Carbon dioxide is a colorless gas, it has a small but sharp odor and a slightly sour taste. Each molecule of carbon dioxide consists of one atom of carbon and two atoms of oxygen. Its chemical formula is CO2. Carbon Dioxide is about 1.5 times heavier than air. The specific volume at atmospheric pressure (101.3 kilopascals) and 70 F (21 C) is 8.74 ft3/lb. Under normal conditions it remains stable, inert and non-toxic. To liquefy CO2 it must be under 300 pound per inch gage(psig) at 0 F or 838 psig at 70 F. Above the critical temperature of 87.9 F, at which all three phases gas, liquid, or solid may exist in equilibrium with one another, CO2 can exist only as a gas, no matter what amount of pressure. When liquid CO2 is cooled to -69.9 F and the pressure drops to 60.4 psig it turns into dry ice snow. All CO2 existing in the atmosphere is estimated to be 720 x 109. Carbon dioxide makes up about 0.03 percent of the air. Although that is a small amount, plants and animals depend upon it for life. Green plants make their nutrients with it. They mix the carbon dioxide with water to make sugar by a process called photosynthesis. From the sugar, the plants then make starch and cellulose. Animals eat the plants and in getting energy from the food, they produce carbon dioxide and return it to the air as they breathe. Research in Muana Loa and the South Pole showed that CO2 content in the atmosphere has increased from a presumed 250 ppm in the pre-industrial era to 315 ppm in 1958 and to 340 ppm in 1984. If this trend continues the CO2 concentration will reach about 600 ppm in the next century. Besides being produced by breathing, carbon dioxide is formed when carbon-containing materials such as wood, coal, and petroleum products are burned with plenty of oxygen in and around the fire. Carbon Dioxide has found many uses in the industrial world. CO2 is not usually taken from the atmosphere because the concentration is so low. The industrial world’s CO2 is commercial produced.
The CO2 production plant, type CBU, is based on the combustion of oil or gas. The flue gas normally contains sulfur dioxide, which is removed by water and soda lye scrubbing. If combustion is based on sulfur free fuel the soda scrubber can be omitted. The flue gas is led via an exhaust through an absorber where the CO2 is absorbed in a MEA lye. The MEA lye is preheated in a lye heat exchanger before being pumped to a stripper tower where, by further heating, CO2 gas is released. The CO2 gas is cooled in a gas cooler and condenser is separated in a high-efficient water separator. After cleaning in a potassium permanganate scrubber, the CO2 is compressed in two stages to 15 barg(217.5 psig), dried to a dew point of -60 C (-76 F) in a fully automatic dehydrator and filtered in a an activated carbon filter. The pure dried CO2 is condensed in a CO2 condenser at a temperature of -30 C (-22 F). The finished CO2 is then pumped to an insulated storage tank for later cylinder filling, re-evaporation etc.
The CO2 recovery plant, type RBU, is based on recovery from CO2-rich sources. Typically from fermenting process where the quality of off-gas is fairly consistent, but also a number of processes within the chemical industry have CO2 gas as a by-product. The raw CO2 first passes through a stainless steel foam trap where any foam is removed. From there the CO2 gas is led to a stainless steel water scrubber where the CO2 gas is washed out for alcohol ad other soluble impurities. The CO2 gas is now compressed to 15 barg (217.5 psig) and filtered in a double activated carbon filtered in order to remove remaining volatiles. The pure CO2 is dried to a dew point of -60 C (-75 F) in a fully automatic dehydrator. The pure dried CO2 is condensed in a CO2 condenser at a temperature of -30 C (-22 F). The liquid CO2 is finally led to an insulated storage tank for later cylinder filling, re-evaporation etc.
It is also produced as a by-product from steam-hydrocarbon reformers used in the production of ammonia, gasoline, and other chemicals. CO2 can be transported three ways: in high pressure uninsulated steel cylinders, as a low-pressure liquid in insulated truck trailers or rail tank cars, and as dry ice. The size of the high-pressure cylinders is limited because of the weight involved. Most commercial cylinders contain either twenty or fifty pounds of CO2. Laws that govern the vehicle weight restrict truck trailers capacity. Right now about twenty tons of liquid CO2 may be shipped on an insulated trailer. Carbon dioxide gas dissolves in water, forming carbonic acid. When this weak acid reacts with some substances, it forms products called carbonates. One carbonate of importance is sodium bicarbonate, also known as baking soda.
