Application of xylan as dispersant in coal water slurry

Abstract

The application belongs to the field of biomass refining and fine chemicals, and particularly relates to application of xylan as dispersant in coal water slurry. The application specifically comprises: (1) dispersing xylan in water to obtain xylan water dispersion, and then performing physical shearing treatment to obtain xylan water colloidal dispersion system, namely the xylan dispersant; (2) mechanically uniformly mixing coal powder and the xylan water colloidal dispersion system to prepare coal water slurry. The application applies xylan as dispersant in coal water slurry, and has the advantages of degradability, green environmental protection, low cost, simple preparation process, mild preparation condition, high dispersing performance, excellent dispersing and viscosity reducing performance of coal water slurry, stability and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass refining and fine chemicals, and particularly relates to application of xylan as dispersant in coal water slurry. BACKGROUND

[0002] Xylan is one of the most important types of hemicellulose, widely exists in broad-leaved wood, oil tea fruit shell, bagasse, straw and other plant biomass, is a natural resource with abundant reserves and renewable, and has great application potential in emulsions, dispersants and other fine chemicals due to its natural surface activity. However, as the main consumer of the above plants, the pulp and paper industry, forestry harvesting and processing industry, still mainly utilizes the large amount of xylan rich in production waste as low-value energy combustion, and produces small molecule chemicals such as furfural and xylitol as an auxiliary approach, which seriously wastes xylan resources. The reason is that the high-value chemical conversion route of xylan usually needs harsh hydrolysis conditions or chemical derivatization means, and the process is complex, the cost is high, and the environmental pollution is serious, which limits the development of xylan-based high-value industrial chemicals.

[0003] Coal water slurry is a new type of clean coal-based liquid fuel made of coal, water and dispersant, which not only inherits the original physicochemical properties of coal and can be atomized and combusted, but also has good rheological property, thixotropy and stability like petroleum, and can be pumped and transported, which greatly improves the combustion efficiency. However, as a thermodynamically unstable system, coal water slurry is strongly dependent on the effective dispersion of hydrophobic coal powder in water by dispersant to ensure the rheological property and stability of the system. Therefore, it is crucial to select a suitable coal water slurry dispersant. At present, the coal water slurry dispersants widely used in the market are mainly classified into naphthalene sulfonate and polycarboxylic acid, both of which have the advantages of good dispersibility, good fluidity and strong viscosity reduction effect, but also have disadvantages such as poor slurry stability, narrow coal type adaptation range, non-renewable petroleum-based raw materials, strong environmental toxicity and the like. SUMMARY

[0004] The purpose of the present application is to solve the problems of low dispersant efficiency, poor stability, single coal type adaptation range, non-renewable petroleum-based raw materials and large environmental toxicity of the existing coal water slurry, and to provide the use of xylan as dispersant in the preparation of coal water slurry.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] The present application provides the use of xylan as dispersant in the preparation of coal water slurry.

[0007] The application is particularly: (1) the xylan is dispersed in water to obtain a xylan water dispersion, and then physical shearing treatment is performed to obtain a xylan water colloidal dispersion system, namely the xylan dispersant; (2) the coal powder is uniformly mixed with the xylan water colloidal dispersion system by mechanical mixing to prepare a coal water slurry, and the weight fractions of the components in the coal water slurry are as follows: coal powder (absolute dry mass) 50-60 parts, water 40-50 parts, and xylan 0.1-0.3 parts.

[0008] Preferably, the coal powder in step (2) includes (but is not limited to) one of lignite with poor pulpability, non-caking coal, long flame coal, and gas coal with easy pulpability, and 1 / 3 coking coal.

[0009] Preferably, the mechanical uniform mixing method in step (2) includes (but is not limited to) one of magnetic stirring, high-speed homogenization, and high-pressure homogenization; the unit volume power density of the high-speed homogenization and high-pressure homogenization treatment is 10-30 W / mL, and the time is 10-30 min; the rotation speed of the magnetic stirring treatment is 400-800 rpm, and the time is 1-10 min.

[0010] Preferably, the physical shearing treatment in step (1) is one of ultrasonic crushing and atmospheric homogenization; the power of the physical shearing treatment is 10-30 W / mL, and the time of the physical shearing treatment is 1-5 min.

