This method is suitable for determining the crystallization point of benzene. GB/T 3145-1982 Determination of the crystallization point of benzene GB/T3145-1982 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Benzene-- Determination of crystallizing point
Benzene-- Determination of crystallizing point This method is applicable to the determination of the crystallization point of benzene. 1 Method Overview
UDC 668.735.1
065.5:543
GB/T 3145-82
(Confirmed in 1990)
Under the prescribed cooling conditions, when the sample to be tested is cooled to a certain temperature, after solid precipitation, the temperature rises again, and the highest temperature reached by the rise is the crystallization point.
2 Instrument
2.1 Small test tube: 125~127 mm long, 15~16 mm outer diameter. Mark a line at a height of 52±1 mm from the bottom of the tube (Figure 1).
2.2 Large test tube: 150152 mm long, 25-27 mm outer diameter (Figure 2). 2.3 Thermometer: 0.02°C (Figure 3). 2.4 Cold bath: 1000 ml beaker, filled with crushed ice as coolant (or other containers, or controllable cooling equipment, humidity can be adjusted to 0°C), effective depth not less than 127 mm. 2.5 Stirrer: Use stainless steel wire with a diameter of 1-2 mm to wind into a spiral, with the ring perpendicular to the axis, and the spiral ring can move freely in the annular space between the inner wall of the small test tube and the thermometer rod. Stirring can be done manually or with the help of an external electromagnet magnetic stirrer, stirring about 60 times per minute. 3 Preparation
3.1 Install a cork on the mouth of the small test tube, make a hole in the middle of the cork, insert the thermometer into the hole, make another small hole next to the hole for inserting the thermometer, pass the stirrer rod through the small hole, and allow it to move up and down freely. 3.2 Install a cork on the mouth of the large test tube, make a hole in the middle of the cork that matches the small test tube, insert the small test tube into the hole, insert it until the mouth of the tube is flush with the upper edge of the cork, and make the center lines of the two tubes coincide. 3.3 Fill the cold bath with crushed ice (or adjust the temperature of the refrigeration equipment to 0℃). 4 Test steps
4.1 Pour the mixed sample into the small test tube to the mark, add 1 drop of distilled water with a dropper, shake vigorously for half a minute, insert the cork with thermometer and stirrer into the small test tube, and adjust the mark of the thermometer at 4.0-4.4℃ to be flush with the upper edge of the cork, the mercury ball of the thermometer is in the center of the test tube, and the lower edge of the mercury ball of the thermometer is about 8-10 mm from the bottom of the small test tube. 4.2 Insert the small test tube with the sample and thermometer directly into the cold bath pre-filled with crushed ice (or refrigeration equipment adjusted at 0℃), and cool the sample in the small test tube to 6℃ under continuous stirring, immediately take it out of the cold bath, wipe off the water marks on the outer wall of the small test tube, quickly insert it into the large test tube, and then insert it into the cold bath together, and continue cooling. 4.3 Continue to stir the sample and observe the temperature reading until the temperature drops to a minimum point, then rises to a maximum point, and remains constant at the maximum point for at least 30 seconds, then continues to drop again, record the constant temperature at the highest point, this point temperature is the crystallization point of the water-containing sample. When reading the temperature, read to 0.01°C.
If the maximum temperature remains constant for less than 30 seconds or the minimum and maximum temperatures are not obvious, re-measure. 4.4 If the sample to be measured is benzene containing water, the measured result shall be corrected according to the following formula and converted into the crystallization point of the sample without water and reported. t=to+t+-+ At2-+-0. 09 ...
National Bureau of Standards 1982-07-20 Issued
（1）
1983-03-01 Implementation
Where: - the crystallization point of the sample without water, (, to-—observed reading, ℃,
GB/T 3145-—82
t, - the calibration value of the thermometer itself, corrected according to the calibration table, ℃, At2 the temperature calibration value of the exposed part of the water column, ℃; 0.09
- the calibration value of the sample containing water converted to the sample without water, ℃. 21t 2 = 0.00016H(to - tB)
Where: 3-the temperature near the middle of the mercury column above the cork observed by the auxiliary thermometer, °C, H-the height of the mercury column of the thermometer exposed outside the cork, expressed in °C. Note: When 24t2 is less than 0.01C, no correction of At2 is required, or correction is made when it is indicated that it is necessary. 5 Precision
The following values ​​are used to judge the reliability of the results (95% confidence level). (2)
5.1 Repeatability: In two laboratories, the same tester, on the same sample, uses this standard The difference between the two results of repeated measurements should not be greater than 0.02°C.
5.2 Reproducibility; In different laboratories, by different testers, on the same sample, the difference between the two results measured using this standard method should not be greater than 0.04°C.
Test results
Take the arithmetic mean of the two parallel test results as the test result. Graticules
Figure 1 Small test tube
Figure 2 Large test tube
Figure 3 Specifications of the thermometer
Additional instructions:
GB/T 3145—82
Test position
A—Immersion mm
Various scale values
Fineest scale line (scale division value)
Long line
Digital representation
Maximum error of scale value
Extension part is allowed to be heated to
B—Total length
C—Outer diameter of rod
[)—·Length of water-sensitive ball
E-Outer diameter of mercury ball||tt ||Scale setting ball bottom to line position
}-distance
ball bottom to line position
G\--scale part length
G-distance
freezing point scale range
H·mercury ball bottom to freezing point distance
reduced part:
【minimum distance to bottom (i.e.)
1-maximum distance to preset part (i.e.)
210~220mmbZxz.net
25~ 35mm
6mm~not selected
100 ~115mm
160 ~175mm
-- 0.2( ~ +.2℃
60~70mm
This standard was proposed by the Ministry of Petroleum Industry of the People's Republic of China and is provided by the oil chemical industry! This standard was drafted by Nanjing Oil Refinery. The main drafter of this standard is Liu Minfu.
From the date of implementation of this standard, the original oil department standard SY2504-73 "Determination of crystallization point of oil" will be replaced. 314
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