WO2014000675A1 - Aeration sheet and method for preparing same - Google Patents

Description

 Aeration sheet and preparation method thereof

Technical field

 The invention belongs to the field of water treatment, and particularly relates to an aeration sheet and a preparation method thereof. Background technique

 In the water treatment aerobic process, a microporous aerator is often used to supply oxygen to the water to meet the oxygen demand of the aerobic process. At present, the microporous aerator used in sewage treatment uses a membrane type microporous aerator, wherein the aeration sheet generally has two kinds of rubber membranes, ceramics and corundum microporous aeration tablets. The rubber diaphragm is provided with a plurality of open and closed micropores. When ventilating, the pressure gas source enters the base of the aerator through the pipeline. Under the action of air pressure, the rubber diaphragm slightly bulges upward and expands the rubber membrane. The micropores on the sheet, the gas is supplied from the micropores to form small bubbles, and the dissolved oxygen is supplied to the sewage treatment tank for biochemical treatment; when the gas supply is stopped, the micropores on the rubber membrane are gradually closed, thereby preventing sewage The sludge is returned to the aerator. In practical applications, as time goes by, the rubber tends to age and harden, and the pore size of the micropores on the membrane gradually expands, causing the generated bubbles to become larger, and the performance of the automatic closure is also deteriorated. The sewage sludge will easily enter the aeration pipe and block the gas source pipe, which will affect the normal operation of the entire aerator. The ceramic and corundum microporous aerators are mainly made of corundum, high temperature solvent and adhesive, and are formed by pressing and high temperature sintering. They have the advantages of corrosion resistance, acid and alkali resistance, aging resistance and long service life. However, in order to prevent water from flowing back into the aerator, the porosity of the aeration sheet is small, the aeration effect is poor, and the fan resistance is large, and the electricity cost is high in the later stage. When the vehicle is stopped, the sewage easily enters the gas distribution pipe and is easily broken. Wait.

In order to solve the above problems, Chinese Patent No. CN1958464A discloses a quartz microporous aerator which uses quartz sand, a high temperature solvent and a binder as raw materials, and is uniformly mixed according to a certain ratio, and then pressed into a blank. Finally, it is calcined at a high temperature of 900-1300 degrees. The prepared aeration sheet compensates for the blank of the silicon aerator on the open field, and has the advantages of good aeration effect, high quality of sewage purification, strong corrosion resistance, strong acid and alkali, and long service life. However, the aeration sheet has the following disadvantages: 1. It is sintered at a high temperature by bonding with quartz sand and an adhesive. Cheng, its pore diameter is difficult to control. When applied, if the pore size of the aeration sheet is too large, the sewage is easy to enter the gas distribution pipeline. In this patent, in order to prevent sewage from entering the gas distribution pipeline, a one-way is specially set on the intake pipeline. Ventilation valve, which increases the cost of aeration system construction; and the pore size is too small, resulting in large fan resistance, poor aeration effect; 2. The aeration sheet needs to be calcined at 900-1300 degrees, the production process is complicated, production The cycle is longer, the energy consumption is higher, calcination generates a large amount of harmful gases, causing environmental pollution; and the porosity of the aeration sheet which is sintered at a high temperature is lowered, and the aeration effect is deteriorated. Summary of the invention

 (1) Technical problems to be solved

 The technical problem to be solved by the invention is that the aperture of the existing aeration sheet is difficult to control, resulting in poor aeration effect and easy entry of sewage into the gas distribution pipeline, thereby providing an aeration sheet with good aeration effect and difficulty in entering the pipeline. At the same time, a method for preparing an aeration sheet with low energy consumption and small environmental pollution is provided.

 (2) Technical plan

 In order to solve the above technical problems, the present invention provides an aeration sheet which is formed by bonding aggregate particles and a hydrophobic binder, and gas molecules capable of passing between adjacent aggregate particles and liquid water molecules are formed. Impervious pores.

 In the above aeration sheet, the pores formed between the adjacent aggregate particles have a pore diameter of 0.001 to 0.5 mm.

 In the above aeration sheet, the hydrophobic binder is from 1 to 8% by weight of the aggregate particles. In the above aeration sheet, the aggregate particles are one or a mixture of quartz sand, slag, ceramsite or glass microspheres; the aggregate particles have a particle diameter of 0.0065-2 mm.

