Chemistry - How to increase the concentration of HCl

Solution 1:

Add Calcium Chloride to destroy the azeotrope. Then distill and capture the vapor phase.

See the second method "Extractive Distillation" here:

http://www.jacobs.com/uploadedFiles/wwwjacobscom/20_Learn_About_Us/25_Products/252_Chemetics/Hydrochloric%20Acid%20Concentration.pdf

(Obviously, proper equipment and safety precautions are essential.)

Solution 2:

Irrespective of the potential hazards to an inexperienced chemist attempting distillation of hydrochloric acid, especially absence of adequate safety measures such as a fume hood, in this case, distillation will not result in a higher concentration of acid. Hydrogen chloride and water form a constant-boiling mixture (azeotrope) at ~20% HCl, which is what you are already starting with. I suggest you read the Wikipedia page on Hydrochloric Acid for starters.