Low-temperature active oxygen degerming explosive salt composition and preparation method thereof

Abstract

The invention relates to a low-temperature active oxygen degerming explosive salt composition and a preparation method thereof. The low-temperature active oxygen degerming explosion salt composition is prepared from the following raw materials in percentage by mass: 60 to 95 percent of an oxidizing agent, 2 to 20 percent of a surfactant, 1 to 10 percent of a modified composite oxide catalyst, 1 to 20 percent of basic salt and 0.1 to 10 percent of an auxiliary agent, wherein the modified composite oxide catalyst is a cerium-iron-manganese composite oxide catalyst. According to the invention, ferric salt, manganese salt and cerium salt are adopted as raw materials to prepare the cerium-iron-manganese composite oxide as the modified composite oxide catalyst, and the cerium-iron-manganese composite oxide catalyst has good catalytic activity and can still efficiently catalyze and decompose sodium percarbonate and promote the generation of active oxygen substances such as hydrogen peroxide at a relatively low temperature; the degradation capability on organic pollutants and the killing effect on microorganisms are enhanced, and the requirements of consumers on low-temperature cleaning and degerming are met.

Description

Technical Field

[0001] The present invention relates to the technical field of detergents, and particularly to a low-temperature active oxygen sterilizing explosion salt composition and a preparation method thereof. Background Art

[0002] With the improvement of people's living quality, the requirements for clothing and household cleaning are no longer limited to removing stains, but also expect to efficiently sterilize at low temperatures while protecting fabrics.

[0003] Traditional cleaning products, such as soaps and washing powders, often have unsatisfactory cleaning effects on some stubborn stains. In a low-temperature environment, their cleaning and sterilizing effects are even worse. Moreover, some products that require high temperatures to achieve the best effects may also damage clothes. Therefore, there is an urgent need for a cleaning product that can more efficiently remove various stains, and at the same time can efficiently sterilize and protect fabrics at low temperatures. Due to the continuous growth of people's demands for efficient cleaning, low-temperature washing, and safe sterilization, low-temperature active oxygen sterilizing explosion salt products have emerged. Low-temperature active oxygen sterilizing explosion salts can exert powerful cleaning and disinfection functions at low temperatures, ensuring the hygiene of the living environment, and are new hot products that conform to the market development trend.

[0004] Explosion salts mainly composed of sodium percarbonate can rapidly decompose into sodium carbonate and hydrogen peroxide when encountering water, and the decomposition of hydrogen peroxide will release active oxygen, thereby generating powerful cleaning and sterilizing capabilities. For example, a tea scale cleaner and its preparation method disclosed in Chinese Patent CN113789226A. This technical solution coordinately exerts excellent tea scale removal ability through the scientific compatibility of sodium tripolyphosphate, sodium bicarbonate, chelating agent, wetting agent, surfactant, oxidant, and auxiliary agent. However, this tea scale cleaner needs to be dissolved in 35°C hot water and diluted into a cleaning solution to play its role. How to develop a product that can improve the dissolution rate and degree of sodium percarbonate in low-temperature water, so that the explosion salt can quickly dissolve and release active ingredients at a lower temperature below 30°C is a problem faced by this field.

[0005] Therefore, there is an urgent need to develop a new technical solution to solve the deficiencies in the prior art and meet the development needs of the current market. Summary of the Invention

[0006] Based on this, the present invention provides a low-temperature active oxygen sterilizing explosion salt composition and a preparation method thereof. The present invention uses iron salt, manganese salt, and cerium salt as raw materials to prepare cerium-iron-manganese composite oxide as a modified composite oxide catalyst, which has good catalytic activity and can still efficiently catalyze the decomposition of sodium percarbonate at a lower temperature, promoting the generation of active oxygen substances such as hydrogen peroxide, enhancing the degradation ability of organic pollutants and the killing effect on microorganisms, and meeting consumers' needs for low-temperature cleaning and sterilization.

