A wet oxidation and anti-scaling treatment process for high-concentration phenol-containing organic wastewater

Abstract

The invention discloses a kind of high-concentration phenol-containing organic wastewater wet oxidation anti-scaling treatment process, described process is: high-concentration phenol-containing organic wastewater regulates the pH value of wastewater to 4~5, adds sulfur-containing substance and catalyst, under the condition of pressure being 3~8MPa, temperature being 200~300 DEG C, carries out wet oxidation reaction, reaction time is 2 6h, obtains treated wastewater. The present invention adds sulfur-containing substance to high-concentration phenol-containing organic wastewater, improves the pH value of wastewater in the heating stage of wet oxidation, then sulfur-containing substance is oxidized to sulfuric acid in the oxidation stage, reduces the pH value of oxidation stage, can significantly improve the coking situation of equipment, extend equipment service life, and do not affect catalytic oxidation efficiency. The treatment method provided by the present invention is suitable for continuous production, is easy to promote and apply in industry.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a wet oxidation and anti-scaling treatment process for high-concentration phenol-containing organic wastewater. Background Art

[0002] High-concentration phenolic organic wastewater is a widespread, difficult-to-biodegrade, and highly hazardous industrial wastewater, primarily originating from coal chemical and petrochemical industries, as well as phenol and phenolic resin production processes. Ingesting more than 1g of phenol can cause protein denaturation and coagulation, leading to acute poisoning and death. Phenol-acetone production wastewater is a highly phenolic, toxic, and hazardous wastewater with a complex composition. In addition to high concentrations of phenol (2000-5000mg / L), it also contains certain amounts of acetone, cumene, acetophenone, 2-phenyl-2-propanol, α-methylstyrene, and other toxic and hazardous substances, as well as certain concentrations of difficult-to-biodegrade organic matter. If discharged untreated, high-phenolic organic wastewater can cause serious environmental pollution, endangering human health and the survival of plants and animals. Therefore, treatment technologies for high-concentration phenolic organic wastewater are of great significance for environmental protection.

[0003] Treatment of high-concentration phenolic organic wastewater can be divided into two approaches: separation and recovery, and oxidative degradation. Separation and recovery technology aims to recover as much phenol as possible from the wastewater, turning waste into valuable resources. However, separation and recovery are costly and have little economic value.

[0004] The main oxidative degradation technologies include advanced oxidation and biological methods. Biological methods require long treatment times and are less efficient for treating high-concentration phenol-containing wastewater. Furthermore, biological methods require pretreatment and desalination before treatment. Advanced oxidation methods include ozone oxidation, electrocatalytic oxidation, and catalytic wet oxidation. Catalytic wet oxidation involves the use of oxygen or air as an oxidant under the action of a catalyst, at high temperatures (120-320°C) and high pressures (0.5-20 MPa), to oxidize large organic molecules in water into small organic or inorganic molecules. It offers advantages such as wide applicability, high salt tolerance, excellent treatment effectiveness, and minimal secondary pollution. Catalytic wet oxidation systems typically consist of a heater (heat exchanger) and an oxidation tower. After being heated to the reaction temperature in the heater, the wastewater is fed into the oxidation tower, where oxygen is introduced for oxidation. However, when using catalytic wet oxidation to treat high-concentration phenol-containing organic wastewater, the heater can become fouled, forming a large amount of black deposits that are difficult to clean. It is speculated that due to the high organic content in the wastewater, the high temperature and high pressure environment causes the organic matter to crack, carbonize, or polymerize, forming coke-like products that adhere to the heater / heat exchanger. This scaling can affect heating efficiency, increase cleaning costs, or shorten equipment life. Therefore, it is necessary to treat and reduce scaling in wet oxidation of high-concentration phenolic organic wastewater. Summary of the Invention

[0005] The purpose of the present invention is to provide a wet oxidation anti-scaling treatment process for high-concentration phenol-containing organic wastewater, reduce the coking degree of equipment, and deeply treat the phenol wastewater to meet discharge requirements.

[0006] The technical solution adopted in the present invention is:

[0007] A wet oxidation and anti-scaling process for treating high-concentration phenol-containing organic wastewater, the process comprising:

[0008] The pH value of high-concentration phenol-containing organic wastewater is adjusted to 4-5, sulfur-containing substances and catalysts are added, and wet oxidation reaction is carried out under the conditions of pressure of 3-8 MPa and temperature of 200-300°C. The reaction time is 2-6 hours to obtain treated wastewater.

[0009] The high-concentration phenol-containing organic wastewater generally contains volatile phenolic substances such as phenol, cresol, xylenol, etc. at a concentration of 2000-5000 mg / L.

