Using an inline process refractometer to measure the concentration of hydrochloric acid solution

Hydrochloric acid is a common inorganic acid and one of the important raw materials in the chemical industry. It is widely used in chemical raw materials, dyes, medicines, food, printing and dyeing, leather, sugar making, metallurgy and other industries. It is also used for the regeneration of ion exchange resins and electroplating and metal surface cleaning agents. In many cases, it is very important to accurately detect the concentration of hydrochloric acid.

There are many ways to determine the concentration of hydrochloric acid. The industrial hydrochloric acid concentration detection methods mainly include physical methods, chemical methods and instrumental methods. In actual operation, the appropriate method can be selected for detection according to the specific situation.

Instrumental method

1. pH meter method: Use a pH meter to determine the pH of the hydrochloric acid solution, and calculate the concentration of hydrochloric acid by constructing a standard curve.

2. UV-visible spectroscopy: The hydrochloric acid solution absorbs specific wavelengths of the ultraviolet or visible spectrum, and the concentration of hydrochloric acid is calculated by measuring the relationship between absorbance and concentration.

3. Colorimetric method: Use standard solution and hydrochloric acid solution to react with a chemical indicator (such as phenolphthalein) respectively, and judge the concentration of hydrochloric acid by comparing the color depth

Chemical method

1. Acid-base titration method: Titrate hydrochloric acid solution with standard base (such as sodium hydroxide solution), and calculate the concentration of hydrochloric acid using the chemical equation of acid-base reaction (such as: NaOH HCl =NaCl H20).

2. Complexometric titration method: Hydrochloric acid reacts with a coordination agent (such as thiodiacetic acid) to form a stable complex, and the concentration of hydrochloric acid is calculated by titrating the consumption of the coordination agent.

3. Reduction titration method: Titrate hydrochloric acid solution with a standard oxidant (such as potassium permanganate solution), and calculate the concentration of hydrochloric acid based on the molar ratio of the reactants.

Physical method

1. Density determination method: Take out a known volume of hydrochloric acid, weigh it with a balance, and use standard hydrochloric acid of known concentration as a reference to calculate the concentration of hydrochloric acid by the change in density.

2. Refractive index determination method: The refractive index of hydrochloric acid solution is proportional to the concentration, and the concentration can be indirectly reflected by measuring the refractive index of hydrochloric acid solution.

The refractive index determination method, that is, the concentration of hydrochloric acid solution is detected by refractometry, is based on the principle of light refraction. The concentration of hydrochloric acid solution is determined by measuring the refraction angle of light when it propagates in the hydrochloric acid solution.

The working principle of the refractometer is based on Snell's law, that is, light will refract when it propagates in two media. When light passes from one medium into another, the propagation speed of the light changes, causing the propagation direction of the light to deflect. This deflection angle is related to the refractive index of the two media.

In order to measure the concentration of a substance, a standard curve needs to be established in advance. The standard curve is obtained by measuring a series of samples of known concentrations. First, a series of samples of known concentrations are prepared and their concentrations are determined using other methods (such as chemical analysis). Then, the refraction angle of these samples is measured using a refractometer, and the measurement results are compared with their known concentrations. By plotting the relationship between the refraction angle and the concentration, a standard curve can be obtained.

Once the standard curve is established, the refractometer can be used to measure samples of unknown concentration.

The measurement accuracy of the refractometer is affected by many factors. First, the transparency of the sample affects the propagation and refraction of light. If the sample is opaque or contains suspended matter, it will lead to inaccurate measurement results.

The hydrochloric acid solution in this plant is clear and transparent, which is conducive to our online process refractometer for real-time concentration detection.

In addition, there is another very important problem in detecting the concentration of hydrochloric acid solution, that is, the product material must be able to withstand the corrosion of high-concentration hydrochloric acid solution.

We use special engineering plastic PEEK as the measuring end of the online refractometer to contact the hydrochloric acid solution, and have achieved good results in practical applications.

Relationship between specific gravity of hydrochloric acid and its concentration and temperature: