This rather dubious project involves getting a standard continuous-spray air freshener can and refilling it with aromatic essential oils before re-pressurising it with butane.
This project involves high pressure combustible gas and oily substances that will absolutely saturate an entire room instantly if it all goes horribly wrong. The possibility of a reaction between some oils and the interior of the can causing internal corrosion is a slight possibility, but probably unlikely. As such you try something like this entirely at your own risk.
You'll need to make a refill adaptor which will probably be the top from an identical can. The type that sprays directly upwards instead of sideways is much better for this application. The fine spray nozzle will have to be drilled out to accept the tip of a plastic inkjet-refill style syringe without the needle. It has to be a friction fit for a good seal. The hole will also have to accommodate the end of a standard butane lighter refill can with an equally tight fit. The only other requirement is that the end that goes onto the aerosol nozzle itself is still a good tight fit and can press the nozzle down to open the internal valve.
This will only work with continuous spray aerosols. It won't work properly with the single shot dosed aerosols that squirt out a measured portion of aroma.
The aerosol can MUST be empty! If it isn't then the pressure will make the syringe act like a pneumatic ram and come out with surprising force. Usually blowing the contents of the syringe over a large area in the process. Remove the plunger from the syringe and press it into the adaptor made earlier and press it onto the top of the empty aerosol can. When everything is a nice tight fit, fill the open syringe with your choice of fragrance oils, leaving a slight air gap at the top. Put the syringe plunger in, and with it gripped firmly in your hand and with your thumb firmly on top depress the aerosols valve and squirt the oil down into the empty can. The small amount of air at the top will ensure all the oil gets pushed through the valve. If you wish you can repeat this process to put more oil in, but note that the can will have a slight pressure now.
When you've got as much oil in as you wish you can pressurise the aerosol by putting the butane refill can into your adaptor and with the aerosol can on a firm surface press the butane can down firmly to open both it's valve and the aerosol's valve simultaneously. At this point you should hear the liquid butane swooshing and bubbling into the aerosol can. This is best done outdoors due to the liberation of combustible gas. And don't do it near a naked flame or while smoking! The two cans will reach an equilibrium point where the gas transfer will slow down. At this point you can retract the butane can quickly to seal both valves instantly and give the aerosol can a good shake to mix the butane and oils. Butane is an incredibly good solvent so they will infuse well. Now put the original cap back on it and try your new aerosol to see how well it works. You should get a fine mist of butane infused with oil that instantly disperses into the air leaving a light fragrance.
It's important to note that pure essential oils are not as strong smelling as synthetic chemicals fragrances, but they produce a very deep and natural aroma. The actual aroma strength varies between oils. Some of the strongest are the citrus ones like orange, lemon,, grapefruit, lime, citronella and lemongrass, while for floral aroma lavender is quite nice. A mixture of lavender and citrus oil produces a multi-level aroma which can be quite pleasant and distinctive.
Keep in mind that the propellant is pure butane, so the usual rules about avoiding naked flames with aerosols apply.