A method for recovering formaldehyde from the filtrate of deglycine

Abstract

The present invention relates to the technical field of preparing glycine by chloroacetic acid method, and in particular to a method for recovering formaldehyde from the filtrate of deglycine, the method comprising the following steps: (1) adding a strong acid to the filtrate of deglycine, heating and refluxing to obtain ammonia and formaldehyde gas; (2) mixing the formaldehyde gas with an absorbent to obtain a formaldehyde solution or a subsequent reaction product. The present invention does not require special equipment and has the advantages of simple process, low investment and easy operation.

Description

Technical Field

[0001] The invention relates to the technical field of preparing glycine by a chloroacetic acid method, and in particular to a method for recovering formaldehyde from a filtrate of deglycine. Background Art

[0002] The chemical formula of formaldehyde is CH2O, with a formula weight of 30. It is a colorless gas with a pungent odor, which is irritating to the eyes and nose. The relative density of the gas phase is 1.067, and the liquid density is 0.815 g / cm 3 . Melting point -92℃, boiling point -19.5℃. Easily soluble in water, methanol and ethanol.

[0003] Formaldehyde is reductive, especially in alkaline solution. It can burn, and its vapor forms an explosive mixture with air, with an explosion limit of 7% to 73%. Formaldehyde can be used as a raw material for the production of pesticides, disinfectants, phenolic resins, urea-formaldehyde resins, vinylon, hexamethylenetetramine, pentaerythritol and other chemicals.

[0004] Hexamine, which is produced by the reaction of formaldehyde and ammonia, is a catalyst for the production of glycine by the chloroacetic acid method. The chloroacetic acid method for producing glycine is currently one of the most commonly used methods for producing glycine. This method uses hexamine as a catalyst, and chloroacetic acid and ammonia react in an aqueous phase to produce glycine and ammonium chloride. After the reaction is completed, methanol is added to precipitate glycine, and hexamine and ammonium chloride are dissolved in the liquid phase. Glycine is separated by centrifugal filtration, and the filtrate from the deglycine is distilled to recover methanol, then evaporated and concentrated, cooled and crystallized, and filtered to recover ammonium chloride. The process flow is as follows: Figure 1 As shown, the reaction formula is as follows:

[0005]

[0006] Figure 1 The mother liquor after filtering out ammonium chloride is reddish brown, commonly known as "red water", and can be used to produce compound fertilizer. In the production process of glycine, hexamethylenetetramine cannot be recycled and can only enter ammonium chloride and "red water". At the same time, the formaldehyde gas produced by the hydrolysis of some hexamethylenetetramine during distillation and evaporation cannot be recycled and can only enter the tail gas system, evaporation condensate and "red water", causing pollution and waste.

[0007] In order to recover hexamine, the following methods are currently used: (1) multiple evaporation and crystallization methods are used to separate ammonium chloride and hexamine; (2) nanofiltration membrane equipment is used to recover hexamine; (3) a strong acid cationic resin continuous chromatography separation system is used to separate the hexamine solution and the ammonium chloride solution. The hexamine solution is concentrated by a reverse osmosis system to obtain a concentrated solution.

[0008] For example, Chinese patent application CN102807497A provides a method of using crystallization technology to separate glycine products and ammonium chloride mixed crystals from the glycine ammonolysis reaction liquid, and the mixed crystals are separated to obtain glycine and industrial-grade ammonium chloride products, while recovering the catalyst urotropine of the ammonolysis reaction. The residual filtrate of the evaporation crystallization of the ammonolysis reaction is evaporated and concentrated, and after evaporating 20%-40% of the water volume of the liquid, a filter aid is added for hot filtration under high temperature conditions of 60°C-80°C. The filtered urotropine containing the filter aid is first dissolved in water and proportioned to a urotropine aqueous solution with a content of 14%-35%. The urotropine solution that has been recovered by the filter aid is decolorized with activated carbon and returned to the glycine production for recycling.

[0009] Chinese patent application CN101648114A provides a method for separating and recovering methenamine and glycine in glycine mother liquor by using nanofiltration membrane. The molecular weight cutoff of the nanofiltration membrane used is 50-300; the operating pressure is 1.8-4.0MPa; the operating temperature is 20℃-50℃; through the separation of the nanofiltration membrane, most of the ammonium chloride in the glycine mother liquor passes through the nanofiltration membrane into the nanofiltration permeate, and methenamine and most of the glycine are retained in the interception liquid. The methenamine and glycine in the interception liquid are recycled.

