Hi everyone! Sorry if I am posting this in the wrong place. Im doing my Msc in chemistry, and I have a little problem with my current experimental setup. This setup have been used before by Phd students, but not for the same experiments I want to do. Any advice would be greatly appriciated! The experimental setup consists of a stainless steel cell with a fixed volume placed inside an incubator (large fridge). There are three valves connected to the incubator, (1) introduction of water (by applying a vacuum to the cell beforehand) and evacuating the cell of water, (2) application of pressure, which is connected to a chosen gas flask, (3) a sampling valve for gas sampling and evacuating the cell of gas. Im want to form methane hydrates, which form at high pressures and low temperatures. I fill the cell with an amount of water, and apply pressure determined through the pressure of the gas flask. The container is then cooled to form hydrates, which gives two phases: hydrate and excess methane gas. What I would like to do is apply carbon dioxide gas, which is thought to replace the methane molecules in the hydrates. However, if I evacuate all the methane gas from the container, the hydrates will melt. I need to evacuate the cell of excess methane gas, while adding CO2 gas without a pressure drop. I was thinking of gradually adding CO2 gas, while evacuating the excess methane gas from another valve. But I think they will form a mixture through diffusion, which makes it hard to completely evacuate the methane gas, no matter how many times i try. Any ideas?