Sulfur compounds, recovery

Total 1991 world production of sulfur in all forms was 55.6 x 10 t. The largest proportion of this production (41.7%) was obtained by removal of sulfur compounds from petroleum and natural gas (see Sulfurremoval and recovery). Deep mining of elemental sulfur deposits by the Frasch hot water process accounted for 16.9% of world production mining of elemental deposits by other methods accounted for 5.0%. Sulfur was also produced by roasting iron pyrites (17.6%) and as a by-product of the smelting of nonferrous ores (14.0%). The remaining 4.8% was produced from unspecified sources. 

Prior to methanation, the gas product from the gasifier must be thoroughly purified, especially from sulfur compounds the precursors of which are widespread throughout coal (23) (see Sulfurremoval and recovery). Moreover, the composition of the gas must be adjusted, if required, to contain three parts hydrogen to one part carbon monoxide to fit the stoichiometry of methane production. This is accompHshed by appHcation of a catalytic water gas shift reaction. 

Because hydrocarbon feeds for steam reforming should be free of sulfur, feed desulfurization is required ahead of the steam reformer (see Sulfur REMOVAL AND RECOVERY). As seen in Figure 1, the first desulfurization step usually consists of passing the sulfur-containing hydrocarbon feed at about 300—400°C over a Co—Mo catalyst in the presence of 2—5% H2 to convert organic sulfur compounds to H2S. As much as 25% H2 may be used if olefins... 

Petroleum. Apart from its use ia petrochemicals manufacture, there are a number of small, scattered uses of lime ia petroleum (qv) production. These are ia making red lime (drilling) muds, calcium-based lubricating grease, neutralization of organic sulfur compounds and waste acid effluents, water treatment ia water flooding (secondary oil recovery), and use of lime and pozzolans for cementing very deep oil wells. 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

Steam Reforming Processes. In the steam reforming process, light hydrocarbon feedstocks (qv), such as natural gas, Hquefied petroleum gas, and naphtha, or in some cases heavier distillate oils are purified of sulfur compounds (see Sulfurremoval and recovery). These then react with steam in the presence of a nickel-containing catalyst to produce a mixture of hydrogen, methane, and carbon oxides. Essentially total decomposition of compounds containing more than one carbon atom per molecule is obtained (see Ammonia Hydrogen Petroleum). 

Sulfur [7704-34-9] S, a nonmetallic element, is the second element of Group 16 (VIA) of the Periodic Table, coming below oxygen and above selenium. In massive elemental form, sulfur is often referred to as brimstone. Sulfur is one of the most important taw materials of the chemical industry. It is of prime importance to the fertilizer industry (see Fertilizers) and its consumption is generally regarded as one of the best measures of a nation s industrial development and economic activity (see Sulfur compounds Sulfurremoval and recovery Sulfuric acid and sulfur trioxide). 

Hydrogen sulfide Refinery gases, crude oil, sulfur recovery, various chemical industries using sulfur compounds Petroleum and chemicals Kraft pulping process Foul odor of rotten eggs irritating to eyes and respiratory tract darkening exterior paint... 

The most widely used pulping process is the kraft process, as shown in Fig. 6-11, which results in recovery and regeneration of the chemicals. This occurs in the recovery furnace, which operates with both oxidizing and reducing zones. Emissions from such recovery furnaces include particulate matter, very odorous reduced sulfur compounds, and oxides of sulfur. If extensive and expensive control is not exercised over the kraft pulp process, the odors and aerosol emissions will affect a wide area. Odor complaints have been reported over 100 km away from these plants. A properly controlled and operated kraft plant will handle huge amounts of material and produce millions of kilograms of finished products per day, with little or no complaint regarding odor or particulate emissions. 

Benzene releases in byproduct recovery operations Naphthalene residues generated in the final cooling tower Sulfur and sulfur compounds recovered from coke oven gas Wastewater from cleaning and cooling (contains zinc, ammonia still lime, decanter tank tar, or tar distillation residues)... 

Power boilers at pulp and paper mills are sources of particulate emissions, S02, and NOx. Pollutants emitted from chemical recovery boilers include S02 and total reduced sulfur compounds (TRS). 

Puacz et al. (1995) developed a catalytic method, based on the iodine-azide reaction, for the determination of hydrogen sulfide in human whole blood. The method involves the generation of hydrogen sulfide in an evolution-absorption apparatus. In addition, the method allows for the determination of sulfide in blood without interference from other sulfur compounds in blood. A detection limit of 4 g/dm3 and a percent recovery of 98-102% were achieved. Although the accuracy and precision of the catalytic method are comparable to those of the ion-selective electrode method, the catalytic method is simpler, faster, and would be advantageous in serial analysis. 

Mueller and Bandaranayake [39] were able to show that more than 95% of the following compounds were oxidised in the first run, when present in the water sample at the 5 mg C per litre level oxalic acid, potassium phthalate, humic acid, glucose, sucrose, ascorbic acid, glycine, and phenol. Only sulfur compounds gave incomplete recoveries [58,88]. 

SOx and NOx removal Combination of steam/water washing and removing the sulfur compounds for recovery of sulfur as a salable product... 

Sulfur recovery is discussed later in the paper. Some liquid absorption processes produce two separate acid gas streams (selective AGR). One stream, containing the majority of sulfur compounds, is sent to the sulfur recovery unit, while the other is vented to atmosphere, environmental regulations permitting. 

Selectivity - solvents generally have different affinities for H2S and CO2. Some processes can remove essentially all of the H2S and many of the other sulfur compounds while leaving most of the CO2 in the treated gas, potentially reducing the cost of the downstream sulfur recovery facilities (4). However, such... 

Sulfur recovery processes convert acid gases containing H2S and other sulfur compounds to elemental sulfur and sulfuric acid. Table II is a summary of many of the available sulfur recovery processes. 

Sulfreen American Lurgl Claus tall gas. Sulfur compounds 1-3Z Raises overall sulfur recovery to 99%. 2000-3000 ppmv sulfur In treated gas. No COS/CS2 conversion... 

Beavon Mark 1 Parsons Claus tall gas 99.8% overall sulfur recovery, <300 ppmv sulfur compounds in treated gas, generally <10 ppmv H2S. Some COS/CS2 conversion... 

The most common waste stream from drying and sweetening operations is spent caustic. The spent caustic is characterized as phenolic or sulfidic, depending on which is present in the largest concentration this in turn is mainly determined by the product stream being treated. Phenolic spent caustics contain phenol, cresols, xylenols, sulfur compounds, and neutral oils. Sulfidic spent caustics are rich in sulfides, but do not contain any phenols. These spent caustics have very high BOD and COD. The phenolic caustic streams are usually sold for the recovery of phenolic materials. 

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