High-pressure speed of sound in pure CO2 and in CO2 with SO2 as an impurity using methanol as a doping agent

•Methanol is a suitable dopant for speed of sound measurements in CO2+impurities.•Experimental c in CO2-rich mixtures CO2+CH3OH, CO2 +SO2 and CO2+CH3OH+SO2.•Extrapolation of c in pure CO2 compared with the literature and the Span-Wagner EoS.•Small effect of methanol on CO2+SO2 in experiments is negligible for modeling.•Validation of the PC-SAFT EoS and the REFPROP 9 software for the studied mixtures.