Process for treating trichlorogalactose wastewater by gradient wet oxidation

Abstract

The application discloses a gradient wet oxidation process for treating trichlorogalactose wastewater, and belongs to the field of wastewater treatment, which comprises the following steps: trichlorogalactose wastewater is mixed with first air and then delivered to a first wet oxidation unit to perform a wet oxidation reaction under a medium temperature condition; the treated wastewater is mixed with second air and then delivered to a second wet oxidation unit to perform a wet oxidation reaction under a high temperature condition; and the treated wastewater is partially returned to the first wet oxidation unit, partially returned to the second wet oxidation unit, and partially discharged. According to the wastewater and the nature of pollutants, the temperature range is accurately controlled, and the pollutants are degraded in stages, so that the pollutants in the wastewater can be efficiently and energy-savingly treated, and the problem of polymerization and coking of trichlorogalactose production wastewater in the air source wet oxidation process is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a process for treating trichlorogalactose wastewater by gradient wet oxidation. BACKGROUND

[0002] Trichlorogalactose is the only functional sweetener using sucrose as raw material, with a sweetness of 600 times that of sucrose, and has a large market demand. In the process of preparing trichlorogalactose by monoester method, the chlorinating agent used in the chlorination step is generally thionyl chloride, and another raw material N,N-dimethylformamide (DMF) is used as a solvent and participates in the reaction. The composition of the product trichlorogalactose-6-ethyl ester material after chlorination is very complex, and due to the decomposition of thionyl chloride and DMF, the material contains a large amount of hydrogen chloride and dimethylamine hydrochloride. Generally, a weak base such as liquid ammonia or ammonia water is added to the trichlorogalactose-6-ethyl ester material to adjust the material to neutral, and finally mixed salts such as ammonium chloride and dimethylamine hydrochloride are produced in the trichlorogalactose-6-ethyl ester material, which enters the subsequent process with the material. Therefore, in the subsequent extraction section, the wastewater produced contains pollutants such as DMF, ammonium chloride and dimethylamine hydrochloride, with a COD generally greater than 80000 mg / L and a salt content greater than 5%, which is a typical high-salt and high-concentration organic wastewater.

[0003] Wet oxidation technology (WAO) refers to the use of air or oxygen as an oxidizing agent to oxidize organic matter in wastewater to CO2, H2O or small molecules that can be biodegraded under high temperature (150-300℃) and high pressure (0.5-8 MPa), which is recognized as an effective means for treating high-salt, high-COD, toxic and hazardous industrial wastewater. The traditional air method wet oxidation method for treating trichlorogalactose is prone to cause partial degradation of pollutants, the main reason being that the process of wet oxidation degradation of pollutants is a free radical reaction, and the degradation process of trichlorogalactose byproducts will lead to a conversion from degradation reaction to polymerization reaction due to insufficient oxygen content. There is a large amount of DMF in trichlorogalactose wastewater, which has good activity and degrades in the range of 120-180℃, first consuming dissolved oxygen in water, while the degradation reaction of the difficult-to-degrade trichlorogalactose byproducts has not yet begun. Therefore, the presence of DMF in trichlorogalactose wastewater will further enhance the polymerization of trichlorogalactose and other byproducts. The generated polymer will block the heat exchanger and pipeline, and thus limit the application of traditional air source wet oxidation in treating trichlorogalactose wastewater.

[0004] CN109485179B (a trichlorogalactose wastewater pretreatment system) uses wet oxidation process for treatment, which utilizes the characteristics of trichlorogalactose polymerization to separate and oxidize the polymerization, which can achieve the effect of pretreatment, but the discharged polymer forms secondary pollution, and the process of discharging the polymer wastes a lot of energy, i.e. it is neither economical nor environmentally friendly. Therefore, it is necessary to develop a new wet oxidation process to avoid the generation of polymer. SUMMARY

[0005] In order to solve the above problems in the prior art, the present application provides a process for gradient wet oxidation treatment of sucralose wastewater, according to the characteristics of pollutants in sucralose waste, i.e. the characteristics of easily degradable DMF, dimethylamine and hardly degradable sucralose by-products, gradient degradation oxidation is carried out, the easily degradable pollutants start to degrade at medium temperature, the hardly degradable pollutants do not start to react at this condition, which can effectively avoid the polymerization of sucralose by-products, in addition, the heat released by the medium temperature oxidation unit is directly used as preheating for the high temperature oxidation unit, which not only reduces the use of heat exchange equipment, but also greatly improves the heat exchange efficiency.

