Industrial Gases

The Industrial Gases Industry: Essential to U.S. Manufacturing, Health Care, Domestic Energy Production and Energy Efficiency

What is the industrial gases industry?

The American industrial gases industry provides essential products to manufacturers, innovators and services that help drive the U.S. economy. Industrial gases producers use advanced technologies to supply gases like oxygen, nitrogen and hydrogen. Many of these gases are used in manufacturing, health care, transportation and other essential industries. While the industrial gases industry uses natural gas, the industrial gases industry is not a producer or distributor of natural gas.

• The industrial gases industry produced approximately $12.2 billion worth of products in 2014 and employed approximately 60,000 American workers.*
• The industrial gases industry supplies products to industries that account for 25% of America’s Gross Domestic Product.*

Liquefaction of Gases

Liquefaction of gases is the process by which substances in their gaseous state are converted to the liquid state. When pressure on a gas is increased, its molecules closer together, and its temperature is reduced, which removes enough energy to make it change from the gaseous to the liquid state.

Critical Temperature and Pressure

Two important properties of gases are important in developing methods for their liquefaction: critical temperature and critical pressure. The critical temperature of a gas is the temperature at or above which no amount of pressure, however great, will cause the gas to liquefy. The minimum pressure required to liquefy the gas at the critical temperature is called the critical pressure. For example, the critical temperature for carbon dioxide is 304K (87.8°F [31°C]). That means that no amount of pressure applied to a sample of carbon dioxide gas at or above 304K (87.8°F [31°C]) will cause the gas to liquefy. At or below that temperature, however, the gas can be liquefied provided sufficient pressure is applied. The corresponding critical pressure for carbon dioxide at 304K (87.8°F [31°C]) is 72.9 atmospheres. In other words, the application of a pressure of 72.9 atmospheres of pressure on a sample of carbon dioxide gas at 304K (87.8°F [31°C]) will cause the gas to liquefy.

Differences in critical temperatures among gases means that some gases are easier to liquefy than others. The critical temperature of carbon dioxide is high enough so that it can be liquefied relatively easily at or near room temperature. By comparison, the critical temperature of nitrogen gas is 126K (–232.6°F [–147°C]) and that of helium is 5.3K (–449.9°F [–267.7°C]). Liquefying gases such as nitrogen and helium obviously present much greater difficulties than does the liquefaction of carbon dioxide.

Methods of Liquefaction

In general, gases can be liquefied by one of three methods: (1) by compressing the gas at temperatures less than its critical temperature; (2) by making the gas do some kind of work against an external force, which causes the gas to lose energy and change to the liquid state; and (3) by making gas do work against its own internal forces, also causing it to lose energy and liquefy.

In the first approach, the application of pressure alone is sufficient to cause a gas to change to a liquid. For example, ammonia has a critical temperature of 406K (271.4°F [133°C]). This temperature is well above room temperature, so it is relatively simple to convert ammonia gas to the liquid state simply by applying sufficient pressure. At its critical temperature, that pressure is 112.5 atmospheres, although the cooler the gas is to begin with, the less pressure is needed to make it condense.

Source: Encyclopedia.com/science