Even if it winds up back in the atmosphere, it's displaced an equivalent amount of new CO2 going into the atmosphere.
Pulling enough CO2 to make a kilogram of propane and then burning that kilogram of propane for electricity is still better than burning a kilogram of freshly fracked propane.
One offsets consumption. One just adds consumption.
Only if your source of electric doesn't add CO2. If you burn coal to make propane you are worse off CO2 wise than using regular propane. We have a lot of wind and solar, but most places they are still a minor part of the electric mix (if this applies to you, it wouldn't be hard to get a lot more wind/solar in your grid).
- This process produces hydrocarbon fuel. It will be burned and the carbon will return to the atmosphere.
I suppose propane could become a chemical feedstock. Then the carbon could theoretically be tied up for a while.