[0011] The size regularity of the xylan is regulated by physical modification, so as to enhance the steric hindrance and hydrophilic and hydrophobic properties of the xylan-based dispersant, improve the adsorption degree on the surface of coal particles, further reduce the interfacial tension of the coal water slurry, and improve the stability and flowability of the coal water slurry.

[0012] Preferably, the weight average molecular weight of the xylan in step (1) is not less than 20,000, and the polydispersity coefficient is not higher than 3.0.

[0013] Preferably, the xylan in step (1) is prepared by the following steps: the agricultural and forestry biomass is crushed and dried, added into an alkali solution, subjected to a cooking reaction, filtered to obtain a filtrate, adjusted to a pH of 4.0-6.0, mixed with an alcohol organic solvent under stirring, precipitated, and dried to obtain the xylan.

[0014] More preferably, the agricultural and forestry biomass raw material is at least one of poplar, eucalyptus, birch, oil tea shell, and corn straw.

[0015] More preferably, the crushing is performed by a mechanical shearing or crushing method to crush the large particle raw material to a diameter of 12-25 mm.

[0016] More preferably, the alkali solution is a sodium hydroxide solution, and the concentration of the alkali solution is 4.00-8.00 wt%.

[0017] More preferably, the ratio of the dry mass of the agroforestry biomass raw material to the volume of the alkali solution is 1g:4mL to 1g:16mL.

[0018] More preferably, the cooking reaction is obtained by the following procedure: heating and holding; the heating is room temperature rotary heating to 115-155℃ at a heating rate of 2℃ / min; the holding is maintaining the temperature for 60-180min after reaching the specified heating temperature.

[0019] More preferably, the pH reagent used for adjusting the pH of the filtrate is an inorganic base and / or an inorganic acid, specifically sodium hydroxide and concentrated hydrochloric acid.

[0020] More preferably, the volume ratio of the filtrate with a pH of 4.0-6.0 to the alcoholic organic solvent is 1:3; the alcoholic organic solvent is at least one of ethanol, propanol and butanediol.

[0021] More preferably, after mixing the filtrate with the alcoholic organic solvent, it needs to be stationary for more than 6h.

[0022] The alkali extraction conditions are closely related to the removal degree of xylan molecular chains, and the means of secondary modification of xylan and the balance of hydrophilic and hydrophobic properties are also inseparable. By optimizing the conditions of alkali extraction, xylan with different chemical composition and molecular weight can be produced to control the network steric hindrance effect and hydrophilic-hydrophobic properties of xylan in water dispersion, and further, by modifying the size of xylan through suitable physical and mechanical means to achieve uniform and orderly arrangement, xylan can be simply and greenly endowed with more excellent hydrophilic-hydrophobic properties, so that the hydrophobic end is stably arranged on the surface of hydrophobic particles, and the hydrophilic end and the steric hindrance effect jointly reduce the surface tension of the particles to prevent particle association.

[0023] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0024] 1. In the present application, xylan is used as a dispersant in coal water slurry, compared with the commonly used petroleum-based coal water slurry dispersant, xylan derived from agroforestry biomass is renewable, and the extraction and physical modification process is green, non-toxic and harmless, and the excellent hydrophilic-hydrophobic properties can greatly reduce the viscosity of coal water slurry, improve the stability and fluidity of the slurry, and broaden the range of coal types suitable for dispersants, effectively dispersing medium-high rank coal powder (such as gas coal and 1 / 3 coking coal) which is easy to be slurried and low rank coal powder (such as lignite, non-caking coal and long flame coal) which is poor in slurryability.

[0025] 2、The present application realizes uniform and orderly size distribution of the xylan by physical and mechanical modification, has good water dispersibility and balanced hydrophilic and hydrophobic characteristics, so that the xylan can be well dispersed in water and stably adsorbed on the surface of hydrophobic coal particles to form steric hindrance, thereby preventing the agglomeration of coal particles and improving the flowability and stability of the coal water slurry as the dispersant.

