How do you properly dispose of empty propane cylinders? These are not refillable tanks.?

If it is truly empty then it is not a hazard and could be disposed of like any scrap metal.

Every few months the garbage collection company for my area has a hazardous materials disposal day. You can drop off old paint, pesticides, gas containers, propane bottles and the such.

Check with your garbage collection company and see if they offer the same service mine does.

in my neighborhood the metal men come around collecting scrap metal, as long as they are empty it should be ok to just throw them away

Throw them in a bonfire and run!!