 In the above aeration sheet, the hydrophobic binder is a fluorine-containing epoxy resin binder, a silicon-containing epoxy resin binder, a silicone binder, a polyurethane, a polyester resin, and a phenol resin. One or a mixture of several of them.

In the above aeration sheet, the aggregate particles are coated with a hydrophobic substance, and the hydrophobic substance is from 1 to 8% by weight of the aggregate particles. In the aeration sheet, the hydrophobic substance is a hydrophobic resin film coated on the aggregate particles, and the hydrophobic resin film is made of a hydrophobic epoxy resin, a phenol resin, a polyurethane resin, and a silicone resin. One or more of the formed films.

 The invention also discloses a method for preparing the above aeration sheet, comprising the following steps: a. mixing the aggregate particles with the hydrophobic binder, pouring into a mixer to stir evenly; b. coating the bone with the hydrophobic binder Pour particles into a molding die;

 c 5-120 ° C placed 1-48 hours solidification molding release to obtain the aeration sheet. Preferably, the aggregate particles are coated with a hydrophobic material prior to step a.

 The curing molding conditions described in the step c were allowed to stand at normal temperature for 24 hours.

 (3) Beneficial effects

 The aerated sheet provided by the above technical solution and the preparation method thereof have the following advantages compared with the prior art:

 (1) The aeration sheet of the present invention is formed by bonding aggregate particles and a hydrophobic binder, and since the hydrophobic binder itself has a function of repelling water, the aeration sheet is bonded to the conventional one. The aerated sheet bonded by the agent can be made permeable and impervious to water. After the operation is stopped, the sewage will not enter the aeration pipe, and there is no danger of clogging.

 (2) The aeration sheet of the present invention uses quartz sand, slag, ceramsite or glass microbeads as aggregate particles, and the aggregate particle size of the aeration sheet is between 0.0065 and 2 mm, and the hydrophobic binder accounts for bone. The mass percentage of the pellets is between 1% and 8%, which can ensure that the aerated sheet is impervious to water in the bottom of 4m; meanwhile, the true porosity of the aerated sheet of the present invention is measured by the test method of GB/T2997-2000. At 55-80%. At the same time, refer to "Aeration equipment oxygenation performance test device and experimental research" [J]. Journal of Qingdao Technological University, 2007,3 (28): 54-57 test method to test the aeration effect of the aeration sheet of the invention As shown in Table 1, the results of Table 1 show that the aeration sheet has lower resistance than the conventional sintered aeration sheet, the oxygenation ability is improved, and the oxygen utilization rate is improved, so that the aeration effect is better.

Among them, the technical parameters are: aerator diameter 215mm, thickness 15mm, water depth 4 meters; Table 1

 (3) The aeration sheet is made of a sintering-free preparation technique, and the production cost is low. Since it does not need to be sintered at a high temperature, the molding process is simple, the preparation cycle is short, the energy consumption is low, energy saving and environmental protection, and mass production is possible. Further, this preparation method avoids the problem that the porosity of the aeration sheet is lowered after the high-temperature sintering, and the aeration effect can be ensured. detailed description

 Specific embodiments of the present invention will be further described in detail below with reference to the embodiments. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

 Example 1

 The aeration sheet of the present invention comprises aggregate particles and a hydrophobic binder coated on the aggregate particles, and adjacent pores between the aggregate particles form pores through which gas molecules can pass and liquid water molecules are impermeable. The pore size of the pores is from 0.001 to 0.5 mm.

 The aggregate particles in this embodiment are a mixture of quartz sand and slag in a weight ratio of 5:1, the particle size of the quartz sand is 0.0065-1 mm, and the particle size of the slag is 0.016-2 mm. The hydrophobic binder is a bisphenol A-type saturated polyester resin, and the hydrophobic binder accounts for 1% by mass of the aggregate particles.

