What Is Dry Ice and How Is It Made?

With temperatures rising over the summer, it's hard to stay away from ice-cold beverages and ice cream to cool down. But did you know that there is a type of ice that turns directly into vapor? Let's dig deeper and discover what is dry ice and what it's mostly used for.

What is dry ice made of? Dry ice is basically solid carbon dioxide that changes directly from a solid to a gaseous phase through the process of sublimation. Carbon dioxide in its gaseous state is a chemical compound that is odor-free, colorless and tasteless. Under pressure and at low temperatures, carbon dioxide becomes an opaque white solid. Dry ice also has a lower temperature compared to water ice, making it an effective cooling agent when other methods of cooling are inefficient or unavailable.

1. Production of Gases

First, gases with a high concentration of carbon dioxide are produced. Carbon dioxide-rich gases are acquired during the refinement process of ammonia and petroleum. The carbon dioxide is suctioned off during the refinement process. Impurities from the carbon dioxide are then removed to ensure that it is “food grade” before being turned into its solid form.

2. Liquefaction of Gases

Carbon dioxide-concentrated gases are then pressurized and refrigerated to turn them into liquid form. Carbon dioxide liquefies at a pressure of approximately 870 lbs. per square inch at room temperature. The pressurized and liquified carbon dioxide is then pumped into holding tanks and shipped in large quantities by tank trucks to dry ice manufacturers.

3. Transfer of Liquified Carbon Dioxide to Tank Trucks

The liquid carbon dioxide is transferred by the tank trucks to the dry ice manufacturer's plant. After the liquid carbon dioxide has been transferred to the huge tanks, it is kept refrigerated and under pressure so it will remain in its liquid state. 4. The pressure is reduced to allow some liquid carbon dioxide to vaporize and to lower the temperature rapidly.

4. Release to the Dry Ice Press

The liquid carbon dioxide is released from the tanks through the pipes and into the dry ice press. The movement of the liquid carbon dioxide from a highly pressurized environment to atmospheric pressure causes it to expand and evaporate quickly, cooling it to its freezing point (-109 degrees Fahrenheit) in the process. Extremely low temperatures solidify the remaining carbon dioxide into a snow-like consistency.

5. Compression Into Blocks

The solidified carbon dioxide is compressed into large blocks of dry ice. A pressure of about 60 tons squashes the snow-like carbon dioxide into a large block of dry ice for about five minutes. The resulting block of dry ice measures about 2 feet wide and 10 inches tall and weighs about 220 lbs.

6. Cutting Into Smaller Blocks

Each block of dry ice is then cut into four smaller blocks and stored in containers at extremely cold temperatures. Using a pneumatic saw, the large block of dry ice is then cut into four parts with each weighing about 55 lbs. Then it is stored in containers in freezing temperatures to prevent sublimation.

7. Wrapping

The final step is wrapping the blocks in paper for safe handling. Through the use of a machine, the blocks of dry ice are wrapped in paper, as any human contact with the dry ice during handling can cause freezer burn. The blocks of dry ice are now ready for shipping to wholesalers and distributors.

Manufactured dry ice also comes in several forms: as a block, as small and cylindrical pellets about 13 or 16 millimeters in diameter, or as tiny cylindrical pieces measuring about one-eighth of an inch in diameter.

Now that you're aware of the properties and uses of dry ice, it's also important to know and practice safety precautions when handling it. As useful as it may be, dry ice can also cause carbon dioxide poisoning and potential injuries such as freezer burn. Here are some safety practices to keep in mind when using dry ice:

As a final tip, remember that summer can also be a season of power outages, so you might find dry ice handy when you have a lot of frozen food in the refrigerator that needs to be kept cold. Just don't forget to remove it from the freezer when the power goes back on!

Featured Image by Bruno Glätsch from Pixabay