Treatment method of waste lye

Abstract

The invention provides a waste alkali liquor treatment method which comprises the following steps: removing oil, carrying out wet oxidation treatment, carrying out sodium persulfate oxidation, regulating acid, regulating alkali, concentrating, freezing and crystallizing, carrying out solid-liquid separation, dehydrating the solid to obtain an anhydrous sodium sulfate product, and enabling the liquid to meet the effluent standard. Aiming at the treatment of the waste lye, a low-temperature wet oxidation and sodium persulfate oxidation mode is adopted, so that the concentration of COD is further reduced, the wet oxidation does not need high temperature, the equipment investment is low, the sodium persulfate oxidation process is carried out in the wet oxidation effluent cooling process, and the waste lye treatment efficiency is improved. The waste heat of the wet oxidation discharged material after heat exchange is fully utilized to thermally catalyze the thermal decomposition of sodium persulfate into sulfate free radicals for degrading residual oil and organic matters in the discharged material, so that the problem that other advanced oxidation mainly comprising hydroxyl free radicals has a poor degradation effect on the wet oxidation discharged water is solved, the discharged material is ensured to have lower organic matters, and the quality of the discharged material is improved. Sodium sulfate meeting group standards can be directly obtained, and resource recycling of salt is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a method for treating waste alkali liquor. Background Art

[0002] The remarkable features of wet oxidation process are wide application range, effective treatment of various types of high-concentration organic wastewater, high treatment efficiency, good COD removal effect, fast oxidation rate, short reaction residence time, less secondary pollution; system reaction heat can be used, less energy is required, and materials and energy can be fully recycled and reused. At present, sulfur-containing ethylene, propylene and refining waste alkali liquor can usually achieve good treatment effects through wet oxidation treatment process.

[0003] Patent CN106746100A provides a method for treating waste alkali liquor from ethylene refining. The process includes flotation oil removal, high-temperature wet oxidation treatment, sulfuric acid treatment, activated carbon adsorption, adjustment of alkali concentration, evaporation concentration and other steps. This invention requires high-temperature wet oxidation, the temperature reaches 240-320°C, and the pressure reaches 6-20Mpa. The cost requirements and operating costs of the device are relatively high, and the adsorbed effluent still contains a lot of organic matter, so that the separated salt contains impurities.

[0004] In the treatment process of waste alkali liquor with high COD content, a higher wet oxidation reaction temperature is generally required. Although the increase in wet oxidation temperature has little effect on energy consumption, it increases the equipment investment requirements, and the economic efficiency of increasing the temperature treatment is not high. The ability of wet oxidation to reduce COD when coupled with other advanced oxidation methods is limited. Therefore, after conventional treatment of waste alkali liquor with high COD content, the effluent still contains a lot of organic matter, which affects the subsequent crystallization salt treatment process, resulting in a high impurity content in the separated salt, and the TOC content in the obtained salt does not meet the group standard for sodium sulfate in coal chemical industry. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a treatment method for waste alkali liquor, which mainly adopts wet oxidation and sodium persulfate oxidation methods, can effectively reduce the COD of effluent, reduce treatment costs, and achieve the recovery of high-purity salt.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] A method for treating waste alkali liquor, comprising:

[0008] (1) Deoiling the waste alkali liquor to reduce the light oil content to below 15 mg / L;

[0009] (2) the waste alkali liquor after oil removal is subjected to wet oxidation treatment at a temperature of 180-220°C;

[0010] (3) cooling the effluent from step (2) and adding sodium persulfate for oxidation;

[0011] (4) adjusting the acidity, alkali content, and concentration of the effluent from step (3);

[0012] (5) The concentrated water in step (4) is subjected to freeze crystallization, solid-liquid separation, and the solid is dehydrated to obtain an anhydrous sodium sulfate product, and the liquid meets the water outlet standard.

[0013] Furthermore, the oil removal adopts conventional treatment methods in the prior art, wherein at least one of flotation oil removal, coalescence oil removal and adsorption oil removal is preferred.

[0014] Furthermore, the temperature of the wet oxidation treatment is preferably 180-200° C., the pressure is 1.6-3.3 MPa, and the reaction time is 40-150 min.

[0015] Furthermore, the cooling in step (3) is to reduce the temperature of the effluent to 50-80° C. The sodium persulfate oxidation treatment of the present invention needs to be carried out at a certain temperature to achieve higher efficiency. This process is carried out in the middle of the cooling of the wet oxidation effluent, with almost no additional energy loss, and COD can be deeply treated.