[0010] Chinese patent application CN104193752A discloses a urotropine recovery process, comprising the following steps: step 1: separating the centrifugal mother liquor from the distillation tower process through a continuous chromatography separation system filled with ammonium-type strongly acidic cationic resin to obtain a urotropine solution and an ammonium chloride solution; step 2: concentrating the urotropine solution using a reverse osmosis system to obtain a urotropine reverse osmosis concentrated solution, and returning the obtained urotropine reverse osmosis concentrated solution to the crystallization process.

[0011] However, these methods all have the problems of special equipment, complicated operation and excessive investment, and are unable to recover the formaldehyde produced by the hydrolysis of urotropine during the operation, and are even more unable to convert urotropine into other recyclable products.

[0012] Therefore, it is very necessary to develop a method for recovering formaldehyde from the filtrate of deglycine that can solve the above-mentioned technical problems. Summary of the invention

[0013] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for recovering formaldehyde by a chemical method which does not require special equipment, has a simple process, requires little investment and is easy to operate.

[0014] In the process of producing glycine by chloroacetic acid method, the components of the filtrate from which glycine is separated by filtration are mainly methanol, water, ammonium chloride, urotropine, and a small amount of glycine. The method of the present invention is to add a strong acid, such as hydrochloric acid or sulfuric acid, to the filtrate, heat it to hydrolyze the urotropine into ammonia and formaldehyde gas, and the ammonia reacts with the strong acid to form an ammonium salt, which is separated and recovered together with the original ammonium chloride in the filtrate in subsequent processes such as distillation, evaporation, crystallization, and filtration. After the formaldehyde gas escapes, it is absorbed by the absorbent to generate a formaldehyde solution or downstream products.

[0015] The present invention is achieved through the following technical solutions:

[0016] A method for recovering formaldehyde from a filtrate of deglycine comprises the following steps:

[0017] (1) adding a strong acid to the filtrate of deglycine, heating and reflux, and obtaining ammonia and formaldehyde gas;

[0018] (2) The formaldehyde gas is mixed with the absorbent to obtain a formaldehyde solution or a subsequent reaction product.

[0019] The filtrate obtained by removing glycine is the filtrate obtained by filtering glycine during the production of glycine by the chloroacetic acid method.

[0020] Preferably, the strong acid comprises at least one of hydrochloric acid and sulfuric acid.

[0021] Preferably, the absorbent includes at least one of water, alcohol, aqueous ammonia and primary amine.

[0022] When the absorbent is water, the formaldehyde gas is mixed with the absorbent to generate a formaldehyde aqueous solution.

[0023] When the absorbent is alcohol, the formaldehyde gas is mixed with the absorbent to generate a formaldehyde alcohol solution.

[0024] More preferably, the alcohol includes at least one of methanol, ethanol, propanol, isopropanol and tert-butanol.

[0025] When the absorbent is aqueous ammonia, the formaldehyde gas is mixed with the absorbent to generate an aqueous hexamethylenetetramine solution.

[0026] When the absorbent is a primary amine, an N-methylation reaction can occur, and the formaldehyde gas reacts with the absorbent to generate a Schiff base of the primary amine, which usually needs to be reduced to obtain a methylated product. The reducing agent of the reduction reaction is one of hydrogen and formic acid. When the reducing agent of the reduction reaction is hydrogen, a catalyst needs to be added. The catalyst is Raney nickel or palladium carbon. When the reducing agent is formic acid, no catalyst needs to be added.

[0027] The water / alcohol solution of formaldehyde, the aqueous solution of urotropine, the Schiff base or methylation product of primary amine are all useful chemical raw materials. The aqueous solution of urotropine can also be directly used in the production of glycine, thereby achieving the purpose of turning waste into treasure; and the filtrate from which most of the urotropine has been removed produces very little formaldehyde in the subsequent process, which is beneficial to the subsequent biochemical treatment of evaporation wastewater.

[0028] Preferably, the method further comprises: reacting the ammonia obtained in step (1) with a strong acid to generate an ammonium salt.

[0029] More preferably, the ammonium salt is recovered together with the ammonium chloride in the filtrate from the deglycine.

[0030] Preferably, the amount of the strong acid used is 0.1%-10% by mass of the filtrate from the deglycine.

[0031] More preferably, the amount of the strong acid used is 0.5%-5% by mass of the deglycine filtrate.

[0032] Preferably, the amount of the absorbent used is 0.01-5 times the amount of the deglycine filtrate by mass.

[0033] More preferably, the amount of the absorbent used is 0.02-1 times the amount of the deglycine filtrate by mass.