[0010] After adjusting the pH value of the wastewater to 4-5, if there is precipitation, filter it first and then carry out wet oxidation reaction.

[0011] The sulfur-containing substance is one or more of sodium bisulfite, sodium thiosulfate or elemental sulfur. The amount of the sulfur-containing substance added is 0.05-2% of the mass of the wastewater, more preferably 0.1-1% of the mass of the wastewater.

[0012] The wet oxidation reaction is carried out in the heater and oxidation tower. The wastewater is pressurized and heated to 200-300°C in the heater, and then sent to the oxidation tower. High-pressure oxygen is introduced into the oxidation tower to oxidize the organic matter in the wastewater.

[0013] Under conventional processes, scaling is likely to occur in heaters and reaction pipes, i.e., a large amount of black attachments are present, which affects the heat exchange efficiency, makes the pipes easily clogged, and the black attachments are difficult to clean.

[0014] Researchers have found that high-concentration phenol-containing organic wastewater is less likely to scale in the heater at higher pH values, but this reduces treatment efficiency during subsequent wet oxidation. Instead, scaling occurs in the oxidation tower due to the large amount of organic matter remaining unoxidized. In wet oxidation reactions, lower pH values ​​generally increase oxidation efficiency, but also lead to more severe scaling during heating.

[0015] One feasible approach is to adjust the wastewater's pH to a higher level during heating, then lower it by adding acid in the oxidation tower. However, wet oxidation systems are high-temperature and high-pressure systems, making the addition of acid in the oxidation tower difficult. Furthermore, the acid addition piping must be resistant to strong acid corrosion, resulting in high equipment costs.

[0016] The present invention creatively proposes adding a sulfur-containing substance to wastewater, adjusting the initial pH to 4-5, and then heating it. This results in a higher pH for the wastewater, significantly reducing scale buildup in the heater. The heated wastewater then enters an oxidation tower for catalytic oxidation, where the sulfur-containing substance is oxidized to sulfuric acid, lowering the pH to 2-3, facilitating the catalytic oxidation reaction.

[0017] The present invention utilizes the characteristics that sulfur-containing substances have a higher pH value in the reduced state and a lower pH value after oxidation, thereby increasing the pH value of high-concentration phenol-containing organic wastewater in the heating stage of wet oxidation and reducing the pH value in the oxidation stage, thereby improving the coking situation and increasing the oxidation efficiency.

[0018] The catalyst is one or more of copper sulfate, copper chloride, ferrous sulfate and ferrous chloride. The dosage of the catalyst is 0.05-0.5% of the mass of the wastewater, more preferably 0.1-0.4% of the mass of the wastewater.

[0019] Furthermore, the catalyst can be added to the initial wastewater or in the oxidation tower after the wastewater has passed through the heater. When a large amount of catalyst is used, some catalyst may precipitate and form coke on the heater. Therefore, it is preferred to add the catalyst after heating to 200-300°C for wet oxidation.

[0020] Preferably, the process is carried out according to the following steps:

[0021] The pH value of high-concentration phenol-containing organic wastewater is adjusted to 4-5, sulfur-containing substances are added, pressurized to 3-8MPa, heated to 200-300°C in a heater, and then sent to an oxidation tower, a catalyst is added, and high-pressure oxygen is introduced to carry out a wet oxidation reaction. The reaction time is 2-6 hours to obtain treated wastewater.

[0022] Furthermore, the reaction temperature of the wet oxidation is preferably 250 to 270°C.

[0023] The reaction pressure is preferably 6 to 7 MPa.

[0024] The reaction time is preferably 3 to 4 hours.

[0025] The TOC of the treated wastewater can reach below 100 mg / L, and the TOC removal rate can reach more than 99%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention addresses the issue of reactor scaling during wet oxidation processes for the first time and demonstrates that adding a sulfur-containing substance to high-concentration phenolic organic wastewater can significantly improve equipment coking and extend its service life without compromising catalytic oxidation efficiency. The treatment method provided by this invention is suitable for continuous production and is readily applicable in industry. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0029] Wastewater sample: Phenol-acetone wastewater from a certain company. Wastewater quality: pH 4.5, COD 12,500 mg / L, solids content 4.8%, TOC 4,600 mg / L, and volatile phenol content 2,498 mg / L.

[0030] Example 1

[0031] Hydrochloric acid was added to phenol-acetone wastewater to adjust the pH value of the wastewater to 2.5. Copper sulfate was used as the catalyst to study the effect of wet oxidation treatment at different temperatures. The results are shown in Table 1 below. The higher the reaction temperature, the better the treatment effect, but at the same time, the power consumption and equipment requirements were higher, and there was obvious coking.

