Process for treating sucralose wastewater through gradient wet oxidation

Abstract

The invention discloses a process for treating sucralose wastewater through gradient wet oxidation, which belongs to the field of wastewater treatment, and comprises the following steps: mixing sucralose wastewater with first air, conveying the mixture to a first wet oxidation unit, and carrying out wet oxidation reaction under a medium temperature condition; mixing the treated wastewater with second air, conveying the mixture to a second wet oxidation unit, and carrying out wet oxidation reaction at high temperature; part of the treated wastewater is returned to the first wet oxidation unit, part of the treated wastewater is returned to the second wet oxidation unit, and part of the treated wastewater is discharged. The temperature range is accurately regulated and controlled according to the properties of the wastewater and the pollutants, the pollutants are degraded in stages, the pollutants in the sewage can be efficiently treated in an energy-saving manner, and meanwhile, the problem that the sucralose production wastewater is polymerized and coked when an air source wet oxidation method is used for treating the sucralose production wastewater is solved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a process for treating sucralose wastewater by gradient wet oxidation. Background Art

[0002] Sucralose is the only functional sweetener made from sucrose. Its sweetness can reach 600 times that of sucrose, and its market demand is large. In the process of preparing sucralose by the monoester method, thionyl chloride is generally used as the chlorinating agent in the chlorination step, and another raw material N,N-dimethylformamide (DMF) is used as a solvent and participates in the reaction. The composition of the product sucralose-6-ethyl ester after the 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 and ammonia water is added to the sucralose-6-ethyl ester material to adjust the material to neutrality. Finally, mixed salts such as ammonium chloride and dimethylamine hydrochloride will be produced in the sucralose-6-ethyl ester material, and enter the subsequent process with the material. Therefore, in the subsequent extraction section, the wastewater generated contains pollutants such as DMF, ammonium chloride and dimethylamine hydrochloride, and the COD is generally greater than 80,000 mg / L, and the salt content is 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 oxidant under high temperature (150-300°C) and high pressure (0.5-8MPa) conditions to oxidize organic matter in wastewater into substances such as CO2, H2O or biodegradable small molecules. It is recognized as an effective means to treat high-salt, high-COD, toxic and harmful difficult-to-degrade industrial wastewater. The traditional air-based wet oxidation method for treating sucralose is prone to polymerization of some difficult-to-degrade pollutants. The main reason is that the process of wet oxidation degradation of pollutants is a free radical reaction. During the degradation of sucralose byproducts, the degradation reaction will be converted into a polymerization reaction due to insufficient oxygen content. There is a large amount of DMF in sucralose wastewater. DMF has good activity and undergoes degradation reactions in the range of 120-180°C. It first consumes dissolved oxygen in the water, and the degradation reaction of difficult-to-degrade sucralose byproducts has not yet begun. Therefore, the presence of DMF in sucralose wastewater will further enhance the polymerization of byproducts such as sucralose. The produced polymers will clog the heat exchangers and pipes, thus limiting the application of traditional air source wet oxidation in the treatment of sucralose wastewater.

[0004] CN109485179B (a sucralose wastewater pretreatment system) uses a wet oxidation process for treatment. It uses the characteristics of sucralose polymerization to separate the polymer and then oxidize it. Although it can achieve the effect of pretreatment, the polymer discharged forms secondary pollution, and the process of discharging the polymer wastes too much energy, which is neither economical nor environmentally friendly. Therefore, it is necessary to research and develop a new wet oxidation process to avoid the generation of polymers. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention proposes a process for treating sucralose wastewater by gradient wet oxidation. According to the characteristics of pollutants in sucralose waste, namely, the easily degradable DMF and dimethylamine and the difficult-to-degrade sucralose by-products, gradient degradation and oxidation are carried out. Under medium temperature conditions, the easily degradable pollutants begin to degrade first, and the difficult-to-degrade pollutants do not start to react under 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 a preheating unit 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 invention adopts the following technical solution:

[0007] A process for treating sucralose wastewater by gradient wet oxidation comprises the following steps:

[0008] (1) mixing the sucralose wastewater with the first air and transporting the mixture to the first wet oxidation unit to perform a wet oxidation reaction under medium temperature conditions;

[0009] (2) the wastewater obtained by the treatment in step (1) is mixed with the second air and transported to the second wet oxidation unit to perform a wet oxidation reaction at a high temperature;

[0010] (3) Part of the wastewater treated in step (2) is returned to the first wet oxidation unit, part is returned to the second wet oxidation unit, and part is discharged.

