Well, in terms of Thermal Engines, you cannot even reach
The reason for this impossibility is a bit complicated and you can find it well explained in many textbooks on thermodynamics.
Here we can say that (again) in terms of a thermal engine the possibility of reaching
Intuitively this cannot be: if you consider a steam engine..well...the smoke has to go somewhere! There must be a tube, an aperture or something to let it go out! The system cannot be closed.
A way to see this impossibility is also to consider Ideal Engines or Carnot Engines; they are ideal meaning NOT that they are
For these kind of engines the efficiency is:
This efficiency could be
Now a bit that it is even weirder....energy degrades in quality when we use it! So when we use energy to do work we reject energy that has a low "quality" meaning that we cannot use it again in an efficient way. Again, the smoke from our steam engine; it is hot, it is a gas....we could use it as a reservoir of energy for an engine, BUT it has a low quaity compared to the energy it came from (stored in coal and freed during combustion).