Consultation on liquid-liquid extraction

@yoelcortes, @yalinli2, @sarangbhagwat Hello, could I ask you some questions about the liquid-liquid extraction unit? Thanks for your help.

a) Does the ```partition coefficients``` in the tutorial refer to the ```octanol-water partition coefficients``` (https://biosteam.readthedocs.io/en/latest/API/units/liquid_liquid_extraction.html#biosteam.units.liquid_liquid_extraction.MixerSettler:~:text=MS1%20%3D%20bst.MixerSettler(%27MS1%27%2C%0A...,%27Methanol%27%2C%20%27Octanol%27)%2C%0A...%20%20%20%20%7D%2C%0A...%20))? The ```partition coefficients``` of methanol in the tutorial (1.38) is different from the ```partition coefficients``` found in the paper (-0.82). What does the ```partition coefficient``` of water and n-octanol mean (https://biosteam.readthedocs.io/en/latest/API/units/liquid_liquid_extraction.html#biosteam.units.liquid_liquid_extraction.MixerSettler:~:text=MS1%20%3D%20bst.MixerSettler(%27MS1%27%2C%0A...,%27Methanol%27%2C%20%27Octanol%27)%2C%0A...%20%20%20%20%7D%2C%0A...%20))? Does it also refer to the ```octanol-water partition coefficient```? Whether it took the logarithm or not?

b) If I use a custom substance (as in the following code) instead of a substance in the database, when performing liquid-liquid extraction, if I want to use ```MixerSettler``` unit, do I need to add other physical properties besides the ```partition coefficient```? When I customize the ```partition coefficient```, is it OK to define the ```n-octanol/water partition coefficient``` for each substance as it did in the tutorial (https://biosteam.readthedocs.io/en/latest/API/units/liquid_liquid_extraction.html#biosteam.units.liquid_liquid_extraction.MixerSettler:~:text=MS1%20%3D%20bst.MixerSettler(%27MS1%27%2C%0A...,%27Methanol%27%2C%20%27Octanol%27)%2C%0A...%20%20%20%20%7D%2C%0A...%20))?
```
Sugar_model=bst.Chemical('Sugar_model',
default=True,
search_db=False,
formula='C10H15O3',
Tb=350.7+273.15,
Hvap=82035.54660,
phase_ref="l",
Tm=70+273.15,
Hfus=29600,
Hf=-790760,
Tc=580,
Pc=2500002,
Vc=0.0005)
```