Method for measuring specific surface area of carbon black

Abstract

The invention belongs to the technical field of pyrolytic carbon black quality detection methods, and particularly relates to a method for determining the specific surface area of carbon black. The method for measuring the specific surface area of the carbon black comprises the following steps: firstly, adding an additive into the carbon black, stirring, centrifuging and filtering; the auxiliary agent is prepared by compounding polyacrylamide, dipolyglycerol dioleate and water; adding water for cleaning, centrifuging, filtering and drying; and finally calculating the specific surface area of the carbon black through a gas adsorption method. According to the method, the carbon black is pretreated, so that the influence of surface oxygen-containing functional groups, aromatic ring impurities and the like on nitrogen adsorption is effectively eliminated, and the problem that the pore structure of the carbon black is damaged by high-temperature degassing in a traditional method is solved through proper microwave irradiation, so that the measured specific surface area result is closer to a true value; methodologies such as precision and repeatability are more stable.

Description

Technical Field

[0001] The invention belongs to the technical field of pyrolytic carbon black quality detection methods, and specifically relates to a method for determining the specific surface area of ​​carbon black. Background Art

[0002] As an important industrial material, carbon black is widely used in rubber, coatings, batteries, composite materials and other fields. Its specific surface area is one of the core parameters for evaluating the performance of carbon black, which directly affects the key properties of the product such as reinforcement, dispersibility and conductivity. At present, the determination method of carbon black specific surface area mainly relies on traditional gas adsorption method and liquid phase adsorption method, but these methods still have many limitations in practical applications, and more efficient, accurate and adaptable technical solutions are urgently needed.

[0003] At present, the industry generally uses the nitrogen adsorption BET method (Brunauer-Emmett-Teller method) to determine the specific surface area of ​​carbon black. This method is based on the multilayer adsorption theory. The single-layer adsorption amount is calculated by the adsorption isotherm of nitrogen on the carbon black surface at liquid nitrogen temperature (77 K), and the specific surface area is then deduced. However, this method has the following significant defects: the surface of carbon black often contains a microporous structure (pore size <2 nm), and the diffusion of nitrogen molecules in the micropores is limited, resulting in a long adsorption equilibrium time, and even unable to accurately reflect the true specific surface area, and the error is large. Moreover, oxygen-containing functional groups or impurities on the surface of carbon black may affect the nitrogen adsorption behavior, causing the results to deviate from the actual value. In addition, additional high-temperature degassing pretreatment is required, which further increases the test cycle.

[0004] In order to circumvent the equipment limitations of the gas adsorption method, some standards recommend the use of the iodine adsorption method or the cetyltrimethylammonium bromide (CTAB) adsorption method to indirectly estimate the specific surface area through liquid phase adsorption. However, such methods also face challenges: iodine molecules (I2) easily react chemically with the functional groups on the surface of carbon black, causing the adsorption amount to deviate from the specific surface area calculation model dominated by physical adsorption, especially in surface oxidized carbon black (such as conductive carbon black). The CTAB method relies on the monolayer adsorption of surfactants on the surface of carbon black, but the hydrophobicity and surface charge differences of carbon black may lead to uneven adsorption layers and poor repeatability (relative error often exceeds 5%). Summary of the invention In order to solve the shortcomings of the prior art, the present invention provides a method for measuring the specific surface area of ​​carbon black. The method has high precision and good repeatability. Through surface pretreatment, the inorganic salt impurities and aromatic hydrocarbon impurities on the surface and internal voids of carbon black are eliminated to eliminate the adsorption effect of gas, and the measurement result is closer to the true value.

[0005] A method for determining the specific surface area of ​​carbon black comprises the following steps: (1) adding an additive to carbon black, stirring, centrifuging, and filtering; the additive is prepared by compounding polyacrylamide, diglycerol dioleate, and water; (2) Wash with water, centrifuge, filter, and dry; (3) Calculate the specific surface area of ​​carbon black by gas adsorption method.

[0006] Preferably, the mass concentrations of polyacrylamide and diglycerol dioleate in the auxiliary agent in step (1) are 1-5% and 0.5-2%, respectively.

[0007] Preferably, the molecular weight of the polyacrylamide in step (1) is 8-10 million.

[0008] Preferably, the amount of the additive added in step (1) is 0.5-2 times the mass of carbon black.

[0009] Preferably, the stirring speed in step (1) is 80-100 rpm, and the stirring time is 25-40 min.

[0010] Preferably, the centrifugal speed in step (1) and step (2) is 1500-2500 rpm, and the centrifugal time is 10-20 min.

