Electric Charge Quantization in SU(3)_C X SU(3)_L X U(1)_X Models
  Basing on the general photon eigenstate and the anomaly cancelation, we have naturally explained the electric charge quantization in two models based on the SU(3)_C X SU(3)_L X U(1)_X gauge group, namely in the minimal model and in the model with right-handed neutrinos. In addition, we have shown that the electric charges of the proton and of the electron are opposite; and the same happens with the neutron and the neutrino. We argue that the electric charge quantization is not dependent on the classical constraints on generating mass to the fermions, but it is related closely with the generation number problem. In fact, both problems are properly solved as the direct consequences of the fermion content under the anomaly free conditions. 
Phung Van Dong and Hoang Ngoc Long