In this paper, two main methods for the determination of coal pitch naphthalene content are discussed: the column method and the suction filtration method. The column method is suitable for the determination of naphthalene content in medium oil (170270 °C) and heavy oil (270300 °C) fractions, emphasizing the technical requirements and experimental procedures of the experimental equipment. The suction filtration method focuses on the determination of naphthalene content in medium oil fractions, and provides relevant instruments and experimental operation guidelines. Both methods ensure the accuracy and reproducibility of experimental results and specify the permissible margin of error. Through the comparison and application of these methods, it provides an effective technical basis for the quality control of coal asphalt.
Coal pitch naphthalene content test (column method)
Purpose and Scope of Application
The purpose of this method was to determine the naphthalene content in road coal asphalt, and the column method was used to analyze the two fractions of medium oil (170~270 °C) and heavy oil (270~300 °C).
Technical requirements for instruments and materials
Chromatograph – requires hydrogen flame ionization identifier
Column temperature – 190°C (actual temperature)
Vaporization temperature – 340°C (surface temperature)
Detection temperature - 200°C (surface temperature)
Carrier gas - pre-column pressure 0.19MPa, flow rate 27mL/min
Gas – Hydrogen, flow rate 55mL/min
Air – flow rate 550 mL/min
Sensitivity—For standards with a naphthalene content of 0.1 g/mL, the naphthalene peak height is not less than 100 mm when the injection volume is 0.5 μL
Resolution R – not less than 1.5
Other instruments
1μLMicrosyringe, 25 mLVolumetric flasks,beakerApison L,Chemically pure benzene, xylene,Infrared lamps, Vacuum Pumps, gas flow meters.
Analytical balance - inductance is not more than 0.2mg
Syringe – 10 mL
6210 red base - particle size 0.18~0.25mm (60~80 mesh), bake in a 300°C oven for 2 hours.
Nitrogen, hydrogen - purity of more than 99.5%.
Compressed air – purified
Methods and Steps:
Column preparation
The ratio of apisone L and 6210 bears is 10:90, first dissolve the weighed fixative solution apisone in an appropriate amount of benzene, slowly add 6210 bears, stir evenly and dry under infrared lamp, and bake in an oven at 110~120 °C for 2 hours after most of the benzene volatilizes. The 2 mL mixture is then pumped with a Vacuum Pump into a washed column with an inner diameter of 3-4 mm and aged at 180°C for 6 hours, after which it is heated to 250°C for another 4 hours.
Standard preparation
Weigh 2.5g of pure naphthalene into a 25mL volumetric flask, accurate to 0.2mg, inject 20mL xylene to dissolve, wait for the naphthalene to be completely dissolved, then add xylene to the engraved line, shake well and store it tightly.
Determination of the linear range
Under the same chromatographic operating conditions, 0.2 μL, 0.4 μL, 0.6 μL, 0.8 μL, and 1.0 μL naphthalene standards were injected with a 1 μL microsyringe for analysis, and the naphthalene peak height was recorded.
The naphthalene peak height was used as the ordinate and the injection amount was used as the abscissa to plot the relationship curve to find the linear relationship range between the concentration and the naphthalene peak height.
Each time the column is changed or the chromatographic operating conditions are changed, the linear range is re-measured.
Sample preparation
According to the distillation method, the fractions of 170~270 °C and 270~300 °C in the coal pitch sample are distilled.
Determination of water content
The water content of the coal asphalt sample is determined and the moisture content in the asphalt sample used is calculated.
Test procedure
The fractions of 170~270 °C and 270~300 °C were injected into the 25mL volumetric flask, the Erlenmeyer flask was rinsed with a small amount of xylene for many times, the rinsing solution was poured into the volumetric flask, and finally the xylene was injected into the engraving line, shaken well and set aside.
Estimate the amount of naphthalene in the fraction sample, inject directly within the linear range of the assay, dilute xylene to the appropriate concentration if it is outside the linear range, and record the dilution factor.
Under the same chromatographic operating conditions, 0.5 μL of the naphthalene standard (two parallel needles) is injected with a 1 μL syringe, and then 0.5 μL of the sample (two parallel needles) is injected. The maximum error of the two needles (measured by the height of the naphthalene peak) shall not exceed 4mm. Note: The dilution factor and injection volume of the sample must be controlled within the measurable range.
The naphthalene peak heights of the standard and sample were recorded separately on the chromatogram.
compute
The naphthalene content of the sample is calculated according to the formula.
report
At least two parallel tests of the same specimen, if the results of the two parallel tests meet the allowable error requirements of the repeatability test, the average value of the test results will be taken as the test results.
Allowable error
The allowable error of the repeatability test is 0.3% when the naphthalene content is less than 3%; 0.6% when the content is greater than or equal to 3%.
Explanation of Provisions
The evaporation content test of bitumen is to determine the amount of distillation contained in the distilled fraction of the sample. Since naphthalene is a volatile substance, too high a naphthalene content in asphalt will cause asphalt to deteriorate and affect the durability of the pavement. For this reason, coal pitch standards usually include limits for naphthalene content. Due to the different determination methods, the fractions intercepted also differ. According to the industry standards of the former Ministry of Metallurgical Industry, this method has been modified by chromatograph, and it is recommended that the user unit purchase the necessary test equipment according to the requirements.
Coal pitch naphthalene content test (suction filtration method)
Purpose and Scope of Application
This method is suitable for the determination of naphthalene content of coal pitch by suction filtration method, and the main analysis of medium oil fraction (170~270 °C).
Technical requirements for instruments and materials
Suction filter - composed of rubber tube connected to the filter flask and the suction pipe or extractor.
Presses
Brinell funnel – 50mm diameter.
Surface dish – diameter 50 mm.
Filter paper – 50 mm diameter.
Beaker – 50 mL.
Balance - inductance not more than 0.018g.
Others – glass rods, etc.
Methods and Steps:
Preparation
Clean and dry the beaker and surface dish and weigh their mass to an accuracy of 0.01g.
Test procedure
1. According to the procedure T0641 for coal pitch distillation test, the distilled medium oil fraction (170~270 °C distillate) needs to be heated, and after the naphthalene contained in it is completely melted, it is poured into a beaker.
Cool to 15 °C and hold for 30 min, then suction filtration on a Brinell funnel lined with filter paper and kept at 15 °C.
3. Spread the filter residue between the filter paper layers and use a press to remove the oil until the filter residue turns white.
4. Move the filter residue to the weighed dish and weigh its total mass.
compute
The naphthalene content of the sample is calculated according to the formula.
report
At least two parallel tests of the same specimen, if the results of the two parallel tests meet the allowable error requirements of the repeatability test, the average value of the test results will be taken as the test results.
Allowable error
The allowable error of the repeatability test is 0.3% when the naphthalene content is less than 3%; 0.6% when naphthalene content is greater than or equal to 3%.
summary
In this paper, two methods for the determination of coal pitch naphthalene content are described in detail: the column method and the suction filtration method. The column method determines the naphthalene content by analyzing the medium and heavy oil fractions, emphasizing the technical requirements of the instrument and the specific experimental procedures to ensure the accuracy of the results. The suction filtration method focuses on the determination of naphthalene content in medium oil fractions, and is simple to operate and easy to implement. The choice of the two methods is based on the experimental conditions and equipment availability, and both can effectively support the quality control of coal asphalt. Overall, these assays provide a scientific basis for evaluating the performance and application of coal pitch.
