What you are calling k_{eq} is the kinetic rate constant k_{kin}, which you can fix at 1e8 and not fit this parameter. What are the values of lnKe and Bpp you are using? Also your values for mass transfer params are unrealistic. k_{film} and D_p should be on the order of 1e-4 and 1e-10 for pH, respectively, then 1e-5 and 1e-12 for mAb. I would recommend you take a look at my post on transport parameters estimation (below). Also, if you want to achieve a better fit to the front of the BT curve, it is recommended to fit D_p or obtain D_p from correlation and fit D_s (this is more physically consistent but also complicates things).
I also noticed the values for your porosities are very strange. Where are you getting these values? It actually matters a lot because it changes how the phase ratio is defined and significantly affects model parameter estimation.