Nitrogen is less dense than air and is one of the main components of air. At standard atmospheric pressure, nitrogen becomes a colorless liquid when cooled to -195.8℃, and a snowlike solid when cooled to -209.8℃. Nitrogen is often used as a preservative because its chemical properties are very inactive and it is not easy to react with other substances at room temperature. But at high temperatures and energies, chemical changes occur with certain substances to make new substances useful to humans.

In the 3D printing industry, nitrogen is mainly used for gas protection and nozzle cooling during 3D printing, so that the printed product surface is smooth without further polishing, and can prevent material oxidation to achieve the best density, with the advantages of simple use, stable performance and easy operation.

N2 under normal pressure of liquid and solid solubility is extremely low, but with the increase of pressure, the solubility increased, especially for the solubility of organic compounds can improve more, even though such as SO2, NH2, C2H4 gas in a liquid or supercritical state also has a good ability to dissolve, but they are not inert substances, and residue in the extract is harmful substances, when CO2 dissolves in water or CO2 containing a certain amount of water, a partial acid, can affect the activity of extracted substances with PH and extraction of quality. Liquid N2 does not have acidity and does not affect the extracted material, so it is safe. Liquid N2 has many advantages as a solvent to replace CO2. As an extraction solvent, liquid N2 can dissolve low and medium molecular weight esters, ketones, alcohols, ethers, aldehydes and non-polar organic compounds, etc., and make some alkaloids, chlorophyll, carotene, hydroxy acids and sugars dissolve in the critical N2.

N2 solvent extraction process can be roughly divided into solvent extraction (extraction liquid and extraction substance separation) and solution regeneration (extraction and extraction agent separation). The extraction rate of the recovered extract should be considered in the extraction process. N2 as a solvent to extract and purify substances is a new subject to be studied deeply. It has high scientific value. The application of N2 to extract food, beverage, oil, flavor, medicine and other substances has been reported at home and abroad.

As an extraction solvent, nitrogen does not damage the structure of natural materials at low temperature, which is conducive to the preservation of material structure. Therefore, the physicochemical properties of N2 can be used to serve us.