Resource utilization method of sulfolane waste liquid

Abstract

The invention relates to a resource utilization method of sulfolane waste liquid. The method comprises the following steps: mixing the sulfolane waste liquid with a photocatalyst, and sequentially carrying out dark reaction and photocatalytic reaction, wherein the photocatalyst is a hierarchical pore silicon oxide / C3N4 composite photocatalyst. The resource utilization method of the sulfolane waste liquid provided by the invention is suitable for resource utilization of the sulfolane waste liquid containing small molecular organic pollutants and inorganic salts. By introducing the hierarchical porous silicon oxide / C3N4 photocatalyst with a large specific surface area, adsorption enrichment and conversion of the sulfolane waste liquid are realized under the conditions of normal temperature and pressure and no additional organic reagent, sulfolane is converted into cyclobutane and sulfuric acid, and cyclobutane directly overflows in a gas form, so that the time and energy consumption cost caused by separation is avoided; small-molecule organic pollutants in the liquid are degraded under the photocatalysis effect, only sulfuric acid generated in the reaction and a small amount of original inorganic salt in the waste liquid exist in the solution, and resource utilization can be achieved through salt separation.

Description

Technical Field

[0001] The invention relates to the technical field of waste liquid treatment, and in particular to a method for resource utilization of sulfolane waste liquid. Background Art

[0002] Sulfolane waste liquid is a hazardous waste generated by aromatics equipment. At present, the industry mainly uses distillation to treat sulfolane waste liquid. Due to the high water content in the waste liquid, the evaporation method consumes a lot of energy, and high temperature can easily cause side reactions such as sulfolane ring opening. When sulfolane waste liquid is treated by biochemical method, sulfolane is degraded into carbon dioxide and sulfur dioxide, etc., which cannot be recycled. Therefore, efficient and energy-saving sulfolane waste liquid harmless recycling technology has become an urgent need in the market.

[0003] In recent years, the resource utilization technology of sulfolane waste liquid has attracted the attention of technical personnel in this field. For example, Luoyang Petrochemical uses delayed coking technology to send sulfolane to the top of the coke tower for recycling, opening up a "green channel" for the treatment of sulfolane waste agent. However, due to the high sulfur content in sulfolane, the process produces harmful waste gases such as hydrogen sulfide or sulfur dioxide, which increases the burden of waste gas treatment and consumes high energy.

[0004] Patent 200610134285.3 discloses a method for recovering sulfolane containing inorganic salts, wherein the inorganic salts are precipitated by a filter aid, and the filter aid is then distilled off by vacuum distillation to remove the inorganic salts in the sulfolane. The method is highly efficient and easy to operate, but the filter aid is toluene, which is an easily-made drug reagent, and the method can only remove specific inorganic salts, and does not remove other small molecular organic pollutants in the waste liquid.

[0005] Patent 201810857047.8 uses an extraction method to recover sulfolane from waste liquid. The concentration of sulfolane in the treated waste liquid is lower than 50 mg / L. However, the extractant used in this method is a mixture of one or more of halogenated hydrocarbons, aromatic hydrocarbons, and ester compounds, and the amount used is large. It also cannot remove small molecular organic pollutants in the waste liquid. Therefore, although the concentration of sulfolane in the treated waste liquid can be lower than 50 mg / L, the COD will still be higher than 100 mg / L and cannot meet the emission standards. Due to the presence of small molecular organic matter and inorganic salts, the recycling of the treated wastewater is also subject to many restrictions. Summary of the invention

[0006] The invention aims to provide a method for resource utilization of sulfolane waste liquid, so as to solve the problems of high energy consumption, high toxicity and difficulty in treating small molecular organic pollutants in the waste liquid in the traditional method for treating the sulfolane waste liquid.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for resource utilization of sulfolane waste liquid, which comprises: mixing the sulfolane waste liquid with a photocatalyst and then sequentially performing a dark reaction and a photocatalytic reaction; wherein the photocatalyst is a multi-level porous silicon oxide / C3N4 composite photocatalyst.

[0008] Optionally, the multilevel porous silica / C3N4 composite photocatalyst comprises multilevel porous silica and C3N4 quantum dots doped in the multilevel porous silica; based on the total weight of the multilevel porous silica / C3N4 composite photocatalyst, the weight percentage of the multilevel porous silica is 10% to 40%, and the weight percentage of the C3N4 quantum dots is 60% to 90%; the specific surface area of ​​the multilevel porous silica / C3N4 composite photocatalyst is 600 to 1000 m 2 / g.

