The White Carbon Footprint

Often called "white carbon", amorphous precipitated silica is an integral component of the tread compound for fuel-efficient tires. The manufacturing process for amorphous precipitated silica is unusual in that a multi-step chemical process is used to convert crystalline silicon dioxide (SiO₂) into a different physical form of silicon dioxide, namely amorphous. This paper will estimate the amount of energy needed for each major step in the manufacturing process. The first step is obtaining sand and a sodium source to convert into an aqueous solution of sodium silicate, either by melting and dissolution or by digestion in a heated sodium hydroxide solution. Next, an acid, usually sulfuric acid, is used to precipitate silica from the aqueous solution; sodium salt is a by-product. Finally, the mixture is washed with large amounts of water to remove the salt, and this water must be removed to achieve the final product form, usually by spray-drying. From the estimates of energy needed to produce the final product delivered to a tire factory, a carbon equivalent value will be calculated using formulas developed by the U.S. Environmental Protection Agency.