[0032] Table 1

[0033]

[0034] Example 2

[0035] Hydrochloric acid was added to the phenol-acetone wastewater to adjust the pH value of the wastewater to 2.5. The wet oxidation treatment effect with different catalyst addition amounts was studied. The results are shown in Table 2 below. The results show that the greater the amount of catalyst added, the better the treatment effect. However, some catalysts will precipitate and adhere to the reactor, aggravating the coking situation. Therefore, it is recommended that the catalyst can be directly fed into the oxidation tower in the project.

[0036] Table 2

[0037]

[0038] Example 3

[0039] Hydrochloric acid was added to phenol-acetone wastewater to adjust the pH to various levels. The effects of different influent pH levels on wet oxidation treatment were investigated. The results, shown in Table 3 below, show that lower influent pH levels resulted in better treatment effectiveness, but this placed greater demands on the equipment material. Furthermore, equipment coking persisted and showed no improvement. In Experiment 2, with an influent pH of 4.5, wet oxidation treatment was less effective, with an effluent pH as high as 8.5 and a TOC removal rate of less than 70%. Because a large amount of organic matter remained unoxidized and decomposed, coking also occurred at high temperatures.

[0040] Table 3

[0041]

[0042]

[0043] Example 4

[0044] Taking into account the coking and oxidation effects of wastewater at different pH values, temperatures, and catalyst dosages, we subsequently added sulfur-containing compounds to the raw water to maintain the wastewater pH at 4-5 during the heating phase. The coking situation was then observed, as shown in Table 4 below. The results in Table 4 indicate that the addition of sulfur-containing substances oxidized the sulfur-containing substances to form sulfuric acid, which lowered the wastewater pH to 2-3. This lowered the wastewater pH during oxidation and improved oxidation efficiency. The higher pH during the heating phase significantly improved the coking of the equipment and extended its service life.

[0045] Table 4

[0046]

[0047]

[0048] In Table 4, no coking occurred in the reactors of Experiments 2, 3, and 4. A small amount of black solid residue was found in the effluent, which could be removed by filtration, and the reactors could be cleaned with clean water.

[0049] From the above experimental results, it can be seen that, taking into account the oxidation effect in actual engineering, the difficulty of coking cleaning and the cost of reagents, the current better wet oxidation anti-coking process for phenol acetone wastewater is to maintain the pH of the inlet water at around 4.5, without adjusting the pH before entering the heat exchanger, and by adding sulfur-containing substances to lower the pH of the system during oxidation, the coking situation of the equipment can be improved, while also ensuring the treatment effect.

Claims

1. A wet oxidation and anti-scaling process for treating high-concentration phenolic organic wastewater, characterized in that The process is: The pH value of high-concentration phenol-containing organic wastewater is adjusted to 4-5, and a sulfur-containing substance and a catalyst are added to perform a wet oxidation reaction under the conditions of a pressure of 3-8 MPa and a temperature of 200-300°C for a reaction time of 2-6 hours to obtain treated wastewater; the sulfur-containing substance is one or more of sodium bisulfite, sodium thiosulfate or elemental sulfur; The wet oxidation reaction is carried out in a heater and an oxidation tower. The wastewater is pressurized and heated to 200-300°C in the heater, and then sent to the oxidation tower. High-pressure oxygen is introduced into the oxidation tower to oxidize the organic matter in the wastewater. At this time, the sulfur-containing substances in the wastewater are oxidized and the pH value of the wastewater drops to 2-3.

2. The process according to claim 1, wherein The amount of sulfur-containing substances added is 0.05-2% of the wastewater mass.

3. The process according to claim 1, wherein The catalyst is one or more of copper sulfate, copper chloride, ferrous sulfate and ferrous chloride.

4. The process according to claim 3, wherein The dosage of the catalyst is 0.05-0.5% of the wastewater mass.

5. The process according to claim 1, wherein The catalyst is added into the initial wastewater, or the catalyst is added into the oxidation tower after the wastewater passes through the heater.

6. The process according to claim 5, wherein The process is as follows: high-concentration phenol-containing organic wastewater is adjusted to a pH value of 4-5, sulfur-containing substances are added, the wastewater is pressurized to 3-8 MPa, heated to 200-300°C in a heater, and then sent to an oxidation tower, a catalyst is added, and high-pressure oxygen is introduced to carry out a wet oxidation reaction. The reaction time is 2-6 hours to obtain treated wastewater.

7. The process according to claim 1, wherein The reaction temperature of wet oxidation is 250~270℃; the reaction pressure is 6~7MPa; and the reaction time of wet oxidation is 3~4h.

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