[0007] An object of the present invention is to provide a low-temperature activated oxygen sterilizing explosion salt composition, and the raw materials of the low-temperature activated oxygen sterilizing explosion salt composition include components with the following mass fractions:

[0008] Oxidant 60-95%

[0009]

[0010] Among them,

[0011] The modified composite oxide catalyst is a cerium-iron-manganese composite oxide catalyst.

[0012] The surface of the cerium-iron-manganese composite oxide catalyst of the present invention has abundant active sites, which can adsorb sodium percarbonate molecules and enrich them on the surface of the catalyst. In the catalyst, iron and manganese elements exist in various oxidation states of Fe 2+ , Fe 3+ , Mn 2+ , Mn 3+ , Mn 4+ , and these variable-valence metal ions can interact with the peroxy bond in sodium percarbonate and promote the cleavage of the peroxy bond through electron transfer, thereby accelerating the decomposition of sodium percarbonate; at the same time, the introduced cerium element in the present invention is beneficial to optimizing the electronic structure, surface properties and crystal structure of the catalyst, can produce a synergistic effect with iron and manganese, further improve the catalytic performance of the catalyst for sodium percarbonate, realize the efficient catalytic decomposition of sodium percarbonate, and accelerate the release process of hydrogen peroxide.

[0013] The hydrogen peroxide generated by the decomposition of sodium percarbonate can further react with the surface active sites of the cerium-iron-manganese composite oxide catalyst, undergo heterolytic cleavage or homolytic cleavage, and generate active oxygen species such as strongly oxidizing hydroxyl radicals (·OH) and superoxide anions (O2 ˉ ). Among them, oxidizing ions such as trivalent iron on the surface of the catalyst can react with hydrogen peroxide to generate Fe 2+ and ·OH, and at the same time Fe 2+ can be re-oxidized to Fe 3+ by other oxidizing substances to form a redox cycle; at the same time, under the combined action of cerium, iron and manganese, the concentration and mobility of active oxygen species on the surface of the catalyst are also improved, promoting the catalytic effect, thereby continuously activating hydrogen peroxide and continuously generating a large amount of active oxygen species such as ·OH.

[0014] In the catalytic oxidation process, reactive oxygen species such as ·OH can attack the chemical bonds in organic pollutant molecules, gradually oxidize and decompose them into harmless substances such as carbon dioxide and water, and enhance the degradation ability of dirt and the killing ability of bacteria by oxidizing various organic pollutants and bacteria without selectivity. Thus, under the cyclic reaction and synergistic action of various substances such as the modified composite oxide catalyst and percarbonate, the explosion salt composition of the present invention can also dissolve quickly and exert the functions of sterilization and decontamination at low temperatures.

[0015] Further, the oxidant is sodium percarbonate; the surfactant is selected from one or more of solid or powder anionic surfactants and solid or powder nonionic surfactants.

[0016] Further, the anionic surfactant is selected from one or more of sulfonates, sulfate esters, phosphates, and amino acids, and the nonionic surfactant is selected from one or more of polyoxyethylene ethers and polyol fatty acid esters.

[0017] Preferably, the anionic surfactant is selected from one or more of sodium alkylbenzene sulfonate (LAS), α-olefin sulfonate (AOS), sodium dodecyl sulfate (K12), and sodium lauroyl glycinate, and the nonionic surfactant is selected from one or more of fatty alcohol polyoxyethylene ether, fatty acid methyl ester polyoxyethylene ether, and alkylphenol polyoxyethylene ether.

[0018] Further, the basic salt is selected from at least one or more of silicates, sulfates, bicarbonates, carbonates, and citrates.

[0019] Further, the auxiliary agent is selected from one or more of preservatives, pigments, flavors, enzyme preparations, defoamers, and corrosion inhibitors.

[0020] Another object of the present invention is to provide a preparation method of the above-mentioned low-temperature active oxygen sterilization explosion salt composition, and the preparation method of the low-temperature active oxygen sterilization explosion salt composition includes the following steps:

[0021] S1. Dissolve iron salt, manganese salt, and cerium salt in a solvent respectively, and then mix them evenly to obtain a mixed metal salt solution;

[0022] S2. Stir and add a precipitant to the mixed metal salt solution, and adjust the pH value and temperature for precipitation;

[0023] S3. Let the precipitate stand and age in the mother liquor;

[0024] S4. Filter and wash the precipitate;

[0025] S5. Dry the washed precipitate, and then calcine it to obtain a modified composite oxide catalyst;

[0026] S6. Mix the modified composite oxide catalyst and other components evenly to obtain a low-temperature active oxygen sterilizing explosion salt composition.