[0006] To achieve the above object, the present application adopts the following technical solution:

[0007] A process for gradient wet oxidation treatment of sucralose wastewater, comprising the following steps:

[0008] (1) mixing the sucralose wastewater with the first air and then conveying it to the first wet oxidation unit for wet oxidation reaction at medium temperature;

[0009] (2) mixing the wastewater obtained in step (1) with the second air and then conveying it to the second wet oxidation unit for wet oxidation reaction at high temperature;

[0010] (3) returning part of the wastewater obtained in step (2) to the first wet oxidation unit, returning part of the wastewater to the second wet oxidation unit, and discharging part of the wastewater.

[0011] Preferably, the medium temperature condition in step (1) is 120-180℃.

[0012] Preferably, the high temperature condition in step (2) is 200-270℃.

[0013] Preferably, the reaction in step (1) or the reaction in step (2) is carried out at a pressure of 5-7 MPa.

[0014] Preferably, the sucralose wastewater contains one or more of dimethylamine, DMF, sucralose-6-ethyl ester or sucralose.

[0015] Preferably, the addition amount Q2 of the first air in step (1) is determined as follows:

[0016] Take 0 as the initial value of Q2, and monitor the oxygen content O2 of the effluent from the first wet oxidation unit, the outlet gage pressure P1 of the first wet oxidation unit and the outlet absolute temperature T1 of the first wet oxidation unit,

[0017] when ,

[0018] When the current Q2 is maintained;

[0019] When and ,

[0020] When and ,

[0021] When and ,

[0022] O2 is in mg / L;

[0023] P1 is in MPa;

[0024] T1 is in K;

[0025] Q2 is the real-time flow of the n th minute, in m 3 / h; n is a positive integer;

[0026] COD is the real-time COD concentration of the effluent of the first wet oxidation unit at the n-1 th minute, in mg / L;

[0027] V2 is a constant between 3.5 and 4;

[0028] V2 is the effective volume of the first wet oxidation unit, in m 3 .

[0029] Preferably, the second air addition amount Q1 in step (2) is determined as follows:

[0030] 0 is taken as the initial value of Q1, and the oxygen content O1 of the effluent of the second wet oxidation unit, the outlet gauge pressure P2 of the second wet oxidation unit and the outlet absolute temperature T2 of the second wet oxidation unit are monitored,

[0031] When ,

[0032] When the current Q1 is maintained;

[0033] When and ,

[0034] when and hour,

[0035] when and hour,

[0036] Wherein, O1 is in mg / L;

[0037] P2 is measured in MPa.

[0038] T2 is in K;

[0039] This refers to the real-time traffic of Q1 at minute n, in milliseconds (m). 3 / h; n is a positive integer;

[0040] The real-time COD concentration of the effluent from the second wet oxidation unit at the (n-1)th minute is expressed in mg / L.

[0041] It is a constant between 3.5 and 4;

[0042] V1 is the effective volume of the first wet oxidation unit, in cubic meters (m³). 3 ;

[0043] Preferably, in step (3), the amount of wastewater W1 returned to the first wet oxidation unit is determined according to the following method:

[0044] When T1 < 393K

[0045] When 393K≤T1≤453K

[0046] When T1 > 453K

[0047] Where T1 is the absolute outlet temperature of the first wet oxidation unit, in K;

[0048] The quantity of W1 at minute n, in meters. 3 / h; n is a positive integer;

[0049] A1 is the target reaction temperature of the first wet oxidation unit, in K;

[0050] The outlet temperature of the first wet oxidation unit at the nth minute, in K;

[0051] T2(n) is the outlet temperature of the second wet oxidation unit at the nth minute, in K;

[0052] W is the initial inflow rate of the trichloro-sucrose wastewater, in m 3 / h.