[0009] Optionally, based on the volume of the sulfolane waste liquid, the added amount of the multi-level porous silica / C3N4 composite photocatalyst is 0.1 to 5 g / L.

[0010] Optionally, the COD in the sulfolane waste liquid is 20 to 3000 mg / L, the concentration of sulfolane is 10 to 1000 mg / L, and the concentration of sulfate is 0 to 100 mg / L.

[0011] Optionally, the dark reaction conditions include: light intensity of 0-0.1 mW / cm 2 The time is 10 to 60 minutes, preferably 20 to 40 minutes; the conditions of the photocatalytic reaction include: the light intensity is 20 to 80 mW / cm 2 The illumination time is 4 to 8 hours; the light source is a 300W xenon lamp pre-installed with a 400 to 800nm ​​filter.

[0012] Optionally, the preparation method of the multi-level porous silicon oxide / C3N4 composite photocatalyst comprises:

[0013] S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution;

[0014] S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution;

[0015] S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution;

[0016] S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining the third solid product.

[0017] Optionally, the mass ratio of the coal gasification fly ash to the alkali in the alkaline solution is 1:(0.5-1.0); the alkali in the alkaline solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkaline solution is 10-30%; the concentration of silicon element in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L.

[0018] Optionally, the mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10).

[0019] Optionally, the molar ratio of the surfactant to the first solution calculated as silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; the surfactant is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide and hexadecylpyridinium bromide, preferably hexadecyltrimethylammonium bromide.

[0020] Optionally, the microwave heating reaction conditions include: microwave heating temperature of 100-150°C, time of 10-50min; the hydrothermal crystallization conditions include: temperature of 50-150°C, preferably 100-120°C; time of 8-48h, preferably 16-32h; the calcination conditions include: temperature of 400-700°C, preferably 500-600°C; time of 1-8h, preferably 2-5h.

[0021] Through the above technical scheme, the resource utilization method of sulfolane waste liquid provided by the present invention is suitable for the resource utilization of sulfolane waste liquid containing small molecular organic pollutants and inorganic salts. By introducing a large specific surface area multi-level porous silica / C3N4 photocatalyst, the adsorption enrichment and conversion of sulfolane waste liquid are realized under normal temperature and pressure without adding organic reagents, wherein sulfolane is converted into cyclobutane and sulfuric acid, and cyclobutane overflows directly in the form of gas, avoiding the time and energy consumption costs caused by separation; small molecular organic pollutants in the liquid are degraded under the action of photocatalysis, and only sulfuric acid generated by the reaction and a small amount of inorganic salts originally in the waste liquid exist in the solution, which can be resource-utilized by salt separation.

[0022] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1This is an electron microscope image of the multi-level porous silicon oxide / C3N4 composite photocatalyst in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0026] The present invention provides a method for resource utilization of sulfolane waste liquid, which comprises: mixing the sulfolane waste liquid with a photocatalyst, and then sequentially performing a dark reaction and a photocatalytic reaction; wherein the photocatalyst is a multi-level porous silicon oxide / C3N4 composite photocatalyst.

[0027] In the present invention, the resource utilization method of sulfolane waste liquid is a method for converting sulfolane in sulfolane waste liquid and completely degrading small molecular organic pollutants by using multi-level porous silicon oxide / C3N4 as a catalyst under visible light irradiation. The method provided by the present invention is green, energy-saving, simple and efficient. The sulfolane in the sulfolane waste liquid can be converted into cyclobutane and sulfuric acid by adsorption enrichment at normal temperature and pressure without adding an organic reagent. The cyclobutane overflows directly in the form of gas, avoiding the time and energy consumption cost caused by separation; the small molecular organic pollutants in the liquid are degraded under the action of photocatalysis, and only sulfuric acid generated by the reaction and a small amount of inorganic salts originally in the waste liquid exist in the solution, and the waste liquid is conducive to reuse.

