Sodium hydroxide solutions hydrogen sulfide removal with

The simplest way of removing hydrogen sulfide is to scrub the hydrocarbon mixture with an aqueous solution of a strong base, such as sodium hydroxide. The hydroxide reacts with the HjS, which is a weak acid, and the hydrogen sulfide removal is quantitative even in a single contact stage. Spent caustic from this operation cannot be regenerated economically. 

Samples are hydrolyzed with hydrochloric acid and stannous chloride solution at elevated temperature, and the evolved carbon disulfide is drawn with an air steam through two gas washing tubes in series containing lead acetate and sodium hydroxide solutions and an absorption tube containing an ethanolic solution of cupric acetate and diethanolamine. Lead acetate and sodium hydroxide remove hydrogen sulfide and other impurities. In the absorption tube, the carbon disulfide forms two cupric complexes of Af,Af-bis(2-hydroxyethyl)dithiocarbamic acid with molecular ratios Cu CS2 of 1 1 and 1 2. These complexes are measured simultaneously by spectrophotometry at 453 nm. 

The Bio-FGD process converts sulfur dioxide to sulfur via wet reduction (10). The sulfur dioxide gas and an aqueous solution of sodium hydroxide are contacted in an absorber. The sodium hydroxide reacts with the sulfur dioxide to form sodium sulfite. A sulfate-reducing bacteria converts the sodium sulfite to hydrogen sulfide in an anaerobic biological reactor. In a second bioreactor, the hydrogen sulfide is converted to elemental sulfur by Thiobacilh. The sulfur from the aerobic second reactor is separated from the solution and processed as a sulfur cake or liquid. The process, developed by Paques BV and Hoogovens Technical Services Energy and Environment BV, can achieve 98% sulfur recovery. This process is similar to the Thiopaq Bioscrubber process for hydrogen sulfide removal offered by Paques. 

Alkali Treatment. Caustic washing is the treatment of materials, usually products from petroleum refining, with solutions of caustic soda. The process consists of mixing a water solution of lye (sodium hydroxide or caustic soda) with a petroleum fraction. The treatment is carried out as soon as possible after the petroleum fraction is distilled, since contact with air forms free sulfur, which is corrosive and difficult to remove. The lye reacts either with any hydrogen sulfide present to form sodium sulfide, which is soluble in water, or with mercaptans, foUowed by oxidation, to form the less nocuous disulfides. 

Sodium and Potassium Hydroxides. Sodium hydroxide [1310-73-2] and potassium hydroxide [1310-58-3] (Class 1, nonregenerative) are commonly used when moisture and carbon dioxide or hydrogen sulfide must be removed simultaneously (4). Fused sticks or solutions of the alkah hydroxides are frequentiy used. These materials must be handled with care to prevent serious skin bums. 

The HTS catalysts are typically produced by precipitation of aqueous solution of iron sulfate and chromium sulfate with sodium carbonate or sodium hydroxide, followed by careful washing to remove essentially all of the residual sulfate. Washing is an important step in the catalyst manufacture, since the residual sulfate converts into hydrogen sulfide when the catalyst is reduced during the process startup, and hydrogen sulfide is a poison to the LTS catalyst located downstream of the HTS bed.t l... 

Several processes have been used to combat acid-rock drainage that has already been formed. Metal precipitation and acid neutralization with lime or limestone is the most common technique used to limit the environmental impact of an acidic, metal-bearing solution from waste material. Metal hydroxide formation is quite simply achieved with moderate changes in the pH of the solution. Metal sulfide formation is typically preferred because the sulfide precipitates are more stable, more quickly formed, and much easier to remove by filtration or sedimentation. However, the sulfide sources (such as hydrogen sulfide gas, sodium sulfide, and thiourea) are very expensive on a per pound of metal removed basis, and can produce a noxious hydrogen sulfide gas emission from the mixing tanks. The chemistry of precipitation is discussed in more detail later. 

Iron ui. iy he removed hy the hydrogen sulfide pressure bottle, precipitation, httl a nureli more, convenient method is to oxidize the iron In die ferric condition, thou pour the solution into a hoi 10 per rent sxluluin of sodium hydroxide. Boil for u time, cool, filter, and wash the ferric hydroxide thoroughly. If much iron is prcsenl the precipitate should he dissolved II acid and the precipitation repeated. Iron may he successfully removed hy I wo or more precipitations with ammonia. 

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