A couple simple ideas.Feed the vapor/gas into a tiny steam engine (available at many hobby shops.) It is easy enough then to close the fluid loop using plastic tubing. If the vapor condenses as steam does then fine, you have an engine and all you need to close the loop is enough power to drive the arc.
If the gas is combustible then it should be possible to run a small model airplane engine (and still close the fluid loop!)
Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