[0016] Furthermore, sodium persulfate is added in step (3) so that the concentration of sodium persulfate in the waste alkali solution is 100-2000 mg / L, preferably 600-1200 mg / L.

[0017] Furthermore, the oxidation time in step (3) is 1-3h.

[0018] After sodium persulfate oxidation treatment, the oil content can be reduced to below 2 mg / L and the COD can be reduced to below 1000 mg / L.

[0019] Furthermore, in step (4), the acid adjustment uses sulfuric acid with a mass fraction of 20-60%, the pH is adjusted to 3-6, and stripping is performed simultaneously; the alkali adjustment uses sodium hydroxide with a mass fraction of 20-60%, the pH is adjusted to 7-10.

[0020] Furthermore, the concentration in step (4) is carried out under vacuum conditions, at a temperature of 40-80° C. and a pressure of -0.2-0 MPa, to concentrate the salt to 150,000-400,000 mg / L.

[0021] Furthermore, the freezing crystallization temperature is 1-14°C, the freezing time is 10-90min, and the stirring rate is 10-300r / min.

[0022] Furthermore, the solid-liquid separation is performed by conventional methods in the prior art, specifically, at least one selected from suction filtration separation and centrifugal separation.

[0023] Furthermore, the dehydration is to remove free water and crystal water, and conventional methods in the prior art can be selected. As a preferred specific embodiment, the dehydration includes centrifugal dehydration and drying dehydration processes; the centrifugal dehydration is high-speed centrifugal dehydration, the speed is 10000-20000r / min, and the time is 10-30min. The drying dehydration is preferably step-by-step drying, specifically, first drying at 40-70°C for 2-4h to remove the remaining free water, and then drying at 100-130°C for 2-4h to remove the crystal water.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) For the treatment of waste alkali liquor, the present invention adopts low-temperature wet oxidation and sodium persulfate oxidation to further reduce the concentration of COD, laying the foundation for obtaining high-purity salt. The wet oxidation of the present invention does not require high temperature and has low equipment investment. The sodium persulfate oxidation process is carried out during the cooling process of the wet oxidation effluent, making full use of the residual heat after the wet oxidation effluent heat exchange to catalyze the thermal decomposition of sodium persulfate into sulfate radicals for degrading the remaining oil and organic matter in the effluent, solving the problem that other advanced oxidation methods based on hydroxyl radicals have poor degradation effects on wet oxidation effluent, ensuring that the effluent has low organic matter, and can directly obtain sodium sulfate that meets the group standard, thereby realizing the resource recovery of salt;

[0026] (2) The method of the present invention has no secondary pollution. Only sodium persulfate oxidant and acid and alkali used in the acid and alkali adjustment processes are introduced during the oxidation process. The final product is sodium sulfate, which provides a prerequisite for the subsequent recovery of high-purity sodium sulfate.

[0027] (3) In the preferred embodiment, the present invention adopts a two-step solid-liquid separation method of first filtering or low-speed centrifugation to initially separate water, and then high-speed centrifugation to dehydrate, which can reduce the impact of organic matter in the liquid on sodium sulfate.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a scanning electron microscope image of the sodium sulfate product in Example 1.

[0030] Figure 2 This is the XRD pattern of the sodium sulfate product in Example 1. DETAILED DESCRIPTION

[0031] The method of the present invention is further described in detail below by way of examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0032] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0033] In the following examples and comparative examples, COD is the oxygen demand required for the complete oxidation of organic matter. The chemical oxygen demand of the sample is tested by a Hach COD analyzer. The total organic carbon is tested by a TOC analyzer. The morphology of the product is tested by a scanning electron microscope, and the crystallinity is tested by an XRD diffractometer. The salt content is determined by ion chromatography. The light oil content is determined by an infrared oil tester. 2- The content was determined by UV spectrophotometry.

[0034] Example 1

[0035] The ethylene waste alkali liquor of a certain refinery has a COD of 23745 mg / L, a sodium sulfide of 18652 mg / L, and an oil content of 97 mg / L. The method of the present invention is used to treat the waste alkali liquor.

[0036] (1) Oil removal: flotation oil removal, the light oil content of waste alkali liquid is 13mg / L.

[0037] (2) Wet oxidation: The effluent from step (1) enters the wet oxidation stage for desulfurization and deodorization. The temperature is 200°C, the pressure is 3.1 MPa, the reaction time is 90 min, the effluent oil content is 4.2 mg / L, the COD is 1622 mg / L, and the S 2- The content is 0.12mg / L.

