A method for determining silanol content in white carbon black

Abstract

The present invention proposes a method for determining the silanol content of silica, comprising the following steps: 1. Weighing a certain mass of silica and spreading it flat in a crucible; 2. Placing the crucible in an atmosphere furnace capable of programmable temperature rise, and purging the silica with nitrogen at a set temperature for a set time; 3. Switching the atmosphere furnace purge gas to ammonia, and subjecting the silica to ammonia adsorption treatment under certain conditions; 4. Switching the atmosphere back to nitrogen, and desorbing the physically adsorbed ammonia from the silica under certain conditions; 5. Removing the sample crucible and weighing the mass, and calculating the silanol content of the measured silica according to a formula. The method for determining the silanol content of silica proposed in the present invention has the advantages of simple operation, accurate results, strong anti-interference ability, good repeatability, and requires a small amount of sample, making it very suitable for testing small batches of silica samples.

Description

Technical Field

[0001] The invention belongs to the field of biomass energy utilization, and particularly relates to a method for determining silanol groups in white carbon black. Background Art

[0002] White carbon black, also known as hydrated silicon dioxide, is a white amorphous granular or powdery substance that is chemically stable, non-toxic, high-temperature resistant, and non-flammable. It has excellent electrical insulation, stability, reinforcement, and thickening properties, and is widely used in industries such as rubber, tires, coatings, toothpaste, medicine, and papermaking. From a microscopic perspective, white carbon black is primarily composed of porous amorphous particles formed by the polymerization of silicon-oxygen tetrahedrons. These particles contain a large number of silanol (Si-OH) groups on their surface and within their pores, which significantly affect their water absorption, oil absorption, and dispersion properties during application. Accurate measurement of their content is necessary in certain applications and is a key indicator in the production and application of white carbon black.

[0003] Traditional methods for testing silanol groups in silica include gas chromatography, chemical titration, infrared spectroscopy, thermogravimetry, and isotope replacement. Gas chromatography utilizes a Grignard reagent (CH3MgI) to react with the active hydrogen in the silanol groups to generate methane, and then determines the number of silanol groups by measuring the amount of methane generated. This method has disadvantages such as a complex operational process and poor repeatability. Chemical titration primarily utilizes the Lewis acidity of the silanol groups in silica to titrate the silanol groups with sodium hydroxide. However, since it cannot guarantee that all silanol groups participate in the reaction and the titration endpoint is difficult to determine, there are significant human influence factors, and the measurement accuracy is greatly limited. The infrared method measures the silanol content by utilizing the principle that the stretching and bending vibrations of the silanol groups absorb infrared light. Due to the many spectral interference factors, it is mostly used for qualitative or semi-quantitative analysis. Thermogravimetry utilizes the condensation and dehydration reaction of the silanol groups under programmed temperature treatment, and measures the mass loss of silica to obtain the silanol content. However, since silica generally contains physically adsorbed water, it significantly interferes with the measurement results, resulting in some controversy surrounding this method. The isotope exchange method uses hydrogen isotopes to replace the hydrogen element of silanol groups, thereby achieving accurate determination of the silanol content. However, this method has disadvantages such as harsh reaction conditions, long time consumption, and expensive reagents, which makes it less commonly used in practice.

[0004] In summary, the traditional method for determining the silanol content has more or less some shortcomings, and it is urgent to develop a more efficient, simple and accurate method for determining the silanol content of silica. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for determining the silanol content of silica.

[0006] This method utilizes the fact that the silanol group of silica is a Lewis acid that can chemically adsorb ammonia. The silanol content is obtained by measuring the chemically adsorbed ammonia content of silica. It has the advantages of simple operation, good repeatability and accurate results.

[0007] In order to achieve the above-mentioned purpose and the above-mentioned technical effect, the present invention is implemented by the following technical solution: A method for determining the silanol content of white carbon black, characterized in that it comprises the following steps:

[0008] Step 1: Weigh a certain amount of silica and spread it evenly in a crucible, and record the sample mass m0;

[0009] Step 2: Place the crucible in an atmosphere furnace capable of temperature programming, purge the silica with nitrogen at a set temperature for a certain period of time, and weigh the silica mass m1;

[0010] Step 3: Switch the purge gas of the atmosphere furnace from nitrogen to ammonia, and perform ammonia adsorption treatment on the silica under certain conditions;

[0011] Step 4: Switch the atmosphere of the furnace back to nitrogen, and desorb the ammonia physically adsorbed on the silica under set conditions;

[0012] Step 5: Take out the sample crucible and weigh it, record the mass m2, and calculate the silanol content of silica according to the formula.

[0013] Preferably, in step 2 of the aforementioned method for determining the silanol content of silica, the atmosphere furnace is a thermogravimetric analysis furnace or a programmable temperature-controlled tubular furnace.

[0014] Preferably, in step 1 of the aforementioned method for determining the silanol content of white carbon black, the certain mass is determined according to the selected atmosphere furnace. When a thermogravimetric analysis furnace is used for analysis, the mass is 10 to 15 mg; when a program-controlled temperature tubular furnace is used, the mass is 1 to 3 g.

