Problems Sulphide, hydrogen

If produced gas contains water vapour it may have to be dried (dehydrated). Water condensation in the process facilities can lead to hydrate formation and may cause corrosion (pipelines are particularly vulnerable) in the presence of carbon dioxide and hydrogen sulphide. Hydrates are formed by physical bonding between water and the lighter components in natural gas. They can plug pipes and process equipment. Charts such as the one below are available to predict when hydrate formation may become a problem. 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

Organic materials Corrosive vapours are sometimes emitted by organic materials used either in packaging or in the manufactured article, and may be troublesome in confined spaces. Some woods, particularly unseasoned oak and sweet chestnut, produce acetic acid (see Section 18.10), and certain polymers used in paints, adhesives and plastics may liberate such corrosive vapours as formic acid and hydrogen sulphide . It may be necessary to carry out exposure trials, particularly where materials capable of liberating formaldehyde or formic acid are involved. Most corrosion problems of this kind can be prevented by using desiccants, and in many cases they are confined to imperfectly cured materials. For an excellent review see Reference 9. 

Doctor et al. (2000) point out the technical problems in the transport infrastructure that could arise from impurities in the C02. Any transport system requires the C02 to be dried to prevent the formation of C02 hydrates. Considerable problems with the formation of iron sulphide in natural gas pipelines indicate that C02 also has to be cleaned of hydrogen sulphide content. 

Thiols can be prepared by the action of alkyl halides with an excess of KOH and hydrogen sulphide. It is an SN2 reaction and involves the generation of a hydrogen sulphide anion (HS ) as nucleophile. In this reaction, there is the possibility of the product being ionised and reacting with a second molecule of alkyl halide to produce a thioether (RSR) as a by-product. An excess of hydrogen sulphide is normally used to avoid this problem. 

Acid dissolution is a particularly favourable approach for carbonates and sulphides, where the matrix anion will be removed during the evolution of carbon dioxide or hydrogen sulphide, and for salts of organic acids, where the anion seldom causes interference problems. Conversely, sulphates can cause problems during flame atomisation and chlorides during furnace atomisation ways of dealing with such problems are discussed below. 

Often the gas pressure is sufficient to use a turbo-expander which cools the gas to below 0 C and causes further condensation of hydrocarbon liquids. Because the gas stream also contains water, gas hydrate and ice formation can be a problem. This is prevented by the addition of an additive such as methanol. Following the removal of condensate, the gas stream is dried and if necessary treated further to remove acid gases such as hydrogen sulphide and carbon dioxide. 

The problems associated with lability of double bonds during the mass spectro-metric examination of monoterpenes have been discussed. The mass spectra of ketones are not as easy to interpret as those of thioketones, the latter having a higher proportion of heteroatom-containing fragments. They are readily available by reaction of the ketones either with phosphorus pentasulphide, or with hydrogen sulphide and dry hydrogen chloride, and are recommended for the study of bicyclic ketones in the norbomane series. ... 

The story of the evolution of life on Earth is relatively straightforward in comparison to the problem of how it first arose. The abiotic synthesis on Earth of the organic compounds necessary for the creation of life appears to require a reducing atmosphere (see Box 1.5). Early experiments with electrical discharges in mixtures of methane, ammonia and hydrogen sulphide in the presence of water created various organic compounds es-... 

Air pollution problems associated with hydrogen sulphide gas and the general population are associated with the foul odour. Sources can be industrial or polluted water. Peak concentrations as high a 0.13 ppm have been reported in the air surrounding industrial sources. At a geothermal site in New Zealand where continuous monitoring was carried out, a concentration of 0.05 ppm was exceeded for 35% of the time over a five-month period. 

Splitting of hydrogen sulphide into hydrogen and sulphnr. This process helps to solve two problems at one blow, namely to purify waters and produce hydrogen. Most effective as "photocatalysts" are suspensions of CdS [68] and those with heterojunction, e g., CdS/Cu S [69] and (Zn,Cd)S/CuxS [70], all provided with catalytically active inclusions of Pt and Ru02. 

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