Input is 10 coal, which is 4x10=40 MJ of energy.
Output is 5 solid fuel, which is 5x12=60 MJ of energy.
Output of 10 petroleum gas, which is 6 MJ of energy.

Somehow, this magical process creates 26 extra MJ of energy than goes in. I'm assuming that the solid fuel is supposed to represent the left over energy (coal stuff) that is not turned into gas. Maybe change that so that only 1 solid fuel is produced. Because, in the wiki article you link, the stuff released from coal is more than just petroleum; there are other gasses that are effectively pollution.

Also, consider using Chemical science packs in the tech tree.

Agree about the energy, will fix this (the solid fuel is supposed to be coke; didn't want to include a new resource). Getting a bit more energy out is ok, though, since the process is endothermic and consumes steam (which costs energy to make). 10 gas, 3 coke would be almost exactly breakeven.
Petroleum gas is a bit of a strange beast in Factorio (how do you make sulphur out of methane?), so I've always considered it to be a mix of gases you get from refining fossil fuels (some light alkanes, some SOx, some SH2, some CO - pretty much the same as coal gas, only different ratios).
I explicitly don't want to use Chemical science, since the whole point is to allow you to limp along to coal liquefaction if you somehow fail to discover oil. Also, the process is arguably older and lower tech than oil refining.