[0028] According to the present invention, optionally, the multilevel porous silica / C3N4 composite photocatalyst includes multilevel porous silica and C3N4 quantum dots doped in the multilevel porous silica. In the present invention, C3N4 exists in the form of quantum dots, the multilevel porous silica is a double-level pore structure including macropores and micropores, and the multilevel porous silica has a large specific surface area, thus having good adsorption performance, and the multilevel porous silica / C3N4 composite photocatalyst formed with the C3N4 quantum dots is conducive to light absorption, and has a good degradation effect on sulfolane waste liquid.

[0029] According to the present invention, optionally, based on the total weight of the multi-level porous silicon oxide / C3N4 composite photocatalyst, the weight percentage of the multi-level porous silicon oxide is 10% to 40%, and the weight percentage of the C3N4 quantum dots is 60% to 90%; the specific surface area of ​​the multi-level porous silicon oxide / C3N4 composite photocatalyst is 600 to 1000 m 2 The above implementation can improve the photocatalytic performance of the multi-level porous silicon oxide / C3N4 composite photocatalyst, and better transform the sulfolane in the sulfolane waste liquid and degrade small molecular organic pollutants.

[0030] According to the present invention, optionally, based on the volume of the sulfolane waste liquid, the added amount of the multi-level porous silica / C3N4 composite photocatalyst is 0.1 to 5 g / L.

[0031] According to the present invention, optionally, the COD in the sulfolane waste liquid is 20 to 3000 mg / L, the concentration of sulfolane is 10 to 1000 mg / L, and the concentration of sulfate is 0 to 100 mg / L.

[0032] According to the present invention, optionally, the conditions of the dark reaction include: light intensity of 0 to 0.1 mW / cm 2 The time is 10 to 60 minutes, preferably 20 to 40 minutes; the conditions of the photocatalytic reaction include: the light intensity is 20 to 80 mW / cm 2 The illumination time is 4 to 8 hours; the light source is a 300W xenon lamp pre-installed with a 400 to 800nm ​​filter.

[0033] According to the present invention, optionally, the method for preparing the multi-level porous silicon oxide / C3N4 composite photocatalyst comprises:

[0034] S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution;

[0035] S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution;

[0036] S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution;

[0037] S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining the third solid product.

[0038] The multi-level porous silicon oxide / C3N4 composite photocatalyst obtained by the preparation method of the present invention is more conducive to light absorption and has a good degradation effect on sulfolane waste liquid.

[0039] According to the present invention, optionally, the mass ratio of the coal gasification fly ash to the alkali in the alkali solution is 1: (0.5-1.0); the alkali in the alkali solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkali solution is 10-30%. In the present invention, the coal gasification fly ash is used as a silicon source to prepare a hierarchical porous silicon oxide precursor, and the coal gasification fly ash can be utilized as a resource.

[0040] According to the present invention, optionally, the concentration of silicon in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L.

[0041] According to the present invention, optionally, the mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10). The present invention is conducive to loading melamine in the multi-level porous silica, and obtaining the multi-level porous silica / C3N4 composite photocatalyst by subsequent calcination.

[0042] According to the present invention, optionally, the molar ratio of the surfactant to the first solution calculated as silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; the surfactant is selected from at least one of cetyltrimethylammonium bromide, cetyltriethylammonium bromide and cetylpyridinium bromide, preferably cetyltrimethylammonium bromide.

[0043] According to the present invention, optionally, the microwave heating reaction conditions include: microwave heating temperature of 100-150°C, time of 10-50min; the hydrothermal crystallization conditions include: temperature of 50-150°C, preferably 100-120°C; time of 8-48h, preferably 16-32h; the calcination conditions include: temperature of 400-700°C, preferably 500-600°C; time of 1-8h, preferably 2-5h.

[0044] The present invention is further illustrated by the following examples, but the present invention is not limited thereto.

[0045] The coal gasification fly ash used in the examples comes from a chemical plant in Anqing, referred to as Anqing ash. Its main chemical composition (by weight) includes: SiO2 (49.4%), Al2O3 (22.8%), CaO (10.3%), Fe2O3 (8.21%), TiO2 (1.26%), Na2O (1.22%), MgO (0.83%), and the rest is residual carbon.