[0053] Preferably, in step (3), the amount W2 of the wastewater returned to the second wet oxidation unit is determined according to the following method:

[0054] when T2< 473 K,

[0055] when 473 K≤ T2≤ 543 K,

[0056] when T2> 543 K,

[0057] wherein T2 is the absolute temperature of the outlet of the second wet oxidation unit, in K;

[0058] W2(n) is the amount of W2 at the nth minute, in m 3 / h.

[0059] A2 is the target reaction temperature of the second wet oxidation unit, in K;

[0060] T2(n) is the outlet temperature of the second wet oxidation unit at the nth minute, in K;

[0061] W is the initial inflow rate of the trichloro-sucrose wastewater, in m 3 / h.

[0062] Preferably, in the process, a control system is used to adjust the respective flow rates of the first air, the second air, the trichloro-sucrose wastewater, the wastewater returned to the first wet oxidation unit, the wastewater returned to the second wet oxidation unit, and the discharged wastewater according to a preset program.

[0063] The present application has the following advantages:

[0064] The process for treating trichloro-sucrose wastewater by gradient wet oxidation provided by the present application degrades and oxidizes the pollutants in the trichloro-sucrose wastewater according to their respective characteristics, i.e., the easily degradable DMF and dimethylamine and the hardly degradable trichloro-sucrose byproducts. The easily degradable pollutants are degraded first at a medium temperature, and the hardly degradable pollutants do not start to react at this temperature, which can effectively avoid the polymerization of the trichloro-sucrose byproducts. In addition, the heat generated by the medium temperature oxidation unit is directly used for preheating the high temperature oxidation unit, which not only reduces the use of heat exchange equipment, but also greatly improves the heat exchange efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 This is a flowchart of the process described in this invention.

[0066] Figure 2 This is a flowchart of the processing procedure in Example 1.

[0067] Figure 3 This is a flowchart of the processing procedure in Example 2.

[0068] Figure 4 This is a flowchart of the processing procedure in Example 3. Detailed Implementation

[0069] The present invention will now be described in detail with reference to specific embodiments.

[0070] Example 1 (Comparative Example)

[0071] The process wastewater from a sucralose production plant was selected. The wastewater had a COD of 80,000 mg / L and was reddish-brown in color. The main organic compounds in the water were dimethylamine, DMF, and sucralose-6-ethyl ester. Figure 2 As shown, the system is designed to process 1m. 3 / h, control the influent flow rate to 1m³ / h 3 With an influent temperature of 120℃ and a pressure of 5MPa, and ensuring that the flow rates of Q1 and Q2 are excessive, the wastewater reacts violently in the intermediate temperature stage of the first wet oxidation unit, releasing significant heat. When it reaches the middle of the tower, it causes DMF and dimethylamine to consume a large amount of oxygen in the water, resulting in an oxygen concentration in the middle water below 2000mg / L. Sucralose-6-ethyl ester begins to polymerize, and when it reaches the top of the tower, the polymer content in the water reaches 5%, the effluent is black, and the system becomes clogged and stops operating.

[0072] The test results are shown in Table 1:

[0073] Table 1. Reaction status of Example 1

[0074]

[0075] Example 2 (Comparative Example)

[0076] like Figure 3 As shown, based on Example 1, according to When the flow rates of Q1 and Q2 are excessive, the reaction of wastewater slows down significantly in the mesophilic stage of the first wet oxidation unit, and the effluent color is significantly removed, but the effluent temperature is low. When entering the second wet oxidation reaction for the second-stage high-temperature wet oxidation, the effluent temperature does not meet the requirements, resulting in the treatment effect not meeting expectations.

[0077] The test results are shown in Table 2:

[0078] Table 2 Reaction condition table of Example 2

[0079]

[0080] Example 3 (Comparative Example)

[0081] As Figure 4 shown, on the basis of Example 2, according to the newly added reflux to the front end of the medium temperature oxidation, the reaction of the wastewater in the medium temperature wet oxidation stage of the first wet oxidation unit is slightly improved, the effluent color removal is obvious, but the effluent temperature reaches the design requirement. When entering the second wet oxidation reaction for two-stage high temperature wet oxidation, the oxidation exothermic heat is low, the effluent temperature cannot reach the requirement, resulting in that the treatment effect cannot reach the expected effect.

