The Manufacturing Process

Making soda ash

• 1 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).

Making baking soda

• 2 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.
• 3 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.
• 4 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.

Sorting and storing the
different grades

• 5 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.
• 6 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.

Quality Control

The quality of sodium bicarbonate is controlled at every stage of the manufacturing process. Materials, equipment, and the process itself are selected to yield sodium bicarbonate of the highest possible quality. According to FMC sources, when the company constructed plants, it chose materials and equipment that would be compatible with the stringent quality requirements for making pharmaceutical grade sodium bicarbonate. FMC also uses Statistical Process Control (SPC) to maintain unvarying daily quality, and key operating parameters are charted to maintain process control. Product quality parameters are recorded by lot number, and samples are kept for two to three years.

All U.S.P. grades meet the United States Pharmacopoeia and Food Chemicals Codex specifications for use in pharmaceutical and food applications. In addition, food grade sodium bicarbonate meets the requirements specified by the U.S. Food and Drug Administration as a substance that is Generally Recognized as Safe (GRAS).

The Future

At the turn of the twentieth century, 53,000 tons (48,071 metric tons) of baking soda were sold annually. While the population increased dramatically, sales by 1990 were down to about 32,000 tons (29,024 metric tons) per year. Self-rising flour and cake and biscuit mixes have decreased the demand for baking soda as an important baking ingredient. Nevertheless, demand for the product is still significant. Commercial bakers (particularly cookie manufacturers) are one of the major users of this product. One of the most important attributes of sodium bicarbonate is that, when exposed to heat, it releases carbon dioxide gas (CO ₂ ) which makes the baking goods rise. Sodium bicarbonate is also used in the pharmaceutical and health industries, and it has other industrial applications as well. It therefore continues to be an important product for today and for the future.

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Date: 2016-03-03; view: 1491