In my story, Saturn’s moon Titan’s methane lakes are inhabited by microorganisms that photosynthesize, converting hydrogen into methane (A process thought possible on Titan after some study). This helps supply the methane continuously cycled through Titan’s atmosphere.
Enter my question. A horse-sized artificial life-form is set loose on Titan that is capable of “breathing” methane in the air (or drinking liquid methane and storing it) and producing hydrogen. Methane isn’t a substitute for oxygen, so the “breathing” process would probably be more similar to eating, but it would be nice if it still “looked” like breathing (for visual effect).
Is this feasible, and if so, how could this process occur? My first thought was combustion, but there’s nothing to combust with (Titan has little oxygen). Could it still be used alone to fuel a physically active animal? Most non-combustion processes I find for methane seem to involve oxygen and carbon dioxide anyway. Complex life without oxygen seems like a tall order, but if there’s an easy approach I’m open to it. Some other questions in this SE mention single-celled life, but I’m not sure if those solutions would apply to a much larger organism.
(If combustion is actually feasible, that would be ideal. Probably too extreme to be true, but I have a dream of the reaction making the creature exhale flames in oxygen-rich environments.)