[0027] Furthermore, the preparation method of the low-temperature active oxygen sterilizing explosion salt composition includes the following steps:

[0028] S1. Accurately weigh a certain amount of iron salt (iron nitrate), manganese salt (manganese nitrate), and modifier salt (cerium nitrate), dissolve them separately in an appropriate amount of deionized water, and then mix evenly to prepare a mixed metal salt solution with a certain concentration.

[0029] S2. While stirring continuously, slowly drop the precipitant (sodium hydroxide solution) into the mixed metal salt solution, and control the pH value and reaction temperature of the solution to co-precipitate the metal ions.

[0030] S3. After the precipitation is completed, let the precipitate stand and age in the mother liquor for a period of time to make the precipitate structure more complete and the crystal grains grow more perfectly.

[0031] S4. Filter with filter paper or filter membrane to separate the precipitate, and wash it with deionized water multiple times.

[0032] S5. Dry the washed precipitate in an oven for several hours to remove moisture, and then transfer it to a muffle furnace for calcination to decompose the hydroxide and convert it into a modified composite oxide catalyst.

[0033] S6. Mix the modified composite oxide catalyst and other components evenly to obtain a low-temperature active oxygen sterilizing explosion salt composition.

[0034] Furthermore, in step S1, in the mixed metal salt solution, the molar ratio of iron ions, manganese ions, and cerium ions is (2 - 3):(2 - 3):1.

[0035] Furthermore, in step S2, the pH value is 8 - 10, and the temperature is 50 - 70 °C.

[0036] Furthermore, in step S3, the standing and aging time is 12 - 24 h.

[0037] Furthermore, in step S5, the calcination temperature is 400 - 600 °C, and the time is 2 - 4 h.

[0038] The present invention has the following beneficial effects:

[0039] The present invention provides a low-temperature activated oxygen sterilizing explosion salt composition, whose main components include oxidants, modified composite oxide catalysts, surfactants and other components. The modified composite oxide catalyst introduces cerium metal into iron and manganese-based catalysts, optimizing the electronic structure and surface activity of the composite catalyst, integrating the advantages of different metals, and realizing the efficient catalytic decomposition of sodium percarbonate through various action mechanisms such as adsorption on surface active sites, electron transfer and promotion of redox cycles, participation of lattice oxygen in reactions, and reduction of reaction activation energy. After compounding the catalyst with components such as oxidants and surfactants, the decontamination and sterilization effects of the explosion salt product at low temperatures are effectively improved, solving the defects existing in the prior art, and having broad application prospects in the fields of cleaners and detergents.

[0040] Meanwhile, the modified composite oxide catalyst of the present invention has good reusability and can be recycled multiple times during the production and use of explosion salts, reducing costs and improving economic benefits. Specific Embodiments

[0041] In order to more clearly illustrate the technical solutions of the present invention, the following examples are listed. The raw materials, reactions and post-treatment means appearing in the examples are all common raw materials on the market and technical means well-known to those skilled in the art, unless otherwise specified.

[0042] The terms "preferred", "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain cases. However, in the same or other cases, other embodiments may also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present invention.

[0043] It should be understood that, unless in any operating example or otherwise indicated, all numbers representing the amounts of ingredients used in the specification and claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and appended claims are approximate values that vary depending on the desired properties to be obtained by the present invention.

[0044] The following raw materials are used in the embodiments of the present invention:

[0045] Sodium α-olefin sulfonate, a surfactant, purchased from Hunan Lichen Aowei Industry Co., Ltd.

[0046] TAED, tetraacetylethylenediamine, purchased from Zhejiang Kingnet Network Co., Ltd.