[0038] (3) Sodium persulfate oxidation: The discharge from step (2) was cooled to 50° C. by heat exchange, and sodium persulfate was added to make the concentration of sodium persulfate in the waste alkali solution 1000 mg / L. The oxidation time was 1.5 h, the oil content of the effluent was 1.8 mg / L, and the COD was 916 mg / L.

[0039] (4) Acid neutralization and decarbonization: The effluent from step (3) is acidified with 30% by mass sulfuric acid to a pH of 4, and stripping is performed simultaneously;

[0040] (5) Alkali adjustment: using 30% by mass of sodium hydroxide to adjust the effluent from step (4) to a pH of 8;

[0041] (6) Concentration: The effluent from step (5) was concentrated under vacuum conditions at a temperature of 60° C. and a pressure of −0.1 MPa. The salt concentration after concentration was 250,000 mg / L.

[0042] (7) Freeze crystallization: The concentrated solution of step (6) was freeze crystallized at a temperature of 4° C., a freezing time of 60 min, and a stirring rate of 100 r / min.

[0043] (8) Solid-liquid separation: The solid and liquid of step (7) are separated by suction filtration, and then further subjected to high-speed centrifugal dehydration at a speed of 10,000 r / min for 20 min, and dehydrated in steps, first drying at 40° C. for 4 h to remove the remaining water, and then drying at 110° C. for 2 h to remove the crystal water, to obtain the final product, anhydrous sodium sulfate.

[0044] Take the anhydrous sodium sulfate product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 42.3 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0045] The scanning electron microscope image of the product anhydrous sodium sulfate is as follows Figure 1 As shown, it can be seen that the product has a better and more regular morphology and belongs to the monoclinic crystal system.

[0046] The XRD diffraction spectrum of the product anhydrous sodium sulfate is as follows Figure 2 As shown, it can be seen that the sodium sulfate product has good crystallinity and has no crystallization peak of impure salts.

[0047] Example 2

[0048] Except that the temperature of sodium persulfate oxidation in step (3) is changed to 80° C., the rest is the same as Example 1.

[0049] The oil content of the effluent is 1.5 mg / L and the COD is 823 mg / L.

[0050] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 36.6 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0051] Example 3

[0052] Except that the time of sodium persulfate oxidation in step (3) is changed to 3 h, the rest is the same as Example 1.

[0053] The oil content of the effluent is 1.6 mg / L and the COD is 737 mg / L.

[0054] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 34.7 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0055] Example 4

[0056] Except that the concentration of sodium persulfate in the waste alkali solution in step (3) is changed to 600 mg / L and the oxidation time is changed to 3 h, the other steps are the same as those in Example 1.

[0057] The oil content of the effluent is 1.7 mg / L and the COD is 872 mg / L.

[0058] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 38.2 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0059] Example 5

[0060] Except that the concentration of sodium persulfate in the waste alkali solution in step (3) is changed to 800 mg / L, the other steps are the same as those in Example 1.

[0061] The oil content of the effluent is 1.9 mg / L and the COD is 973 mg / L.

[0062] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 47.3 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0063] Example 6

[0064] Except that the concentration of sodium persulfate in the waste alkali solution in step (3) is changed to 1200 mg / L, the other steps are the same as those in Example 1.

[0065] The oil content of the effluent is 1.1 mg / L and the COD is 638 mg / L.

[0066] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 27.3 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0067] Example 7

[0068] Except that the temperature of the freezing crystallization in step (7) is changed to 12° C., the rest is the same as in Example 1.

[0069] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 38.5 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0070] Example 8

[0071] Except that the rotation speed of high-speed centrifugal dehydration in step (8) is 20000 r / min, the rest is the same as Example 1.

[0072] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 37.1 mg / kg sodium sulfate, which meets the production standard of sodium sulfate in the coal chemical industry.

[0073] Comparative Example 1

[0074] Except that the sodium persulfate oxidation process in step (3) is not performed, the other steps are the same as those in Example 1.

[0075] The oil content of the effluent is 4.2 mg / L and the COD is 1622 mg / L.

[0076] Take an appropriate amount of the obtained sodium sulfate product and measure the total organic carbon. The TOC content of the product is calculated to be 107.5 mg / kg sodium sulfate, which does not meet the production standard of sodium sulfate in the coal chemical industry. This shows the importance of the sodium sulfate oxidation step.