[0026] 3、The present application applies the xylan as a dispersant in the coal water slurry, has the advantages of degradability, green environmental protection, low cost, simple preparation process, mild preparation conditions, high dispersing performance, excellent dispersion and viscosity reduction of the coal water slurry, stability and the like. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The rheological property diagrams of the coal water slurry without adding a dispersant and the coal water slurry mixed with different dispersants, wherein the coal water slurry mixed with the product of Example 2 refers to the coal water slurry prepared in Example 2, and the coal water slurry mixed with a commercial polycarboxylic dispersant refers to the coal water slurry prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] The present application will be further described in detail below in combination with examples and drawings, but the embodiments of the present application are not limited thereto. The raw materials involved in the present application can be directly purchased from the market. For the process parameters not specifically mentioned, the conventional techniques can be referred to.

[0029] Example 1

[0030] The eucalyptus wood is crushed to a diameter of 12-25 mm and then dried, 100 g of absolute dry raw material (water content less than 15%) is weighed, and a sodium hydroxide solution with a concentration of 4.00 wt% is mixed with the raw material in a rotary digester at a ratio of 1:4 (w:v, unit g / mL), and heated from room temperature (25℃) to 115℃ at a heating rate of 2℃ / min, and then kept for 60 min to complete the digestion reaction; after the reaction is completed, the reaction liquid is filtered and collected, and the pH is adjusted to 6 with hydrochloric acid, then stirred and added to anhydrous ethanol (the volume ratio of the mixed solution to ethanol is 1:3) to precipitate the xylan, and after standing for 6 h, the xylan is separated by centrifugation; the separated xylan is washed with a 70% ethanol solution for more than three times, and then placed in a ventilated place to volatilize ethanol, and then dried to obtain the xylan.

[0031] The xylan is dispersed in water to form a water suspension, and the xylan solution is continuously treated for more than 1 min under the condition of ice water bath using an ultrasonic probe at a power of 10 W / mL to obtain a xylan water colloidal dispersion system with uniform and stable size, i.e. the xylan dispersant.

[0032] The lignite powder is added into the xylan hydrocolloid dispersion system according to the proportion, and the water coal slurry is prepared by stirring at a speed of 600 rpm for 5 min in a magnetic stirrer at room temperature; the weight fractions of the components in the water coal slurry are as follows: lignite powder (absolute dry mass) 55 parts, water 44.8 parts, xylan 0.2 parts.

[0033] Example 2

[0034] The poplar powder is crushed to a diameter of 12-25 mm and then dried, 100 g of the absolute dry raw material (moisture content less than 15%) is weighed, and a sodium hydroxide solution with a concentration of 7.00 wt% is mixed with the raw material in a rotary digester at a ratio of 1:4 (w:v, unit g / mL), and heated from room temperature (25°C) to 135°C at a heating rate of 2°C / min, and then kept for 60 min to complete the digestion reaction; after the reaction is completed, the reaction liquid is filtered and collected, and the pH is adjusted to 6 with hydrochloric acid, then stirred and added to anhydrous propanol (the volume ratio of the mixed solution to propanol is 1:3) to precipitate xylan, and after standing for 6 h, the xylan is separated by centrifugation; the separated xylan is washed with a 70% propanol solution for more than three times, and then placed in a well-ventilated place to evaporate propanol, and then dried to obtain xylan.

[0035] The xylan is dispersed in water to form a water suspension, and a constant-pressure homogenizer is used to treat the xylan solution under the condition of ice water bath at a power of 15 W / mL for more than 3 min to obtain a xylan hydrocolloid dispersion system with uniform and stable size, i.e. the xylan dispersant.

[0036] The non-caking coal powder is added into the xylan hydrocolloid dispersion system according to the proportion, and the water coal slurry is prepared by mechanically mixing at a power of 20 W / mL for 20 min in a high-speed homogenizer at room temperature; the weight fractions of the components in the water coal slurry are as follows: non-caking coal powder (absolute dry mass) 55 parts, water 44.8 parts, xylan 0.2 parts.