[0082] The test results are shown in Table 3:

[0083] Table 3 Reaction condition table of Example 3

[0084]

[0085] Example 4

[0086] As Figure 1 shown, on the basis of Example 3, according to the newly added reflux to the front end of the high temperature oxidation, when the wastewater enters the second wet oxidation reaction for two-stage high temperature wet oxidation, the oxidation starting temperature is improved, the exothermic heat is improved, the effluent temperature reaches the requirement, and the treatment effect reaches the expected effect.

[0087] The test results are shown in Table 4:

[0088] Table 4 Reaction condition table of Example 4

[0089]

[0090] Example 5

[0091] On the basis of Example 4, according to when O2 is greater than (wherein T1 is the absolute temperature at the outlet of the first wet oxidation unit, unit: K, P1 is the outlet gage pressure of the first wet oxidation unit, unit: MPa), the Q2 dosage is reduced, and the dosage is in the following form:

[0092]

[0093] When O1 is greater than (wherein T2 is the absolute temperature at the outlet of the second wet oxidation unit, unit: K, P2 is the outlet gage pressure of the second wet oxidation unit, unit: MPa), the Q1 dosage is reduced, and the dosage is in the following form:

[0094]

[0095] When T1 < 393 K, increase W1 flow,

[0096] When 393 K ≤ T1 ≤ 453 K,

[0097] When T1 > 453 K, decrease W1 flow A1 is the target reaction temperature of the first wet oxidation unit, in °C.

[0098] When T2 < 473 K, increase W2 flow,

[0099] When 473 K ≤ T2 ≤ 543 K,

[0100] When T2 > 543 K, decrease W2 flow

[0101] After treatment, the oxidation energy consumption is reduced by 20%, and the reactor volume is reduced by 50% compared to Example 4.

Claims

1. A process for the treatment of trichlorogalactose waste water by gradient wet oxidation characterized in that, The process comprises the following steps: (1) the trichloro-sucrose wastewater is mixed with the first air and then sent to the first wet oxidation unit to perform wet oxidation reaction under medium temperature conditions; the medium temperature conditions are 120-180℃; (2) the wastewater obtained by step (1) is mixed with the second air and then sent to the second wet oxidation unit to perform wet oxidation reaction under high temperature conditions; the high temperature conditions are 200-270℃; (3) the wastewater obtained by step (2) is partially returned to the first wet oxidation unit, partially returned to the second wet oxidation unit, and partially discharged; the amount W1 of the wastewater returned to the first wet oxidation unit is determined according to the following method: When T1 < 393 K, ; when 393 K < T1 < 453 K, ; When T1> 453 K, ; wherein T1 is the absolute temperature at the outlet of the first wet oxidation unit, in K; For the nth minute, the amount of W1 in m 3 / h; n is a positive integer; A1 is the target reaction temperature of the first wet oxidation unit, in K; Tn is the temperature at the outlet of the first wet oxidation unit, in K, for the nth minute; Tn is the temperature, in K, at the outlet of the second wet oxidation unit for the nth minute; W is the influent flow rate of the initial trichlorogalactose wastewater, in m 3 / h; the amount W2 of the wastewater returned to the second wet oxidation unit is determined according to the following method: When T2 < 473 K, ; when 473 K < T2< 543 K, ; When T2> 543 K, ; wherein T2 is the absolute temperature at the outlet of the second wet oxidation unit, in K; For the nth minute, amount of W2 in units of m 3 / h; A2 is the target reaction temperature of the second wet oxidation unit, in K; Tn is the temperature, in K, at the outlet of the second wet oxidation unit for the nth minute; W is the influent flow rate of the initial trichlorogalactose wastewater, in m 3 / h; the reaction in step (1) or the reaction in step (2) is performed under a pressure of 5-7 MPa; the trichloro-sucrose wastewater contains dimethylamine, DMF, trichloro-sucrose-6-ethyl ester and trichloro-sucrose.

2. The process according to claim 1, characterized in that, In the process, a control system is used to adjust the respective flow rates of the first air, the second air, the trichloro-sucrose wastewater, the wastewater returned to the first wet oxidation unit, the wastewater returned to the second wet oxidation unit, and the discharged wastewater according to the set program.

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