Grades hydrogen sulfide

Elemental phosphoms from the electrothermal process is a distilled product of high purity and yields phosphoric acid pure enough for most industrial uses without any further treatment. The main impurity is ca 20—100 ppm arsenic present in the phosphoms as the element and in the phosphoric acid as arsenious acid. To remove the arsenic, the phosphoric acid destined for food, pharmaceutical, and some industrial-grade appHcations is treated with excess hydrogen sulfide, filtered, and blown with air to strip out excess H2S. This treatment generally reduces the arsenic content of the phosphoric acid to less than 0.5 ppm. The small amount of filter cake is disposed of in approved chemical landfills. 

Solutions of hydrogen sulfide, because of hydrogen-induced cracking. Grades of steel are available for certain ranges of pH and hydrogen sulfide partial pressure. 

Respiratory distress was noted in 2 workers exposed to >40 ppm hydrogen sulfide for <25 minutes (Spolyar 1951). Male volunteers were exposed to hydrogen sulfide concentrations up to 5 ppm for more than 16 minutes after graded exercise that was performed to exhaustion (Bhambhani and Singh 1991). 

Hydrogen sulfide promoted corrosion can be a serious problem (150) the best solution is prevention. Corrosion problems can be minimized by choice of the proper grades of steel or corrosion resistant alloys, usually containing chromium or nickel (150, 151) and avoiding generation of H S by sulfate reducing bacteria in situations where H S is not initially present. Cathodic protection of casing is often effective for wells less than 10,000 feet deep (150). 

Severe hydroprocessing required to refine ultra-low sulfur fuel grades generates hydrogen sulfide as a by-product. If low levels of hydrogen sulfide remain soluble in the finished fuel, the possibility exists for hydrogen sulfide-initiated corrosion of copper and the resulting failure of the ASTM D-130 specification for finished fuel. 

Contracts for acetylene-grade carbide are usually based on size and gas yidd specification, and indude penalties for carbide that fails to meet specified gas yidd. The sizes generally available in the trade are based on established U.S. Government specifications. In general gas yidds range from 280—300 L/kg and depend on the screen size of the carbide. The most important standard is the method of expressing gas yidd, which in the United States is at 15°C and 101 kPa (1 atm). Gas impurities are typically 0.05% by volume phosphine, 0.15% by volume hydrogen sulfide, and 0.001% arsine. 

Information regarding the physical and chemical properties of benzene is shown in Table 3-2. The major impurities found in commercial products are toluene, xylene, phenol, thiophene, carbon disulfide, acetylnitrile and pyridine (NIOSH 1974). Commercial refined benzene-535 is free of hydrogen sulfide and sulfur dioxide, but contains a maximum of 1 ppm thiophene and a maximum of 0.15% nonaromatics. Refined nitration-grade benzene is free of hydrogen sulfide and sulfur dioxide. Benzene is also commercially available as thiophene-free, 99 mole%, 99.94 mole% and nanograde quality (HSDB 1996). 

Grade Technical, containing 98% acetylene and not more than 0.05% by volume of phosphine or hydrogen sulfide 99.5%. 

Derivation Methanol and hydrogen sulfide. Grade 98.0% purity. 

Derivation Direct mining by Frasch process, low-grade ores by Chemico process, smelter waste gas, sour natural gas, coal, iron pyrites, gypsum, solvent extraction of volcanic ash, petroleum, coke oven gas, photolysis of hydrogen sulfide. 

Grade 99%, free of hydrogen sulfide and sulfur dioxide, technical 95%, research 99.9%. 

Furnace phosphoric acid is pure enough for most uses as obtained directly from the process. Food-grade applications require removal of traces of arseni-ous oxide (Table 10.6). Arsenic is present to the extent of 50-180 ppm (as AS2O3 equivalent) in the feed phosphorus because of the similarity of its chemical properties to those of phosphorus (same group in the periodic table). This ends up in the product acid on oxidation and hydration [1]. It may be removed by the addition of the requisite amount of sodium sulfide or hydrogen sulfide to the furnace acid, which precipitates it as the arsenic III and V sulfides (e.g., Eq. 10.20). 

High purity grade chemicals, inorganic refined from technical grades Hydrated alumina silicate powder Hydrazine Hydrochloric acid Hydrocyanic acid Hydrogen sulfide Hydrosulfites Hypophosphites Indium chloride Inorganic acids, except nitric or phosphoric Iodides... 

Rubin HH, Arieff AJ. 1945. Carbon disulfide and hydrogen sulfide clinical study of chronic low-grade exposures. J Ind Hyg Toxicol 27 123-129. 

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