[0037] Example 3

[0038] Birch is crushed to a diameter of 12-25 mm and dried, 100 g of absolute dry raw material (moisture content less than 15%) is weighed and mixed with a 7.00 wt% sodium hydroxide solution in a rotary digester at a ratio of 1:8 (w:v, unit g / mL) and heated to 115°C at a heating rate of 2°C / min from room temperature (25°C) and kept for 180 min to complete the digestion reaction; after the reaction is completed, the reaction solution is filtered and collected, and the pH is adjusted to 6 with hydrochloric acid, then stirred and added to butanediol (the volume ratio of the mixed solution to butanediol is 1:3) to precipitate xylan, and after standing for 6 h, xylan is separated by centrifugation; the separated xylan is washed with 70% butanediol solution for more than three times, and then placed in a ventilated place to evaporate butanediol, and then dried to obtain xylan.

[0039] The xylan is dispersed in water to form a water suspension, and an ultrasonic probe is used to treat the xylan solution continuously for more than 2 min at a power of 30 W / mL in an ice water bath to obtain a xylan water colloidal dispersion system, i.e. the xylan dispersant, which is uniform and stable in size.

[0040] 1 / 3 of the coking coal powder is added to the xylan water colloidal dispersion system in a proportion, and is uniformly mixed in a high-pressure homogenizer at room temperature at a power of 15 W / mL for 30 min to prepare a coal water slurry; the weight fractions of the components in the coal water slurry are as follows: coking coal powder (absolute dry mass) 55 parts, water 44.8 parts, xylan 0.2 parts.

[0041] Example 4

[0042] Oil tea fruit shell is crushed to a diameter of 12-25 mm and dried, 100 g of absolute dry raw material (moisture content less than 15%) is weighed and mixed with a 5.50 wt% sodium hydroxide solution in a rotary digester at a ratio of 1:12 (w:v, unit g / mL) and heated to 135°C at a heating rate of 2°C / min from room temperature (25°C) and kept for 60 min to complete the digestion reaction; after the reaction is completed, the reaction solution is filtered and collected, and the pH is adjusted to 6 with hydrochloric acid, then stirred and added to anhydrous ethanol (the volume ratio of the mixed solution to ethanol is 1:3) to precipitate xylan, and after standing for 6 h, xylan is separated by centrifugation; the separated xylan is washed with 70% ethanol solution for more than three times, and then placed in a ventilated place to evaporate ethanol, and then dried to obtain xylan.

[0043] The xylan is dispersed in water to form a water suspension, and an ultrasonic probe is used to treat the xylan solution continuously for more than 2 min at a power of 30 W / mL in an ice water bath to obtain a xylan water colloidal dispersion system, i.e. the xylan dispersant, which is uniform and stable in size.

[0044] According to the proportion, the gas coal powder is added into the xylan water colloidal dispersion system, and the water coal slurry is prepared by stirring at a speed of 800 rpm for 4 min under room temperature; the weight fractions of the components in the water coal slurry are as follows: gas coal powder (absolute dry mass) 55 parts, water 44.8 parts, xylan 0.2 parts.

[0045] Example 5

[0046] The corn straw is crushed to a diameter of 12-25 mm and then dried, 100 g of the absolute dry raw material (moisture content less than 15%) is mixed with a sodium hydroxide solution with a concentration of 8.00 wt% at a ratio of 1:16 (w:v, unit g / mL) in a rotary digester, and then heated from room temperature (25°C) to 155°C at a heating rate of 2°C / min and kept for 120 min to complete the digestion reaction; after the reaction is completed, the reaction liquid is collected by filtration, and then the pH is adjusted to 6 by adding hydrochloric acid, and then the xylan is precipitated by stirring and adding anhydrous ethanol (the volume ratio of the mixed solution to ethanol is 1:3), and then the xylan is separated by centrifugation after standing for 6 h; the separated xylan is washed with a 70% ethanol solution for more than three times, and then placed in a ventilated place to evaporate ethanol, and then dried to obtain the xylan.

[0047] The xylan is dispersed in water to form a water suspension, and the xylan solution is continuously treated for more than 2 min at a power of 25 W / mL using an ultrasonic probe in an ice water bath to obtain a relatively uniform and stable xylan water colloidal dispersion system, i.e. the xylan dispersant.

[0048] According to the proportion, the long flame coal powder is added into the xylan water colloidal dispersion system, and the water coal slurry is prepared by stirring at a speed of 400 rpm for 10 min under room temperature; the weight fractions of the components in the water coal slurry are as follows: long flame coal powder (absolute dry mass) 55 parts, water 44.8 parts, xylan 0.2 parts.

