Application and preparation technology of standard gas

Standard gas is an industry term for leading gas, and standard gas is a standard substance. Standard materials are highly uniform, stable and accurate measurement standards. They have the basic function of reproducing, preserving and transferring the value. They are used to calibrate measuring instruments and measurement processes in the fields of physics, chemistry, biology and engineering measurement. , Evaluate the accuracy of the measurement method and the detection ability of the testing laboratory, determine the characteristic value of the material or product, and conduct the value arbitration.

      Whether it is laboratory chromatographic analysis or calibration of online analytical instruments, a large amount of high-quality standard gas is required to accurately calculate the content of components in the product. Therefore, standard gases have been widely used in product quality supervision and quality control, instrument calibration, atmospheric environment monitoring, medical and health, clinical testing, and evaluation of analytical methods. In recent years, the petrochemical industry has developed rapidly. When petroleum is used as a raw material to produce polymer-grade ethylene, propylene, hydrogen, benzene, and p-xylene products, the analysis of product composition is realized by chromatographic analysis.

1. Preparation of standard mixed gas

      The standard mixed gas is prepared by using a high-purity gas as a dilution gas and adding one or more other high-purity gases. Standard gas preparation methods mainly include weighing method, partial pressure method, volume method, permeation method, saturation method, electrolysis method, exponential dilution method, flow ratio mixing method, etc. From the perspective of gas dynamics, it is divided into static gas distribution method and Dynamic gas distribution method. The static gas distribution method is obtained by returning a certain amount of gaseous or vaporous raw material gas into a container with a known volume, filling it with diluent gas, and mixing it.

2. Preparation method of single component

      The method of preparing a single-component standard gas varies depending on the nature of the substance. For liquid substances with strong volatility, they can be prepared by their volatilization effect, and those that cannot be prepared by volatilization can be prepared by chemical reaction methods.

Standard mixed gas preparation technology

1. Pressure ratio method: In this method, when preparing a mixed gas, the pressure of each component is measured and the gas is distributed according to the specified concentration.

2. Static volume method: At present, the national standard still uses static volume method for gas distribution device.

3. Gravimetric method: This method uses a high-load precision balance to weigh each gas component in the steel cylinder, and calculate the concentration of the standard gas in the steel cylinder according to the mass ratio of each component.

4. Permeation tube method: Permeation tube is a kind of equipment to provide raw material gas source, mainly composed of a small container for raw material liquid and permeable membrane.

5. Mass flow ratio method: This method uses the flow ratio mixing method to prepare the standard gas. Therefore, the accurate measurement of the flow rate is the key to ensuring the preparation.