Most hot air desoldering stations use pure nitrogen, for obvious reasons. The footprint of the air flow should be slightly larger than the component.

It can destroy PCBs though, I've seen it done by careless operators.

 

If you are desoldering through-hole components, heat from the bottom (solder side). For surface mount, you will want a collar on a standard heat gun. The best collar I have, I made from 1.25 inch conduit that I cut to 3 inches and squeezed 3/4 of the output side shut. That left me with a hole about a half inch for heat output. Let the gun warm up before putting such restrictive collars on. Some guns tolerate this better than others. If you have a gun with multiple heat settings, use the lowest that will provide solder melting temps ~440deg F. If the gun is the type with a high of 1100 deg F or more, the restrictive collar will not bother it much at all on a low setting.

If you do not have a desk or bench vise, get one.

Place the PCB in the vice, air gun in one hand and pliers in the other. Pull while heating.. This happens quickly so you do not need to overly heat the board and remaining components.

 

http://www.opencircuits.com/Salvage_Parts_and_Sources#Salvage_Techniques

Skimmed over this article.........seriously doubt I would use, let alone recommend using a propane torch to salvage components, unless the like of soldered-in 1/4" male spade terminals which the heat won't damage anyway.............

Nice list of salvage sources tho'