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

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

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

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

[0015] Preferably, the dosage Q2 of the first air in step (1) is determined according to the following method:

[0016] Taking 0 as the initial value of Q2, and monitoring the oxygen content O2 of the outlet water of the first wet oxidation unit, the outlet gauge pressure P1 of the first wet oxidation unit, and the outlet absolute temperature T1 of the first wet oxidation unit,

[0017] when hour,

[0018] when When, maintain the current Q2 unchanged;

[0019] when and hour,

[0020] when and hour,

[0021] when and hour,

[0022] Among them, the unit of O2 is mg / L;

[0023] The unit of P1 is MPa;

[0024] T1 unit is K;

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

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

[0027] 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 dosage Q1 of the second air in step (2) is determined according to the following method:

[0030] Taking 0 as the initial value of Q1, and monitoring the oxygen content O1 of the outlet water 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,

[0031] when hour,

[0032] when When , keep the current Q1 unchanged;

[0033] when and hour,

[0034] when and hour,

[0035] when and hour,

[0036] Among them, O1 unit is mg / L;

[0037] The unit of P2 is MPa;

[0038] T2 unit is K;

[0039] The real-time flow of Q1 at the nth minute, in m 3 / h; n is a positive integer;

[0040] The real-time COD concentration of the effluent of the second wet oxidation unit at the n-1th minute, in mg / L;

[0041] is a constant between 3.5 and 4;

[0042] V1 is the effective volume of the first wet oxidation unit, in m 3 ;.

[0043] Preferably, in step (3), the amount W1 of wastewater 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] Wherein, T1 is the absolute temperature at the outlet of the first wet oxidation unit, in K;

[0048] The amount of W1 in the nth minute, in m 3 / h; n is a positive integer;

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

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

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

[0052] W is the initial influent flow rate of sucralose wastewater, in m 3 / h.

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

[0054] When T2<473K,

[0055] When 473K≤T2≤543K,

[0056] When T2>543K,

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

[0058] is the amount of W2 in the nth minute, in units of m 3 / h;

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

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

[0061] W is the initial influent flow rate of sucralose wastewater, in m 3 / h.

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

[0063] The beneficial effects of the present invention are:

[0064] The gradient wet oxidation process for treating sucralose wastewater proposed in the present invention performs gradient degradation oxidation according to the characteristics of pollutants in sucralose waste, namely, the easily degradable DMF and dimethylamine and the difficultly degradable sucralose byproducts. Under medium temperature conditions, the easily degradable pollutants begin to degrade first, and the difficultly degradable pollutants do not start to react under this condition, which can effectively avoid the polymerization of sucralose byproducts. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 The present invention is a flow chart of the process.

[0066] Figure 2 This is a flow chart of the treatment process in Example 1.

[0067] Figure 3 This is a flow chart of the treatment process in Example 2.

[0068] Figure 4 This is a flow chart of the treatment process in Example 3. DETAILED DESCRIPTION

[0069] The present invention is described in detail below with reference to specific embodiments.

[0070] Example 1 (Comparative Example)

[0071] The process wastewater of a sucralose production enterprise was selected. The wastewater quality was COD 80000mg / L, the water was reddish brown, and the main organic matter in the water was dimethylamine, DMF and sucralose-6-ethyl ester. Figure 2 As shown, the system is designed to handle 1m 3 / h, control the water flow rate to 1m 3 / h, the inlet water temperature is 120℃, the pressure is 5MPa, and the flow of Q1 and Q2 is guaranteed to be excessive. The wastewater reacts violently in the medium-temperature stage in the first wet oxidation unit, releasing obvious heat. When it reaches the middle of the tower, DMF and dimethylamine consume a large amount of oxygen in the water, causing the oxygen concentration in the middle water to be lower than 2000mg / L. Sucralose-6-ethyl ester begins to polymerize. When it reaches the top of the tower, the polymer in the water reaches 5%, the effluent is black, and the system is blocked and suspended.

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

[0073] Table 1 Reaction status table 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 controlled excessively, the reaction of wastewater in the medium temperature stage of the first wet oxidation unit slows down significantly, and the chromaticity of the effluent is significantly removed, but the effluent temperature is low. When entering the second wet oxidation reaction for the second stage of high temperature wet oxidation, the effluent temperature does not meet the requirements, resulting in the treatment effect not meeting the expected effect.

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

[0078] Table 2 Reaction status table of Example 2

[0079]

[0080] Example 3 (Comparative Example)

[0081] like Figure 4 As shown, based on Example 2, according to With the newly added flow back to the front end of medium-temperature oxidation, the reaction of wastewater in the medium-temperature wet oxidation stage of the first wet oxidation unit is slightly improved, and the chromaticity of the effluent is significantly removed, but the effluent temperature meets the design requirements. When entering the second wet oxidation reaction for the second stage of high-temperature wet oxidation, the oxidation exothermic heat is low, and the effluent temperature does not meet the requirements, resulting in the treatment effect not meeting the expected effect.