 The aeration sheet is produced by the following method:

 a. The aggregate particles and the polyester resin bisphenol A type saturated polyester resin are mixed at a weight ratio of 100:1, and then poured into a mixer to be uniformly stirred;

 b. The aggregate particles to which the hydrophobic binder is bonded are poured into a molding die; c is released after being solidified and molded at 5 ° C for 48 hours to obtain the aeration sheet. Example 2

This embodiment is basically the same as the aeration sheet structure of Embodiment 1, and the difference is: The aggregate particles of the aeration sheet are coated with a layer of hydrophobic polytetrafluoroethylene. The aggregate particles are a mixture of quartz sand and ceramsite in a weight ratio of 4:2, the quartz sand has a particle size of 0.65-2 mm, and the ceramsite has a particle size of 0.036-0.45 mm. The hydrophobic polytetrafluoroethylene is 8 wt% of the aggregate particles.

 The method of applying the hydrophobic polytetrafluoroethylene to the aggregate particles is:

1) heating the hydrophobic polytetrafluoroethylene to a molten state;

 2) when the aggregate particles are heated to 210 ° C, the hydrophobic polytetrafluoroethylene is added, and stirred and mixed for 30 seconds to uniformly disperse the hydrophobic polytetrafluoroethylene on the surface of the aggregate particles;

 3) adding a hexamethylenetetramine curing agent (0.015 wt% of the aggregate particles) to the mixture prepared above, stirring and kneading, and curing for 60 seconds;

 4) Add oxidized polyethylene wax lubricant (0.00wt% of aggregate granules) to the solidified mixture, stir evenly, cool, and sieve.

 The hydrophobic binder is a phenolic resin rosin modified phenolic resin, and the hydrophobic binder accounts for 8% by mass of the aggregate particles.

 The aeration sheet is produced by the following method:

 a. The aggregated particles coated with hydrophobic polytetrafluoroethylene and the hydrophobic binder are mixed at a weight ratio of 25:2, and then poured into a mixer to be uniformly stirred;

 b. Pour the aggregate particles bonded with the hydrophobic binder into a molding die; c, after being placed at room temperature for 24 hours, and then demolded to obtain the aerated sheet. Example 3

 In this embodiment, the aggregate particles constituting the aeration sheet are formed by mixing ceramsite and glass microbeads at a weight ratio of 2:1, and the ceramsite has a particle diameter of 0.075-0.6 mm. The beads have a particle size of 0.04 - 0.15 mm. The aeration sheet comprises aggregate particles and a hydrophobic binder disposed between the aggregate particles, and an aperture of the pores between the adjacent aggregate particles is

0.1-0.3mm.

Wherein the hydrophobic binder is a fluorine-containing epoxy resin binder 2,2-bisphenol hexafluoropropyl The bismuth glycidyl ether, the hydrophobic binder accounts for 4% by mass of the aggregate particles. The aeration sheet is produced by the following method:

 a. The aggregate particles and the hydrophobic binder are poured into the mixer after 25:1 and stirred uniformly; b. The aggregate particles bonded with the hydrophobic binder are poured into the molding die; c at 50 The aeration sheet was obtained by demolding at ° C for 10 hours after solidification molding. Example 4

 In this embodiment, the aggregate particles constituting the aeration sheet are coated with a hydrophobic phenolic resin film, and the aggregate particles are a mixture of quartz sand and glass microbeads in a weight ratio of 5:1, and the particle size of the quartz sand The particle size of the glass beads is 0.04 - 0.3 mm, and the particle size is 0.04 - 0.15 mm. The hydrophobic phenolic resin is 1 wt% of the aggregate particles. The hydrophobic phenolic resin is obtained by copolymerizing maleic anhydride with sodium vinyl sulfonate.

 The method of coating the phenolic resin on the aggregate particles is:

 1) heating the phenolic resin to a molten state;

 2) when the aggregate particles are heated to 220 ° C, the phenolic resin is added, and the mixture is stirred for 60 seconds to uniformly disperse the phenolic resin on the surface of the aggregate particles;

 3) adding an aliphatic amine curing agent (10% by weight of the aggregate particles) to the mixture prepared above, stirring and kneading, and curing for 120 seconds;

 4) Add the stearic acid amide lubricant (1.25 wt% of the aggregate particles) to the cured mixture, stir well, cool, and sieve.

 The hydrophobic binder is a phenolic resin rosin-modified phenolic resin, and the hydrophobic binder accounts for 5% by mass of the aggregate particles.