[0047] The amylase model is Stainzyme Plus Evity 24T, and the protease model is BLAZE EVITY 100T, which are purchased from Novozymes Enzyme Preparation Company.

[0048] The components and mass fractions of the low-temperature ozone sterilization explosion salt compositions of Examples 1-3 are shown in Table 1.

[0049] Table 1 Components and mass fractions of Examples 1-3

[0050]

[0051]

[0052] The preparation method of the low-temperature ozone sterilization explosion salt compositions of Examples 1-3 includes the following steps:

[0053] S1. Dissolve 1.07 g of iron nitrate, 0.75 g of manganese nitrate, and 0.43 g of cerium nitrate (molar ratio 3:3:1) in 20 mL of deionized water respectively to obtain an iron salt solution, a manganese salt solution, and a cerium salt solution. Then mix the iron salt solution, the manganese salt solution, and the cerium salt solution evenly and make up the volume to 100 mL to obtain a mixed metal salt solution with a total concentration of iron, manganese, and cerium ions of 0.1 mol / L;

[0054] S2. While stirring continuously, slowly dropwise add a sodium hydroxide solution (concentration 1 mol / L) to the mixed metal salt solution, adjust the pH value to 8.5, and the temperature to 70 °C to obtain a mixed precipitate of iron, manganese, and cerium hydroxides;

[0055] S3. Let the precipitate stand and age in the mother liquor for 24 h;

[0056] S4. After filtering and separating the precipitate, wash it with deionized water;

[0057] S5. Dry the washed precipitate at 120 °C for 3 h, then transfer it to a muffle furnace and calcine it at 500 °C for 3 h to obtain a modified composite oxide catalyst;

[0058] S6. According to the above mass fractions, mix the modified composite oxide catalyst and other components evenly to obtain a low-temperature ozone sterilization explosion salt composition.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that steps S1-S5 are deleted, and the modified composite oxide catalyst is replaced with manganese dioxide of equal mass, and other components and the preparation method are the same as those of Example 1.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that in step S1, cerium nitrate is not added, and other components and preparation methods are the same as those in Example 1.

[0063] Test Example 1

[0064] Explosion salt active oxygen test

[0065] Peroxides in the detergent will produce hydrogen peroxide in the aqueous solution. Hydrogen peroxide and potassium permanganate undergo an oxidation-reduction reaction in an acidic solution, releasing oxygen. After the titration is completed, the added potassium permanganate will make the solution remain faintly pink to determine the end point.

[0066] After thoroughly mixing the explosion salt sample with a weighing spoon, take a sample from the bottom of the explosion salt, weigh 10 g of the sample (accurate to 0.001 g), record the sample weight m, transfer it to a 2000 mL beaker, then fill a 1000 mL single-scale volumetric flask with water at 23°C ± 1°C to the scale and add it to the sample. Stir vigorously with a magnetic stirrer for 2 min (with the vortex approaching the bottom of the beaker) to dissolve the sample. There may be a small amount of insoluble catalysts, TAED, etc. in the solution, which do not need to be removed. Pipette 50 mL of the sample solution into a conical flask, add 25 mL of sulfuric acid solution (sulfuric acid solution with c(1 / 2H2SO4) = 5 mol / L), and titrate with a standard titration solution of c(1 / 5KMnO4) = 0.1 mol / L until it turns faintly pink, and the end point is when it does not fade for at least 15 s. Record the volume V of the potassium permanganate standard solution consumed.

[0067] The active oxygen content is calculated as mass fraction X, and the value is expressed in %: X = (c * V * 16) / m;

[0068] Where: c - the accurate concentration of the potassium permanganate standard solution c(1 / 5KMnO4) = 0.1 mol / L, in mol / L; V - the volume of the potassium permanganate standard solution consumed in the determination, in mL; m - the mass of the sample, in g.

[0069] The test results are shown in Table 2.

[0070] Table 2 Test results of active oxygen content

[0071]

[0072] It can be concluded from Table 2 that the explosion salt compositions of Examples 1 - 3, with a specific modified composite oxide catalyst as a component, have excellent effects on the release of active oxygen under low-temperature conditions, superior to Comparative Examples 1 and 2 with replaced modified catalysts, and with the increase in the content of the modified catalyst, the release effect of active oxygen is better.

