If you're below 50, you can still get the box containing the solvent, but you can't open it. It is bound to account like other store free items. If you have room to save it until you reach level 50, you can do that. Or, since the box is a store item, you can also mail it to someone else by paying 2 Mithril Coins.
If you're level 50+ but not near level cap, you can open the box, and the solvent itself is not bound. They sell easily on AH for 25-30g or more. If you want to keep it for when you reach level cap, the solvents do stack, so if you accumulate several, they'll only take up one slot.