[0011] Preferably, the specific operation of the gas adsorption method in step (3) includes: S1 irradiates the carbon black treated in step (2) with microwaves and records the mass m1; S2 is then placed in an atmosphere furnace and adsorbed with carbon dioxide first, recording the mass m2; then the mixed gas is used for purging and adsorption, and the mass m3 is recorded after equilibrium; finally, the specific surface area of ​​carbon black is calculated as follows: S = [(m2-m1) × N A ×A / M1+(m3-m2)×N A ×B / 34] / m1, Where S is the specific surface area of ​​carbon black, in m 2 / g; N A is 6.023×10 23 ; A is the corrected area of ​​carbon dioxide molecule 0.20×10 -18 , unit is m 2 ; B is the corrected mixed gas molecular area constant 0.15×10 -18 , unit is m 2 ; The average molar mass of the mixed gas Mmix is: Mmix=XN2×MN2+XAr×MAr.

[0012] XN2 and XAr: are the mole fractions of nitrogen and argon respectively.

[0013] MN2=28.01g / mol (molar mass of nitrogen).

[0014] MAr=39.95g / mol (molar mass of argon).

[0015] Mmix=0.5×28.01+0.5×39.95=14.005+19.975=33.98g / mol≈34g / mol.

[0016] Preferably, step S1 is to irradiate carbon black with 2.45 GHz microwaves under helium protection, wherein the power of the microwave irradiation is 50-120 W and the time of the microwave irradiation is 5-15 min.

[0017] Preferably, in step S2, the flow rate of carbon dioxide is 60-100 mL / min, and the flow rate of the mixed gas is 30-50 mL / min.

[0018] Preferably, the mixed gas in step S2 includes nitrogen with a molar fraction of 45-55% and argon with a molar fraction of 45-55%, the carbon dioxide adsorption time is 0.5-1h, and the mixed gas adsorption time is 2-4h.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention effectively eliminates the effects of oxygen-containing functional groups on the surface and inner pores of carbon black, aromatic ring impurities, etc. on gas adsorption by pretreating carbon black, and solves the problem of high-temperature degassing in traditional methods that destroys the pore structure of carbon black by appropriate microwave irradiation, so that the measured specific surface area result is closer to the true value, with better precision and repeatability, and more stable methodology.

[0020] (2) The determination method of the present invention uses CO2 to preferentially adsorb on micropores, and uses its high diffusivity to accurately fill the micropores; then a mixed gas is used at a low flow rate to gently sweep and cover the mesopores and remaining mesopores. The lower limit of micropore specific surface area detection is extended to 0.5nm, and the error is <±3% (traditional method ±7%); the efficiency is improved and the total test time is ≤5 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is the FTIR spectrum of the carbon black obtained by pyrolysis of the present invention.

[0022] Figure 2 The microscopic morphology of pyrolytic carbon black, where from left to right are the microscopic morphologies of pyrolytic carbon black at temperatures of 1200°C, 1300°C, and 1400°C. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific embodiments. The raw materials in the following examples are all commercially available conventional raw materials. The oil sludge of the present invention is taken from a hazardous waste disposal company in Qingdao, Shandong Province, my country. The supplier of polyacrylamide is Shandong Ruihai New Material Technology Co., Ltd., model 5801, with a molecular weight of 8 million to 10 million.

[0024] The present invention adopts the method of treating oil sludge to prepare carbon black sample, and the preparation method is as follows: (1) Dry the solid sludge at 105℃ for 12h, crush it, pass it through a 60-mesh sieve, and then pass it through a 2 L min-1 vacuum chamber at 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃. -1 The mixture was pyrolyzed in nitrogen for 10 min.

[0025] (2) The carbon black particles produced during the pyrolysis reaction are precipitated with the gas phase products and accumulated on the metal filter membrane in the downstream metal filter. The filter membrane is made of stainless steel fiber sintered felt with a micron-sized pore size. The subsequent tar enters the dichloromethane washing bottle in the cold water bath for absorption, and the filtered gas is collected by an aluminum air bag.

[0026] (3) The metal filter membrane used to filter carbon black was cleaned with 100 ml of dichloromethane solution by ultrasonic vibration for 30 min five times to ensure that the oil substances adsorbed on the surface of carbon black were completely eluted. The cleaned carbon black sample was filtered through a 0.22 µm organic filter membrane and dried at 105 °C for 24 h to obtain pyrolytic carbon black for future use.

[0027] 1. Characterization of Pyrolytic Carbon Black 1.1 Elemental composition and ash content of pyrolytic carbon black The elemental composition and ash content of pyrolytic carbon black were determined using the Vario MACRO cube element analyzer from Elementar, Germany. The element content, element molar ratio and ash content of carbon black obtained by pyrolysis at different temperatures are shown in Table 1.

