, it can be seen that thiourea is added to the reactor, and crystallization and separation are difficult, and sulfur element is introduced into the system, which is not conducive to subsequent treatment. By comparing Example 2 with Comparative Example 3, it can be seen that the mother liquor is directly evaporated and concentrated, and ammonium chloride is obtained by centrifugation, and then urea is added to react, no precipitate is generated, and no chloromethane is generated when the temperature is raised to 80° C., and impurities such as hexamethylenetetramine and methanol still remain in the mother liquor. The content of ammonium chloride obtained is low, which does not meet the standard requirements of industrial ammonium chloride.

[0019] The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

Claims

1. A method for recycling mother liquor in a glycine production process, characterized in that: The method comprises the following steps: S1. Passing hydrogen chloride gas into the mother liquor in the glycine production process to obtain a hydrolyzate; S2, centrifuging the hydrolyzate to obtain an ammonium chloride product, and the centrifugal filtrate enters the next step for treatment; S3, adding urea to the centrifugal filtrate for reaction, and after the reaction is completed, centrifugation is then performed to obtain a solid product urea-formaldehyde resin and a secondary centrifugal filtrate; S4. The secondary centrifugal filtrate is heated to remove methanol from the filtrate and recover methyl chloride. The temperature is then continued to be raised to remove water from the filtrate to obtain evaporated condensed water. The methyl chloride is collected as a by-product, the evaporated condensed water is reused in glycine production, and the evaporated residual liquid is treated as an organic fertilizer.

2. The method for recycling mother liquor in the production process of glycine according to claim 1, characterized in that: In the step S1, the amount of hydrogen chloride gas introduced is controlled to be 10%-20% of the mass of the parent glycine.

3. The method for recycling mother liquor in the production process of glycine according to claim 1, characterized in that: In the step S3, the reaction temperature is 40-60° C. and the reaction time is 1-3 hours.

4. The method for recycling mother liquor in the production process of glycine according to claim 1, characterized in that: In step S3, the amount of urea added is 10%-12% of the mass of the mother liquor.

5. The method for recycling mother liquor in the production process of glycine according to claim 1, characterized in that: In step S4, the temperature of the filtrate for removing methanol to generate methyl chloride is controlled at 60-90°C, and the temperature of the filtrate for removing water is controlled at 95-105°C.

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