[0049] Comparative Example 1

[0050] The commercial polycarboxylic acid dispersant is dispersed in water to form a water suspension, and the above solution is continuously treated for more than 3 min at a power of 15 W / mL using a normal pressure homogenizer in an ice water bath to obtain a relatively uniform and stable commercial polycarboxylic acid dispersion system, i.e. the dispersant for Comparative Example 2.

[0051] The non-caking coal powder is added into a commercial polycarboxylic acid dispersing system according to a proportion, and a coal water slurry is prepared by placing the mixture in a high-speed homogenizer at room temperature for 20 min with a power of 20 W / mL; the weight fractions of the components in the coal water slurry are as follows: 55 parts of non-caking coal powder (absolute dry mass), 44.8 parts of water, and 0.2 parts of commercial polycarboxylic acid dispersant.

[0052] Table 1 shows the test results of the chemical components, molecular weight, and polydispersity coefficient of the products (xylan) prepared in the embodiments. As shown in the table, after the extraction conditions and physical and mechanical modification means are regulated, xylan with different chemical component proportions is obtained, so as to balance the hydrophilic-hydrophobic performance of the xylan as a whole, enhance the adhesion to the hydrophobic coal particle surface, and effectively disperse in water, which is beneficial to the preparation of coal water slurry with excellent dispersion stability; xylan with different molecular weights and molecular weight distributions is obtained, which is beneficial to the embodiments 1-5 to play a better steric hindrance effect as a coal water slurry dispersant, so as to improve the dispersion stability of the coal water slurry.

[0053] Table 1 shows the test results of the chemical components, molecular weight, and polydispersity coefficient of the products (xylan) prepared in the embodiments. As shown in the table, after the extraction conditions and physical and mechanical modification means are regulated, xylan with different chemical component proportions is obtained, so as to balance the hydrophilic-hydrophobic performance of the xylan as a whole, enhance the adhesion to the hydrophobic coal particle surface, and effectively disperse in water, which is beneficial to the preparation of coal water slurry with excellent dispersion stability; xylan with different molecular weights and molecular weight distributions is obtained, which is beneficial to the embodiments 1-5 to play a better steric hindrance effect as a coal water slurry dispersant, so as to improve the dispersion stability of the coal water slurry.

[0054]

[0055] Table 2 shows the application performance test results of the coal water slurries prepared in the embodiments 1-5. As shown in the table, when lignite, non-caking coal, long flame coal, gas coal, and 1 / 3 coking coal are selected, the concentration of the coal water slurry is 55wt%, and the concentration of the xylan dispersant is 0.20wt%, the xylan prepared in the embodiments 1-5 is used to prepare coal water slurry, and the viscosity of the coal water slurries prepared by the embodiments 1-5 is far lower than 1200 mPa·s except for the viscosity of the coal water slurry prepared by the embodiment 5, which meets the requirements of the national standard for coal water slurry and has A-level continuous flowability. After the slurries are placed for 24 hours, the products of the embodiments 1-5 all ensure excellent A-level stability.

[0056] Table 2 shows the application performance test results of the coal water slurries prepared in the embodiments 1-5. As shown in the table, when lignite, non-caking coal, long flame coal, gas coal, and 1 / 3 coking coal are selected, the concentration of the coal water slurry is 55wt%, and the concentration of the xylan dispersant is 0.20wt%, the xylan prepared in the embodiments 1-5 is used to prepare coal water slurry, and the viscosity of the coal water slurries prepared by the embodiments 1-5 is far lower than 1200 mPa·s except for the viscosity of the coal water slurry prepared by the embodiment 5, which meets the requirements of the national standard for coal water slurry and has A-level continuous flowability. After the slurries are placed for 24 hours, the products of the embodiments 1-5 all ensure excellent A-level stability.

[0057] *Flowability: A for continuous flow; B for intermittent flow; C for no flow.

