Here you can calculate the pressure drop of circular pipes for certain gases. Three input-selectors for gas-mixtures allow you to select the gases with their volume percentages. You can see the mixture gas-density and gas-viscosity at the end of the first table. Density is temperature and pressure corrected, whereas viscosity is only compensated for temperature ( is nearly independent of gas pressure for p<10 bar ).
Please be careful with the input of the "gas flow": these are not norm liters but volume liters. That is, if you want to calculate the pressure drop at 3 bara , i.e., you have to provide the volume flow at that pressure: 300 l/h @ 1 bara would become 100 l/h @ 3bara.
More information formulas involved to your left.