Determination Method of Benzene Crystallization Point
Benzene is a colorless, sweet-smelling, and volatile liquid with the chemical formula C₆H₆. It belongs to aromatic hydrocarbons and is also an important basic raw material in the petrochemical industry. It is poorly soluble in water but highly soluble in organic solvents, and is often used as a solvent itself. Benzene is highly toxic and classified as a Group 1 carcinogen by the World Health Organization (WHO). Long-term exposure may cause serious diseases such as leukemia. It is widely present in industrial products such as coatings, adhesives, and fuels, and is also used in the manufacture of chemicals such as dyes, pharmaceuticals, and pesticides.
Experimental Purpose:
The main purpose of determining the benzene crystallization point is to evaluate the purity and quality of benzene, and provide key data support for the optimization of production processes in related industries. Specifically:
Purity Evaluation: The crystallization point of benzene is directly related to its purity. By determining the crystallization point, we can judge whether there are impurities in benzene and thus evaluate its quality.
Process Optimization: In fields such as petrochemicals and materials science, the crystallization point data of benzene is crucial for controlling material states and optimizing production processes.
Standard Compliance: The determination is carried out in accordance with the national standard GB/T 3145-2023 to ensure the accuracy and comparability of experimental results.
Experimental Samples and Instruments:
Experimental Samples：Benzene,Distilled water
Experimental Instruments:SH406B Fully Automatic Crystallization Point Tester (compliant with the standard GB/T 3145)
Experimental Procedures:
1.Sample Preparation:Take a homogeneous benzene sample, measure approximately 50 mL with a graduated cylinder, and pour it into a dry test tube. Add 1 drop of distilled water, shake the test tube vigorously for half a minute to disperse the water evenly in the sample.
2.Instrument Assembly:Insert a thermometer into the test tube (the mercury bulb of the thermometer is located at the center of the test tube, with the bottom about 8~10 mm away from the bottom of the test tube), and fix it with a cork to ensure that the thermometer scale line is flush with the upper edge of the cork. Insert the assembled test tube into a double-layer sleeve (the air sleeve can be filled with thermal insulation materials to reduce heat loss).
3.Cooling and Stirring:Immerse the test tube in a cold bath (such as an ice bath or semiconductor refrigeration equipment), start the stirring device, and stir the sample at a constant speed. Continue cooling until the temperature of the sample drops to about 6℃, then immediately take out the test tube, wipe off the water stains on the outer wall, and quickly reinsert it into the cold bath for further cooling.
4.Crystallization Point Determination:Observe the temperature change. When solids precipitate in the sample, the temperature will first drop to the lowest point, and then rise to the highest point due to the heat released by crystallization. Record the temperature when the highest point remains constant for 30 seconds as the crystallization point of the water-containing sample.
Experimental Results
Record the temperature at which the temperature of the benzene sample rises to the highest point during cooling and stabilizes for 30 seconds: 5.30℃.