[0015] Preferably, in step 2 of the aforementioned method for determining the silanol content of silica, the set temperature is 105 to 200° C., the nitrogen purge flow rate is 50 to 100 mL / min, and the certain time is 30 to 60 min.

[0016] Preferably, in step three of the aforementioned method for determining the silanol content of silica, the certain conditions refer to an adsorption temperature of 20 to 40° C., an ammonia flow rate of 50 to 100 mL / min, and an adsorption time of 1 to 4 h.

[0017] Preferably, in step 4 of the aforementioned method for determining the silanol content of silica, the set conditions are that the desorption temperature is 105-150° C. and the desorption time is 30-60 min.

[0018] Preferably, in step 5 of the aforementioned method for determining the silanol content of white carbon black, the content may be the silanol mass percentage content or the silanol number, and the calculation formulas are as follows:

[0019]

[0020]

[0021] Where, is the mass fraction of silanol groups, ρ OH is the number of silanol groups, N A is Avogadro's constant, S is the specific surface area of ​​silica, M OH is the molar mass of the hydroxyl group.

[0022] The beneficial effects of the present invention are:

[0023] 1. The thermogravimetric analysis furnace and programmable temperature-controlled tubular furnace used in this method are both common laboratory equipment. Nitrogen and ammonia are also conventional gases that are easy to obtain and simple to operate.

[0024] 2. The present invention measures the chemically adsorbed ammonia of silica under programmed temperature conditions, overcoming the influence of physically adsorbed water when measuring silanol groups by traditional thermogravimetric method, and the measurement process will not damage silica. Compared with other methods such as chemical titration and gas chromatography, the present invention does not require the use of chemical reagents, has a short operation process, high measurement accuracy, small external interference factors, and good stability. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0026] In this example, homemade white carbon black prepared by temperature-controlled combustion of rice husks was used as raw material. The silanol content of the prepared white carbon black was determined by this method, and the traditional chemical titration method (for specific operating methods, refer to the "Test Method for Surface Hydroxyl Content of Fumed Silica" T / FSI 049-2020) was used for measurement as a comparison.

[0027] Example 1

[0028] A method for determining the silanol content of white carbon black comprises the following steps:

[0029] Step 1: Weigh 3 g of silica and spread it evenly in a crucible;

[0030] Step 2: Place the crucible in a programmed temperature tube furnace, connect the carrier gas, check the air tightness of the device, turn on the nitrogen purge, control the gas flow rate to 50 mL / min, and heat the tube furnace to 200°C at a heating rate of 10°C / min. Maintain for 2 h, then lower the furnace temperature to room temperature under nitrogen purge conditions, take out the crucible and weigh it, and record the total mass m1;

[0031] Step 3: Place the crucible back into the furnace and continue to purge the silica at room temperature at an ammonia flow rate of 50 mL / min for 2 hours. The sample can be taken out and weighed several times during the process until the mass no longer increases to ensure that the ammonia is fully adsorbed.

[0032] Step 4: Switch the carrier gas back to nitrogen, heat the tube furnace to 150°C at a heating rate of 10°C / min, hold for 1 hour, and then continue to cool the furnace temperature down to room temperature under nitrogen purge;

[0033] Step 5: Take out the sample crucible and weigh it, record the mass m2, and calculate the silanol content of silica according to the following formula 1.

[0034]

[0035] After the above steps, the silanol content of the prepared white carbon black was measured to be 3.43%, and the silanol content measured by the group standard T / FSI 049-2020 was 3.45%.

[0036] Example 2

[0037] A method for determining the silanol content of white carbon black comprises the following steps:

[0038] Step 1: Weigh 2 g of silica and spread it evenly in a crucible;

[0039] Step 2: Place the crucible in a programmed temperature tube furnace, connect the carrier gas, check the air tightness of the device, turn on the nitrogen purge, control the gas flow rate to 80 mL / min, and heat the tube furnace to 180°C at a heating rate of 10°C / min. Maintain for 1.5 hours, then lower the furnace temperature to room temperature under nitrogen purge conditions, take out the crucible and weigh it, and record the total mass m1;

[0040] Step 3: Place the crucible back into the furnace and continue to purge the silica at room temperature at an ammonia flow rate of 80 mL / min for 3 hours. The sample can be taken out and weighed several times during the process until the mass no longer increases to ensure that the ammonia is fully adsorbed.

[0041] Step 4: Switch the carrier gas back to nitrogen, heat the tube furnace to 120°C at a heating rate of 10°C / min, hold for 1 hour, and then continue to cool the furnace temperature down to room temperature under nitrogen purge;

[0042] Step 5: Take out the sample crucible and weigh it, record the mass m2, and calculate the silanol content of silica according to the following formula 1.

[0043]

[0044] After the above steps, the silanol content of the prepared white carbon black was measured to be 3.46%, and the silanol content measured by the group standard T / FSI 049-2020 was 3.45%.

