Hydrochloric Acid (HCl):
HCl can be produced on purpose (burner method) or as a by product. The burner method produces cleaner material with fewer impurities.
While there are many uses for HCl, the one market that can cause wild swings in Oil&Gas, since they use large volumes in drilling wells.
Most industrial HCl comes as a by product of Polyurethane (TDI), which is used to (primarily) to make car seats.
Note: If Rig counts (Oil&Gas) go up and new auto sales go down, you could have a supply issue.
Up Stream Materials/Building Blocks:
TDI (By product)
Titanium Dioxide (By product)
Down Stream Materials Consuming Hydrochloric Acid:
Keller's Reagent Aluminum Etch