[0034] The beneficial effects of the present invention are:

[0035] The filtrate obtained after treatment has removed most of the hexamethylenetetramine, and there is basically no hexamethylenetetramine that can be hydrolyzed in the subsequent distillation and evaporation processes. Therefore, the formaldehyde content in the evaporated condensed water and the mother liquor after filtering ammonium chloride (commonly known as "red water") is very low, which is conducive to its subsequent biochemical treatment and has environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the general process flow chart for producing glycine by the chloroacetic acid method.

[0037] Figure 2 The figure is a diagram of an industrial device for recovering formaldehyde from the filtrate of deglycine according to the present invention.

[0038] Description of reference numerals:

[0039] 1-strong acid dropping tank; 2-reactor; 3-reactor condenser; 4-gas-liquid separator; 5-formaldehyde buffer tank; 6-three-way valve; 7-circulation pump; 8-formaldehyde absorption kettle; 9-ingredient dropping tank; 10-packing absorption tower; 11-absorption tower condenser; 12-liquid receiving tank; 13-emptying pipeline; 14-secondary condenser. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0041] The present invention combines Figure 2 The working process is as follows:

[0042] The reactor 2 is filled with the filtrate of deglycine. A strong acid, such as hydrochloric acid, sulfuric acid, etc., is added to the reactor 2 through a strong acid dropping tank 1. The strong acid reacts with the filtrate of deglycine and is heated and refluxed to hydrolyze most of the urotropine therein into ammonia and formaldehyde gas. The ammonia and strong acid generated by the hydrolysis of urotropine generate ammonium salts, which are recovered together with ammonium chloride in the original filtrate in subsequent processes. The formaldehyde gas generated by the hydrolysis of urotropine is discharged from the top outlet of the reactor 2, condensed by the reactor condenser 3, separated by the gas-liquid separator 4, and the separated condensate is refluxed to the reactor 2 through a reflux pipe, and the gas containing formaldehyde is discharged through a formaldehyde buffer. The flushing tank 5 reaches the formaldehyde absorption kettle 8; the formaldehyde absorption kettle 8 adds absorbent through the batching dropping tank 9, and the absorbent flows in the circulation pipeline composed of "formaldehyde absorption kettle 8-circulation pump 7-packing absorption tower 10", so as to realize the cyclic absorption of formaldehyde gas, and the unabsorbed gas enters the absorption tower condenser 11 from the top outlet of the packing absorption tower 10 for condensation, and the condensed absorbent flows into the liquid receiving tank 12 for recovery; the gas escaping from the liquid receiving tank 12 is secondary condensed through the secondary condenser 14, and the condensate flows back to the liquid receiving tank 12, and the non-condensable gas is emptied through the exhaust pipe 13; the absorption completion liquid is pumped into the storage tank through the three-way valve 6.

[0043] Example 1

[0044] See also Figure 2 , a method for recovering formaldehyde from a filtrate of deglycine, comprising the steps of:

[0045] (1) 2000 kg of the filtrate from the deglycine solution (containing 1.2% hexamethylenetetramine and 0.05% formaldehyde) was added to a 3000 L reactor 2, and concentrated hydrochloric acid was added to the reactor 2 through a strong acid adding tank 1. The pH value was adjusted to 4 with concentrated hydrochloric acid. The amount of concentrated hydrochloric acid added was about 124 kg;

[0046] (2) steam heating and reflux reaction of the reactor 2; when the temperature in the reactor 2 rises to 65° C., formaldehyde gas is condensed through the reactor condenser 3 and escapes from the gas-liquid separator 4;

[0047] (3) 200L of water is added to the formaldehyde absorption kettle 8 through the batching drop tank 9 to absorb the formaldehyde gas, and heat is released during absorption. The formaldehyde absorption kettle 8 is cooled with cold water at 5-10°C; the unabsorbed gas is condensed by the absorption tower condenser 11 and the secondary condenser 14 and recovered in the liquid receiving tank 12;

[0048] (4) After about 40 minutes of reaction, almost no formaldehyde gas escaped, the absorption was stopped, and the air inlet valve was closed; the formaldehyde content in the absorption liquid obtained by the formaldehyde absorption kettle 8 was detected to be 6.5%;

[0049] After the formaldehyde is recovered from the filtrate of deglycine according to the above steps, Figure 1 After the subsequent distillation process to remove methanol, the water is evaporated and dehydrated by a triple-effect evaporator. The formaldehyde content in the evaporated water is 80 mg / L, and the formaldehyde content in the final "red water" is 50 mg / L.

