Hydrogen chloride dehydration method

A method of dehydrating hydrogen chloride gas through a multi-step process, the method comprising:

• a first dehydration step of bringing hydrogen chloride gas and concentrated sulfuric acid into contact with each other;
• and
• a second dehydration step of bringing hydrogen chloride gas that has been obtained through the first dehydration step into contact with concentrated sulfuric acid,
• wherein a concentration of the concentrated sulfuric acid used in the second dehydration step is higher than a concentration of the concentrated sulfuric acid used in the first dehydration step,
• wherein at least part of the concentrated sulfuric acid that has been used in the second dehydration step is reused in the first dehydration step,
• wherein the multi-step process consists of the first dehydration step, the second dehydration step, and a third dehydration step carried out after the second dehydration step,
• wherein at least part of concentrated sulfuric acid that has been used in the third dehydration step is reused in the second dehydration step,
• a concentration of the concentrated sulfuric acid reused in the second dehydration step after having been used in the third dehydration step is not lower than 96 wt %,
• a concentration of the concentrated sulfuric acid reused in the first dehydration step after having been used in the second dehydration step is not lower than 85 wt % and lower than 96 wt %, and
• a concentration of the concentrated sulfuric acid after having been used in the first dehydration step is not lower than 75 wt % and lower than 85 wt %.