[0077] Comparative Example 2

[0078] Except that the sodium persulfate oxidation process is replaced by the ozone oxidation process in step (3), the other steps are the same as those in Example 1. The operating conditions of the ozone oxidation are: the ozone dosage is 2000 mg / L, and the residence time is 2 h.

[0079] The oil content of the effluent is 2.4 mg / L, and the effluent COD is 1478 mg / L.

[0080] Take an appropriate amount of the product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product was calculated to be 89.4 mg / kg sodium sulfate, which did not meet the production standard of sodium sulfate in the coal chemical industry, indicating that after wet oxidation, the advanced oxidation based on hydroxyl radicals did not have a more effective oxidation effect on the waste alkali solution.

[0081] Comparative Example 3

[0082] Except that the sodium persulfate oxidation process is replaced by the electrocatalytic oxidation process in step (3), the other steps are the same as those in Example 1. The operating conditions of the electrocatalytic oxidation are: the current density is set to 100 mA / cm 2 , stay time 2h.

[0083] The oil content of the effluent is 2.8 mg / L, and the effluent COD is 1528 mg / L.

[0084] Take an appropriate amount of product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product was calculated to be 94.6 mg / kg sodium sulfate, which did not meet the production standard of sodium sulfate in the coal chemical industry, indicating that after wet oxidation, the advanced oxidation based on hydroxyl radicals was poor in oxidizing the waste alkali liquid.

[0085] Comparative Example 4

[0086] Except that the high-speed centrifugal dehydration process is not performed in step (8), the rest is the same as Example 1.

[0087] Take an appropriate amount of product and dissolve it in a volumetric flask to measure the total organic carbon. The TOC content of the product is calculated to be 86.7 mg / kg sodium sulfate, which does not meet the production standard of sodium sulfate in the coal chemical industry, indicating that high-speed centrifugal separation can efficiently separate the water carried by the salt and reduce the pollution of the salt caused by organic matter in the water.

Claims

1. A method for treating waste alkali liquor, comprising: (1) Remove oil from the waste alkali solution to reduce the light oil content to below 15 mg / L; (2) The waste alkali liquid after oil removal is subjected to wet oxidation treatment at a temperature of 180-220°C; (3) cooling the effluent from step (2) and adding sodium persulfate for oxidation; (4) Acidification, alkali adjustment and concentration of the effluent from step (3); (5) The concentrated effluent from step (4) is subjected to freeze crystallization, solid-liquid separation, and the solid is dehydrated to obtain anhydrous sodium sulfate product, and the liquid meets the effluent standard.

2. The method according to claim 1, characterized in that The temperature of the wet oxidation treatment is 180-200°C.

3. The method according to claim 1, characterized in that The pressure of the wet oxidation treatment is 1.6-3.3 MPa, and the reaction time is 40-150 min.

4. The method according to claim 1, characterized in that: The cooling in step (3) is to reduce the outlet water temperature to 50-80°C.

5. The method according to claim 1, characterized in that In step (3), sodium persulfate is added to make the concentration of sodium persulfate in the waste alkali solution be 100-2000 mg / L.

6. The method according to claim 1, characterized in that The oxidation time in step (3) is 1-3h.

7. The method according to claim 1, characterized in that In step (4), the acid adjustment uses sulfuric acid with a mass fraction of 20-60%, and the pH is adjusted to 3-6, and stripping is performed simultaneously; the alkali adjustment uses sodium hydroxide with a mass fraction of 20-60%, and the pH is adjusted to 7-10.

8. The method according to claim 1, characterized in that The concentration in step (4) is carried out under vacuum conditions, at a temperature of 40-80°C and a pressure of -0.2-0 MPa, to concentrate the salt to 150,000-400,000 mg / L.

9. The method according to claim 1, characterized in that: The temperature of the freezing crystallization is 1-14° C., and the freezing time is 10-90 minutes.

10. The method according to claim 1, characterized in that The dehydration includes centrifugal dehydration and drying dehydration processes.

11. The method according to claim 10, characterized in that The centrifugal dehydration is high-speed centrifugal dehydration, with a rotation speed of 10000-20000 r / min and a time of 10-30 min.

12. The method according to claim 10, characterized in that The drying and dehydration is a step-by-step drying process, which is first drying at 40-70° C. for 2-4 hours to remove the remaining free water, and then drying at 100-130° C. for 2-4 hours to remove the crystal water.

Images