[0028] Table 1

[0029] The results of elemental analysis show that the C content in pyrolytic carbon black is 93.4-97.6%. In addition, pyrolytic carbon black also contains miscellaneous elements such as O, H, N and S. These miscellaneous elements mainly come from organic hazardous waste raw materials, are released with volatiles during the pyrolysis process, and are brought into the carbon black when the carbon black is generated. Ash is defined as the amount of residue after combustion in a high-temperature furnace, which mainly comes from inorganic impurities and dissolved inorganic salts in the raw materials and process water (quenching, wet granulation). Ash content analysis shows that the ash content of pyrolytic carbon black obtained by pyrolysis at 1000-1400℃ ranges from 1.07-1.62%.

[0030] The C / H ratio of mature carbon black particles is about 10, so the carbon black particles formed by pyrolysis carbon black at a pyrolysis temperature ≥ 1200°C are mature carbon black particles. The H content in carbon black is directly related to its available active sites. The lower the C / H ratio, the higher the reactivity of carbon black. Therefore, the higher the pyrolysis temperature, the lower the reactivity of the produced carbon black.

[0031] 1.2 Detection of surface functional groups of pyrolytic carbon black using FTIR The sample was mixed with KBr at a ratio of 1:100, pressed into a sheet using a tablet press, and then scanned using an FTIR spectrometer. The FTIR spectrum of the carbon black obtained by pyrolysis of the present invention is shown in Figure 1 , showing that the FTIR curves of pyrolytic carbon black and commercial carbon black are very similar, with several obvious broad peaks, so pyrolytic carbon black is composed of different molecular substances.

[0032] FTIR spectrum at 2800-3000 cm -1 The absorption spectrum in the range is very weak, indicating that there is basically no aliphatic CH functional group in pyrolytic carbon black. The H element obtained by elemental analysis mainly exists in the form of aromatic CH bonds in pyrolytic carbon black. -1 The weak absorption peak at 1700-925cm -1 The obvious absorption bands in the range of 1637 cm-1 dominate, representing the π bonds in amorphous carbon. -1 The absorption peak at represents the aromatic C=C (sp 2 ) bond stretching vibration. 1400-1000cm -1 The broad absorption band at 1300 cm -1 The broad band at is due to aliphatic crosslinking in the aromatic sp 2 The defects are caused by the formation of non-hexagonal rings inside the layer. 925-700cm -1 The absorption spectrum appearing in the range represents the bending vibration of the aromatic out-of-plane CH bonds in carbon black.

[0033] In summary, the elemental composition, ash content and FTIR spectrum analysis of carbon black show that the pyrolytic carbon black prepared by the present invention using oil sludge contains inorganic impurities and inorganic salts, as well as aromatic, aliphatic and aromatic cross-linked related substances, which will affect the adsorption of gas, the accuracy of the final specific surface area result, and the stability of the detection when testing the performance of carbon black, especially when using nitrogen adsorption method to characterize the specific surface area. The present invention further explores the method for determining the specific surface area as follows.

[0034] 2. Specific surface area test experiment of pyrolytic carbon black of the present invention 2.1 Specific surface area test method of pyrolytic carbon black of the present invention (1) First, add 1 times the amount of auxiliary agent to the pyrolytic carbon black prepared in the present invention, stir at a speed of 90 rpm for 30 minutes, centrifuge at a speed of 2000 rpm for 15 minutes, and filter; the auxiliary agent is a 1% polyacrylamide (relative molecular weight M=8 million-10 million) and 0.5% diglycerol dioleate aqueous dispersion; (2) Then the carbon black was washed with 1 times the amount of water, centrifuged at 2000 rpm for 15 min, filtered, and dried at 105 °C for 2 h; (3) Calculate the specific surface area of ​​carbon black by gas adsorption method.

[0035] S1. Irradiate the carbon black treated in step (2) with 2.45 GHz microwaves under helium protection, with a power of 80 W and an irradiation time of 5 min, and record the mass m1; S2, then placed in an atmosphere furnace, first adsorbed with carbon dioxide molecules for 1h, with a flow rate of 60mL / min, and the mass m2 was recorded; then a mixed gas with a molar concentration of 50% nitrogen and 50% argon was used for purging and adsorption for 2h, with a flow rate of 30mL / min, and the mass m3 was recorded after equilibrium; finally, the specific surface area of ​​carbon black was calculated as follows: S = [(m2-m1) × N A ×A / M1+(m3-m2)×N A ×B / 34] / m1, Where S is the specific surface area of ​​carbon black, in m 2 / g; N A is 6.023×10 23 ; A is the corrected area of ​​carbon dioxide molecule 0.20×10 -18 , unit is m 2 ; B is the corrected mixed gas molecular area constant 0.15×10 -18 , unit is m 2 .

