Acetylene volumetric method for detecting the content of CaC2 components

Determination of Calcium Carbide Content by Acetylene Volume Method Technical support provided by Inner Mongolia Menghua Chemicals Co.,Ltd,This method refers to determining the calcium carbide (CaC₂) content in a sample by reacting calcium carbide (CaC₂) with water to generate acetylene (C₂H₂) gas and measuring the volume of acetylene produced.

Test Environment:Standard atmospheric pressure (20°C, 101.3 kPa)

Test Standard:GB/T 10665-2004

Reaction Equation:

CaC₂ + 2H₂O → C₂H₂↑ + Ca(OH)₂

I. Experimental Instruments and Reagents:

1.  Acetylene gas generator (or calcium carbide gas yield determination apparatus).

2.  Generator apparatus configuration:

 (1) Generator main body: A container with an airtight lid (equipped with a stirrer).

 (2) Gas meter: A liquid displacement-type volumetric gas meter, connected to the generator, used to collect and measure the gas volume. The meter is equipped with a leveling bottle (balance bottle).

 (3) Laboratory balance, with a precision error within 0.01 g.

 (4) The generator must be equipped with a thermometer and a barometer.

 (5) Test reagents: Saturated salt solution (used in the gas meter to reduce the solubility of acetylene in water). Distilled water or deionized water.

 (6) Sample scoop.

II. Instrument Check Before Experiment:

Check if all connecting parts of the gas yield determination apparatus are tight to ensure no gas leakage.

Check if the liquid level in the gas meter is at the zero point.

III. Experimental Procedure:

1.  Generator Water Bottle Filling and Sealing: Add a certain amount of water (usually about 50 mL, specific amount according to instrument specifications) into the outer cylinder of the generator. 

Tighten the water bottle lid, check if the conduits are clear, and ensure there is no gas or water leakage, confirming good sealing.

2.  Sampling: Use a sample scoop to place calcium carbide on the balance. Precisely weigh a prepared calcium carbide sample (our company typically uses a sample weight of 50g or 100g, recorded as m). 

Carefully transfer the sample into the dry inner cylinder of the acetylene generator, taking care not to spill the sample. The tested particle size must be precise, avoiding significant errors in particle size. 

Sieving can be used if conditions allow.

Tested particle sizes: 2mm, 5mm, 10mm, 15mm, 25mm, 50mm, 80mm.

3.  Reaction Apparatus Setup and Operation:

(1) Place the calcium carbide sample into the reactor and inject water, allowing the sample to fully contact the water and react, producing gas.

(2) Open the exhaust valve to purge the air from the generator and conduits using the generated acetylene gas. This operation removes air from the conduits and also expels the initially produced, less pure acetylene gas.

(3) Close the exhaust valve and direct the gas into the gas meter. Adjust the leveling bottle so that the liquid level inside it is even with the liquid level inside the measuring tube. Read the initial gas volume V₁ at this point. Simultaneously record the current temperature T₁ (°C) and atmospheric pressure P (kPa).

4.  Reaction and Measurement:

Shake vigorously or stir the generator continuously to allow the calcium carbide to react fully with the water.

The reaction is exothermic; wait for the generator to cool down close to room temperature. Intermittent shaking can be done during this period.

When the gas volume no longer increases and the temperature stabilizes (difference from room temperature not exceeding 0.5°C), adjust the leveling bottle again to level the liquid surfaces, and read the final gas volume V₂. Record the final temperature T₂ (Typically, the average value T of T₁ and T₂ is used for calculations).

Cleaning: Open the exhaust valve to discharge the waste gas. Clean the generator for the next use.

5.  Result Calculation:

Calculate the volume of acetylene gas produced by the sample under standard conditions (V₀):

Use the gas state equation to convert the measured gas volume to the volume under standard conditions (0°C, 101.325 kPa).

The formula is:

V₀ = (V₂ - V₁) × [ (P - Pw) / 101.325 ] × [ 273.15 / (273.15 + T) ]

V₂ - V₁: Measured acetylene gas volume (L)

Explanation/Note:

P: Atmospheric pressure during the experiment (kPa)

Pw: Saturated vapor pressure of the saturated salt solution at temperature T (kPa) (This value is much lower than that of pure water; it can be obtained from tables. Using salt solution aims to reduce this value and minimize error).

T: Average temperature inside the gas meter (°C)

6.  Calculate the calcium carbide content (ω):

According to the chemical equation, 1 mole of CaC₂ (64.10 g) generates 1 mole of C₂H₂ (occupying 22.4 L at standard conditions).

The formula is:

ω (CaC₂) = (V₀ × 64.10) / (22.4 × m) × 100%

Explanation/Note:

V₀: Acetylene volume under standard conditions (L)

m: Sample mass (g)

64.10: Molar mass of calcium carbide (g/mol)

22.4: Molar volume of acetylene at standard conditions (L/mol)

The result is the mass percentage content of calcium carbide.