[0046] Example 1

[0047] A method for resource utilization of sulfolane waste liquid, the steps of which are as follows:

[0048] (1) Preparation of photocatalyst: Weigh 3 g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6 mL of a 20% NaOH solution, add the same raw materials mentioned above into four tubes, and place them in a microwave digestion instrument at the same time. React for 30 min under microwave-assisted heating conditions at 130° C., then separate the solid and liquid to obtain desiliconized ash and a first solution; combine the first solutions, and adjust the silicon concentration in the first solution to 5 g / L. Accurately measure 100mL of the first solution, add 1.04g CTAB, stir evenly, add acetic acid to adjust the pH to 11.0, transfer to a 200mL hydrothermal kettle, and hydroheat at 110℃ for 24h to obtain a second solution; centrifuge the second solution to obtain a second solid product, wash the second solid product to neutrality, weigh 1.0g of the second solid product and mix with 30mL deionized water and 8.6g melamine and stir for 30min to obtain a third solution; centrifuge the third solution to obtain a multi-level porous silica powder loaded with melamine; put the above powder into a crucible, cover it with a lid, and calcine it in a muffle furnace at 550℃ for 4h to obtain a multi-level porous silica / C3N4 composite photocatalyst. The electron microscope image is as follows Figure 1 As shown, it can be seen that C3N4 quantum dots are loaded on the multi-level porous silica. The weight percentage of multi-level porous silica in the multi-level porous silica / C3N4 composite photocatalyst is 15.2%, and the weight percentage of C3N4 is 84.8%; the specific surface area of ​​the multi-level porous silica / C3N4 composite photocatalyst is 755m 2 / g.

[0049] (2) A 300W xenon lamp (with a light intensity of 50mW / cm2) pre-installed with a 400-800nm ​​filter was used. 2 ) The sulfolane waste liquid with 2 g / L of multi-level porous silica / C3N4 composite photocatalyst was treated with visible light. Before turning on the light source, dark adsorption of the composite photocatalyst and the sulfolane waste liquid was performed (light intensity was 50 mW / cm 2 ), and the photocatalytic experiment was started again after reaching adsorption equilibrium, and the dark adsorption time was 30min. The COD in the sulfolane waste liquid to be treated in this embodiment was 2573mg / L, the concentration of sulfolane was 135mg / L, and the sulfate concentration was 34mg / L. After adsorption for 30min, the COD in the waste liquid was 2061mg / L, and the sulfate concentration was 32mg / L. After the photocatalytic reaction for 6h, the COD in the waste liquid was 0mg / L, and the concentration of sulfate ions was 140mg / L.

[0050] Calculations show that the COD removal rate is 99.5%, and all the sulfur in sulfolane is converted into sulfate.

[0051] Example 2

[0052] A method for resource utilization of sulfolane waste liquid, the steps of which are as follows:

[0053] (1) Preparation of photocatalyst: Weigh 3 g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6 mL of a 20% NaOH solution, add the same raw materials mentioned above into four tubes, and place them in a microwave digestion instrument at the same time. React for 30 min under microwave-assisted heating conditions at 130° C., then separate the solid and liquid to obtain desiliconized ash and a first solution; combine the first solutions, and adjust the silicon concentration in the first solution to 5 g / L. Accurately measure 100 mL of the first solution, add 1.04 g of CTAB, stir evenly, add acetic acid to adjust the pH to 11.0, transfer to a 200 mL hydrothermal kettle, and hydrothermal at 110°C for 24 hours to obtain a second solution; centrifuge the second solution to obtain a second solid product, wash the second solid product to neutrality, weigh 1.2 g of the second solid product, mix with 30 mL of deionized water and 8.6 g of melamine and stir for 30 minutes to obtain a third solution; centrifuge the third solution to obtain a multi-level porous silica powder loaded with melamine; put the above powder into a crucible, cover it with a lid, and calcine it at 550°C in a muffle furnace for 4 hours to obtain a multi-level porous silica / C3N4 composite photocatalyst. The weight percentage of multi-level porous silica in the multi-level porous silica / C3N4 composite photocatalyst is 11.1%, and the weight percentage of C3N4 is 88.9%; the specific surface area of ​​the multi-level porous silica / C3N4 composite photocatalyst is 741 m 2 / g.