[0073] Test Example 2

[0074] Explosion Salt Detergency Test

[0075] Soiled Cloth: International soiled cloth (commercially available, cloth numbers are shown in Table 3); Washing machine model specification: white FCY10R4W.

[0076] Preparation of Soiled Cloth: Cut the required international soiled cloth into small cloth pieces of 6 cm x 6 cm. For each group of tests, 2 pieces of each type of stain are needed and numbered in sequence.

[0077] Whiteness Measurement: Stack the same type of soiled cloth test pieces and use a fluorescence whiteness meter to read the whiteness values before and after washing one by one at 457 nm. For the pre-wash whiteness, take two points on each side (front and back) of the test piece to measure the whiteness value, and take the average of the four measurements as the pre-wash whiteness of the test piece; for the post-wash whiteness, measure the whiteness value in the same way, and take the average of the four measurements as the post-wash whiteness of the test piece.

[0078] Cut the national standard soiled cloth JB-00 into 35 cm x 60 cm as the base cloth (the size of the base cloth can be adjusted according to the number and arrangement of the test pieces). Nail the cut soiled cloth pieces to the base cloth with a cloth nailing machine. The washing machine is pre-cleaned by self-cleaning the barrel, and prepare accompanying laundry (including laboratory coats, shirts and towels) with a weight of 2 kg to ensure that the weight of the accompanying laundry is the same for each group of experiments. Take a piece of polyester cloth with stains nailed on it and the accompanying laundry and put them into the drum washing machine. Before washing, control the washing water temperature at 20 °C and the water hardness at 250 ppm (containing 0.167 g of anhydrous calcium chloride AR and 0.2037 g of magnesium chloride hexahydrate AR per liter of water). Put 20 g of explosion salt into the washing machine for each group of experiments and wash in the cotton clothing mode. After the washing process is over, take out the test fabric from the washing machine, flatten all kinds of soiled cloth, place it in a cool and dark place to dry. After drying the washed small soiled cloth, remove it from the polyester cloth, iron it with an iron, and then sort and arrange it to measure the post-wash whiteness value.

[0079] Result Evaluation:

[0080] Calculation of Detergency Value R: R = (Soiled cloth Yt - Soiled cloth Yo) / (White cloth Yw - Soiled cloth Yo) * 100%;

[0081] Where the white cloth is: national standard soiled cloth, cloth number CN-11;

[0082] In the formula: Yt - post-wash whiteness value; Yo - pre-wash whiteness value; Yw - average whiteness value of the pre-wash white cloth.

[0083] White cloth whiteness = (White cloth Yt - White cloth Yo) * 100%

[0084] The test results are shown in Table 3, and the results are retained to two decimal places.

[0085] Table 3 Detergency Test

[0086]

[0087]

[0088] As can be seen from the test results in Table 3, the explosion salt compositions of Examples 1-3 have excellent detergency effects on 20 kinds of international soiled cloths under low-temperature conditions, and with the increase of the modified catalyst, the detergency effect is better, and the detergency performance is significantly superior to that of Comparative Examples 1 and 2 with the replacement catalyst.

[0089] Test Example 3

[0090] Test on bactericidal and disinfection effects

[0091] Microbial culture: Escherichia coli was selected as the test strain. Escherichia coli was inoculated into LB liquid medium and cultured with shaking at 37 °C for 12 h, and the OD600nm was measured to adjust the concentration of the bacterial suspension to 10 8 ~10 9 CFU / mL.

[0092] Disinfection experiment: Prepare a 20 wt% explosion salt solution (dissolved in sterile water), take 10 mL of the solution in a sterile test tube, add 0.1 mL of the bacterial suspension, mix immediately and place it in a constant temperature water bath at 25 °C for 20 min.

[0093] At the same time, a positive control (10 mL of sterile water + 0.1 mL of bacterial suspension) and a negative control (10 mL of explosion salt solution) were set up.

