Baking soda is a white crystalline powder (NaHCO 3 ) better known to chemists as sodium bicarbonate, bicarbonate of soda, sodium hydrogen carbonate, or sodium acid carbonate. It is classified as an acid salt, formed by combining an acid (carbonic) and a base (sodium hydroxide), and it reacts with other chemicals as a mild alkali. At temperatures above 149 degrees Celsius (300 degrees Fahrenheit), baking soda decomposes into sodium carbonate (a more stable substance), water, and carbon dioxide. Baking soda, or sodium bicarbonate, comes from soda ash obtained either through the Solvay process or from trona ore, a hard, crystalline material.
The Manufacturing Process
- Soda ash can be manufactured chemically using the Solvay process, or it can be made from trona ore. If trona ore is used, it must first be mined. After it has been brought to the surface, the trona ore is transported to a variety of processing plants. There, the ore is refined into a slurry of sodium sesquicarbonate, an intermediate soda ash product that actually contains both soda ash (sodium carbonate) and baking soda (sodium bicarbonate).
- Next, the intermediate soda ash solution is put into a centrifuge, which separates the liquid from the crystals. The crystals are then dissolved in a bicarbonate solution (a soda ash solution made by the manufacturer) in a rotary dissolver, thereby becoming a saturated solution. This solution is filtered to remove any non-soluble materials and is then pumped through a feed tank to the top of a carbonating tower.
- Purified carbon dioxide is introduced into the bottom of the tower and held under pressure. As the saturated sodium solution moves through the tower, it cools and reacts with the carbon dioxide to form sodium bicarbonate crystals. These crystals are collected at the bottom of the tower and transferred to another centrifuge, where excess solution (filtrate) is filtered out. The crystals are then washed in a bicarbonate solution, forming a cake-like substance ready for drying. The filtrate that is removed from the centrifuge is recycled to the rotary dissolver, where it is used to saturate more intermediate soda ash crystals.
- The washed filter cake is then dried on either a continuous belt conveyor or in a vertical tube drier called a flash dryer. The theoretical yield from the process, according to the Church & Dwight Company, is between 90 and 95 percent, and the baking soda manufactured is more than 99 percent pure.
- An illustration of the baking soda manufacturing process. A key step in the process occurs in the carbonating tower. Here, the saturated soda ash solution moves from the top of the tower downward. As it falls, the solution cools and reacts with carbon dioxide to form sodium bicarbonate crystals—baking soda. After filtering, washing, and drying, the crystals are sorted by particle size and packaged appropriately.
- Next, the dried crystals of sodium bicarbonate are separated into various grades by particle size. Standard grades of sodium bicarbonate and special grades are manufactured to meet customers’ specific requirements, and particle size is the major determinant of grades. Powdered #1 and fine granular #2 have a wide range of uses in foods, chemicals, and pharmaceuticals. Granular grades #4 and #5 are found in foods and doughnuts, cleaning compounds, pharmaceuticals, and many other products. Industrial grade sodium bicarbonate is used in diverse applications, including oil well drilling fluids, fire extinguishing materials, and water treatment.
- Each grade goes to a holding bin wherein atmosphere, carbon dioxide, and moisture content are controlled to “cure” the product. Once cured, the grades are ready to be packaged and shipped.