Multistage Membrane Separation and Purification Process and Apparatus for Separating High Purity Methane Gas

An apparatus for purifying methane gas comprising:

• supply part to supply biogas;
• compression and cooling part to compress and cool down the biogas supplied from the supply part;
• and
• purification part containing the 4-stage polymer separation membrane system for gas separation to separate carbon dioxide from the gas compressed and cooled down in the compression and cooling part wherein the residue stream of the first polymer separation membrane is connected to the second polymer separation membrane, the residue streams of the second polymer separation membrane is connected to the third polymer separation membrane, and the permeate stream of the second polymer separation membrane is connected to the fourth polymer separation membrane.