[0036] 2.2 Methodological validation 2.2.1 Precision test The specific surface area of ​​the mature carbon black sample prepared by pyrolysis at 1200-1400°C was measured according to the above-mentioned measurement method and repeated 6 times. All measurement results are shown in Table 2 below.

[0037] Table 2

[0038] Note: The temperature in the table is the pyrolysis temperature for preparing carbon black.

[0039] 2.2.2 Repeatability test The mature carbon black prepared by pyrolysis at 1200-1400°C was sampled in different laboratories at different time periods, and the specific surface area was measured according to "2.1 Specific surface area test method of pyrolytic carbon black of the present invention" of the present invention. The test was conducted twice, and the results are shown in Table 3 below.

[0040] Table 3

[0041] Note: The temperature in the table is the pyrolysis temperature for preparing carbon black.

[0042] 2.2.3 Traditional method for determining the specific surface area of ​​pyrolytic carbon black The specific surface area of ​​the mature pyrolytic carbon black prepared by pyrolysis at 1200-1400°C of the present invention was measured by conventional low-temperature nitrogen adsorption method, the results are shown in Table 4, and then the measurement was continued for 5 times, and the precision results are shown in Table 5.

[0043] Table 4

[0044] Table 5

[0045] Note: The temperature in the table is the pyrolysis temperature for preparing carbon black.

[0046] 2.2.4 Screening experiment 1) The screening experiment of the pretreatment process is shown in Table 6, and the rest is the same as the method 2.1 of the present invention. The measurement results of the same researcher in the same laboratory are shown in Table 6.

[0047] Table 6

[0048] After screening experiments, it was found that the use of polyacrylamide M=8 million-10 million, diglycerol dioleate and water to clean carbon black can effectively enter its pores, dissolve inorganic impurities and aromatic impurities on its surface and inside the pores, and eliminate the influence of its impurities on the specific surface area determination. By trying the gas flow rate and gas adsorption type, it achieved a better stable adsorption effect in a shorter time.

[0049] The above detailed description is a specific description of one feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for determining the specific surface area of ​​carbon black, characterized in that: The method comprises the following steps: (1) adding an additive to carbon black, stirring, centrifuging, and filtering; the additive is prepared by compounding polyacrylamide, diglycerol dioleate, and water; (2) Wash with water, centrifuge, filter, and dry; (3) Calculate the specific surface area of ​​carbon black by gas adsorption method.

2. The measuring method according to claim 1, characterized in that The mass concentrations of polyacrylamide and diglycerol dioleate in the auxiliary agent in step (1) are 1-5% and 0.5-2% respectively.

3. The measuring method according to claim 1, characterized in that The molecular weight of the polyacrylamide in step (1) is 8-10 million.

4. The measuring method according to claim 1, characterized in that The amount of the additive added in step (1) is 0.5-2 times the mass of carbon black.

5. The measuring method according to claim 1, characterized in that The stirring speed in step (1) is 80-100 rpm, and the stirring time is 25-40 min.

6. The measuring method according to claim 1, characterized in that The centrifugal speed in step (1) and step (2) is 1500-2500 rpm, and the centrifugal time is 10-20 min.

7. The measuring method according to claim 1, characterized in that The specific operation of the gas adsorption method in step (3) includes: S1 irradiates the carbon black treated in step (2) with microwaves and records the mass m1; S2 is then placed in an atmosphere furnace and adsorbed with carbon dioxide first, recording the mass m2; then the mixed gas is used for purging and adsorption, and the mass m3 is recorded after equilibrium; finally, the specific surface area of ​​carbon black is calculated as follows: S=[(m2-m1)×N A ×A / M1+(m3-m2)×N A ×B / 34] / m1, Where S is the specific surface area of ​​carbon black, in m 2 / g; N A is 6.023×10 23 ; A is the corrected area of ​​carbon dioxide molecule 0.20×10 -18 , unit is m 2 ; B is the corrected mixed gas molecular area constant 0.15×10 -18 , unit is m 2 ; M1 is the molar mass of carbon dioxide.

8. The measuring method according to claim 7, characterized in that Step S1 is to irradiate carbon black with 2.45 GHz microwaves under helium protection, the power of the microwave irradiation is 50-120 W, and the time of the microwave irradiation is 5-15 min.

9. The measuring method according to claim 7, characterized in that In step S2, the flow rate of carbon dioxide is 60-100 mL / min, and the flow rate of the mixed gas is 30-50 mL / min.

10. The measuring method according to claim 9, characterized in that The mixed gas in step S2 includes nitrogen with a molar fraction of 45-55% and argon with a molar fraction of 45-55%, the carbon dioxide adsorption time is 0.5-1h, and the mixed gas purge adsorption time is 2-4h.

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