In this paper we consider the barotropic compressible quantum Navier-Stokes
equations with a linear density dependent viscosity and its limit when the
scaled Planck constant vanish. Following recent works on degenerate
compressible Navier-Stokes equations, we prove the global existence of weak
solutions by the use of a singular pressure close to vacuum. With such singular
pressure, we can use the standard definition of global weak solutions which
also allows to justify the limit when the scaled Planck constant denoted by
ϵ tends to 0