Development of Continuous Gas Generation Method for Hydrogen Chloride Using Azeotropic Hydrochloric Acid System

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.

Mechanism of Magic Number NaCl Cluster Formation from Electrosprayed Water Nanodroplets

“…The number of H 3 O + consistently dropped to zero, mediated by both IEM ejection and proton transfer from H 3 O + to Cl – . HCl molecules generated by the latter process rapidly evaporated from the droplet (in <100 ps), consistent with the high volatility of HCl gas . The transient presence of HCl is evident from the five singular spikes along the bottom of Figure D, which reflect the occurrence of five H 3 O + to Cl – proton transfer events (see also t = 7 ns in Figure B).…”

“… − We revised our modeling strategy to address this discrepancy, guided by the following considerations: Electrolytically generated − H 3 O + can acidify ESI nanodroplets down to pH ≈ 0 . Under these highly acidic conditions, anions such as Cl – can pair with H 3 O + , − followed by occasional HCl formation (H 3 O + + Cl – → H 2 O + HCl) . These reactions are favored at water/vapor interfaces, , suggesting facile HCl formation in ESI nanodroplets because of their high surface-to-volume ratio and their low pH.…”

“…93 Under these highly acidic conditions, anions such as Cl − can pair with H 3 O + , 94−96 followed by occasional HCl formation (H 3 O + + Cl − → H 2 O + HCl). 97 These reactions are favored at water/ vapor interfaces, 98,99 suggesting facile HCl formation in ESI nanodroplets because of their high surface-to-volume ratio and their low pH. The computational implementation of HCl formation is explained in the Methods section.…”

“…HCl molecules generated by the latter process rapidly evaporated from the droplet (in <100 ps), consistent with the high volatility of HCl gas. 97 The transient presence of HCl is evident from the five singular spikes along the bottom of Figure 3D, which reflect the occurrence of five H 3 O + to Cl − proton transfer events (see also t = 7 ns in Figure 2B). Most of these Cl − escape events took place during the first few ns of droplet evaporation, rapidly generating conditions where n NA+ > n Cl− (Figure 3D).…”