 The aeration sheet is produced by the following method:

 a. The phenolic resin-coated aggregate particles and the hydrophobic binder are mixed at a weight ratio of 20:1, and then poured into a mixer to be uniformly stirred;

 b. pouring the aggregate particles bonded with the hydrophobic binder into the molding die;

c The aerated sheet was obtained by demolding at 120 ° C for 1 hour after solidification molding. The size of the aggregate particles of the present invention cannot be selected at the time of screening and does not have to be unified One particle size; therefore, it is within the scope of the present invention that the particle size of the aggregate particles is, for example, 0.0085 mm, 0.01 mm, 0.05 mm, 0.2 mm, 0.4 mm, 1.5 mm, etc. within the above particle size range.

 As an alternative to the present invention, the hydrophobic binder may also be one of or a mixture of a silicone-containing epoxy resin binder, a silicone binder, and a polyurethane.

 The hydrophobic resin film coated on the aggregate particles may also be a film formed of one or more of a hydrophobic epoxy resin, a polyurethane resin, and a silicone resin. The hydrophobic substance may be 2 wt%, 2.5 wt%, 3 wt%, 6 wt%, or 7 wt% of the aggregate particles.

 Preferably, the hydrophobic epoxy resin is a glycidyl ether epoxy resin, a glycidyl ester epoxy resin, a glycidylamine epoxy resin, a linear aliphatic epoxy resin, an alicyclic ring. Oxygen resin, polysulfide rubber modified epoxy resin, polyamide resin modified epoxy resin, polyvinyl alcohol tert-butylaldehyde modified epoxy resin, nitrile rubber modified epoxy resin, phenolic resin modified epoxy resin, Polyester resin modified epoxy resin, urethane aldehyde melamine resin modified epoxy resin, furfural resin modified epoxy resin, vinyl resin modified epoxy resin, isocyanate modified epoxy resin or silicone resin modified epoxy resin One or more of the hydrophobic phenolic resins are one or more of a xylene modified phenolic resin, an epoxy resin modified phenolic resin or a silicone modified phenolic resin.

 Further, the hydrophobic resin as described above can be obtained by modification by the following method, and the specific modification method is:

 An epoxy resin such as phthalic anhydride or maleic anhydride is copolymerized with an oil-soluble monomer: decyl acrylate, decyl methacrylate, ethacrylic acid, acetic acid Vinyl ester, allyl acetate, sodium vinyl sulfonate, methyl vinyl ether, methyl allyl ether, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, Any of diethylaminopropyl acrylate, dimethylaminobutyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

Alternatively, the epoxy resin can be modified to form a graft polymer; a hydrophilic group of the epoxy resin, such as a hydroxyl group, is reacted with a hydrophobic functional monomer to join them; Hydrophobic functional monomers are: Benzene oxime, decyl benzaldehyde (a large class), the reaction of hydroxyl groups with aldehyde groups.

 Alternatively, the epoxy resin may be subjected to a substitution reaction, and under a catalytic reaction of light, chlorine is used to participate in the substitution reaction, and a halogen is attached to the epoxy resin to improve hydrophobic properties.

 Further, a curing agent may be added to the hydrophobic resin film, and different curing agents may be added to different resins, wherein the curing agent is selected as follows:

 For glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidylamine epoxy resin, linear aliphatic epoxy resin, alicyclic epoxy resin, polysulfide rubber modified epoxy resin , polyamide resin modified epoxy resin, polyvinyl alcohol tert-butyraldehyde modified epoxy resin, nitrile rubber modified epoxy resin, phenolic resin modified epoxy resin, polyester resin modified epoxy resin, urine aldehyde Melamine resin modified epoxy resin, furfural resin modified epoxy resin, vinyl resin modified epoxy resin, isocyanate modified epoxy resin or silicone resin modified epoxy resin, preferred curing agent is fatty amine, alicyclic ring Any one or more of an amine, an aromatic amine, a polyamide, an acid anhydride, and a tertiary amine;

 For a xylene modified phenolic resin, an epoxy resin modified phenolic resin or a silicone modified phenolic resin, a preferred curing agent is hexamethylenetetramine;

 For the silicone resin, a preferred curing agent is any one or more of dibutyl dilaurate or N, N, Ν', N'-tetramethyl phosphonium salt;

 For hydrophobic polyurethane resins, the curing agent is an adduct of TDI and ruthenium, a prepolymer of TDI and a hydroxyl group-containing component, and a one-component moisture curing agent, a trimer of TDI.

