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It is produced by reacting sodium chlorate with a reducing agent like sulfur dioxide: 2 NaClO 3 + H 2 SO 4 + SO 2 → 2 ClO 2 + 2 NaHSO 4. Chlorine dioxide is sometimes used in combination with chlorine, but it is used alone in ECF (elemental-chlorine-free) bleaching sequences. It is used at moderately acidic pH (3.5 to 6).
Sulfur dioxide is a mild but useful reducing agent. It is oxidized by halogens to give the sulfuryl halides, such as sulfuryl chloride: SO 2 + Cl 2 → SO 2 Cl 2. Sulfur dioxide is the oxidising agent in the Claus process, which is conducted on a large scale in oil refineries. Here, sulfur dioxide is reduced by hydrogen sulfide to give ...
This is the mechanism of bleaches based on sulfur dioxide. [13] Sunlight acts as a bleach through a process leading to similar results: high-energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive ...
Elemental chlorine bleaching uses chlorine and hypochlorite. Elemental chlorine-free bleaching is more environmentally friendly since it eliminates the use of hypochlorite and replaces chlorine with chlorine dioxide or sodium chlorate. [3] Totally chlorine-free bleaching utilizes oxygen and hydrogen peroxide. This is the most environmentally ...
The pulping liquor for most sulfite mills is generated by treating various bases (alkali metal or alkaline earth hydroxides) with sulfur dioxide: SO 2 + MOH → MHSO 3 MHSO 3 + MOH → M 2 SO 3 + H 2 O. Similar reactions are effected with divalent cations (Mg2+, Ca2+) and using carbonates in place of hydroxide.
The chemicals used are: 1) sulfite salts with an excess of sulfur dioxide and 2) caustic soda and sodium sulfide (kraft process). The lignin of the wood is made soluble, resulting in fibre separation into whole fibres. Further purification by bleaching can also be done.
Various byproducts containing hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and other volatile sulfur compounds are the cause of the malodorous air emissions characteristic for pulp mills utilizing the kraft process. [23] [24] The sulfur dioxide emissions of kraft-pulp mills are much lower than those from sulfite ...
Sulfur dioxide is a disinfectant. It also acts as a potent antioxidant , protecting both the color and delicate flavors of wine. A high dose would be 3 grams of potassium metabisulfite per six-gallon bucket of must or around 132 milligrams per liter (yielding roughly 75 ppm of SO 2 ) prior to fermentation; then 6 grams per six-gallon bucket ...