In a near future society, man will be mining asteroids far from Earth. One technology on board their ships is a hydrocarbon assembler. It takes in energy, water and carbonaceous asteroid matter and assembles hydrocarbon chains of various lengths and release the oxygen from the water for breathing or other uses.
This is dumb machine that cranks out multiple moles of hydrocarbon molecules of particular length, it doesn't do smart replicator-like molecular assembly. This assembler maybe be able to do simple assembly tasks like lining the chains up or laying them in an overlapping patterns.
I know fuel is made from hydrocarbon chains, but what other materials can be made from them?