Using a lattice Boltzmann model, the phase separation of a binary fluid in the presence of immobile, penetrable particles is studied in two dimensions. The particles are preferentially wetted by one of the fluid components. At early times, the hydrodynamic flow promotes the growth of the fluid domains. At later times, the domains are pinned to a finite size if there is a sufficiently strong interaction between the particles and the compatible fluid. The final size of the domains depends on the specific strength of the particle-fluid interaction and on the particle concentration. These results indicate that the domain size can be tailored by varying the chemical nature and the number of the particles.