[0054] (2) A 300W xenon lamp (with a light intensity of 50mW / cm2) pre-installed with a 400-800nm ​​filter was used. 2 ) The sulfolane waste liquid with 2 g / L of multi-level porous silica / C3N4 composite photocatalyst was treated with visible light. Before turning on the light source, dark adsorption of the composite photocatalyst and the sulfolane waste liquid was performed (light intensity was 50 mW / cm 2 ), and the photocatalytic experiment was started again after reaching adsorption equilibrium, and the dark adsorption time was 30min. The COD in the sulfolane waste liquid to be treated in this embodiment was 400mg / L, the concentration of sulfolane was 97.5mg / L, and the sulfate concentration was 32mg / L. After adsorption for 30min, the COD in the waste liquid was 265mg / L, and the sulfate concentration was 32mg / L. After the photocatalytic reaction for 6h, the COD in the waste liquid was 6mg / L, and the concentration of sulfate ions was 110mg / L.

[0055] Calculations show that the COD removal rate is 98.5%, and all the sulfur in sulfolane is converted into sulfate.

[0056] Comparative Example 1

[0057] The test method of this comparative example is the same as that of Example 1, except that: no photocatalyst is added to the waste liquid, and it is directly irradiated under visible light, specifically: a 300W xenon lamp pre-installed with a 400-800nm ​​filter is used to perform visible light catalytic treatment on the sulfolane waste liquid. The COD concentration of the sulfolane waste liquid used is 2573mg / L, and the sulfate concentration is 38.0mg / L. After 30min of adsorption, the COD concentration in the waste liquid is 2573mg / L, and the sulfate concentration is 38.0mg / L. After 6h of photocatalytic reaction, the COD in the waste liquid is 2548mg / L, and the concentration of sulfate ions is 32mg / L.

[0058] Calculations show that the COD removal rate is 1% and the sulfur in sulfolane is not converted into sulfate.

[0059] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0060] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0061] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for resource utilization of sulfolane waste liquid, characterized in that: The method comprises: mixing the sulfolane waste liquid with a photocatalyst and then sequentially performing a dark reaction and a photocatalytic reaction; wherein the photocatalyst is a multi-level porous silicon oxide / C3N4 composite photocatalyst.

2. The method according to claim 1, wherein: The multi-level porous silicon oxide / C3N4 composite photocatalyst comprises multi-level porous silicon oxide and C3N4 quantum dots doped in the multi-level porous silicon oxide; Based on the total weight of the multi-level porous silicon oxide / C3N4 composite photocatalyst, the weight percentage of the multi-level porous silicon oxide is 10% to 40%, and the weight percentage of the C3N4 quantum dots is 60% to 90%; The specific surface area of ​​the multi-level porous silicon oxide / C3N4 composite photocatalyst is 600-1000m 2 / g.

3. The method according to claim 1, wherein: Based on the volume of the sulfolane waste liquid, the added amount of the multi-level porous silicon oxide / C3N4 composite photocatalyst is 0.1-5 g / L.

4. The method according to claim 1, wherein: The COD in the sulfolane waste liquid is 20-3000 mg / L, the concentration of sulfolane is 10-1000 mg / L, and the concentration of sulfate is 0-100 mg / L.

5. The method according to claim 1, wherein: The conditions of the dark reaction include: light intensity of 0-0.1 mW / cm 2 The time is 10 to 60 minutes, preferably 20 to 40 minutes; the conditions of the photocatalytic reaction include: the light intensity is 20 to 80 mW / cm 2 The illumination time is 4 to 8 hours; the light source is a 300W xenon lamp pre-installed with a 400 to 800nm ​​filter.

6. The method according to claim 1, wherein: The preparation method of the multi-level porous silicon oxide / C3N4 composite photocatalyst comprises: S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution; S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution; S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution; S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining the third solid product.

7. The method according to claim 6, wherein: The mass ratio of the coal gasification fly ash to the alkali in the alkali solution is 1:(0.5-1.0); The alkali in the alkali solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkali solution is 10-30%; The concentration of silicon in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L.

8. The method according to claim 6, wherein: The mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10).

9. The method according to claim 6, wherein: The molar ratio of the surfactant to the first solution calculated as silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; The surfactant is at least one selected from the group consisting of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide and hexadecylpyridinium bromide, preferably hexadecyltrimethylammonium bromide.

10. The method according to claim 1, wherein: The microwave heating reaction conditions include: microwave heating temperature of 100-150°C and time of 10-50min; The hydrothermal crystallization conditions include: temperature of 50-150°C, preferably 100-120°C; time of 8-48h, preferably 16-32h; The calcination conditions include: a temperature of 400-700° C., preferably 500-600° C.; and a time of 1-8 hours, preferably 2-5 hours.

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