Hydrogen is a very important industrial gas in chemical processes. It is very volatile; therefore, it can escape from the process units and its mass balance is not always correct. In many industrial processes where hydrogen is reacted, kinetics are often related to hydrogen pressure. The right thermodynamic properties of hydrogen can be found for a process simulation and optimization; they can be estimated by the Grayson-Streed model. In the case studied, a methanol plant with a capacity of 150,000 tons/year, the flow rate of hydrogen (H[2]) can be optimized using nonlinear programming, but good estimates of thermodynamic properties of hydrogen had to be found. In the case study, the model is in relatively good agreement with experimental measurements in the existing methanol production plant. An additional flow rate of hydrogen can increase the methanol production by 1.2%. Total potential profit increase of the additional methanol production was estimated to be 30 kEUR/a (or 10[to the third power] euros/year). (Contains 2 figures and 3 tables.)