240v Inline Fan running On 120v?
The fan may or may not work on 120V, it's impossible to say without more information.  Best not to risk it.  It might be possible to rewire the fan to run on 120V--many appliance motors are dual-voltage, depending on how the windings are connected--but again, it's impossible to say without more information.

Running a 240V device from two separate 120V branch circuits is not safe or compliant with electrical codes in the US.  Your country may be different on the code front, but it's still not safe.

Consider what happens when you have one (male) plug connected to one circuit, and the other (male) plug not plugged into anything.  The unconnected male plug will be connected to 120V from the other circuit through the fan motor.  The motor is almost certainly low enough in impedance that you now have exposed contacts sitting at 120V with the ability to apply a lethal amount of current to anyone who comes into contact with them.

So don't do it.  Have an electrician run a proper 240V circuit or get a 120V fan.