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

[0083] Table 3 Reaction status of Example 3

[0084]

[0085] Example 4

[0086] like Figure 1 As shown, based on Example 3, according to With the newly added flow back to the front end of high-temperature oxidation, when the wastewater enters the second wet oxidation reaction for the second-stage high-temperature wet oxidation, the oxidation starting temperature increases, the exothermic heat increases, the outlet water temperature meets the requirements, and the treatment effect reaches the expected effect.

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

[0088] Table 4 Reaction status of Example 4

[0089]

[0090] Example 5

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

[0092]

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

[0094]

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

[0096] When 393K≤T1≤453K,

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

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

[0099] When 473K≤T2≤543K,

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

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

Claims

1. A process for treating sucralose wastewater by gradient wet oxidation, characterized in that: The following steps are involved: (1) mixing the sucralose wastewater with the first air and transporting the mixture to the first wet oxidation unit to perform a wet oxidation reaction under medium temperature conditions; (2) the wastewater obtained by the treatment in step (1) is mixed with the second air and transported to the second wet oxidation unit to undergo a wet oxidation reaction at a high temperature; (3) Part of the wastewater treated in step (2) is returned to the first wet oxidation unit, part is returned to the second wet oxidation unit, and part is discharged.

2. The process according to claim 1, characterized in that The medium temperature condition described in step (1) is 120~180℃.

3. The process according to claim 1, characterized in that The high temperature condition described in step (2) is 200~270℃.

4. The process according to claim 1, characterized in that The reaction in step (1) or the reaction in step (2) is carried out at a pressure of 5 to 7 MPa.

5. The process according to claim 1, characterized in that The sucralose wastewater contains one or more of dimethylamine, DMF, sucralose-6-ethyl ester or sucralose.

6. The process according to claim 1, characterized in that The dosage Q2 of the first air in step (1) is determined according to the following method: Taking 0 as the initial value of Q2, and monitoring the oxygen content O2 of the outlet water of the first wet oxidation unit, the outlet gauge pressure P1 of the first wet oxidation unit, and the outlet absolute temperature T1 of the first wet oxidation unit, When O2< hour, ; when ≤O2≤ When, maintain the current Q2 unchanged; When O2> ,and *When 100%<2%, ; When O2> , and 2%≤ *When 100%<5%, ; When O2> ,and *When 100%≥5%, ; Among them, the unit of O2 is mg / L; The unit of P1 is MPa; T1 unit is K; The real-time flow of Q2 at the nth minute, in m 3 / h; n is a positive integer; The real-time COD concentration of the effluent of the first wet oxidation unit at the n-1th minute, in mg / L; is a constant between 3.5 and 4; is the effective volume of the first wet oxidation unit, in m 3 .

7. The process according to claim 1, characterized in that The dosage Q1 of the second air in step (2) is determined according to the following method: Taking 0 as the initial value of Q1, and monitoring the oxygen content O1 of the outlet water 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, When O1< hour, ; when ≤O1≤ When , keep the current Q1 unchanged; When O1> ,and hour, ; When O1> ,and hour, ; When O1> ,and hour, ; Among them, O1 unit is mg / L; The unit of P2 is MPa; T2 unit is K; The real-time flow of Q1 at the nth minute, in m 3 / h; n is a positive integer; The real-time COD concentration of the effluent of the second wet oxidation unit at the n-1th minute, in mg / L; is a constant between 3.5 and 4; is the effective volume of the first wet oxidation unit, in m 3 ;.

8. The process according to claim 1, characterized in that In step (3), the amount W1 of wastewater returned to the first wet oxidation unit is determined according to the following method: When T1<393K, ; When 393K≤T1≤453K, ; When T1>453K, ; Wherein, T1 is the absolute temperature at the outlet of the first wet oxidation unit, in K; The amount of W1 in the nth minute, in m 3 / h; n is a positive integer; A1 is the target reaction temperature of the first wet oxidation unit, in K; is the outlet temperature of the first wet oxidation unit at the nth minute, in K; is the outlet temperature of the second wet oxidation unit at the nth minute, in K; is the initial influent flow rate of sucralose wastewater, in m 3 / h.

9. The process according to claim 1, characterized in that In step (3), the amount W2 of wastewater returned to the second wet oxidation unit is determined according to the following method: When T2<473K, ; When 473K≤T2≤543K, ; When T2>543K, ; Wherein, T2 is the absolute temperature at the outlet of the second wet oxidation unit, in K; is the amount of W2 in the nth minute, in units of m 3 / h; A2 is the target reaction temperature of the second wet oxidation unit, in K; is the outlet temperature of the second wet oxidation unit at the nth minute, in K; is the initial influent flow rate of sucralose wastewater, in m 3 / h.

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

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