[0058] *Stability: A for water separation amount accounting for ≤2% of the volume of the coal slurry; B for 2%< water separation amount accounting for ≤5% of the volume of the coal slurry; C for 5%< water separation amount accounting for ≤10% of the volume of the coal slurry; D for water separation amount accounting for >10% of the volume of the coal slurry

[0059] Figure 1Rheological property chart of the product of Example 2 of the present application. Rheological property is an important index affecting the transportation of coal water slurry. The relationship between the shear rate and shear stress of the slurry is fitted by using Herschel-Bulkley model, and the result of the fitting parameters can be used to judge the pros and cons of the rheological property of the slurry. As can be seen from the chart: after the apparent viscosity of the coal water slurry tends to be stable, compared with the coal water slurry without adding dispersant (containing 55 parts by mass of absolute dry non-sticky coal powder and 45 parts by mass of water), the coal water slurry mixed with the xylan prepared in Example 2 can effectively reduce the viscosity of the coal water slurry; compared with the coal water slurry mixed with the commercial polycarboxylic dispersant (Comparative Example 1), the viscosity-reducing and dispersing properties of the xylan prepared in Example 2 of the present application are better.

[0060] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. Use of xylan as a dispersant in the preparation of coal water slurry, characterized in that, The application specifically is: (1) dispersing xylan in water to obtain a xylan water dispersion, and then performing physical shearing treatment to obtain a xylan hydrocolloid dispersion system, namely a xylan dispersant; (2) mechanically uniformly mixing coal powder and the xylan hydrocolloid dispersion system to obtain a coal water slurry. The weight parts of the components in the coal water slurry are as follows: 50-60 parts of coal powder, 40-50 parts of water, and 0.1-0.3 parts of xylan, wherein the coal powder is calculated according to the absolute dry mass; the xylan has a weight average molecular weight of not less than 20,000 and a polydispersity coefficient of not higher than 3.

0.

2. Use according to claim 1, characterized in that, The coal powder in step (2) comprises one of lignite, non-caking coal, long flame coal, gas coal, and 1 / 3 coking coal.

3. Use according to claim 1, characterized in that, The mechanical uniform mixing mode in step (2) comprises one of magnetic stirring, high-speed homogenization, and high-pressure homogenization; the unit volume power density of high-speed homogenization and high-pressure homogenization is 10-30 W / mL, and the time is 10-30 min; the rotating speed of magnetic stirring is 400-800 rpm, and the time is 1-10 min.

4. Use according to claim 1, characterized in that, The physical shearing treatment in step (1) is one of ultrasonic crushing and atmospheric homogenization; the power of the physical shearing treatment is 10-30 W / mL, and the time of the physical shearing treatment is 1-5 min.

5. The use according to claim 1, characterized in that, The xylan in step (1) is prepared by the following steps: crushing and drying agroforestry biomass, adding alkali liquor, performing a cooking reaction, filtering to obtain a filtrate, adjusting the pH of the filtrate to 4.0-6.0, mixing the filtrate with an alcoholic organic solvent under stirring, taking the precipitate, and drying to obtain xylan.

6. Use according to claim 5, characterized in that, The agroforestry biomass is at least one of poplar wood, eucalyptus wood, birch wood, oil tea fruit shell, and corn straw; The crushing is a method of crushing large particle raw materials to a diameter of 12-25 mm by mechanical shearing or crushing.

7. Use according to claim 5, characterized in that, The alkali liquor is a sodium hydroxide solution, and the concentration of the alkali liquor is 4.00-8.00 wt%; The ratio of the absolute dry mass of the agroforestry biomass raw material to the volume of the alkali liquor is 1 g:4 mL-1 g:16 mL; The cooking reaction is obtained by the following procedures: heating and holding; the heating is rotary heating from room temperature to 115-155℃ at a heating rate of 2℃ / min; the holding is maintaining the specified heating temperature for 60-180 min after reaching the specified heating temperature.

8. Use according to claim 5, characterized in that, The pH reagent used for adjusting the pH of the filtrate is an inorganic base and / or an inorganic acid, the inorganic base is sodium hydroxide, and the inorganic acid is concentrated hydrochloric acid; The volume ratio of the filtrate with a pH of 4.0-6.0 to the alcoholic organic solvent is 1:3; the alcoholic organic solvent is at least one of ethanol, propanol, and butanediol; After mixing the filtrate with the alcoholic organic solvent, it needs to be left standing for more than 6 h.

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