TL431 / TLV431 supercapacitor voltage clamping circuit
Your circuit as you have it has several problems:


The BC557 is unsuitable since it is rated to only 100mA.
Q2 has no collector resistor so is held out of saturation and will get hot (very hot).
Trying to get Q3 into saturation is pointless, you should spread the dissipation between the resistor and the output transistor.
You need to positively turn off the ouptut transitor or leakage may be a problem.
You have very little headroom for the TLV431, though it will work. 


I'd suggest the following components may be viable at 2A charging current:







simulate this circuit &ndash; Schematic created using CircuitLab

The waveforms would be like this:



The output stage (both resistor and transistor) have to dissipate about 5.3W. power resistors are vey expensive so it's best to keep the BD437 out of saturation and spread the power between them. If you have multiple Supercaps then you are going to need to consider how much power is dissipated when you have multiple units connected together.
Maybe you should consider a fan.