[0094] Neutralization and dilution: After the action was completed, immediately add 1 mL of neutralizer (sodium thiosulfate solution with a mass concentration of 0.1%) to the test tube, mix well and perform 10-fold serial dilutions.

[0095] Colony counting: Take 0.1 mL of the diluted solution and spread it on a nutrient agar plate, culture it at 37 °C for 24 h, and count the number of colonies.

[0096] Calculate the sterilization rate: Sterilization rate = (1 - number of colonies in the experimental group / number of colonies in the positive control group) × 100%

[0097] The test results are shown in Table 4.

[0098] Table 4 Results of sterilization rate determination

[0099] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Sterilization rate 99.98％ 99.99％ 99.99％ 99.90％ 99.94％

[0100] As can be seen from the test results in Table 4, Examples 1-3 and Comparative Examples 1-2 all have good bactericidal effects, and the explosion salt compositions of Examples 1-3 have a higher sterilization rate under low-temperature conditions, proving that the modified composite oxide catalyst of the present invention can significantly improve the sterilization effect of the explosion salt composition.

[0101] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Accordingly, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

[0102] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-temperature ozone sterilizing explosion salt composition, characterized in that, The raw materials of the low-temperature activated oxygen sterilizing explosion salt composition include components with the following mass fractions: Oxidant 60 - 95% Surfactant 2 - 20% Modified composite oxide catalyst 1 - 10% Alkaline salt 1 - 20% Auxiliary agent 0.1 - 10%; Wherein, The modified composite oxide catalyst is a cerium-iron-manganese composite oxide catalyst.

2. The low-temperature active oxygen sterilizing explosion salt composition according to claim 1, wherein The oxidant is sodium percarbonate; the surfactant is selected from one or more of solid or powder anionic surfactants, solid or powder non-ionic surfactants.

3. The low-temperature active oxygen sterilizing explosion salt composition according to claim 2, wherein The anionic surfactant is selected from one or more of sulfonates, sulfate esters, phosphates, amino acids, and the non-ionic surfactant is selected from one or more of polyoxyethylene ethers, polyol fatty acid esters.

4. The low-temperature ozone sterilization explosion salt composition according to claim 1, wherein The alkaline salt is selected from at least one or more of silicates, sulfates, bicarbonates, carbonates, citrates.

5. The low-temperature active oxygen sterilizing explosion salt composition according to claim 1, characterized in that, The auxiliary agent is selected from one or more of preservatives, pigments, flavors, enzyme preparations, defoamers, corrosion inhibitors.

6. The preparation method of the low-temperature active oxygen sterilizing explosion salt composition according to any one of claims 1-5, characterized in that, The preparation method of the low-temperature activated oxygen sterilizing explosion salt composition includes the following steps: S1. Dissolve iron salt, manganese salt and cerium salt in a solvent respectively, and then mix them evenly to obtain a mixed metal salt solution; S2. Stir and add a precipitant to the mixed metal salt solution, and adjust the pH value and temperature for precipitation; S3. Let the precipitate stand and age in the mother liquor; S4. Filter and wash the precipitate; S5. Dry the washed precipitate, and then calcine it to obtain a modified composite oxide catalyst; S6. Mix the modified composite oxide catalyst and other components evenly to obtain a low-temperature activated oxygen sterilizing explosion salt composition.

7. The preparation method of the low-temperature active oxygen sterilizing explosion salt composition according to claim 6, characterized in that, In step S1, in the mixed metal salt solution, the molar ratio of iron ions, manganese ions and cerium ions is (2 - 3):(2 - 3):

1.

8. The preparation method of the low-temperature active oxygen sterilization explosion salt composition according to claim 6, characterized in that, In step S2, the pH value is 8 - 10, and the temperature is 50 - 70 °C.

9. The preparation method of the low-temperature active oxygen sterilization explosion salt composition according to claim 6, characterized in that, In step S3, the standing and aging time is 12 - 24 h.

10. The preparation method of the low-temperature ozone sterilization explosion salt composition according to claim 6, characterized in that, In step S5, the calcination temperature is 400 - 600 °C, and the time is 2 - 4 h.

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