The preferred (and often only) method for the management of old propane cylinders and canisters is to recycle them. Never put a propane cylinder or canister into a dumpster or other disposal container and avoid cutting the cylinder with a torch or cutting wheel. The cylinder may still contain propane and is a potential fire and explosion hazard.
Some household hazardous waste collection programs will accept a limited variety of propane cylinders and canisters for recycling. See if your city or county has such a program. Propane cylinders and canisters must be completely empty before recycling. If it isn't empty, connect the cylinder or canister to a propane-burning device such as your campstove or BBQ grill to burn off the residual propane.
Some local propane distributors and larger propane retailers may accept old propane cylinders for recycling as a service to their customers. Contact propane distributors and larger retailers in your area to see if any of them offer this service. Also, some propane exchange companies will take your old cylinder and charge a one-time upgrade fee in exchange for new equipment.
Propane cylinders and many campstove canisters are made of metal and can be recycled as scrap metal. Local scrap metal dealers can be found in the phone directory under listings for scrap metal processing. Always call ahead to confirm that they accept propane cylinders and/or canisters for metals recovery.