[0050] Example 2

[0051] 2000kg of the filtrate of deglycine (containing 1.2% urotropine and 0.05% formaldehyde) was put into a 3000L reactor, and the pH value was adjusted to 4 with concentrated hydrochloric acid. The amount of concentrated hydrochloric acid added was about 124kg. The jacket steam was turned on for reflux reaction. When the temperature in the reactor rose to 65°C, formaldehyde gas escaped. 240kg of dilute ammonia water with a content of 7% was used to absorb the formaldehyde gas. Heat was released during absorption, and the absorption kettle was cooled with cold water at 5-10°C. After about 40 minutes of reaction, almost no formaldehyde gas escaped, and the absorption was stopped and the air inlet valve was closed. After heating, stirring and reacting at 38°C-42°C for 3 hours, a small amount of ammonia water was used to adjust the pH value to 8-9, and the reaction was continued for 30 minutes before the end. The urotropine content in the absorption liquid was detected to be 8.3%.

[0052] After the methanol is removed in the subsequent distillation process, the water is evaporated and dehydrated using a triple-effect evaporator. The formaldehyde content in the evaporated water is 90 mg / L, and the formaldehyde content in the "red water" is 48 mg / L.

[0053] Example 3

[0054] 1000kg of the filtrate of deglycine (containing 1.2% hexamethylenetetramine and 0.08% formaldehyde) was placed in a 3000L reactor, and the pH value was adjusted to 4 with concentrated hydrochloric acid. The amount of concentrated hydrochloric acid added was about 124kg. The jacket steam heating was started and the reaction was refluxed. When the temperature in the reactor rose to 65°C, formaldehyde gas escaped. 250kg of methanol in which 37.2kg of aniline was dissolved was used to absorb the formaldehyde gas. After about 40 minutes of reaction, almost no formaldehyde gas escaped, and the absorption was stopped. The aniline methanol solution that absorbed the formaldehyde gas was placed in an autoclave, and 0.5kg of Raney nickel was added to the autoclave. After hydrogen replacement, hydrogen was added to 0.8MPa, and the reaction was kept at 90°C to 100°C until the pressure no longer dropped. The temperature was lowered, and the unreacted hydrogen was discharged. The conversion rate of aniline to N-methylaniline was 95% after sampling and detection. The reaction liquid was rectified and redistilled to obtain 34.8 kg of N-methylaniline.

[0055] After the methanol is removed in the subsequent distillation process, the water is evaporated and dehydrated using a triple-effect evaporator. The formaldehyde content in the evaporated water is 90 mg / L, and the formaldehyde content in the "red water" is 55 mg / L.

[0056] Comparative Example

[0057] 2000kg of the filtrate from the removal of glycine (containing 1.2% hexamethylenetetramine and 0.05% formaldehyde) was put into a 3000L distillation tower, and after distillation to remove methanol, it entered a triple-effect evaporator. After evaporation, the temperature was lowered, ammonium chloride was precipitated, and the material was filtered to obtain ammonium chloride and "red water". The formaldehyde content in the distilled water was 650mg / L, and the formaldehyde content in the "red water" was 2800mg / L.

[0058] The above detailed description is a specific description of one feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for recovering formaldehyde from a filtrate of deglycine, characterized in that: The steps include: (1) Add a strong acid to the filtrate of deglycine, heat and reflux, and obtain ammonia and formaldehyde gas; ammonia reacts with the strong acid to form ammonium salt; (2) The formaldehyde gas is mixed with an absorbent to obtain a formaldehyde solution or a reaction product; The deglycine filtrate is the filtrate obtained after filtering glycine during the production of glycine by the chloroacetic acid method; The absorbent includes at least one of water, alcohol, ammonia and primary amine; When the absorbent is water, the formaldehyde gas and the absorbent are mixed to generate a formaldehyde aqueous solution; When the absorbent is alcohol, the formaldehyde gas is mixed with the absorbent to generate a formaldehyde alcohol solution; When the absorbent is aqueous ammonia, the formaldehyde gas is mixed with the absorbent to generate an aqueous urotropine solution; When the absorbent is a primary amine, the formaldehyde gas is mixed with the absorbent to generate a Schiff base of the primary amine.

2. The method according to claim 1, characterized in that The strong acid includes at least one of hydrochloric acid and sulfuric acid.

3. The method according to claim 1, characterized in that The Schiff base of the primary amine is reduced to obtain the methylated form of the primary amine.

4. The method according to claim 1, characterized in that: The alcohol includes at least one of methanol, ethanol, propanol, isopropanol and tert-butanol.

5. The method according to claim 1, characterized in that: The ammonium salt is recovered together with the ammonium chloride in the filtrate of deglycine.

6. The method according to claim 1, characterized in that The amount of the strong acid used is 0.1%-10% of the amount of the deglycine filtrate by mass.

7. The method according to claim 1, characterized in that The amount of the absorbent used is 0.01-5 times the amount of the filtrate from the deglycine reaction, based on mass.

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