 For unsaturated polyesters (polymers of terephthalic acid and ethylene glycol), the curing agent added at room temperature is ketone peroxide and cobalt citrate; the curing agent added during heating is tert-butyl peroxybenzoate One or more of an ester, a peroxydicarbonate, a dimercapto peroxide, a t-hexyl peroxyoctanoate, and a diester of peroxydicarbonate.

Moreover, the hydrophobic substance may also be any one or a combination of polytetrafluoroethylene, vegetable oil, silicon copper, siloxane, hydrocarbon, and copolymerized polyvinylidene chloride. Preferably, the hydrocarbon comprises paraffin, kerosene, diesel, crude oil, petroleum distillate, solvent oil and aliphatic solution. Any one or combination of agents.

 Wherein the hydrophobic substance is coated on the aggregate particles, and the method of applying the hydrophobic substance to the aggregate particles is spraying, impregnating or soaking aggregate particles on a hydrophobic substance. Chemically coating the aggregate particles in the liquid solution; or coating the film sheet with the hydrophobic material into the aggregate particles; or placing the heated aggregate particles in the hydrophobic material, melting the hydrophobic material to the bone The particles are coated; or the hydrophobic material is applied to the aggregate particles by electroplating, plasma spraying, sputtering, fluidization, and powder coating.

 It is apparent that the above-described embodiments are merely illustrative of the examples and are not intended to limit the embodiments. Other variations or modifications of the various forms may be made by those skilled in the art in light of the above description. There is no need and no way to exhaust all of the implementations. Obvious changes or variations resulting therefrom are still within the scope of protection created by the present invention. Industrial applicability

 The invention provides an aeration sheet and a preparation method thereof, which are formed by bonding aggregate particles and a hydrophobic binder, and gas molecules formed between adjacent aggregate particles can pass through and liquid water molecules cannot penetrate. Through the pores. The pore diameter of the pore formed between the adjacent aggregate particles is

0.001-0.5mm. The hydrophobic binder is from 1 to 8% by weight of the aggregate particles. The aggregate particles are one or a mixture of several of quartz sand, slag, ceramsite or glass microbeads. The aggregate particles have a particle diameter of 0.0065 to 2 mm. The hydrophobic binder is one or a combination of a fluorine-containing epoxy resin binder, a silicon-containing epoxy resin binder, a silicone binder, a polyurethane, a polyester resin, and a phenol resin. mixture. The aggregate particles are coated with a hydrophobic substance, and the hydrophobic substance is from 1 to 8% by weight of the aggregate particles. The hydrophobic substance is a hydrophobic resin film coated on the aggregate particles, and the hydrophobic resin film is one or more of a hydrophobic epoxy resin, a phenol resin, a polyurethane resin, and a silicone resin. a formed film. The aeration sheet provided by the invention has the function of repelling water due to the hydrophobic binder itself, and the aeration sheet can realize the function of permeable and watertight compared with the conventional aerated sheet of the ordinary adhesive, stopping After the operation, the sewage will not enter the aeration pipeline, there is no blockage The risk of plugging; the aerated sheet is made of quartz sand, slag, ceramsite or glass microbeads as aggregate particles, wherein the particle size of the aggregate particles is between 0.0065 and 2 mm, and the hydrophobic binder accounts for aggregate particles. The mass percentage is between 1-8%, which can ensure that the aeration sheet is impervious to water in the 4m water bottom; the true porosity of the aeration sheet is controlled at 55-80%; the aeration sheet is compared with the ordinary sintered aeration. The resistance of the sheet is lowered, the oxygenation capacity is increased, and the oxygen utilization rate is increased, so the aeration effect is better. The aeration sheet provided by the invention is applied to the field of water treatment, the aeration sheet has the property of being breathable and impervious to water, and can ensure watertightness in the bottom of 4 m; the true porosity can be controlled within the range of 55-80%; Low, high oxygenation capacity, high oxygen utilization rate, good aeration effect, and strong practicality. At the same time, the present invention also provides a method for preparing an aeration sheet, comprising the following steps: a. mixing the aggregate particles with a hydrophobic binder and pouring it into a mixer to stir evenly; b. coating the hydrophobic binder The aggregate particles are poured into a molding die; c. The aeration sheet is obtained by placing the molding at a temperature of 5-120 ° C for 1-48 hours. Preferably, the aggregate particles are coated with a hydrophobic substance prior to step a. The curing molding conditions described in the step c were allowed to stand at room temperature for 24 hours. The preparation method of the aeration sheet provided by the invention adopts the technology of no-sintering preparation, and the production cost is low; since the high-temperature sintering is not required, the molding process is simple, the preparation period is short, the energy consumption is low, energy saving and environmental protection, and large-scale Production; and, the preparation method avoids the problem of lowering the porosity of the aeration sheet after high-temperature sintering, and can ensure the aeration effect. The preparation method of the aeration sheet provided by the invention is applied to the field of water treatment, the preparation method has the advantages of low production cost, simple molding process, short preparation period, low energy consumption, energy saving and environmental protection, and avoids aeration sheet after high temperature sintering The problem of reduced porosity can ensure aeration effect and can be produced on a large scale.

