The first possibility is simply to take them to a local tip – déchetterie. Not all, however, accept empty gas bottles (bouteilles de gaz) so we advise you to check the council’s website or phone the tip to ask first.
Otherwise, the gas sector in France recommends that you take the bottle into a shop that sells that specific brand so it can be recycled for reuse.
You may even get a reimbursement of part of the price you paid if you have a bulletin de consignation that you kept from the original purchase.
If in doubt, there is more information about how to identify the make of the bottle and a local seller of the brand at the France Gaz Liquides.