Hydrogen sulfide removal products

Process selectivity indicates the preference with which the process removes one acid gas component relative to or in preference to another. For example, some processes remove both hydrogen sulfide and carbon dioxide, whereas other processes are designed to remove hydrogen sulfide only. Thus it is important to consider the process selectivity for hydrogen sulfide removal compared to carbon dioxide removal, ie, the carbon dioxide-to-hydrogen sulfide ratio in the natural gas, in order to ensure minimal concentrations of these components in the product. 

The factors affecting the hydrogen sulfide removal from Elkton field gas were evaluated in the extensive optimization study [70]. It was carried out to apply activated carbon based adsorption/oxidation to the industrial environment. In order to make the process as simple and economical as possible the temperature, pressure, O/H2S ratio, water vapor content in the feed gas, minimizing production of SO2 and time achieving high conversion of H2S to sulfur and water were varied [70], Moreover, the efficiency of using thermally regenerated carbon was evaluated. 

Sitz et al. (2003) worked on amine-aldehyde condensates, and they concluded that these cou-densates are suitably used for hydrogen sulfide removal from the produced fluids to meet the sales specification for the maximum allowable hydrogen sulfide concentration in the gas of 4 ppm. But one of the drawbacks associated with the products is their expensiveness. 

Many different methods have been developed for CO2 and hydrogen sulfide removal, some of which are briefly discussed later. Concentrates of hydrogen sulfide obtained as by-products of gas desulfurization are often converted by partial oxidation to elanental sulfur (Claus process). 

In the production process, inadvertent reaction with moisture, acids, and heat may result in the release of small amounts of hydrogen sulfide. Therefore, an exhaust air system is recommended for handling cerium sulfide pigments. The exhaust air might also require scrubbing for hydrogen sulfide removal, and state, local and national regulations should be carefully consulted. 

Since the absorbent and waste products are liquids, the process can be operated in either a batch or continuous mode. Data from treating trials at two plants are given in Table 16-4. Case A was operated as a batch process using a conventional bubble tower. Case B was a continuous operation with the triazine injected into the gas ahead of a converted iron sponge tower. In both cases, complete hydrogen sulfide removal was observed. Triazine product consumption ranged from 0.04 to 0.06 gal/MMscf per ppm of H2S in the feed gas. 

Hot product char carries heat into the entrained bed to obtain the high heat-transfer rates required. Feed coal must be dried and pulverized. A portion of the char recovered from the reactor product stream is cooled and discharged as product. The remainder is reheated to 650—870°C in a char heater blown with air. Gases from the reactor are cooled and scmbbed free of product tar. Hydrogen sulfide is removed from the gas, and a portion is recycled to serve as the entrainment medium. 

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. 

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. 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Chevron s WWT (wastewater treatment) process treats refinery sour water for reuse, producing ammonia and hydrogen sulfide [7783-06-04] as by-products (100). Degassed sour water is fed to the first of two strippers. Here hydrogen sulfide is stripped overhead while water and ammonia flow out the column bottoms. The bottoms from the first stripper is fed to the second stripper which produces ammonia as the overhead product. The gaseous ammonia is next treated for hydrogen sulfide and water removal, compressed, and further purified. Ammonia recovery options include anhydrous Hquid ammonia, aqueous Hquid ammonia, and ammonia vapor for incineration. There are more than 20 reported units in operation, the aimual production of ammonia from this process is about 200,000 t. 

This reaction can also be mn in a continuous fashion. In the initial reactor, agitation is needed until the carbon disulfide Hquid phase reacts fully. The solution can then be vented to a tower where ammonia and hydrogen sulfide are stripped countercurrendy by a flow of steam from boiling ammonium thiocyanate solution. Ammonium sulfide solution is made as a by-product. The stripped ammonium thiocyanate solution is normally boiled to a strength of 55—60 wt %, and much of it is sold at this concentration. The balance is concentrated and cooled to produce crystals, which are removed by centrifiigation. 

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