Claims

Right, profit, need to ask for books 11. One type of exposed aerated gas sheet, whose characteristic features are:  The aerated gas sheet is formed by adhering and bonding the particles of the bone aggregate material and the water-binding adhesive agent, and adjacent to each other. The intergranular shape between the particles of the bone aggregate material forms a pore space gap in which the gas gas molecules can pass through and the liquid water state water molecules cannot pass through. . .  22. The exposed air-gas sheet described in the root claim according to the rights and interests of the claim 11, the special features of which are:  The pore diameter of the pore gap formed by the intergranular particles of the adjacent adjacent bone aggregate particles is 00..000011--00..55 mmmm. .  33. According to the rights and interests of the claim, the exposed air-gas sheets described in 22, the special features are as follows:  The hydrophobic water-binding adhesive agent is ll--88 wwtt%% of the granules of the bone aggregate. .  44. The exposed air-conditioning sheet according to any one of the preceding claims, wherein the characteristic is characterized by: The granules of the granules are one of a kind of stone quartz sand, a slag slag, a terracotta granule or a glass slab microbead or a mixture of several kinds thereof The granule diameter of the granules of the bone aggregate material is 00..00006655--22 mmmm. .  55. The exposed air-conditioning sheet according to any one of the items 11-44 according to the claim of the right of claim, wherein the characteristic is characterized by: The water-water adhesive bonding agent is a fluorine-containing fluorine-containing epoxy resin resin grease bonding agent, a silicon-containing silicon ring epoxy resin resin grease bonding agent, and organic One of a silicone-silicone bonding agent, a polyurethane resin, a polyester resin resin, and a phenolic phenolic resin resin, or several of them Mixed mixture. .  66. The exposed air-conditioning sheet according to any one of the items 11-55 according to the claim of the right of claim, wherein the characteristic is characterized by: The granules of the material particles are coated with a hydrophobic and water-repellent material substance, and the hydrophobic and water-repellent material substance is ll- of the granules of the bone aggregate material. -88wwtt%%. .  77. According to the rights and interests of the claim, the exposed air-gas sheet described in 66, the special features are as follows: The hydrophobic and hydrophobic aqueous substance substance described above is a hydrophobic and hydrophobic aqueous resin resin film which is coated on the particles of the bone aggregate material, as described above. The hydrophobic aqueous resin resin film is composed of a hydrophobic aqueous epoxy resin resin, a phenolic phenolic resin resin, a polyurethane resin resin, and a silicon tree.

 88. A method for preparing a preparation for the preparation of a right to obtain an air-conditioning sheet according to any one of the items 11-77, wherein the characteristic features are included in the method. The following steps:  a. Mix the aggregate granules with the hydrophobic binder and pour into the mixer to stir evenly; b. pouring the aggregate particles coated with the hydrophobic binder into the forming mold; c. The aeration sheet can be obtained by placing the mold at 5-120 ° C for 1-48 hours. 9. A method of preparing an aerated sheet according to claim 8, wherein: said aggregate particles are coated with a hydrophobic substance prior to step a.  The method for producing an aeration sheet according to claim 8 or 9, wherein the curing molding conditions described in the step c are carried out at room temperature for 24 hours.