[0045] Example 3

[0046] A method for determining the silanol content of white carbon black comprises the following steps:

[0047] Unlike Examples 1 and 2, this embodiment uses a thermogravimetric analyzer to test the silanol content. Since the thermogravimetric analyzer can record the mass change of the sample in real time, there is no need to repeatedly take out the sample for weighing. Therefore, the implementation steps of this method can be simplified as follows: set the thermogravimetric analyzer heating program, first, under a nitrogen purge of 50mL / min, the furnace temperature is raised from room temperature to 150℃ at a heating rate of 10℃ / min, and maintained for 1.5h; continue to lower the furnace temperature to room temperature under nitrogen purge, switch the carrier gas to ammonia, set the ammonia flow rate to 100mL / min, and maintain for 2h; switch back to nitrogen again, raise the furnace temperature to 120℃ at a heating rate of 10℃ / min, and maintain for 1h. After the program is set, weigh 10mg of silica and spread it flat in a thermogravimetric crucible and place it in the thermogravimetric analysis furnace. The measurement is performed according to the set program. After the measurement is completed, the mass m1 of silica before ammonia adsorption and the mass m2 after ammonia adsorption are read, and the silica silanol content is calculated according to the following formula 1.

[0048]

[0049] After the above steps, the silanol content of the prepared white carbon black was measured to be 3.44%, and the silanol content measured by the group standard T / FSI 049-2020 was 3.45%.

[0050] Example 4

[0051] A method for determining the silanol content of white carbon black comprises the following steps:

[0052] The specific implementation steps are the same as those in Example 3, except that: under a nitrogen purge of 60 mL / min, the furnace temperature is raised from room temperature to 120°C at a heating rate of 10°C / min and maintained for 2 hours; the furnace temperature is lowered to room temperature under nitrogen purge, the carrier gas is switched to ammonia, the ammonia flow rate is set to 80 mL / min, and maintained for 3 hours; the nitrogen is switched back again, the furnace temperature is raised to 120°C at a heating rate of 10°C / min, and maintained for 1 hour. After the above thermogravimetric procedure is completed, the mass m1 of the white carbon black before ammonia adsorption and the mass m2 after ammonia adsorption are read according to the following formula

[0053] The number of silanol groups in silica was calculated using formulas 1 and 2.

[0054]

[0055]

[0056] After the above steps, the number of silanol groups of the prepared white carbon black was measured to be 6.2OH / nm 2 The number of silanol groups measured by group standard T / FSI 049-2020 is 6.1OH / nm 2 .

Claims

1. A method for determining silanol content in silica, characterized in that: The following steps are involved: Step 1: Weigh a certain amount of silica and spread it flat in a crucible, and record the sample mass. m 0; Step 2: Place the crucible in an atmosphere furnace that can be programmed to heat up, purge the white carbon black with nitrogen at the set temperature for a certain period of time, take out the crucible and weigh it, and record the mass. m 1; Step 3: Switch the purge gas of the atmosphere furnace to ammonia, and perform ammonia adsorption treatment on the white carbon black under certain conditions; Step 4: Switch the atmosphere back to nitrogen and desorb the physically adsorbed ammonia on the silica under set conditions; Step 5. Take out the sample crucible and weigh it, record the mass m 2. Calculate the silanol content of silica according to the formula; Wherein, in the step 5, the content refers to the mass percentage of silanol, and the calculation formula is as follows: （1） Where, φ is the mass fraction of silanol; Alternatively, in step 5, the content refers to the number of silanol groups, and the calculation formula is as follows: （2） Where, φ is the mass fraction of silanol, ρ OH is the number of silanol groups, N A is Avogadro's constant, S is the specific surface area of ​​silica, M OH is the molar mass of the hydroxyl group.

2. The method for determining the silanol content of white carbon black according to claim 1, wherein: In the step 2, the atmosphere furnace is a thermogravimetric analysis furnace or a program-controlled temperature tube furnace.

3. The method for determining the silanol content of white carbon black according to claim 2, wherein: The certain mass in step 1 is determined according to the selected atmosphere furnace. When the atmosphere furnace is a thermogravimetric analysis furnace, the certain mass satisfies 10-15 mg; when the atmosphere furnace is a programmable temperature-controlled tubular furnace, the certain mass satisfies 1-3 g.

4. The method for determining the silanol content of white carbon black according to claim 1, wherein: In step 2, the temperature range is set to 105-200° C., the nitrogen purge flow rate is 50-100 mL / min, and the set time is 30-60 min.

5. The method for determining the silanol content of white carbon black according to claim 1, wherein: In step 3, the certain conditions refer to an adsorption temperature of 20-40° C., an ammonia flow rate of 50-100 mL / min, and an adsorption time of 1-4 h.

6. The method for determining the silanol content of white carbon black according to claim 1, wherein: In the step 4, the setting conditions are that the desorption temperature is 105-150° C. and the desorption time is 30-60 min.

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