Density Data of Two (H2 + CO2) Mixtures and a (H2 + CO2 + CH4) Mixture by a Modified Burnett Method at Temperature 673 K and Pressures up to 25 MPa Cheng, S.; Shang, F.; Ma, W.; Jin, H.; Sakoda, N.; Zhang, X.; Guo, L.; Journal of Chemical & Engineering Data 2019, 64, 1693-1704