How solid carbon dioxide (CO2) is produced

(1.) First, gases with a high concentration of carbon dioxide are produced. Such gases can be a byproduct of another process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation

(2.) Second, the carbon dioxide-rich gas is pressurized and refrigerated until it liquifies 

(3.) Next, the pressure is reduced. When this occurs some liquid carbon dioxide vaporizes, causing a rapid lowering of temperature of the remaining liquid (the vaporized CO2 will absorb some of the heat from the liquid when it vaporized).

(4.) Finally, the extreme cold causes the liquid to solidify into a snow-like consistency 

CO2 melting point is −56.6 °C; −69.8 °F; 216.6 K (Triple point at 5.1 atm) 

CO2 sublimation condition is −78.5 °C; −109.2 °F; 194.7 K (1 atm)
Diagram of solid CO2 production