Abstract
Standard gases are often prepared using high-pressure gas cylinders. However, it is difficult to accurately prepare a known concentration of hydrogen chloride (HCl) gas using this method because HCl is highly corrosive and adsorptive. In this study, a simple method for the continuous generation of HCl gas was developed using a diffusion tube containing hydrochloric acid and a nitrogen carrier gas. The concentration of HCl produced from this system was almost unstable, but constant gas generation was realized for several hours when azeotropic hydrochloric acid (20.6% HCl in water) and a temperature near the azeotropic point (108.5 °C) were used, resulting in the generation of 103.6 ppm (mean, n = 5) of HCl gas with a relative standard deviation (RSD) of 2.34%. In this case, the percentage of HCl present in the entire gas mixture of HCl and water vapor was 22.5%, which is almost equivalent to the HCl content in the azeotropic hydrochloric acid (20.6%). The HCl concentration could also be controlled by changing the flow rate of the carrier gas. This work demonstrates a simple technique based on the diffusion theory that allows for the constant, controllable generation of a known concentration of HCl gas using an azeotropic hydrochloric acid system.
Highlights
Hydrogen chloride (HCl) is a pungent, highly corrosive, and toxic substance [1].It dissolves in water and exists in gaseous or aerosol forms in the atmosphere [2].Gaseous hydrogen chloride (HCl) is directly released into the atmosphere from volcanos [3], waste incineration [4], coal combustion [4,5], biomass burning [6], and manufacturing processes [4]; it is produced from the sea-salt dechlorination of the marine boundary layer [7]
HCl gas was generated for approximately 5 h using a generation system with azeotropic hydrochloric acid at 108.5 ◦ C, and its concentration was measured every hour with both mercury(II) thiocyanate spectrophotometry and the detector tube method
The mean HCl concentration determined from five measurements taken during the course of gas generation was determined by spectrophotometry to be 103.6 ppm (v/v; converted to the value at 20 ◦ C) (2.35% of relative standard deviation (RSD)) and by the detector tube method to be 106.7 ppm (v/v at 20 ◦ C)
Summary
Hydrogen chloride (HCl) is a pungent, highly corrosive, and toxic substance [1].It dissolves in water and exists in gaseous or aerosol forms in the atmosphere [2].Gaseous HCl is directly released into the atmosphere from volcanos [3], waste incineration [4], coal combustion [4,5], biomass burning [6], and manufacturing processes [4]; it is produced from the sea-salt dechlorination of the marine boundary layer [7]. Hydrogen chloride (HCl) is a pungent, highly corrosive, and toxic substance [1]. It dissolves in water and exists in gaseous or aerosol forms in the atmosphere [2]. Gaseous HCl is directly released into the atmosphere from volcanos [3], waste incineration [4], coal combustion [4,5], biomass burning [6], and manufacturing processes [4]; it is produced from the sea-salt dechlorination of the marine boundary layer [7]. HCl is often used in an aqueous form as hydrochloric acid to produce materials such as fertilizers, textiles, rubbers, and electronics [10]. The concentration of gaseous HCl used in such workplaces is often on the scale of ppm [11,12]; this is dangerous because when HCl gas is inhaled and contacts moisture in the upper respiratory tract it rapidly dissociates [13]
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