The food and beverage industry is the main industrial consumer of carbon dioxide. It serves as a protective gas to manufacture sensitive food, used in deep freezing and added to beverages. An ordinary soft drink is made of a sweetening agent, edible acids, and natural or artificial flavors. Soft drinks include cola beverages, fruit-flavored drinks, ginger ale and root beer. The characteristic sparkle and fizz is because of the content of carbonated water dissolved under pressure. Because of the carbonation, soft drinks are sometimes called soda pop, soda, or pop. Tight bottling holds the pressure until the bottle top is removed. Then the gas effervesces, or bubbles out. The carbonation in the beverage helps to protect it against spoilage. The manufacturers of these products must pay special attention to the purity and uniformity of the ingredients. These ingredients are water, carbon dioxide, sugar or a sugar substitute(corn syrup), acids, flavoring, and sometimes coloring. The water is usually taken from the municipal source, but the makers still must purify it to insure a uniform taste. Finishing soft drinks are made by diluting the flavored syrup in carbonated water. After the syrup and carbonated water are mixed, the sugar level drops from 51 – 60 percent to 8 – 13 percent. The mixing and carbonation is done almost entirely by automated machines.
CO2 is very cheap to purchase, Pepsi buys natural CO2 liquid from Mountaineer Gas at three cents a pound. Approximately one pound makes eight two liters or twenty-four twenty ounces. Pepsi said that they put more CO2 in a plastic twenty ounces (approximately 3.5 volumes) than in a twenty-ounce can(3.2 volumes). A glass bottle keeps more carbon dioxide than a plastic bottle does because plastic is permeable. A can can keep CO2 for approximately thirty to thirty-nine weeks compared to the plastic’s shelf life of only three weeks.
The first attempts to make carbonated soft drinks were the result of a desire to duplicate the naturally effervescent, mineral-rich waters that flowed from the springs at well-known European spas. Early experimenters believed that the effervescence was the source of the reputed healthful properties of the waters, and they therefore concentrated on this gaseous nature.
By the late 1700’s numerous reports of such experiments and investigations were published in a journal of the Royal Society of London. Among the authors was Joseph Priestley, who received the society’s Copley medal for his reports on “fixed air” and its mixture with water. Joseph Priestly made the first soda water in 1772. Scientists throughout Europe and the United States engaged in experiments with carbonation. In 1775 John Mervin Nooth described a special apparatus for preparing small quantities of effervescent waters. Many other devices followed, and in the years 1789 to 1821 factories and bottling plants opened in cities throughout Europe. In the United States bottled soda water was available as early as 1807.
Numerous advertisements included claims that soft drinks “pepped up” tired people, calmed the nervous system, or made the unhappy feel carefree. Some pharmacies sold soft drinks that contained such, then legal, drugs as heroin, codeine, and cocaine. These are no longer found in beverages, but many soft drinks still contain the stimulant caffeine.
Dealers bottled and sold sparkling water flavored with various mixtures of aromatic oils, fruit essences, sugar, and spices. During the next 80 years, containers of soda water were distributed to restaurants and pharmacies. There soft drinks were mixed by putting a little flavored syrup in a glass and filling the glass with soda water. Carbonate drinks come in a variety of containers, such as glass bottles, tin or aluminum cans, and plastic bottles. Vending machines dispense the drinks in cups, cans, or bottles.
In 1980 Coke announced they were substituting 50 percent of the sugar for high fructose corn syrup allowing the bottlers to sell the finished product cheaper and not risk the flavor of the drink. Pepsi would have done the same because corn syrup is a lot cheaper than sugar but since Pepsi has such a complex and delicate flavor over Coke, you could taste the difference where as in Coke it was unnoticeable. But finally the corn syrup industry improved the quality of the corn syrup and in 1983 Pepsi Co. approved the use of high fructose corn syrup as a substitute for half the sugar used to make Pepsi. At about that same time, Coke announced an increase from 50 percent corn syrup to 75 percent corn syrup only to go about a year later to announced that they were going 100 percent corn syrup.
In 1984, in response to the public demand for more healthful and less fattening foods, manufacturers began making soft drinks with natural juice added. Vitamin-enriched soft drinks and sugar-, caffeine-, and sodium-free soft drinks also became popular in the late 20th century.